Ground-based experimental study on the contamination potential of a freely expanding 10 N bi-propellant thruster plume

Abstract

Satellite thruster plume constituents pose a challenge when it comes to estimating their potential to degrade or contaminate spacecraft surfaces. Therefore, ESA has commissioned a study that covers the characterization of two European bi-propellant attitude control thruster plumes and their potential contamination impact. In this regard, a freely expanding 10 N MMH/MON bi-propellant thruster plume is investigated in this ground-based experimental campaign. Methods of investigation include quartz-crystal microbalances (QCM), material sample impingement, high-speed imaging of the nozzle exit and mass spectrometry (MS) measurements. QCM experiments supply data on mass flux as well as desorption rates at temperatures ranging from 80 to 300K, which help to estimate the impact of plume gas on surfaces of different temperatures. The optical and chemical analysis of actual spacecraft surface material witness coupons that were exposed to the plume under a wide range of angles, spanning from plume centreline to the backflow region, complements this study. Furthermore, high-speed imaging of the thruster nozzle supports the interpretation of results with information on ejected droplet velocities, trajectories and size distribution, especially regarding potential droplet impact features which were identified on witness materials in the first part of this on-going study.