Experience of Using COTS for Space Ion-Thruster In Space and Radiation Hardness Testing
Robert-Jan Koopmans, Emre Ceribas, Thomas Hörbe, Bernhard Seifert, René Sedmik
FOTEC Forschungs- und Technologietransfer GmbH, Wiener Neustadt, Austria
Abstract
The IFM (Indium FEEP (Field Effect Emission Propulsion) Multi-Emitter) Nano Thruster currently under development at FOTEC was originally intended to be used in CubeSats operating in LEO (Low Earth Orbit). To reduce the costs as much as possible and thus make it attractive for CubeSat missions, the PPU (Power Processing Unit) consists entirely of COTS (Commercial Off-the-Shelf) components. The demand for propulsion systems for small satellites in orbits beyond LEO is growing. The corresponding radiation environment in MEO (Medium Earth Orbit) and beyond is harsher than in LEO. For this reason, a test campaign was designed and executed to find out how resilient the current PPU is to radiation.
The initial goal of the tests was to determine the functionality of the PPU up to level P, or 30 krad. The test was then further extended to level R, or 100 krad, and level A, or 300 krad. Rather than qualifying individual components according ECSS and MIL standards, system level radiation tests were conducted for which no standard exists. Three types of total ionizing dose (TID) tests were conducted at the TEC-Laboratory (Seibersdorf, Austria):
- a low dose rate test (0.015 rad/s) of the epoxy glue used to fix the emitter crown
- a low dose rate test (0.015 rad/s) of the PPU
- a high dose rate test (1.5 rad/s) of the PPU
As the crown emitter in the thruster can only operate under vacuum conditions, a functional test box was designed and built to mimic the firing of the crown emitters during irradiation.
During the test campaign, the irradiation of the PPU was several times interrupted. During these interruptions a full characterization of the PPU was performed. It could thus be determined which components had a reduced performance or were completely broken. The same characterization was performed with a PPU that had undergone the same firing simulation, but was not irradiated. In this way, a distinction could be made between components failing due to gamma radiation and due to other problems. In some cases, bipolar and CMOS devices demonstrate a sensitivity of the electrical parameter degradation at low dose rates. In order to determine the extent of this sensitivity the same test was performed three more times at a high dose rate. Each time the orientation of the PPU w.r.t. the radiation source was changed to investigate the effect of internal scattering of the gamma rays. At the end of the irradiation, all PPUs were subjected to accelerated aging by means of a thermal vacuum test at 100°C for 1 week at FOTEC. After this period, a full characterization of the PPUs were performed again.
Acknowledgments
The authors are grateful to the help of Seibersdorf Laboratories received during the preparation and execution of the test campaign at the TEC-Laboratory (Seibersdorf, Austria). The work leading to the results is funded by ESA under contract number 4000116898/16/NL/EM.