| Attitude defines the orientation between the body axis and a desired reference frame. Determination of this body frame attitude is required in spacecraft, aircraft, sea-craft, land-craft and missile control, guidance and navigation. In addition to real-time computation, the requirements for attitude determination are: high accuracy, small latency, high frequency, calculation efficiency, robustness, and low cost.; In this thesis, two new methods for attitude determination are proposed: (1) tightly integrating measurements from two Global Position System (GPS) antennae and an Inertial Navigation System (INS); or, (2) tightly integrating GPS, INS, and magnetometer measurements.; The contributions of this research fall into six categories: (1) Magnetometer/GPS/INS attitude determination . This research analyzed and defined the theory necessary to use magnetometer based trajectory relative distance measurements for position and heading calibration of an INS. An experimental system implementing the theory was designed and tested. Experimental results are included. (2) Two antennae GPS/INS attitude determination. This research analyzed, designed, implemented, and tested a two-antenna carrier phase differential GPS aided INS capable of accurately estimating the full vehicle state (i.e., position, velocity, attitude, angular rate, acceleration). Experimental results are included. (3) Real-time integration . This research analyzed the various computation, communication, and measurement latency issues necessary to implement a reliable realtime vehicle navigation system. The implementation runs in QNX on a laptop computer. (4) Measurement modeling. This research has derived models relating the noncollocated magnetometer and GPS antenna measurements to the calculated INS states. The models include noise modeling and relations to the INS error state as required for INS error calibration via a Kalman filter based a complementary filter. (5) Integer ambiguity resolution . The integer ambiguity resolution process was optimized to ensure integrity. Given that the application is safety critical, incorrect integers could not be tolerated. In addition, new methods were developed to speed the integer resolution process by using constraints imposed by the IMU measurements. (6) Vehicle lateral control. This research includes the first implementation and demonstration of carrier phase (CP) DGPS aided INS based vehicle lateral control. Lateral control was achieved using three different navigation approaches: single antenna CP DGPS/INS, two-antenna CP DGPS/INS, and magnetometer/CP DGPS/INS. In all cases, reliable control was achieved in realtime with centimeter accuracy navigation and decimeter accuracy control. |
