Precise State Determination Of Formation Satellite For Earth Observation Using GPS

Satellite formation flying means two or more satellites flying with characteristics of short distance and relative movement between the satellites, compared with ordinary constellation. It enables the use of a "virtual big satellite", where multiple distributed satellites can be coordinated to act as one. This will enable new scientific missions involving coordinated and distributed measurements, leading to enhance synthetic apertures for earth mapping interferometry.Control and application of satellite formation require measurement of the formation states. The states include absolute and relative position, attitude and clock bias separately. Measurement of relative clock bias is a key problem for inter-satellite synchronization. Relative states are more important for certain formation flying missions, such as those proposed for the earth-observation space distributed radar, whose accuracy of relative position reaches centimeter and that of relative attitude reaches minutes.The GPS system provides an array of sensing options for a satellite formation simultaneously, which include absolute positioning, relative positioning, attitude estimation and precise timing. However, in order to improve the precision of relative states and resolve GPS ambiguity quickly, other measurements should be provided. One is inter-satellite 'GPS-like' carrier phase and code cross link range.This dissertation consists of 6 chapters and appendix. Chapter 1 briefly introduces the satellite formation flying technology, especially the status of its states determination using GPS. With earth observing application, chapter 2 describes the inter-satellite relative movement functions and orbital design for ordinary earth observing satellite formation. In chapter 3, 4 and 5, aiming at three earth observing satellite formation, the models and the numerical simulation studies of whole determination of formation states are presented particularly using measurement from GPS, inter-satellite cross link range, and combination of these two measurements. In these parts, the mathematical models of states determination have been built, and then the techniques of different phase ambiguity initialization and different phase with multi-epochs have been studied. Further more, the dissertation analyses the influence of states coupling, the relativity of the difference measurements, and the influence of states determination precision results from theattitude changing during movement of the formation. Specially, using three dimensional net constraints and combining all measurements to entirely resolve the states, the simulation analysis of formation flying satellites with about 1 kilometer distance has been done. The results indicate that the accuracy of relative position reaches centimeter, the relative attitude reaches minutes and the clock bias reaches about ten nsec. Chapter 6 consists of conclusions and future work.