Choosing Objectives in Over-Subscription Planning

Many NASA planning problems are over-subscription problems – that is, there are a large number of possible goals of differing value, and the planning system must choose a subset that can be accomplished within the limited time and resources available. Examples include planning for telescopes like Hubble, SIRTF, and SOFIA; scheduling for the Deep Space Network; and planning science experiments for a Mars rover. Unfortunately, existing planning systems are not designed to deal with problems like this – they expect a well-defined conjunctive goal and terminate in failure unless the entire goal can be achieved. In this paper we develop techniques for over-subscription problems that assist a classical planner in choosing which goals to achieve, and the order in which to achieve them. These techniques use plan graph cost-estimation techniques to construct an orienteering problem, which is then used to provide heuristic advice on the goals and goal order that should be considered by a planner.