Celestial Aided Inertial Navigation by Tracking High Altitude Vehicles
Celestial and inertial navigation systems work well together as an alternative to Global Positioning System. Inertial systems provide constant dead reckoning updates but is subject to drift. Celestial systems provide updates with its passive stellar measurements to correct the inertial drift. Stellar measurements normally update attitude only by tracking the angular positions of known stars. However, by tracking reference objects with known positions against a background of stars, the observer's position and velocity can be updated as well. Using a MATLAB tool developed by the Air Force Research Laboratory, this research simulates the navigation performance of a low flying aircraft tracking a higher flying aircraft as the reference object. Three different scenarios are studied: 1) stellar observations providing attitude updates only, 2) aircraft observations providing bearing measurements to known position and velocities, and 3) both stellar and aircraft observations. Additionally, the observation frequency will be a variable parameter to determine its effect on navigation accuracies. The sensor measurements are combined using an extended Kalman filter.