The Study On The Attitude And Relative Orbit Determination With Some Correlative Problems Of The Distributed SAR Satellites

Recently, the distributed SAR satellites develop rapidly. Compared with the single SAR satellite, the distributed SAR satellites have many advantages: The viability has been enhanced obviously; The combination of baselines and models of observation are flexible; The target identification ability is improved. So the distributed SAR satellites have already become a research focus. Our research lab also starts the 863 project of the "Research on the Overall Distributed Satellites SAR System Technique ".In order to ensure the image quality of SAR, higher precision of the attitude and the formation movement of SAR satellites are required. All measurement must be performed in high dynamic environment, so the real-time of the measurement must be improved. Our research is developed around these difficulties. The emphases of GPS phase measurement include integer ambiguity resolution and cycle slip, which are the primary effect factors of precision and real-time. In order to improve precision, a long PN code has been uesd. So the capture of long PN code will effect the real-time. To SAR satellites themselves, the disturbing force is the primary factor which effects the attitude and the formation movement. Our research includes: how to precisely measure the attitude and the relative movement of SAR satellites. Integer ambiguity, cycle slip, capture of GPS signal (GPS-like signal) are also researched. On the basis of the prophase work, disturbing force is researched, so the paper has more engineering sense.The development of GPS (GPS-like) measurement technique in recent years is reviewed in this paper firstly. Then the measurement principle and the several describing manners of satellite attitude are discussed completely. The observables and the error sources in GPS measurement are introduced. The primary content is in the third chapter to the seventh chapter. The primary contents are as follows:1. In chapter 3, the typical attitude control mode and the gravity grads moment of SAR satellite are researched, and the disturbed attitude dynamics mode is established. The Maximum-likehood Kalman filtering is proposed to resolve the attitude. The simulation shows the advantage of the proposed algorithm.2. In chapter 4, J₂ disturbing force which effects the SAR satellites formation is researched. The relative range change rules are summed up, and the magnitudes of the change are worked out. The rules show that the appropriate correction must be adopted to ensure the SAR satellites formation to be in the need precision bound steadily. Then the improved UKF square root filtering is adopted to resolve the relative movement of SAR satellites formation. Finally, the simulation is made. The result shows the advantages of the proposed algorithm compared with EKF and UKF.3. Integer ambiguity resolution is very important to GPS measurement under the high dynamic condition. In chapter 5, a new ambiguity resolution algorithm aided with the triple difference observables is proposed. This algorithm can work out the ambiguity floating resolution faster, and improves the precision. A new decorrelation method is proposed to avoid possible sick factorization in Gauss transformation. Finally, an efficient search strategy is used. Compared with the famous LAMBDA (Least-Squares Ambiguity Decorrelation Adjustment) algorithm, the proposed algorithm has higher real-time and reliability.4. Cycle slip is another important problem to GPS dynamic measurement. There is not a common adaptive algorithm. In chapter 6, an algorithm is proposed which utilizes the triple difference observables to detect the cycle slip and corrects cycle slip by baseline length constraint. The simulation shows the effectiveness of this algorithm.5. The capture of GPS(GPS-like) signal is the precondition of GPS measurements. Along with the development of CDMA navigation system, the using of long PN code is a current. SAR satellites are under high dynamic, which the capture of long PN code will effect the real-time seriously. In chapter 7, a new fast correlation algorithm based FWT is proposed. The synchronization method of sub-code of multiple code is proposed to overcome the difficulty which blocks the use of FWT. Performance analysis shows that this algorithm can reduce correlation time greatly. In addition, a new improved algorithm, which is Auto Decision Threshold Level Control algorithm, is also proposed. Theoretics analysis and simulation show that this algorithm makes false alarm lower and the detection probability higher, and the acquisition time is reduced greatly.At last, the summarizer is made. The advice of the farther research is put forward.