Rapid Repair Method for Spacecraft Plan Failures using Temporal Decoupling Strategy

There are various uncertainties in space exploration missions, which have a significant impact on plan execution and may result in plan failures. Most of the impacts of uncertainties can be summarized as the temporal uncertainty of action and the uncertainty of action's effects caused by the temporal uncertainty. In such case, remote control from the Earth cannot handle that problem in time, especially in deep space missions, due to the long distance between the spacecraft and the ground station. Therefore, this paper proposes a rapid plan repair method for spacecraft plan failures using temporal decoupling strategy, which enables the spacecraft to repair the failed plan autonomously and quickly while executing part of the plan. First, a decoupling strategy of temporal constraint network for failed plan is designed. In order to enable the spacecraft to continue executing some actions when the plan failures, the inexecutable actions in the failed plan are detected based on the causal relationship between the failed actions and the plan. And the temporal network of the failed plan is decoupled into a consistent network with executable actions and an inconsistent network with inexecutable actions by temporal constraint reasoning. Next, a conflict resolution method based on constraint relaxation is proposed for inconsistent temporal network. By analysing the interaction between variables within the network, a support list for domain of variable was constructed. Subsequently, a decremental constraint reasoning algorithm is designed to dynamically relax inconsistent constraints in the support list, thereby rapidly repairing the inconsistent temporal network. Then, a fusion method for temporal network based on the optimization of execution time is proposed, which integrates the repaired network with the executing network, enabling the spacecraft to repair the failed plan while continuing to execute some operations. Finally, experiments on domains about small celestial body exploration are run and the empirical results demonstrate the effectiveness and efficiency of this method.