1 A Constraint-Based Approach to Satellite Scheduling Joseph C. Pemberton and Flavius Galiber, III pemberto@psrw.com flavius@psrw.com Pacific-Sierra Research 1400 Key Boulevard, Suite 700 Arlington, VA 22209 Abstract Satellite scheduling, like all scheduling, is the problem of mapping tasks (observation, communication, downlink, control maneuvers, etc.) to resources (sensor satellites, relay satellites, ground stations, etc.). Through our work on satellite scheduling problems, we have encountered many different constraints that are particular to the satellite-scheduling domain. In this paper, we will introduce the satellite mission-operation scheduling problem, describing the problem constraints that are particular to satellite scheduling, and then present the constraint-based techniques that we have used to address these problems. 1 Introduction In general, satellite scheduling is the problem of mapping tasks (observations, communications, downlinks, control maneuvers, etc.) to resources (sensor satellites, relay satellites, ground stations, etc.). Satellite scheduling problems differ from traditional scheduling problems in several ways. Perhaps the most obvious difference between satellite scheduling and traditional scheduling problems is the fact that some of the resources (i.e., the satellites) are orbiting the earth. This places an additional set of constraints on when a task can be executed. Satellite-scheduling problems oftentimes involve periodic tasks, variable length tasks, and tasks that can be preempted. In addition, satellite-scheduling problems are usually over constrained. Thus, satellite scheduling can usually be viewed as a constraint-optimization problem rather than a constraint-satisfaction problem. Although the term satellite scheduling has been applied to many different aspects of a satellite’s operation (e.g., design planning, launch control, lifecycle, etc.), we will focus on scheduling mission operations 1 , namely the day-to-day activities of an operational satellite. Mission operation activities include payload operations (e.g., using a sensor on the satellite to collect data), bus operations (e.g., maintaining the health and status of the vehicle) and communications operations (e.g., transmitting data between satellites or to the ground and receiving information or commands from a ground station). 1 This class of satellite-scheduling problems is often referred to as Satellite Mission Planning.