Embedding planning technology into satellite systems

Abstract

Satellites will need increasing amounts of autonomy in order to maximize their mission capabilities even in the face of events that may disrupt their systems. This paper describes an on-board planning and execution system for satellites that schedules system tasks and responds to real-time events. The system consists of a mission planner that schedules nominal activities, a threat response planner that schedules actions to mediate external threats to the satellite and its mission, and an executive that takes the resulting plan and commands the satellite subsystems. A state-based simulation of a satellite system was developed and used to demonstrate the planning and execution system. I. Introduction There is an increasing need to develop on-board autonomy for satellite systems, both to increase their productivity and to protect them from hazards and threats such as component faults, approaching space debris, and dangerous space weather. We are developing an integrated system that demonstrates solutions to many of the challenges inherent in developing embedded planning systems for satellites. The Highly Autonomous Mission Manager for Event Response (HAMMER) system is designed to allow a satellite to operate and respond to threats even when it is not in communication with the ground or when time constraints require immediate response to threats. The HAMMER system attempts to meet mission objectives even in the face of threats. HAMMER prioritizes multiple, competing user goals and requests and determines an optimal ordering of satellite tasks to conserve resources and maximize capability. End user goals and requests are expected to come to the satellite asynchronously as the satellite is operating. Thus, new task schedules will need to be generated on-the-fly. Threats are also expected occur asynchronously and require on-the-fly replanning to counter the threats and still attempt to meet mission objectives. User requests will be at a high level (e.g., take an image of location X by time Y and download to location Z) and will need to be turned into a detailed plan of low-level satellite actions. The tight coupling between end user goals, mission planning, threat response, and task execution is a key challenge for these systems. HAMMER integrates an on-board execution system with two different on-board planning and scheduling systems: a Mission Planner (MP) that plans optimal sequences of actions to achieve mission goals, and a Threat Response Planner (TRP) that refines the mission plan with pre-planned responses to threats. The benefits of the HAMMER system are that it: 1) can receive high-level end user goals and produce optimal satellite plans; 2) can respond to threats without ground intervention; 3) is scalable and reusable because the core components are model-driven.