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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
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
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.
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
- flight thruster is awaiting integration, fit checks into the
structure have been performed
- fuel supply unit has been delivered and awaiting integration
- power supply electronics are in their final stage of assembly
- launch date: slated for September 1996
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.
- Institute for Space Systems
, University of Stuttgart, Germany
- Arcjet Thruster
Last updated: Nov 12, 1996
by Ralf Zimmermann, DL1FDT