Precise Orbit Determination for CHAMP using GPS Data from BlackJack Receiver

摘要

The CHAMP satellite was launched into a 450-km low-Earth orbit in July 2000, to support geoscientific and atmospheric research. The mission is managed by GFZ in Germany, and NASA is one of three international partners. Among the scientific instruments on board is an advanced codeless, dual-frequency GPS receiver developed by the Jet Propulsion Laboratory (JPL). This "Blackjack" receiver supports several important operational and scientific functions. In addition to disseminating precise timing and navigation information to the spacecraft, the Blackjack receiver collects GPS tracking information to support precise orbit determination (POD) activities on the ground. The receiver also supports the collection of atmospheric limb sounding measurements and GPS specular reflection signals through side- and down-looking antennae respectively. In this paper we present results for CHAMP POD using the precise GPS measurements collected by the BlackJack receiver through the up-looking antenna. We will describe the quality of the tracking data, the tuning of the reduced- dynamic model for the 450-km orbit, and the various methods of evaluating the orbit accuracy. Comparisons of overlapping orbit solutions suggest that the GPS-based CHAMP orbits are accurate to sub-decimeter level. This is further supported by tests of independent measurements with precise satellite laser ranging (SLR) systems. We will also describe orbit solutions obtained with different strategies and dynamic models, and discuss the possible remaining error sources and ways to further improve the orbit solutions.