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First application of an arcjet thruster for the orbit control of a non-geostationary satellite.

Fabrication Responsibility:
Dieter M. Zube (Germany)
Average Power Dissipation:
750 Watts (when on)


Developed at the Institute for Space Systems at the University of Stuttgart in Germany, the ammonia arcjet will provide for station-keeping and minor orbit adjustments after the Phase 3D spacecraft is in final orbit. Compared to the 400 Newton thrust of the primary propulsion system, this motor's puny 100 milliNewtons isn't much, however, its efficiency is much higher over long burn times. Thrust is accomplished by striking an electrical arc at the tip of the arcjet motor and then feeding a small quantity of gaseous ammonia fuel through the arc. The rapid heating expands the gas to generate highly efficient thrust. Having the Arcjet motor on board the Phase 3D spacecraft for the first time provides a long-term capability to make minor orbit adjustments to correct for the kinds of instabilities introduced by lunar and solar perturbations that are predicted to cause reentry of the OSCAR 13 spacecraft in late 1996.

The flight unit arcjet motor has been fabricated and delivered. Full duration firing tests have been conducted at the University of Stuttgart with good results. The components for the plumbing system to convey ammonia from propellant tanks, heat it to a gaseous state and meter its flow to the motor have been incorporated into the PFA.


Funded by the German Space Agency DARA the development of a 750 W ammonia arcjet for the orbit-fine-control of the amateur radio satellite AMSAT P3-D was initiated at the IRS (Institute for Space Systems, University of Stuttgart, Germany) in 1994. This "project ATOS" (Arcjet Thruster on OSCAR Satellite) is the derivative of the IRS ARTUS-arcjet family started in 1990. Changes of the thruster compared to the ARTUS engine were adaptations to the lower power level, ammonia instead of hydrazine as fuel and life-time extending measures. The ATOS-thruster will be flown on the P3-D spacecraft.

The satellite is slated for launch in the Fall of 1996 on a ARIANE-5 launch. Its basic 16h orbit will be achieved by several firings of a 400 N chemical thruster. This orbit will feature a high eccentricity and inclination (->Molnya-type) to provide long satellite visibility for its main users on the northern hemisphere. The fine tuning of the orbit will be accomplished with the ATOS-arcjet thruster. There will be a total of 52 kg of ammonia as arcjet fuel, sufficient for 600 hours of arcjet-operation or some five years of orbit control, with a one hour thruster firing scheduled every third day, the length of the thruster firing depending on the battery capacity. During a three months long lifetime test a thruster lifetime of 1010 hours had already been demonstrated in the IRS laboratories.

Performance data

 nominal power to the arcjet : 750 W
 arc current :                 7.7 A
 arc voltage :                 97 V
 mass flow :                   24 mg/s
 thrust :                      115 mN
 specific impulse :            480 s
 accomplished lifetime :       1010 h
 including                     1010 ignitions
 thruster weight :             480 g
The complete arcjet system consists of the arcjet thruster, the fuel supply unit and the power supply electronics. This power supply transforms the 28 VDC from the satellite power bus into the 800 W maximum current regulated arcjet power. This electronic module with an efficiency of 93% is designed by Dr. K. Meinzer from AMSAT DL, who is also the overall satellite project manager. The fuel supply unit regulates the flow of gaseous ammonia from the two fuel tanks to the thruster. Its ammonia resistant valves and ammonia vaporizer were supplied by a Russian space company.

Project status as of October 1995

This page originated from the original web page at the IRS, with the friendly approval of Dieter Zube. To get further information on the ATOS motor, please have a look the Web pages at the IRS in Germany.
Last updated: Nov 12, 1996
by Ralf Zimmermann, DL1FDT