Space Debris Nudging - a Very First Step in Laser Propulsion

Kurzfassung

The increasing amount of space debris in the low Earth orbit (LEO) constitutes a significant threat for satellite operations like Earth observation, communications, and scientific missions. The vast majority of space debris objects consists of fragments from explosions and collisions, where already an object of only 10 cm in size has the potential to entirely destroy a whole satellite. Moreover, such a collision implies the risk of a cascading effect by generating subsequent collisions with the newly generated fragments contributing to an exponential growth of the space debris population, known as the Kessler effect, that bears the potential to transform certain orbital regions unusable for space operations for several decades. Prior to a necessary large-scale removal of space debris as a long-term solution, object nudging by ground-based high-power laser stations might constitute a very first step in both space debris remediation – as well as in the technological evolution of laser propulsion: Already a debris velocity change by Delta-v = 1 mm per second, taking place 24 hours before a predicted time of closest approach (TCA) in LEO would yield a displacement of Delta-x = 259 meters of the debris on its orbital trajectory 24 hours later at TCA. This might be sufficient for collision avoidance (CA) if orbital data is known precisely enough. Exploring the opportunity of laser-based collision avoidance in space, we report about main findings from our LARAMOTIONS study, funded by the European Space Agency, and our internally funded PARAMOTIONS study on the fundamentals of applying momentum remotely to space debris objects using high-power lasers from ground. The expected outcome in terms of imparted Delta-v is evaluated in numerical analyses for a LEO space debris population of 9101 objects using adaptive optics and high-precision laser tracking and ranging. As propulsion mechanisms, we compare pure photon pressure with recoil from laser-induced surface ablation. The latter is modeled assuming coherent coupling of 5000 laser emitters with 20 J pulse energy each, whereas for the former analysis on photon pressure 2 combined 20 kW commercially (soon-to-be) available continuous wave (CW) high power lasers are assumed. The obtained results on feasibility are carefully considered against technological constraints as well as issues of operational safety.