France to debut plasma propulsion

Villaroche-Engineers at French aerospace engine constructor SNECMA Moteurs are busily preparing for the launch of Europe's first satellite equipped with plasma thrusters. Chartered by France's National Center for Space Research, the Stentor experimental telecommunication satellite will be placed in orbit early next year. It will carry four plasma thrusters, two manufactured by SNECMA, and two supplied by the Russian company Fakel, a pioneer in plasma propulsion technology.

Developed by the Soviets to control satellite altitude, plasma propulsion has been regarded as too expensive by the West. SNECMA, however, began collaborating with the Russians in the early 1990s to make plasma propulsion more practical. With launch of the Stentor, SNECMA believes the technology will emerge as a viable option for future space exploration.

"Thanks to plasma propulsion, one can carry less fuel for the same performance," explains Pierre Dumazert, plasma propulsion manager at SNECMA Moteurs. "The saving in mass can be a determining factor when considering the overall profitability of a satellite."

Dumazert calculates that by replacing chemical propulsion for the altitude control of geo-stationary telecommunication satellites, plasma engines can save approximately 600 to 700 Kg on a takeoff mass of 3.5 metric tons. The weight savings, Dumazert asserts, can be used either to boost payload, or to increase operating life of the satellite.

In contrast to large quantities of chemical propellants, plasma propulsion generates thrust using xenon and electricity. Cathode-generated electron bombardment of xenon atoms creates an electron/xenon ion mixture. An electric field accelerates the plasma while an orthogonal magnetic field induces a circular movement. This motion boosts thruster efficiency by increasing the probability of collisions between atoms and electrons.

On leaving the magnetic field, the electrons are attracted by the system's anode to complete the electrical circuit. The ions themselves are ejected from the engine to produce a force sufficient enough to propel a satellite in zero gravity.

Plasma propulsion for the present is limited to small thrusters for satellite altitude control, but SNECMA is working on higher power engines that in five to ten years may place satellites in orbit. "It is possible that we will be able to eliminate all liquid fuel on certain satellites, nearly doubling their payload," says Dumazert.