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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."
"$9 a gallon? Let's just orbit a bit longer till we find a cheaper one."
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