It has it hand-wave, this assumption, this yada yada at the core of our long-term space programs. If we can bring astronauts back to MONTHSlet’s find ice there. And if we find that ice in sufficient quantities, we’ll break it down into hydrogen and oxygen, and yada yadawe’ll use that fuel to fly deeper into the solar system, maybe even to Mars. And when we get there Marswe will see more ice on the Red Planet. We mine that, mix it with carbon dioxide in the atmosphere, and yada yadawe will 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 administrators. Bill Nelson and SpaceX’s Elon Musk. But here’s the thing: No one has successfully turned water into rocket fuel, not for a spaceship of any significant size. A startup called General Galactic, led by a pair of twenty-something engineers, aims to be the first.

This fall, General Galactic plans to launch a 1,100-pound satellite, using water to supply its only in-orbit propellant. If it works, it doesn’t just start solving yada yada The problem is, it could make US satellites more maneuverable at a time when there is an increasing possibility of conflict in space.

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

That’s right, kindness long-term plan, at least. For starters, Mattison, a former SpaceX engineer, and its CTO, Luke Neise, a veteran of Varda Space, has purchased a spot on a Falcon 9 rocket launch. The scheduled departure is in October or later in the fall.

There are, broadly simplified, two main types of engines you can use in your spacecraft. You can get a fuel like liquid methane, maybe mix it with an oxidizer, and burn it. That’s called chemical propulsion, and every big rocket you see flying uses some variation of that method, because it gives more thrust, even if it’s less efficient.

Or you can take a gas like xenon, zap it with electricity, and shoot it out of the spacecraft, either an ionized gas or a plasma. That’s called electric propulsion—again, I’m oversimplifying. And “it’s very, very low thrust. People jokingly call it a space burp,” Mattison said. “But it lasts forever. The effectiveness is insane.” Enough burps over time can be very effective. Electric propulsion is used to keep satellites in their proper orbits and to power space probes dawnsent by NASA to explore the asteroid belt.

Water is not good for electrical or chemical activation. But it may be enough for BOTH. Unlike, say, liquid methane, you don’t have to worry about water accidentally exploding on your spacecraft or cooling it to -260 degrees Fahrenheit or boiling if your satellite is facing the sun.

General Galactic plans to demonstrate both methods during the Trinity mission. For chemical propulsion, it uses electrolysis to split water into hydrogen and oxygen, then burns the hydrogen, with oxygen as an oxidizer. For the electrical propulsion system—it’s called “hall thruster”—it will split the water, then apply enough electrical energy to turn the oxygen into plasma. From there, you use a magnetic field to shape the plasma and shoot it.