Research on Cm-level kinematic precise orbit determination for GRACE based on zero-difference method

Thanks to the high performance of the spaceborne GPS receiver and the availability of precise IGS orbit and clock products, Zero-difference kinematic precise orbit determination (POD) has turned out to be a new method in orbit determination for the LEO satellites. Zero-difference Kinematic POD, which is based on the GPS measurements only from the spaceborne GPS receiver, is independent of force models and orbit design. From that point of view, kinematic POD is well suited for the Earth Observation satellites at very low altitudes, such as CHAMP, GRACE and GOCE et al. This paper reviews the basic zero-difference GPS model, and the corrections in the model are discussed. A block-wise least squares algorithm, which firstly separates the parameters in to groups and then solves the parameter by elimination and back-substitution, is discussed and proposed for the kinematic orbit determination. The orbit solutions for one week of GRACE observations are calculated Comparisons with the published Rapid Science Orbit (RSO) indicate that the accuracy in radial, along-track and cross-track direction can achieve 5.5cm, 5.5cm and 6.6cm respectively, and the RMS in distance is better than 8.6cm.