ASPEN – Automated Planning and Scheduling for Space Mission Operations

This paper describes the ASPEN system for automation of planning and scheduling for space mission operations. ASPEN contains a number of innovations including: an expressive but easy to use modeling language, multiple search (inference) engines, iterative repair suited for mixed-initiative human in loop operations, real-time replanning and response (in the CASPER system), and plan optimization. ASPEN is being used for the Citizen Explorer (CX-1) (August 2000 launch) and the 2 Antarctic Mapping Missions (AMM-2) (September 2000). ASPEN has also been used to automate ground communications stations – automating generation of tracking plans for the Deep Space Terminal (DS-T). ASPEN has been used to demonstrate automated command generation and onboard planning for rovers and is currently being evaluated for operational use for the Mars-01 Marie Curie rover mission. CASPER, the soft real-time versions of ASPEN, has been demonstrated with the Jet Propulsion Laboratory (JPL) Mission Data Systems (MDS) Control Architecture prototypes. Overview Planning and scheduling spacecraft operations involves generating a sequence of low-level spacecraft commands from a set of high-level science and engineering goals. ASPEN (Automated Scheduling and Planning ENvironment) encodes spacecraft operability constraints, flight rules, spacecraft hardware models, science experiment goals, and operations procedures to allow for automated generation of low-level spacecraft sequences. By automating the command sequence generation process and by encapsulating the operations specific knowledge, ASPEN enables space missions to be controlled by a small operations team thereby reducing costs. ASPEN is an object-oriented system that provides a reusable set of software components that implement the elements commonly found in complex planning/scheduling systems. These include: • An expressive constraint modeling language to allow the user to define naturally the application domain • A constraint management system for representing and maintaining spacecraft operability and resource constraints, as well as activity requirements • A set of search strategies for plan generation and repair to satisfy hard constraints • A language for representing plan preferences and optimizing these preferences • A soft, real-time replanning capability • A temporal reasoning system for expressing and maintaining temporal constraints • A graphical interface for visualizing plans/schedules (for use in mixed-initiative systems in which the problem solving process is interactive). Automated planning and scheduling technology offers considerable promise in automating spacecraft operations. Planning and scheduling spacecraft operations involves generating a sequence of lowlevel spacecraft commands from a set of high-level science and engineering goals (see (Chien et al., 1998b) for an overview). In this paper, we discuss ASPEN and its use of an iterative repair algorithm for planning and scheduling as well as for replanning and rescheduling. ASPEN is a reconfigurable planning and scheduling software framework (Fukunaga et al., 1997). Spacecraft knowledge is encoded in ASPEN under seven core model classes: activities, parameters, . This work was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.