A plasma engine for exploring space

The machine starts up. A light gradually appears through the little window on top. As it gains in intensity, the light goes from a hazy, pale pink to purplish-blue. This is plasma, a substance that could be used in the future to control the movement of small satellites and space probes.

This machine is part of Félicien Filleul’s Master’s project. A 26-year-old physics student at EPFL, Filleul also did a Minor in Space Technologies. Through this project, which he did at the Swiss Plasma Center in collaboration with the Space Engineering Center (eSpace), Filleul contributed to the effort to develop plasma-fueled satellite propulsion engines. Research on this groundbreaking technology has been ongoing for around 10 years.

“Plasma engines could work really well with small satellites like Cubsats, which are sent into orbit without any way to control or adjust how they move,” said Filleul. So the objective is to develop a system of low-power but steady thrusters that are highly precise and consume little energy. Scientists could use them to maintain or correct the satellites’ orbit or orientation, or to set up a constellation of Cubsats, in which several of these small satellites are networked for the needs of individual missions.

Particle soup
“Plasma is perfect for this type of propulsion,” said Filleul. “We make it out of xenon gas, a single gram of which provides 10 times more acceleration than the same quantity of traditional fuels.”

Plasma is neither solid, liquid nor gas – it is the fourth state of matter. While less familiar than the other three states of matter, plasma is used in everyday items such as neon signs and television screens. It is very common in the universe and can be found in the sun and other stars.

Plasma is made by heating xenon in a vacuum at temperatures so high that the electrons are pulled out of their orbit around the nucleus. They come to form a ‘soup’ of highly charged particles. More plasma can be generated by sending a helicon-type electromagnetic wave – which spreads as it turns like a corkscrew – through the soup. Scientists can freely adjust the substance’s density by controlling the wave’s intensity.

Heading for Mercury
Filleul’s project focused on the antenna used to generate the helicon wave. The antenna, designed and developed at EPFL by the startup Helyssen, lends itself to plasma engines that are both small and light. And those are two major concerns in the area of space technology. “My job was to test the antenna with different densities and qualities of plasma, in order to find the ones that will work best in space,” said Filleul.

But the fun doesn’t stop there for Filleul. Next year, he will work at the European Space Agency (ESA) on a plasma-propulsion system for the BepiColombo mission, which in 2018 will launch two probes headed for the planet Mercury.