Science-fiction-like electric thruster uses air particles as fuel

7 Mar 2018

The new air-breathing ion thruster could propel satellites into orbit for years on end. Image: ESA/Sitael

ESA has unveiled some science-fiction-like technology with the first firing of an electric thruster that could power spacecraft for years on end.

Since humans first escaped Earth’s orbit almost 60 years ago, we have been heavily reliant on chemical rocket propulsion to get us there, and even when we look to going to the moon or Mars.

However, research into new ways to move spacecraft around continues, with the European Space Agency (ESA) announcing, in a world-first, that it has built and fired an electric thruster to ingest scarce air molecules from the top of the atmosphere.

Future Human

By replacing onboard propellant with atmospheric molecules as fuel, a whole new class of satellites could be sustained in orbit for extremely long periods of time, and could be used at the outer fringes of atmospheres of other planets, such as drawing on the carbon dioxide of Mars.

The thruster was developed by a firm called Sitael in Italy and performed in a large vacuum chamber that simulates the environment at an altitude of 200km.

Unlike chemical engines, this thruster has no valves or complex parts as everything works on a passive basis, with the only requirement being power to the coils and electrodes, creating an extremely robust drag-compensation system.

One of the greatest challenges the engineers faced in its development was to design a new type of intake that can efficiently collect the air molecules it needs for fuel.

Electric spacecraft

A future air-breathing space mission in low orbit around Earth. Propelled at around 7.8kps, the satellite would ingest air molecules from the top of the atmosphere (left) to fire its ion thruster (right), providing thrust to overcome atmospheric drag, allowing it to stay in low orbit indefinitely. Image: ESA-Medialab/A Di Giacomo

‘No longer simply a theory’

Sitael designed a dual-stage thruster to ensure better charging and acceleration of the incoming air, which is harder to achieve than in traditional electric propulsion designs.

For example, ESA’s GOCE satellite managed to travel in Earth’s low orbit for more than five years with an early electric thruster, but was limited by the 40kg of xenon it carried on board that acted as the propellant.

However, this latest thruster partially replaced xenon with a nitrogen-oxygen mixture, showing it could function off air particles.

“When the xenon-based blue colour of the engine plume changed to purple, we knew we’d succeeded,” said Louis Walpot of ESA.

“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.”

Colm Gorey was a senior journalist with Silicon Republic