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ELECTRIC PROPULSION FOR SATELLITES
by Max LangeNew satellites are soon to be powered by so called electric propulsion systems. Probably everyone has read about so called ion propulsion systems in science fiction novels, allowing astronauts to travel long distances in space. Even though such technical miracles are not available today, a small version of such an electric rocket motor, for the use with satellites, has been developed in Germany. Its first application is planned for the new European news satellite Artemis.
Electric propulsion systems, unlike the traditional chemical engines, generate only little thrust, such not being able to lift-off a rocket from the earth. However, these systems are well capable for a long-term operation over days or weeks to effect orbital and position changes of satellites. Also, they don't need much fuel, but large amounts of electric energy which can be easily supplied by the solar generators of modern satellites.
In the RIT-10 electric propulsion, which has been developed by the University of Gießen and which Dasa is preparing for operation with the Artemis satellite, a noble gas is ionized and then accelerated. The system's 30 km/sec exit flow speed is well superior to all chemical engines, which can reach 4,5 km/sec at the best. However, RIT-10's big advantage is the variability of the thrust from 0,3 to 25 mN (millinewton). At 15 mN of thrust only 500 watts of electrical power are used.
RIT-10 was already successfully tested five years ago on board the European technology satellite Eureca. The test had to be terminated early though, due to a short in a cable.
Before Artemis is launched, the Atos electric propulsion system of the University of Stuttgart will be in space. Atos is installed on board the amateur radio satellite Amsat-P3D which is to be launched next year with the third test launch of Ariane 5. Atos is a so called Arcjet motor, which is heating fuel through a light arc and ejecting it with high speed. This engine generates a relatively high thrust of 115 mN.
The University of Gießen is meanwhile working on an even stronger ion engine with approximately 200 mN of thrust, and Stuttgart is working on a plasma propulsion for even higher thrust values. The German Aerospace Research Institute (DLR) is currently evaluating if the planned European moon mission Small-1 can be equipped with such an ion engine.
Groups in England, France, and the USA are working on this engine technology also. NASA has been experimenting with such propulsion systems since the sixties. A first practical test is planned for the New Millennium space probe, scheduled for launch in 1998.
From page 48 of FLUG REVUE 12/96
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Last updated November 19, 1996