Removal of Small-Sized Space Debris by Laser-Ablative Momentum Generation

Kurzfassung

Small-sized space debris objects pose a challenging threat for space security: Within a size range of 1 to 10 centimeters they are still large enough to cause severe damage to space assets but, moreover, they are almost too small to be detected and monitored. Recent progresses in laser-based debris monitoring yield promising results in detection and tracking of debris objects and enable for the short-term solution of obstacle avoidance maneuvers. For the long run, however, it has to be analyzed whether and how the usage of high energy lasers can provide for a reliable solution of the space debris problem in the abovementioned particle size range. Laser-based space debris removal concepts have been around for decades now. Nevertheless, practical implementation is still connected to great technological risks. Most of the concepts plan to utilize the laser ablative process at the target. To investigate this common aspect in detail and to reduce the risk of misleadingly extrapolating parameters, we now experimentally investigated the generation of impulse under realistic conditions as to be expected in a real space scenario. A Nd:YAG based, 10 ns pulsed MOPA laser system providing a pulse energy of 80 J was weakly focused to a diameter of 3 cm onto debris-like targets with different sizes, shapes and materials. The target masses ranged between 1 g to 3 g, indeed representing dangerous objects, and were in free fall within a vacuum during single pulse irradiation. High speed 3Dtracking was applied to deduce the kinetic properties induced by the ablation process. Finally, the data was compared to raytracing based simulation results. Differences between materials and mechanical dynamics are discussed. In simulations we explore operational safety issues as well as both potential and limitations of laser-ablative momentum generation, in particular with respect the accumulation of residual heat from the ablation process. For this purpose, we use Monte Carlo simulations in order to analyze how restrictions in laser pointing accuracy as well as random target orientation affect the predictability of laser-ablative momentum generation. Moreover, pulse number restrictions are discussed in order to avoid target melting and its compactification.