RPOD - Real-Time Precise Orbit Determination
One key component of any GNSS receiver is the navigation solution, i.e. the determination of position, velocity and time. It can be observed that for the GPS receiver applications, which are in the focus of the RUAG Space product development, the real-time navigation solution has evolved from a basic feature, which allows for autonomous operation of a stand-alone instrument, to an element being crucial for the complete mission.
The evolution of the respective performance requirements became so stringent that they go beyond classical navigation and require precise orbit determination (POD) in real-time, already onboard the satellite.
RSA defined and implemented a real-time navigation solution in the MetOP GRAS project, where the position requirement was 100 m, and refined it in successor projects, where the requirement was tightened to 20 m in the three dimensions. Although, this advanced navigation solution already shows a very good performance, the required position, velocity and time (PVT) accuracy of missions currently being developed, and planned, respectively, exceeds the performance capabilities of the first RSA implementation.
A very fruitful cooperation with the Institute of Navigation and Satellite Geodesy of the Graz University of Technology, which disposes of an internationally acknowledged know-how on precise orbit determination and satellite navigation, has been established.
In order to meet this overall target several prerequisites and accompanying measures had to be accomplished. An assessment of the main error sources and their actual magnitude was performed. For high-end receivers the GPS system errors are the dominant errors, which, however, have decreased over the last years.
In order to determine the actual navigation performance of a selected algorithm, it was necessary to have justified assumptions on the GPS error. Furthermore, a validation environment has been established, which provides the possibility to quantify the actual performance. An enhanced navigation algorithm was then identified and tested, which can be implemented in real-time receivers with the next generation of space qualified processors.
RUAG Space GmbH - Georg Grabmayr
Graz University of Technology, Institute of Navigation and Satellite Geodesy (TUG-INAS) - Prof. Bernhard Hofmann-Wellenhof