Optimal Guidance Control Strategies for Spacecraft Attaches to A Small Body
摘要: 以小天体伴飞附着任务为工程背景,针对探测器在小天体复杂弱引力场条件下附着这一难题,研究了最优制导控制策略。首先,考虑在小天体极区实施附着任务,建立并简化动力学模型,给出约束条件和基于时间-燃耗最优的混合性能指标要求。然后,采用相平面法设计了最优制导律,利用极限环设计最优开关控制律;同时,采用高斯伪谱法把附着小天体的最优制导问题转化成非线性规划问题,利用Matlab/GPOPS优化工具包求取最优数值解。最后,加入已有的基于矢量测量的自主光学导航模块构建GNC仿真回路,对两种最优制导控制策略进行仿真验证。结果表明:两种制导控制策略都能满足任务要求,但基于相平面法得到的最优制导控制具有一定风险,而基于高斯伪谱法得到的最优制导控制精度更高、燃耗更少,适于工程应用。Abstract: The issue of spacecraft attaching to a small body with complex weak gravitation field is challenging. In this paper, two optimal guidance control strategies are addressed with the mission background of accompany flight and attaching to a small body. First, taking the attaching mission in polar area of small body into consideration, dynamics model is constructed and simplified, as well as the constraints and time-fuel integrated optimal performance index is described. Secondly, phase plane method (PPM) is used to design optimal guidance, and optimal on-off control is given by limit circle. Next, Gauss pseudospectral method (GPM) is utilized to transform optimal guidance problem into nonlinear program (NLP) problem, and MATLAB/GPOPS optimal tool software package is utilized to obtain the numerical solution of guidance. Finally, the vector measurement based autonomous optical navigation given in the previous work is introduced to GNC simulation loop, and the two optimal guidance control strategies are verified. Simulation results show that both of them meet the requirement of mission, but the phase plane method based optimal guidance control is a little risky, while the Gauss pseudospectral method based optimal guidance control has a lower fuel consumption and higher accuracy, so the latter is feasible for engineering practice.