Interstellar Flight Today
Doug
Suppose we had to abandon the Earth for whatever reason.
Is it possible to construct an interstellar spaceship given today's
technology?
Related questions:
How quickly could said ship be constructed?
Would devoting most industries to the effort make a difference, or is
there too much specialization required?
How would it be powered?
Doug
Jason Bontrager
>
> Question for the group:
>
> Suppose we had to abandon the Earth for whatever reason.
Then we go to Mars, or the Asteroid Belt, or the Moon.
Or did you mean that we have to abandon the Solar System?
> Is it possible to construct an interstellar spaceship given today's
> technology?
Yeah, I think so. It'd just be real slow.
> Related questions:
>
> How quickly could said ship be constructed?
What do you want it/them to do? Carry all 8G humans
to Epsilon Eridani in 5 subjective years? Or carry
Earth genetic material to a "suitable" planetary system
before that system's sun goes out? Something in between?
Jason B.
John Savard
part:
>Is it possible to construct an interstellar spaceship given today's
>technology?
Yes, using hydrogen bombs and a pusher plate.
Unfortunately, with today's technology, we couldn't actually construct
one that would carry any *people* on it.
In fact, lifting that requirement, Pioneer 10 would qualify as an
"interstellar spaceship".
Unless perhaps we *could* construct an L-5 type habitat...
with such an _enormous_ solar collection mirror that the light of one
star would suffice to provide light and energy for its inhabitants.
The laws of optics probably forbid that.
OK, how about an L-5 habitat with a nuclear power source that would
last for tens of thousands of years? We might be able to do that.
John Savard
http://members.shaw.ca/quadibloc/index.html
John Schilling
>Question for the group:
>Suppose we had to abandon the Earth for whatever reason.
>Is it possible to construct an interstellar spaceship given today's
>technology?
It may be; some of the more grandiose plans for the Orion nuclear pulse
drive would have been capale of a few percent of light speed if they
worked as plans. Only the earlier, less ambitious versions had any sort
of detail design work or test data behind them, and even *they* had a lot
more work ahead of them. So it isn't certain that the interstellar model
would have been possible at all, but it isn't certain.
This still takes rather more than a human lifetime to reach the nearest
stars, so we're talking a generation ship. We can't build completely
closed ecologies that last that long, of course, but we can make up the
difference with consumables - if the life support system recycles food,
water, and air with evem 95% efficiency we "only" need about a hundred
tons of supplies per passenger to keep everyone alive for the duration.
Good thing Orion spacecraft can be made big...
Also a "good" thing that you are apparently postulating the Earth becoming
uninhabitable, because the big problem with an Orion starship is that
launching one goes a long way towards making the Earth uninhabitable in
the first place.
>Related questions:
>How quickly could said ship be constructed?
Years. Freeman Dyson suggested that an Orion starship with a few tens of
thousands of tons of payload could be built at a cost of one-tenth of the
US Gross National Product. That was thirty years ago, and we're richer
now than we were then, but this is a huge undertaking.
>Would devoting most industries to the effort make a difference, or is
>there too much specialization required?
It seems to take the United States a couple years to convert to an emergency
economy focused entirely on one endeavour, and the lead time on anything as
big as a starship is going to be another couple years. Figure in five years,
best case, we could have a starship coming off the assembly line every month.
>How would it be powered?
Hydrogen bombs, a few hundred thousand per starship. Our entire present
nuclear arsenal, including decomissioned warheads and vaults full of raw
plutonium and HEU, remanufactured to optimal designs for starship production,
*might* suffice for the first ship. Anything after that, we are going to
have to divert an enormous ammount of industry to uranium mining, breeder
reactors, and the like just for the raw materials for the bombs.
Again, I note that all of this is highly speculative. I would not bet on
it working at all, though you can plausibly handwave away the difficulties
if you need it for the setting of an SF story or RPG. And we are talking,
at best, a few dozen starships carrying a few hundred people to a nearby
star. None of them ever having seen Earth, but most having talked to people
who saw Earth once upon a time.
--
*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 *
Paul F. Dietz
> Hydrogen bombs, a few hundred thousand per starship. Our entire present
> nuclear arsenal, including decomissioned warheads and vaults full of raw
> plutonium and HEU, remanufactured to optimal designs for starship production,
> *might* suffice for the first ship. Anything after that, we are going to
> have to divert an enormous ammount of industry to uranium mining, breeder
> reactors, and the like just for the raw materials for the bombs.
However, the amount of plutonium (or enriched uranium) needed
for a fusion bomb is only a weak function of its yield. You
don't need much more to make a gigaton bomb than a megaton
bomb. You need much more fusion fuel, and you need much more
tamper material for the secondary (and tertiary, etc.). So
it might make sense to make the starship Really Big and use
very large bombs.
Deuterium is probably the cost driver. Perhaps they'll
obtain it on Mars or Venus, where the D/H ratios are some
5 or 100 times that of Earth, respectively.
Paul
John Savard
<di...@interaccess.com> wrote, in part:
>So
>it might make sense to make the starship Really Big
That would also go a long way towards solving the problem of making a
closed ecology.
John Savard
http://members.shaw.ca/quadibloc/index.html
Grinch
How would we even know where to go?
>Doug
Christopher M. Jones
> Question for the group:
>
> Suppose we had to abandon the Earth for whatever reason.
>
> Is it possible to construct an interstellar spaceship given today's
> technology?
No. Not with sufficient passenger size to evacuate even a
fraction of the Earth. Nor even to provide a seed for a new
colony.
> Related questions:
>
> How quickly could said ship be constructed?
Depends on when in the future we have to construct it. Even
with rather futuristic technology it will take a long time
just to build something that large and mine and refine the
huge quantity of propellant to send it on its way. Nanotech
let's you skip ahead quite a bit, but even then you won't be
able to make 'em in between cups of coffee. And it's still
going to take quite a while just to bring enough raw energy
to bear on enough materials to build enough ships to evacuate
6 odd billion people.
> Would devoting most industries to the effort make a difference, or is
> there too much specialization required?
Wouldn't help now, since even that level of effort is
insufficient to build one interstellar colonization ship.
If we had enough time (maybe a century or two) where we
absolutely *knew* we best be gettin' out of the Solar
System then maybe we could develop the industries and
technologies to do it. But even then, shipping 6
billion people to another Solar System is a rather dodgy
proposition.
> How would it be powered?
There are many possibilities. One of the best
candidates is a fusion rocket. Other good candidates
are an anti-matter powered photon rocket, a Nuclear
Salt Water Rocket, and a pulsed nuclear explosive
rocket (Orion). Way down the list are Ion engines,
Hall thrusters, light sails, mag sails, magneto-
plasma dynamic thrusters, nuclear thermal rockets,
and other systems which lack both the thrust and the
efficiency (exhaust velocity) to accelerate many
gigatons of material up to any reasonable fraction of
light-speed.
--
That's wiggidy whack yo!
Christopher M. Jones
> On 31 Mar 2002 08:27:45 -0800, tr...@cinci.rr.com (Doug) wrote:
>
> >Question for the group:
> >
> >Suppose we had to abandon the Earth for whatever reason.
> >How would it be powered?
>
> How would we even know where to go?
Within the next few decades we will have a very good
understanding of the stars in our local planetary
neighborhood and the planetary systems around them.
Although, if the only objective is to "get away", then
building an interstellar ship (or fleet of ships) capable
of supporting all the billions of humanity for probably
interstellar journey durations (100s of years at the
least) solves the problem already. They do not
particularly need somewhere else to go to, other than as
a source for energy and raw materials (which they will
eventually run out of) and as a place to live in comfort
(rather than as a place to live out of necessity). And,
if we only have to abondon Earth (rather than the Solar
System), then the problem becomes *enormously* easier,
and possibly achievable within a few generations if a
worldwide concerted effort is made.
--
Jane, stop this crazy thing!
Doug
The questions come from another newsgroup I'm reading, and it seemed
to me that it would be possible to create an interstellar ship in a
relatively short amount of time but the only reason we'd do it is
because something catastrophic would happen to wreck the solar system.
Black hole ripping the sun apart or something. Anything short of
that wouldn't be impetus enough to do it.
Since we're talking "today" (give or take a couple of years -
supposing we had to start tomorrow) I assume it'd have to be a
generation ship since there isn't enough time to work out a way around
relativity. Or anything else fancy. Just stuff we have laying around
the planet now.
Even given global launch capability, I would bet that many countries
would work for themselves, although it's possible that the US, Russia,
Japan and the ESA would team up since we already work together. If
they all could be coordinated, that's a lot of payloads that could be
put into orbit in a pretty short time. Plus we could take the ISS and
the shuttles along. Not to mention the external fuel tanks on the
shuttles.
Still, we're talking about only a few thousand people at best getting
a ticket. The rest of the human and animal cargo would have to go as
frozen sperm samples (a good hedge against inbreeding as well as
potential colonization).
So we have to make something gigantic, big enough for a closed
ecosystem yet with some slop in the system, with enough room for a
couple thousand people and all their supplies, with robust recycling
and manufacturing facilities and lots of spare parts.
I suppose we could canibalize the power systems of our nuclear sub and
aircraft carrier fleets, although I don't know if those power plants
would survive the trip into space. (And visions of Be Forever Yamato
dance in our heads.)
As far as propulsion, is it possible to put chemical rockets on the
thing? Somehow get solid boosters up there, maybe by using the
plane-launched Pegasus rockets?
If nothing else, it's an entertaining thought problem.
Doug
Doug
> How would we even know where to go?
I'd aim for one of the systems we know has gas giants, banking on the
hope that it'd also have Earthlike worlds.
Doug
James Nicoll
Paul F. Dietz <di...@interaccess.com> wrote:
>
>Deuterium is probably the cost driver. Perhaps they'll
>obtain it on Mars or Venus, where the D/H ratios are some
>5 or 100 times that of Earth, respectively.
Well, yes but isn't that because there is so little
hydrogen at all on either world and the mechanism by which H
is removed removes lighter isotopes faster? How do the absolute
quantities of D compare?
--
"I think you mean 'Could libertarian slave-owning Confederates, led by
SHWIers, have pulled off a transatlantic invasion of Britain, in revenge
for the War of 1812, if they had nukes acquired from the Sea of Time?'"
Alison Brooks (? - 2002)
LizM7
> If we had enough time (maybe a century or two) where we
> absolutely *knew* we best be gettin' out of the Solar
> System then maybe we could develop the industries and
> technologies to do it. But even then, shipping 6
> billion people to another Solar System is a rather dodgy
> proposition.
I suspect that a bunch of the effort of the following century would be
spent on birth control so that we *wouldn't* be shipping six plus
billion people to another solar system.
- Liz
Paul F. Dietz
> Well, yes but isn't that because there is so little
> hydrogen at all on either world and the mechanism by which H
> is removed removes lighter isotopes faster? How do the absolute
> quantities of D compare?
Yes, but the quantity that remains is still far larger
than would be used in a starship. The deuterium in Venus's
atmosphere, IIRC, would form a sphere 10 km across if
separated and liquified. The energy from fusing it to helium
would be roughly enough to remove Venus's atmosphere from the
planet.
A ton of deterium, fully fused, would produce 100 megatons of
energy. So a starship with 100,000 bombs, each in the gigaton
range, would require millions of tons of deuterium.
Paul
Erik Max Francis
> Yes, but the quantity that remains is still far larger
> than would be used in a starship. The deuterium in Venus's
> atmosphere, IIRC, would form a sphere 10 km across if
> separated and liquified. The energy from fusing it to helium
> would be roughly enough to remove Venus's atmosphere from the
> planet.
But as you must know, what really counts is not the total quantity, but
rather its accessibility.
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ Nationalism is an infantile sickness.
\__/ Albert Einstein
Alcyone Systems' Daily Planet / http://www.alcyone.com/planet.html
A new, virtual planet, every day.
John Schilling
>On Sun, 31 Mar 2002 17:02:41 -0600, "Paul F. Dietz"
><di...@interaccess.com> wrote, in part:
>>So it might make sense to make the starship Really Big
>That would also go a long way towards solving the problem of making a
>closed ecology.
Not necessarily. The most successful closed ecologies to date have been
small ones, no bigger than a few rooms in research lab somewhere. Making
it big doesn't help much, and making it needlessly complex hurts. KISS.
John Schilling
It is far from certain that you would find a world you could live on
without an artificial, closed life support system.
It is absolutely certain that you will fail if you don't master the art
of artificial, closed life support systems, in deep space yet, because
the trip will take a century or more even if you *aren't* picky about
your destination. Several centuries if you insist on a known planetary
system.
Planets would be nice, but what we *need* are raw materials to replenish
and then expand our mostly closed ecology space habitats, and we need them
before the difference between "closed ecology" and "mostly closed ecology"
kills everybody. Alpha Centauri only a century or so away with the most
optimistic Orion starship proposals, and seems likely to have comets and
asteroids in fair number.
Anthony Buckland
> ...Is it possible to construct an interstellar spaceship given today's
>technology?
>
>
>It may be; some of the more grandiose plans for the Orion nuclear pulse
>drive would have been capale of a few percent of light speed if they
>worked as plans. Only the earlier, less ambitious versions had any sort
>of detail design work or test data behind them, and even *they* had a lot
>more work ahead of them. So it isn't certain that the interstellar model
>would have been possible at all, but it isn't certain.
>
>This still takes rather more than a human lifetime to reach the nearest
>stars, so we're talking a generation ship. ...
>
The trouble with using technologies like this that need a massive
consumption of anything is that they will need an equally massive
consumption of something at the other end to slow down. You
have to transport hundreds, perhaps thousands of megatons of
bombs with the ship, they have to work when they get there (no
repair facilities to visit, or resources to mine, on the way), and
you have to expend the extra energy to accelerate the bombs
as well as your ship. You can't exactly use atmospheric
braking at a few percent of the speed of light, even assuming
you find a convenient planet and can steer towards it in time.
John Schilling
>John Schilling wrote:
>> Hydrogen bombs, a few hundred thousand per starship. Our entire present
>> nuclear arsenal, including decomissioned warheads and vaults full of raw
>> plutonium and HEU, remanufactured to optimal designs for starship
>> production, *might* suffice for the first ship. Anything after that,
>> we are going to have to divert an enormous ammount of industry to uranium
>> mining, breeder reactors, and the like just for the raw materials for the
>> bombs.
>However, the amount of plutonium (or enriched uranium) needed
>for a fusion bomb is only a weak function of its yield. You
>don't need much more to make a gigaton bomb than a megaton
>bomb. You need much more fusion fuel, and you need much more
>tamper material for the secondary (and tertiary, etc.). So
>it might make sense to make the starship Really Big and use
>very large bombs.
Possibly, but we are already talking about ships weighing nearly half
a million tons at liftoff and propelled by hydrogen bombs in the tens
of megatons, costing on the order of a trillion dollars. I'm not sure
there's all that much room for making them bigger, practically speaking.
>Deuterium is probably the cost driver. Perhaps they'll
>obtain it on Mars or Venus, where the D/H ratios are some
>5 or 100 times that of Earth, respectively.
Lithium is going to be a problem as well. Again, current stockpiles
of both lithium and deturerium (the latter mostly as heavy water) may
be adequate for the first ship, but we're going to need massive
industrial mobilization for anything more.
And once you are at the point where lithium and deuterium are your
cost drivers, the advantage of making the ships bigger diminishes.
The redundancy of a fleet is probably a better bet.
Doug
> tr...@cinci.rr.com (Doug) writes:
>
> >Grinch <oldn...@mindspring.com> wrote
> >>
> >> How would we even know where to go?
>
> >I'd aim for one of the systems we know has gas giants, banking on the
> >hope that it'd also have Earthlike worlds.
>
> and then expand our mostly closed ecology space habitats, and we need them
> before the difference between "closed ecology" and "mostly closed ecology"
> kills everybody. Alpha Centauri only a century or so away with the most
> optimistic Orion starship proposals, and seems likely to have comets and
> asteroids in fair number.
Is it possible, then, to build a ship big enough to be the "first
stage" to get to our asteroid belt and gather enough material there
for the long push?
Doug
Paul F. Dietz
> >However, the amount of plutonium (or enriched uranium) needed
> >for a fusion bomb is only a weak function of its yield. You
> >don't need much more to make a gigaton bomb than a megaton
> >bomb. You need much more fusion fuel, and you need much more
> >tamper material for the secondary (and tertiary, etc.). So
> >it might make sense to make the starship Really Big and use
> >very large bombs.
>
> Possibly, but we are already talking about ships weighing nearly half
> a million tons at liftoff and propelled by hydrogen bombs in the tens
> of megatons, costing on the order of a trillion dollars. I'm not sure
> there's all that much room for making them bigger, practically speaking.
Where does this $1 T cost come from? The bombs? If so, making
them bigger doesn't necessarily make them proportionally more
expensive (especially if deuterium is available more cheaply
from an off-planet source). If anything, big bombs become easier
to build -- there's a reason current bombs have lower yield than
the first H bomb.
A big thermonuclear bomb could also be optimized for propulsion.
The final stage could be in the shape of a flattened pancake so
that the fireball would tend to expand axially. The bigger
the bomb, the larger the achievable aspect ratio of this pancake.
> Lithium is going to be a problem as well.
You don't need lithium to make an H-bomb. Mike used liquid
deuterium. Lithium deuteride is certainly more *practical*
in current thermonuclear weapons, but perhaps not in this
application.
Paul
Erik Max Francis
> Where does this $1 T cost come from? The bombs? If so, making
> them bigger doesn't necessarily make them proportionally more
> expensive (especially if deuterium is available more cheaply
> from an off-planet source). If anything, big bombs become easier
> to build -- there's a reason current bombs have lower yield than
> the first H bomb.
It's because using huge yield thermonuclear weapons to destroy
terrestrial targets is a waste. As the yield goes up, more and more
energy just goes into space rather than into your target.
Paul F. Dietz
> > If anything, big bombs become easier
> > to build -- there's a reason current bombs have lower yield than
> > the first H bomb.
>
> It's because using huge yield thermonuclear weapons to destroy
> terrestrial targets is a waste. As the yield goes up, more and more
> energy just goes into space rather than into your target.
Oh, certainly it's *desirable* to make the bombs smaller (and
lighter.) The point is the first one wasn't small, because it
was easier to make it big.
Paul
Johnny1A
The most likely result would be war on the nastiest, largest scale the
human race ever saw, as everyone strove to get _their_ descendents on
the ships.
Shermanlee
Paul F. Dietz
> The most likely result would be war on the nastiest, largest scale the
> human race ever saw, as everyone strove to get _their_ descendents on
> the ships.
Offer them the chance to ship gametes instead.
Paul
George William Herbert
It wasn't small because the first fuel they were able to calculate
results for was cryogenic deuterium, and it's got a lousy density,
combined with the 60-inch diameter of the primary stage.
It wasn't easier to make it big per se; the physics that was
understood first required bigger devices. The engineering end
of it wasn't particularly easier because it was larger.
They very rapidly shrunk as lithium deuteride was tested and proven
to work as fusion fuel, which is about six times denser than LD,
and smaller primaries were developed. And further development has
improved the performance even more and more and more...
-george william herbert
gher...@retro.com
George William Herbert
>The final stage could be in the shape of a flattened pancake so
>that the fireball would tend to expand axially. The bigger
>the bomb, the larger the achievable aspect ratio of this pancake.
In a vacuum, there's no fireball per se, only bomb fragments.
With *some* effort, you can shape the expansion of bomb fragments,
but generally they're so energetic that within a few bomb major
radii they're pretty well distributed spherically.
>> Lithium is going to be a problem as well.
>
>You don't need lithium to make an H-bomb. Mike used liquid
>deuterium. Lithium deuteride is certainly more *practical*
>in current thermonuclear weapons, but perhaps not in this
>application.
I'm not sure why. We're producing something like 10,000 tons/year
of lithium now worldwide, which if deuterated works out to enough
LiD for around a practical combined bomb yield of 320 GT/yr in
"clean" devices, and probably 700 GT/yr in "dirty" devices.
-george william herbert
gher...@retro.com
Paul F. Dietz
> In a vacuum, there's no fireball per se, only bomb fragments.
>
> With *some* effort, you can shape the expansion of bomb fragments,
> but generally they're so energetic that within a few bomb major
> radii they're pretty well distributed spherically.
No. If the 'pancake' has a large aspect ratio the
expansion of the plasma will be quasi-one-dimensional,
perpendicular to its surface. By the time the
plasma expands to a distance on the order of the radius
of the pancake, most of the plasma's initial thermal
energy will already have been converted to macroscopic
kinetic energy along the axis of the pancake (or have been
radiated as x-rays.)
(A similar thing happens to the planar expansion induced
in a laser-supported detonation wave launcher.)
> I'm not sure why. We're producing something like 10,000 tons/year
> of lithium now worldwide, which if deuterated works out to enough
> LiD for around a practical combined bomb yield of 320 GT/yr in
> "clean" devices, and probably 700 GT/yr in "dirty" devices.
I'm thinking of a massive vehicle with several hundred
thousand 1 GT bombs.
Paul
Paul F. Dietz
> It wasn't small because the first fuel they were able to calculate
> results for was cryogenic deuterium, and it's got a lousy density,
> combined with the 60-inch diameter of the primary stage.
> It wasn't easier to make it big per se; the physics that was
> understood first required bigger devices. The engineering end
> of it wasn't particularly easier because it was larger.
>
> They very rapidly shrunk as lithium deuteride was tested and proven
> and smaller primaries were developed. And further development has
> improved the performance even more and more and more...
Yes, as we became more sophisticated we knew enough to make smaller
devices work. The bigger device did not need this sophistication.
The first LiD bombs were also very big (15 MT for Castle Bravo,
for example).
Bigger is easier. Scale up a bomb and the fusion capsule tamper
becomes thicker. As a result, it takes longer for the radiation
to leak through it. The fusion fuel also takes longer to expand.
This means fusion goes on for a longer time, and the fuel doesn't
have to be compressed as much. A heavier wall can be interposed
between the primary and the secondary, reducing neutron preheating.
Deuterium does have a lousy density, but it's much more compressible
than LiD.
Paul
Charles R Martin
> George William Herbert wrote:
>
> > In a vacuum, there's no fireball per se, only bomb fragments.
> >
> > With *some* effort, you can shape the expansion of bomb fragments,
> > but generally they're so energetic that within a few bomb major
> > radii they're pretty well distributed spherically.
>
> No. If the 'pancake' has a large aspect ratio the
> expansion of the plasma will be quasi-one-dimensional,
> perpendicular to its surface. By the time the
> plasma expands to a distance on the order of the radius
> of the pancake, most of the plasma's initial thermal
> energy will already have been converted to macroscopic
> kinetic energy along the axis of the pancake (or have been
> radiated as x-rays.)
>
> (A similar thing happens to the planar expansion induced
> in a laser-supported detonation wave launcher.)
This sounds very interesting, but I'm getting lost in pancakes, radii,
and axial and perpendicular expansions. Can you back up a little and
define these? If I'm following you, you're saying
- the bomb package is arranged to have much more stuff in width than
height, ie
__________________
(__________________)
|<---r-->|
- but it sounds (from expansion "axially" and "perpendicular to its
surface") that it expands
A
_________|_________
(__________________)
|
V
as shown by the arrows, and that
- by the time the whole mess has expanded along the axial line as far
as 1 r that the majority of the energy has been converted to motion
of the remnants of hot gases.
Is that it?
>
>
> > I'm not sure why. We're producing something like 10,000 tons/year
> > of lithium now worldwide, which if deuterated works out to enough
> > LiD for around a practical combined bomb yield of 320 GT/yr in
> > "clean" devices, and probably 700 GT/yr in "dirty" devices.
>
> I'm thinking of a massive vehicle with several hundred
> thousand 1 GT bombs.
Cool! I want one too.
As long as you're up.
--
I once complained to my father that I didn't seem to be able to do things the
same way other people did. Dad's advice? 'Margo, don't be a sheep. People hate
sheep. They eat sheep.' -- Margo Kaufmann
_______________________________________________________________________________
Charles R (Charlie) Martin Broomfield, CO 40N 105W
Paul F. Dietz
> Is that it?
Yes.
Paul
John Savard
wrote, in part:
>Not necessarily. The most successful closed ecologies to date have been
>small ones, no bigger than a few rooms in research lab somewhere. Making
>it big doesn't help much, and making it needlessly complex hurts. KISS.
I figure the simplest solution is to take the one we know that works,
and copy it as exactly as possible. In order to not leave too much
out, we will need a large scale.
Essentially, assume a *lot* of plant life is required, over a lot of
area of land and water, to support a tiny animal population. That
increases the odds the thing will work. Include humans, who are rather
bulky, in that population, and your minimum size goes up.
John Savard
http://members.shaw.ca/quadibloc/index.html
John Schilling
>> >Grinch <oldn...@mindspring.com> wrote
Yes, but why bother? We've got plenty of raw materials here on Earth
to build and stock our hypothetical starships as we please. The limiting
factor is not availability of raw materials, but ability to boost those
materials up to a few percent of light speed. That limits us, in our
hypothetical evacuate-the-Earth scenario, to maybe a million tons of
supplies divided among a few dozen ships. It's the same million tons
whether you get it on Earth or in the Asteroid belt.
OK, maybe 1.002 million tons if you get it from the Asteroid belt, on
account of you saving the trouble of lifting the stuff off the Earth.
If you're headed for Alpha Centauri, the "lift stuff off the Earth" part
of the voyage is negligible.
John Schilling
>John Schilling wrote:
>> >However, the amount of plutonium (or enriched uranium) needed
>> >for a fusion bomb is only a weak function of its yield. You
>> >don't need much more to make a gigaton bomb than a megaton
>> >bomb. You need much more fusion fuel, and you need much more
>> >tamper material for the secondary (and tertiary, etc.). So
>> >it might make sense to make the starship Really Big and use
>> >very large bombs.
>> Possibly, but we are already talking about ships weighing nearly half
>> a million tons at liftoff and propelled by hydrogen bombs in the tens
>> of megatons, costing on the order of a trillion dollars. I'm not sure
>> there's all that much room for making them bigger, practically speaking.
>Where does this $1 T cost come from? The bombs? If so, making
>them bigger doesn't necessarily make them proportionally more
>expensive (especially if deuterium is available more cheaply
>from an off-planet source). If anything, big bombs become easier
>to build -- there's a reason current bombs have lower yield than
>the first H bomb.
It's not just the bombs; the ship itself is not going to be cheap.
~$1 trillion for a ~500,000 ton spacecraft comes to $2000/kg. That's
about right, on average, for aerospace hardware. A Boeing 747 right
off the assembly line costs about $2000/kg. That's what it actually
costs to build large structures and fit them out with all the necessary
systems, to aerospace standards.
And no, you don't get to handwave away the "aerospace standards" part
by saying Orions are so powerful we don't need to get fanatical about
things like weight and reliability, that we can build them like
battleships. Interstellar travel is *hard*; the only way this scheme
even possibly works is if we couple the power of an Orion drive with
every bit of weight reduction imaginable. And then it has to last
for more than a century.
So we are talking about a huge battleship built to aerospace standards.
That costs a trillion dollars or so, and it isn't dominated by the price
of the bombs in the fuel tank. Not that those won't be a couple hundred
billion dollars or so.
John Schilling
>On 1 Apr 2002 11:51:58 -0800, schi...@spock.usc.edu (John Schilling)
>wrote, in part:
>>Not necessarily. The most successful closed ecologies to date have been
>>small ones, no bigger than a few rooms in research lab somewhere. Making
>>it big doesn't help much, and making it needlessly complex hurts. KISS.
>I figure the simplest solution is to take the one we know that works,
>and copy it as exactly as possible. In order to not leave too much
>out, we will need a large scale.
If by "the one that we know works", you mean Earth's natural biosphere,
then A: that is so hideously complex a system that it belongs nowhere
in the same sentence as "simplest solution", and B: the one attempt so
far to copy it has *not* worked.
The other ones that we know work, the ones that have worked repeatedly
in the past, are very simple. A couple of guys in a sealed laboratory,
a few thousand square feet of high-intensity agriculture under sun lamps,
half a dozen species of plants, and nothing more. And you don't even
need that much - you can *buy* a completely functional closed ecology,
in a glass sphere the size of a softball, for $79 plus shipping and
handling.
<http://www.eco-sphere.com/how_to_order.html>
Average life of about 2-3 years, demonstrated maximum life of 8 years.
And that's about 8 years longer than Biosphere 2 lasted before they had
to break the seal.
"Keep it Simple" does not mean "duplicate the most complex system we can
find, because we don't know any better". We know better.
Christopher M. Jones
> tr...@cinci.rr.com (Doug) writes:
> >Is it possible, then, to build a ship big enough to be the "first
> >stage" to get to our asteroid belt and gather enough material there
> >for the long push?
>
> Yes, but why bother? We've got plenty of raw materials here on Earth
> to build and stock our hypothetical starships as we please. The limiting
> factor is not availability of raw materials, but ability to boost those
> materials up to a few percent of light speed. That limits us, in our
> hypothetical evacuate-the-Earth scenario, to maybe a million tons of
> supplies divided among a few dozen ships. It's the same million tons
> whether you get it on Earth or in the Asteroid belt.
>
> OK, maybe 1.002 million tons if you get it from the Asteroid belt, on
> account of you saving the trouble of lifting the stuff off the Earth.
> If you're headed for Alpha Centauri, the "lift stuff off the Earth" part
> of the voyage is negligible.
Ummm, no. Mass fraction is mass fraction, pure and simple,
there are no shortcuts around the rocket equation. Even
using highly advanced technology that allowed you to
accelerate to escape velocity from Earth's surface with a
mass fraction of only 2:1 (which represents a propulsion
system with an effective exhaust velocity of about 15 km/s)
the effort of launching off of Earth would be as great a
task as building the interstellar spaceship itself. There
are many propulsion systems that have the necessary
efficiency to provide the delta V, but in order to take
off from Earth's surface they must be able to generate
greater than 9.8 Newtons of thrust per kilogram of gross
vehicle mass, which is a daunting challenge.
Building the bulk of the spacecraft using space based
resources saves a heck of a lot of effort.
--
Here are your messages: "You have 30 minutes to move your car", "You have 10
minutes", "Your car has ben impounded", "Your car has been crushed into a cube",
"You have 30 minutes to move your cube"
pervect
"Grinch" <oldn...@mindspring.com> wrote in message
news:kv8fau8mooc72vsdg...@4ax.com...
> How would we even know where to go?
By constructing a ultra-long baseline interferometer to scan for planets at
the same time the starship is constructed. This idea is stolen from the
computer game Alpha Centuari, but the idea makes sense IMO.
John Schilling
If your "highly advanced technology" is only good for 15 km/s
exhaust velocity, you aren't building a starship, not no way,
not no how.
We are postulating the limiting case of a thermonuclear Orion
drive, with an effective exhaust velocity of 7,500 km/s. And
an acceleration of ~ 1G. I will repeat my skepticism as to
the feasibility of such a system, but it can't be entirely
ruled out. If realized, it gives you launch to orbit with
a mass fraction of 1.001:1 or maybe 1.002:1.
Assuming you are willing to live with the consequences, which
include obliterating everything within a hundred kilometers of
your launch site, dumping a hundred tons of fallout into the
stratosphere, and zorching every piece of electronics sight.
But this is an emergency evacuation scenario, so that may not
be a problem.
Johnny1A
That would help a little, but you'd still get wars as people tried to
get their _living_ descendents aboard the ships (to say nothing of
themselves).
Shermanlee
John Savard
wrote, in part:
>"Keep it Simple" does not mean "duplicate the most complex system we can
>find, because we don't know any better". We know better.
The failure of Biosphere 2 seemes to demonstrate we _don't_ know
better. The ones that do work - your examples - are all-natural, no
pumps, no activated charcoal filters, and so on. Also, none of your
examples has lasted about 1000 years, that is, a time an order of
magnitude larger than a human lifetime.
I agree that we can't attempt to duplicate Earth's complete ecology.
Russia won't co-operate, for one thing. (Sable are one of the species
of animals on Earth.)
But even in the most simplified form, it will take many acres of land
- and water - to support a handful of astronauts indefinitely.
John Savard
http://members.shaw.ca/quadibloc/index.html
Timothy Little
>The failure of Biosphere 2 seemes to demonstrate we _don't_ know
>better.
You do realize you just made his point, don't you?
Biosphere 2 was an example of trying to put together a sample of the
most complex ecosystem the designers could fit into an enclosed space,
and failed miserably. It is an example of the *worst* that CELSS has
to offer, not the best. We do know better, since much more simplifed
ecosystems *have* succeeded. Are you actually familiar with the
research in this field, or just with projects that got mass-media time
like Biosphere 2?
- Tim
John Schilling
>On 2 Apr 2002 10:23:20 -0800, schi...@spock.usc.edu (John Schilling)
>wrote, in part:
>>"Keep it Simple" does not mean "duplicate the most complex system we can
>>find, because we don't know any better". We know better.
>The failure of Biosphere 2 seemes to demonstrate we _don't_ know
>better. The ones that do work - your examples - are all-natural, no
>pumps, no activated charcoal filters, and so on. Also, none of your
>examples has lasted about 1000 years, that is, a time an order of
>magnitude larger than a human lifetime.
The failure of Biosphere 2 demonstrates that eccentric Texas billionaires
don't know how to do better. As for the rest of us, many of my examples
*do* have pumps, filters, and so on. Last longer than Biosphere 2, before
having to break the seals, as well. You need to check up on NASA's CELSS
Human-Rated Test Facility, Russia's BIOS 1 through 3, the McDonnel Douglas
Long-Duration Life Support Testing Program, Japan's "Biosphere J", and the
like.
It is these systems, not stunts like "Biosphere 2", that will serve as the
basis for future long-duration closed-ecology life support systems in space.
>But even in the most simplified form, it will take many acres of land
>- and water - to support a handful of astronauts indefinitely.
The systems which, unlike "Biosphere 2", actually *work*, do not take
many acres of land. Hundreds of square meters of land, and a few dozen
species of plants and animal.