New spacecraft propulsion system ready for tests

Posted by Emma Woollacott

While electric propulsion (EP) of spacecraft is already competing successfully with chemical thrusters, the cost has been extremely high.

But a team at the Institute of Plasma Physics and Laser Microfusion in Warsaw says it's been able to cut the cost dramatically by using a new propellant.

EP - frequently used for for attitude control, as well as orbit transfer and as for the main propulsion system for deep space missions - generally relies on xenon.

But the Warsaw team has created a Hall effect thruster optimised to work with krypton, a much more affordable noble gas.

Chemical propulsion is invaluable for the launch of payloads into space. The thrust, generated exclusively from the energy released by combustion of the propellants, is very large, but limited to durations of the order of seconds or minutes.

In space, however, where atmospheric drag is negligible, technologies delivering much lower thrust over months or years make much more sense.

Hall effect thrusters convert the propellant into a plasma and produce thrust using an external electrical power source, most typically solar panels. Charged plasma particles can be accelerated by an electric field to high velocities, producing a low thrust - but operating over long durations.

They've been in use since the 1970s in unmanned space flights, where they make it possible to manoeuvre precisely and correct satellite orbits. Recently, devices of this type have also increasingly been used as the main propulsion system for deep space missions.

The propellant used in the vast majority of Hall effect thrusters is xenon, a very rare and therefore expensive noble gas. Krypton, though, is up to ten times less expensive. And while it takes slightly more energy to produce krypton ions, they are lighter than xenon ions and therefore require lower acceleration voltages to achieve the same velocity.

The new thruster is a medium-power, continuous-thrust propulsion device, weighing less than 5kg and operating at a power of about half a kilowatt.

“The SMART-1 lunar space probe sent by the European Space Agency (ESA) had a xenon thruster with power below 2 kW. It accelerated the vehicle by 3,6 km/s," says Dr Serge Barral from IPPLM.

"Our thruster could therefore prove suitable as a main propulsion system in small spacecrafts."

The team now plans to test its prototype in vacuum conditions.

“If the outcome of the tests is positive, optimization of the device and a round of assessment tests will follow," says project leader Dr Jacek Kurzyna.

"The project, submitted to the second PECS call (Plan for European Cooperating State, an agreement concluded between Poland and ESA), has been recommended for funding. If funding is confirmed, this project will mark the beginning of the qualification process."