New satellite thruster could run on thin air for low-orbit or Mars missions

An electric thruster using thin air as propellant could create a “new class” of satellites for long-life flights in low orbit and even around Mars, the European Space Agency (ESA) has said.

The ESA claimed a “world first” after leading a team which built and fired the thruster in laboratory testing. The agency hopes the system, developed by Sitael in Italy, could propel satellites to enable long flights in the upper atmosphere with no on-board fuel.

In low orbits around 200km above the Earth, air molecules hit satellites and cause drag, gradually slowing them down and causing them to lose altitude. Electric thrusters can compensate for the drag but have previously relied on propellants such as xenon, which kept the ESA’s GOCE gravity mapper in orbit at 250km for five years before running out.

The new thruster could “scoop up” air molecules at typical speeds of 7.8km/s. The system has no valves or complex parts, only needing power for coils and electrodes which give particles electric charge. The charged particles are accelerated and ejected to provide thrust.

“You have got a renewable resource that’s right there – all you need to do is add electrical power which you can get from solar arrays, so it takes away those lifetime limits due to the drag,” said spacecraft engineer Peter Roberts from the University of Manchester. Roberts is scientific coordinator on the Discoverer programme, a separate EU-funded research project also exploring atmosphere-breathing electric propulsion.

Air-breathing satellites’ long lives could make low-orbits more commercially viable, Roberts said.

“Most earth observation satellites actually have relatively long lifetimes, but they achieve that by flying at higher altitudes to avoid the vast majority of the drag,” he told Professional Engineering. “If you can halve the altitude, you can halve the diameter of the aperture of a telescope and still get the same resolution imagery.”

The ESA first tested its dual-stage thruster with xenon gathered from a particle beam generator in a vacuum chamber. The agency then partially replaced the xenon with high-speed nitrogen and oxygen, mimicking the atmosphere at 200km altitude.

“When the xenon-based blue colour of the engine plume changed to purple, we knew we’d succeeded,” said ESA engineer Louis Walpot. “This result means air-breathing electric propulsion is no longer simply a theory but a tangible, working concept, ready to be developed to serve one day as the basis of a new class of missions.”

Atmosphere-breathing electric thrusters could also work in the outer fringe atmospheres of other planets, the ESA said, potentially drawing on the carbon dioxide atmosphere of Mars, for example.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.