Franz Georg Hey

Parametric Study of HEMP-Thruster Downscaling to

Many on-going European Space Agency (ESA) science and earth observation missions are based on precision attitude control and formation flying. All these missions impose strong requirements on propulsion system which should provide low thrust, low noise, and high-precision thrust vectors in up to 16 directions. Also as most of these missions have a platform with limited solar cell arrays, the power consumption of the propulsion system should be as low as possible. The idea of using a small high-efficiency multistage plasma thruster (HEMPT) system for such missions is very attractive because of its relatively low complexity and low system mass. Thus, the ability of downscaling a HEMPT to the μN range is investigated experimentally. A measurement campaign studying systematically the influence of the geometrical dimensions of main thruster parameters on operation, beam profile, and ion acceleration is presented. Additionally the anode material was varied and showed relevance to ion acceleration distribution. The minimum achieved thrust was 50 μN at an anode voltage of 600 V, corresponding to a specific impulse of 230 s. Operation points with thrusts of 180 and 360 μN demonstrate a specific impulse of 610 and 860 s, respectively.

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In this paper, we present our ongoing micronewton thrust balance development, which fulfils the laser interferometer space antenna requirements. In the context of the development of highly precise thrusters for attitude control of satellites for future space missions, test facilities for the characterization and qualification of thrusters need to be developed in parallel. The presented thrust balance has a resolution of 0.1 μN in a bandwidth between 1 and 10-3 Hz. As a general measurement principle, we chose a pendulum balance. The setup consists of two pendulums to enable a common mode rejection. To suppress the eigenfrequency of the pendulums, a damping system based on an eddy current brake is part of the balance assembly. A heterodyne laser interferometer is used as the translation sensor. Different measurements were performed to investigate the noise performance of the pendulum. The results are presented and analyzed. The measurement system was used to measure the thrust of a micro-high efficiency multistage plasma thruster.

N Thrust Levels

In line with the requirements (table 1.3) a micro-Newton thruster test facility has been developed. The facility consists of a vacuum tank, a highly precise thrust balance, a plasma diagnostics setup and all other necessary hardware to perform EP development, testing and characterisation. As introduced in chapter 1, section 1.4, the micro-Newton thruster test facility developed can be used for the complete characterisation of AOCS thruster candidates for future scientific space missions such as LISA.

Development of a Highly Precise Micronewton Thrust Balance

Electric thrusters use the same principles as chemical rockets to propel spacecraft, however the ejected mass consists basically of charged particles. Furthermore, the acceleration of the propellant particles is not powered by the energy stored in the propellant, but rather by an external power source. This changes the way the parameters of the thruster are calculated.

Micro-Newton Thruster Test Facility

As mentioned in the introduction, Airbus started the development of the micro- Newton HEMPT in 2009 with the goal to demonstrate that the HEMPT technology could be used for highly precise AOCS. Until that time various laboratory μHEMPT had been built and tested.