GPS-based attitude algorithms for low-cost satellite missions

This dissertation describes research in the area of spacecraft attitude determination using the Global Positioning System (GPS). Two techniques are investigated. The first involves the use of carrier phase differences between two antennas. This method is for determining the orientation of a spinning satellite. The second approach uses a single antenna and the signal-to-noise ratio of GPS measurements to estimate a single vehicle axis. It is applicable to any type of satellite.; The carrier phase method estimates both the orientation of the spacecraft spin vector and the frequencies of its motion. The frequency algorithms involve both frequency and time domain techniques. The attitude algorithms use averaging and filtering methods. Data are analyzed from both a computer simulation of GPS measurements and a ground experiment designed to simulate the motion of a spinning satellite. The results demonstrate pointing errors of less than 0.25 deg and frequency errors under 0.01 rpm.; The primary SNR-based method uses angle observables mapped from SNR measurements. These angles are applied in a Maximum Likelihood Estimate of the boresight vector of a GPS antenna. Mapping functions are created from either GPS data or from an antenna gain pattern. Measurements from one antenna are sufficient for single-axis attitude.