Orbit determination for the GOCE satellite

Abstract Precise Orbit Determination (POD) for the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first core explorer mission by the European Space Agency (ESA), forms an integrated part of the so-called High-Level Processing Facility (HPF). Two POD chains have been set up referred to as quick-look Rapid and Precise Science Orbit determination or RSO and PSO, respectively. These chains make use of different software systems and have latencies of 1 day and 2 weeks, respectively, after tracking data availability. The RSO and PSO solutions have to meet a 3-dimensional (3D) position precision requirement of 50 cm and a few cm, respectively. The tracking data will be collected by the new Lagrange GPS receiver and the predicted characteristics of this receiver have been taken into account during the implementation phase of the two chains. This paper provides an overview of the two POD processing chains and includes a description of the required input, auxiliary and output products. Both chains have been tested with real data from the German CHAMP and the EUMETSAT MetOp satellites, which carry a BlackJack and GRAS GPS receiver, respectively. The consistency between CHAMP and MetOp orbit solutions computed with the final implementation of the different chains was found to be better than 10 cm in 3D position when use is made of high-quality GPS ephemeris and clock solutions. In addition, test results with data from a GOCE End-to-End (E2E) simulator which incorporates a model of the Lagrange receiver have been included. The differences between all orbit solutions was found to be of the order of a few cm for all directions. The precision requirements for the two chains were thus not only met with E2E simulated data, but also with real data from CHAMP and MetOp.

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