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Accumulate Fuel at Space Station?



 
 
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  #1  
Old February 5th 04, 06:06 AM
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Default Accumulate Fuel at Space Station?

I would like to know why we don't travel to Mars by first lifting many
loads of fuel to the space station. The actual spaceship would be
assembled in space, at the space station, from parts that are lifted
there the same as the fuel is lifted, by conventional rockets. Perhaps
20 to 50 trips would be necessary to finally have a suitable ship with
lots of fuel. However, the payload to fuel ratio of this ship would be
far greater than a ship launched from earth, since it has already
escaped most of earths gravity. Also, the thrust required might be only
1/20 of what it would be if launched from earth, so a small propulsive
system will do the job. I'm assuming a human crew; they would be taken
to the space station at appropriate times by conventional rockets or the
space shuttle.

This is not my idea; It has probably already been studied, but since I
never hear about it I assume there must be some catch to this idea.

If anyone knows something about the status of this idea I would very
much like to read about it.

Mitchell Timin

--
"Many are stubborn in pursuit of the path they have chosen, few in
pursuit of the goal." - Friedrich Nietzsche

http://annevolve.sourceforge.net is what I'm into nowadays.
Humans may write to me at this address: zenguy at shaw dot ca
  #2  
Old February 6th 04, 08:18 PM
HOST Comp JimS
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Default Accumulate Fuel at Space Station?

I would like to know why we don't travel to Mars
by first lifting many loads of fuel to the space
station. The actual spaceship would be assembled
in space... 20 to 50 trips would be necessary...


Perhaps something like that will be done someday, but
there are some disadvantages. For one thing, storing
tons of flammable fuel at a space station might be somewhat
dangerous. Also, assembling things in space is a slow,
difficult process. And the cost of making 20 to 50 trips
would be huge.

James
  #3  
Old February 10th 04, 03:42 AM
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Default Accumulate Fuel at Space Station?

HOST Comp JimS wrote:

I would like to know why we don't travel to Mars
by first lifting many loads of fuel to the space
station. The actual spaceship would be assembled
in space... 20 to 50 trips would be necessary...


Perhaps something like that will be done someday, but
there are some disadvantages. For one thing, storing
tons of flammable fuel at a space station might be somewhat
dangerous. Also, assembling things in space is a slow,
difficult process. And the cost of making 20 to 50 trips
would be huge.


But how does the cost, and time, compare with making one trip with 20 to
50 times the total mass? Can we even do it? It needs a detailed
systems study, which probably has already been done. If not, why not?
If so, I would like to know the results.

I think the fuel danger is not excessive. The fuel containers could be
kept at a considerable distance from the station, on a wire heading
toward the earth. Tidal forces would keep the wire taught. That might
be necessary if they were solid fuel, which could explode if hit by a
micro-meteorite.

OTOH, if the fuel was two components, say oxygen and hydrogen, then
neither oxygen tanks not hydrogen tanks are explosive on their own. To
keep them cold in space mainly requires sheilding from sunlight.

m

--
"Many are stubborn in pursuit of the path they have chosen, few in
pursuit of the goal." - Friedrich Nietzsche

http://annevolve.sourceforge.net is what I'm into nowadays.
Humans may write to me at this address: zenguy at shaw dot ca
  #5  
Old February 11th 04, 06:42 PM
HOST Comp JimS
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Default Accumulate Fuel at Space Station?

The actual spaceship [for Mars] would be assembled
in space... 20 to 50 trips would be necessary...


the cost of making 20 to 50 trips would be huge.


But how does the cost, and time, compare with
making one trip with 20 to 50 times the total mass?



Are you asking if we could build a rocket that could carry the
equivalent of 50 shuttle payloads? I guess it's theoretically
possible, but I doubt if it's practical.

Your original question asked about the practicality of a Mars
mission that required a *massive* amount of mass being
lifted into orbit and then assembled in orbit, and I'm just
saying that it would probably be too expensive to get funded.
NASA will need to find cheaper ways of getting there.

James
  #7  
Old February 12th 04, 12:35 PM
hop
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Default Accumulate Fuel at Space Station?

(HOST Comp JimS) wrote in message ...
I would like to know why we don't travel to Mars
by first lifting many loads of fuel to the space
station. The actual spaceship would be assembled
in space... 20 to 50 trips would be necessary...


Perhaps something like that will be done someday, but
there are some disadvantages. For one thing, storing
tons of flammable fuel at a space station might be somewhat
dangerous. Also, assembling things in space is a slow,
difficult process. And the cost of making 20 to 50 trips
would be huge.

James


erm, the space station *already* stores and transfers tons of
extremely toxic, hypergolic fuel.
http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&group=sci.space.station&safe=off&selm=wBcWb.1820 %242Z2.1249%40amsnews05.chello.com
(watch for URL wrap)
quote:
Total propellant load available: 4115 kg (9072 lb) as of 2/5/04
[SM(755) +

FGB(2701) + Progress M(0) + Progress M-1(659)]. (Capability: SM -- 860
kg;
FGB -- 6120 kg).

Furthermore, progress already has the cabability to transfer fuel to
the FGB or SM. This technology is fairly well tested, having been in
use since the Salyut stations in the '70s. The ESA ATV will also have
this capability,
http://www.esa.int/export/SPECIALS/A...ZJ0VMOC_0.html

That said, ISS isn't in a good orbit to use as a stepping stone, the
propellants in question are not ideal (at least for leaving earth
orbit), and the amounts deliverable in a single launch are quite
small. Re-using the technology could make sense, in a phantasy
universe where an a US/Russian/Euro mars mission could actually take
place.
  #8  
Old February 12th 04, 06:10 PM
Dr John Stockton
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Default Accumulate Fuel at Space Station?

JRS: In article , seen in
news:sci.space.science, nafod40 posted at Wed, 11
Feb 2004 08:30:18 :-
wrote:
I think the fuel danger is not excessive. The fuel containers could be
kept at a considerable distance from the station, on a wire heading
toward the earth. Tidal forces would keep the wire taught. That might
be necessary if they were solid fuel, which could explode if hit by a
micro-meteorite.

OTOH, if the fuel was two components, say oxygen and hydrogen, then
neither oxygen tanks not hydrogen tanks are explosive on their own. To
keep them cold in space mainly requires sheilding from sunlight.


We could send up water, then just let solar array-powered electrolysis
slowly do its magic to make the fuel. Two years for a bag of fuel? No
problem, no rush.

That way no volatile components in the launch. You could freeze the
water, and use it as part of the structure of the launch vehicle to
reduce weight. Alternate launch techniques such as rail guns? The
payload would certainly tolerate the G's.


To do a reasonably useful mission requires, give or take an order of
magnitude or so, enough fuel to accelerate a ton by 10 km/s, putting 0.5
* 1000 * 10000^2 = 5E10 joules into the payload; given the way a rocket
works, the energy in the fuel must be significantly greater - say
double, giving 1E11 joules.

The solar constant is about 1400 W/m^2; assume solar panel efficiency
about 35% which means 5E2 W/m^2 available, 5E2 J/s/m^2. A year is 3E7
s, giving 1.5E10 J/yr/m^2.

On that basis, a modest 6 m^2 panel allows for a mission per year.

That's well-enough placed with respect to the ballpark to justify a
calculation using better figures. The efficiencies above are
intentionally generous.

Load momentum is 1E7 units; to get that in a year needs a thrust of
about 0.3 N. What Isp can an 0.3 N H-O rocket give? I think of the
electrolysed gases being fed directly to an engine, so producing a
continuous-thrust mission running on sunlight and water.

--
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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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  #9  
Old February 13th 04, 11:27 AM
Markus Redeker
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Default Accumulate Fuel at Space Station?

(hop) writes:

[...]

That said, ISS isn't in a good orbit to use as a stepping stone,


Which orbit would you prefer?

--
Markus Redeker Hamburg, Germany
 




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