Study On Autonomous Orbit And Attitude Determination For SAR Spacecraft Based On GPS

With the rapid development and application of Micro-Satellites, It is very anxious to reduce the cost and complexity of satellites?measurement and control system, and improve the precise of satellites?orbit and attitude determination. Then the on-board GPS technique emerged as the times require. GPS provide a novel approach of on-board measurement for LEO. This paper investigates on-board GPS autonomous orbit and attitude determination aimed at SAR spacecraft The result proved feasibility and reliability of on-board GPS. It provides the theory base for GPS space application The first part of this paper reviews GPS development and application in many fields, especially in outer space in recent years, and brings forward the idea that autonomous orbit and attitude determination using on-board GPS for SAR spacecraft Gives the Analysis of GPS measurement model in detail. The second part of this paper discusses the theory of SAR spacecraft autonomous orbit determination using on-board GPS. Due to the limitation which as a result of geometric orbit determination桮PS signal discontinuity lead to failure of orbit determination, this part brings forward a new algorithm of autonomous and precise orbit determination, which integrated GPS measurement model and SAR spacecraft dynamics model, using extend Kalman filter(EKF) to estimate the position and speed of SAR. Based on the GPS measurement equation and SAR spacecraft dynamics equation, the EKF navigation algorithm and responding flow chart were described in detail. The result of computer simulation proves that the algorithm is feasible, which satisfies SAR spacecraft application at a certain extent. The third part of this paper discusses the principle of SAR spacecraft autonomous attitude determination using GPS antenna array and difference carrier phase measurement. First of all, this part describes some coordinate systems and the transform relationships between of them. And a quatemion attitude model was put forward. Then, make clear that the precise, real-time and reliable are the key problem of attitude determination using on-board GPS for SAR spacecraft Based on these, a reliable algorithm has been brought forward, which integrated SAR spacecraft抯 attitude dynamics, attitude kinematics model and GPS carrier phase interferometry model, using EKF to estimate attitude of SAR spacecraft After 7 Abstract setting up these models, the flow chart of GPS attitude determination was described in detail. The result of simulation which compared to single-point attitude determination, proves the feasibility and reliability of this algorithm. The fourth part of this paper makes emphasis on investigating of GPS carrier phase integer ambiguity. Integer ambiguity is a veiy important, and also difficult problem of GPS difference carrier phase application. Only when the cortect integer ambiguity resolved, precise attitude of SAR spacecraft will be reached. Aim at the real-time requirement, this part brings forward a very efficient algorithm which based on LAMBDA. The fifth part of this paper analyses the error source of SAR spacecraft orbit and attitude determination using on-board GPS. Investigates the effects which (3PS satellites geometry distribution, length of between antenna, multipath act on orbit and attitude determination. And some methods which be used to reduce error effect were brought forward. The sixth part of this paper...