Precise Relative Orbit Determination of Low Earth Orbit Formation Flights using GPS Pseudorange and Carrier-Phase Measurements

Formation flying is emerging as an important technology on achieving the tight mission requirements of imaging and remote sensing systems, especially radio interferometry and synthetic aperture radar (SAR) applications. A higher absolute and relative position and orbit knowledge is always sought in these kinds of applications. Such requirements can be met to a large extent by manipulation of GPS data. Carrier-phase Differential GPS (CDGPS) measurements can also be used to further increase the accuracy in relative position and orbit determination dramatically. Using a geometric model has a clear advantage of generality and wide applicability, independent of complex dynamic models for different types of platforms. Hence, the proposed approach uses input from GPS receiver on the master satellite and pseudorange based absolute position estimates from the slave satellites. In addition, single-difference (SD) phase measurements between the master and the slave satellites are also required, which provide very accurate relative distance information. SD information is input into a Kalman filter to determine the relative orbits within the formation to a higher precision. In this paper, we present a geometrical approach to relative orbit determination and present an algorithm for the refinement of position estimates through combining carrier-phase and pseudorange data