Study On Terminal Guidance Of Flyby Spacecraft

Flyby is a new way of space-based target observation, which plays an important role in missions such as spaceconfrontation and on-orbit servicing. Precisely steering the spacecraft to the fly-by point nearby the target is one of the key technologies. Therefore, methods of terminal guidance for flyby are studied.The dynamic model of flyby is established, which is the foundation of later research. Equations of Six-degree motion of the spacecraft and the target are presented and the method of attitude control is studied, In addition, mass equations and calculation equations of relative motion are added.The optimal guidance based on the maximum principle is studied. Firstly, the process of flyby is transformed to the question of optimal control by the equations of relative motions in inertial coordinate systems and performance index which synthetizes the time and fuel. The expressions of optimal direction and working hours of thrust are deduced, then the plans of optimal guidance is explained. Finally, the method is validated and influences that error and key parameters impact on the method is analyzed by simulation..The terminal guidance based on proportional navigation is investigated. The relation between the light of sight(LOS) rates and relative velocity according to the relative motion in LOS coordinate systems. The LOS rates of the spacecraft to the virtual point are calculated after the LOS rates of spacecraft to the target and relative positons are obtained, which the the proportional navigation is raised founded on. Finally, the method is validated and influences that error impact on the method is analyzed by simulation.The offset guidance based on the standard LOS rates is studied. The standard LOS rates of spacecraft with regard to the target is obtained by standard trajectory and cubic spline function. The offset between real and standard LOS rates under the same approaching distance is guided to zero. Simulation is carried out to analyzing the influence of errors and validates the method.Terminal guidances for flyby missions are provided by the research, at the same time, the working is also useful to the space mission such as rendezvous and deep-space exploration.