Research On Spacecraft Rendezvous Guidance Schemes Under Thrust Constraints

Rendezvous is one of spacecraft relative motion forms. It needs complicated maneuvering control strategies while the chaser is moving to the target. Practical rendezvous problems are treated under complicated conditions of kinds of space missions such as minimum time, optimal energy consumption, and thrust constraints. So it’s very important to design proper guidance schemes for different missions.In the background of spacecraft rendezvous, this paper proposes two guidance schemes which are based on satisficing control algorithm and model predictive control algorithm considering thrust constraints respectively.First, relative dynamic model is deducted. Then the model is transformed while variable t is substituted with true anomaly θ. Free flying around is a special situation, and its analytic solutions are solved by integrating dynamic equations, and state transition matrix is also obtained at the same time. The simulation results represent that free-flying orbit is an accurate ellipse where the rendezvous initial state is chose.Then, this paper discusses the satisficing control theory which a novel guidance approach to rendezvous based on is introduced to solve control magnitude and direction constraints with a linear quadratic performance index. Later system stability is analyzed because some variable parameters affect values of closed-loop poles. We choose reasonable parameters values to simulate for the validity of this algorithm.Later, the paper introduces the theory of model predictive control(MPC) and applies it to rendezvous. The relative dynamic model is discretized to create predictive model so that we can get guidance scheme with and without constraints while thrust constraints are taken into consideration with a discrete linear quadratic performance index. Three important factors influencing system stability includes receding horizon control law, terminal value function and terminal constraints collection. The former two are received by iterating, and the last one is acquired based on LMI theory. Simulation results are received and it validates the MPC method.At last, the performance of two algorithms is analyzed with comparative method in terms of initial-points feasible region, constraints requirements, rendezvous time, performance index and energy-consumption index. By comparing, we find that satisficing control algorithm can deal with situations with strict constraints in global region, and it has the characteristics of better performance and energy-consumption indexes but more time. For MPC algorithm, it fits to handle loose constraints situations with less rendezvous time but worse performance and energy-consumption indexes, and its initial state should be chose carefully. So this section provides a foundation to design proper guidance scheme for different space missions.