Design Of Final Approaching Control Law For Autonomous Rendezvous Of Spacecrafts

In recent years, China has completed manned space flight and lunar exploration in the initial phase. With the background of the following deep space exploration program and more complex space missions all in the demand of space rendezvous technology, this dissertation systematically studies on control law of spacecraft rendezvous in the final approaching stage. Based on the differences of the Spacecraft orbits, the main contents of this paper are divided into two parts: the first part focuses on the design of the control law for spacecraft running in the circular orbit under multiple constraints; while the other part takes into the consideration of elliptical orbit to design the control law with robustness.Firstly based on the analysis for the development histories of autonomous rendezvous in space and the research status of our country, we introduce the derivation process of classical Clohessy and Wilshire equation which is used to describe relative motion between spacecrafts. Then with the foundation of this equation and some improvements, the Lawden equation is obtained which is applied for the description of the relative motion in elliptical orbit. By analyzing the task of spacecraft rendezvous, the target for the rendezvous could be concluded into tracking a designed reference signal. Therefore, this paper applies parametric eigenstructure assignment method to control law design based on model reference tracking.Furthermore, when spacecrafts run in circular orbit, the control law would be designed under two conditions: one is affected by control constraints; the other situation takes into consideration that inertial information for the system is uncertain due to environment disturbance and measurement error. On the first condition, the theory of positive definite matrix is applied for converting time-varying constraints of the control outputs into the constraints of a specific matrix confined to positive definite matrix. As a result, it can be easy to determine whether the controls satisfy constraints. The approaching control law is composed of the system poles and free parametric vectors which could be fixed through solving the optimization problem with constraints we established to connect the system performance. When the control law works in the system with different terminal conditions, we could see the values of controls are well within the prescribed area through system simulation. In conclusion, the simulation results show that the controls are limited as we wish and the system asymptotically tracks a given signal. To the second condition, the uncertainty model is constructed to propose a robust control law. While solving the parameters in the control law, we add constraints to keep the system stable. Though the results of system simulation are created by different deviation ratio of inertial information, system can still keep asymptotically stable when tracking reference signals which proves the control law can effectively deal with uncertain inertial information in spacecraft rendezvous.Finally, based on the Lawden equation for relative motion of spacecrafts, another control laws would be proposed to tackle the features brought by elliptical orbit. After entirely analyzing the Lawden equation, the coefficients, made of inertia information, own periodical slow time-varying characteristics. And this leads to impossibility of the acquirement of the accurate real-time value. Therefore, we design the robust control law for establishing the model under the standard of relative motion for circular orbit with uncertainties. Simulation results show that in different eccentricity elliptical orbit, the system achieves very high precision when tracking a given signal. Moreover, the effectiveness of this design method could be proved as well.