Validating and improving the orbit determination of Cryosat-2

Validating and improving the orbit determination of Cryosat-2

Root, B.C.

Ambrosius, B.A.C. (mentor)

Aerospace Engineering

Space Engineering

Astrodynamics & Space Missions

2012-03-29

The Cryosat-2 mission is an European Space Agency mission with the main objective to measure and monitor the variation in sea-ice and main ice sheets on Earth, located at Greenland and Antarctic. The satellite's main instrument is a state of the art altimeter, which can measure the distance between the satellite and the ice surface with extreme accuracy. To extract the variation in height of the ice surfaces from these measurements, it is important to know where the satellite was at the time of the measurements. The method that is used to obtain this is called Precise Orbit Determination (POD). POD combines accurate measurements together with physical models related to the satellite, in such a way that it can determine accurate orbit solutions for the satellite. This report is a discussion about the validation and improvement of the orbit determination of the Cryosat-2 mission. The current orbit determination process that is available is validated on three different subjects. First, a new data format for Satellite Laser Ranging (SLR) measurements was investigated, which is called the Consolidated Ranging Data format. SLR measurements are accurate range measurements that are used to validate the orbit of Cryosat-2. A converter is written that could convert the new data format, in such a way that the current orbit determination software could use it. Several features of the new data format were examined, for potential improvements. The second investigation was about the generation of the Doris beacon coordinates and their effect on the POD. The Doris system is the main orbit determination system onboard the satellite. Due to different abrupt and slow motions of the Earth surface, the Doris beacons moves with respect to the defined reference frame. A new definition of the Doris beacon coordinates, called DPOD2008, is used in the Cryosat-2 orbit estimation. The solution of the coordinates sets were validated and other coordinate sets were used, to conclude that DPOD2008 was generating the best orbit solution for Cryosat-2. The final investigation was on the solar radiation pressure modeling of Cryosat-2. Currently, a 6-panel box model is used as defined by ESA. In the empirical residual accelerations a signal is visible which has correlation with the solar radiation pressure. It was decided to use micro models generated by the University College London at the research group of Prof. Marek Ziebart for the solar radiation pressure computations. Two micro models are constructed, although the implementation of the UCL models in the GEODYN software is delivering unsuspected results. Several bugs are fixed or bypassed in the implementation of the models, but still clear differences between the internal GEODYN model and the UCL model implementation are visible. Recommendations are given for further research in the micro model investigation for the solar radiation pressure computation.

Precise orbit determination
Cryosat
Satellite Laser Ranging

http://resolver.tudelft.nl/uuid:47aab967-8658-4ece-9a87-4b7903f3b8fc

2012-04-11

Student theses

master thesis

(c) 2012 Root, B.C.