基于非线性干扰观测器的航天器相对姿轨耦合控制

针对带挠性附件的服务航天器在近距离逼近失控目标航天器时的控制问题，考虑由于推进安装偏差导致的姿轨耦合，通过选用相对位置和相对姿态四元数作为状态向量，建立了服务航天器与失控目标航天器的相对位置和姿态动力学方程。考虑服务航天器的挠性附件影响，挠性振动可以视为位置和姿态控制系统微分有界的干扰。基于反馈线性化方法提出了非线性反馈控制律，设计了非线性干扰观测器，用于补偿可建模干扰，并基于所提非线性反馈控制律和非线性干扰观测器设计了复合控制器，其中非线性干扰观测器用于补偿挠性附件产生的干扰。数字仿真及半物理实物闭环验证表明，利用所设计的复合控制器能够有效补偿干扰，同时在对失控目标航天器跟踪时具有很好的鲁棒性。 

Nonlinear disturbance observer based control for relative position and attitude coupled spacecraft

This paper studies the control problem of approaching and docking autonomously system including an on-orbit servicing spacecraft with flexible appendages and an out-of-control target considering the coupled relative position and attitude dynamic. Choosing the relative position and the relative attitude quaternion as the system state and considering the relative position and attitude coupled which is produced by the propulsion installation error, the relative position and attitude coupled dynamics model of the servicing spacecraft with respect to the out-of-control target is established in the form of state equation. While considering the flexible appendages of servicing spacecraft, the vibration from flexible appendages is modeled as a derivative-bounded disturbance to the position and attitude control system of the rigid body. Then a nonlinear feedback control algorithm is proposed based on feedback linearization. Aimed at attenuating the modeled disturbance, a disturbance-observer-based control is formulated for feed forward compensation of the elastic vibration. Then a composite controller with a hierarchical architecture is designed by combining disturbance-observer-based control and nonlinear feedback control, where disturbance-observer-based control is used to compensate the disturbance from the flexible appendages. Numerical simulations and semi-physicd closed-loop experiments are performed to demonstrate that by using the composite hierarchical control law, disturbances can be effectively attenuated and the nonlinear feedback control law is robust with perfect tracking performance.