Slow Re-entry
arne97
atmosphere in a blaze of heat.
I assume that this is a method of shedding speed.
The moon lander , lacking an atmosphere, depended on rockets to
slow descent.
What with broken tiles and what-not, isn't there a better way to
get a ship down those last 200 miles than turning it into a meteorite ?
What about expendable drag devices ?
How much fuel would be needed to slow the vehicle in orbit to a
relatively safe landing speed?
Arne
Doc O'Leary
"arne97" <gahad...@yahoo.com> wrote:
> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?
Not according to the rocket scientists. But what do they know, right?
> What about expendable drag devices ?
And in space it precisely will drag against what? Or what would you
propose they stick out in the high atmosphere that would be both
reliable and expendable at over Mach 20? Bonus points if you can
actually pack it small enough to fit in the Shuttle itself. This leads
to the "black box" joke: Why don't they just make the whole Shuttle out
of it? They did!
> How much fuel would be needed to slow the vehicle in orbit to a
> relatively safe landing speed?
Slightly less fuel than was needed to get the vehicle into orbit in the
first place. Well, a lot less if you consider how much fuel you'd have
to burn to get that fuel in orbit in the first place, but the point
stands. You'd have to build what amounts to a launch vehicle for the
current launch vehicle.
Simon Morden
> In article <1123426483....@g44g2000cwa.googlegroups.com>,
> "arne97" <gahad...@yahoo.com> wrote:
> >
>> What with broken tiles and what-not, isn't there a better way to
>>get a ship down those last 200 miles than turning it into a meteorite ?
>>relatively safe landing speed?
> >
> Slightly less fuel than was needed to get the vehicle into orbit in the
> first place. Well, a lot less if you consider how much fuel you'd have
> to burn to get that fuel in orbit in the first place, but the point
> stands. You'd have to build what amounts to a launch vehicle for the
> current launch vehicle.
If LEO is something like 4.5km/s, that's the amount of delta V you need
to shed. Either aerobrake or reverse thrust.
There's nothing magical about orbit - look up some of the high-altitude
jumps which were made in glorified space-suits. The reason those guys
didn't turn into fireworks was that they weren't moving that fast...
Simon Morden
Stephen Horgan
You have to shed the velocity. Doing it slowly implies the use of
reaction mass, which you then have to carry. There is nothing wrong
with the principle as far as I know but the engineering problem with
current technology is formidable.
--
Stephen Horgan
"intelligent people will tend to overvalue intelligence"
Erik Max Francis
Orbital speed is 7-8 km/s. You need to shed that much speed in order to
avoid burning up in the atmosphere. Furthermore, you need to shed it
fast, because reducing your speed will make you drop inward due to
orbital mechanics, which means that you'll touch the atmosphere if you
don't shed it all quickly.
On the contrary, using reentry is a very effective and efficient way to
get to the surface of a terrestrial planet with an atmosphere from orbit
safely and effectively.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
It is one thing to praise discipline, and another to submit to it.
-- Cervantes
Mad Bad Rabbit
> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?
Yes, a space-elevator ; but we need several thousand kilometers
of superstrong cable that we're not able to manufacture just yet.
--
>;k
Edward Cherlin
> The shuttle, as well as most other space vehicles, enter the
> atmosphere in a blaze of heat.
> I assume that this is a method of shedding speed.
Yup.
> The moon lander, lacking an atmosphere, depended on rockets to
> slow descent.
Yup. It can do that in the lower gravity of the moon.
> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?
Definitely not if it's the Shuttle. But all landings on Earth, Mars, and
Titan have used aerobraking in the high atmosphere, even if they used
parachutes lower down. Venus also, I believe.
> What about expendable drag devices?
They're called tiles.
If you can come up with a parachute that can operate at several thousand
degrees, and cords that can hold it to the Shuttle at those temperatures
and at 25,000 mph, feel free *NOT* to post your kookery here or anywhere
else on Usenet. When you have a working prototype, we'd be delighted to
read about you on the news.
> How much fuel would be needed to slow the vehicle in orbit to a
> relatively safe landing speed?
One humongous external tank and two solid rocket boosters should do it. Same
delta-V going down as going up, same gravity well.
> Arne
Jim Burns
The space elevator is certainly the solution I want, mostly
because it seems to me that I'll be more likely be able to
pay for a ticket into space via the space elevator than via
some descendant of the Space Suttle.
How about Spaceship One, though? When I saw them on 60 Minutes,
my impression was (1) they're using a revolutionary design
to passively orient the ship for proper re-entry, and (2)
they don't look like they're using NASA-style ceramic-foam tiles.
OK, so all they've done so far is pop out of the atmosphere
and drop back in, but I would think their engineers are
designing for a future with true orbital flight -- and
return from orbit. Do they have a Clever Plan to make the
heat of re-entry not quite so hot?
Jim Burns
Hop David
Jim Burns wrote:
> Mad Bad Rabbit wrote:
>
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>
>>> What with broken tiles and what-not, isn't there a better
>>>way to get a ship down those last 200 miles than turning it
>>>into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>
>
> The space elevator is certainly the solution I want, mostly
> because it seems to me that I'll be more likely be able to
> pay for a ticket into space via the space elevator than via
> some descendant of the Space Suttle.
>
> How about Spaceship One, though? When I saw them on 60 Minutes,
> my impression was (1) they're using a revolutionary design
> to passively orient the ship for proper re-entry,
For a suborbital re-entry. Orbital re-entry is a completely different
animal.
--
Hop David
http://clowder.net/hop/index.html
Lorenzo L. Love
Google >rotating space tether<
Ben Bradley
wrote:
>How about Spaceship One, though? When I saw them on 60 Minutes,
>my impression was (1) they're using a revolutionary design
>to passively orient the ship for proper re-entry, and (2)
>they don't look like they're using NASA-style ceramic-foam tiles.
>OK, so all they've done so far is pop out of the atmosphere
>and drop back in,
That's the secret. I didn't see 60 minutes, but I wouldn't be
surprised if they glossed over the difference between a suborbital and
orbital flight, and the differences in re-entry (it being TV, I'd be
very surprised if anyone other than Miles O'brien got it right). Space
Ship One, when coming back down from essentially a dead stop 60 miles
high, reached a speed of (just a ballpark guess) Mach 2 to Mach 3.
Something coming into the atmosphere from orbit is going at about Mach
23. It's a huge difference in speed and the amount of kinetic energy
being turned into heat.
>but I would think their engineers are
>designing for a future with true orbital flight -- and
>return from orbit. Do they have a Clever Plan to make the
>heat of re-entry not quite so hot?
I doubt it. Their plans are probably just like everyone else's:
figure out how to deal with the heat.
Maybe a super-duper rocket engine that operates in outer space will
be developed that gives a large enough thrust to slow down something
with the mass of the Shuttle so that it can just 'drop' into the
atmosphere, and have much less stringent hull designs for re-entry.
The engine would have to go down with the spacecraft, or perhaps it's
detachable and can then accelerate itself back to orbital speed to
rendevous with and decelerate another craft. Perhaps a nuclear powered
device would have enough power, but it's going to need reaction mass
from somewhere, and it's too expensive to to send it up from Earth.
Reaction mass might come from the Moon or the Astroid belt.
But making such an engine is surely beyond current budgets of
organizations such as NASA, much less the Space Ship One people. It
also has its pitfalls. If it fails after firing for 10 percent of what
it normally would take to 'stop' something in orbit, that something
will enter the atmosphere at near full orbital speed, perhaps without
being designed to do that.
To bring something like Space Ship One out of orbit, the engine
would also have to bring it down to 60 miles and leave it at a
standstill. If the craft were dropped from the usual LEO height (110
to 300 miles), it would have had at least 50 extra miles of freefall
acceleration due to gravity before hitting the atmosphere.
It takes something like ten or 20 times the energy to get something
going horizontally at orbital speed than it does to get it 100 miles
above the Earth's surface. Likewise, you have to slow down from the
orbital speed to come back (unless you want to make a supersonic
landing).
>Jim Burns
Steve Charlton
arne97 <gahad...@yahoo.com> writes
other as they pass with a very very strong and very very stretchy bungie
cord. Ssstttrrreeetttccchhh. They both stop relative to each other, they
both release the cord (at the same time) and drop vertically into the
atmosphere (as does the cord). Much less energy to shed. Much less heat
build up (the cord might get a tad warm).
Alternatively, if A releases the cord and B doesn't, tttwwwaaannnnggg! A
drops safely into the atmosphere and B + cord go zooming away at almost
twice the original speed.
Of course, when we can make a bungie cord that good, an orbital tether
will be no problem.
[Early morning review: I seem to need either more sleep or less alcohol
or both, but I'm leaving this last in anyway. Its not like this is a
serious thread.]
I don't recall anyone proposing an orbital bungie before so here goes.
Take two big masses (asteroids say) one on either end of the cord. Their
centre of mass would be in geo-stationary orbit. One is moving towards
Earth, the other away. The inbound one, decelerated by the bungie, just
touches the ground, everybody on it jumps off, everybody who wants a
really wild ride jumps on and up you go! An hour or 3 later the other
mass, with its passengers, touches down briefly and the situation
repeats. Of course, you'd need motors on the rocks, to keep everything
balanced, stop them hitting each other, smashing the odd city, etc.
There's even a tag-line for the T.V. advert - "Disney World Orbital -
what a ride!" B-)
--
Steve Charlton | You may have trouble getting
st...@gnirekoms.freeserve.co.uk | permission to aerobrake or
hint: ^^^^^^^^^ | lithobrake asteroids on Earth!
reverse this | - James D Nicoll
Marten Kemp
I wonder if sticking a whopping big ablative heat shield
(the kind of thing that was used for all the re-entry
capsules from Mercury to Apollo) on the bottom might
work. You'd have to replace it after each flight but
you wouldn't have to fiddle with those pesky tiles.
The weight differential is something upon which more
knowledgable people than I can comment.
--
-- Marten Kemp
(Fix name and ISP to reply)
Alcore
On Mon, 8 Aug 2005, Marten Kemp wrote:
[snip]
>I wonder if sticking a whopping big ablative heat shield
>(the kind of thing that was used for all the re-entry
>capsules from Mercury to Apollo) on the bottom might
>work. You'd have to replace it after each flight but
>you wouldn't have to fiddle with those pesky tiles.
>
>The weight differential is something upon which more
>knowledgable people than I can comment.
[snip]
My thought on the subject was the concept of a re-entry "sled"...
Essentially, construct the entire high-heat re-entry portion of the
vehilcle as a one-piece shell that is "snap on" replaceable.
I like the notion of an ablative ceramic or metalic "belly shield" that
can be swapped out by 3 guys with screw-guns and a lifting rig for the
ship in about 20 minutes.
Gene P.
Slidell, LA
--
Alcore Nilth - The Mad Alchemist of Gevbeck
alc...@uurth.com
Edward Cherlin
>
> On Mon, 8 Aug 2005, Marten Kemp wrote:
>
> [snip]
>>I wonder if sticking a whopping big ablative heat shield
>>(the kind of thing that was used for all the re-entry
>>capsules from Mercury to Apollo) on the bottom might
>>work. You'd have to replace it after each flight but
>>you wouldn't have to fiddle with those pesky tiles.
>>
>>The weight differential is something upon which more
>>knowledgable people than I can comment.
What I want to know is how you get the shield *up* each time. You can't fold
it up and put it in the glove compartment. Besides, every kg of mass of the
thing comes out of payload.
> [snip]
>
> My thought on the subject was the concept of a re-entry "sled"...
>
> Essentially, construct the entire high-heat re-entry portion of the
> vehilcle as a one-piece shell that is "snap on" replaceable.
>
> I like the notion of an ablative ceramic or metalic
Metals conduct heat well, so they don't work as heat shields. Most of them
melt or oxidize at high temperatures, or both.
> "belly shield" that
> can be swapped out by 3 guys with screw-guns
Not metal screws, obviously, so what were you thinking?
> and a lifting rig for the
> ship in about 20 minutes.
I get it. Instead of the fiddly little tiles that have to be glued on one at
a time (and a large fraction of them break in the process because they have
to be so thin and light), we go for one humongous but equally thin
full-belly shield that breaks before you can get it into its shipping
crate, or even out of the mold where it's made. And then we only screw it
on in as many other places as we can do in what's left of our 20 minutes,
so that it will flap against the ship and break into little bitty pieces on
lift-off, and we won't have to worry about the weight on reentry.
Oh, wait, that means that it won't be there to shield the ship. Rats. It was
such a great idea. And we could have used the shipping crates for
low-income housing.
> Gene P.
> Slidell, LA
Stan
}In article <1123426483....@g44g2000cwa.googlegroups.com>,
}arne97 <gahad...@yahoo.com> writes
}> The shuttle, as well as most other space vehicles, enter the
}>atmosphere in a blaze of heat.
}> I assume that this is a method of shedding speed.
(snip)
}Two space craft A and B, orbiting in opposite directions. They snag each
}other as they pass with a very very strong and very very stretchy bungie
}cord. Ssstttrrreeetttccchhh. They both stop relative to each other, they
}both release the cord (at the same time) ...
"Two space craft A and B, orbiting in opposite directions..."
So, to descend from the orbit of the space station, the shuttle would
have to "bungie-snag" something the same size orbiting in the exact
opposite direction. Hmmm...with the craft traveling a bit more than
5 KM/sec (someone check my orbital mechanics; I was never really good
at it) this means they would be passing each othe at more than 10 KM/sec.
More importantly, it would be that the space station would have a "visitor"
going by at a speed (& how many times a day?) that would surely make the
inhabitants a bit nervous.
Stan.
No 33 Secretary
news:stanleyh-080...@pdx-ppp131.pop1.net:
Plus, even slowing down by "bungee cord" would have to take long enough for
both objects to re-enter the atmosphere at high speed before they're done
slowing down. Because if they don't, the passengers are going to be tomato
paste from deceleration.
--
Terry Austin
www.hyperbooks.com
Campaign Cartographer now available
Gene P.
On Mon, 8 Aug 2005, Edward Cherlin wrote:
>What I want to know is how you get the shield *up* each time. You can't fold
>it up and put it in the glove compartment. Besides, every kg of mass of the
>thing comes out of payload.
Attatched to the ship, just like we do now, of course.
>> [snip]
>>
>> My thought on the subject was the concept of a re-entry "sled"...
>>
>> Essentially, construct the entire high-heat re-entry portion of the
>> vehilcle as a one-piece shell that is "snap on" replaceable.
>>
>> I like the notion of an ablative ceramic or metalic
>
>Metals conduct heat well, so they don't work as heat shields. Most of them
>melt or oxidize at high temperatures, or both.
>
>> "belly shield" that
>> can be swapped out by 3 guys with screw-guns
>
>Not metal screws, obviously, so what were you thinking?
Okey dokey... How about carbon fiber retaining pins then? You know,
something strong, reasonably heat resistant (they will be on the *inside*
of the shield, after all), and lightweight...
>> and a lifting rig for the
>> ship in about 20 minutes.
>
>I get it. Instead of the fiddly little tiles that have to be glued on one at
>a time (and a large fraction of them break in the process because they have
>to be so thin and light), we go for one humongous but equally thin
>full-belly shield that breaks before you can get it into its shipping
>crate, or even out of the mold where it's made. And then we only screw it
>on in as many other places as we can do in what's left of our 20 minutes,
>so that it will flap against the ship and break into little bitty pieces on
>lift-off, and we won't have to worry about the weight on reentry.
>
>Oh, wait, that means that it won't be there to shield the ship. Rats. It was
>such a great idea. And we could have used the shipping crates for
>low-income housing.
I'm thinking somebody needs some decaf.
Who said *anything* about using the same ceramic material as the existing
shuttle tiles? That stuff is designed to survive re-entry intact... not
ablate. It has *serious* structural and material properties deficiencies
for use outside of it's design envelope.
So let me try again... It's a *disposable* *easy-to-replace* heat shield.
Choose *new* materials that meet those guidelines.
(I have real trouble believing that, given the materials science
improvements since the Shuttle system selected its heat shield material in
the 70's, we aren't capable of some more advanced engineering today.)
Gene P.
Slidell LA
John Schilling
>
>
>Mad Bad Rabbit wrote:
>>
>> "arne97" <gahad...@yahoo.com> wrote:
>>
>> > What with broken tiles and what-not, isn't there a better
>> > way to get a ship down those last 200 miles than turning it
>> > into a meteorite ?
[...]
>How about Spaceship One, though? When I saw them on 60 Minutes,
>my impression was (1) they're using a revolutionary design
>to passively orient the ship for proper re-entry, and (2)
>they don't look like they're using NASA-style ceramic-foam tiles.
That's because they don't fly any faster than an SR-71. World
of difference between Mach 3 and Mach 30.
Yes, kudos for the revolutionary design providing passive stability
during re-entry, but that was only for *stability*. It had nothing
to do with the thermal protection issue. Rutan's passively-stable
vehicle, re-entering from Low Earth Orbit, would need the "ceramic
foam tiles" or something equivalent.
>OK, so all they've done so far is pop out of the atmosphere
>and drop back in, but I would think their engineers are
>designing for a future with true orbital flight -- and
>return from orbit. Do they have a Clever Plan to make the
>heat of re-entry not quite so hot?
Perhaps, but not that they are talking about. It's a hard problem;
one that we know how to solve, but not one that we know how to make
trivial.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
John Reiher
No 33 Secretary <taustin...@hyperbooks.com> wrote:
> Plus, even slowing down by "bungee cord" would have to take long enough for
> both objects to re-enter the atmosphere at high speed before they're done
> slowing down. Because if they don't, the passengers are going to be tomato
> paste from deceleration.
When they did the tethered satellite experiment on the shuttle, the
tether generated a large voltage. This occurred because the tether was
moving through the earth's magnetic field. Theoretically you can pull
power from a tether and decelerate the attached ship. The more you pull,
the more you decelerate.
This may be a way to slow down a ship without using fuel.
--
The Kedamono Dragon
Pull Pinky's favorite words to email me.
http://www.ahtg.net
Have Mac, will Compute
Check out the PowerPointers Shop at:
http://www.cafeshops.com/PowerPointers
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Erik Max Francis
> When they did the tethered satellite experiment on the shuttle, the
> tether generated a large voltage. This occurred because the tether was
> moving through the earth's magnetic field. Theoretically you can pull
> power from a tether and decelerate the attached ship. The more you pull,
> the more you decelerate.
>
> This may be a way to slow down a ship without using fuel.
It'll certainly slow your ship, since the electrical energy must come
from your orbital kinetic energy. But, as was pointed out earlier, low
Earth orbit is not very far from the atmosphere, so you must shed your
orbital speed very quickly to avoid hitting the atmosphere at high
speed. To shed your orbital speed rapidly through this fast means
you'll be generating tremendous amounts of electrical energy in a very
short period of time. Turned to heat, which it ultimately must be, that
will liberate as much energy as would have been liberated in you hitting
the atmosphere at orbital speed, since energy is conserved. That's
still very, very bad.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
I only regret that I have but one life to lose for my country.
-- Nathan Hale
No 33 Secretary
news:kedamono.Poit-4A4...@text-west.newsfeeds.com:
> In article <Xns96AC76EFAFC63ta...@216.168.3.50>,
> No 33 Secretary <taustin...@hyperbooks.com> wrote:
>
>> Plus, even slowing down by "bungee cord" would have to take long
>> enough for both objects to re-enter the atmosphere at high speed
>> before they're done slowing down. Because if they don't, the
>> passengers are going to be tomato paste from deceleration.
>
> When they did the tethered satellite experiment on the shuttle, the
> tether generated a large voltage. This occurred because the tether was
> moving through the earth's magnetic field. Theoretically you can pull
> power from a tether and decelerate the attached ship. The more you
> pull, the more you decelerate.
>
> This may be a way to slow down a ship without using fuel.
>
You just completely missed my point, didn't you? Yes, you did.
If you slow down _slowly_, you will fall out of orbit before you are done
"slowing down." When you fall out of orbit, you will fall in to the
atmosphere. Not when you want to - when you're done "slowing down," but
much, much quicker, because you are no longer in orbit.
It's physics, and there's no clever way around it.
John Reiher
Erik Max Francis <m...@alcyone.com> wrote:
> John Reiher wrote:
>
> > This may be a way to slow down a ship without using fuel.
>
> It'll certainly slow your ship, since the electrical energy must come
> from your orbital kinetic energy. But, as was pointed out earlier, low
> Earth orbit is not very far from the atmosphere, so you must shed your
> orbital speed very quickly to avoid hitting the atmosphere at high
> speed. To shed your orbital speed rapidly through this fast means
> you'll be generating tremendous amounts of electrical energy in a very
> short period of time. Turned to heat, which it ultimately must be, that
> will liberate as much energy as would have been liberated in you hitting
> the atmosphere at orbital speed, since energy is conserved. That's
> still very, very bad.
I'm not saying it was perfect, but it is an alternate to other methods.
As for the power being generated, you either have some hellacious
capacitors or you use it somehow.
Use the power to run an Ion drive? A mass driver? Running a laser and
vaporizing LEO garbage? Beam the power at another tether ship to boost
it into a higher orbit?
Yeah, it's problem, but, it is a novel way to resolve the problem.
Erik Max Francis
> I'm not saying it was perfect, but it is an alternate to other methods.
>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?
>
> Yeah, it's problem, but, it is a novel way to resolve the problem.
Except it doesn't resolve the problem. Again, the amount of energy you
need to liberate is so large and you need to get rid of it so quickly
(you need to shed almost all your kinetic energy before you start to dip
in the atmosphere, and as soon as you start shedding it you descend into
a lower orbit) that even if you were try to use this method to convert
the kinetic energy into electrical energy and then get rid of it, the
conversion process qualifies as an explosion.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
History is a set of lies agreed upon.
-- Napoleon Bonaparte
No 33 Secretary
> In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier,
>> low Earth orbit is not very far from the atmosphere, so you must shed
>> your orbital speed very quickly to avoid hitting the atmosphere at
>> high speed. To shed your orbital speed rapidly through this fast
>> means you'll be generating tremendous amounts of electrical energy in
>> a very short period of time. Turned to heat, which it ultimately
>> must be, that will liberate as much energy as would have been
>> liberated in you hitting the atmosphere at orbital speed, since
>> energy is conserved. That's still very, very bad.
>
> I'm not saying it was perfect, but it is an alternate to other
> methods.
No. It's not. It presents exactly the same problems with heat on reentry as
the present methods. Only worse. Plus other, even more deadly problems.
>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?
>
> Yeah, it's problem, but, it is a novel way to resolve the problem.
>
No. It's not. It's not even a novel way to kill our astronauts.
John Reiher
Erik Max Francis <m...@alcyone.com> wrote:
> > Yeah, it's problem, but, it is a novel way to resolve the problem.
>
> Except it doesn't resolve the problem. Again, the amount of energy you
> need to liberate is so large and you need to get rid of it so quickly
> (you need to shed almost all your kinetic energy before you start to dip
> in the atmosphere, and as soon as you start shedding it you descend into
> a lower orbit) that even if you were try to use this method to convert
> the kinetic energy into electrical energy and then get rid of it, the
> conversion process qualifies as an explosion.
Point taken. However, the tethered power generation system is a means to
move satellites and even the ISS about in orbit:
http://science.nasa.gov/newhome/headlines/ast08sep97_1.htm
It's even been considered for deorbiting boosters for satellites. It's
technology that will be used as it reduces the need for fuel to maintain
orbit in LEO.
But yeah, for "slow landing", it's not feasible, too much power is
required.
So, what about a big-arsed balloon? You need drag, so how about
inflating a balloon about 1km in diameter around the thing you want to
deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
generate a manure load of drag.
Erik Max Francis
> Point taken. However, the tethered power generation system is a means to
> move satellites and even the ISS about in orbit:
>
> http://science.nasa.gov/newhome/headlines/ast08sep97_1.htm
>
> It's even been considered for deorbiting boosters for satellites. It's
> technology that will be used as it reduces the need for fuel to maintain
> orbit in LEO.
No one disputed that tethered systems, electromagnetic or not, can move
things around into higher and lower orbits. But an electromagnetic
tether system cannot deorbit from low Earth orbit to a soft landing.
> So, what about a big-arsed balloon? You need drag, so how about
> inflating a balloon about 1km in diameter around the thing you want to
> deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
> generate a manure load of drag.
How does that solve the problem? The big balloon either enters too
steep and burns up or enters too shallow and skips off. Reentry
vehicles are the shape they are because that provides sufficient lift to
keep the vehicle at the right entry corridor so that it doesn't burn up
and it manages to shed its speed enough so that it can make a soft landing.
These things aren't accidents, reentry systems work the way they do for
a good reason. If there were an easy, obvious alternate solution, we'd
be using it!
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
All of your moonlight whispers / Counterfeit, counterfeit love
-- Lamya
Arthur Kimes
wrote:
] Orbital speed is 7-8 km/s. You need to shed that much speed in order
to
] avoid burning up in the atmosphere. Furthermore, you need to shed it
] fast, because reducing your speed will make you drop inward due to
] orbital mechanics, which means that you'll touch the atmosphere if you
] don't shed it all quickly.
I've heard entry angle is critical. Too steep, you burn up real
fast. Too shallow, you skip off.
I have a question about that "too shallow" deal. So you skip
off. You've used up some delta-v and are still going to re-enter the
atmosphere real soon (depending on how far you skipped off). Assuming
you can orient the ship - couldn't you do a series of re-entries at a
too-shallow angle so that when you were finally going too slow to skip
off you had a lot less speed to burn off?
Somebody else mentioned ablative shielding. What's the
difference in weight between the current fragile tiles and a old
fashioned mercury-gemini shield big enough for the shuttle? I'm
assuming ablative shielding was so heavy that they resorted to tiles
instead but I'm curious as to what the difference was.
**Hello, My name is Inigo Montoya; You stole my tagline; Prepare to die.**
Erik Max Francis
> I've heard entry angle is critical. Too steep, you burn up real
> fast. Too shallow, you skip off.
> I have a question about that "too shallow" deal. So you skip
> off. You've used up some delta-v and are still going to re-enter the
> atmosphere real soon (depending on how far you skipped off). Assuming
> you can orient the ship - couldn't you do a series of re-entries at a
> too-shallow angle so that when you were finally going too slow to skip
> off you had a lot less speed to burn off?
Keep in mind the entry angle is not the orientation of your ship
(although obviously that's important too), but the angle of your ship's
velocity vector relative to a tangent. If you're in orbit, attempt a
reasonable deorbit and choose too shallow of an angle, you'll skip off,
and yes, you'll reintersect the Earth's atmosphere again, but it's
unlikely that your entry angle on your second attempt will be any
better. If you burn enough fuel you can of course change that, but it's
not just orientation, it's your velocity at interface.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
uray
news:42f80a32...@news.la.sbcglobal.net...
> On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
> wrote:
>
> ] Orbital speed is 7-8 km/s. You need to shed that much speed in order
> to
> ] avoid burning up in the atmosphere. Furthermore, you need to shed it
> ] fast, because reducing your speed will make you drop inward due to
> ] orbital mechanics, which means that you'll touch the atmosphere if you
>
> ] don't shed it all quickly.
>
> I've heard entry angle is critical. Too steep, you burn up real
> fast. Too shallow, you skip off.
> I have a question about that "too shallow" deal. So you skip
> off. You've used up some delta-v and are still going to re-enter the
> atmosphere real soon (depending on how far you skipped off). Assuming
> you can orient the ship - couldn't you do a series of re-entries at a
> too-shallow angle so that when you were finally going too slow to skip
> off you had a lot less speed to burn off?
In the case of returning from Earth orbit, yes. I believe with Apollo it
was a different story, their velocity was so high they really would "skip
off" into Solar orbit.
It's all a matter of balancing economics and technology over estimated
risks. To much redundancy and the vehicle never leaves the pad, not enough
and it blows up. I'm not an expert but my best guess is that a "Skipping
return" would involve a lot more complexities in planning and execution.
Each of those complexities adds an element of risk. Those complexities could
result in the Shuttle trying to land in the middle of the Pacific ocean :(
The question is: Which gives the higher overall chance of successfully
achieving the mission goals while minimizing the risks?
It's not an easy question to answer and hopefully a lot of people brighter
than me are considering it.
uray
news:kedamono.Poit-9E8...@text-west.newsfeeds.com...
> In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier, low
>> Earth orbit is not very far from the atmosphere, so you must shed your
>> orbital speed very quickly to avoid hitting the atmosphere at high
>> speed. To shed your orbital speed rapidly through this fast means
>> you'll be generating tremendous amounts of electrical energy in a very
>> short period of time. Turned to heat, which it ultimately must be, that
>> will liberate as much energy as would have been liberated in you hitting
>> the atmosphere at orbital speed, since energy is conserved. That's
>> still very, very bad.
>
> I'm not saying it was perfect, but it is an alternate to other methods.
>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?
All the fancy ideas require a lot more pieces. It's proving very difficult
to beat the original and tried and true method of re-entry, simple and
effective. A capsule with a heat shield protected from launch damage and
equipped with redundant parachutes for final descent. Works on land as well
as at sea. In fact, it will land just about anywhere, screw the damn ground
controllers.
Jim Burns
Erik Max Francis wrote:
>
> John Reiher wrote:
>
> > So, what about a big-arsed balloon? You need drag, so how about
> > inflating a balloon about 1km in diameter around the thing you
> > want to deorbit slowly? Even in the next to vacuum of LEO, a
> > 1km balloon should generate a manure load of drag.
>
> How does that solve the problem? The big balloon either enters
> too steep and burns up or enters too shallow and skips off.
> Reentry vehicles are the shape they are because that provides
> sufficient lift to keep the vehicle at the right entry corridor
> so that it doesn't burn up and it manages to shed its speed
> enough so that it can make a soft landing.
I seem to remember being told that the shuttle is a lifting body.
Of course, every time I hear a description of piloting the
shuttle, someone uses a phrase close to "glides like a brick."
I'm guessing, though, that the longer time spent in atmosphere
gave us a lower maximum "braking" temperature and that this
was part of a plan to give us a re-usable heat shield.
How far could that be taken? You give two options here:
a steep drop into the atmosphere or a skip out of the atmosphere.
What about hypersonic gliding in the very thin upper atmosphere?
It seems to me that if there is enough force in the atmosphere
to slow a ship down, there could be enough force to provide
lift.
Of course, the kind of wing shaped for hypersonic gliding
in near vacuum would most likely be very different from
pretty much any kind of flight in the lower atmosphere.
But let's just say NASA finally pried that Area 51 technology
loose from the DoD and the new shuttle reconfigures its
wings for the different conditions on the way down:
1) Am I right in thinking that extending the reentry would
lower the maximum skin temperature of the reentry vehicle?
2) /Is/ hypersonic flight in a near vacuum theoretically
possible?
3) Do we (someone) know how to do it?
4) How different would the wings be from something that could
fly lower down and land?
5) Suppose DoD doesn't give up it's Wierd Tech. How crazy would
you have to be to build a ship to try to fly on top the
atmosphere, inside it and land?
> These things aren't accidents, reentry systems work the way they
> do for a good reason. If there were an easy, obvious alternate
> solution, we'd be using it!
Ah, but that was before we had the Area 51 technology!
For me, making suggestions like this isn't a way of
suggesting those engineers were idiots or that I am the
Gigantic Brain (true though that may be). It's fun!
It's educational! And, at my most serious, it's a lot
like panning for gold in a played-out mine. I know ...
I'm not going to find anything worth my time, but
I can dream.
Jim Burns
Hop David
Say you instantly shed 7.7 km/sec and dropped like a stone from 350 km
altitude. It would take you about 4 minutes to reach an altitude of 80
km. The mesosphere starts at that altitude and that is where meteors
start burning up.
Shed velocity gradually and it would take you longer to reach the
mesosphere since you still have angular velocity and are enjoying the
lift of centrifugal force over most the burn. Losing 7.7 km/sec over 5
minutes would subject the occupants to about 2.6 g. Not comfortable but
it certainly wouldn't make passengers "tomato paste".
I believe that presently an 80 meter/sec burn is done from 350 LEO and
that drops the perigee into the mesosphere. It takes about 45 minutes to
reach the perigee.
>
> It's physics, and there's no clever way around it.
>
--
Hop David
http://clowder.net/hop/index.html
Hop David
uray wrote:
> "Arthur Kimes" <ar...@yahoo.com> wrote in message
> news:42f80a32...@news.la.sbcglobal.net...
>
>>On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
>>wrote:
>>
>>] Orbital speed is 7-8 km/s. You need to shed that much speed in order
>>to
>>] avoid burning up in the atmosphere. Furthermore, you need to shed it
>>] fast, because reducing your speed will make you drop inward due to
>>] orbital mechanics, which means that you'll touch the atmosphere if you
>>
>>] don't shed it all quickly.
>>
>>I've heard entry angle is critical. Too steep, you burn up real
>>fast. Too shallow, you skip off.
>>I have a question about that "too shallow" deal. So you skip
>>off. You've used up some delta-v and are still going to re-enter the
>>atmosphere real soon (depending on how far you skipped off). Assuming
>>you can orient the ship - couldn't you do a series of re-entries at a
>>too-shallow angle so that when you were finally going too slow to skip
>>off you had a lot less speed to burn off?
>
>
> In the case of returning from Earth orbit, yes. I believe with Apollo it
> was a different story, their velocity was so high they really would "skip
> off" into Solar orbit.
A skip would shed some velocity. Apollo would have to be going faster
than escape velocity. Seems to me unlikely.
Do you have a cite?
Michael Ash
>>
>> In the case of returning from Earth orbit, yes. I believe with Apollo it
>> was a different story, their velocity was so high they really would "skip
>> off" into Solar orbit.
>
> A skip would shed some velocity. Apollo would have to be going faster
> than escape velocity. Seems to me unlikely.
Even going slower than escape velocity, a skip would leave Apollo on a
trajectory that would take a significant amount of time to return to the
Earth, probably hours or days. The command module simply wouldn't have had
enough supplies for the occupants to have survived that long, even if the
next reentry would have been at a suitable angle.
That said, this kind of reentry is apparently practical and has been used.
According to the Wikipedia entry
(http://en.wikipedia.org/wiki/Skip_reentry), it was used on the Zond lunar
explorers.
Bryan Derksen
<madbad...@yahoo.com> wrote:
>"arne97" <gahad...@yahoo.com> wrote:
>
>> What with broken tiles and what-not, isn't there a better way to
>> get a ship down those last 200 miles than turning it into a meteorite ?
>
>Yes, a space-elevator ; but we need several thousand kilometers
>of superstrong cable that we're not able to manufacture just yet.
Actually, I don't think a space elevator would be too useful to
something that's in a 200 mile orbit. The elevator's not moving at
orbital velocity, so to dock with it at the 200 mile mark you'd need
to kill your velocity with respect to the ground. That's the problem
that we're trying to deal with anyway.
For something in geosynchronous orbit or close to it, yes, a space
elevator is ideal. For lower orbits a rotating tether might work okay.
Bryan Derksen
wrote:
>Of course, the kind of wing shaped for hypersonic gliding
>in near vacuum would most likely be very different from
>pretty much any kind of flight in the lower atmosphere.
>But let's just say NASA finally pried that Area 51 technology
>loose from the DoD and the new shuttle reconfigures its
>wings for the different conditions on the way down:
I recall once long ago reading an article about "hypersonic
waveriders", hypothetical aircraft designed for ultra-high-speed
flight in the upper atmosphere. Perhaps they could be inverted to be
negative lifting bodies generating a high pressure zone _above_
themselves, pushing themselves downward so that they wouldn't go
hurtling off into space. They would essentially be in a low-altitude
powered orbit. A spacecraft reentering on a shallow "skip-off"
trajectory could perhaps use this effect to hold itself down in the
upper atmosphere instead.
http://www.aerospaceweb.org/design/waverider/main.shtml has some
information about waveriders in general, but doesn't discuss this
aspect of their use so I have only my fallable memory to rely on now.
Sorry.
Steve Charlton
>stan...@delete-this-crap-xprt.net (Stan) wrote in
>news:stanleyh-080...@pdx-ppp131.pop1.net:
>
>> Steve Charlton <st...@nospam.freeserve.co.uk> wrote:
>>
>> }In article <1123426483....@g44g2000cwa.googlegroups.com>,
>> }arne97 <gahad...@yahoo.com> writes
>> }> The shuttle, as well as most other space vehicles, enter the
>> }>atmosphere in a blaze of heat.
>> }> I assume that this is a method of shedding speed.
>> (snip)
>> }Two space craft A and B, orbiting in opposite directions. They snag
>> each }other as they pass with a very very strong and very very
>> stretchy bungie }cord. Ssstttrrreeetttccchhh. They both stop relative
>> to each other, they }both release the cord (at the same time) ...
>>
>> "Two space craft A and B, orbiting in opposite directions..."
>>
>> So, to descend from the orbit of the space station, the shuttle would
>> have to "bungie-snag" something the same size orbiting in the exact
>> opposite direction. Hmmm...with the craft traveling a bit more than
>> 5 KM/sec (someone check my orbital mechanics; I was never really good
>> at it) this means they would be passing each othe at more than 10
>> KM/sec.
>>
>> More importantly, it would be that the space station would have a
>> "visitor" going by at a speed (& how many times a day?) that would
>> surely make the inhabitants a bit nervous.
Nobody said do it just outside the space station (see below) and anyway,
computers are already good at orbital mechanics, plotting such an
intercept should be child's play for them by the time we can make such
extraordinary materials.
>Plus, even slowing down by "bungee cord" would have to take long enough for
>both objects to re-enter the atmosphere at high speed before they're done
>slowing down. Because if they don't, the passengers are going to be tomato
>paste from deceleration.
TAustin,
There are 300 miles to fall from the space station to the top of the
atmosphere and only 100 miles of atmosphere. I believe it's only the
last 50 miles or so that really slows a spacecraft down. What makes you
think that the bungie can't slow them down without squashing the crew
with g-forces while they fall 300 miles, when atmospheric drag can do it
in 50 miles or so?
Back of an envelope calculations follow: I know, I know, I missed a lot
out; rotation of the Earth, fall off in g with height, variable
elasticity of the bungie as it stretches, etc. but I think its close
enough. I also took easy approximations and dropped fractions. Its late
and I haven't checked them, its also been a long time since college.
Feel free to check me if you want.
Deceleration from initial velocity of 10,000 m/s
v = at. 10,000 = at. (1)
We need to know how long we've got (t). Lets get that.
Distance to fall = 300 miles = 480km = 480,000m
Time to fall 480,000m under gravity
D = 0.5at^2. (2)
D = 480000m, a = g = 10m/s^2,
Rearranging gives:-
t = (2D/a)^0.5 = (960000/10)^0.5 = 96000^0.5 = 310s
Now we know how long we have for the ACME bungie to do its stuff - 310s.
Substitute t into (1).
10000 = a*310,
rearranging gives
a = v/t = 10000/310 = 32m/s = just over 3g - so no tomato paste
passengers then.
Actually, you'd want to start from a lower orbit, otherwise you'll hit
atmosphere too fast (approx. 3000m/s). You'd get too much heating. If we
raise the g-limit we can fall for less time. Six g would probably be the
limit. Using that we can fall for 160 seconds, which means a fall of
128,000m = 128km = 80 miles and we hit atmosphere at 1600m/s, so we
could get quite close to the top of the atmosphere and still only need
to pull 6g for 160s. That would bring the 2 space craft into the
atmosphere at only Mach 4. I guess we'd want pick somewhere between 3g
and 6g.
I'm pleased to see my idea would work after all. I'd been worried.
That's what you get for writing to usenet while both tired and under the
influence. Must try Irish Coffee next time. B-)
--
Steve Charlton | You may have trouble getting
st...@gnirekoms.freeserve.co.uk | permission to aerobrake or
hint: ^^^^^^^^^ | lithobrake asteroids on Earth!
reverse this | - James D Nicoll
Erik Max Francis
> Even going slower than escape velocity, a skip would leave Apollo on a
> trajectory that would take a significant amount of time to return to the
> Earth, probably hours or days. The command module simply wouldn't have had
> enough supplies for the occupants to have survived that long, even if the
> next reentry would have been at a suitable angle.
That's right. According to the NASA mission reports for Apollo XI,
entry interface was at 36 194 ft/s at an altitude of about 400 000 ft;
that's 11.034 km/s at an altitude of about 120 km, or just a shade under
escape speed from Earth. That's an extremely elliptical orbit from the
Earth, and even if the results of other bodies' gravity (like the Moons)
wouldn't perturb it -- it would be highly unwise.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
There is another world, which is not of men.
-- Li Bai
Michael Ash
> On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
> <madbad...@yahoo.com> wrote:
>
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>> What with broken tiles and what-not, isn't there a better way to
>>> get a ship down those last 200 miles than turning it into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>
> Actually, I don't think a space elevator would be too useful to
> something that's in a 200 mile orbit. The elevator's not moving at
> orbital velocity, so to dock with it at the 200 mile mark you'd need
> to kill your velocity with respect to the ground. That's the problem
> that we're trying to deal with anyway.
Consider that something in low orbit doesn't need to boost to geosync, it
just needs to boost into an elliptical orbit where the high end of the
orbit is at the same speed as the space elevator at that altitude. I don't
know what kind of savings that gets you, but I expect it would be
significant. It's still more fuel than dropping altitude enough to hit the
atmosphere, but it's better than coming to a complete stop.
Also consider that there's almost no reason to be in a 200-mile orbit in
the first place if a space elevator is available. With the possible
exception of some military systems, almost everything you can do using
equipment put up in a really expensive launcher at 200 miles can be done
better using equipment put up in a cheap launcher a high altitude.
Gene P.
On Mon, 8 Aug 2005, Erik Max Francis wrote:
[snip]
>How does that solve the problem? The big balloon either enters too
>steep and burns up or enters too shallow and skips off. [...]
"Skips off"... You've been watching too many movies.
Once you are in a closed orbit that intersects the atmosphere, you *will*
deorbit entirely. You might re-emerge once or twice, but eventually the
energy lost on each pass will lower the overall height of the orbit until
you *don't* re-emerge.
This myth is the result of the Apollo program moon returns. The moon
return orbit is so large (I.e. It's high enough to reach the moon!) that
if the capsule were to re-emerge, it's next pass could be days or weeks...
in which case the astronauts would surly have expired from exhaustion of
air and power supplies...
If I'm not mistaken, the lunar return orbit for Apollo 13 was actually an
escape trajectory... i.e. If they'd missed and not re-entered they had
enough speed to leave the Earth/Moon entirely. This was done so that they
would get back faster... before they ran out of air.
So, "skips off" is a myth. Once in an atmosphere intersecting orbit,
falling completely out of the sky is inevitable.
There is a problem with "skimming" the top of the atmosphere though.
Instead of a quick wash of the Dragon's Breath of re-entry, the process
becomes a slow roast... Each pass will generate some heat. And
unfortunately, once the ship has risen high enough to quit generating that
heat, it still has no easy way to shed it. It gradually soaks through the
insulation and bakes the ship.
If you do re-entry quickly, the outside skin gets so hot, that it
transfers a lot of the heat back to the atmosphere once the fast
heat-creating part of re-entry is done. This works because the air soaks
up and carries away the heat much better than the insulation underneath
the heatshield. There is no air to do this in space... so the insulation
heats up slowly until it's in equilibrium with the heat shield.
Ash Wyllie
>On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
><madbad...@yahoo.com> wrote:
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>> What with broken tiles and what-not, isn't there a better way to
>>> get a ship down those last 200 miles than turning it into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>Actually, I don't think a space elevator would be too useful to
>something that's in a 200 mile orbit. The elevator's not moving at
>orbital velocity, so to dock with it at the 200 mile mark you'd need
>to kill your velocity with respect to the ground. That's the problem
>that we're trying to deal with anyway.
Beanstalks have, and cause, real problems for all objects not in
geosynchronous orbit.
>For something in geosynchronous orbit or close to it, yes, a space
>elevator is ideal. For lower orbits a rotating tether might work okay.
-ash
Cthulhu in 2005!
Why wait for nature?
No 33 Secretary
news:42F82A5B...@tabletoptelephone.com:
>
>
> No 33 Secretary wrote:
>> John Reiher <kedamo...@Narf.mac.com> wrote in
>> news:kedamono.Poit-4A4...@text-west.newsfeeds.com:
>>
>>
>>>In article <Xns96AC76EFAFC63ta...@216.168.3.50>,
>>> No 33 Secretary <taustin...@hyperbooks.com> wrote:
>>>
>>>
>>>>Plus, even slowing down by "bungee cord" would have to take long
>>>>enough for both objects to re-enter the atmosphere at high speed
>>>>before they're done slowing down. Because if they don't, the
>>>>passengers are going to be tomato paste from deceleration.
>>>
>>>When they did the tethered satellite experiment on the shuttle, the
>>>tether generated a large voltage. This occurred because the tether
>>>was moving through the earth's magnetic field. Theoretically you can
>>>pull power from a tether and decelerate the attached ship. The more
>>>you pull, the more you decelerate.
>>>
>>>This may be a way to slow down a ship without using fuel.
>>>
>>
>> You just completely missed my point, didn't you? Yes, you did.
>>
>> If you slow down _slowly_, you will fall out of orbit before you are
>> done "slowing down." When you fall out of orbit, you will fall in to
>> the atmosphere. Not when you want to - when you're done "slowing
>> down," but much, much quicker, because you are no longer in orbit.
>
> Say you instantly shed 7.7 km/sec and dropped like a stone from 350 km
> altitude.
If you _instantly_ shed, well, pretty much any amount of velocity, you have
experienced infinite deceleration, and are not a fine red paste on the
front of the cabin.
Try again.
<stuff based on impossible, and deadly, mistake snipped as irrelevant>
No 33 Secretary
John Reiher
No 33 Secretary <taustin...@hyperbooks.com> wrote:
> You have no idea what you're talking about.
I agree... I'm not sure to what or about who, even if its me Austin's
talking about. :-)
I mean that's one reason for this group, to ask those "stupid questions"
and be "educated" in what may happen. (+/- 25%)
That brings up the other question: One man recovery vehicles.
http://www.astronautix.com/craftfam/rescue.htm
MOOSE is the most unique of the recovery systems postulated. I'm not
even sure it would work.
John Schilling
Reiher says...
>So, what about a big-arsed balloon? You need drag, so how about
>inflating a balloon about 1km in diameter around the thing you want to
>deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
>generate a manure load of drag.
Which will cause it to slow down, which will cause it to fall out of
orbit, and so in a matter of minutes your big-arsed balloon will not
be in the near-vacuum of LEO, but in the upper atmosphere.
At that point, it will be generating much much more than a shitload of
drag, and a corresponding ammount of heat, and the only question is
whether it will be torn apart before it vaporizes or vice versa.
Either way, leaving the payload in the upper atmosphere at near-orbital
velocity, reducing the problem to one previously found to be Difficult.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
John Schilling
Reiher says...
>
>In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier, low
>> Earth orbit is not very far from the atmosphere, so you must shed your
>> orbital speed very quickly to avoid hitting the atmosphere at high
>> speed. To shed your orbital speed rapidly through this fast means
>> you'll be generating tremendous amounts of electrical energy in a very
>> short period of time. Turned to heat, which it ultimately must be, that
>> will liberate as much energy as would have been liberated in you hitting
>> the atmosphere at orbital speed, since energy is conserved. That's
>> still very, very bad.
>I'm not saying it was perfect, but it is an alternate to other methods.
>As for the power being generated, you either have some hellacious
>capacitors or you use it somehow.
>Use the power to run an Ion drive? A mass driver? Running a laser and
>vaporizing LEO garbage? Beam the power at another tether ship to boost
>it into a higher orbit?
>Yeah, it's problem, but, it is a novel way to resolve the problem.
The problem is, a Space Shuttle using this technique to decelerate from
orbital velocity before falling into the atmosphere, will be generating
several *billion* watts of electric power.
The system that can effectively use several billion watts of electric
power, will not fit inside a space shuttle. The system that can simply
store power being pumped in at several billion watts, will not fit inside
a space shuttle. The system that can even just harmlessly dissipate
several billion watts of electric power, will not fit inside a space
shuttle. Just the wiring harness to deliver several billion watts of
electric power to the load, will not fit inside a space shuttle.
The best you can hope for, is to melt the tether the moment you turn it on.
Billions of watts of power in one place calls for brute-force thermodynamics,
not playing around with electricity.
George W Harris
wrote:
:In article <kedamono.Poit-DB7...@text-west.newsfeeds.com>, John
:Reiher says...
:
:>So, what about a big-arsed balloon? You need drag, so how about
:>inflating a balloon about 1km in diameter around the thing you want to
:>deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
:>generate a manure load of drag.
:
:Which will cause it to slow down, which will cause it to fall out of
:orbit, and so in a matter of minutes your big-arsed balloon will not
:be in the near-vacuum of LEO, but in the upper atmosphere.
:
:At that point, it will be generating much much more than a shitload of
:drag, and a corresponding ammount of heat, and the only question is
:whether it will be torn apart before it vaporizes or vice versa.
:Either way, leaving the payload in the upper atmosphere at near-orbital
:velocity, reducing the problem to one previously found to be Difficult.
Clearly the answer isn't just one balloon, but
many concentric balloons. Say, ninety-nine lift balloons.
--
e^(i*pi)+1=0
George W. Harris For actual email address, replace each 'u' with an 'i'.
Hop David
Michael Ash wrote:
> Hop David <hopspageHA...@tabletoptelephone.com> wrote:
>
>>>In the case of returning from Earth orbit, yes. I believe with Apollo it
>>>was a different story, their velocity was so high they really would "skip
>>>off" into Solar orbit.
>>
>>A skip would shed some velocity. Apollo would have to be going faster
>>than escape velocity. Seems to me unlikely.
>
>
> Even going slower than escape velocity, a skip would leave Apollo on a
> trajectory that would take a significant amount of time to return to the
> Earth, probably hours or days. The command module simply wouldn't have had
> enough supplies for the occupants to have survived that long, even if the
> next reentry would have been at a suitable angle.
And that would be an earth orbit even if it does take awhile to return
to perigee. Uray was saying it would skip off into Solar orbit.
>
> That said, this kind of reentry is apparently practical and has been used.
> According to the Wikipedia entry
> (http://en.wikipedia.org/wiki/Skip_reentry), it was used on the Zond lunar
> explorers.
Hop David
No 33 Secretary wrote:
> <stuff based on impossible, and deadly, mistake snipped as irrelevant>
>
You just completely missed my point, didn't you? Yes, you did.
It would take 4 minutes to reach the mesosphere in a worst case
scenario. 5 minutes if deceleration is more gradual.
5 minutes is plenty of time to shed 7.7 km/sec without being squished to
tomatoe paste.
Hop David
No 33 Secretary wrote:
> You have no idea what you're talking about.
>
No. It is you who don't know what you're talking about.
There is plenty of time to lose your orbital velocity before you drop
into the mesosphere.
You can salvage your credibility one of two ways:
You can admit you're wrong.
You can support your argument with physics, math and numbers.
I'm predicting you'll respond with ad hominem.
If you fulfill my prediction it will be time to plonk your pathetic
troll ass.
No 33 Secretary
>
>
> No 33 Secretary wrote:
>
>> <stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>
>
> You just completely missed my point, didn't you?
You are an idiot.
> Yes, you did.
>
> It would take 4 minutes to reach the mesosphere in a worst case
> scenario. 5 minutes if deceleration is more gradual.
>
> 5 minutes is plenty of time to shed 7.7 km/sec without being squished to
> tomatoe paste.
>
Now address the discussion of how much energy needs to be shed, and how,
and how you fit the equipment to do so in to a vehicle smaller than the
equipment.
You are an idiot. Your idea is stupid.
No 33 Secretary
>
>
> No 33 Secretary wrote:
>> You have no idea what you're talking about.
>>
>
> No. It is you who don't know what you're talking about.
I know you are, but what am I?
>
> There is plenty of time to lose your orbital velocity before you drop
> into the mesosphere.
>
> You can salvage your credibility one of two ways:
>
> You can admit you're wrong.
>
> You can support your argument with physics, math and numbers.
>
>
> I'm predicting you'll respond with ad hominem.
>
> If you fulfill my prediction it will be time to plonk your pathetic
> troll ass.
>
That is correct. You _will_ killfile me, because I do not allow retards to
read my posts.
Hop David
No 33 Secretary wrote:
> Hop David <hopspageHA...@tabletoptelephone.com> wrote in
> news:42F916D1...@tabletoptelephone.com:
>
>
>>
>>No 33 Secretary wrote:
>>
>>
>>><stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>>
>>You just completely missed my point, didn't you?
>
>
> You are an idiot.
>
>
>>Yes, you did.
>>
>>It would take 4 minutes to reach the mesosphere in a worst case
>>scenario. 5 minutes if deceleration is more gradual.
>>
>>5 minutes is plenty of time to shed 7.7 km/sec without being squished to
>>tomatoe paste.
>>
>
> Now address the discussion of how much energy needs to be shed, and how,
> and how you fit the equipment to do so in to a vehicle smaller than the
> equipment.
Completely irrelevant to your contention that there is no time to
decelerate before hitting the mesosphere.
>
> You are an idiot. Your idea is stupid.
>
*plonk*
Erik Max Francis
> "Skips off"... You've been watching too many movies.
>
> Once you are in a closed orbit that intersects the atmosphere, you *will*
> deorbit entirely. You might re-emerge once or twice, but eventually the
> energy lost on each pass will lower the overall height of the orbit until
> you *don't* re-emerge.
No one said anything about a deorbiting object skipping off into solar
orbit; in fact, we've talked at great length about how that _doesn't_
happen in a too-shallow deorbit burn. You could stand to read a bit
more of the thread before jumping in.
"Skips off" just means that it rises back up, before rising back down
again. When people talk about skipping rocks off lake, do you think
they mean that the rock rises up into the stratosphere? No.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Life is a predicament which precedes death.
-- Henry James
Erik Max Francis
> I seem to remember being told that the shuttle is a lifting body.
> Of course, every time I hear a description of piloting the
> shuttle, someone uses a phrase close to "glides like a brick."
Well, it _is_ a lifting body. It's just not a great one compared to a
plane. If it weren't a lifting body, it wouldn't glide at all; it would
fall like a rock.
Erik Max Francis
> MOOSE is the most unique of the recovery systems postulated. I'm not
> even sure it would work.
It would sure be a hell of a ride.
Erik Max Francis
> Clearly the answer isn't just one balloon, but
> many concentric balloons. Say, ninety-nine lift balloons.
Guards!
Dr John Stockton
2005 08:15:44, seen in news:rec.arts.sf.science, Michael Ash
<mi...@mikeash.com> posted :
>Bryan Derksen <bryan....@shaw-spamguard.ca> wrote:
>> Actually, I don't think a space elevator would be too useful to
>> something that's in a 200 mile orbit. The elevator's not moving at
>> orbital velocity, so to dock with it at the 200 mile mark you'd need
>> to kill your velocity with respect to the ground. That's the problem
>> that we're trying to deal with anyway.
>
>Consider that something in low orbit doesn't need to boost to geosync, it
>just needs to boost into an elliptical orbit where the high end of the
>orbit is at the same speed as the space elevator at that altitude. I don't
>know what kind of savings that gets you, but I expect it would be
>significant. It's still more fuel than dropping altitude enough to hit the
>atmosphere, but it's better than coming to a complete stop.
The altitude required is about 18700 miles from the centre of the Earth
- <URL:http://www.merlyn.demon.co.uk/gravity3.htm#FaB>.
From a circular orbit, Delta-V to escape is Root(0.5) of that needed to
stop; and significantly less is needed just to get onto the stalk at the
stated height. A beanstalk provides an economical, but not cheap, route
to LEO; but for earth return aerobraking is cheaper. To get to LEO from
the stalk, jump off a little lower, aerobrake to the right apogee, and
do a circularisation burn.
I could modify the page to show the speeds involved.
--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
John Schilling
Yes, but as such an assembly came over the horizon, wouldn't it likely
be mistaken for some sort of UFO? That's the sort of solution only a
Captain Kirk wannabe would come up with; in the same league as playing
with matches amidst cans of gasoline...
Edward Cherlin
> On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
> wrote:
>> I've heard entry angle is critical. Too steep, you burn up real
>> fast. Too shallow, you skip off.
> I have a question about that "too shallow" deal. So you skip
> off. You've used up some delta-v and are still going to re-enter the
> atmosphere real soon (depending on how far you skipped off). Assuming
> you can orient the ship - couldn't you do a series of re-entries at a
> too-shallow angle so that when you were finally going too slow to skip
> off you had a lot less speed to burn off?
First, it is the angle of the ship's course that is critical to the
temperature. The attitude of the ship relative to that course is also
important, but is a much smaller factor. After you do the first skip, you
end up entering the air again at a steeper angle, which you may not be able
to survive at any attitude.
Atmospheric skipping works for planetary probes shedding excess velocity in
order to enter orbit (with a modest burn at the opposite, higher end of the
ellipse to move the lower end high enough above the atmosphere). It doesn't
work for landing from orbit.
The fundamental problem is that we have no way to launch ships that can
carry fuel for a powered descent. Powered descent requires exactly the same
ratio of fuel to payload as powered ascent in the same gravity well. So the
Shuttle would have to have the same giant liquid-fuel tank and two solid
boosters coming down as going up. Where do they come from? What lifts them
to orbit?
Any ballistic descent has to shed several km/sec of velocity in the upper
atmosphere, by conversion to heat. The shielding has to be extremely light,
extremely strong, a very poor conductor that therefore concentrates heat on
its surface, but will not melt at the temperatures involved. The engineers
have been over this ground. Without radical redesign, the Shuttle cannot be
shielded cheaply. The redesign would mean that the result would not be a
Shuttle.
We should have been using unmanned Big Dumb Boosters all along, saving half
to two-thirds of the cost of every launch. You just let some parts burn up
in the atmosphere. Much cheaper than all this gold-plated reusable stuff.
If the space business had been left to the private sector, we would still
have all of the useful satellites (comm, imaging, science) and possibly the
Superconducting Supercollider on the ground, instead of the idiot space
station up there. We could have paid for the Hubble mirror to be tested on
the ground and fixed for a few million dollars, instead of losing one of
the instruments and wasting a Shuttle launch on a repair mission at a cost
of hundreds of millions. We could have put some of the money into research
on semi-autonomous repair robots that could be launched on the relatively
cheap boosters and then left in orbit with a few sets of spare parts.
Now a space elevator gives you slow re-entry. If the necessary materials can
be made, it might even be cheaper than rockets. But we won't know for a
while.
Edward Cherlin
> On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
> <madbad...@yahoo.com> wrote:
>
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>> What with broken tiles and what-not, isn't there a better way to
>>> get a ship down those last 200 miles than turning it into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>
> Actually, I don't think a space elevator would be too useful to
> something that's in a 200 mile orbit. The elevator's not moving at
> orbital velocity, so to dock with it at the 200 mile mark you'd need
> to kill your velocity with respect to the ground. That's the problem
> that we're trying to deal with anyway.
The point is that we don't need to be in orbit at 200 miles. You go up the
elevator, do the job, and head back down. Forget the ship.
> For something in geosynchronous orbit or close to it, yes, a space
> elevator is ideal.
Since it's easier on the elevator to get to geosynchronous orbit than to
LEO, that's what we do. We can discuss matching velocities at
geosynchronous orbit and higher for interplanetary craft or Earth-Moon
craft, whenever we get engines capable of several km/sec delta-V using less
than their own mass of fuel and reaction mass.
> For lower orbits a rotating tether might work okay.
Crawling out to the end of a tether and letting go at the right moment to go
into orbit sounds feasible to me. Catching a tether from orbit sounds like
a nightmare.
Erik Max Francis
> The point is that we don't need to be in orbit at 200 miles. You go up the
> elevator, do the job, and head back down. Forget the ship.
At 200 mi, you're going to be moving way too fast relative to everything
in a 200 mi orbit to be useful. You can't forget the ship, you'll need
a deltavee application to get from the beanstalk at 200 mi to the target
in orbit at the same 200 mi. And a quite significant one.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
It's hard to say what I want my legacy to be when I'm long gone.
-- Aaliyah
Edward Cherlin
>
> On Mon, 8 Aug 2005, Edward Cherlin wrote:
>
>>What I want to know is how you get the shield *up* each time. You can't
>>fold it up and put it in the glove compartment. Besides, every kg of mass
>>of the thing comes out of payload.
>
> Attached to the ship, just like we do now, of course.
>
>>> [snip]
>>>
>>> My thought on the subject was the concept of a re-entry "sled"...
>>>
>>> Essentially, construct the entire high-heat re-entry portion of the
>>> vehilcle as a one-piece shell that is "snap on" replaceable.
>>>
>>> I like the notion of an ablative ceramic or metallic
>>
>>Metals conduct heat well, so they don't work as heat shields. Most of them
>>melt or oxidize at high temperatures, or both.
>>
>>> "belly shield" that
>>> can be swapped out by 3 guys with screw-guns
>>
>>Not metal screws, obviously, so what were you thinking?
>
> Okey dokey... How about carbon fiber retaining pins then? You know,
> something strong, reasonably heat resistant (they will be on the *inside*
> of the shield, after all), and lightweight...
No, they will go *through* the shield. Every one will have to seal
perfectly, even while the shield is ablating out from under them.
>>> and a lifting rig for the
>>> ship in about 20 minutes.
>>
>>I get it. Instead of the fiddly little tiles that have to be glued on one
>>at a time (and a large fraction of them break in the process because they
>>have to be so thin and light), we go for one humongous but equally thin
>>full-belly shield that breaks before you can get it into its shipping
>>crate, or even out of the mold where it's made. And then we only screw it
>>on in as many other places as we can do in what's left of our 20 minutes,
>>so that it will flap against the ship and break into little bitty pieces
>>on lift-off, and we won't have to worry about the weight on reentry.
>>
>>Oh, wait, that means that it won't be there to shield the ship. Rats. It
>>was such a great idea. And we could have used the shipping crates for
>>low-income housing.
>
> I'm thinking somebody needs some decaf.
>
> Who said *anything* about using the same ceramic material as the existing
> shuttle tiles?
Not I. I don't care what you make your shield out of, because your design
goals are mutually contradictory. You can't secure an object that size to
anything in 20 minutes. You can't make something that large and that thin
that can hold itself together under gravity.
> That stuff is designed to survive re-entry intact... not
> ablate. It has *serious* structural and material properties deficiencies
> for use outside of it's design envelope.
>
> So let me try again... It's a *disposable* *easy-to-replace* heat shield.
And if it ablates, it starts off much thicker and heavier than the tiles. No
matter what you make it out of, it doesn't snap on and get screwed tight in
20 minutes.
> Choose *new* materials that meet those guidelines.
Well, if you have handwavium, no problem. No, there is no material that is
as light as the tiles even at greater thickness, ablates, and can be
manufactured in form-fitting shuttle size and shape, that won't break
unless fully supported at all times. You can't make a single-piece titanium
overcoat that size, much less any ceramic, and we haven't even started on
thermal expansion.
> (I have real trouble believing that, given the materials science
> improvements since the Shuttle system selected its heat shield material in
> the 70's, we aren't capable of some more advanced engineering today.)
More advanced, yes. Indistinguishable from magic, no. Actually, the tiles
have been improved greatly since the 70's, as have most Shuttle components
and subsystems.
> Gene P.
> Slidell LA
Edward Cherlin
> Two space craft A and B, orbiting in opposite directions.
Problem #1. No spacecraft are ever launched in the direction opposite the
Earth's rotation.
> They snag each
> other as they pass with a very very strong and very very stretchy bungie
> cord.
Problem #2. It's made of handwavium.
> Ssstttrrreeetttccchhh.
We start with two craft going at orbital speed, about 5 mi/sec, or 8 km/sec.
When they snag each other, the stretchy-stretchy bungy cord starts to
decelerate them at, oh, 5 g's (problem #3), or 50 m/sec/sec each.
> They both stop relative to each other, they
> both release the cord (at the same time)
So it takes something like 160 sec for them to come to rest, and during that
time they have moved more than 600 km apart (Problem #4). At this point
they trash the cord, which snaps back to its original length, and then
burns up on re-entry. No problem there. However, at a lower rate of
deceleration, say 3 Gs (which is tolerable for humans), the cord has to
stretch so far that it dips into the atmosphere and breaks before the craft
come to a stop.
> and drop vertically into the
> atmosphere (as does the cord). Much less energy to shed. Much less heat
> build up (the cord might get a tad warm).
Falling from 300 km altitude to 60 km altitude with negligible drag
accelerates the ships and cord to several km/sec again. But yes,
significantly less than orbital velocity.
Problem #5. The craft is descending vertically into atmosphere, maximizing
the rate at which it encounters thicker air, and thus the rate of heating.
Problem #6. The craft has a minute or two in vertical fall to drop its
velocity to substantially less than Mach 1 in preparation for the landing
process (powered, glider, or parachute). It must accordingly decelerate at
some 10s of Gs. In the normal return from orbit, a craft in the upper
atmosphere can move thousands of kilometers horizontally through the air
and just a few kilometers vertically while shedding velocity over a much
longer period of time at much lower deceleration.
Edward Cherlin
> I seem to remember being told that the shuttle is a lifting body.
> Of course, every time I hear a description of piloting the
> shuttle, someone uses a phrase close to "glides like a brick."
No, it glides OK. It just steers like a brick. You don't get a chance to
pull up from a landing and go look for thermals to get some altitude before
you try again. You land right the first time or not at all.
Edward Cherlin
>
>
> No 33 Secretary wrote:
>
>> <stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>
>
> You just completely missed my point, didn't you? Yes, you did.
>
> It would take 4 minutes to reach the mesosphere in a worst case
> scenario. 5 minutes if deceleration is more gradual.
Umm, weren't we talking about free fall from LEO altitude to the mesosphere?
Where did this deceleration come from?
> 5 minutes is plenty of time to shed 7.7 km/sec without being squished to
> tomatoe paste.
True. But not helpful.
Edward Cherlin
> Edward Cherlin wrote:
>
>> The point is that we don't need to be in orbit at 200 miles. You go up
>> the elevator, do the job, and head back down. Forget the ship.
>
> At 200 mi, you're going to be moving way too fast relative to everything
> in a 200 mi orbit to be useful. You can't forget the ship, you'll need
> a deltavee application to get from the beanstalk at 200 mi to the target
> in orbit at the same 200 mi. And a quite significant one.
That assumes that you only want to deal with orbiters. I'm talking about a
job that you want to be 200 mi up for, but that doesn't depend on anything
in orbit.
Anyway, if you want to get to something in orbit, climb the elevator until
you get to a point where your velocity corresponds with an orbit that takes
you down to the altitude you want to get to. Then you need to match
velocities when you arrive, which is much easier than going from rest on
the elevator to an orbit at the same altitude.
Mad Bad Rabbit
news:H6OdnRYcQtC...@speakeasy.net:
> Edward Cherlin wrote:
>
>> The point is that we don't need to be in orbit at 200 miles. You go
>> up the elevator, do the job, and head back down. Forget the ship.
>
> At 200 mi, you're going to be moving way too fast relative to
> everything in a 200 mi orbit to be useful. You can't forget the ship,
> you'll need a deltavee application to get from the beanstalk at 200 mi
> to the target
> in orbit at the same 200 mi. And a quite significant one.
If we spend $$ trillions to put up a space elevator, I expect ships
generally won't be /allowed/ in a 200 mile orbit, and would quickly
be intercepted and forced to de-orbit.
Related issue:
How would one clean all the minor space junk out of those orbits?
Maybe hit them with targetted chunks of dry ice, to knock the junk
into atmosphere-crossing orbits (and then the dry ice sublimates)?
--
>;k
Marten Kemp
You're gonna land when you run out of altitude.
The trick is running out in the right place.
--
-- Marten Kemp
(Fix name and ISP to reply)
Simon Morden
> In article <icthf1tahecphjela...@4ax.com>, George W Harris says...
>
>
>>On 9 Aug 2005 10:45:16 -0700, John Schilling <schi...@spock.usc.edu>
>>wrote:
>
>
>>:In article <kedamono.Poit-DB7...@text-west.newsfeeds.com>, John
>>:Reiher says...
>
>>:drag, and a corresponding ammount of heat, and the only question is
>>:whether it will be torn apart before it vaporizes or vice versa.
>>:Either way, leaving the payload in the upper atmosphere at near-orbital
>>:velocity, reducing the problem to one previously found to be Difficult.
>
>
>> Clearly the answer isn't just one balloon, but
>>many concentric balloons. Say, ninety-nine lift balloons.
>
>
> Yes, but as such an assembly came over the horizon, wouldn't it likely
> be mistaken for some sort of UFO? That's the sort of solution only a
> Captain Kirk wannabe would come up with; in the same league as playing
> with matches amidst cans of gasoline...
>
>
Damn you all to hell! My city's just turned to dust!
No 33 Secretary
news:%SiKe.1253$dk5....@newssvr21.news.prodigy.com:
> Hop David wrote:
>
>>
>>
>> No 33 Secretary wrote:
>>
>>> <stuff based on impossible, and deadly, mistake snipped as
>>> irrelevant>
>>>
>>
>> You just completely missed my point, didn't you? Yes, you did.
>>
>> It would take 4 minutes to reach the mesosphere in a worst case
>> scenario. 5 minutes if deceleration is more gradual.
>
> Umm, weren't we talking about free fall from LEO altitude to the
> mesosphere? Where did this deceleration come from?
Out his ass, I imagine.
Bryan Derksen
<edward....@etssg.com> wrote:
>That assumes that you only want to deal with orbiters. I'm talking about a
>job that you want to be 200 mi up for, but that doesn't depend on anything
>in orbit.
There are some good reasons for being in a 200 mile orbit. A satellite
doing high-resolution mapping or spying, for example, would want to be
moving rather than just hanging off a stationary tower.
Bryan Derksen
<edward....@etssg.com> wrote:
>Steve Charlton wrote:
>
>> Two space craft A and B, orbiting in opposite directions.
>
>Problem #1. No spacecraft are ever launched in the direction opposite the
>Earth's rotation.
It's rare, but some are. Seasat for example:
http://southport.jpl.nasa.gov/scienceapps/seasat.html
Israel's location on the eastern shore of the Mediterranian with
not-so-friendly countries located in the other directions means that
the satellites they launch from their territory have to go west,
though I haven't found a listing in my brief search.
>When they snag each other, the stretchy-stretchy bungy cord starts to
>decelerate them at, oh, 5 g's (problem #3), or 50 m/sec/sec each.
...
>So it takes something like 160 sec for them to come to rest, and during that
>time they have moved more than 600 km apart (Problem #4).
...
>Problem #5. The craft is descending vertically into atmosphere, maximizing
>the rate at which it encounters thicker air, and thus the rate of heating.
...
>Problem #6. The craft has a minute or two in vertical fall to drop its
>velocity to substantially less than Mach 1 in preparation for the landing
>process (powered, glider, or parachute).
All four of these problems can be resolved by not shedding _all_ of
one's velocity via bungee, instead just using the bungee technique to
greatly reduce the velocity of an otherwise normal reentry. The craft
can also use aerodynamic effects to start moving horizontally again
once they get lower.
5 Gs isn't that big a problem on its own, though - fighter pilots
routinely endure such accelerations.
Bryan Derksen
<edward....@etssg.com> wrote:
>Gene P. wrote:
>> Okey dokey... How about carbon fiber retaining pins then? You know,
>> something strong, reasonably heat resistant (they will be on the *inside*
>> of the shield, after all), and lightweight...
>
>No, they will go *through* the shield. Every one will have to seal
>perfectly, even while the shield is ablating out from under them.
They don't have to go all the way through the shield, just far enough
into it to grip it. This can be done at bumps on the back of the
shield so that it doesn't even reduce the thickness of the protective
layer.
How were the ablative heat shields on the many capsules that have used
them over the years attached?
>Not I. I don't care what you make your shield out of, because your design
>goals are mutually contradictory. You can't secure an object that size to
>anything in 20 minutes. You can't make something that large and that thin
>that can hold itself together under gravity.
He mentioned a "lifting rig" in the initial post. It wouldn't need to
hold itself together under gravity, first it's supported by the
lifting rig and then after it's attached it's supported by the
spacecraft. You're searching really hard for problems with this and I
think you're getting some false positives here.
Hop David
Edward Cherlin wrote:
> Hop David wrote:
>
>
>>
>>No 33 Secretary wrote:
>>
>>
>>><stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>>
>>You just completely missed my point, didn't you? Yes, you did.
>>
>>It would take 4 minutes to reach the mesosphere in a worst case
>>scenario. 5 minutes if deceleration is more gradual.
>
>
> Umm, weren't we talking about free fall from LEO altitude to the mesosphere?
> Where did this deceleration come from?
Umm, Austin's Aug. 5 posts:
"... Because if they don't, the passengers are going to be tomato paste
from deceleration."
and
"If you slow down _slowly_, you will fall out of orbit before you are
done "slowing down." When you fall out of orbit, you will fall in to the
atmosphere. Not when you want to - when you're done "slowing down," but
much, much quicker, because you are no longer in orbit."
Derek Lyons
>>
>>> Clearly the answer isn't just one balloon, but
>>>many concentric balloons. Say, ninety-nine lift balloons.
>>
>> Yes, but as such an assembly came over the horizon, wouldn't it likely
>> be mistaken for some sort of UFO? That's the sort of solution only a
>> Captain Kirk wannabe would come up with; in the same league as playing
>> with matches amidst cans of gasoline...
>>
>>
>
>Damn you all to hell! My city's just turned to dust!
Ashes to ashes...
D.
--
Touch-twice life. Eat. Drink. Laugh.
-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
Gene P.
>On Wed, 10 Aug 2005 07:38:58 GMT, Edward Cherlin
><edward....@etssg.com> wrote:
>>Gene P. wrote:
>>> Okey dokey... How about carbon fiber retaining pins then? You know,
>>> something strong, reasonably heat resistant (they will be on the *inside*
>>> of the shield, after all), and lightweight...
>>
>>No, they will go *through* the shield. Every one will have to seal
>>perfectly, even while the shield is ablating out from under them.
>
>They don't have to go all the way through the shield, just far enough
>into it to grip it. This can be done at bumps on the back of the
>shield so that it doesn't even reduce the thickness of the protective
>layer.
Exactly what I had in mind.
>How were the ablative heat shields on the many capsules that have used
>them over the years attached?
Well, the essential difference was that they *weren't* attached so much as
integral to the structure.
>>Not I. I don't care what you make your shield out of, because your design
>>goals are mutually contradictory. You can't secure an object that size to
>>anything in 20 minutes. You can't make something that large and that thin
>>that can hold itself together under gravity.
>
>He mentioned a "lifting rig" in the initial post. It wouldn't need to
>hold itself together under gravity, first it's supported by the
>lifting rig and then after it's attached it's supported by the
>spacecraft. You're searching really hard for problems with this and I
>think you're getting some false positives here.
Thanks for the supportive words. I had pretty much decided to write off
the discussion as a loss to Troll predation.
As for the concept itself, the more I think about it, the more I can see
that it would probably wind up heavier than the current system.
With that said, given the amount of work that must be put into maintaining
this "reusable" tile system, I'm thinking that it might be cheaper to junk
it and use a tile material that's physically tougher, can be used in
larger "squares" (with fewer seams), but that can only withstand a single
re-entry each. Don't spend all the money to inspect and test all of them
on every flight, just replace them! And since they're physically
tougher, they will be a lot more resistant to glancing debris impact on
takeoff.
(When you can just about build a new heat shield from scratch for the
amount of money used to inspect and repair it after each flight, you
should consider doing so.)
Gene P.
Slidell LA
--
Alcore Nilth - The Mad Alchemist of Gevbeck
alc...@uurth.com
Hop David
Edward Cherlin wrote:
> Falling from 300 km altitude to 60 km altitude with negligible drag
> accelerates the ships and cord to several km/sec again. But yes,
> significantly less than orbital velocity.
About 2 km/sec, less than a 1/3 orbital velocity. And less than 1/9 the
kinetic energy.
>
> Problem #5. The craft is descending vertically into atmosphere, maximizing
> the rate at which it encounters thicker air, and thus the rate of heating.
>
> Problem #6. The craft has a minute or two in vertical fall to drop its
> velocity to substantially less than Mach 1 in preparation for the landing
> process (powered, glider, or parachute). It must accordingly decelerate at
> some 10s of Gs. In the normal return from orbit, a craft in the upper
> atmosphere can move thousands of kilometers horizontally through the air
> and just a few kilometers vertically while shedding velocity over a much
> longer period of time at much lower deceleration.
>
Daffy Duck's nemesis Marvin the Martian might use a bungee cord to slow
down his space ship but I don't expect it'll ever be used in the real world.
However, if space craft could refuel in orbit, slow reentry might be
doable. Direction of deceleration thrust would be more controllable
than with a bungee cord. It'd be possible to hit the atmosphere with a
velocity vector nearly tangent to the atmosphere.
I have wondered about the possibilities if there were orbital depots
well supplied with oxygen, water and other materials from the Moon and
Near Earth Objects.
Erik Max Francis
> That assumes that you only want to deal with orbiters. I'm talking about a
> job that you want to be 200 mi up for, but that doesn't depend on anything
> in orbit.
Like what?
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
A father is a thousand schoolmasters.
-- Louis Nizer
Erik Max Francis
> If we spend $$ trillions to put up a space elevator, I expect ships
> generally won't be /allowed/ in a 200 mile orbit, and would quickly
> be intercepted and forced to de-orbit.
A beanstalk is going to require essentially cleaning out all material in
orbit below geostationary orbit, whether it's useful satellites or space
junk. Most operational satellites are below geostationary, so this
eliminating a large set of use cases, many of which can't be fixed by
simply sticking something on the beanstalk.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Derek Lyons
>>How were the ablative heat shields on the many capsules that have
>>used them over the years attached?
>
>Well, the essential difference was that they *weren't* attached so
>much as integral to the structure.
Not in any US design. Typically the heatshield was bolted into place.
Mad Bad Rabbit
True, but a space elevator might be worth putting up with substitutes:
- high altitude balloons and drones for spying, mapping, and regional
communications relaying.
- statites (using solar sails or magsails) to hang out above the poles.
- 100-km tall radio masts (if we have the materials science to build
a beanstalk, we can probably build these as well).
--
>;k
Michael Ash
Compare a spy satellite launched into a 200-mile orbit at a cost of
$10,000/pound, with one in a geosync-like orbit at a cost of $5/pound,
which one is going to get better results? You could easily make your
optics ten times larger and still be able to put up ten times as many
satellites, for true global coverage.
Ash Wyllie
>Related issue:
Really big balloons filled with low density foam?
-ash
Cthulhu in 2005!
Why wait for nature?
Ash Wyllie
>Bryan Derksen <bryan....@shaw-spamguard.ca> wrote:
Beanstalks are in tension, towers are in compression. What is good for a
beanstalk is unlikely to be good for a tower.
There are a number of jobs that need to be done in orbit, and low ones at
that. GPS and satellite phones platforms need to be bigger and have much
larger power supplies if they are in GEO. ANd not to forget that the phone
transmitter also needs to be larger to reach a GEO satellite.
For any given telescope, actual resolution is going to be about 10x better if
it is in LEO than GEO.
Ross Presser
> Edward Cherlin wrote:
>
>> That assumes that you only want to deal with orbiters. I'm talking about a
>> job that you want to be 200 mi up for, but that doesn't depend on anything
>> in orbit.
>
> Like what?
Like launching an LEO satellite, which will destroy your beanstalk on the
next orbit...
Dr John Stockton
2005 11:39:25, seen in news:rec.arts.sf.science, Ash Wyllie
<as...@lr.net> posted :
> GPS and satellite phones platforms need to be bigger and have much
>larger power supplies if they are in GEO. ANd not to forget that the phone
>transmitter also needs to be larger to reach a GEO satellite.
Once a beanstalk thick enough at the bottom to gave a reasonable lift
capacity has been built, ISTM that it should be comparatively easy and
cheap to build others, especially ones with small or zero lift capacity;
these could be spread along the Equator and tied together at about GEO
level.
Comms gear can then be put on the stalks well below GEO level. From
latitude 60 deg, on the same meridian as a stalk, the lowest point on
the stalk that can be seen is Root3*R away, where R is the Earth's
radius. While large, that's a lot less than GEO distance. From
latitude 30 deg, it reduces to R/Root3.
Such as Ecuadorians and Kenyans could use space-borne comms platforms at
all heights from 0 to GEO.
--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
Derek Lyons
>> There are some good reasons for being in a 200 mile orbit. A satellite
>> doing high-resolution mapping or spying, for example, would want to be
>> moving rather than just hanging off a stationary tower.
>
>Compare a spy satellite launched into a 200-mile orbit at a cost of
>$10,000/pound, with one in a geosync-like orbit at a cost of $5/pound,
>which one is going to get better results?
The bird in the 200 mile orbit.
>You could easily make your optics ten times larger and still be able to put
>up ten times as many satellites, for true global coverage.
ROTFLMAO.
Michael Ash
> Michael Ash <mi...@mikeash.com> wrote:
>
>>> There are some good reasons for being in a 200 mile orbit. A satellite
>>> doing high-resolution mapping or spying, for example, would want to be
>>> moving rather than just hanging off a stationary tower.
>>
>>Compare a spy satellite launched into a 200-mile orbit at a cost of
>>$10,000/pound, with one in a geosync-like orbit at a cost of $5/pound,
>>which one is going to get better results?
>
> The bird in the 200 mile orbit.
>
>>You could easily make your optics ten times larger and still be able to put
>>up ten times as many satellites, for true global coverage.
>
> ROTFLMAO.
I appreciate unconstructive ridicule as much as the next guy, but would
you care to explain *why* you're saying this? Why does the low-altitude
spy satellite automatically do a better job, even though the high-altitude
one could have vastly better/larger optics and instruments, due to the
lower cost of boosting it into orbit?
I have no doubt that contemporary spy satellites can do amazing things,
but why couldn't the same amazing technology do even more amazing things
when freed from rather restrictive size and weight limitations?
Eivind Kjorstad
Geosynch orbit is around 22000 miles over the equator. This is more than
100 times the distance of the 200-mile orbit, even to the equator, if
you want to observe other areas it gets worse. (both because of the
distance and because of going trough the atmosphere in a nonvertical
i.e. longer direction.)
10 times as large an aperture isn't going to cut it.
Eivind Kjørstad
Eivind Kjorstad
> There are a number of jobs that need to be done in orbit, and low ones
> at that. GPS and satellite phones platforms need to be bigger and have
> much larger power supplies if they are in GEO. ANd not to forget that
> the phone transmitter also needs to be larger to reach a GEO
> satellite.
For comms there's a more fundamental problem too: latency.
No matter how good a transmitter and receiver you have, GEO is 36000 km
away, minimum, more if you're not at the equator. So a roundtrip will
take no less than 0.25s because of that pesky slow speed of light.
This is highly annoying on a phone-circuit, and enough to make the
circuit simply unusable for some other types of communications.
Eivind Kjørstad
Aaron Denney
The optics themselves are quite costly. I don't know about costly
enough to make it obviously ridiculous, or even make the lower orbit
better.
--
Aaron Denney
-><-
how...@brazee.net
that have such.
James Burns
If you build a multiple-mirror telescope, I think it would
be possible to build a facility with the same or better
angular resolution. I think orbit would even have some
advantages over a ground-based facility. Lack of vibration
is what springs to my mind.
I'm not sure about getting an equivalent light-gathering
ability. Since that would scale as the area of the mirrors,
</scribble, scribble, scribble> three mirrors with diameter
6D would gather as much light at 22,000 mi as one mirror
with diameter D at 200 mi. It seems feasible.
I don't know what they could do to get rid atmospheric
effects. Maybe some variation on the rubber mirrors
they're using now in ground-based telescopes? let's
leave developing that system as an exercise for the
reader.
Jim Burns
James Burns
> >
> >Compare a spy satellite launched into a 200-mile orbit at a
> >cost of $10,000/pound, with one in a geosync-like orbit at a
> >cost of $5/pound, which one is going to get better results?
>
> The bird in the 200 mile orbit.
>
> >You could easily make your optics ten times larger and still
> >be able to put up ten times as many satellites, for true
> >global coverage.
>
> ROTFLMAO.
One advantage for the GEO spy satellite over LEO just
occurred to me. At GEO, it's easier to hide where we're
looking and when.
Jim Burns
Derek Lyons
>One advantage for the GEO spy satellite over LEO just
>occurred to me. At GEO, it's easier to hide where we're
>looking and when.
ROTFLMAO.
An LEO bird moves - a GEO bird doesn't. How precisely does this help
hide where we are looking?
Derek Lyons
>If you build a multiple-mirror telescope, I think it would
>be possible to build a facility with the same or better
>angular resolution. I think orbit would even have some
>advantages over a ground-based facility. Lack of vibration
>is what springs to my mind.
Except you won't *be* in orbit - you'll be attached to a beanstalk.
(Which will not be free from vibration.)
George W Harris
wrote:
:James Burns <burn...@osu.edu> wrote:
:
:>One advantage for the GEO spy satellite over LEO just
:>occurred to me. At GEO, it's easier to hide where we're
:>looking and when.
:
:ROTFLMAO.
:
:An LEO bird moves - a GEO bird doesn't. How precisely does this help
:hide where we are looking?
How dumb are you? A GEO bird can look
anywhere in its much larger footprint any time. An
LEO bird has a much smaller footprint, and has to be
over where it's looking. Maybe you should get
checked for epilepsy, you're always going into
convulsions and rolling around on the floor.
:
:D.
--
"The truths of mathematics describe a bright and clear universe,
exquisite and beautiful in its structure, in comparison with
which the physical world is turbid and confused."
-Eulogy for G.H.Hardy
George W. Harris For actual email address, replace each 'u' with an 'i'
John Schilling
>> ROTFLMAO.
In order to achieve even one-meter optical resolution from geotationary
orbit, a spy satellite would need to have a twenty-four meter primary
mirror.
This is rather beyond the state of the art even for ground-based telescopes,
which face essentially *no* size and weight restrictions.
And one-meter resolution is fairly modest for "spy satellites"; useful,
but the big NRO birds are generally believed to be capable of doing an
order of magnitude better. So now you need a primary mirror the size
of a small football stadium, maintained to sub-micron precision across
the whole surface.
IOW, no, you *can't* "easily make your optic ten times larger". All
you can do is make space launch ten times easier, but space launch and
large optics are two different problems. If we could build the optics
for a GEO spysat, a beanstalk might or might not help us launch them,
but we *can't build the optics*.
--
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