The MICROLAS concept: precise thrust generation in the Micronewton range by laser ablation

Abstract

Results from experimental work and hydrodynamic simulations on the MICROLAS concept for a pulsed laser-ablative microthruster without moving components are presented. The propellant surface is scanned and ablated by single high-intensity laser pulses yielding a fixed impulse bit in the nNs range. The variation of the laser pulse repetition rate over several orders of Magnitude allows access to various thrust levels. Laser-induced thrust of around 25 μN is generated for aluminum targets with laser pulses of 8 ns pulse length at a repetition rate of 1 kHz with an average laser power of 2.3 W. Thrust noise is around 1 µN/sqrt(Hz). A servo loop for laser operation is proposed in order to minimize thrust noise. Since increasing roughness of the propellant surface in long-term ablation might yield thrust noise, propellant targets are investigated by profilometric surface analysis after ablation by ultrashort laser pulses of 10 ps pulse length. Surface roughness after material removal in several layers is analyzed with respect to laser fluence and spot overlap. Simulation results for specific impulse, impulse coupling coefficient and jet efficiency are discussed with respect to laser parameters and target material.