This Startup Thinks It Can Make Rocket Fuel From Water. General Galactic, cofounded by a former SpaceX engineer, plans to test its water-based propellant this fall. If successful, it could help usher in a new era of space travel. There's been this hand-wave, this assumption, this at the core of our long-term space programs. If we can return astronauts to the moon, we'll find ice there.