A concept image of a flying refueling craft for satellites, similar to what NASA hopes to achieve for other spacecraft.

A spaceship isn't much use if it doesn't have the juice to go somewhere. And if you're an astronaut bouncing around destinations like the moon, random asteroids, Lagrange points, and Mars, you'll probably need an interstellar gas station.

NASA has launched an "In-Space Cryogenic Propellant Storage and Transfer Demonstration Mission Concept (PDF)" study, which is essentially a call for scientific institutions around the globe to help create a space gas station. Those wishing to build a fueling stop in the sky have until May 23 to submit their proposals.

Cryogenic propellants used in rocket engines are usually made of liquid hydrogen and liquid oxygen. Both liquids reside in enormous insulated containers and are pumped through an expansion chamber, then mixed and ignited in the combustion chamber. The result is an incredible amount of power per gallon of cryogenic proellant, up to 40 percent higher than other rocket fuels.

However, there are many challenges to creating a gas station in the stars. The primary objectives of the study are to address key elements including a fail-safe way to transfer the propellants from a storage container to a ship. The difficulty is high since hydrogen tends to leak (it's the smallest element), and can eventually deteriorate the container it's stored in.

An artist's rendition of a possible space gas station (fortunately, this is not one of the NASA submissions).

There's also the need to eliminate the boil-off rate of the highly reactive liquids, an issue that could arise if the sun were to overheat the fuel storage tank. If the tank gets too hot, the liquids will essentially boil, turning into vapor, and must then be passed through a pressure release valve. While this would avert an explosion, it would also waste potential fuel.

Perhaps in a dozen generations we'll be filling up on rest stops in space, but for now, I'll stick with my 93 Octane. With an R&D cost expected to be near $200 million-$300 million for the study alone, $4-per-gallon gas suddenly doesn't sound so expensive.

(Via Network World)