ESA tests electric ion thruster fueled only by air molecules

The thruster collects molecules from the top of the atmosphere and gives them electric charges so they can be accelerated and ejected to provide thrust. The concept was developed and tested in by Italian aerospace company Sitael, which tested a prototype in a vacuum environment that mimicked conditions found 200 km above the Earth’s surface.

The most challenging part of the project was developing an intake system that would compress the collected air molecules rather than allow them to bounce about randomly. They needed a thruster that would ensure better charging and acceleration, something hard to achieve with traditional electric propulsion designs.

Molecules of air at the top of the atmosphere are captured by a novel type of intake, then collected and compressed to the point of becoming thermalised ionised plasma, at which point they can be given an electric charge to accelerate them and eject them to provide thrust.

ESA/A. Di Giacomo

Sitael collaborated with QuinteScience in Poland for the solution – A dual-stage thruster that electrically charges the incoming air so it provides thrust once it’s ejected. This system allows the thruster to eject the charged air molecules at a typical speed of 7.8 km/s.

And the design is ridiculously simple – There are no valves or complex parts, and it all works on a simple, passive basis. All that is needed is power to the coils and electrodes, creating an extremely robust drag-compensation system.

The air-breathing thruster was initially run with standard xenon propellant, causing a bluish plume, which was then progressively replaced with a mixture of nitrogen and oxygen to represent Earth’s atmosphere. Success was marked by the thruster plume changing to purple.

ESA/Sitael

According to ESA’s Louis Walpot, the research 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.”

Why this new concept is important
Rocket motors are traditionally fueled by a mixture of gases containing argon, freon, nitrogen, and propane. And the most powerful thrusters use a bipropellant mixture of monomethylhydrazine and dinitrogen tetroxide, according to Tech Times.

Air-breathing thruster using a mixture of nitrogen and oxygen, Notice the purple-pink plume.

ESA

Using the bipropellant mixture is a tricky process because it ignites an explosion. However, if used in fueling a thruster, the mixture helps produce around 2.7 tons of thrust and burn 9.8 tons of propellant in a span of 1,000 seconds. This has been used to propel satellites into low-Earth orbit and was used to power the Space Shuttle’s maneuvering system.

But the ESA’s new electric ion thruster propelled by air molecules would make developing thrusters much safer for aeronautical engineers and pave the way for longer missions that would have less of a risk for explosions.

ESA’s Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) gravity-mapper flew as low as 250 km (158 miles) for more than five years thanks to an electric ion thruster that continuously compensated for air drag. But once the 40 kilograms of xenon it used as a propellant was used up, the mission was over. Now, with the air-breathing thruster, time in orbit could be unlimited.