Development of a Plasma Diagnostic System

With evermore stringent requirements towards pointing accuracy and platform stability, in both commercial and scientific missions, AirbusDS has initiated the development of micronewton class ion engines for applications in attitude control systems. Here the Friedrichshafen branch of AirbusDS pursues the development of a downscaled version of the High EfficiencyMultistage Plasma Thruster (HEMP-T), an electric thruster type currently flown on OHB’s smallGEO bus. In contrast to cold gas systems, which can deliver comparable thrust levels and are currently used as means of attitude control on such highly complex missions as LISA pathfinder, these micronewton HEMP-Ts exhibit a higher performance in terms of specific impulse as well as thrust controllability. With this they enable extended mission lifetime or propellant mass reductions while also increasing attitude control precision. Within the scope of this activity a test facility was developed, consisting of a vacuumchamber containing a thrust balance aswell as the supporting equipment such as vacuum control and data acquisition hardware. In addition to direct thrust measurements performed on each of the design iterations of the thruster it is necessary to investigate the thruster plume geometry and ion energy distribution. While direct thrust measurements, via the highly precise thrust balance already included in the existing test facility, allow for the determination of the thruster performance they do not give an insight into the specific loss mechanisms which cause the observed thrust level or specific impulse to deviate from the ideally attainable values. Here the plume shape can give an indication of the divergence losses encountered by the thruster while the energy of the expelled propellant ions can indicate deficiencies in the thruster design concerning the complex internal magnetic topology necessary for the proper operation of this type of thruster. Building on the experience gathered using an existing, rudimentary, plasma diagnostic system, as well as an extensive literature survey, this document describes the design, development and testing of a plasma diagnostic system based on a novel sensor concept which enables both plume shape determination as well as ion energy distribution measurement in a compact package. This effort includes the redesign of the sensor positioning hardware as well as the associated data acquisition system. Initially an overview of the technologies relevant to this work is given. This includes the description of the basic working principle of the thruster under investigation here, the plasma diagnostic probes which have been deemed viable candidates as an outcome of the preceding literature survey as well as a detailed overview of the existing test facility, indicating potentials for improvement with the introduction of the new diagnostic system. This introduction is followed by the description of the system engineering approach taken in the the scope of this work in order to facilitate the development of this complex diagnostic tool within the temporal and monetary limitations imposed on this project. The main portion of the work described in the following focuses on the development of the novel sensor, which is identified as the optimumsolution in the preceding system engineering section. With the supporting systems for sensor actuation, data collection and post-processing in place the work closes with an exemplary thruster test which derives an indirect thrust measurement from the data collected with the new system and comparing it with a measurement taken by the validated highly precise thrust balance. Good agreement between the two values is shown.Aerospace Engineerin