Attitude Determination of Spacecraft Using Phase Measurements of Standalone COTS GPS Receivers

The attitude determination of satellite has been executed in many satellite missions using different sensors like magnetometer, gyroscopes and sun sensors but the cost, weight and power requirements motivate the researchers for standalone GPS based attitude determination system. The attitude determination of small satellites can be obtained by using the phase based measurements from at least three commercialofftheshelf (COTS) GPS antennas/receivers mounted on the surface of the satellite with known baseline measurements. The code measurements are not as accurate as the phase measurements so this research contribution presents the GPS phase-based attitude determination algorithm while post processing the static test data and implementing the algorithm in MATLAB environment. The single-point positioning is used for determining the position of the Master antenna, and differential positioning is done to find the slave antennas' position and baseline coordinates after implementing the LAMBDA method for ambiguity resolution. Finally, attitude is determined and compared using the Unscented Kalman filter. Various GPS signal and system errors like ephemeris, clock. Ionospheric and Tropospheric errors along with satellite geometry are also calculated. The GNSS Based attitude determination for short baseline using COTS GPS receiver with three antennas are explored analytically and implemented in MATLAB environment using the real static GPS data in RINEX format