Robust adaptive coordination controller for a spacecraft equipped with a robotic manipulator

Free-flying robotic spacecraft play a significant role in the space industry today. Unlike ground-based robots, the manipulator motion in a space robot can cause undesirable disturbances to the spacecraft platform, causing its attitude to change, potentially disrupting communication and solar energy collection processes as a result. Thus, coordinated control of both the spacecraft attitude and the manipulator motion become essential for successful space operations. Though past research has developed dynamic models for spacecraft manipulators, the contribution of reaction wheels to the angular momentum of the entire system needs further consideration. This paper reformulates the dynamic equations of a free-flying space robot by taking the aspect of reaction wheels into account. A diagonalization method is introduced to decouple the highly nonlinear multi-input/multi-output system model. A novel adaptive variable structure control method is then applied to implement a robust coordination controller for the space robot subjected to system uncertainties. Simulations are carried out on a spacecraft model with a 3-degree-of-freedom manipulator mounted on it to demonstrate the robustness of the proposed approach. Comparisons with sliding mode control show that the new controller results in faster settling times, which leads to maintaining uninterrupted communication links and efficient solar energy harvesting.