Stephanie Karg

Microthruster Research Activities at DLR Stuttgart—Status and Perspective

DLR Stuttgart has recently expanded its laser propulsion research activities towards micropropulsion. The paper presents an experimental outline for the scientific scope of the research at DLR. The current status of the high vacuum facilities with a test stand for ablation diagnostics as well as a planned torsion pendulum thrust stand are reported together with an outlook on further extensions to the existing setup. An overview on laser characteristics, key figures of merit and their specified measurement range is given with respect to suitable ablation materials and their impulse bit generation in a laser pulsed microthruster.

Thrust noise minimization in long-term laser ablation of propellant material in the nanosecond and picosecond regime

Abstract. The avoidance of any moving parts in a microthruster exhibits a great potential for low-noise thrust generation in the micronewton range. This is required, e.g., for scientific missions that need attitude and orbit control systems with exquisite precision. Laser ablation propulsion offers the opportunity of permanent inertia-free, electro-optical delivery of laser energy to access the propellant entirely without moving it. New propellant is accessed by ablating the previous surface in layers, essentially damaging the surface with a laser over and over again. The resulting surface properties for different fluences and scanning patterns were investigated for multiple layers of aluminum, copper, and gold. The pulse-length-specific issues of various ablation mechanisms such as vaporization, spallation, and phase explosion are accounted for by the use of a 10-ps laser system and a 500-ps laser system. We show that the surface roughness produced with 500-ps laser pulses is approximately twice the surface roughness generated by using 10-ps laser pulses. Furthermore, with 500-ps pulses, the surface roughness shows low dependency on the fluence for carefully chosen scanning parameters. Therefore, we conclude that laser pulse duration differences in the picosecond and nanosecond regimes will not necessarily alter surface roughness properties.

Review on Japanese-German-U.S. Cooperation on Laser-Ablation Propulsion

We report on an international cooperation between Nagoya University (NU), Japan and DLR Stuttgart, Germany on scaling issues in laser ablative propulsion. Lessons learned from collaborative work in the laboratory will be summarized with respect to the comparability of experimental methods and corresponding standardization issues. With the background of previous experimental research at the University of Alabama in Huntsville (UAH), experimental work with CO2 lasers in a moderate (NU) and high (DLR) pulse energy range on laser ablation of POM is presented. Prolometry results of target surfaces are compared withuence distributions from beam propagation modeling. Ablation fromat targets is reported with respect to energy and area scaling and compared with results from ablative propulsion employing parabolic nozzles.