Electric thruster sucks in the scarce air molecules at the top of the Earth’s atmosphere, using them as propellant to fight drag
The European Space Agency (ESA) has test-fired an engine that opens the path for a novel class of low-flying Earth-orbiting space missions. Called an air-breathing electric thruster, it is designed to work at the top of the Earth’s atmosphere. It sucks in the scarce air molecules and uses them as propellant. Low-flying satellites, those in orbits of about 200-300km altitude, are gradually pulled out of orbit by the drag of the residual atmosphere.
For example, ESA’s GOCE mission operated in this region of space. It flew for five years thanks to an electric thruster that used xenon fuel to counteract the atmospheric drag. When the 40kg of xenon ran out, however, the spacecraft fell to Earth and burned up in the atmosphere.