On Orbital Fuel Stations

dylanduck writes "Being able to fill up your spacecraft from a fuel depot in orbit round the Earth or Moon is key to the long-term prospects of astronauts exploring the solar system, according to NASA engineers. Trouble is NASA doesn't want to build it themselves. So there's $5 million for any enterprising groups who can develop a simple version themselves."

Comments

Re:Hmmm

[Darkman, Walkin Dude]

There might be methods whereby you wouldn't need to carry the fuel with you, for example with a space elevator. However, just what advantages would a space elevator offer over a tower launch? (I've used parts of this post before, but I have since refined my ideas). I contacted a man responsible for a similar idea a while back, the skyramp (warning: hideous javascript menu may break firefox), Carlton Meyer, and had a dialogue in which he pointed me to a tower launch archive.

The ideas I see bandied about there are similar to what I had in mind, which would be essentially an 11km tall tower (think pylons rather than skyscrapers, based at sea), with evacuated airless launch tubes, using nuclear reactors to power a maglev or pulley system to accelerate vessels to escape velocity. These would then emerge above the end of the troposphere, with it's associated weather and air pressure, and have little to no fuel needed to match the earth's gravity, meaning you could do a lot more while you were up there. At a reasonable acceleration (5 to 7 g's) you would be in geostationary orbit. From there you could build a fully system wide ship or ships, as its much easier to escape the planet's gravity from GEO than from the surface.

Not only would this enable multiple launches daily, it is, unlike the space elevator, readily achievable with today's technology, and financially viable as well. Given NASA had an annual budget of $16.2 billion for 2005, and a nuclear power plant costs a cool billion to build, give or take, we could have this up and running in a few years.

Delivering Fuel

[DanielRavenNest]

When I worked at Boeing, I was in charge of a fuel-depot study.
The method we looked at was a BFG to launch the fuel into orbit.
The big gun used hydrogen gas that is quickly heated in a heat
exchanger, then pushes a 600 kg projectile to 2/3 of orbital
speed. The projectile uses some onboard fuel to go the rest
of the way to orbit, then delivers the remaining 100 kg of fuel
to the orbital gas station. The projectile de-orbits and is
recovered to be reused. The projectile is rugged enough that
it can land on anything without damage.

The big gun is very cheap ($100M) compared to electromagnetic
launchers, because it is basically a length of pipe, compared
to a series of coils, switches, and big power supplies. On the
other hand, it is more expensive to operate.

The velocity split between the gun and the projectile depends
on the size of the projectile and how much traffic there is to
orbit. For the case we were studying, delivering fuel to
carry comsats to GEO, we were launching 100 kg a day, or 30 tons/yr
(allowing for downtime).

DRN

Re:Delivering Fuel

[rufty_tufty]

Attempt to use BFG to get into orbit - mostly successful, damn politics though.
http://www.astronautix.com/articles/abroject.htm

Re:Delivering Fuel

[tarpitcod]

I wonder if it is feasible to fire a solid block of ice (projectile shaped) into orbit. I wonder how much would ablate due to frictional heating. If you use a large enough electrical arc at the base you could use some of the ice of the projectile as the reaction mass.

The density is obviously lower than liquid water - but theres no throw away / reuse of the casing required.

Making the projectiles would require freezing water into the projectile form. It may be cost effective to make a larger solid ice projectile and accept the ablative loss.

If you really want to get serious about space exploration you have to consider the energy density of what your sending. The best use of the ice / water on orbit may be as reaction mass for a nuclear thermal rocket.

--Tarp

Re:Hmmm

[Eivind]

Is 11km really enough that you don't need to worry about air-friction emerging from the tube at escape-velocity ? (well almost, you said geosynch orbit. But that is like 90% escape-velocity anyway)

I very very very much doubt it. Even at 31km you still have 1% of the sea-level air-pressure, and at 9km healthy people can still breathe unaided. (as witnessed by the fact that people have climbed Mt. Everest without oxygen)

I don't know the air-pressure at 11km, but I'd guess around 15% of that at sea-level. Are you suggesting that punching trough 15% of sea-level air at speeds around 40.000km/h causes negligble frictional losses ?

I haven't done the math, but I think it's more likely the resulting friction would make re-entry look gentle, thus you'd need to start out going *even* faster to compensate the frictional losses.

In short, I think releasing a spacecraft at 11km with sufficient speed to reach geosynch is impossible, you would have to release it with such a speed that it'd immediately burn up.

Not necessarily.

[WindBourne]

Assume it is water to be split. First it has easy requirements for storage. Compared to h2 and o2, it is positively trivial to store and work with (in liquid and solid form). 2'nd, this does not need to be shot up there. It could also be shot up an electronic railgun, or a maglev, to get the initial acceleration. It should be possible to get it going into top subsonic and then allow a much smaller rocket to take it up. Nice advantage of this, is that it could be used on a continutal basis for other cargo that is relatively inert to high Gs.

Re:In outer space the asteroid captures YOU!

[mwheeler01]

Given the mass of a space station or an asteriod, the attraction of gravity really wouldn't have any real noticeable pull on either object. The asteroid would have to be ginourmous, and therefore unmanageable to have any real pull and I think at that point they start calling them small planets.