Repairing Plans On-the--y

Even with the most careful advance preparation and even with inbuilt allowance for some degree of contin gency plans need to be altered to take into account execution circumstances and changes of requirements We have developed methods for repairing plans to ac count for execution failures and changes in the execu tion situation We rst developed these methods for the Optimum aiv planner designed to support space craft assembly integration and veri cation 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 sub sequently re ned the methods for the O Plan planner and incorporated plan repair methods into the system This paper describes the algorithms used for plan re pair in O Plan and gives an example of their use