Knowledge based tools for hubble space telescope planning and scheduling: constraints and strategies

The Hubble Space Telescope (HST) presents an especially challenging scheduling problem since a year's observing program encompasses tens of thousands of exposures facing numerous coupled constraints. This article discusses recent progress in the development of planning and scheduling tools which augment the existing HST ground system. General methods for representing activities, constraints and constraint satisfaction, and time segmentation have been implemented in a scheduling testbed. The testbed permits planners to evaluate optimal scheduling time intervals, calculate resource usage and to generate long- and medium-range plans. Graphical displays of activities, constraints and plans are an important feature of the system. High-level scheduling strategies using rule based and neural net approaches have been implemented.