Abstract:
Global Position System(GPS) has long since been used for position determination, the interest to use GPS for attitude determination shifted about two decades before.The need to control the attitude of a spacecraft is mostly to obtain a desired pointing accuracy. Installing a GPS receiver on-board a spacecraft provides the opportunity to use a single lightweight, low-cost sensor for a multitude of functions: position, velocity, attitude, attitude rate and time. This consolidation of resources is likely to lead to an overall savings in cost, power, weight and complexity of spacecraft, with elimination of many di erent sensor. The attitude dynamics of a spinning spacecraft under no disturbance torque is studied and the results are extended to spacecraft under sinusoidal disturbance torque. The radar-Earth footprint of the space based radar satellite, OceanSat2 by ISRO is modelled and a PD controller is designed to achieve a drift rate of 0.166 deg/s. Using psuedorange measurements of GPS the position of the spacecraft is estimated using Least-Squares method, which gives a maximum estimation error of 10m. The gyro measurements and the carrier phase measurements were used to develop an Extended Kalman Filtering algorith to estimate the attitude of the spacecraft. The maximum attitude and gyro bias estimation errors were found out to be 0:50 and 0.002rad/s.