Research On Collision And Collision Avoidance For Satellites In Formation Flight

For ensuring the safety of the formation-flying satellites, it is necessary to assess the risk of collisions between satellites and to work out maneuver strategy to avoid collisions. The thesis analyzed the collision problems caused by perturbations and faults of equipments between satellites in formation flight by probability, dynamics analysis and fault diagnosis, and then formulated collision avoidance strategies. The main work and achievements are summarized as follows:(1) The methodology of computing the collision probability for short-term encounters and long-term encounters was summarized. Then an approach of fault diagnosis for dynamic systems was introduced, and collision avoidance strategies were described in details.(2) The methods of computing the collision probability were studied in-depth. For short-term encounters, the collision probability was computed by integrating the the marginal two-dimension pdf over the collision cross-sectional area which was formed by the volume swept by the combined sphere. Subsequently, three more approaches of computing the collision probability were introduced. Meanwhile, the results were compared with the four formulations. For long-term encounters, a method of computing the total collision probability was illustrated. A time-varying coordinate was defined. And the total collision probability could be calculated by projecting the combined covariance and the sphere into the coordinate. For evaluating the risk of satellites formation efficiently, quasi maximum instantaneous collision probability was defined.(3) Assuming a circular reference orbit, the safety evaluation criteria was figured out based on the collision probability. Two ways of implementing maneuvers to reduce chance of colliding were designed. One was based on the collision probability. Firstly, the direction of the maneuver is determined by finding the gradient of the collision probability with respect to maneuver direction. Once the maneuver direction is determined, its magnitude was found using the relationship between the collision probability and the maneuver velocity. The other maneuver approach was developed by the geometry formation of closest approach. The algorithm obtained the optimal maneuver velocity giving the miss distance constraint.(4) A kind of method of fault diagnosis which was based on analytic redundancy analysis was proposed for wireless metrology equipment and GPS metrology equipment. Firstly, the relative state vectors between the satellites were estimated with extended kalman filtering using measurement data, which were from wireless metrology and GPS metrology, and the relative state equation. Then the residual vector was gained. On the basis of this, two fault detection methods were presented. The one was based on weighted sum-squared residual,and the other wasχ2-based detection method. Finally, the results of the two methods were compared by the simulation.