He who radiates is lost
Brett Evill
Missiles/torpedoes will be vulnerable to ECM, I guess. Will it be possible
to have guided-missile frigates in space with buckets of ECCM, guiding
their torpedoes by remote control?
Will it be worth attempting stealth technologies to avoid observation, or
is IR always going to give you away? How conspicuous will spaceships'
drives be at range?
Will spaceships be painted black to prevent telescopic detection, or
mirrored to bounce laser-beams? Perhaps ships with heat-superconducting
armour will not be susceptible to significant damage by laser beams,
because they will have large radiating surfaces. Will that protect them
from particle beams?
How effective are nuclear warheads going to be in space? Sure they won't
do blast damage, but neutrons and gamma-rays might still be effective.
What about nuclear claymore mines? Nuke-pumped grasers?
Are KE weapons going to be effective, or is guidance and delivery going to
cause problems? A ship might kill itself running into a crowbar, but how
easy is it to get a crowbar in front of a ship?
What ranges are plausible for engagement? Are these long enough that
random evasion will be effective against beam weapons?
--
Brett Evill
To reply by e-mail, remove 'spamblocker.' from <b.e...@spamblocker.tyndale.apana.org.au>
Erik Max Francis
> Missiles/torpedoes will be vulnerable to ECM, I guess. Will it be
> possible
> to have guided-missile frigates in space with buckets of ECCM, guiding
> their torpedoes by remote control?
Not necessarily by remote control, but your torpedoes will have to be
clever to make it to the target.
> Will it be worth attempting stealth technologies to avoid observation,
> or
> is IR always going to give you away? How conspicuous will spaceships'
> drives be at range?
If you're talking about something like a fusion feed drive, then
basically whenever you fire your engines you'll be visible across the
whole system. Lay-in-wait stealth will probably be very important, but
once you make your move you will be a sitting duck. Which means you'll
only move or open fire when you're assured of a kill.
> Will spaceships be painted black to prevent telescopic detection, or
> mirrored to bounce laser-beams?
It's doubtful that the coating of the ship is really going to be the
problem, since what's _really_ going to give you away is lighting your
drive or firing ordnance.
I don't know if it would be _mirrored_, though, since that's almost
doing your best to be seen. Perhaps some kind of corner-mirrored
surface which is designed to ablate easily, and still stay somewhat
shiny. Underneath this reflective armor would be normal armor to try to
deflect detonations or kinetic damage.
> How effective are nuclear warheads going to be in space? Sure they
> won't
> do blast damage, but neutrons and gamma-rays might still be effective.
Not terribly, but they're still good for something. A near miss will
send the ship reeling, and a contact hit will certainly take care of the
ship.
In space combat it pretty much looks like the first to get a hit wins.
This isn't really surprising; it's true of most combat these days (air
combat, submarine combat, etc.). The weapons will be devastating enough
that if you land a hit it does so much damage that the ship, even if it
has survived, is out of the fight.
> What about nuclear claymore mines? Nuke-pumped grasers?
Mines are not terribly likely, unless you're talking about some sort of
lay-in-wait device that launches itself at intruders. Nuke-pumped gamma
ray lasers are theoretical.
> Are KE weapons going to be effective, or is guidance and delivery
> going to
> cause problems? A ship might kill itself running into a crowbar, but
> how
> easy is it to get a crowbar in front of a ship?
Kinetic weapons have the disadvantage of that they're unguided, but have
an advantage in that their unguided, as well; they can't be
countermeasured. Since they don't have their own exhaust trail, it also
means you can't easily see them coming quite as easily as a drive-guided
missile or torpedo.
Further you can have a number of different kinds of kinetic weapons,
including the equivalent of shot (many small pebbles), or even
projectiles intended to deform into large, mostly-connected ring shapes,
for instance.
In normal ballistics, the goal is to deposit all the bullet's energy
into the victim, because that way maximum damage is done. That probably
won't be the case with space combat with kinetic weapons; you want the
projectiles to move fast so that they can't be dodged, and plus a clean
puncture through gives you two breathing-air holes for the price of one.
> What ranges are plausible for engagement? Are these long enough that
> random evasion will be effective against beam weapons?
Here's one way to look at it -- ships that engage in combat within easy
beam weapons range won't be in combat for very long.
My thinking is that it will be very much like submarine warfare; ships
slink around, looking for an enemy. When they find one, it becomes a
game of cat-and-mouse until one slips up. Then kinetic or missile
ordnance is fired, and when a hit is landed, the winner closes in for a
kill with beam weapons.
That's the way I see it, anyway.
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@sade.alcyone.com
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/ Susan Sontag
Joe
(Brett Evill) wrote:
>So, what are plausible technologies and tactics for space combat?
>
snip
All of this was thrashed out pretty thoroughly about 5 or six months
ago. Here Check Deja News for 'realistic space battles' thread.
I reckon the conclsuion was that stealth was worthless except under
very special circumstances under any plausible near future technology.
As for what weapons well that depends on your technology assumptions
regards
Joe
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iol dot ie
Tommy the Terrorist
b.e...@spamblocker.tyndale.apana.org.au writes:
>Will spaceships be painted black to prevent telescopic detection, or
>armour will not be susceptible to significant damage by laser beams,
>because they will have large radiating surfaces. Will that protect them
>from particle beams?
Definitely mirrored.
1) A black ship is a "blackbody", which is to say, unless your crew likes
life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
accessories.
2) "heat superconduction" has been claimed here to be a myth of Niven's
unrelated to reality, and it seems believable. Heat by its nature is
distributed between all sorts of random vibrational modes - how can it
move QUICKLY, without pausing or getting sidetracked?
3) As another thread pointed out, a black ship is a COLD ship, since it
loses all that energy it's busy radiating, and gets back only weak
distant sunlight. Unless it's near the sun - then it bakes.
4) A mirrored ship sounds like a bright object. But what's it going to
reflect? The sky in space is none too bright. So long as it has flat
surfaces (like a Stealth bomber) it will send sunlight or bright
starlight in a narrow and controllable range of directions.
5) For those who say meaningless: the ship will spend most of its time in
ballistic flight. During that time it will be almost invisible, a mere
floating meteor in boundless space. In theory, a skilled adversary would
have calculated its course precisely when its engines were running, or
would be able to detect it by powerful radars or other resource-intensive
techniques. In practice, the opponent of a ship might well turn out to
be a lone pirate with a weak infrared scanner, travelling a little
quickly or slowly in a major "shipping lane" (cheap transfer orbit).
Even if the adversary is a major government with many resources, it is
more likely that they will miss a lone smuggler, fugitive, or rebel "crop
duster" if that ship is particularly inobtrusive. They might track the
launch and guess the trajectory, but if there is a steady flow of
smugglers and refugees and illegal immigrants and so forth, they may not
have the manpower to catch a major fraction of the "offenders". And with
the right virus, you only need one ship...
Ian
>So, what are plausible technologies and tactics for space combat?
>
>Missiles/torpedoes will be vulnerable to ECM, I guess. Will it be possible
>to have guided-missile frigates in space with buckets of ECCM, guiding
>their torpedoes by remote control?
Lightspeed communications delay makes guiding anything by remote control
pretty much unworkable. Everything must be self-guided over the sorts of
distances likely to be involved.
ECM is of limited usefulness in space battles, where ships and weapons
will be seperated by vast empty distances. It's harder to confuse the
enemy about where you are in such an environment. Of course since ECM
isn't tremendously hard, and the enemy is going to see you even if you
don't use it, it will probably be used. Just not to huge effect.
>Will it be worth attempting stealth technologies to avoid observation, or
>is IR always going to give you away? How conspicuous will spaceships'
>drives be at range?
Stealth is only useful under very limited circumstances. You have to
build a huge radiator structure to dissipate heat in one direction, you
can't accelerate at any point in which you are in the enemy's view, and
you are screwed if he has sensors in the direction you are radiating
heat from. In other words, it could be useful to sneak your ships into
close range from deep space for an intricately planned surprise attack
(involving months drifting under special radiator shields, and then
ditching the shields when you reach the point where you will be detected
anyway). It is not a useful strategy in battle. Sensors small enough to
be carried on board (large) ships could detect pretty much any engine in
operation anywhere in the solar system.
>Will spaceships be painted black to prevent telescopic detection, or
>mirrored to bounce laser-beams?
A mirrored surface probably wouldn't be very useful. It would only
affect lasers, and even then would only reduce the power of the laser
attack for a fraction of a second before the mirror at that spot boiled
away.
>Perhaps ships with heat-superconducting
>armour will not be susceptible to significant damage by laser beams,
"Heat-superconducting armor"? To my knowledge, no such thing exists.
Normal superconductors superconduct electricity, but _not_ heat.
>How effective are nuclear warheads going to be in space?
They will destroy a ship if they explode very close to it. If they don't
explode very close, then they are little more than an annoyance that
blinds exposed sensors. Even the largest warheads won't seriously damage
a shielded space warship if they explode over a kilometer away, and in
space a kilometer is pretty short range.
>Sure they won't
>do blast damage, but neutrons and gamma-rays might still be effective.
>What about nuclear claymore mines? Nuke-pumped grasers?
Nuclear-pumped lasers would do impressive damage, if they hit. If you're
in a situation where it is easier to evade beam weapons than to hit with
them, and each side fires a hundred laser pulses for every one that
hits, then nuke-pumped lasers aren't very useful because they only fire
one shot, and a short one at that. Tremendous power only matters if you
can be reasonably sure of a hit.
>Are KE weapons going to be effective, or is guidance and delivery going to
>cause problems? A ship might kill itself running into a crowbar, but how
>easy is it to get a crowbar in front of a ship?
Crowbar-sized objects would have to be guided, and subject to
countermeasures. Filling the area around a ship with pebble-sized or
smaller debris, however, will cause serious damage unless it can
outright fly around the area.
>What ranges are plausible for engagement? Are these long enough that
>random evasion will be effective against beam weapons?
Range is entirely dependant on the sorts of weapons used. Spacecraft may
launch missiles at _huge_ distances, depending on the technology, and
most of the battle may consist of trying to keep the other guys' weapons
out of range. Beam weapon engagements between opponents reasonably
capable of manouvering, will happen at a few hundred thousand kilometers
at most, otherwhise virtually every shot will miss.
At a guess, though, space battles will not involve a lot of strategic
manouvering. Both sides know where the other guy is, where the other guy
wants to go, and roughly what course he has to take to get there. If one
side wants to completely avoid the other and has any capability of doing
so, they do, and no battle happens. Otherwhise the "battle" is a pretty
straighforward approach of the two forces, with both conducting small
manouvers to make sure the enemy doesn't hit them from extreme range. At
some point before firing starts, both sides launch their long-range
missiles, and possibly a screen of interceptors. As the missiles and
interceptors pass each other, they duke it out with energy weapons,
kinetic-kill, and a few nukes and then whatever is left from each side's
launch goes past toward the opposing fleet. Each fleet uses
point-defense countermeasures against the enemy, tries last-minute
invasions, and then takes whatever damage the missiles deal. Repeat this
for multiple volleys of missiles, until the fleets are within a few
hundred thousand kilometers when they start pelting each other with
energy weapons. They can fly past each other shooting, in which case
likely one side or the other will be utterly destroyed, or one side can
decide it is defeated and try to break off from battle as quickly as
possible, preserving what it has left. This may not be feasible
depending on how remaining fuel reserves compare to their velocity.
The dominant rules of space battle are:
1. You can't hide. The enemy probably knows where you are the moment you
launch.
2. You can run or fight, but you will typically have to pick one of the
two long before battle is joined, and then you're stuck with it.
3. There isn't much room for tactics and strategy. Pretty much
everything is automated, and the what your computers calculate as the
best possible attack strategy probably really is the best possible
attack strategy. If battle is joined, and both sides have a good idea of
what the capabilities of the other side's ships are, the result will be
a lot more predictable than we are used to.
4. If the engagement moves into short range (ie beam weapon range), it
will probably be decided in a single pass. This is because at those
kinds of ranges, it is very easy to hit the enemy and very hard to avoid
being hit. Both sides will keep hitting each other with deadly accuracy
until one of them is no longer capable of shooting. The exception is if
both sides pass each other at _extremely_ high speed, but this isn't
likely to happen if the primary objective of one side is to do as much
damage to the other side as possible (in which case it will decelerate,
slowing relative velocity).
5. You may know where the other guy is from extreme range, but due to
lightspeed delay, none of your weapons actually have a chance of hitting
him until they get fairly close. The range of the weapons themselves
isn't the determing factor at all, range of engagement is determined by
the size and manouverability of the enemy. Thus, your weapons are
effective against large, stationary, or slow-moving targets at far, far
longer ranges than they are against the average warship.
6. Anything which can't manouver had better be very heavily protected,
or had better not let you get anywhere near it. This tends to elimenate
the "happy medium" of space stations, they die if an enemy fleet gets in
close. Anything that can't move, and move fast, had better have huge
amounts of shielding and lots and lots of countermeasures,
point-defense, and whatnot. Only fortified targets on planets, moons, or
within large asteroids have a chance of surviving a close attack by an
enemy space fleet. These bases will compensate for their lack of
mobility with means of defense that spacecraft cannot have due to weight
restrictions. They will be extremely heavily armored (probably with most
of the important parts deep underground), and have large numbers of
defensive batteries that can destroy spacecraft at long range simply by
putting up so much fire that something is bound to be hit.
7. The most effective way to destroy planetary installations is not by
using warships, but by using the warships to clear out enemy space
forces so you can bombard the planet with asteroids or mass nuclear
assault. Conventional invasion is effectively impossible, since the
defenses will destroy your invasion force if they are stil functional,
and the only reliable way to take out the defenses is with mass
bombardment. A successful planetary assault will not allow you to
capture any installations intact except those that are deep underground,
and to capture those you have to send in ground forces that were very
expensive to transport across space. This means capture of installations
isn't really a viable alternative, unless you get the enemy to surrender
upon the threat of destruction.
Ian
>If you're talking about something like a fusion feed drive, then
>basically whenever you fire your engines you'll be visible across the
>whole system. Lay-in-wait stealth will probably be very important, but
>once you make your move you will be a sitting duck. Which means you'll
>only move or open fire when you're assured of a kill.
Lay-in-wait stealth isn't very useful, since maintaining basic minimal
power and running ships' computers, let along actually having a crew,
radiates enough heat to be detectable at extremely long range. Modern
telescopic IR sensors could detect a space shuttle _manouvering
thruster_ firing beyond the asteroid belt.
>> Will spaceships be painted black to prevent telescopic detection, or
>> mirrored to bounce laser-beams?
>
>It's doubtful that the coating of the ship is really going to be the
>problem, since what's _really_ going to give you away is lighting your
>drive or firing ordnance.
Actually, being anything except a totally inert piece of junk is going
to produce enough IR to be detectable at long range.
>> Are KE weapons going to be effective, or is guidance and delivery
>> going to
>> cause problems? A ship might kill itself running into a crowbar, but
>> how
>> easy is it to get a crowbar in front of a ship?
>
>Kinetic weapons have the disadvantage of that they're unguided, but have
>an advantage in that their unguided, as well; they can't be
>countermeasured. Since they don't have their own exhaust trail, it also
>means you can't easily see them coming quite as easily as a drive-guided
>missile or torpedo.
Actually you can see them when they're launched and compute their exact
trajectory with ease. If they use engines to change course, you can see
that too. About the only unknown is that once they get very close, they
could explode fragments all over the place and you might not have time
to manouver. Still, the only real way to beat them is to outmanouver
them entirely, if you fly through a cloud of pebbles you have to accept
a chance of being hit.
>> What ranges are plausible for engagement? Are these long enough that
>> random evasion will be effective against beam weapons?
>
>Here's one way to look at it -- ships that engage in combat within easy
>beam weapons range won't be in combat for very long.
>
>My thinking is that it will be very much like submarine warfare; ships
>slink around, looking for an enemy. When they find one, it becomes a
>game of cat-and-mouse until one slips up. Then kinetic or missile
>ordnance is fired, and when a hit is landed, the winner closes in for a
>kill with beam weapons.
>
>That's the way I see it, anyway.
Cat and mouse doesn't happen. It's been discussed on this NG before, but
the simple fact is, it's a LOT easier to detect infrared emissions in
space than you probably think.
Ian
>5) For those who say meaningless: the ship will spend most of its time in
>ballistic flight. During that time it will be almost invisible, a mere
>floating meteor in boundless space. In theory, a skilled adversary would
>have calculated its course precisely when its engines were running, or
>would be able to detect it by powerful radars or other resource-intensive
>techniques. In practice, the opponent of a ship might well turn out to
>be a lone pirate with a weak infrared scanner, travelling a little
>quickly or slowly in a major "shipping lane" (cheap transfer orbit).
>Even if the adversary is a major government with many resources, it is
>more likely that they will miss a lone smuggler, fugitive, or rebel "crop
>duster" if that ship is particularly inobtrusive. They might track the
>launch and guess the trajectory, but if there is a steady flow of
>smugglers and refugees and illegal immigrants and so forth, they may not
>have the manpower to catch a major fraction of the "offenders". And with
>the right virus, you only need one ship...
This is only relevant for engagements against "lone wolf" types who are
trying to sneak through some sort of blockade - in which case it's
probably just as easy to sneak in something on a "legitimate" transport
anyway. Not really relevant to the concept of space warfare, only
interplanetary terrorism. And with interplanetary travel technology,
viruses aren't likely to be any sort of global-scale threat, technology
to effectively contain outbreaks probably exists. Worst a terrorist
could do is nuke a few major cities. Lots of damage, sure, but it won't
likely win a war.
Erik Max Francis
> Lay-in-wait stealth isn't very useful, since maintaining basic minimal
> power and running ships' computers, let along actually having a crew,
> radiates enough heat to be detectable at extremely long range. Modern
> telescopic IR sensors could detect a space shuttle _manouvering
> thruster_ firing beyond the asteroid belt.
If they already know where to look. It's a big solar system.
> Actually you can see them when they're launched and compute their
> exact
> trajectory with ease. If they use engines to change course, you can
> see
> that too.
And the missile can compute your course changes and adjust accordingly
as well.
--
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Alcyone Systems / irc maxxon (efnet) / finger m...@sade.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
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J. Clarke
--
--John
Reply to jclarke at eye bee em dot net.
Ian wrote in message <35fca23b...@news.ktchnr1.on.wave.home.com>...
>Erik Max Francis <m...@alcyone.com> wrote:
>
>>If you're talking about something like a fusion feed drive, then
>>basically whenever you fire your engines you'll be visible across the
>>whole system. Lay-in-wait stealth will probably be very important, but
>>once you make your move you will be a sitting duck. Which means you'll
>>only move or open fire when you're assured of a kill.
>
>Lay-in-wait stealth isn't very useful, since maintaining basic minimal
>power and running ships' computers, let along actually having a crew,
>radiates enough heat to be detectable at extremely long range. Modern
>telescopic IR sensors could detect a space shuttle _manouvering
>thruster_ firing beyond the asteroid belt.
>
>>> Will spaceships be painted black to prevent telescopic detection, or
>>> mirrored to bounce laser-beams?
>>
>>It's doubtful that the coating of the ship is really going to be the
>>problem, since what's _really_ going to give you away is lighting your
>>drive or firing ordnance.
>
>Actually, being anything except a totally inert piece of junk is going
>to produce enough IR to be detectable at long range.
>
>>> Are KE weapons going to be effective, or is guidance and delivery
>>> going to
>>> cause problems? A ship might kill itself running into a crowbar, but
>>> how
>>> easy is it to get a crowbar in front of a ship?
>>
>>Kinetic weapons have the disadvantage of that they're unguided, but have
>>an advantage in that their unguided, as well; they can't be
>>countermeasured. Since they don't have their own exhaust trail, it also
>>means you can't easily see them coming quite as easily as a drive-guided
>>missile or torpedo.
>
>Actually you can see them when they're launched and compute their exact
>trajectory with ease. If they use engines to change course, you can see
Ian
>Ian wrote:
>
>> Lay-in-wait stealth isn't very useful, since maintaining basic minimal
>> power and running ships' computers, let along actually having a crew,
>> radiates enough heat to be detectable at extremely long range. Modern
>> telescopic IR sensors could detect a space shuttle _manouvering
>> thruster_ firing beyond the asteroid belt.
>
>If they already know where to look. It's a big solar system.
A modern telescope would need to know where to look, yes. The
warship-mounted "sensor of the future" (TM) can likely scan the entire
solar system in ten minutes or less.
>> Actually you can see them when they're launched and compute their
>> exact
>> trajectory with ease. If they use engines to change course, you can
>> see
>> that too.
>
>And the missile can compute your course changes and adjust accordingly
>as well.
Which is my entire point. Everyone knows exactly where everything is (or
at least where it was, adjusting for lightspeed delay). Problem is that
in a contest between a complex kinetic missile and a spacecraft, this
gives the spacecraft and it's point defense and/or antimissiles the
advantage. The best strategy for kinetic weapons is the "shotgun"
effect, fragmenting into a cloud of particles at whatever the optimal
range to ensure the enemy can't get out of the way is.
Ian
>They could detect it _if_ they were pointed at it.
Today's telescopes could detect it if they were pointed at it.
Tomorrow's scanning IR sensor could easily trace enough sky to scan the
solar system in hours, or even minutes, and it _will_ pick up anything
whose temperature is above background.
Tom Breton
>
> In article <b.evill-0509...@tynslip1.apana.org.au> Brett Evill,
> b.e...@spamblocker.tyndale.apana.org.au writes:
> >Will spaceships be painted black to prevent telescopic detection, or
> >mirrored to bounce laser-beams? Perhaps ships with heat-superconducting
> >armour will not be susceptible to significant damage by laser beams,
> >because they will have large radiating surfaces. Will that protect them
> >from particle beams?
>
> Definitely mirrored.
>
> 1) A black ship is a "blackbody", which is to say, unless your crew likes
> life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
> accessories.
I'd expect a ship to glow in IR, yes, unless extraordinary measures
are taken.
But not because of the crew's need for warmth. The surface of the
spaceship could be considerably colder than room temperature and still
be at thermal equilibrium, between 3K outside and room temperature
inside.
Rather, all sources of waste heat "count", and the engines will be a
big deal for any spaceship you can think about combat with.
Stealth measures mite include refrigerating most of the spaceship's
surface and moving the heat into (say) a pit on the surface so that
from some angles the ship is easily visible, while from other angles
it's not showing IR at all.
Another stealth approach, if far enuff away from the enemy, mite be to
spread out a really large surface and trickle just a little heat into
it, so that even tho its radiation is lower frequency, it still
rejects a lot of heat.
That has exponential problems, tho. Lowering the temperature linearly
reduces the heat energy rejected exponentially. If (EG) it was at a
temperature of 90 K, it would reject 1/100th as much heat per unit
area as if it were at room temperature (c.233 K). And 90 K is still
solidly in the far infrared.
I am mostly retreading last discussion.
> 2) "heat superconduction" has been claimed here to be a myth of Niven's
> unrelated to reality, and it seems believable. Heat by its nature is
> distributed between all sorts of random vibrational modes - how can it
> move QUICKLY, without pausing or getting sidetracked?
Indeed, "heat superconduction" is meaningless. How would heat be
"lost to friction/resistance/etc" anyways? "lost heat" is just heat
again!
> 3) As another thread pointed out, a black ship is a COLD ship, since it
> loses all that energy it's busy radiating, and gets back only weak
> distant sunlight. Unless it's near the sun - then it bakes.
Yes, altho you could say that underneath that black skin it's really
well insulated or something.
> 4) A mirrored ship sounds like a bright object. But what's it going to
> reflect? The sky in space is none too bright. So long as it has flat
> surfaces (like a Stealth bomber) it will send sunlight or bright
> starlight in a narrow and controllable range of directions.
Exactly.
Tom
J. Clarke
Given that all the astronomers and all the telescopes in the world haven't
yet succeeded in locating all the asteroids, I think that finding a single
spacecraft by pointing an infrared sensor at it is exceedingly unlikely
unless it is very close.
Chris Lawson
>Today's telescopes could detect it if they were pointed at it.
>Tomorrow's scanning IR sensor could easily trace enough sky to scan the
>solar system in hours, or even minutes, and it _will_ pick up anything
>whose temperature is above background.
OK, folks, let's assume for the sake of argument that anything
that radiates IR will be easily detected. This leaves several
possible tactics.
1. Cold, ballistic weapon. This would need to be launched out of
range (which could mean months between launch and strike).
2. Directional IR radiation. As far as I can tell, a rocket that
only radiates in one direction would be a pretty impressive bit
of engineering.
3. Using shields. A rocket could accelerate all it likes provided
it was hidden by a planet or star. The problems are (i) it's
pretty hard to hide behind a planet unless you're already
in-system; (ii) it requires that the target occupt a limited
volume of space -- any two widely-separated, communicating ships
would be immune to this form of stealth.
4. Overkill. Make the missile so massive and fast that it doesn't
matter if the enemy detects it. This would only work against
unmaneuvrable targets such as planets, moons, very large orbital
stations, etc. And it's not really stealth :-)
5. Shotgun missile. Once the missile gets within range it
separates into (pick a number) warheads. It would be extremely
difficult for the target to defend against this sort of attack.
Even if the attacker couldn't afford a thousand warheads per
missile, he can still use say 10 warheads and 990 decoys to
exhaust the target defences.
Suffice to say, in a space battle, the crucial technology may be
scanner range rather than weapon power.
Any other possible tactics?
regards,
Chris Lawson
Ian
>Ian wrote in message <35f7e532...@news.ktchnr1.on.wave.home.com>...
>>"J. Clarke" <nos...@nospam.nospam> wrote:
>>
>>>They could detect it _if_ they were pointed at it.
>>
>>Today's telescopes could detect it if they were pointed at it.
>>Tomorrow's scanning IR sensor could easily trace enough sky to scan the
>>solar system in hours, or even minutes, and it _will_ pick up anything
>>whose temperature is above background.
>
>Given that all the astronomers and all the telescopes in the world haven't
>yet succeeded in locating all the asteroids, I think that finding a single
>spacecraft by pointing an infrared sensor at it is exceedingly unlikely
>unless it is very close.
Last I checked, asteroids were not detected by infrared. They are, after
all, exactly the same temperature as the space around them, what with
not having electronics, crews, and power systems inside them generating
heat.
Infrared is by far the best detection method in space, providing you
want to detect warm objects. Radar and visual-wavelength searches are a
hell of a lot harder.
Ian
>iadm...@undergrad.math.uwaterloo.ca (Ian) wrote:
>
>>Today's telescopes could detect it if they were pointed at it.
>>Tomorrow's scanning IR sensor could easily trace enough sky to scan the
>>solar system in hours, or even minutes, and it _will_ pick up anything
>>whose temperature is above background.
>
>OK, folks, let's assume for the sake of argument that anything
>that radiates IR will be easily detected. This leaves several
>possible tactics.
>
>1. Cold, ballistic weapon. This would need to be launched out of
>range (which could mean months between launch and strike).
"Out of range" means "outside the solar system". We are talking
_billions_ of kilometers. A completely cold projectile also can't have
electronics active to watch out for interception - the enemy still has a
chance to detect it at closer range using non-IR means, and intercept
it.
>2. Directional IR radiation. As far as I can tell, a rocket that
>only radiates in one direction would be a pretty impressive bit
>of engineering.
Directional radiation is a viable method of IR stealth. The problem is
that the limits to its effectiveness are such that the whole ship still
has to be relatively cold. It doesn't work when your engines are on,
especially since the exjaust plume itself probably radiates a lot of IR.
And its "directionality" is limited, the most you could compress it
(even with a _large_ directional radiator assembly) would be to a 60
degree or so cone. Better make sure there are no enemy forces in a whole
60 degrees of sky...
>3. Using shields. A rocket could accelerate all it likes provided
>it was hidden by a planet or star. The problems are (i) it's
>pretty hard to hide behind a planet unless you're already
>in-system; (ii) it requires that the target occupt a limited
>volume of space -- any two widely-separated, communicating ships
>would be immune to this form of stealth.
It also requires that the side trying to do the detecting doesn't have
other ships or recon drones in a position to observe the "hidden"
acceleration.
>5. Shotgun missile. Once the missile gets within range it
>separates into (pick a number) warheads. It would be extremely
>difficult for the target to defend against this sort of attack.
>Even if the attacker couldn't afford a thousand warheads per
>missile, he can still use say 10 warheads and 990 decoys to
>exhaust the target defences.
Depends if they are ballistic or homing warheads. If kinetic, the enemy
could simply avoid them. If homing (ie each of them is actually a
fair-sized missile itself), you'r just using a lot of ordnance to try
and flood target defenses.
Decoys are of limited usefulness depending on scanner technology. It's
plausible that decoys light enough that you could deploy a truly
substantial number of them, could be identified as such very quickly by
a sufficiently advanced sensor/computer combination. Among other things,
a projectile is identified as a real missile the moment it uses its
engine. So "ballistic decoys" _might_ be workable, but they could be
avoided much more easily than guided projectiles, and if it's a
ballistic kinetic-kill weapon, then decoys are a bit pointless because a
"decoy" is also a kinetic-kill projectile. Putting guided missiles in
with decoys is fairly unworkable too - the defender can just put his
priority on shooting projectiles which have fired an engine, displaying
that they are real missiles.
>Suffice to say, in a space battle, the crucial technology may be
>scanner range rather than weapon power.
I'm fairly sure that this won't be true. In a plausible battle between
space warships, scanner tech for both sides will likely be much more
than enough so that the real range limit for scanners is caused by
lightspeed delay. At "combat ranges" of a few million kilometers or less
(when energy and projectile weapons have a chance of hitting), both
sides are likely to have scanners that see everything they really need
to see.
Paul Dietz
> yet succeeded in locating all the asteroids, I think that finding a single
> spacecraft by pointing an infrared sensor at it is exceedingly unlikely
> unless it is very close.
Most astronomers aren't looking for asteroids, and do not
observe in the IR (especially from above the atmosphere).
Most telescopes also have very narrow fields of view.
The "fast" telescopes with wide fields of view used
in NEO searches are few in number, funded miserably,
and work in visible light.
Paul
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>Ian wrote in message <35f7e532...@news.ktchnr1.on.wave.home.com>...
>>>"J. Clarke" <nos...@nospam.nospam> wrote:
>>>
>>>
>>>Today's telescopes could detect it if they were pointed at it.
>>>Tomorrow's scanning IR sensor could easily trace enough sky to scan the
>>>solar system in hours, or even minutes, and it _will_ pick up anything
>>>whose temperature is above background.
>>
>>yet succeeded in locating all the asteroids, I think that finding a single
>>spacecraft by pointing an infrared sensor at it is exceedingly unlikely
>>unless it is very close.
>
>all, exactly the same temperature as the space around them, what with
>not having electronics, crews, and power systems inside them generating
>heat.
All infrared is is a little bit different wavelength. Doesn't alter the
nature of the problem. And asteroids are not "at exactly the same
temperature as the space around them", the are at an equilibrium temperature
considerably above that of the cosmic background radiation. In point of
fact in the visible and the infrared an asteroid is a bright spot in the
darkness, and you problem is (a) detecting that bright spot and (b)
distinguishing it from all the other bright spots.
>Infrared is by far the best detection method in space, providing you
>want to detect warm objects. Radar and visual-wavelength searches are a
>hell of a lot harder.
The trouble is that (a) a dim warm object takes a pretty sensitive detector
with a small enough field of view that other bright warm objects don't mask
the target and (b) space is absolutely _full_ of "warm objects".
J. Clarke
background a different problem from detecting an object which glows in
visible against a dark background? And you'd be surprised at how many
astronomers are looking for asteroids. And given that astronomers have been
looking for asteroids ever since the first one was found, it seems that if
there was some quick way to find them it would have been implemented by now.
Only way you do it is to point a detector at a piece of sky, image, and then
analyze the image. Some rapidly whirling infrared detector may spot an
incoming ship, but it's also going to spot the Sun, 9 planets, dozens of
moons, thousands or millions of asteroids, and billions and billions of
stars. So how do you tell which of those is a ship?
If an incoming spaceship was the only object out there radiating infrared it
would be one thing, but it is not, and it is likely to be a fairly dim
object in that regard as well.
--
--John
Reply to jclarke at eye bee em dot net.
Paul Dietz wrote in message <35F2CA9D...@interaccess.com>...
>> Given that all the astronomers and all the telescopes in the world
haven't
>> yet succeeded in locating all the asteroids, I think that finding a
single
>> spacecraft by pointing an infrared sensor at it is exceedingly unlikely
>> unless it is very close.
>
John Schilling
>Ian wrote in message <35f7e532...@news.ktchnr1.on.wave.home.com>...
>>"J. Clarke" <nos...@nospam.nospam> wrote:
>>
>>>They could detect it _if_ they were pointed at it.
>>
>>Today's telescopes could detect it if they were pointed at it.
>>Tomorrow's scanning IR sensor could easily trace enough sky to scan the
>>solar system in hours, or even minutes, and it _will_ pick up anything
>>whose temperature is above background.
>Given that all the astronomers and all the telescopes in the world haven't
>yet succeeded in locating all the asteroids, I think that finding a single
>spacecraft by pointing an infrared sensor at it is exceedingly unlikely
>unless it is very close.
Given that most astronomers are engaged in research so intently focused on
tiny, remote corners of the universe that they would probably never notice
Jupiter in their entire professional careers, I don't know that this really
means much.
The fraction of the astronomical community's resources devoted to the search
for near-Earth, or even anywhere-in-the-solar-system, objects, is miniscule.
And the astronomical community as a whole has only a tiny fraction of the
resources of the world's military forces. The ability or inability of the
world's astronomers to comprehensively map the asteroids says nothing about
the ability of future spacefaring military forces to accomplish similar feats.
--
*John Schilling * "You can have Peace, *
*Member:AIAA,NRA,ACLU,SAS,LP * or you can have Freedom. *
*University of Southern California * Don't ever count on having both *
*Aerospace Engineering Department * at the same time." *
*schi...@spock.usc.edu * - Robert A. Heinlein *
*(213)-740-5311 or 747-2527 * Finger for PGP public key *
Erik Max Francis
> "Out of range" means "outside the solar system". We are talking
> _billions_ of kilometers. A completely cold projectile also can't have
> electronics active to watch out for interception - the enemy still has
> a
> chance to detect it at closer range using non-IR means, and intercept
> it.
You keep saying this, but can we have some figures on detection
capabilities?
For instance, let's say that our hypothetical infrared sensor can
resolve to magnitude 20 in the J band. In the ISO system, the J band
(wavelength 1.24 um, frequency 242 THz) has its zeroth magnitude at 1587
Jy, which is 1.587 x 10^-23 W/(m^2 Hz). At that frequency, that
corresponds to a flux of 3.84 x 10^-9 W/m^2.
Magnitude 20 is [100^(1/5)]^20 times dimmer, or exactly 10^8 times
dimmer, which puts the infrared flux for magnitude 20 at 3.84 x 10^-17
W/m^2.
As an example of how good this is, at a distance of 1 au = 150 Gm, you
detection threshhold for infrared emissions would be 10.9 MW. Anything
dimmer (in infrared) and you wouldn't be able to see it.
Do you have any figures backing up your claims on the effectiveness of
infrared for basically making _everything_ in the solar system instantly
trackable?
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@sade.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
USA / icbm 37 20 07 N 121 53 38 W / &tSftDotIotE
\
/ It is only to the individual that a soul is given.
/ Albert Einstein
J. Clarke
long time and not completed the job, I seriously doubt that anyone is going
to come up with some magic sensor that can do it in thirty seconds. And
while the paid astronomers aren't for the most part hunting for asteroids,
there are thousands of amateurs doing so, with considerable success. The
nature of the problem doesn't change because the military is working on it.
--
--John
Reply to jclarke at eye bee em dot net.
John Schilling wrote in message <6suqmn$99h$1...@spock.usc.edu>...
Paul Dietz
> only radiates in one direction would be a pretty impressive bit
> of engineering.
The problem is radiation from the rocket plume.
This was discussed in the previous incarnation of
this thread some month ago. You can get at least
some performance (several km/s) with very low IR
signature by using helium as reaction mass in a
nuclear thermal engine. Helium, being monatomic,
has no rotational or vibrational modes to store
energy for emission in the IR, and its electronic
excited states are at ~20 eV and above, which is
very high by thermal standards. The only concern
would be detection of the plume by interaction with
solar UV.
Direct radiation from the engine itself could
be restricted to a small solid angle with shields/
mirrors.
Paul
Paul Dietz
> background a different problem from detecting an object which glows in
> visible against a dark background?
It's different because (1) the atmosphere is not transparent to IR
in some of the wavelengths of interest, and (2) the telescope and
atmosphere *radiate* IR in the wavelengths of interest. You can
overcome this by putting cryogenic telescopes in space, but that's
currently expensive. In a future with space battleships it would
not be.
> And you'd be surprised at how many
> astronomers are looking for asteroids.
The number is a small fraction of the astronomical community,
both in number of observers and fraction of funding. And,
they're using visible light.
> And given that astronomers have been
> looking for asteroids ever since the first one was found, it seems that if
> there was some quick way to find them it would have been implemented by now.
> Only way you do it is to point a detector at a piece of sky, image, and then
> analyze the image.
Asteroids have been ignored, or reviled, by most astronomers for much of
this
century. They interfere with observation of deep sky objects.
Truly productive scans for NEOs use a time integration technique
in which the image is moved (by rotation of the earth) over a CCD
(or CCDs), with the charge being clocked to track the image. This
scans a strip across the sky. Repeat twice and look for moving
dots and/or streaks. This had to wait for sufficiently good CCDs,
cheap enough computers, software, and the funding to put it all
together. Only recently has this started to happen.
> If an incoming spaceship was the only object out there radiating infrared it
> would be one thing, but it is not, and it is likely to be a fairly dim
> object in that regard as well.
Imagining that current astronomical technology will still
be used in a future where interplanetary battleships are built
is an interestingly selective failure of the imagination.
Paul
Erik Max Francis
> Well, there are a lot of technological variables to consider, so as a
> baseline let's use today. What would happen if we mounted a single, 2
> meter aperture modern telescope to detect visual and near-IR radiation
> in space (We could use it to sweep across the entire sky within a few
> hours)? Turns out we can detect a space shuttle manouvering thruster
> firing from at least 15 million kilometers. Space shuttle main engines
> would be detectable from 20 billion kilometers (waaay outside the
> orbit
> of Pluto). A fairly small (not terribly larger than space shuttle)
> size
> ship using ion thrusters to accelerate at 1/1000 of a g would be
> detectable from 100 million kilometers or so. These calculations are
> from a post by John Schilling on 1/2/98.
I dug up his post, it's at
http://www.dejanews.com/getdoc.xp?AN=312184581
Quite frankly, I think there's something wrong with his numbers. The
detection threshhold that he gives is 2.5 x 10^-17 W/m^2, which is not
too different from the estimate I got based on an assumption of a
limiting magnitude of 20 (3.84 x 10^-17 W/m^2).
With a limiting flux of 2.5 x 10^-17 W/m^2, for a plume to be visible at
20 Tm, the source power must be 130 GW, all in the bands in which the
sensor is operating (he notes that this is a visual/near-infrared
system). Are the Space Shuttle main engines capable of 130 GW? I don't
have any figures in front of me.
And at a distance of 15 Gm, the limiting power is about 71 kW, which
sounds more reasonable.
John Schilling
>Well, given that the astronomical community has been about it for a rather
>long time and not completed the job, I seriously doubt that anyone is going
>to come up with some magic sensor that can do it in thirty seconds. And
>while the paid astronomers aren't for the most part hunting for asteroids,
>there are thousands of amateurs doing so, with considerable success. The
>nature of the problem doesn't change because the military is working on it.
The nature of the problem doesn't change, but the ammount of resources
being devoted to the problem does. By about three or four orders of
magnitude. And that makes for qualitatively different results. You
may say that the astronomical community has been about "it" for a very
long time, but all the manpower and equipment devoted to asteroid-hunting
in all of recorded history probably wouldn't add up to a month's worth
of the global military budget for sensors, sensor operators, sensor
platforms, and assorted logistical support.
You might as well judge the feasibility of antisubmarine warfare by
the frequency with which fisherman, oceanographers, and recreational
divers stumble across submarines.
Leonard Erickson
>> 2) "heat superconduction" has been claimed here to be a myth of Niven's
>> unrelated to reality, and it seems believable. Heat by its nature is
>> distributed between all sorts of random vibrational modes - how can it
>> move QUICKLY, without pausing or getting sidetracked?
>
>
> Indeed, "heat superconduction" is meaningless. How would heat be
> "lost to friction/resistance/etc" anyways? "lost heat" is just heat
> again!
As Niven envisioned it, "heat superconductivity" is essentially
infinite thermal conductivity. That is, the temp of the object is
uniform, even if one portion is receiving substantially more heat input
than the rest.
So if you had a long rod, and placed one end in the fire, all of it
would be too hot to handle.
>> 3) As another thread pointed out, a black ship is a COLD ship, since it
>> loses all that energy it's busy radiating, and gets back only weak
>> distant sunlight. Unless it's near the sun - then it bakes.
>
> Yes, altho you could say that underneath that black skin it's really
> well insulated or something.
In which case the crew or equipment roasts in a *very* short period of
time. Heat not radiated winds up as an increase in internal temp.
--
Leonard Erickson (aka Shadow)
sha...@krypton.rain.com <--preferred
leo...@qiclab.scn.rain.com <--last resort
John Schilling
>Ian wrote:
>> Well, there are a lot of technological variables to consider, so as a
>> baseline let's use today. What would happen if we mounted a single, 2
>> meter aperture modern telescope to detect visual and near-IR radiation
>> in space (We could use it to sweep across the entire sky within a few
>> hours)? Turns out we can detect a space shuttle manouvering thruster
>> firing from at least 15 million kilometers. Space shuttle main engines
>> would be detectable from 20 billion kilometers (waaay outside the
>> orbit
>> of Pluto). A fairly small (not terribly larger than space shuttle)
>> size
>> ship using ion thrusters to accelerate at 1/1000 of a g would be
>> detectable from 100 million kilometers or so. These calculations are
>> from a post by John Schilling on 1/2/98.
>I dug up his post, it's at
> http://www.dejanews.com/getdoc.xp?AN=312184581
>Quite frankly, I think there's something wrong with his numbers. The
>detection threshhold that he gives is 2.5 x 10^-17 W/m^2, which is not
>too different from the estimate I got based on an assumption of a
>limiting magnitude of 20 (3.84 x 10^-17 W/m^2).
There was a factor of 4*pi error in my initial post; I don't recall
exactly where offhand, but one of the readers caught it fairly quickly
and I was able correct for it. IIRC, the range of the original sensor
as described should be reduced by sqrt(4*pi), or seventy percent, giving
space shuttle detection at "only" six billion kilometers. A mark II
sensor restoring the original performance required a somewhat more
expensive detector array, but still (barely) within reach of current
technology.
>With a limiting flux of 2.5 x 10^-17 W/m^2, for a plume to be visible at
>20 Tm, the source power must be 130 GW, all in the bands in which the
>sensor is operating (he notes that this is a visual/near-infrared
>system). Are the Space Shuttle main engines capable of 130 GW? I don't
>have any figures in front of me.
The SSMEs produce a shade under 5 GW each, and the solid boosters 33 GW.
So figure 80 GW at launch. Not all of that is radiated, of course. Not
even most of it. But the radiated fraction times the missing 4*pi is
probably fairly close to 130 GW.
>And at a distance of 15 Gm, the limiting power is about 71 kW, which
>sounds more reasonable.
The smallest attitude control thrusters on the space shuttle run at
140 kw, so again the numbers tend to match up.
Which is the missing half of the equation in most analyses. Space
travel requires, well, astronomical energies, and it is remarkably
difficult to hide astronomical energy releases against effectively
zero background. One can handwave about hyperefficient drives or
clever directional radiators or whatnot, but even a tiny fraction
of a percent of the energy leaking out as isotropic radiation will
kill you. Until someone repeals the second law of thermodynamics,
I am quite skeptical about proposals to do *anything* with an
efficiency that requires more nines to express than I can count on
one hand, which is pretty much what practical stealth in space would
require.
Ian
>> "Out of range" means "outside the solar system". We are talking
>> _billions_ of kilometers. A completely cold projectile also can't have
>> electronics active to watch out for interception - the enemy still has
>> a
>> chance to detect it at closer range using non-IR means, and intercept
>> it.
>
>You keep saying this, but can we have some figures on detection
>capabilities?
Well, there are a lot of technological variables to consider, so as a
baseline let's use today. What would happen if we mounted a single, 2
meter aperture modern telescope to detect visual and near-IR radiation
in space (We could use it to sweep across the entire sky within a few
hours)? Turns out we can detect a space shuttle manouvering thruster
firing from at least 15 million kilometers. Space shuttle main engines
would be detectable from 20 billion kilometers (waaay outside the orbit
of Pluto). A fairly small (not terribly larger than space shuttle) size
ship using ion thrusters to accelerate at 1/1000 of a g would be
detectable from 100 million kilometers or so. These calculations are
from a post by John Schilling on 1/2/98.
So even with _today's_ technology, any major engine burn can be detected
to Pluto's orbit and beyond, use of manouvering thrusters or low-thrust,
highly efficient engines out to many millions of kilometers. Detection
of objects which are merely radiating, not thrusting, is a bit harder to
calculate since their surface area and exact temperature must be taken
into account among other things.
By the time interplanetary warships are feasible, it's likely that IR
detection technology will be at least 10 times as sensitive as it is
today, perhaps much more - and dedicated observation stations, keeping
in comminication with warships for long-range threat warning, could use
telescopes with apertures _far_ larger than 10 meters.
So it's plausible to have warships that can detect extraordinarily small
engine firings, or large ships that are not firing engines at all, over
100 million kilometers away, and that can detect main engines firing
well beyond Pluto's orbit. Dedicated observation stations, using arrays
of very large telescopes, can likely detect any operational warship out
to billions of kilometers whether its engines are firing or not,
communicate this information to the warships, who can then use pinpoint
tracking telescopes to get a lock on these far-off targets and keep tabs
on them.
Ian
>So how is detecting an object which glows in infrared against a dark
>background a different problem from detecting an object which glows in
>visible against a dark background?
Asteroids don't radiate in visible, they only reflect what visible light
from the stars and the sun hits them. In contrast, any object with a
temperature above that of the background actually _radiates_ infrared.
Warm objects in deep space are simply much brighter in infrared than
they are in the visible spectrum.
>analyze the image. Some rapidly whirling infrared detector may spot an
>incoming ship, but it's also going to spot the Sun, 9 planets, dozens of
>moons, thousands or millions of asteroids, and billions and billions of
>stars.
No, it's NOT going to spot most of those.
It's not going to spot asteroids, they're not warmer than background.
And it's not going to spot most of the stars, they _are_ the background.
Sure it'll spot the sun and the planets and particularly bright stars,
but it will instantly disregard these because their exact positions are
known.
Ian
>Well, given that the astronomical community has been about it for a rather
>long time and not completed the job, I seriously doubt that anyone is going
>to come up with some magic sensor that can do it in thirty seconds. And
>while the paid astronomers aren't for the most part hunting for asteroids,
>there are thousands of amateurs doing so, with considerable success. The
>nature of the problem doesn't change because the military is working on it.
No, the scope of resources dedicated is what changes. By a LOT. The
telescopic array of a single spaceborn, dedicated IR observation station
would easily exceed the combined capabilities of every telescope on
Earth ever used for searching for near-Earth objects. Sort of like the
difference between a pre-WWII research radar, and the modern US air
defense net.
Ian
>With a limiting flux of 2.5 x 10^-17 W/m^2, for a plume to be visible at
>20 Tm, the source power must be 130 GW, all in the bands in which the
>sensor is operating (he notes that this is a visual/near-infrared
>system). Are the Space Shuttle main engines capable of 130 GW? I don't
>have any figures in front of me.
130 GW is a lot of power, but a liquid fueled rocket capable of lifting
a space shuttle into orbit is a pretty big, bright engine.
John Park
about 16 MJ/kg. Guessing that the combustion of the shuttle's fuel produces
about 5000 t of water, and neglecting the kinetic energy of the shuttle
itself, the energy released is about 80 TJ. If the burn time is about
1000 sec this gives a power of ca. 80 GW. In the right ballpark at least.
--John Park
Ian
>As Niven envisioned it, "heat superconductivity" is essentially
>infinite thermal conductivity. That is, the temp of the object is
>uniform, even if one portion is receiving substantially more heat input
>than the rest.
>
>So if you had a long rod, and placed one end in the fire, all of it
>would be too hot to handle.
Problem is there are no known substances which superconduct heat, nor
any known mechanism by which this could occur. Niven seemed to simply
assume that "superconductor" meant superconductor in all senses, when it
really just means "of electricity".
Superconducting electricity just means that the electricity travels
through the object as fast as it normally does, but resistance doesn't
occur. There is no "resistance" to heat - it's just a bunch of
vibrational kinetic energy transmitted between atoms. You'd have to
increase the speed of transmission of this energy to lightspeed for heat
"superconductivity", which means that the atoms in question would have
to be vibrating at lightspeed... oops, that's impossible.
Ian
>Which is the missing half of the equation in most analyses. Space
>travel requires, well, astronomical energies, and it is remarkably
>difficult to hide astronomical energy releases against effectively
>zero background. One can handwave about hyperefficient drives or
>clever directional radiators or whatnot, but even a tiny fraction
>of a percent of the energy leaking out as isotropic radiation will
>kill you. Until someone repeals the second law of thermodynamics,
>I am quite skeptical about proposals to do *anything* with an
>efficiency that requires more nines to express than I can count on
>one hand, which is pretty much what practical stealth in space would
>require.
Stealthed engines, yeah, basically impossible. It's just barely possible
to coast at stealth levels that would reduce detection ranges from most
angles tremendously, _if_ your ship is capable of running very cold (ie
no engines, no main power, any crew in suspended animation and
nonessential computers deactivated). Sort of makes stealth useless for
anything but getting up to speed billions of kilometers away, and
coasting for months to get within a few million kilometers of the enemy
before detection.
Brett Evill
>Given that all the astronomers and all the telescopes in the world haven't
>yet succeeded in locating all the asteroids, I think that finding a single
>spacecraft by pointing an infrared sensor at it is exceedingly unlikely
>unless it is very close.
alt.non.sequitur
Asteroids are in thermal equilibrium. They won't show up on IR. Spaceships
cannot be in thermal equilibrium, they must radiate in IR.
The question that seems of more concern to me is whether these sensors
will be able readily to distinguish asteroids from *stars*.
--
Brett Evill
To reply by e-mail, remove 'spamblocker.' from <b.e...@spamblocker.tyndale.apana.org.au>
Erik Max Francis
> Problem is there are no known substances which superconduct heat, nor
> any known mechanism by which this could occur. Niven seemed to simply
> assume that "superconductor" meant superconductor in all senses, when
> it
> really just means "of electricity".
To be fair to Niven, I think it's clear that he knew this. He
specifically talked about "heat superconductors," clearly distinguishing
them from normal superconductors. While superconduction of heat is
physically baseless, he _was_ specifically distinguishing between normal
superconduction and the science-fictional premise which he was using in
his stories.
Paul Dietz
> cannot be in thermal equilibrium, they must radiate in IR.
No.
(Hint: asteroids are typically not very reflective. Where
does the energy absorbed from sunlight go?)
Paul
Brett Evill
<di...@interaccess.com> wrote:
It warms them up until they radiate heat as fast as they absorb it. This
condition is called 'thermal equilibrium'. Ooh! Look! That's the condition
that I said that they would be in.
An ideal black body, that absorbs every milliwatt of radiation that falls
on it can still be in thermal equilibrium with its surroundings. And when
you do the physics, it turns out that you expect such a black body to be
in thermal equilibrium when is is the same temperature as its surroundings
(averaged by subtended angle).
But a working spaceship, that has to radiate all of its waste heat as well
as reflecting or reradiating the sunlight that falls on it. So a working
spaceship will always be warmer than an asteroid at the same distance from
the Sun, and will have a higher-frequency and brighterr IR signature.
J. Clarke
--
--John
Reply to jclarke at eye bee em dot net.
Paul Dietz wrote in message <35F324B7...@interaccess.com>...
>> So how is detecting an object which glows in infrared against a dark
>> background a different problem from detecting an object which glows in
>> visible against a dark background?
>
>It's different because (1) the atmosphere is not transparent to IR
>in some of the wavelengths of interest, and (2) the telescope and
>atmosphere *radiate* IR in the wavelengths of interest. You can
>overcome this by putting cryogenic telescopes in space, but that's
>currently expensive. In a future with space battleships it would
>not be.
You haven't demonstrated any difference that would reduce the level of
effort required, merely.
>> And you'd be surprised at how many
>> astronomers are looking for asteroids.
>
>The number is a small fraction of the astronomical community,
>both in number of observers and fraction of funding. And,
>they're using visible light.
Which is irrelevant, unless perhaps you can demonstrate that is easier to
build an IR sensor that can scan wide areas and distinguish a spaceship from
all the other emitters than it is to build a visible spectrum sensor to
perform that task.
>> And given that astronomers have been
>> looking for asteroids ever since the first one was found, it seems that
if
>> there was some quick way to find them it would have been implemented by
now.
>> Only way you do it is to point a detector at a piece of sky, image, and
then
>> analyze the image.
>
>Asteroids have been ignored, or reviled, by most astronomers for much of
>this
>century. They interfere with observation of deep sky objects.
Yes, they do, and they are being cataloged among other things so that the
astronomers know when an asteroid will be interfering in that manner.
>Truly productive scans for NEOs use a time integration technique
>in which the image is moved (by rotation of the earth) over a CCD
>(or CCDs), with the charge being clocked to track the image. This
>scans a strip across the sky. Repeat twice and look for moving
>dots and/or streaks. This had to wait for sufficiently good CCDs,
>cheap enough computers, software, and the funding to put it all
>together. Only recently has this started to happen.
And how long does it take to scan the entire sky with such a sensor?
>> If an incoming spaceship was the only object out there radiating infrared
it
>> would be one thing, but it is not, and it is likely to be a fairly dim
>> object in that regard as well.
>
>Imagining that current astronomical technology will still
>be used in a future where interplanetary battleships are built
>is an interestingly selective failure of the imagination.
I'm sorry, but optics is optics. If you want to postulate some baloneytron
that detects spaceships by magic, that's fine, but if you are going to claim
that they can be detected by infrared then you're going to have to make a
case for it, which you have not.
>
> Paul
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>So how is detecting an object which glows in infrared against a dark
>>background a different problem from detecting an object which glows in
>>visible against a dark background?
>
>from the stars and the sun hits them. In contrast, any object with a
>temperature above that of the background actually _radiates_ infrared.
>Warm objects in deep space are simply much brighter in infrared than
>they are in the visible spectrum.
Are they? Do you have numbers to support this contention? In any case,
they are still objects against a background containing many other objects,
so how do you distinguish?
>>analyze the image. Some rapidly whirling infrared detector may spot an
>>incoming ship, but it's also going to spot the Sun, 9 planets, dozens of
>>moons, thousands or millions of asteroids, and billions and billions of
>>stars.
>
>No, it's NOT going to spot most of those.
>
>It's not going to spot asteroids, they're not warmer than background.
Asteroids are not warmer than "background"? What exactly do you believe the
temperature of an asteroid to be and what do you believe the temperature of
the background to be?
>And it's not going to spot most of the stars, they _are_ the background.
They are? Then what is all that black area up there? You really should
read an elementary astronomy book before you pontificate you know.
>Sure it'll spot the sun and the planets and particularly bright stars,
>but it will instantly disregard these because their exact positions are
>known.
I see. So all that an enemy has to do is align himself between your sensor
the sun or a bright star and it ignores him. Great design. In any case
until the entire galaxy is mapped this will work only in developed systems,
not in the hinterlands where a ship is operating alone.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>Well, given that the astronomical community has been about it for a rather
>>long time and not completed the job, I seriously doubt that anyone is
going
>>to come up with some magic sensor that can do it in thirty seconds. And
>>while the paid astronomers aren't for the most part hunting for asteroids,
>>there are thousands of amateurs doing so, with considerable success. The
>>nature of the problem doesn't change because the military is working on
it.
>
>No, the scope of resources dedicated is what changes. By a LOT. The
>telescopic array of a single spaceborn, dedicated IR observation station
>would easily exceed the combined capabilities of every telescope on
>Earth ever used for searching for near-Earth objects.
Why do you keep harping on "near earth objects"? They are not the only
asteroids out there.
>Sort of like the
>difference between a pre-WWII research radar, and the modern US air
>defense net.
This is fine if you can afford to dedicate a station to this task. But how
about if your ship is out in the boonies? Is is going to tow your station
along everywhere it goes?
In my first post on this topic, which you obviously neglected to read, I
stated clearly that the infrared method _might_ work in a star system with
an established industrial base, but not for a ship operating alone. So
kindly in the future restrain your remarks to that context and not the one
which I have already stipulated.
J. Clarke
--
--John
Reply to jclarke at eye bee em dot net.
John Schilling wrote in message <6svorr$aj7$1...@spock.usc.edu>...
>"J. Clarke" <nos...@nospam.nospam> writes:
>
>>Well, given that the astronomical community has been about it for a rather
>>long time and not completed the job, I seriously doubt that anyone is
going
>>to come up with some magic sensor that can do it in thirty seconds. And
>>while the paid astronomers aren't for the most part hunting for asteroids,
>>there are thousands of amateurs doing so, with considerable success. The
>>nature of the problem doesn't change because the military is working on
it.
>
>
>The nature of the problem doesn't change, but the ammount of resources
>being devoted to the problem does. By about three or four orders of
>magnitude. And that makes for qualitatively different results. You
>may say that the astronomical community has been about "it" for a very
>long time, but all the manpower and equipment devoted to asteroid-hunting
>in all of recorded history probably wouldn't add up to a month's worth
>of the global military budget for sensors, sensor operators, sensor
>platforms, and assorted logistical support.
>
>You might as well judge the feasibility of antisubmarine warfare by
>the frequency with which fisherman, oceanographers, and recreational
>divers stumble across submarines.
>
>
J. Clarke
"radiating heat" was another way to say "emitting infrared". So what does
that do to your argument?
Yes, the object is the same temperature as its surroundings, averaged by
subtended angle. The trouble with this is that those surroundings are mostly
very cold sink with one very hot source, so the equilibrium temperature is
somewhere between.
What do you believe the radiation temperature of the background to be, and
the radiation temperature of an asteroid?
--
--John
Reply to jclarke at eye bee em dot net.
Brett Evill wrote in message ...
J. Clarke
Second item, what is the probability that a spacecraft operated by someone
who understands the capabilities of your sensors is going to be doing one of
these things at the exact time that you have the sensor pointed at it?
--
--John
Reply to jclarke at eye bee em dot net.
Ian wrote in message <36002309...@news.ktchnr1.on.wave.home.com>...
>Erik Max Francis <m...@alcyone.com> wrote:
>
Brett Evill
>Asteroids are not warmer than "background"? What exactly do you believe the
>temperature of an asteroid to be and what do you believe the temperature of
>the background to be?
The IR signature of the cosmic background is equivalent to a black body
radiating at an effective temperature of 3K.
Thermal equilibrium at the orbit of the Earth is about 260-270K. It varies
inversely with the square root of distance from the Sun.
Black-body radiation varies with the fourth power of the temperature, and
the frequency of the maximum on the power curve is proportional to the
temperature.
It would seem that the obvious way to distinguish stars, inert lumps, and
working spacecraft is to measure their brightness (CCD cameras will do
this) at several different wavelengths in the IR and visible. This will
allow you to work out roughly at what wavelength the maximum of power is,
and that will let you sort them into temperature categories.
Of course, this is hard to do with ground-based instruments because the
atmosphere is largely opaque to IR, especially in the longer wavelengths,
and because all of your instruments are sitting in a warm bath of air. To
detect deep IR photons, you really need to use instruments that are too
cool to emit much thermal radiation at the relevant frequencies. But
cyrogenic cooling is conparatively easy in vaccuum.
It certainly seems to me that detection of working spacecraft can be made
rapid and mechanical. The only problem I can see it that if the sweeping
telescopes have a narrow field of view a complete 4.pi steradian sweep
might take a while. Can anyone think of a reason why the field of view
need be small or the sweeping slow.
Paul Dietz
> >overcome this by putting cryogenic telescopes in space, but that's
> >currently expensive. In a future with space battleships it would
> >not be.
>
> You haven't demonstrated any difference that would reduce the level of
> effort required, merely.
(with annoyance) I had assumed some intelligence on the part
of the reader. Think -- the whole spacewar scenario assumes
a level space ability far beyond what we have today, with
much lower cost to reach space and operate in space. That
by itself makes space telescopes (cryogenic or otherwise)
less difficult.
> >The number is a small fraction of the astronomical community,
> >both in number of observers and fraction of funding. And,
> >they're using visible light.
>
> Which is irrelevant, unless perhaps you can demonstrate that is easier to
> build an IR sensor that can scan wide areas and distinguish a spaceship from
> all the other emitters than it is to build a visible spectrum sensor to
> perform that task.
No, it is not irrelevant. The small effort being expended
on asteroid searches shows that you can't use current results
as a limit of what a larger scale program would do.
> >Imagining that current astronomical technology will still
> >be used in a future where interplanetary battleships are built
> >is an interestingly selective failure of the imagination.
> I'm sorry, but optics is optics. If you want to postulate some baloneytron
> that detects spaceships by magic, that's fine, but if you are going to claim
> that they can be detected by infrared then you're going to have to make a
> case for it, which you have not.
Bigger apertures, better sensors, better computers. All
of this is easier than building space battleships.
Paul
Paul Dietz
> >> cannot be in thermal equilibrium, they must radiate in IR.
> >
> >No.
> >
> >(Hint: asteroids are typically not very reflective. Where
> >does the energy absorbed from sunlight go?)
>
> It warms them up until they radiate heat as fast as they absorb it. This
> condition is called 'thermal equilibrium'. Ooh! Look! That's the condition
> that I said that they would be in.
And your contention that they would not show up on IR
is completely wrong. Yes, they warm up until they are in
a kind of equilibrium (not thermodynamic equilibrium in
its precise sense). BUT... they are then much warmer
than 2.73K, and would show up quite nicely in the IR.
Look, IR observations are *already* used to estimate
albedos of asteroids (if not to search for them).
> An ideal black body, that absorbs every milliwatt of radiation that falls
> on it can still be in thermal equilibrium with its surroundings. And when
> you do the physics, it turns out that you expect such a black body to be
> in thermal equilibrium when is is the same temperature as its surroundings
> (averaged by subtended angle).
There's your confusion: you are confusing a state
of dynamic equilibrium with the much more strictly
defined state of thermodynamic equilibrium. This
asteroid cannot in thermodynamic equilibrium with
its surroundings, since the surroundings itself
(sun, microwave background) are not in thermodynamic
equilibrium.
Paul
Ian
>Are they? Do you have numbers to support this contention? In any case,
>they are still objects against a background containing many other objects,
>so how do you distinguish?
There is a nice device which, given the sensory return from an object
and a catalog of all known objects with their positions, is capable of
determining whether the sensory return is of a known or unknown object,
and giving ideas as to such characteristics as its location, velocity,
and temperature.
This miracle of science is called a "computer".
Your assertion is sort of like "an airplane flying at mach 2 is just an
object against a background of other objects, with other similar objects
around it, so how does a radar distinguish enemy aircraft"?
If one is fighting space battles in the solar system with advanced IR
observation technology, the following factors are likely to be true:
1. The positions of space objects, bright stars, friendly ships, and
other IR emitters will be recorded and known.
2. Detecting any object which is accelerating, emitting anything other
than IR, or doing anything un-rocklike, and then keeping track of which
object it is, is trivial.
3. Relative motion to multiple observers can easily be used to calculate
distance to an object, which allows strength of emission to be used to
calculate the temperature of the object. Since live ships must be hotter
than floating rocks, any object within the solar system that is hotter
than a floating rock is man-made and should be investigated further.
4. The scanning IR sensor is not the only sensor the ship possesses - if
anything is suspicious or hard to identify, more powerful and/or
different sensors may be pointed specifically at it to find out what it
is.
>>Sure it'll spot the sun and the planets and particularly bright stars,
>>but it will instantly disregard these because their exact positions are
>>known.
>
>I see. So all that an enemy has to do is align himself between your sensor
>the sun or a bright star and it ignores him.
Actually he will show up as an unexpected cold or warm spot unless his
distance from you and his level of radiation mean he is just as bright
as what he's between you and.
Also, he'd have to _stay_ between you and the object, which is going to
be damn hard if you're both moving. He'd need to accelerate either to
get in position, or stay in position. And if he accelerates, he is _far_
more detectable, and probably far brighter than any natural radiating
body (excepting the sun, at least).
>Great design. In any case
>until the entire galaxy is mapped this will work only in developed systems,
>not in the hinterlands where a ship is operating alone.
"Developed systems"? Developed SYSTEMS? This is NOT a discussion about a
world where FTL exists, since we cannot have any sort of plausible
discussion about that at all. Maybe ships can radiate their waste heat
into hyperspace, or maybe warp power cores can be detectable clear
across the galaxy! The context of this discussion has been
interplanetary war within the solar system.
Ian
>>Sort of like the
>>difference between a pre-WWII research radar, and the modern US air
>>defense net.
>
>This is fine if you can afford to dedicate a station to this task. But how
>about if your ship is out in the boonies? Is is going to tow your station
>along everywhere it goes?
What, exactly, are the "boonies" when a pair of observation stations in
Earth orbit can scan the entire solar system?
>In my first post on this topic, which you obviously neglected to read, I
>stated clearly that the infrared method _might_ work in a star system with
>an established industrial base, but not for a ship operating alone.
You are apparently the only person in this entire discussion which is
assuming inter_stellar_ travel, which is an entirely different ball game
from the interplanetary war the rest of us are talking about.
Ian
>First item, how long an exposure is required to achieve these results.
>Second item, what is the probability that a spacecraft operated by someone
>who understands the capabilities of your sensors is going to be doing one of
>these things at the exact time that you have the sensor pointed at it?
They don't know when our sensors are pointed at it (which is likely once
an hour or more frequently - with multiple ships and multiple
observation stations, quite plausibly, once a minute). Meaningful
acceleration requires _sustained_ burn. Not to mention that the exhaust
plume of any system that leaves one, doesn't cool instantly. And that
powerful enough sensors will detect any spaceship with running power.
Steve Hix
> > >> Asteroids are in thermal equilibrium. They won't show up on IR.
> > > >> Spaceships cannot be in thermal equilibrium, they must radiate in IR.
> > >
> > >No.
> > >
> > >(Hint: asteroids are typically not very reflective. Where
> > >does the energy absorbed from sunlight go?)
> >
> > It warms them up until they radiate heat as fast as they absorb it. This
> > condition is called 'thermal equilibrium'. Ooh! Look! That's the condition
> > that I said that they would be in.
You don't understand equilibrium, apparently.
It does *not* mean "no emission", nor does it mean "emitting at the
3 degree Kelvin level" (in this case).
All it means is that the body is at equilibrium, it isn't changing
it's temperature. It's a steady state condition.
The moon can be looked at as a (really big) asteroid...does it
show up in IR?
Brett Evill
> unrelated to reality, and it seems believable. Heat by its nature is
> distributed between all sorts of random vibrational modes - how can it
> move QUICKLY, without pausing or getting sidetracked?
I find that when I stir a cup of tea with a sterling silver spoon my
finger get hot a lot more quickly than when I stir a cup of coffee with a
stainless-steel spoon. Perhaps it's something to do with the thermal
differences between coffee and tea.
Sarcasm aside, a spaceship threatened by a laser weapon will probably spin
to spread the heat out, and it will probably have a shiny surface to
reflect the beam away (will this be a few atoms thickness of lithium of
half an inch of silver?).
Another obvious strategy is to use a hull material with high thermal
conductivity so as to spread the heat out through a large thermal mass and
over a large radiating surface. The people who make strongboxes use a
layer of copper under the hardened stell shell to accomplish this. Is
there something that would be better than copper for filling this role on
spacecraft?
Tom Breton
>
> Ian wrote in message <3602278f...@news.ktchnr1.on.wave.home.com>...
> >"J. Clarke" <nos...@nospam.nospam> wrote:
> >
> >>Well, given that the astronomical community has been about it for a rather
> >>long time and not completed the job, I seriously doubt that anyone is
> going
> >>to come up with some magic sensor that can do it in thirty seconds. And
> >>while the paid astronomers aren't for the most part hunting for asteroids,
> >>there are thousands of amateurs doing so, with considerable success. The
> >>nature of the problem doesn't change because the military is working on
> it.
> >
> >No, the scope of resources dedicated is what changes. By a LOT. The
> >telescopic array of a single spaceborn, dedicated IR observation station
> >would easily exceed the combined capabilities of every telescope on
> >Earth ever used for searching for near-Earth objects.
>
> Why do you keep harping on "near earth objects"? They are not the only
> asteroids out there.
Because earth-crossing asteroids are the ones that are most heavily
being searched for. They are the most important to find, because they
mite smack into Earth, an event whose significance should not be
underestimated.
Tom
Tom Breton
>
> In article <35F3CDAC...@interaccess.com>, Paul Dietz
> <di...@interaccess.com> wrote:
>
> >> Asteroids are in thermal equilibrium. They won't show up on IR. Spaceships
> >> cannot be in thermal equilibrium, they must radiate in IR.
> >
> >No.
> >
> >(Hint: asteroids are typically not very reflective. Where
> >does the energy absorbed from sunlight go?)
>
> It warms them up until they radiate heat as fast as they absorb it. This
> condition is called 'thermal equilibrium'. Ooh! Look! That's the condition
> that I said that they would be in.
Yes, they are in thermal equilibrium wrt the radiative panorama
around them. Well, close to it: consider eccentric orbits and
rotation that rearranges its albedo wrt radiative sources & sinks. EG,
an asteroid that was half white and half black would have distinctly
different equilibrium temperatures depending on which part was facing
the sun. Anyways...
However, their thermal equilibrium is not the same as the 3K
background radiation, which is the backdrop it is to be detected
against.
Tom
J. Clarke
>>> You can
>> >overcome this by putting cryogenic telescopes in space, but that's
>> >currently expensive. In a future with space battleships it would
>> >not be.
>>
>> You haven't demonstrated any difference that would reduce the level of
>> effort required, merely.
>
>(with annoyance) I had assumed some intelligence on the part
>of the reader. Think -- the whole spacewar scenario assumes
>a level space ability far beyond what we have today, with
>much lower cost to reach space and operate in space. That
>by itself makes space telescopes (cryogenic or otherwise)
>less difficult.
If you actually read the messages to which you were responding and thought
about the issues being raised for a while then you would be less annoyed.
The level of space ability is irrelevant. It takes x number of observations
with y sensitivity and z field of view in order to search the entire sky for
an object. It doesn't matter one iota whether what frequency the object is
radiating. The frequency affects the details of the device, but not the
logistics of the search.
Furthermore, if you had actually read the messages you would see that I have
stipulated, several times now, that an incoming spacecraft could be detected
by the sort of sensors that would be present in a _developed_ star system.
The sort of sensors that a single ship could carry would be quite different,
unless you are suggesting that all the military resources of a civilization
would be present in a single ship.
>> >The number is a small fraction of the astronomical community,
>> >both in number of observers and fraction of funding. And,
>> >they're using visible light.
>>
>> Which is irrelevant, unless perhaps you can demonstrate that is easier to
>> build an IR sensor that can scan wide areas and distinguish a spaceship
from
>> all the other emitters than it is to build a visible spectrum sensor to
>> perform that task.
>
>No, it is not irrelevant. The small effort being expended
>on asteroid searches shows that you can't use current results
>as a limit of what a larger scale program would do.
A red herring sir. Tell me why the _logistics_ are different for IR.
Remember that to reliably detect incoming spaceships this "small effort" has
to be repeated every few minutes. That makes it a _much_ larger effort.
>> >Imagining that current astronomical technology will still
>> >be used in a future where interplanetary battleships are built
>> >is an interestingly selective failure of the imagination.
>
>> I'm sorry, but optics is optics. If you want to postulate some
baloneytron
>> that detects spaceships by magic, that's fine, but if you are going to
claim
>> that they can be detected by infrared then you're going to have to make a
>> case for it, which you have not.
>
>Bigger apertures, better sensors, better computers. All
>of this is easier than building space battleships.
How do bigger apertures help? One can see most asteroids with a back yard
telescope. How do better sensors help? The ones that your typical backyard
astronomer can buy are sufficient to the task. How do better computers
help? Computers can't collect data, just interpret it.
>
> Paul
J. Clarke
wrote:
>
>>Asteroids are not warmer than "background"? What exactly do you believe
the
>>temperature of an asteroid to be and what do you believe the temperature
of
>>the background to be?
>
>The IR signature of the cosmic background is equivalent to a black body
>radiating at an effective temperature of 3K.
>
>Thermal equilibrium at the orbit of the Earth is about 260-270K. It varies
>inversely with the square root of distance from the Sun.
>
>Black-body radiation varies with the fourth power of the temperature, and
>the frequency of the maximum on the power curve is proportional to the
>temperature.
>
>It would seem that the obvious way to distinguish stars, inert lumps, and
>working spacecraft is to measure their brightness (CCD cameras will do
>this) at several different wavelengths in the IR and visible. This will
>allow you to work out roughly at what wavelength the maximum of power is,
>and that will let you sort them into temperature categories.
So let's see, basically you're going to take spectra with several different
instruments? How long is it going to take you do this for the entire sky?
>Of course, this is hard to do with ground-based instruments because the
>atmosphere is largely opaque to IR, especially in the longer wavelengths,
>and because all of your instruments are sitting in a warm bath of air. To
>detect deep IR photons, you really need to use instruments that are too
>cool to emit much thermal radiation at the relevant frequencies. But
>cyrogenic cooling is conparatively easy in vaccuum.
>
>It certainly seems to me that detection of working spacecraft can be made
>rapid and mechanical. The only problem I can see it that if the sweeping
>telescopes have a narrow field of view a complete 4.pi steradian sweep
>might take a while. Can anyone think of a reason why the field of view
>need be small or the sweeping slow.
The larger the field the more objects are in it. The rate of sweep is going
to be controlled by the amount of time necessary to secure enough data for
your analysis. For your spectrum you'll need multiple images with different
filters as a minimum, or else you'll need to do spectrographic analysis of
every object in the field. How long does that take?
>
>--
>Brett Evill
>
>To reply by e-mail, remove 'spamblocker.' from
<b.e...@spamblocker.tyndale.apana.org.au>
--
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>Are they? Do you have numbers to support this contention? In any case,
>>they are still objects against a background containing many other objects,
>>so how do you distinguish?
>
>There is a nice device which, given the sensory return from an object
>and a catalog of all known objects with their positions, is capable of
>determining whether the sensory return is of a known or unknown object,
>and giving ideas as to such characteristics as its location, velocity,
>and temperature.
So exactly how do you get all of this data into the computer for a solar
system which you have never entered before?
>This miracle of science is called a "computer".
>Your assertion is sort of like "an airplane flying at mach 2 is just an
>object against a background of other objects, with other similar objects
>around it, so how does a radar distinguish enemy aircraft"?
Not quite. Other objects don't fly Mach 2. But many objects have
temperatures of the sort that are comfortable for humans.
>If one is fighting space battles in the solar system with advanced IR
>observation technology, the following factors are likely to be true:
>
>1. The positions of space objects, bright stars, friendly ships, and
>other IR emitters will be recorded and known.
In a developed star system much of this will be known.
>2. Detecting any object which is accelerating, emitting anything other
>than IR, or doing anything un-rocklike, and then keeping track of which
>object it is, is trivial.
And of course your opponent is going to cooperate by doing one of these
things when you have a sensor pointed at him.
>3. Relative motion to multiple observers can easily be used to calculate
>distance to an object, which allows strength of emission to be used to
>calculate the temperature of the object.
Sorry, but strength of emission has no relationship whatsoever to
temperature. How does a single vessel obtain "relative motion to multiple
observers"?
>Since live ships must be hotter
>than floating rocks, any object within the solar system that is hotter
>than a floating rock is man-made and should be investigated further.
The temperature of a spaceship is going to be that temperature which the
crew finds comfortable. It may be hotter, colder, or the same as any given
rock depending on the distance of the rock from its primary and its
emissivity and absorptance curves. In any case the _apparent_ temperature
can be adjusted by coatings with tailored emissivity. That is something
that we know how to do _now_.
>4. The scanning IR sensor is not the only sensor the ship possesses - if
>anything is suspicious or hard to identify, more powerful and/or
>different sensors may be pointed specifically at it to find out what it
>is.
Like what?
>
>>I see. So all that an enemy has to do is align himself between your
sensor
>>the sun or a bright star and it ignores him.
>
>Actually he will show up as an unexpected cold or warm spot unless his
>distance from you and his level of radiation mean he is just as bright
>as what he's between you and.
So now you're using a sensor that can image this ship? That's a pretty
high-res sensor, with a very narrow field of view.
>Also, he'd have to _stay_ between you and the object, which is going to
>be damn hard if you're both moving. He'd need to accelerate either to
>get in position, or stay in position. And if he accelerates, he is _far_
>more detectable, and probably far brighter than any natural radiating
>body (excepting the sun, at least).
Depends on what kind of engine he is using. How hot would the exhaust from
a mass-driver be?
>
>"Developed systems"? Developed SYSTEMS? This is NOT a discussion about a
>world where FTL exists, since we cannot have any sort of plausible
>discussion about that at all. Maybe ships can radiate their waste heat
>into hyperspace, or maybe warp power cores can be detectable clear
>across the galaxy! The context of this discussion has been
>interplanetary war within the solar system.
Oh, I see. So you are talking about only our one solar system? In that
case the traffic control net knows where everything is anyway and why do you
need to bother with all this IR stuff?
J. Clarke
"Tom Breton" wrote in message ...
>"J. Clarke" <nos...@nospam.nospam> writes:
>> Why do you keep harping on "near earth objects"? They are not the only
>> asteroids out there.
>
>Because earth-crossing asteroids are the ones that are most heavily
>being searched for. They are the most important to find, because they
>mite smack into Earth, an event whose significance should not be
>underestimated.
Most heavily being searched for by _who_? And in any how is the method used
to search for an earth-crossing asteroid different from that used to search
for a main-belt asteroid?
I guess you're another one who equates "astronomy" with what is done by
people with big budgets, totally ignoring the vast quantity of grunt work
like looking for asteroids that is performed by amateurs.
>
> Tom
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>>This is fine if you can afford to dedicate a station to this task. But
how
>>about if your ship is out in the boonies? Is is going to tow your station
>>along everywhere it goes?
>
>What, exactly, are the "boonies" when a pair of observation stations in
>Earth orbit can scan the entire solar system?
Well, you can start out with wherever this ship that is entering the solar
system came from.
>>In my first post on this topic, which you obviously neglected to read, I
>>stated clearly that the infrared method _might_ work in a star system with
>>an established industrial base, but not for a ship operating alone.
>
>You are apparently the only person in this entire discussion which is
>assuming inter_stellar_ travel, which is an entirely different ball game
>from the interplanetary war the rest of us are talking about.
If we are assuming only the one solar system then there are going to be so
many sensors of so many kinds in place that this discussion of some magic IR
scanner is pointless.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>First item, how long an exposure is required to achieve these results.
>>Second item, what is the probability that a spacecraft operated by someone
of
>>these things at the exact time that you have the sensor pointed at it?
>
>They don't know when our sensors are pointed at it (which is likely once
>an hour or more frequently - with multiple ships and multiple
>observation stations, quite plausibly, once a minute).
No, they don't know. But pointing a sensor at every point in the sky once a
minute is going to take a _lot_ of sensors. And one little bomb or even a
cloud of spray paint could easily take out such an inviting target.
> Meaningful
>acceleration requires _sustained_ burn.
Define "meaningful" and "sustained". We've put objects in solar escape with
burns of a few minutes.
>Not to mention that the exhaust
>plume of any system that leaves one, doesn't cool instantly.
So use a mass driver and throw out cryogenically cooled rocks.
>And that
>powerful enough sensors will detect any spaceship with running power.
How?
Ian
>>There is a nice device which, given the sensory return from an object
>>and a catalog of all known objects with their positions, is capable of
>>determining whether the sensory return is of a known or unknown object,
>>and giving ideas as to such characteristics as its location, velocity,
>>and temperature.
>
>So exactly how do you get all of this data into the computer for a solar
>system which you have never entered before?
Irrelevant to the discussion, as I have already said. Only our solar
system is relevant. Routine travel to alien systems would require FTL,
which introduces such a wild card that no meaningful conclusions may be
drawn about space battles with it.
>>Your assertion is sort of like "an airplane flying at mach 2 is just an
>>object against a background of other objects, with other similar objects
>>around it, so how does a radar distinguish enemy aircraft"?
>
>Not quite. Other objects don't fly Mach 2.
Of course they do. The ground flies by the aircraft at a relative
velocity of mach 2, and other aircraft (whether friendly or enemy) fly
around at varying relative speeds.
>>If one is fighting space battles in the solar system with advanced IR
>>observation technology, the following factors are likely to be true:
>>
>>1. The positions of space objects, bright stars, friendly ships, and
>>other IR emitters will be recorded and known.
>
>In a developed star system much of this will be known.
Yes, and "undeveloped" star systems are irrelevant to the discussion.
>>2. Detecting any object which is accelerating, emitting anything other
>>than IR, or doing anything un-rocklike, and then keeping track of which
>>object it is, is trivial.
>
>And of course your opponent is going to cooperate by doing one of these
>things when you have a sensor pointed at him.
He won't know when I have a sensor pointed at him. If he is neither
accelerating, emitting anything other than IR, or doing anything
un-rocklike, then he is not a threat, and I can wait longer for my
sensors to finally identify him.
>>3. Relative motion to multiple observers can easily be used to calculate
>>distance to an object, which allows strength of emission to be used to
>>calculate the temperature of the object.
>
>Sorry, but strength of emission has no relationship whatsoever to
>temperature.
It has every relationship to temperature when distance to an object is
known, WHICH I SAID IN THE ABOVE SENTENCE. Have you forgotten how to
read?
>How does a single vessel obtain "relative motion to multiple
>observers"?
It doesn't have to, since there are other vessels and observation
satellites spread across the solar system.
>>Since live ships must be hotter
>>than floating rocks, any object within the solar system that is hotter
>>than a floating rock is man-made and should be investigated further.
>
>The temperature of a spaceship is going to be that temperature which the
>crew finds comfortable. It may be hotter, colder, or the same as any given
>rock depending on the distance of the rock from its primary and its
>emissivity and absorptance curves.
Since the position of all objects is known, the temperature a rock
should be _at that position_ is known. A live ship at that position will
always be hotter than a rock at that position.
>In any case the _apparent_ temperature
>can be adjusted by coatings with tailored emissivity.
Over time, all energy generated must be radiated, or the ship will get
hotter and hotter. Actually, it would get hotter and hotter quite fast.
>>4. The scanning IR sensor is not the only sensor the ship possesses - if
>>anything is suspicious or hard to identify, more powerful and/or
>>different sensors may be pointed specifically at it to find out what it
>>is.
>
>Like what?
Optical telescopes. RADAR. More precise infrared telescopes. In general,
narrow-field but very accurate sensors.
>>Actually he will show up as an unexpected cold or warm spot unless his
>>distance from you and his level of radiation mean he is just as bright
>>as what he's between you and.
>
>So now you're using a sensor that can image this ship? That's a pretty
>high-res sensor, with a very narrow field of view.
It doesn't have to image the ship. Any ship of different apparent
luminosity to what it is sitting in "front" of will increase or reduce
the luminosity of that object viewed even as a point source, and so will
be detectable. Once the discrepancy is detected, narrow-field sensors
can be used to examine what is going on.
>>Also, he'd have to _stay_ between you and the object, which is going to
>>be damn hard if you're both moving. He'd need to accelerate either to
>>get in position, or stay in position. And if he accelerates, he is _far_
>>more detectable, and probably far brighter than any natural radiating
>>body (excepting the sun, at least).
>
>Depends on what kind of engine he is using. How hot would the exhaust from
>a mass-driver be?
The exhaust heat is irrelevant, as the waste heat produced by the
electromagnetic acceleration process would heat up the entire ship.
>>"Developed systems"? Developed SYSTEMS? This is NOT a discussion about a
>>world where FTL exists, since we cannot have any sort of plausible
>>discussion about that at all. Maybe ships can radiate their waste heat
>>into hyperspace, or maybe warp power cores can be detectable clear
>>across the galaxy! The context of this discussion has been
>>interplanetary war within the solar system.
>
>Oh, I see. So you are talking about only our one solar system? In that
>case the traffic control net knows where everything is anyway and why do you
>need to bother with all this IR stuff?
Oh yes, just like in a modern war, when everything from enemy fighters
to stealth bombers to ballistic missile subs conveniently registers
itself with Global Traffic Control so that everyone knows where it is.
Ian
>>What, exactly, are the "boonies" when a pair of observation stations in
>>Earth orbit can scan the entire solar system?
>
>Well, you can start out with wherever this ship that is entering the solar
>system came from.
Tsk tsk. We can't discuss other systems, because interstellar travel
introduces a tech level and tech assumptions (ie FTL) which make it
fruitless. The current discussion is based on plausible near-future
technology (in fact the whole IR thread assumes detection systems no
more than 10 times more sensitive than those we can build today).
>>>In my first post on this topic, which you obviously neglected to read, I
>>>stated clearly that the infrared method _might_ work in a star system with
>>>an established industrial base, but not for a ship operating alone.
>>
>>You are apparently the only person in this entire discussion which is
>>assuming inter_stellar_ travel, which is an entirely different ball game
>>from the interplanetary war the rest of us are talking about.
>
>If we are assuming only the one solar system then there are going to be so
>many sensors of so many kinds in place that this discussion of some magic IR
>scanner is pointless.
I would hardly call known, plausible technology that we could walk out
and build tomorrow (albeit it would cost a lot) a "magic IR scanner".
The whole point of the original discussion was specifically that you
_can't_ hide in plausible interplanetary warfare. You simply walked in,
completely ignored what was being discussed, and began to demonstrate
your ignorance in the basic workings of infrared sensors.
Ian
>>They don't know when our sensors are pointed at it (which is likely once
>>an hour or more frequently - with multiple ships and multiple
>>observation stations, quite plausibly, once a minute).
>
>No, they don't know. But pointing a sensor at every point in the sky once a
>minute is going to take a _lot_ of sensors. And one little bomb or even a
>cloud of spray paint could easily take out such an inviting target.
It would not be at all hard to have a single ship-mounted array that
could scan the sky once every few hours. So now if you have one fleet of
ships in communication, you're scanning the sky every five or ten
minutes.
>> Meaningful
>>acceleration requires _sustained_ burn.
>
>Define "meaningful" and "sustained". We've put objects in solar escape with
>burns of a few minutes.
That much acceleration that fast leaves an exhaust plume that can be
detected after the acceleration is finished. More efficient space drives
require longer burns, less efficient drives tend to leave very hot
exhausts. Detectable either way. Not to mention the ship is detectable
at very long range even when its engines are off.
>>Not to mention that the exhaust
>>plume of any system that leaves one, doesn't cool instantly.
>
>So use a mass driver and throw out cryogenically cooled rocks.
Then your entire ship is glowing with waste heat until that's
dissipated, which is going to take just as long.
>>And that
>>powerful enough sensors will detect any spaceship with running power.
>
>How?
Because, as you apparently missed when it was posted MANY times earlier
in the thread, even the sensors which could be mounted on a single ship
can easily detect an object only a few degrees above background millions
of kilometers away, and a dedicated observation station could detect it
billions of kilometers away.
Brett Evill
Breton") wrote:
>However, their thermal equilibrium is not the same as the 3K
>background radiation, which is the backdrop it is to be detected
>against.
Quite true. My bad.
Brett Evill
>Brett Evill wrote in message ...
>>It would seem that the obvious way to distinguish stars, inert lumps, and
>>working spacecraft is to measure their brightness (CCD cameras will do
>>this) at several different wavelengths in the IR and visible. This will
>>allow you to work out roughly at what wavelength the maximum of power is,
>>and that will let you sort them into temperature categories.
>
>So let's see, basically you're going to take spectra with several different
>instruments? How long is it going to take you do this for the entire sky?
Nope, I combine the instruments, like a colour camera. This will work fine
if the pixels on the image plate are smaller than the smallest image the
optics can produce (no problem).
>The larger the field the more objects are in it. The rate of sweep is going
>to be controlled by the amount of time necessary to secure enough data for
>your analysis. For your spectrum you'll need multiple images with different
>filters as a minimum, or else you'll need to do spectrographic analysis of
>every object in the field. How long does that take?
I don't need a full spectrographic analysis. Three images in different
wavelengths produce all the data I need. I can take three pictures in
different wavelengths simultaneously witha colour TV camera, so it can't
be beyond the bounds of possibility.
Exposure time minima and field of view limitations might well impose a
minimum time to scan the sky, but I don't know what it would be. Since the
objects you are looking for are distinguished by colour rather than shape
it should be possible to do a fast scan with a low-resolution instrument
and a close scan of interesting patches with a high-res instrument. But
perhaps that would suggest camouflage strategies.
Brett Evill
>Remember that to reliably detect incoming spaceships this "small effort" has
>to be repeated every few minutes. That makes it a _much_ larger effort.
Well, that depends how many objects that enemies could hide behind are up
close. If you are talking about spotting ships at an AU, or even 1% of an
AU, a scan every few hours ought to give timely information.
Anyway, this is now clearly a quantitative argument, and it will take
numbers to settle it. How large a field of view is possible for a 'colour'
IR telescope with the resolution to match this task? How long would an
exposure have to be?
Or would perhaps some other strategy work better? Ships and stars will
both show up in single-wavelength IR, but the ships will be able to be
distinguished by their motion wrt the starfield if they have indeed enough
motion that detecting them is time-critical.
Leonard Erickson
> Ian wrote:
>
>> Well, there are a lot of technological variables to consider, so as a
>> baseline let's use today. What would happen if we mounted a single, 2
>> meter aperture modern telescope to detect visual and near-IR radiation
>> in space (We could use it to sweep across the entire sky within a few
>> hours)? Turns out we can detect a space shuttle manouvering thruster
>> firing from at least 15 million kilometers. Space shuttle main engines
>> would be detectable from 20 billion kilometers (waaay outside the
>> orbit
>> of Pluto). A fairly small (not terribly larger than space shuttle)
>> size
>> ship using ion thrusters to accelerate at 1/1000 of a g would be
>> detectable from 100 million kilometers or so. These calculations are
>> from a post by John Schilling on 1/2/98.
>
> I dug up his post, it's at
>
> http://www.dejanews.com/getdoc.xp?AN=312184581
>
> Quite frankly, I think there's something wrong with his numbers. The
> detection threshhold that he gives is 2.5 x 10^-17 W/m^2, which is not
> too different from the estimate I got based on an assumption of a
> limiting magnitude of 20 (3.84 x 10^-17 W/m^2).
Try working it based on a detector that triggers upon receipt of *one*
photon. As I recall, that's what modern optical and near-IR sensors
have as a sensitivity level.
> With a limiting flux of 2.5 x 10^-17 W/m^2, for a plume to be visible at
> 20 Tm, the source power must be 130 GW, all in the bands in which the
> sensor is operating (he notes that this is a visual/near-infrared
> system). Are the Space Shuttle main engines capable of 130 GW? I don't
> have any figures in front of me.
Doesn't sound too unreasonable. The power ratings of rocket engines are
rather surprising.
--
Leonard Erickson (aka Shadow)
sha...@krypton.rain.com <--preferred
leo...@qiclab.scn.rain.com <--last resort
Leonard Erickson
> By the time interplanetary warships are feasible, it's likely that IR
> detection technology will be at least 10 times as sensitive as it is
> today, perhaps much more - and dedicated observation stations, keeping
> in comminication with warships for long-range threat warning, could use
> telescopes with apertures _far_ larger than 10 meters.
Actually, your first assumption is incorrect. We are *currently* at the
point where the detectors register individual photons striking them.
You *can't* get more sensitive than that.
You could increase the aperture, or extend the range for which that
sensitivity applies. And you can add cheap computing power for
*interpreting* the signals.
Leonard Erickson
> Asteroids are in thermal equilibrium. They won't show up on IR. Spaceships
> cannot be in thermal equilibrium, they must radiate in IR.
Being in thermal equilibrium means that you *radiate* as much energy as
you absorb. Asteroids are in sunlight, and thus they radiate in the IR.
> The question that seems of more concern to me is whether these sensors
> will be able readily to distinguish asteroids from *stars*.
*Completely* different emmision spectrum. The asteroids are at around
200-300 K. Even red dwarf stars are at temps more along the lines of
800 K.
Brett Evill
sha...@krypton.rain.com (Leonard Erickson) wrote:
>b.e...@spamblocker.tyndale.apana.org.au (Brett Evill) writes:
>
>> Asteroids are in thermal equilibrium. They won't show up on IR. Spaceships
>> cannot be in thermal equilibrium, they must radiate in IR.
>
>Being in thermal equilibrium means that you *radiate* as much energy as
>you absorb. Asteroids are in sunlight, and thus they radiate in the IR.
Yep, I got that eventually. They are cooler than ships because they have
to radiate only the heat from the Sun, whereas the ships have to reflect
or radiate all that plus the power output of their generators &c. But I
was wrong in my estimate of how much the light intensity from the Sun
would dominate the average temperature of the sky. It was one of my more
stupid errors, when I reflect that the Earth is not all that cold.
>> The question that seems of more concern to me is whether these sensors
>> will be able readily to distinguish asteroids from *stars*.
>
>*Completely* different emmision spectrum. The asteroids are at around
>200-300 K. Even red dwarf stars are at temps more along the lines of
>800 K.
It was a little while before worked out how to build a wide-field
instrument that would compare spectra in sufficient detail without
requiring too much data analysis. After all, I'm an economist, not an
astronomer. Also, owing to a hardware error in the connection between my
keyboard and my chair I typed 'asteroid' where perhaps 'ship' would have
made more sense.
Chris Lawson
Thanks for he interesting post, Ian.
>>1. Cold, ballistic weapon. This would need to be launched out of
>>range (which could mean months between launch and strike).
>"Out of range" means "outside the solar system". We are talking
>_billions_ of kilometers. A completely cold projectile also can't have
>electronics active to watch out for interception - the enemy still has a
>chance to detect it at closer range using non-IR means, and intercept
>it.
Agreed. But it's till plausible to use a cold ballistic weapon
that "wakes up" at close range for final targetting, presumably
when it is too close for the defences to do much about. However,
this really only works for (i) long-delayed attacks since the
ballistic phase will have to be extensive (as you say,
out-of-system) and (ii) relatively immobile targets such as
planets, orbitals, etc., where you *know* where they're going to
be in a few motnhs' time.
>>3. Using shields. A rocket could accelerate all it likes provided
>>it was hidden by a planet or star. The problems are (i) it's
>>pretty hard to hide behind a planet unless you're already
>>in-system; (ii) it requires that the target occupt a limited
>>volume of space -- any two widely-separated, communicating ships
>>would be immune to this form of stealth.
>It also requires that the side trying to do the detecting doesn't have
>other ships or recon drones in a position to observe the "hidden"
>acceleration.
Sure. That was the point of my "two widely-separated,
communicating ships." I was talking about the *minimum* effective
detection. Using multiple probes scatteredd throughout a system
is simply the extended (and more effective) case.
[snip]
>>Suffice to say, in a space battle, the crucial technology may be
>>scanner range rather than weapon power.
>I'm fairly sure that this won't be true. In a plausible battle between
>space warships, scanner tech for both sides will likely be much more
>than enough so that the real range limit for scanners is caused by
>lightspeed delay. At "combat ranges" of a few million kilometers or less
>(when energy and projectile weapons have a chance of hitting), both
>sides are likely to have scanners that see everything they really need
>to see.
IOW, what you are saying is that stealth will be virtually
impossible; scanner technology is therefore not the crucial
factor. Instead a battle will be won on weapon power and speed
versus defensive ability and maneuvrability.
regards,
Chris
regards,
Chris Lawson
Jeff Suzuki
: 1) A black ship is a "blackbody", which is to say, unless your crew likes
: life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
: accessories.
So does a large fraction of the night sky. The problem is distinguishing
between "ship radiating as if it had been in the sun" from "ship-sized rock
radiating as if it had been in the sun."
There are a lot of false analogies made between stealth aircraft and stealth
spacecraft. IR, radar, etc. work on aircraft because there is nothing
"natural" in the sky that reflects radar the way an airplane does, or radiates
heat the way an airplane does. If it reflects radar or radiates heat, it
shouldn't be in the sky. But there's a lot of radar reflecting and heat
radiating junk out there...and any intelligent commander is going to make use
of it, a la (various submarine movies).
Jeffs
Ian
>>I'm fairly sure that this won't be true. In a plausible battle between
>>space warships, scanner tech for both sides will likely be much more
>>than enough so that the real range limit for scanners is caused by
>>lightspeed delay. At "combat ranges" of a few million kilometers or less
>>(when energy and projectile weapons have a chance of hitting), both
>>sides are likely to have scanners that see everything they really need
>>to see.
>
>IOW, what you are saying is that stealth will be virtually
>impossible; scanner technology is therefore not the crucial
>factor. Instead a battle will be won on weapon power and speed
>versus defensive ability and maneuvrability.
Yes. Scanners will, regardless of disagreements on the precise level of
their effectiveness, always be able to detect enemy ships millions of
kilometers away at a minimum. You will always see the enemy well before
you can shoot him (and vice versa), and in fact you will usually see him
in time to conduct manouvers such as assembling your forces in the ideal
configuration, changing your velocity and heading in regard to the enemy
to what you want it to be (if you possess the delta v), et cetera.
Indeed, the engagement will be won primarily with weapon power. Speed in
itself isn't even all that important either in the tactical sense. You
can run away, or prevent the enemy from running away, if your velocity
and delta v are advantageous. Beyond that, all velocities are relative
and facings are usually as desired... being the side with the most delta
v allows you to control the range of engagement under some
circumstances, but not much beyond that. The important component in
regard to engines is manouverability... if you can accelerate faster and
longer than the enemy, you can jink back and forth wildly, using
lightspeed delay to reduce the effective range of his weapons.
High delta v, and thus the ability to control the range of engagement,
is only a real advantage if there is a substantial difference in the
manouverability/size component between the two forces, making one
substantially harder to hit than the other. The hard-to-hit side would
probably prefer to fight at longer range, the easy-to-hit side at
shorter range, _for engagement with unguided weapons_.
My final conclusion is that speed and delta v are useful, but not nearly
as important as weapons. Sensors are irrelevant. Armor and passive
defenses are largely unworkable due to the velocities and mass
restrictions involved. That leaves weapons, which are very important.
Weapons to take out the enemy ship, and weapons to take out the enemy's
weapons. He who has the most, wins.
Plausible interplanetary space battles look like a long time drifting in
the middle of nowhere, followed by faceoffs between fleets
computer-controlled gun and missile platforms rushing toward each other
at high speed. Once the two forces enter into effective weapons range of
each other, it's over very fast.
Keith Morrison
> There are a lot of false analogies made between stealth aircraft and stealth
> spacecraft. IR, radar, etc. work on aircraft because there is nothing
> "natural" in the sky that reflects radar the way an airplane does, or radiates
> heat the way an airplane does. If it reflects radar or radiates heat, it
> shouldn't be in the sky. But there's a lot of radar reflecting and heat
> radiating junk out there...and any intelligent commander is going to make use
> of it, a la (various submarine movies).
But the vast majority of that junk falls into the category of stuff
that you can discriminate against easily. Your submarine analogy
is not quite right. Think of a forest with an enemy armed with
a knife (or other short-range weapon) who is camouflaged. If he's
sitting still, you can't see him. Then again, he can't do anything
to you. If he moves, you can see him.
But unlike the forest, once he starts moving he has to make himself
visible again to stop. If he doesn't it becomes trivial to determine
his location.
--
Keith Morrison
kei...@polarnet.ca
Ian
>Tommy the Terrorist (may...@newsguy.com) wrote:
>
>: 1) A black ship is a "blackbody", which is to say, unless your crew likes
>: life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
>: accessories.
>
>So does a large fraction of the night sky. The problem is distinguishing
>between "ship radiating as if it had been in the sun" from "ship-sized rock
>radiating as if it had been in the sun."
A ship which is generating some of its own heat will radiate this _in
addition to_ whatever it is reflecting from the sun. As the original
poster said (in different words), the only way a ship is going to
radiate like a natural object in the same position would radiate is if
its internal temperature is 3 degrees Kelvin or so.
>There are a lot of false analogies made between stealth aircraft and stealth
>spacecraft. IR, radar, etc. work on aircraft because there is nothing
>"natural" in the sky that reflects radar the way an airplane does, or radiates
>heat the way an airplane does.
You might have a point if IR and Radar were limited to finding aircraft
in open sky. Terrain-scanning radar, infrared sensors used on ground
combat vehicles, FLIR, and the like beg to disagree with you.
>But there's a lot of radar reflecting and heat
>radiating junk out there...
Actually, no, there isn't.
There is the sun. Any idiot knows when he is looking at the sun.
There are the planets and moons. A mildly competent sensory computer
will have no trouble saying "gee, this IR return looks exactly like
Venus should look, and surprise surprise, it is coming from exactly
where Venus should be".
There are the asteroids, however, they are all quite cold. Any sensor
which picks them up and establishes their distance (via repeated
exposures to detect motion, and/or two or more different sensors
triangulating), will instantly recognize them as unpowered objects.
Given the strength of IR emission and the distance to the object, it's
easy to see that they are radiating exactly as much energy as they
receive. Not to mention that since the asteroids aren't going anywhere,
it's not hard to examine something, find out "hey that's an asteroid",
and keep track of its movements for future reference.
There are stars. However, most of them don't radiate in the right
frequency because even the coldest of them are a lot hotter than any
spaceship. They are also something whose position doesn't change, so
once identified they can be kept track of.
That about covers it for space objects.
>and any intelligent commander is going to make use
>of it, a la (various submarine movies).
Problem is he can't.
Say I am the attacker, travelling through the solar system. Say the
defender wants to hide from me using Space Object X. He has only two
choices - put the object directly between me and him, or put himself
directly between me and the object.
If he puts himself behind the object, fine, I can't see him. Only he
can't put himself behind stars, or anything that is too small to hide
him, so that rules out everything except planets, moons, and large
asteroids. These are small enough in number that if I don't have another
ship or asset somewhere that can see the other side (reasonably likely
that I do), he still has a very limited number of hiding places whose
exact location is known to me. Not the best places to hide.
Additionally, he has the problem that he can't hide and move at the same
time. Unless he wants to take a very weird course going the opposite way
away from me with the planet in between us, which is only good for
running away, he has to sit behind the planet while I run around the
solar system doing whatever I feel like.
If he puts himself between me and the object, first thing he had better
do is hope my sensors aren't capable of noticing him as a warm or cold
spot in front of the object. Second, he has to stay _exactly_ between me
and the object. This is a pretty impressive navigational task,
especially if I am given to making course changes, and for that reason
isn't practical unless he is pretty close to the object in question (so
he doesn't have to move large distances when I change course).
Erik Max Francis
> You don't understand equilibrium, apparently.
>
> It does *not* mean "no emission", nor does it mean "emitting at the
> 3 degree Kelvin level" (in this case).
>
> All it means is that the body is at equilibrium, it isn't changing
> it's temperature. It's a steady state condition.
Indeed. Take, for instance, Ceres. Ceres comes to thermal equilibrium
when it reradiates all of its solar insolation. Ceres' semimajor axis
is 2.77 au = 414 Gm, which means that the solar insolation at that
distance is thus 178 W/m^2 (about 13% of the insolation at Earth orbit).
Ceres' radius is 457 km, which means that the area perpetually exposed
to sunlight is about 6.56 x 10^11 m^2. This puts the total amount of
solar luminosity falling on Ceres at 117 TW.
If, in thermal equilibrium, Ceres radiates this energy throughout its
whole body, then that means the total emitting surface area is 2.62 x
10^12 m^2. An application of the blackbody power law then gives a
temperature (using the rough approximation that it radiates as a
blackbody) of 168 K.
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@sade.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
USA / icbm 37 20 07 N 121 53 38 W / &tSftDotIotE
\
/ Many things are lost for want of asking.
/ (an English proverb)
Erik Max Francis
> *Completely* different emmision spectrum. The asteroids are at around
> 200-300 K. Even red dwarf stars are at temps more along the lines of
> 800 K.
Red dwarfs are at 2000-3000 K. The Sun radiates at about 6000 K.
J. Clarke
--
--John
Reply to jclarke at eye bee em dot net.
Brett Evill wrote in message ...
>In article <35f4a...@news1.ibm.net>, "J. Clarke" <nos...@nospam.nospam>
wrote:
>
>>Brett Evill wrote in message ...
>
>>>It would seem that the obvious way to distinguish stars, inert lumps, and
>>>working spacecraft is to measure their brightness (CCD cameras will do
>>>this) at several different wavelengths in the IR and visible. This will
>>>allow you to work out roughly at what wavelength the maximum of power is,
>>>and that will let you sort them into temperature categories.
>>
>>So let's see, basically you're going to take spectra with several
different
>>instruments? How long is it going to take you do this for the entire sky?
>
>Nope, I combine the instruments, like a colour camera. This will work fine
>if the pixels on the image plate are smaller than the smallest image the
>optics can produce (no problem).
>
>>The larger the field the more objects are in it. The rate of sweep is
going
>>to be controlled by the amount of time necessary to secure enough data for
>>your analysis. For your spectrum you'll need multiple images with
different
>>filters as a minimum, or else you'll need to do spectrographic analysis of
>>every object in the field. How long does that take?
>
>I don't need a full spectrographic analysis. Three images in different
>wavelengths produce all the data I need. I can take three pictures in
>different wavelengths simultaneously witha colour TV camera, so it can't
>be beyond the bounds of possibility.
>
>Exposure time minima and field of view limitations might well impose a
>minimum time to scan the sky, but I don't know what it would be. Since the
>objects you are looking for are distinguished by colour rather than shape
>it should be possible to do a fast scan with a low-resolution instrument
>and a close scan of interesting patches with a high-res instrument. But
>perhaps that would suggest camouflage strategies.
>
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>>There is a nice device which, given the sensory return from an object
>>>and a catalog of all known objects with their positions, is capable of
>>>determining whether the sensory return is of a known or unknown object,
>>>and giving ideas as to such characteristics as its location, velocity,
>>>and temperature.
>>
>>So exactly how do you get all of this data into the computer for a solar
>>system which you have never entered before?
>
>Irrelevant to the discussion, as I have already said. Only our solar
>system is relevant. Routine travel to alien systems would require FTL,
>which introduces such a wild card that no meaningful conclusions may be
>drawn about space battles with it.
>
>>>Your assertion is sort of like "an airplane flying at mach 2 is just an
>>>object against a background of other objects, with other similar objects
>>>around it, so how does a radar distinguish enemy aircraft"?
>>
>>Not quite. Other objects don't fly Mach 2.
>
>Of course they do. The ground flies by the aircraft at a relative
>velocity of mach 2, and other aircraft (whether friendly or enemy) fly
>around at varying relative speeds.
I see what you're asserting here, but it's not really on point. In fact
aircraft _can_ hide in ground clutter. It's a standard technique.
>>>If one is fighting space battles in the solar system with advanced IR
>>>observation technology, the following factors are likely to be true:
>>>
>>>1. The positions of space objects, bright stars, friendly ships, and
>>>other IR emitters will be recorded and known.
>>
>>In a developed star system much of this will be known.
>
>Yes, and "undeveloped" star systems are irrelevant to the discussion.
>
>>>2. Detecting any object which is accelerating, emitting anything other
>>>than IR, or doing anything un-rocklike, and then keeping track of which
>>>object it is, is trivial.
>>
>>And of course your opponent is going to cooperate by doing one of these
>>things when you have a sensor pointed at him.
>
>He won't know when I have a sensor pointed at him. If he is neither
>accelerating, emitting anything other than IR, or doing anything
>un-rocklike, then he is not a threat, and I can wait longer for my
>sensors to finally identify him.
He isn't? Not a threat to _what_? If he's just behaving like a rock that
is on a collision course with your sensor array then he's sure as _HELL_ a
threat. In your developed solar system there are going to be many, many
destinations which can be damaged. It's not enough to determine that the
rock is a spacecraft five minutes before it blows your main base to Hell.
>>>3. Relative motion to multiple observers can easily be used to calculate
>>>distance to an object, which allows strength of emission to be used to
>>>calculate the temperature of the object.
>>
>>Sorry, but strength of emission has no relationship whatsoever to
>>temperature.
>
>It has every relationship to temperature when distance to an object is
>known, WHICH I SAID IN THE ABOVE SENTENCE. Have you forgotten how to
>read?
I read just fine. Temperature for a perfect black body determines the
emission spectrum. The difference in blackbody temperatures between the
body and the background, combined with the surface area of the object
determines the strength of emission. You can, given that information, use
the strength of emission to determine distance, but to determine temperature
you look at the spectrum, not the intensity.
>>How does a single vessel obtain "relative motion to multiple
>>observers"?
>
>It doesn't have to, since there are other vessels and observation
>satellites spread across the solar system.
In which case your continuous infrared scans looking for spaceships are kind
of pointless.
>>>Since live ships must be hotter
>>>than floating rocks, any object within the solar system that is hotter
>>>than a floating rock is man-made and should be investigated further.
>>
>>The temperature of a spaceship is going to be that temperature which the
>>crew finds comfortable. It may be hotter, colder, or the same as any
given
>>rock depending on the distance of the rock from its primary and its
>>emissivity and absorptance curves.
>
>Since the position of all objects is known, the temperature a rock
>should be _at that position_ is known. A live ship at that position will
>always be hotter than a rock at that position.
If the position of all objects is known then how does this spaceship manage
to avoid having its position known? And why will a live ship at that
position always be hotter than a rock at that position? Tailor the
emissivity of the hull properly and it can have any arbitrary temperature.
You assume that the radiation curve for the ship and for a rock are
necessarily the same. They are not.
>>In any case the _apparent_ temperature
>>can be adjusted by coatings with tailored emissivity.
>
>Over time, all energy generated must be radiated, or the ship will get
>hotter and hotter. Actually, it would get hotter and hotter quite fast.
Yes, it must be radiated. That does not mean that it must be radiated at
any given frequency. You really should take courses in heat transfer and
optics some time.
>>>4. The scanning IR sensor is not the only sensor the ship possesses - if
>>>anything is suspicious or hard to identify, more powerful and/or
>>>different sensors may be pointed specifically at it to find out what it
>>>is.
>>
>>Like what?
>
>Optical telescopes. RADAR. More precise infrared telescopes. In general,
>narrow-field but very accurate sensors. Radar is hardly a "narrow-field
but very accurate sensor" compared to infrared. So you point an optical
telescope at it and what does it see? Yet another rock. Or has it not
occurred to you that anyone who can build a spaceship can dummy it up to
look like a rock?
>
>>>Actually he will show up as an unexpected cold or warm spot unless his
>>>distance from you and his level of radiation mean he is just as bright
>>>as what he's between you and.
>>
>>So now you're using a sensor that can image this ship? That's a pretty
>>high-res sensor, with a very narrow field of view.
>
>It doesn't have to image the ship. Any ship of different apparent
>luminosity to what it is sitting in "front" of will increase or reduce
>the luminosity of that object viewed even as a point source, and so will
>be detectable. Once the discrepancy is detected, narrow-field sensors
>can be used to examine what is going on.
So a ship in front of the sun is going to reduce the apparent luminosity of
the sun enough to allow you to detect the ship? Calcualate the magnitude of
the reduction.
>>>Also, he'd have to _stay_ between you and the object, which is going to
>>>be damn hard if you're both moving. He'd need to accelerate either to
>>>get in position, or stay in position. And if he accelerates, he is _far_
>>>more detectable, and probably far brighter than any natural radiating
>>>body (excepting the sun, at least).
>>
>>Depends on what kind of engine he is using. How hot would the exhaust
from
>>a mass-driver be?
>
>The exhaust heat is irrelevant, as the waste heat produced by the
>electromagnetic acceleration process would heat up the entire ship.
What exhaust heat? The temperature of the exhaust from a mass-driver is
whatever the designers of the system want it to be. And what waste heat
from superconducting magnets?
>>>"Developed systems"? Developed SYSTEMS? This is NOT a discussion about a
>>>world where FTL exists, since we cannot have any sort of plausible
>>>discussion about that at all. Maybe ships can radiate their waste heat
>>>into hyperspace, or maybe warp power cores can be detectable clear
>>>across the galaxy! The context of this discussion has been
>>>interplanetary war within the solar system.
>>
>>Oh, I see. So you are talking about only our one solar system? In that
>>case the traffic control net knows where everything is anyway and why do
you
>>need to bother with all this IR stuff?
>
>Oh yes, just like in a modern war, when everything from enemy fighters
>to stealth bombers to ballistic missile subs conveniently registers
>itself with Global Traffic Control so that everyone knows where it is.
Whenever "Global Traffic Control" happens, yes, this is precisely what will
occur. Anything not registered and looks like a potential problem gets
intercepted, just as happens in the US in controlled airspace now.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>>What, exactly, are the "boonies" when a pair of observation stations in
>>>Earth orbit can scan the entire solar system?
>>
>>Well, you can start out with wherever this ship that is entering the solar
>>system came from.
>
>Tsk tsk. We can't discuss other systems, because interstellar travel
>introduces a tech level and tech assumptions (ie FTL) which make it
>fruitless.
Of course we can. Just assume that FTL doesn't affect sensor technology.
>The current discussion is based on plausible near-future
>technology (in fact the whole IR thread assumes detection systems no
>more than 10 times more sensitive than those we can build today).
I see. So you're taking this one type of sensor which is easily defeated
and putting all your eggs in that basket? Why do you need this magic
central sensor in your industrially developed solar system?
>>>>In my first post on this topic, which you obviously neglected to read, I
>>>>stated clearly that the infrared method _might_ work in a star system
with
>>>>an established industrial base, but not for a ship operating alone.
>>>
>>>You are apparently the only person in this entire discussion which is
>>>assuming inter_stellar_ travel, which is an entirely different ball game
>>>from the interplanetary war the rest of us are talking about.
>>
>>If we are assuming only the one solar system then there are going to be so
>>many sensors of so many kinds in place that this discussion of some magic
IR
>>scanner is pointless.
>
>I would hardly call known, plausible technology that we could walk out
>and build tomorrow (albeit it would cost a lot) a "magic IR scanner".
I would, because you haven't demonstrated that infrared technology can do
what you want it to do.
>The whole point of the original discussion was specifically that you
>_can't_ hide in plausible interplanetary warfare. You simply walked in,
>completely ignored what was being discussed, and began to demonstrate
>your ignorance in the basic workings of infrared sensors.
>
Nope, I pointed out the ignorance on that topic and a few others of all
involved. Hint--learn what a "blackbody curve" is before you post more of
your twaddle.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>>They don't know when our sensors are pointed at it (which is likely once
>>>an hour or more frequently - with multiple ships and multiple
>>>observation stations, quite plausibly, once a minute).
>>
>>No, they don't know. But pointing a sensor at every point in the sky once
a
>>minute is going to take a _lot_ of sensors. And one little bomb or even a
>>cloud of spray paint could easily take out such an inviting target.
>
>It would not be at all hard to have a single ship-mounted array that
>could scan the sky once every few hours. So now if you have one fleet of
>ships in communication, you're scanning the sky every five or ten
>minutes.
Yep, having a fleet is real handy, but what if you don't? If a full sky
scan takes a few hours, which you have yet to demonstrate with any sort of
calculation, and if your opponent happens to do something which allows you
to distinguish him from a rock during the few milliseconds your sensor is
pointed at him, then you might detect him. But most of the time your sensor
will not be pointed at your opponent, so you're relying excessively on luck
here.
>
>>> Meaningful
>>>acceleration requires _sustained_ burn.
>>
>>Define "meaningful" and "sustained". We've put objects in solar escape
with
>>burns of a few minutes.
>
>That much acceleration that fast leaves an exhaust plume that can be
>detected after the acceleration is finished. More efficient space drives
>require longer burns, less efficient drives tend to leave very hot
>exhausts. Detectable either way. Not to mention the ship is detectable
>at very long range even when its engines are off.
You haven't demonstrated that the ship is detectable in any meaningful way.
As for burns, there are ways to hide those you know. If Jupiter is between
your sensor and the ship then you aren't going to see any burns, plumes, or
anything else. And this assumes that the exhaust is not cryogenically
chilled ball bearings or some such.
>
>>>Not to mention that the exhaust
>>>plume of any system that leaves one, doesn't cool instantly.
>>
>>So use a mass driver and throw out cryogenically cooled rocks.
>
>Then your entire ship is glowing with waste heat until that's
>dissipated, which is going to take just as long.
Why is your ship "glowing with waste heat"? Pure electromagnetic systems
can be very, very efficient.
>>>And that
>>>powerful enough sensors will detect any spaceship with running power.
>>
>>How?
>
>Because, as you apparently missed when it was posted MANY times earlier
>in the thread, even the sensors which could be mounted on a single ship
>can easily detect an object only a few degrees above background millions
>of kilometers away, and a dedicated observation station could detect it
>billions of kilometers away.
Look, sir, several people have already corrected you on this point, and you
have ignored them, and earlier you told me I was ignorant concerning
infrared. So I will not be gentle. Ian, you twit, GROK THE FUCKING
CONCEPT, _EVERYTHING_ IS ABOVE BACKGROUND EXCEPT THE BACKGROUND.
If your ignorant twaddle were in fact the truth then you would have helium
for blood because the planet you inhabit would have the temperature of your
beloved background.
Detection is not useful if you detect billions of objects.
Erik Max Francis
> Try working it based on a detector that triggers upon receipt of *one*
> photon. As I recall, that's what modern optical and near-IR sensors
> have as a sensitivity level.
Hmm, detecting 1 photon/s in the red spectrum (say, 740 nm wavelength;
410 THz frequency) is power of 2.7 x 10^-19 W, which distributed over a
2 m-aperture (area pi m^2) is a flux density of 8.6 x 10^-20 W/m^2, or
several hundred times dimmer.
Ian
>Ian wrote in message <3619c11f...@news.ktchnr1.on.wave.home.com>...
>>"J. Clarke" <nos...@nospam.nospam> wrote:
>>
>>>>What, exactly, are the "boonies" when a pair of observation stations in
>>>>Earth orbit can scan the entire solar system?
>>>
>>>Well, you can start out with wherever this ship that is entering the solar
>>>system came from.
>>
>>Tsk tsk. We can't discuss other systems, because interstellar travel
>>introduces a tech level and tech assumptions (ie FTL) which make it
>>fruitless.
>
>Of course we can. Just assume that FTL doesn't affect sensor technology.
First, it has absolutely nothing to do with the original subject of
discussion anyway.
Second, it must intrinsically affect sensor technology, if merely by
affecting the avoidance of sensors. If my ship can pop into hyperspace
whenever I want to get to my destination, what does it matter how
effective the enemy's sensors are in real space?
Third, it presumes a higher level of technology than we can plausibly
project. The discussion of interplanetary warfare made a fairly small
number of assumptions. As soon as we try to discuss interstellar travel,
a huge number of assumptions are generated all of a sudden. It becomes
impossible to talk with any amount of authority about what things would
be like without picking a set of assumptions on such things as the
capability of FTL, overall advancement of technology (is it easy to use
nanotech to build a kilometer-wide telescope out of an asteroid?),
amount of power available to ships, type of weapons, etc. But there is
no one best set of assumptions to pick - in fact there is a
mind-numbingly huge number of sets of assumptions to pick.
>>The current discussion is based on plausible near-future
>>technology (in fact the whole IR thread assumes detection systems no
>>more than 10 times more sensitive than those we can build today).
>
>I see. So you're taking this one type of sensor which is easily defeated
You have yet presented a single effective method to defeat it.
>and putting all your eggs in that basket? Why do you need this magic
>central sensor in your industrially developed solar system?
"Central sensor"? ??
I don't know what your problem is but it obviously includes a convenient
lack of memory.
I originally posted an all-around description of interplanetary space
combat, complete with a one-paragraph mention that sensor technology
would likely be so advanced that everyone knows where everyone else is.
You disagreed with this, and said that no sensor could do this. I said
that multiple IR sensors could do this, you said no they couldn't. I
have conclusively demonstrated that they can, now you are trying to
retroactively change the subject to why this is meaningful? It's
meaningul because my original point is now proven.
>>>If we are assuming only the one solar system then there are going to be so
>>>many sensors of so many kinds in place that this discussion of some magic
>IR
>>>scanner is pointless.
>>
>>I would hardly call known, plausible technology that we could walk out
>>and build tomorrow (albeit it would cost a lot) a "magic IR scanner".
>
>I would, because you haven't demonstrated that infrared technology can do
>what you want it to do.
I have conclusively demonstrated in every mention that it can do exactly
what I want it to, as have other people. You have repeatedly failed to
demonstrate any failings of an IR sensor net. Every objection you have
raised has hinged upon a cold ship which has accelerated well outside
the solar system, which I originally specifically mentioned would be
detectable at long range, or on attempting to hide from a single ship
which has no access to other sensor platforms. Since my entire original
point was the performance of opposing fleets of ships, in the context of
a battle within the solar system, that's hardly relevant.
>>The whole point of the original discussion was specifically that you
>>_can't_ hide in plausible interplanetary warfare. You simply walked in,
>>completely ignored what was being discussed, and began to demonstrate
>>your ignorance in the basic workings of infrared sensors.
>
>Nope, I pointed out the ignorance on that topic and a few others of all
>involved. Hint--learn what a "blackbody curve" is before you post more of
>your twaddle.
Blackbody curves are completely and utterly irrelevant to the subject
under discussion, in that they're useless in preventing one from being
detected by an IR sensor net.
Before you try and accuse other people of being ignorant, perhaps you
had better learn basic concepts of thermodynamics like waste heat.
Ian
>Yep, having a fleet is real handy, but what if you don't?
With the parameters under discussion, plausible interplanetary warfare,
I have one or more ships each with one or more sensors and access to
sensor satellites. Asking what would happen if I had one ship with no
support is like asking "what would naval warfare be like if you had one
ship with no support and no satellites".
>If a full sky
>scan takes a few hours, which you have yet to demonstrate with any sort of
>calculation
I posted a reference to the original post where it was calculated. If
you don't know how to use Dejanews, tough.
>>That much acceleration that fast leaves an exhaust plume that can be
>>detected after the acceleration is finished. More efficient space drives
>>require longer burns, less efficient drives tend to leave very hot
>>exhausts. Detectable either way. Not to mention the ship is detectable
>>at very long range even when its engines are off.
>
>You haven't demonstrated that the ship is detectable in any meaningful way.
Except for those all those nasty calculations that various people
posted, and you ignored.
>As for burns, there are ways to hide those you know. If Jupiter is between
>your sensor and the ship then you aren't going to see any burns, plumes, or
>anything else.
And I can't see the ship either because there's a planet in the way...
only this assumes I have no assets that can see the other side of the
planet, which is extremely unlikely.
>And this assumes that the exhaust is not cryogenically
>chilled ball bearings or some such.
Tsk tsk, you're forgetting thermodynamics again. The heat has to go
somewhere, if it doesn't go into the exhaust then it will be radiated by
the ship.
>>
>>>>Not to mention that the exhaust
>>>>plume of any system that leaves one, doesn't cool instantly.
>>>
>>>So use a mass driver and throw out cryogenically cooled rocks.
>>
>>Then your entire ship is glowing with waste heat until that's
>>dissipated, which is going to take just as long.
>
>Why is your ship "glowing with waste heat"? Pure electromagnetic systems
>can be very, very efficient.
How do you generate the power before using it? "Pure electromagnetic
systems" don't generate power.
>>Because, as you apparently missed when it was posted MANY times earlier
>>in the thread, even the sensors which could be mounted on a single ship
>>can easily detect an object only a few degrees above background millions
>>of kilometers away, and a dedicated observation station could detect it
>>billions of kilometers away.
>
>Look, sir, several people have already corrected you on this point, and you
>have ignored them, and earlier you told me I was ignorant concerning
>infrared. So I will not be gentle. Ian, you twit, GROK THE FUCKING
>CONCEPT, _EVERYTHING_ IS ABOVE BACKGROUND EXCEPT THE BACKGROUND.
Apparently you are incapable of paying attention to what other people
say. I will repeat myself one last time, just in case you are capable of
understanding.
1. Sensor detects object above background.
2. Computer checks to see if it's return and position match a natural
object that is supposed to be there. If it's a known natural object -
and pretty much all natural objects will be known - it's elimenated.
3. If it hasn't been elimenated, pinpoint sensors look at it to try and
determine what it is. If it looks like a natural object, it's flagged as
"looks like natural object". If it's a ship it's flagged as
"unidentified ship". Its course is calculated and added to the database,
and whatever it is, the computer identifies if it is going anywhere
interesting.
>Detection is not useful if you detect billions of objects.
Of course it is. That's just a problem for the computers and the
navigation database. And these are "plausible future computers", which
are hundreds of times (at least) more powerful than the most powerful
supercomputer in the world today. It can check and track billions of
objects using a tiny majority of its processing power while the whole
crew plays Quake XXXVII.
Ian
>>Of course they do. The ground flies by the aircraft at a relative
>>velocity of mach 2, and other aircraft (whether friendly or enemy) fly
>>around at varying relative speeds.
>
>I see what you're asserting here, but it's not really on point. In fact
>aircraft _can_ hide in ground clutter. It's a standard technique.
It used to be a standard technique, but is _far_ less effective with
modern computer-assisted, downward looking radars. The point is it has
little to do with the radar, all you need is a computer that can pick
out something that's behaving unusually for a piece of "ground".
>>>And of course your opponent is going to cooperate by doing one of these
>>>things when you have a sensor pointed at him.
>>
>>He won't know when I have a sensor pointed at him. If he is neither
>>accelerating, emitting anything other than IR, or doing anything
>>un-rocklike, then he is not a threat, and I can wait longer for my
>>sensors to finally identify him.
>
>He isn't? Not a threat to _what_?
Not a threat to anything.
>If he's just behaving like a rock that
>is on a collision course with your sensor array then he's sure as _HELL_ a
>threat.
An inert rock on a collision course with my sensor array can be detected
with IR on non-IR sensors when it is millions of kilometers away.
An inert object can hide from me if it's halfway across the solar system
for me, but there is absolutely no way in hell that any object will get
close enough to my ship to do it harm without being seen. For one thing,
my computers won't normally consider "cold" objects dangerous, but they
will raise a giant red flag about anything that has an off chance of
actually hitting the ship.
>In your developed solar system there are going to be many, many
>destinations which can be damaged. It's not enough to determine that the
>rock is a spacecraft five minutes before it blows your main base to Hell.
My main base, or any important installation will cannot manouver, is
presumably going to have large-scale sensors of all kinds. Not only IR,
sensors for all wavelengths, and active radar. Anything spaceship-sized
is no harder to detect than a fast-moving asteroid, and will be detected
tens of millions of kilometers out. And it had better have done its
accelerating when it was billions of kilometers outside the solar
system, or else I detected it while it was getting up to speed.
Remember, detecting cold objects won't be an issue most of the time
anyway, because they have to accelerate some time in order to actually
get to me, and to avoid detection in acceleration phase they'd have to
do it a loooong way away.
Also note that this cold object will still be receiving as much solar
radiation as an asteroid, that is, it will be hotter than background
radiation. It will have the temperature of an asteroid, but asteroids
don't tend to head straight for one of my fixed installations.
>>>How does a single vessel obtain "relative motion to multiple
>>>observers"?
>>
>>It doesn't have to, since there are other vessels and observation
>>satellites spread across the solar system.
>
>In which case your continuous infrared scans looking for spaceships are kind
>of pointless.
No, if those multiple vessels and observation systems don't actually use
a detection system (like IR scanners) they are not going to find
anything. The capabilities of IR are still quite relevant - if multiple
ships and observation satellites spread across the system used active
radar or visual-wavelength scans, it would not be that hard to hide
anywhere there aren't any sensors within a few million klicks.
>>Since the position of all objects is known, the temperature a rock
>>should be _at that position_ is known. A live ship at that position will
>>always be hotter than a rock at that position.
>
>If the position of all objects is known then how does this spaceship manage
>to avoid having its position known?
The position of all _natural space objects_ is known because, being
natural space objects, they do not go accelerating around all over the
place. Everything will stay in its orbit or position with the exception
of some asteroids, and regular checkups on unknown objects will keep
track of where most of them are.
> And why will a live ship at that
>position always be hotter than a rock at that position? Tailor the
>emissivity of the hull properly and it can have any arbitrary temperature.
No, it can't. The ship must _always_, over time, radiate all the waste
heat that it generates. If there is _any_ active electronics or
machinery on board the ship, it will generate waste heat. All of that
waste heat will be eventually be radiated as infrared radiation.
>You assume that the radiation curve for the ship and for a rock are
>necessarily the same. They are not.
Both the ship and the rock must radiate all energy they absorb, and all
waste heat they generate. Since the rock doesn't generate any waste
heat, the ship with the same surface area must always radiate more
energy.
>>>In any case the _apparent_ temperature
>>>can be adjusted by coatings with tailored emissivity.
>>
>>Over time, all energy generated must be radiated, or the ship will get
>>hotter and hotter. Actually, it would get hotter and hotter quite fast.
>
>Yes, it must be radiated. That does not mean that it must be radiated at
>any given frequency.
Who said sensors were limited to looking for one exact frequency?
>>Optical telescopes. RADAR. More precise infrared telescopes. In general,
>>narrow-field but very accurate sensors.
>Radar is hardly a "narrow-field
>but very accurate sensor" compared to infrared. So you point an optical
>telescope at it and what does it see? Yet another rock. Or has it not
>occurred to you that anyone who can build a spaceship can dummy it up to
>look like a rock?
They can dummy it up all they want, but if it's the right size/shape
that it could possibly contain a spaceship, and it is heading in an
un-asteroid-like direction, it'll be red-flagged and if it so much as
peeps it will be identified. Asteroids which go within a certain
distance of my assets will be evaded, redirected, or destroyed as a
matter of course.
Also, dummying up a ship as an asteroid assumes a significant allocation
of mass and effort to hiding, a strategy which will only be used for
"special occasions", not everyday warships. It's only useful if you're
going to spend all your time between the target, and some point outside
the solar system, costing "dead".
>>It doesn't have to image the ship. Any ship of different apparent
>>luminosity to what it is sitting in "front" of will increase or reduce
>>the luminosity of that object viewed even as a point source, and so will
>>be detectable. Once the discrepancy is detected, narrow-field sensors
>>can be used to examine what is going on.
>
>So a ship in front of the sun is going to reduce the apparent luminosity of
>the sun enough to allow you to detect the ship?
If he is close enough to me or any sensor, yes. If he's not, I really
don't care about him - he'll be detected as soon as he stops tooling
around the sun. And there's still the problem that he's going to have
difficulty being between two widely-dispersed sensors and the sun.
Having two or more widely-dispersed sensors, considering the entire
solar system, is not exactly going to be rare. Heck, if he really wants
to, he can hang around in really close solar orbit and nothing is going
to detect him unless I make a really big effort to search close solar
orbit - except that since he didn't launch from the sun, I probably saw
him when he was heading for it anyway.
>>>Depends on what kind of engine he is using. How hot would the exhaust
>from
>>>a mass-driver be?
>>
>>The exhaust heat is irrelevant, as the waste heat produced by the
>>electromagnetic acceleration process would heat up the entire ship.
>
>What exhaust heat? The temperature of the exhaust from a mass-driver is
>whatever the designers of the system want it to be. And what waste heat
>from superconducting magnets?
Okay, let me make a suggestion. Pick up a copy of a textbook which
includes the laws of thermodynamics. Read them.
EVERYTHING you do produces waste heat. Absolutely everything. The more
energy you expend, the more waste heat you produce. Generating the power
for your superconducting magnets produces waste heat (that's where most
of it will come from, actually). Running power around inside your ship
to the magnets produces waste heat. The interaction of the magnetic
fields generated produces waste heat in the railgun and the projectile.
The cryogenic cooling process you use to produce a perfectly cold
projectile produces waste heat (I'd be impressed to see how you manage
to cool the projectile _after_ it's been launched, which is when all the
magnetic stress is on it, anyway).
>>>Oh, I see. So you are talking about only our one solar system? In that
>>>case the traffic control net knows where everything is anyway and why do
>you
>>>need to bother with all this IR stuff?
>>
>>Oh yes, just like in a modern war, when everything from enemy fighters
>>to stealth bombers to ballistic missile subs conveniently registers
>>itself with Global Traffic Control so that everyone knows where it is.
>
>Whenever "Global Traffic Control" happens, yes, this is precisely what will
>occur. Anything not registered and looks like a potential problem gets
>intercepted, just as happens in the US in controlled airspace now.
And just as happens in _any_ airspace during a war. The whole point of
military air defense systems, IFF, etc., is that all friendly stuff
identifies itself to you, but for some reason the enemy never bothers to
do so. The prospect of being intercepted if he doesn't identify himself
does not matter to the enemy, since if he identifies himself, he
guarantees that he will get intercepted.
Tommy the Terrorist
>: 1) A black ship is a "blackbody", which is to say, unless your crew likes
>: life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
>: accessories.
>So does a large fraction of the night sky. The problem is distinguishing
>between "ship radiating as if it had been in the sun" from "ship-sized rock
>radiating as if it had been in the sun."
The main problem with this is that anybody with something that can sense
a ship in real time must CERTAINLY and unavoidably have voluminous
archives of the movements of every ship-sized hunk of rock, space
derelict, and probably floating wing nut in the solar system. You're
talking about a tremendous observational capacity to find the ship in the
first place, and to omit from this capability the power of memory - well,
it's like those laser guns in the movies where the users still have to
try to aim them and usually miss. It's anachronistic!
>There are a lot of false analogies made between stealth aircraft and stealth
>spacecraft. IR, radar, etc. work on aircraft because there is nothing
>"natural" in the sky that reflects radar the way an airplane does, or radiates
>heat the way an airplane does. If it reflects radar or radiates heat, it
>shouldn't be in the sky. But there's a lot of radar reflecting and heat
>radiating junk out there...and any intelligent commander is going to make use
>of it, a la (various submarine movies).
I'll wager that there's a lot more junk in the sky than there is in empty
space. Giant hailstones, commercial jet liners, flocks of geese, weather
balloons, and the occasional UFO (shhhh, it's a SECRET... ;) ). But it's
not enough to matter much.
Also, keep in mind that a ship trying to hide behind a rock or in front
of one will have immense troubles keeping in line with it, unless it's ON
the rock, which I can at least technically throw out from consideration
because it's "landed" and not "flying". If the searching ship moves, it
can't move without glowing like a star. Even if it COULD move without
glowing like a star, it still can't predict the searcher's movements
because of lightspeed delay. So it's not hiding behind rocks or in front
of them except when it's landing. Pointing big nasty guns at freighters
and telling the captain you'll blow them all away unless they stay mum
about you being in their shadow is still fair game, though.
The real question about having reflective ships is - why NOT? It's a
very simple method of making a ship much harder to see when it's still.
It should even help in those undesired but conceivable situations where
all the power inside the cabin is out, (Apollo 13). The only drawback is
that if you can do it absolutely PERFECTLY, then you might overheat over
a period of days - so you have to remember to make a little borehole
someplace that sends a thin beam of IR out in some direction where you
hope no one will see it. A small problem. A larger problem is figuring
out a material or set of materials that can reflect everything from radar
to visible perfectly, then designing it so that the reflections can't be
used to make you visible, but the very technology you say is irrelevant
is what already is a start in this direction. (I'm not sure about the
state of IR reflection but I can't believe that the military doesn't have
good approximations to it already)
Concealing the drive seems much more difficult, of course - but there
might be an intermediate worth considering. I've seen various
descriptions of ships using light pressure from lasers to navigate. If
your ship uses "attitude jets" that reflect this laser out various holes
for fine navigation, then the enemy sees your ship glow like a star, then
calculates the course - but you might be thousands of miles off that
course by the time he or his torpedoes get there. Chaff can also be used
to throw off calculations - not only can you release it to confuse course
calculations or homing missiles (while I wouldn't expect missiles to be
so dumb in the future, the chaff might be very smart, and the missiles
are out of real-time contact with any other computing facilities), but
since the enemy doesn't know the weight of the chaff or (probably) its
three-dimensional trajectory, he doesn't know what reactive force it had
on your ship. Escape pods probably make good "chaff" too, if it comes to
that - let the enemy fight your combat computer for the last few minutes
of your ship's existence while you inconspicuously become very reflective
and hope he misses you and goes away. (Though I have a feeling this may
be a forlorn hope, as little fleets of robotic drones are probably very
good about searching for and collecting space junk)
Brett Evill
>How many pixels do you need in order to compute your spectrum?
Strictly speaking, only two. One between the temperature of a rock a and a
ship, and one between a ship and a star. But why not go for three, for
better discrimination in dubious cases? You could hard-wire the
differencing into the substrate of the CCD (or whatever) chip, and need
minimal computer processing.
Tom Breton
>
> "J. Clarke" <nos...@nospam.nospam> wrote:
>
> >>They don't know when our sensors are pointed at it (which is likely once
> >>an hour or more frequently - with multiple ships and multiple
> >>observation stations, quite plausibly, once a minute).
> >
> >No, they don't know. But pointing a sensor at every point in the sky once a
> >minute is going to take a _lot_ of sensors. And one little bomb or even a
> >cloud of spray paint could easily take out such an inviting target.
>
> It would not be at all hard to have a single ship-mounted array that
> could scan the sky once every few hours. So now if you have one fleet of
> ships in communication, you're scanning the sky every five or ten
> minutes.
>
You don't want to be scanning at predictable intervals like that. If
you did, I could implement a very effective stealth measure: Time
bursts of emission in sync with your scanning rate, but lasting for a
short fraction thereof. If you miss the first burst, you missed them
all.
The mechanics of periodic heat emission are probably weird but should
pose no theoretical problems.
Tom
Tom Breton
>
>
>
> "Tom Breton" wrote in message ...
> >"J. Clarke" <nos...@nospam.nospam> writes:
> >> Why do you keep harping on "near earth objects"? They are not the only
> >> asteroids out there.
> >
> >Because earth-crossing asteroids are the ones that are most heavily
> >being searched for. They are the most important to find, because they
> >mite smack into Earth, an event whose significance should not be
> >underestimated.
>
> Most heavily being searched for by _who_?
Is that really a stumper? By the total of everyone who is likely to
find a new asteroid. I will hand-wave the assumption that almost
anyone can distinguish new vs known asteroids is well aware of the
possibilities of collision and would prefer to find an earth crosser,
for fame or public service or whatever motivation.
> And in any how is the method used
> to search for an earth-crossing asteroid different from that used to search
> for a main-belt asteroid?
I admit, I am largely going on reports that draw a distinction without
saying anything about the methodology.
I cannot guess what human ingenuity has come up with wrt optimizing
the search for earth-crossers. But I'll give you this idea: Since
earth-crossers tend to be nearer, one can expect a longer streak or a
more noticeable jump in a shorter time. I'll leave it to you to see
how this information can enable more efficient searching.
> I guess you're another one who equates "astronomy" with what is done by
> people with big budgets, totally ignoring the vast quantity of grunt work
> like looking for asteroids that is performed by amateurs.
>
That was uncalled for and untrue.
Tom
J. Clarke
misunderstood.
There are several "off budget" activities in astronomy. To say that "a tiny
part of the budget" is devoted to searching for asteroids and to equate that
with a low level of effort is kind of like claiming that "a tiny part of the
budget" is devoted to raising cats and dogs, and then to equate that with
there being few cats and dogs. Searching for asteroids is one of the areas
where most of the actual grunt work is performed by unpaid observers in
unfunded observatories, and I doubt that anyone really knows how many people
are doing that.
When one searches for an asteroid, one is actually searching simply for a
moving object. The technique used in the era where most astronomy was done
with photographic methods was to use a device called a "blink microscope",
which held two photographic plates of the same section of the sky, taken
several hours or days apart. They were carefully aligned so that the stars
on both plates overlapped and the observer then rapidly flipped a mirror
back and forth so that he could compare the two. Any moving object would
seem to "jump" back and forth. I believe that current technology is to take
two exposures using a CCD and then use a computer to subtract one from the
other, so that the only thing left is objects that have moved.
In either case the amount of motion depends on many factors, including the
distance of the object, the geometry of the situation, and the time between
observations. Remember that the apparent motion of an object when seen from
Earth on any given day can be forward, backward, or stationary--this is what
led the Medieval astronomers to their epicycles within epicycles within
epicycles. But regardless the amount of motion will not be known for any
given object until after it is detected. Even then one has no idea whether
it is earth-crossing until one had made several observations--at least three
points are required for a preliminary orbit and then several more widely
space for refinement. Having discovered an object, one still has no idea
whether it is previously unknown until one reports it to the clearinghouse
for such information, whose name and address escape me--I believe that it is
an office of the International Astronomical Union but for some reason
nagging at the back of my mind is the notion that it is a separate entity.
The only manner in which I can imagine that a search for NEOs would be
different would be that some assumption was made concerning their orbits
which would cause one to search a different part of the sky from that used
for general asteroid searches. In that case the NEO search would be a
supplement to the more conventional searches, looking for the oddballs in
high inclination orbits or some such.
Certainly one would prefer to find an asteroid that will bring one fame and
fortune, but one would also prefer to find the next truly spectacular comet,
and in either case it's a matter of luck rather than any particular
methodology which will bring about the desired result.
I suspect that the actual distinction between searching for NEOs and
searching for "moving objects in the solar system" is mainly for the benefit
of obtaining funding--it's a lot easier to sell a politician the idea of
funding a search for a dinosaur killer than it is on selling him the idea of
spending money cataloguing all the rocks in the Solar System. The result is
the same either way.
--
--John
Reply to jclarke at eye bee em dot net.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>It used to be a standard technique, but is _far_ less effective with
>modern computer-assisted, downward looking radars. The point is it has
>little to do with the radar, all you need is a computer that can pick
>out something that's behaving unusually for a piece of "ground".
So how does one make a pulse-doppler passive infrared sensor?
>>>He won't know when I have a sensor pointed at him. If he is neither
>>>accelerating, emitting anything other than IR, or doing anything
>>>un-rocklike, then he is not a threat, and I can wait longer for my
>>>sensors to finally identify him.
>>
>>He isn't? Not a threat to _what_?
>
>Not a threat to anything.
You either don't have enough imagination or aren't paranoid enough to design
defensive systems. Anyone who smugly asserts that a given class of object
is "not a threat to anything" is asking the universe to kick him in the
butt.
>>If he's just behaving like a rock that
>>is on a collision course with your sensor array then he's sure as _HELL_ a
>>threat.
>
>An inert rock on a collision course with my sensor array can be detected
>with IR on non-IR sensors when it is millions of kilometers away.
And when it's millions of kilometers away, say 6 hours out, what do you do
about it? Given no FTL travel and operations constrained by near future
technology as you insist on doing?
>An inert object can hide from me if it's halfway across the solar system
>for me, but there is absolutely no way in hell that any object will get
>close enough to my ship to do it harm without being seen. For one thing,
>my computers won't normally consider "cold" objects dangerous, but they
>will raise a giant red flag about anything that has an off chance of
>actually hitting the ship.
Yes, it will be seen, just like many other objects. So why do you single
that object out to do something about instead of doing something about all
the other objects out there?
>My main base, or any important installation will cannot manouver, is
>presumably going to have large-scale sensors of all kinds. Not only IR,
>sensors for all wavelengths, and active radar. Anything spaceship-sized
>is no harder to detect than a fast-moving asteroid, and will be detected
>tens of millions of kilometers out. And it had better have done its
>accelerating when it was billions of kilometers outside the solar
>system, or else I detected it while it was getting up to speed.
How did it get billions of kilometers outside the solar system if it's not a
<gasp> _starship_? And yes, it will be seen. But why will you bother to do
anything about it except log it? And how will IR be better than radar and
optical sensors for this purpose?
>Remember, detecting cold objects won't be an issue most of the time
>anyway, because they have to accelerate some time in order to actually
>get to me, and to avoid detection in acceleration phase they'd have to
>do it a loooong way away.
You still haven't demonstrated that acceleration makes detection easier.
>Also note that this cold object will still be receiving as much solar
>radiation as an asteroid, that is, it will be hotter than background
>radiation. It will have the temperature of an asteroid, but asteroids
>don't tend to head straight for one of my fixed installations.
No, but they may come close. Or have you systematically altered the orbits
of all asteroids that come within X distance of one of your installations?
>>>>How does a single vessel obtain "relative motion to multiple
>>>>observers"?
>>>
>>>It doesn't have to, since there are other vessels and observation
>>>satellites spread across the solar system.
>>
>>In which case your continuous infrared scans looking for spaceships are
kind
>>of pointless.
>
>No, if those multiple vessels and observation systems don't actually use
>a detection system (like IR scanners) they are not going to find
>anything. The capabilities of IR are still quite relevant - if multiple
>ships and observation satellites spread across the system used active
>radar or visual-wavelength scans, it would not be that hard to hide
>anywhere there aren't any sensors within a few million klicks.
They'll use some kind of scanner, but I don't see any real advantages to
infrared. You're going to know where there is any facility large enough to
construct a spacecraft unless it is on a planetary surface, so you just have
to watch those locations to see if any of them launch a spacecraft, then you
can track it by a variety of means. There is no need for your full-sky
infrared scans unless you are expecting an extrasolar visitor, or something
popping out of hyperspace in the middle of your star system.
>>>Since the position of all objects is known, the temperature a rock
>>>should be _at that position_ is known. A live ship at that position will
>>>always be hotter than a rock at that position.
>>
>>If the position of all objects is known then how does this spaceship
manage
>>to avoid having its position known?
>
>The position of all _natural space objects_ is known because, being
>natural space objects, they do not go accelerating around all over the
>place. Everything will stay in its orbit or position with the exception
>of some asteroids, and regular checkups on unknown objects will keep
>track of where most of them are.
So how did this spacecraft manage to avoid having its construction and
launching observed? Some "secret rebel base" where nobody managed to notice
all the _inbound_ traffic needed to bring the rebels, tools, materials, etc
to the base? Seems to me that it would be cheaper, easier, and more
reliable to maintain observation on locations with sufficient industrial
base to create spacecraft than to maintain full-sky scans.
>> And why will a live ship at that
>>position always be hotter than a rock at that position? Tailor the
>>emissivity of the hull properly and it can have any arbitrary temperature.
>
>No, it can't. The ship must _always_, over time, radiate all the waste
>heat that it generates. If there is _any_ active electronics or
>machinery on board the ship, it will generate waste heat. All of that
>waste heat will be eventually be radiated as infrared radiation.
>
>>You assume that the radiation curve for the ship and for a rock are
>>necessarily the same. They are not.
>
>Both the ship and the rock must radiate all energy they absorb, and all
>waste heat they generate. Since the rock doesn't generate any waste
>heat, the ship with the same surface area must always radiate more
>energy.
And you have not demonstrated that such radiation of more energy will make
the ship look in any way different from a rock.
>>>>In any case the _apparent_ temperature
>>>>can be adjusted by coatings with tailored emissivity.
>>>
>>>Over time, all energy generated must be radiated, or the ship will get
>>>hotter and hotter. Actually, it would get hotter and hotter quite fast.
>>
>>Yes, it must be radiated. That does not mean that it must be radiated at
>>any given frequency.
>
>Who said sensors were limited to looking for one exact frequency?
Nobody. You don't seem to be able to grasp the concept that the only
difference between two objects at different temperatures from the viewpoint
of distinguishing them by their infrared emissions is the peak frequency of
their blackbody curves. You seemt to think that the radiation from a hot
object is at the same frequency as for a cold one but more intense, which is
not the case, as you would know if you actually knew something about the
blackbody curves you claim are irrelevant. And if you actually knew
something about them you would also know that a given amount of energy can
be radiated at _any_ temperature by altering the size of the radiator, and
that the actual peak frequency and shape of the radiation curve can be
adjusted by altering the surface properties of the object.
>>>Optical telescopes. RADAR. More precise infrared telescopes. In general,
>>>narrow-field but very accurate sensors.
>
>>Radar is hardly a "narrow-field
>>but very accurate sensor" compared to infrared. So you point an optical
>>telescope at it and what does it see? Yet another rock. Or has it not
>>occurred to you that anyone who can build a spaceship can dummy it up to
>>look like a rock?
>
>They can dummy it up all they want, but if it's the right size/shape
>that it could possibly contain a spaceship, and it is heading in an
>un-asteroid-like direction, it'll be red-flagged and if it so much as
>peeps it will be identified. Asteroids which go within a certain
>distance of my assets will be evaded, redirected, or destroyed as a
>matter of course.
So it goes "outside that distance" until too late for you do do anything
about it it lights up huge drives, plows in, and blows your facility to
Kingdom Come. Unless of course that distance is so huge that space
navigation in the vicinity of whatever it is protecting becomes impossible.
>Also, dummying up a ship as an asteroid assumes a significant allocation
>of mass and effort to hiding, a strategy which will only be used for
>"special occasions", not everyday warships. It's only useful if you're
>going to spend all your time between the target, and some point outside
>the solar system, costing "dead".
You mean like the B-2 is only useful for "special occasions"? You plan your
capabilities based on what the enemy _can_ do, not what you think he _will_
do.
>>So a ship in front of the sun is going to reduce the apparent luminosity
of
>>the sun enough to allow you to detect the ship?
>
>If he is close enough to me or any sensor, yes. If he's not, I really
>don't care about him - he'll be detected as soon as he stops tooling
>around the sun. And there's still the problem that he's going to have
>difficulty being between two widely-dispersed sensors and the sun.
>Having two or more widely-dispersed sensors, considering the entire
>solar system, is not exactly going to be rare. Heck, if he really wants
>to, he can hang around in really close solar orbit and nothing is going
>to detect him unless I make a really big effort to search close solar
>orbit - except that since he didn't launch from the sun, I probably saw
>him when he was heading for it anyway.
Again you assume you know where he's going. How close does he have to be
before you can determine that he is reducing the apparent luminosity of the
Sun?
>>>>Depends on what kind of engine he is using. How hot would the exhaust
>>from
>>>>a mass-driver be?
>>>
>>>The exhaust heat is irrelevant, as the waste heat produced by the
>>>electromagnetic acceleration process would heat up the entire ship.
>>
>>What exhaust heat? The temperature of the exhaust from a mass-driver is
>>whatever the designers of the system want it to be. And what waste heat
>>from superconducting magnets?
>
>Okay, let me make a suggestion. Pick up a copy of a textbook which
>includes the laws of thermodynamics. Read them.
Pick up a copy of a textbook which includes a discussion of
superconductivity, Read it.
>EVERYTHING you do produces waste heat. Absolutely everything. The more
>energy you expend, the more waste heat you produce. Generating the power
>for your superconducting magnets produces waste heat (that's where most
>of it will come from, actually). Running power around inside your ship
>to the magnets produces waste heat. The interaction of the magnetic
>fields generated produces waste heat in the railgun and the projectile.
>The cryogenic cooling process you use to produce a perfectly cold
>projectile produces waste heat (I'd be impressed to see how you manage
>to cool the projectile _after_ it's been launched, which is when all the
>magnetic stress is on it, anyway).
There is no railgun. The device is a mass driver. Look them up, they are
not the same. Running power around using superconductors produces
negligible losses. The projectiles were pre-cooled. The projectile does
not have to be "perfectly cold", merely close enough to the cosmic
background that it doesn't show up on your sensors. Any structure which is
not part of the magnetic mechanism is made of a nonconductive material which
does not experience any eddy currents and is thus not heated by the magnetic
fields. So is the projectile--it is held in a superconducting bucket which
is also cryogenically cooled. The actual power was stored prior to launch.
Didn't occur to you that someone might actually design a system intended to
defeat your sensors at great expense did it? There might be some slight
losses due to inefficiency of the system, but they are easily handled by
tailored emission curves.
You really need to quit oversimplifying engineering problems to homilies
like "EVERYTHING you do produces waste heat". You also have to learn to
quit telling people with earned degrees in physics and engineering and years
of experience in the field to "pick up a copy of a textbook which includes
the laws of thermodynamics and read it".
>>Whenever "Global Traffic Control" happens, yes, this is precisely what
will
>>occur. Anything not registered and looks like a potential problem gets
>>intercepted, just as happens in the US in controlled airspace now.
>
>And just as happens in _any_ airspace during a war.
It does? So exactly what did the Somalians or the Bosnians intercept?
>The whole point of
>military air defense systems, IFF, etc., is that all friendly stuff
>identifies itself to you, but for some reason the enemy never bothers to
>do so.
IFF identifies a friendly. That does not mean that anything not squawking a
friendly IFF remains undetected.
>The prospect of being intercepted if he doesn't identify himself
>does not matter to the enemy, since if he identifies himself, he
>guarantees that he will get intercepted.
He gets intercepted anyway if he moves into an environment as sensor-rich as
US controlled airspace, unless he has carefully planned his actions and
designed his vehicle so that it is difficult to detect using the
technologies he knows are in place.
J. Clarke
--
--John
Reply to jclarke at eye bee em dot net.
Brett Evill wrote in message ...
>In article <35f5a...@news1.ibm.net>, "J. Clarke" <nos...@nospam.nospam>
wrote:
>
>>How many pixels do you need in order to compute your spectrum?
>
>Strictly speaking, only two. One between the temperature of a rock a and a
>ship, and one between a ship and a star.
This would work fine if blackbody emission was monochromatic at a given
temperature and if the temperature of a rock was the same for all rocks.
But with two sensors all you know is that there are two objects out there
with particular infrared intensities at particular frequencies.
>But why not go for three, for
>better discrimination in dubious cases?
Better, but you still don't really know the temperature of the object.
Incidentally, you've cut the sensitivity of your device by a factor of 3 by
doing this.
>You could hard-wire the
>differencing into the substrate of the CCD (or whatever) chip, and need
>minimal computer processing.
In any case, by careful tailoring of the spectral emission characteristics
of the object this device could be defeated--instead of the ship being an
ideal black body it's a gray body with its peak emissivity at "rock"
temperature. Tailored emission is not something that is done commonly
because it's expensive, but anyone who has made any kind of serious study of
solar-power systems is aware of the capability, as it is potentially useful
in the engineering of solar collectors. You might want to check out
Kreith's book on Solar Engineering, which touches on this, and any good text
on modern optics for some discussion of one method that can be used.
J. Clarke
>"J. Clarke" <nos...@nospam.nospam> wrote:
>
>>Of course we can. Just assume that FTL doesn't affect sensor technology.
>
>First, it has absolutely nothing to do with the original subject of
>discussion anyway.
>
>Second, it must intrinsically affect sensor technology, if merely by
>affecting the avoidance of sensors. If my ship can pop into hyperspace
>whenever I want to get to my destination, what does it matter how
>effective the enemy's sensors are in real space?
If you don't have effective real-space sensors and if he knows that then
he'll approach you in real space.
>Third, it presumes a higher level of technology than we can plausibly
>project. The discussion of interplanetary warfare made a fairly small
>number of assumptions. As soon as we try to discuss interstellar travel,
>a huge number of assumptions are generated all of a sudden. It becomes
>impossible to talk with any amount of authority about what things would
>be like without picking a set of assumptions on such things as the
>capability of FTL, overall advancement of technology (is it easy to use
>nanotech to build a kilometer-wide telescope out of an asteroid?),
>amount of power available to ships, type of weapons, etc. But there is
>no one best set of assumptions to pick - in fact there is a
>mind-numbingly huge number of sets of assumptions to pick.
There's no one best set of assumptions concerning the level of technology in
a solar system sufficiently industrialized that one has to worry about being
attacked by spacships from elsewhere in the solar system, either. This is
far enough in the future that a good deal of technology that we are
incapable of imagining at this time will exist.
>You have yet presented a single effective method to defeat it.
Actually, I've presented several. However your grasp of heat transfer and
optics is not sufficient for you to comprehend their nature. Instead you
continue to harp on your naive notion of the nature of thermal emissions and
unfounded assumptions concerning the amount of waste heat emitted by an
engine whos operation you clearly do not understand.
>"Central sensor"? ??
>
>I don't know what your problem is but it obviously includes a convenient
>lack of memory.
Any sensor system that can perform real-time scans of the entire sky with
sufficient sensitivity and precision to detect and characterize spacecraft
in flight is going to be a rather large, bulky array, not something you
stick on the back of your bicycle. So there are going to be one or more of
these facilities, which would be centralized sensors. There's not going to
be one of these on every spaceship.
>I originally posted an all-around description of interplanetary space
>combat, complete with a one-paragraph mention that sensor technology
>would likely be so advanced that everyone knows where everyone else is.
>You disagreed with this, and said that no sensor could do this. I said
>that multiple IR sensors could do this, you said no they couldn't. I
>have conclusively demonstrated that they can, now you are trying to
>retroactively change the subject to why this is meaningful? It's
>meaningul because my original point is now proven.
Nope, you haven't proven anything except that infrared sensors can detect
particular events at particular distances if they are pointed in the right
direction during the event. You have not addressed a variety of issues
other than to wave your arms and claim that it wouldn't happen.
>>I would, because you haven't demonstrated that infrared technology can do
>>what you want it to do.
>
>I have conclusively demonstrated in every mention that it can do exactly
>what I want it to, as have other people.
No, you have not.
>You have repeatedly failed to
>demonstrate any failings of an IR sensor net.
I've addressed several.
> Every objection you have
>raised has hinged upon a cold ship which has accelerated well outside
>the solar system, which I originally specifically mentioned would be
>detectable at long range, or on attempting to hide from a single ship
>which has no access to other sensor platforms.
Or a cold ship with a cold exhaust.
>Since my entire original
>point was the performance of opposing fleets of ships, in the context of
>a battle within the solar system, that's hardly relevant.
But if you are detecting _fleets_ launched inside the solar system, that's
going to be such a major event wherever it happens that if you don't have
someone watching the facility where such fleets are located then your
superiors are going to have you served to their cat for dinner. You don't
need this full-sky scanning IR system because you're going to have half the
sensors in Christendom pointed at that base. Not to mention that CNN will
be reporting the departure of this fleet before the light reaches your
sensor.
>>Nope, I pointed out the ignorance on that topic and a few others of all
>>involved. Hint--learn what a "blackbody curve" is before you post more of
>>your twaddle.
>
>Blackbody curves are completely and utterly irrelevant to the subject
>under discussion, in that they're useless in preventing one from being
>detected by an IR sensor net.
If you believe that then you don't understand blackbody curves.
>Before you try and accuse other people of being ignorant, perhaps you
>had better learn basic concepts of thermodynamics like waste heat.
Where does this waste heat come from in a system using stored power and
superconductivity?
Really, your argument boils down to "infrared can detect everything because
I say it can", and your objection to a cold ship with a cold exhaust is that
you can't imagine how to build such a thing.
Jeff Suzuki
: Last I checked, asteroids were not detected by infrared. They are, after
: all, exactly the same temperature as the space around them, what with
: not having electronics, crews, and power systems inside them generating
: heat.
Can we kill a falsehood here? Space _isn't_ "cold". If you're within the
orbit of the Earth around the sun, space is pretty hot; look at Skylab's first
few days in orbit when the heat shield failed to deploy and the station was in
danger of becoming uninhabitably hot.
Put it into perspective: in Earth orbit, a square meter absorbs around 400
watts of solar power. If a body is in temperature equilibrium, that square
meter is therefore radiating as much power as four normal human beings. Two
square meters radiate as much power as a normal (20th century) city-dwelling
human being.
Jeffs
Jeff Suzuki
: The main problem with this is that anybody with something that can sense
: a ship in real time must CERTAINLY and unavoidably have voluminous
: archives of the movements of every ship-sized hunk of rock, space
: derelict, and probably floating wing nut in the solar system.
Ever read how MIRVs were originally developed?
The idea was that the USSR had ABMs. So the US set up ICBMs to deploy with
several decoys, all of which looked like real warheads to a 1960s radar
screen. (At some point, some bright boy decided "Hey, why not _make_ them real
warheads?")
First: as I said, there's a lot of junk. Any attacker is going to bring
their own junk, just to make things more difficult. (They'll probably also do
things to make small, cheap junk look like big, dangerous warships...it's easy
enough to do _today_)
Second: an IR sensor by itself won't give you distance. It'll give you the
location of an object on an imaginary two dimensional spherical surface. Also
on that surface is every other radiating body in the solar system. To find
range (and determine whether something is "dangerous radiating junk" as
opposed to "harmless radiating junk"), you'll need something active. Ever
hear of a HARM? In space, these have infinite "hang time": you could drop a
few hundred into a deployment area, and they'll go after anything that lights
up with active sensors.
So: sure, you can find them with IR. But it might not do you any good.
Jeffs
John Schilling
>First item, how long an exposure is required to achieve these results.
That was one of the design parameters for the sensor in question. One
hour to scan the entire sky with one sensor. If there are a dozen sensor
platforms within range of a given target, that target will be in the field
of view of a sensor on average once every five minutes.
>Second item, what is the probability that a spacecraft operated by someone
>who understands the capabilities of your sensors is going to be doing one of
>these things at the exact time that you have the sensor pointed at it?
If the spacecraft wishes to use its engines for more than five minutes or
so, it has no choice but to accept that it will be visible to enemy sensors.
That's five minutes of total operation during the mission - it doesn't matter
whether you run continuously or in occasional short bursts. Once the total
operation time reaches five minutes, odds are you've had the engines on at
the instant you were under observation by the enemy.
Anyone who understands the capabilities of these sensors, understands that
it is not possible to conceal any maneuver of any tactical or strategic
significance from a competent opponent, accepts this reality, and develops
spacecraft and tactics for high-visibility operations.
--
*John Schilling * "You can have Peace, *
*Member:AIAA,NRA,ACLU,SAS,LP * or you can have Freedom. *
*University of Southern California * Don't ever count on having both *
*Aerospace Engineering Department * at the same time." *
*schi...@spock.usc.edu * - Robert A. Heinlein *
*(213)-740-5311 or 747-2527 * Finger for PGP public key *
John Schilling
>Tommy the Terrorist (may...@newsguy.com) wrote:
>: 1) A black ship is a "blackbody", which is to say, unless your crew likes
>: life at 3 Kelvin, it's going to glow a cherry red to anybody with IR
>: accessories.
>So does a large fraction of the night sky. The problem is distinguishing
>between "ship radiating as if it had been in the sun" from "ship-sized rock
>radiating as if it had been in the sun."
>There are a lot of false analogies made between stealth aircraft and stealth
>spacecraft. IR, radar, etc. work on aircraft because there is nothing
>"natural" in the sky that reflects radar the way an airplane does,
However, there are lots of things on the *ground* that reflect radar the
way airplanes do. Including the ground itself. And the ground is usually
within the field of view of radar systems looking for air targets. So
the analogy holds, and extends to some extent to the measures used to
distinguish between targets and clutter.
>heat the way an airplane does. If it reflects radar or radiates heat, it
>shouldn't be in the sky. But there's a lot of radar reflecting and heat
>radiating junk out there...and any intelligent commander is going to make use
>of it, a la (various submarine movies).
One of the traditional ways to distinguish targets from clutter is to map
the clutter. Provide the sensor with a list of every natural radar
reflector or IR emitter in the field of view, or if necessary the total
natural radar reflectivity or IR emissivity within each resolution cell,
and have it subtract this from each return.
Another is to look at the finer details of any signal return that does
attract the sensor's attention. No natural target is going to have the
continuously varying doppler of a spacecraft under acceleration, or the
characteristic Xenon emission lines of a plasma thruster plume, or the
blackbody pattern of a metal radiator surface at 700 K. Just having the
primary sensor independantly sensitive to three or four spectral bands
would probably be enough, and a dedicated target-discrimination sensor
can handle the occasional fuzzy case. Which then gets added to the
clutter map if necessary.
Nothing can stop a relatively small target from hiding in the signature
of a larger natural target, of course. But presuming the enemy has
several widely-dispersed sensor platforms, hiding in the signature of a
large natural target means hiding *at* a large natural target. You
can't move from that point without being noticed, which begs the question
of how you got there without being noticed in the first place, and in
any event you are now talking about stealthy asteroid bases and not
stealthy spaceships.
A spacecraft maneuvering in open space is not going to be mistaken for
a natural object no matter how cleverly it camoflages itself, because
it won't be in the same place as any known natural object, and because
unknown natural objects large enough to be mistaken for spaceships will
be as rare and thus as inherently suspicious as an actual spaceship,
and because it won't really look all that much like a natural object
one the enemy starts looking closely and/or it starts doing any of
the spaceship-like activities that you sent it out to do in the first
place.
Keith Morrison
> The idea was that the USSR had ABMs. So the US set up ICBMs to deploy with
> several decoys, all of which looked like real warheads to a 1960s radar
> screen. (At some point, some bright boy decided "Hey, why not _make_ them real
> warheads?")
>
> First: as I said, there's a lot of junk. Any attacker is going to bring
> their own junk, just to make things more difficult. (They'll probably also do
> things to make small, cheap junk look like big, dangerous warships...it's easy
> enough to do _today_)
Big deal. So they've just put up a bigger sign to announce their
presence.
> Second: an IR sensor by itself won't give you distance. It'll give you the
> location of an object on an imaginary two dimensional spherical surface.
And that's why you use two or more separated sensors and that
really obscure mathematical technique called "triangulation".
--
Keith Morrison
kei...@polarnet.ca
John Schilling
>Ian (iadm...@undergrad.math.uwaterloo.ca) wrote:
>: Last I checked, asteroids were not detected by infrared. They are, after
>: all, exactly the same temperature as the space around them, what with
>: not having electronics, crews, and power systems inside them generating
>: heat.
>Can we kill a falsehood here? Space _isn't_ "cold". If you're within the
>orbit of the Earth around the sun, space is pretty hot; look at Skylab's first
>few days in orbit when the heat shield failed to deploy and the station was in
>danger of becoming uninhabitably hot.
>Put it into perspective: in Earth orbit, a square meter absorbs around 400
>watts of solar power.
1,358 watts, actually. However, virtually all of that energy is coming
from one very small region of the sky. A sensor looking in any other
direction will see a 3 degree kelvin background, against which any
emitter will stand out likean incandescent light.
A sensor staring at the sun will be useless, but given two or more
widely seperated sensor platforms any target will be visible against
the cold background to at least one of the sensors.
>If a body is in temperature equilibrium, that square meter is therefore
>radiating as much power as four normal human beings. Two square meters
>radiate as much power as a normal (20th century) city-dwelling human being.
Which makes such bodies visible. They absorb a great deal of energy from
the decidedly anisotropic radiation environment, but invariably reradiate
it in a much more uniform fasion. So except from a single direction, they
are observed to emit at well above background. Natural objects are clearly
visible from the moment anyone makes a serious (by military standards) effort
to look for them, resulting in their being immediately catelogued for future
reference, and artificial targets are clearly visible from the moment of
deployment, and detected as soon as anyone notices them in a place where
none of the catalogued natural objects are supposed to be.