Research on Thruster Plume Flow and Plume Induced Contamination at DLR, and Applications to Space Exploration Flight Projects

Abstract

Space mission science objectives and evolving scientific instrumentation place ever more challenging constraints on the characterization and control of spacecraft induced environments and contamination. This is demonstrated by current missions and flight projects, such as Mars 2020 and Europa Clipper, and particularly by mission concepts in formulation and development, as exemplified by Europa and Enceladus lander missions, and comet sampling mission concepts. Contamination science is a critical component of upcoming and proposed missions focused on the detection of organics and life, and spacecraft plume induced contamination is a major contamination vector for all types of space exploration missions: orbiters, lander, rovers and sampling missions. Plumes of chemical thrusters interact with spacecraft surfaces, as the vacuum environment allows them to expand to well upstream of the nozzle exit plane. Thruster plumes are thus a source of parasitic forces, moments, heat loads, and particularly of contamination and surface erosion. Plume contaminants may be gaseous, liquid and/or solid and have been demonstrated to severely degrade functional surfaces on spacecraft, affecting power and thermal budgets, as well as scientific payloads and mission design. Despite decades of research effort both on orbit and in ground-based test facilities, obtaining reliable experimental data to construct models with sufficient accuracy remains a challenging task. The Spacecraft Department in the DLR Institute for Aerodynamics and Flow Technology has a long history in researching plume flow and plume impingement effects in vacuum environments, during which it became apparent that conventional, mechanically pumped vacuum chambers are insufficient to replicate the free thruster plume expansion and thus adequately reproduce the transport of potential plume contaminants in space. The unique DLR High-Vacuum Plume Test Facility for Chemical Thrusters (STG-CT) was designed and built specifically to study the plume expansion of actual orbital thrusters and to assess their contamination potential. This talk discusses the challenges in studying plume induced contamination in ground-based test facilities and the particular capabilities of STG-CT, as currently exploited in collaboration with JPL Contamination Control Engineering and the Europa Lander Project.