Laser-based removal of irregularly shaped space debris

Kurzfassung

Whereas the feasibility of laser space debris removal by high energy laser pulses has been shown in various concept studies and laboratory proofs of principle, we address the upcoming question for the effectiveness and responsibility associated with this technique. The large variety of shapes of space debris implies the great challenge of predicting amount and direction of the impulse imparted to the target. We present our recently developed C++ code EXPEDIT allowing for discretization of both laser beam and debris target. Selfshading effects of the target are taken into account by a ray-tracing module which furthermore allows simulation of various beam profiles. The corresponding variation of the fluence throughout the target surface is considered with respect to its impact on the local momentum coupling coefficient. Simulation results are compared with earlier findings from the literature. Special attention is paid to the impact of incidence angle and ablation threshold. A database for laser-matter interaction with aluminum is set up from hydrodynamic simulations and is used for parameter studies taking various laser pulse lengths into account. Simple target geometries that have been analyzed analytically earlier in the literature as well as complex and realistic debris are investigated with respect to imparted impulse and angular momentum. Since slight variations of the initial debris target position and orientation within the laser spot may yield large differences with respect to translational and angular momentum, a large number of randomized laser engagements are simulated in order to gain a representative insight into the predictability of the laser pulse impact to the debris object. Beyond the classical definition of laser-matter-interaction efficiency in comparison with flat target experiments in the laboratory, we introduce the ratio of lateral momentum (perpendicular to the beam propagation axis) to axial momentum (alongside the beam propagation axis) as a figure of merit to classify the kinematic behavior of various target geometries under pulsed laser irradiation. We identify highly cooperative targets like, e.g., spheres, as well as targets which are strongly sensitive to their orientation towards the laser beam, e.g., plates, and might exhibit a poor performance in laser debris removal. Nevertheless, despite limited predictability for the motion of a particular debris object caused by a single laser pulse, the suitabilityof laser-based debris removal like a reliable orbital sweeping broom is discussed.