There’s been this hand-wave, this assumption, this yada yada at the core of our long-term space programs. If we can return astronauts to the moon, we’ll find ice there. And if we find that ice in sufficient quantities, we’ll break it down into hydrogen and oxygen, and yada yada, we’ll use that fuel to fly deeper into the solar system, maybe even to Mars. And if we get to Mars, we’ll find even more ice on the Red Planet. We’ll mine that, combine it with the carbon dioxide in the atmosphere, and yada yada, we’ll use that to fly the astronauts back.

It’s an idea that’s been around since the Apollo era and has been touted in recent years by the likes of former NASA administrator Bill Nelson and SpaceX’s Elon Musk. But here’s the thing: No one has ever successfully turned water into rocket fuel, not for a spaceship of any significant size. A startup called General Galactic, led by a pair of twentysomething engineers, is aiming to be the first.

This fall, General Galactic plans to fly an 1,100-pound satellite, using water to supply its only propellant in-orbit. If it works, it not only could start to solve the yada yada problem, it could make US satellites more maneuverable at a time when there’s a growing possibility of a conflict in space.

“Everybody wants to go build a moon base or a Mars base or whatever. Who's going to pay for it? How does it actually work?” asks Halen Mattison, CEO of General Galactic. “Our vision is to go build a gas station on Mars,” he adds, “but also eventually build out the refueling network” in between.