Modelling of laser-based thrust generation for space debris removal

Kurzfassung

A possible method for the active removal of space debris is the irradiation of the debris with a pulsed laser system. With sufficient power the surface layer of the debris object is ablated and yields thrust, which will ideally lower the perigee of the debris object. The direction of the thrust is independent of the direction from which the debris object is irradiated, it is normal to the local surface. This thesis investigates the effects caused by complex shapes and varying orientation of a debris object on the thrust vector. The tool EXPEDIT was written in C++ in order to calculate the impulse transferred by laser ablation, taking into account variation of the fluence, self-shadowing and complex geometries. Parameter studies were undertaken in order to investigate the behavior of the laser-debris system. The figure of merit x was introduced as the ratio of radial to axial impulse components with respect to the laser beam propagation vector. In order to describe the axial component eta_j was introduced, a variation of the eta_c from Phipps, Acta astron. 93:418 (2014). Eta_j is the ratio of the actually achieved axial impulse to the maximum possible axial impulse. EXPEDIT was used to gain estimates for xi and eta_j for three exemplary cases for different fluences in order to include a varying coupling coefficient. It should be noted that these simulations yielded values for xi and eta_j that were more problematic than expected. For a plate-shaped debris object eta_j ranged from 0.1 to 0.3 and xi from 0.4 to values slightly above 1. Some possible methods to improve the efficiency of the laser-based de-orbit are proposed.