Principle of laser ranging on space debris
The constant increase in the number of space missions has led to a high density of so-called "space debris". This space debris is the result of explosions of missile upper stages, surface degradations based on the harsh conditions in space and satellite collisions. As a result of radar based and passive optical observations and computer simulations, the determination of the height dependent distribution of space debris items is possible. In LEO (Low Earth Orbit)at 900 km and 1400 km and in GEO (Geosynchronous Orbit, 35800 km high), an accumulation of these objects has been determined. This results in an increased risk to the infrastructure located there, such as communication satellites in LEO. If the population exceeds a critical threshold value, a cascade effect is imminent whereby the debris objects continue to multiply as a result of inter-debris collisions. A first step in avoiding damage to satellite systems is therefore the exact and comprehensive recording of the trajectory data of all critical objects with dimensions larger than 1 cm. As a result of the non-predictable influences that act in orbit on the trajectory data, such as atmospheric friction or solar particleradiation, the trajectory data must be updated in the event of imminent collisions. To be able to determine this trajectory data with a high level of efficiency and accuracy, at the Institute of Technical Physics laser-based methods to ascertain the distance are combined with passiveoptical tracking. Debris objects are initially detected with an observation telescopeusing solar illumination and are then actively illuminated. Methods for target tracking and for the compensation of atmospheric interference are being developed for this. Simulation calculations for the laser beam propagation in turbulent atmosphere support the designof a system. These methods are then tested on a laser test range under horizontalpropagation. The development of a suitable laser beam source with a high beam quality, pulse energy and repetition rates in the kHz range is running parallel. This system will be adapted or operation in the field after successful functional verification in the laboratory. The initial objective is the set-up and operation of a "space debris monitoring platform". Later on, when the relevant high-power lasers are available, it will be possible to remove cm-class space debris using laser-based methods.