You’re right, there’s no air in space, but there’s enough to squirt about in very low orbits
Schema of the European Space Agency’s air breathing electric propulsion engine
The European Space Agency has hailed the successful test of an air-breathing engine that works in space.
The engines don’t need the oxygen found in air to burn. Instead, as the ESA has explained here, the idea is to collect air, compress it, give it a charge and then squirt it out to provide thrust.
The engine has no moving parts and all that’s needed to power the engine is electricity. Spacecraft can generally harvest that from the Sun.
The concept’s been used before by the ESA’s GOCE gravity-mapping mission, but it carried 40kg of Xenon gas to provide it with thrust so it could change altitude when its orbit became low. And once it ran out of propellant … you can guess the rest.
Hence the interest in an engine that can harvest air to keep a satellite aloft and in very low orbits. Anything in such an orbit that wants to stay there will need a periodic boost, as the drag caused by the outer reaches of the atmosphere slow spacecraft and degrade their orbits.
The tests were done in a vacuum chamber that simulated travel at 7.8 km/second at an altitude of 200km. The ESA said the tricky part was designing the engine so that it collected air, rather than having it bounce off.
Of course there’s plenty more work to be done to build a space-ready engine of this type. The ESA has not announced plans to do so, but is nonetheless chuffed that its boffins have proven this concept because there’s no reason it wont work on other planets that possess an atmosphere. If they’re correct, that raises the prospect of sending sats to all sorts of places without having to worry about shipping fuel, too. Which means either more satellites, or bigger payloads, or both! ®