Qualifciation test series of the indium needle FEEP micro-propulsion system for LISA Pathfinder

Abstract

The Laser Interferometer Space Antenna project (LISA) is a co-operative program between ESA and NASA to detect gravitational waves by measuring distortions in the space–time fabric. LISA Pathfinder is the precursor mission to LISA designed to validate the core technologies intended for LISA. One of the enabling technologies is the micro-propulsion system based on field emission thrusters necessary to achieve the uniquely stringent propulsion requirements. A consortium consisting of Astrium GmbH and the University of Applied Sciences Wiener Neustadt (formerly AIT) was commissioned by ESA to develop and qualify the micro-propulsion system based on the Indium Needle FEEP technology. Several successful tests have verified the proper Needle Field Emission Electric Propulsion (FEEP) operation and the thermal and mechanical design of subcomponents of the developed system. For all functional tests, the flight representative Power Control Unit developed by SELEX Galileo S.p.A (also responsible for the Micro-Propulsion Subsystem (MPS) development) was used. Measurements have shown the exceptional stability of the thruster. An acceptance test of one Thruster Cluster Assembly (TCA) over 3600 h has shown the stable long term operation of the developed system. During the acceptance test compliance to all the applicable requirements have been shown such as a thrust resolution of 0.1 μN, thrust range capability between 0 and 100 μN, thrust overshoot much lower than the required 0.3 μN+3% and many others. In particular important is the voltage stability of the thruster (±1% over the duration of the testing) and the confirmation of the very low thrust noise. Based on the acceptance test the lifetime of the thruster is expected to exceed 39,000 h generating a total impulse bit of 6300 Ns at an average thrust level of 50 μN. A flight representative qualification model of the Needle FEEP Cluster Assembly (DM1) equipped with one active TCA has performed a qualification program consisting of acceptance, vibration, shock, and thermal vacuum test. During the last test, the thermal vacuum test (TVT), a performance decrease was observed. According to a preliminary analysis, this performance decrease is not linked to the thermal conditions simulated in the TVT but might be rather linked to secondary effects of the TVT set-up.