Recent experiments on thruster plume induced contamination

Abstract

Contamination induced by orbital reaction control thruster plumes is known to be degrading the thermo-optical properties of spacecraft functional surfaces, distorting measurements from sensitive instrumentation and impeding the detection of organics. Scientists and engineers use models describing the transport of solid, liquid and gaseous ejecta from thrusters. However, these models are backed by only very few reliable experiments, as it is challenging to maintain the required background pressure for free plume expansion in ground-based test facilities, and systematic experiments in orbit are expensive. The DLR high-vacuum plume test facility Göttingen for chemical thrusters (STG-CT) is a unique cryogenically pumped vacuum chamber, that is capable of maintaining a free plume expansion during (pulsed) operation of reaction control thrusters up to the 20 Newton thrust level. This is achieved by cooling the test section walls to just over four Kelvin. A standard test setup involves in-situ mass spectrometry, quartz crystal microbalances, material samples and a high-speed camera that monitors the nozzle exit. We report on recent test campaigns involving monopropellant hydrazine thrusters and first results of current contamination experiments with bipropellant thrusters.