GPS Based Onboard Orbit Determination S/W (Goods) for IRS (Indian Remote Sensing) Satellites
- Paper number
IAC-07-B4.3.05
- Author
Mr. Kartik Raju, Indian Space Research Organisation (ISRO), India
- Coauthor
Mr. S.C. Ratnakara, Indian Space Research Organisation (ISRO), ISAC, India
- Coauthor
Mr. A.S. Ganeshan, Indian Space Research Organisation (ISRO), India
- Year
2007
- Abstract
Global Positioning System receivers provide highly accurate time and position information, and use a constellation of navigation satellites maintained by the US DOD in order to accurately determine their own position. Although designed for terrestrial geo location and navigation, the system can be employed in the highly dynamic environment in Low Earth Orbit. The receiver technology has advanced to a stage where GPS receivers can now routinely be carried on smaller platforms. Since Selective Availability has been switched off, accuracies in the order of 10-20m in all axis are achievable for simple position fixes. A space borne GPS receiver is different from a terrestrial receiver, as it travels at great velocity relative to the GPS constellation, and satellites tracked change constantly. As a consequence it has to cope with higher Doppler shifts and Doppler shift rates. In LEO this can be of the order of ±60kHz. Consequently, the receiver only has a short time available to perform a frequency/code search in order to lock onto the spread spectrum GPS signals. In order to predict GPS satellite visibility, the antenna geometry and orbital dynamics of the host satellite must be well known. Orbit determination using GPS receivers on small satellites was demonstrated in Indian Remote Sensing Satellite(IRS) IRS-P5(Cartosat-1) and is being implemented on Cartosat-II .IRS class of satellites also carries two SPS (Standard Positioning System) units to provide instantaneous GPS-navigational solution for the spacecraft. GOODS (GPS Based Onboard Orbit Determination Software) methodology has been developed for IRS class of satellites. GOODS will take SPS Solution as measurement and improve the Satellite State Vector using Kalman Filter. SPS hardware unit, which is present onboard the spacecraft provides instantaneous solutions at 1sec. Experience on such data indicates that the instantaneous solutions are noisy. In view of this an onboard filtering algorithm is planned to smooth the data and provide the solutions for further use. GOODS will carry out this activity. The GPS based Onboard Orbit Determination (GOODs) filters the instantaneous solutions from SPS using a constant gain filter. This methodology provides updated state vectors at regular instants of time. Computation of state vector at Onboard request time, which need not match with constant intervals, can be carried out by J2 propagation. For GPS based Onboard Orbit Determination accelerations due to drag, solar radiation pressure, as well as gravitational perturbations from the Sun and the Moon can be safely neglected because SPS measurements are available at 1 sec. This methodology has worked on two IRS missions.
- Abstract document
- Manuscript document
IAC-07-B4.3.05.pdf (🔒 authorized access only).
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