Repairing Plans On-the-fly

Even with the most careful advance preparation, and even with inbuilt allowance for some degree of contingency, plans need to be altered to take into account execution circumstances and changes of requirements. We have developed methods for repairing plans to account for execution failures and changes in the execution situation. We first developed these methods for the Optimum-AIV planner designed to support spacecraft assembly, integration, and verification at ESA, and later deployed for Ariane IV payload bay AIV. This system was itself based on our Nonlin and O-Plan planning algorithms and plan representation. We subsequently refined the methods for the O-Plan planner and incorporated plan repair methods into the system. This paper describes the algorithms used for plan repair in O-Plan and gives an example of their use.