Precise Orbit Determination for the TerraSAR-X Mission

Abstract

The TerraSAR-X synthetic aperture radar mission relies exclusively on GPS tracking for a precise post-facto orbit reconstruction. Besides a redundant MosaicGNSS single-frequency receiver, the satellite carries the Integrated GPS Occultation Receiver (IGOR), which provides low noise code- and carrier phase measurements on both the L1 and L2 frequencies. As part of the TerraSAR-X ground segment an automated precise orbit determination system has been built up at the German Space Operations Center (DLR/GSOC). The employed reduced-dynamic batch least-squares filter is designed to work with both ionosphere-free L1/L2 carrier phase data and the ionosphere-free L1 code/carrier combination. Depending on the available GPS receiver and measurement types, a 3D rms position accuracy between 1 m (MosaicGNSS single-frequency data) and 5-10 cm (IGOR dual-frequency data) has been demonstrated in pre-mission tests. Following a description of the TerraSAR-X mission and spacecraft, the paper describes the adopted orbit determination algorithms and processing methodology. The theoretical background is complemented with practical results from the CHAMP and GRACE missions as well as GPS signal simulator tests.