Stefan Scharring, German Aerospace Center (DLR); Jens Rodmann, German Aerospace Center (DLR); Wolfgang Riede, DLR
Keywords: laser ranging, network analysis, orbit determination, space debris, Low Earth Orbit, state vector, covariance propagation, cloud coverage
Abstract:
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 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 network of the International Laser Ranging Service. Therefore, 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.
However, as an optical ranging method, laser ranging requires clear skies and, at the current state-of-the-art, terminator conditions at the laser ranging site in order to allow for target observation. Hence, the performance of any laser ranging network is strongly affected by orbital parameters of the observation targets, laser station distribution and local weather conditions.
In our paper, recent findings from a large system study on the performance of a global laser-ranging network are presented. Whereas the simulation methodology has been presented earlier at AMOS 2018, the current work shows a detailed performance analysis with respect to representative orbital object classes, available or conceivable station sites as well as realistic restrictions due to cloud coverage.
For simulation configuration, orbital parameters of space objects in LEO have been statistically analyzed and clustered. A set of six orbit types with different semi-major axes and inclinations has been identified as representative for approximately 75% of all prevailing LEO objects. For this selection, laser ranging networks of different sizes from 5 up to 50 laser ranging stations have been investigated.
Simulations of laser-based measurements from each ranging network are analyzed in terms of orbit determination accuracy and covariance propagation. Whereas the former is reviewed during a 30-day period of continuous target tracking, the latter is considered both in-between two different station transits with laser ranging as well as for a subsequent 5-day period without any further ranging measurements. For network performance characterization, the remaining position uncertainty of laser ranging data serves as a figure of merit.
In particular, the results on network performance are mirrored against different configurations of the global station distribution under consideration of the respective orbital parameters. Moreover, network performance results are characterized with respect to downtimes due to weather restrictions. For this purpose, an 11-year month-specific statistics on the diurnal variations of cloud coverage at each ranging location is employed.
Requirements on network sizing and station distribution are discussed with respect to operational demands in space situational awareness. In sum, a networking approach in laser ranging constitutes a viable technology for the reduction of prevailing uncertainties in orbital data of LEO objects and can particularly be expected to serve as a prerequisite for future enhancements in the field of collision alerts for space operations.
Date of Conference: September 17-20, 2019
Track: Orbital Debris