Plasma physical and material physical aspects of the application of atmospheric gases as a propellant for Ion-Thruster of the RIT-Type

摘要

It is very important to compensate all kind of disturbances to maintain the satellite in the desired orbit. The propulsion system needs a quite huge amount of propellant to generate the required thrusts. This is valid either for chemical and electric propulsion systems, whereas the electric system needs less propellant mass.The limited propellant mass of the satellite and the resulting thrust-ability are often the limiting factor for the mission lifetime of the spacecraft, especially when the decelerating atmospheric drag is comparable high in low target orbits.The usage of surrounding atmospheric gases as a propellant is an interesting and promising approach to extend the mission lifetime of a satellite and to reduce launch coast and launch mass. In combination with an electric propulsion system, where the propellant is accelerated electrically and not burned, high beam velocities and the required thrust levels can be achieved. The objective of this thesis was the proof of principle, if and under which kind of limitations a radio frequency ion thruster can be operated with atmospheric gases and to perform the correlated characterizations of the propulsion system. Therefore, a RIT in the ARTEMIS-configuration was operated and tested with different propellants. In addition to the performance characterization, lifetime tests were also performed. Beside Oxygen, Nitrogen and Xenon (as a reference gas) two additional gas mixtures have been tested, which were based on the target orbit height. A numerical performance model was derived from the measured values, compared, and verified with the developed theory. To improve the overall performance and the resistance of the thruster, some useful modifications have been identified and implemented during the tests.It could be demonstrated that the RIT-technology is well suited for the application with atmospheric propellants and that high thrust levels can be achieved even with this propellants. The observed dissociation of oxygen and the resulting effects, which have been identified in some measurements, should be investigated in more detail with the help of plasma monitors and mass spectrometers. In addition, the design and tests of the propellant gathering unit have to be considered and will require further work.