Stefan Scharring, DLR; Gerd Wagner, German Aerospace Center (DLR), Institute of Technical Physics; Jürgen Kästel, German Aerospace Center (DLR), Institute of Technical Physics; Wolfgang Riede, DLR; Jochen Speiser, German Aerospace Center (DLR), Institute of Technical Physics
Keywords: space debris, collision avoidance, high energy laser, laser ablation, atmospheric beam propagation, laser guide star, laser-matter interaction, adaptive optics
Abstract:
Due to the increasing amount of space debris, several laser-based concepts on orbit modification have been proposed in the recent years. In particular, remotely based momentum transfer to space debris via photon pressure appears to become feasible, due to the commercial availability of cw lasers with an average power output beyond the 10 kW level. For the purpose of space debris collision avoidance, simulations have already shown that sufficiently high velocity increments of approximately 1 cm/s can be achieved by target irradiation during several laser station transits.
In contrast, momentum coupling caused by laser ablation exceeds coupling by photon pressure by 3 to 5 orders of magnitude. Therefore, ablation is typically discussed as a suitable mechanism for laser-based debris removal by perigee lowering during multiple high energy laser station transits. Regarding space debris collision avoidance, however, already a single high energy laser pulse yielding material ablation at the surface of a debris object might have the same impact instantaneously as exerting photon pressure during multiple cw laser station transits within several days. Therefore, ground-based operation of a single-pulse high energy laser for power beaming into orbit could be suitable for debris collision avoidance as well. However, the availability of high energy lasers beyond the 10 kJ pulse energy level is so far restrained to research institutes for fusion experiments.
For both cw and pulsed lasers, remotely based momentum transfer incorporates additional challenges like laser beam propagation through the turbulent atmosphere as well as laser interaction with debris targets of unknown shape and material.
In simulations we assess the effects of atmospheric constraints like laser power loss due to aerosol extinction as well as laser beam broadening and pointing jitter as a result from atmospheric turbulence. For the compensation of turbulence, the usage of adaptive optics is explored in terms of a suitable transmitter configuration in combination with a laser guide star. Based on the ESA DISCOS catalogue, virtual targets with simplified geometric shapes are employed to investigate laser-matter-interaction with rocket bodies, mission-related objects and inactive payloads. In addition, the NASA Standard Breakup Model serves as a reference for fragments from collisions and explosions yielding an ensemble of 9101 debris targets in the Low Earth Orbit. For these objects, a study on laser-ablative recoil is carried out on a raytracing-based code considering both the unknown target orientation as well as residual laser pointing errors constituting sources of randomness in overall 5 dimensions (3 rotational, 2 translational) which are addressed in a Monte Carlo approach. Laser momentum coupling is calculated for the computed laser fluence distribution at the mean altitude of the particular debris object. As input for the calculation of laser-matter interaction, experimental data from the irradiation of aluminum, copper, and steel as representative space debris materials are employed.
The simulation results on laser-imparted momentum are discussed in terms of irradiation elevation angle, displacement on the orbital trajectory, momentum transfer uncertainty, success probability, debris material and limitations due to debris size, mass, and the required minimum fluence for the initiation of a laser ablation process.
Date of Conference: September 14-17, 2021
Track: Conjunction/RPO