Future improvements in conjunction assessment and collision avoidance using a combined laser tracking/nudging network

Kurzfassung

The expected significant increase of space launch activities in the next years, both from spacefaring nations and in the private sector, yields an enhanced risk of space debris generation. In this regard, space situational awareness (SSA) is mandatory not only for the protection of active space missions, but as a prerequisite to prevent aggravation of the space debris environment by cascading effects of secondary debris generation due to in-space collisions. High accuracy in laser ranging to space objects (within a meter or better) has already been demonstrated, e.g., by the International Laser Ranging Service (ILRS) network. Thus, laser ranging can be considered as a highly promising sensor technology for space surveillance in the Low Earth Orbit (LEO) which has the potential to complement existing radar facilities in terms of achievable state vector accuracy. Furthermore several laser-based concepts on orbit modification have been proposed in the recent years. In particular, momentum transfer to space debris via photon pressure appears to become feasible, due to advancements in adaptive optics and the commercial availability of high power lasers with an average power output beyond the 10 kW level. This allows for the setup of a network of comparably cost-efficient laser stations for momentum transfer in the near future paving the way for the capability to remotely operate space debris in particular in terms of debris vs. debris collision avoidance maneuvers. In the scope of the conceptual study LARAMOTIONS (SSA P3-SST-XV) funded by the European Space Agency (ESA) simulations of a ground-based laser tracking and momentum transfer network have been carried out in order to estimate the subsequent improvements in conjunction assessment and collision avoidance for operational satellites as well as for debris vs. debris encounters. Therefore, the software generates reference trajectories from a Two-Line-Element (TLE) catalogue for any number of target objects in LEO. From these trajectories station passes as well as random measurement samples are computed and the orbit determination process is simulated yielding the collision rate and false alert rate of the given network. Special emphasis is taken on considering station downtimes due to weather conditions by introducing a station-specific duty cycle based on the analysis of historical weather data. Afterwards a momentum transfer network can be simulated. In order to achieve this, forces induced by photon pressure are computed from tabulated data of target-specific Laser-Matter-Interaction simulations and are applied to the object’s trajectories. A second laser tracking simulation based on the modified orbits eventually shows the advantages of the given system in terms of conjunction analysis and avoidance, in particular considering debris vs. debris collisions for which at present collision avoidance maneuvers are not yet available. The paper will outline the software architecture as well as the results for different network geometries considering the number of stations, their geographical distribution and different duty cycle values. Among the results, the effects of the network geometry and station distribution on the achievable orbit accuracy will be presented. Two operational scenarios will be compared: On-demand tracking in response to conjunction alerts and a laser catalog scenario yielding the maximum number of objects, which can continuously be tracked by a given network independently from radar-based SSA data. Finally, an outlook will be given regarding future simulations and possible enhancements of the simulation environment.