Investigation of Laser-Ablative Micropropulsion as an Alternative Thruster Concept for Precise Satellite Attitude and Orbit Control

Kurzfassung

Microthrust engines (µN-mN) with high specific impulse and long lifetime that allow for precision attitude and orbit control are a prerequisite for planned and future missions for geodetic purposes or astronomic science [1]. The potential of laserablative microthrusters for meeting these demands is being investigated at the Institute of Technical Physics [2, 3]. The concept is based on layer-by-layer removal of a thin layer of material by focusing short laser pulses on a metal surface creating plasma or vapor (laser ablation) [4]. The recoil of the ablated material leads to momentum transfer to the target, which results in sub-µN to mN thrust levels for high repetition rate laser sources [5]. Additionally, by implementing electro-optic beam steering, moving parts that can be a significant disturbing factor for precise thrusters can be avoided in this concept. A thrust balance based on a torsional pendulum has been constructed for measurements in vacuum. Sub-µN thrust levels have been measured in tests with a calibrated voice coil. In addition modification of the sample surface after ablation is determined by using a white light interferometry profiler. Moreover, divergence and velocity distribution of ions in the ablation plume are investigated by Faraday cup measurements. These diagnostics provide information on the influence of laser, surface and material parameters which are important figures of merit for the evaluation and optimization of laser ablative microthrusters.