How does the electric propulsion work in satellites

New trend: electric drive in space

Cars with electric motors are no longer uncommon. Space engineers are now increasingly relying on “electric”: the “Eutelsat 172B” satellite is intended to prove that such a drive works and also saves costs.

“Eutelsat 172B” is scheduled to take off in June. It is the first telecommunications satellite built in Europe that is completely electrically powered. "We are at the point where electric drives are no longer classified as pioneering [technologies]," says Lisa Martin Perez from the German Aerospace Center (DLR). "I think sooner or later everything will be electric."

At Airbus, “Eutelsat 172B” is just the beginning. Recently, 50 percent of customers have opted for a purely electric drive for new orders.

Less fuel needed

This has one major advantage: it is significantly more efficient and has to take a lot less fuel into space. This leaves either more space for the payload or the satellite is lighter. This saves the operator money, because cheaper launchers can be used for smaller satellites to travel into space.

Electric space drives work very differently than e-cars or electrically powered drones. There is a simple reason for this, as David Futterer from DLR explains: In a vacuum, there is nothing to repel against. “In space you need some kind of fuel to move forward.” With classic drives, these are chemicals that react with one another. “You can actually think of it as a small explosion,” says Futterer. This creates thrust that pushes the spacecraft forward.

Ionized gas provides thrust

“In the electric engine you have a noble gas, usually xenon, which is ionized, that is, electrically excited.” An electric field then ejects it from the drive nozzle, thus generating thrust. This is why one speaks of an ion thruster. The necessary electricity comes from solar panels, which are used in telecommunications satellites anyway.

The big disadvantage: The thrust is significantly weaker than with a chemical engine. This is why electric drives have so far mainly been used to correct the position in space: when the satellite has arrived in its orbit at an altitude of 36,000 kilometers, the orbit must occasionally be corrected so that it does not drift.

However, “Eutelsat 172B” now also uses an electric drive for its journey: after taking off from the European spaceport in Kourou in French Guiana, the Ariane rocket places it in a so-called transfer orbit. From there, the satellite must come into its final orbit on its own. Because of the weak push, it takes significantly longer than models based on the old principle to reach the goal - several months instead of a few days. It also takes longer before the operator can earn money with his new satellite.

"The price pressure is getting bigger"

In 2015, the American Airbus rival Boeing was the first manufacturer to build all-electric telecommunications satellites and send them into space. With the support of Esa, the Bremen-based company OHB is developing its Electra platform for small, electrically powered telecommunications satellites weighing less than three tons. A first start is planned for 2021.

DLR expert Futterer sees the reasons for the electrical trend on the one hand in the advancing technological maturity, but also in a rethinking in the market: "The price pressure on satellite operators is increasing, and with it the acceptance of new, cost-saving technologies." Arnaud de Rosnay, Director of the satellite business at the manufacturer Airbus Defense and Space, says: “My analysis is that the satellites adapt to the launchers.” New load carriers have come onto the market that offer interesting prices, but only have space for smaller loads.

Researchers as pioneers

For research missions into deep space, electric drives have been used for a long time. In 2003, for example, the first European lunar probe “Smart-1” flew to travel with the earth. First, the American space probe "Deep Space 1" used an ion drive. Because electric drives accelerate continuously for much longer, they ultimately reach very high speeds.

NASA is also researching electric drives with a view to future manned Mars missions. "If you actually want to transport people with electric drives, the engines have to be much larger and deliver a lot more thrust," says Lisa Partin Perez from DLR. "We're working on that."

science.ORF.at/dpa

More on this topic: