Grace precise orbit determination

GRACE (Gravity Recovery And Climate Experiment) is a satellite mission whose primary objective is to map, with unprecedented accuracy, the long- to medium-wavelength coefficients of the Earth's gravity field and to observe its temporal variations. To satisfy this objective as well as other applications (e.g. atmospheric profiling by radio occultation), accurate orbits for GRACE are required. One of the key science instruments aboard GRACE is the K-Band Ranging (KBR) system, which measures the dual one-way range change between both GRACE satellites with a precision of about 1 micrometer per second. Therefore, a new challenge in Precise Orbit Determination (POD) has to be faced with the available high accuracy KBR data from GRACE. This paper presents the investigation of contribution of the KBR data to GRACE Precise Orbit Determination. The GRACE orbits can be determined with an absolute accuracy of approximately 5 cm in each direction by using GPS tracking data with or without KBR data. The KBR data can be used to improve the accuracy of the distance between two GRACE satellites. The results indicate that the relative orbit accuracy is under a millimeter in position and about I micrometer per second for GRACE using both GPS and KBR data.