Simulation of Space Debris Heating in Laser-Ablative Orbit Modification Manoeuvers

Kurzfassung

The idea to modify orbits of space debris objects is now around for few decades. There have been several sophisticated models proposed that calculate the impulse on the target upon laser irradiation, but yet the residual heat has been of less interest. The scope of this thesis was to implement heat transfer due to laser irradiation into an already existing FEM-model that solves for the heat equation. The absorptance was calculated by employing the Lambert-Beer law. The ablation dynamics have been considered by implementing the continuity, momentum and energy balances. In addition, the existing simulation tools are limited to only a few materials, e.g. aluminium, thus the implementation of various further materials into the model was also conducted. Emerging thermal stress and the shock wave propagation due to the rapid heating and the following expansion has been investigated. It was shown, that the risk of spallation or cracking is rather low for solid bodies made up of one continuous material. Eventually the model was validated using an existing verified 1D simulation code and available experimental data for various materials. It has been found, that materials with high thermal conductivity, e.g. copper, tend to have lower impulse coupling coefficients, also the optical properties, such as the reflectivity, have big influence on the ablation behaviour. As for the optimum laser parameters, it has been found that both, pulse length and wavelength should be chosen to be as short as possible. The material, from the present selection, with the highest impulse coupling coefficient has been iron. This data for the impulse coupling coefficient and the residual heat can be used to access the consequences of repeated laser orbit modification manoeuvrers and thus give an important statement on the reasonableness of laser debris removal