Modeling navigation system performance of a satellite-observing star tracker tightly integrated with an Inertial Measurement Unit.

摘要

As Global Positioning System (GPS) and similar systems have been developed, less emphasis has been placed on the use of celestial navigation, or star sighting for position determination. Celestial navigation has been used previously for heading correction in aircraft by observing known stars and the local horizon. An emerging technique is to determine a position by observing satellites in addition to stars, which satellites allow for local position estimation.;This dissertation defines the navigation system using this satellite-observing method to tightly integrate a star tracker, an Inertial Measurement Unit (IMU), and a barometric altimeter using an Extended Kalman Filter (EKF). Models of each of these components are described with emphasis added to the accuracy of the star tracker measurement of a satellite. Several system configurations are simulated comparing the performance of the estimate with respect to IMU grade, star tracker measurement accuracy, satellite orbit height, and measurement time interval parameters. In addition to system component parameters, two other variables are introduced: ephemeris error correction from a remote sensor and satellite selection algorithm.;Experimental observations, using a visible band star tracker integrated with a navigation grade IMU, showed that the observer's position can be estimated with a median distance root mean square (drms) position error of test cases of 39 m when observing satellites in Medium Earth Orbit (MEO) orbit. The drms position error was less than 65 m for 90% of test cases and was less than 21 m in 10% of the cases.;Additionally, power requirements were calculated for a satellite signal operating in imaging bands, such that a Low Earth Orbit (LEO) orbiting satellite constellation could be detected during the day. This type of signal would make it possible to operate the star tracker integrated navigation system in GPS-degraded environments with similar duration and comparable accuracy of GPS.