DESIGN AND TEST OF THERMAL VACUUM CHAMBERS FOR TESTING OF ELECTRIC PROPULSION SYSTEMS INTEGRATED IN CUBESAT

As the usage of small satellites is increasingly associated with commercial interests and economic success is strongly linked to the life-time of satellites, propulsion systems for drag compensation and general mission flexibility becomes more and more important. Electric propulsion (EP) offers high specific impulse, thereby reducing the amount of propellant, weight, and system complexity needed for the same maneuver capability, as compared to chemical propulsion systems. Especially in the market of small satellites (<50 kg), which presently shows an exponential annual increase in the number of satellite being launched, EP is becoming the preferred choice for many mission scenarios.
In order to ensure proper functionality of all propulsion components, extensive testing on ground becomes mandatory. However, propulsion system testing is a very complex task as the required tests involve a large number of parameters such as exhaust plume properties, generated thrust, thermal characteristics, and longevity.
The CubeSat mission CLIMB will use a FEEP thruster to raise its orbit from 500 km to about 1000 km (apogee altitude). In preparation of this mission, and to identify solution for dealing with the thermal load on the spacecraft, generated by the propulsion system, a series of thermal vacuum tests was conducted. For those tests, two new thermal vacuum facilities were designed and operated. In extension of the existing facilities at FOTEC, the new TVC allows testing of larger test items (e.g. nanosatellites with deployed solar array), extended temperature range and significantly increased heating and cooling rate. Furthermore, in order to allow operation of the thruster during a thermal vacuum test, the University of Applied Sciences Wiener Neustadt (FHWN) has developed a new test facility suitable for such tests.
The series of tests with those two TVCs served to identify the optimal thermal control system (consisting of a suitable thermal path from the thruster to a heat rejection plate) and its characteristic such as material choice, surface properties etc. The present paper summarizes the two TVC designs and the test results and provides an outlook of the operational scheme, which was developed to ensure proper operation of the propulsion system for the 3 years mission time.