Engineering notes kinematic navigation of geostationary satellites formation using indian regional navigation satellites observables

The first attempt in India to determine the accuracy of autonomous navigation of geostationary satellites either solo or in formation, using Indian Regional Navigation Satellites signals is discussed. Seven of these are spread out over 32 to 131.5°E, and from 29°N to 29°S. The method employs a pair of single-frequency IRNSS receivers, exchanging their raw measurements via a dedicated serial data link at uhf. Each receiver computes its absolute and relative position by processing the differential pseudorange and carrier phase to smooth the estimates. In absolute positioning, using pseudorange measurements, the worst estimation error ellipsoid for a geostationary communication satellite at 74.02°E is found to be about ±1 m in longitude, 1.8 m in latitude, and 5 m in altitude, quite consistent with the ellipsoidal geometry of this navigation bassinet. The absolute velocity of the communication satellite is estimated using three-point range rate formula using three successive carrier phase measurements, eliminating integer ambiguity in the process. The velocity estimation error is found to oscillate at twice the orbit frequency in local orbit frame. The worst amplitudes of the errors are found to be 0.05 m/s in longitude, 0.03 m/s in latitude, and 0.4 m/s in altitude.