Design of the Remote Agent Experiment for Spacecraft Autonomy 1 3 3 1 3 3 Douglas E

Design of the Remote Agent Experiment for Spacecraft Autonomy 1 3 3 1 3 3 Douglas E. Bernard , Gregory A. Dorais , Chuck Fry , Edward B. Gamble Jr. , Bob Kanefsky , James Kurien , 3 2 4 4 3 1 William Millar , Nicola Muscettola , P. Pandurang Nayak , Barney Pell , Kanna Rajan , Nicolas Rouquette , 1 5 Benjamin Smith , Brian C. Williams 1 2, 3, 4, 5 Jet Propulsion Laboratory, NASA Ames Research Center, MS 269-2 California Institute of Technology Moffett Field, CA 94035 2 4800 Oak Grove Drive Recom Technologies @ Ames 3 Pasadena, CA 91109 Caelum Research @ Ames 4 818-354-2597 RIACS @ Ames [email protected], 650-604-4756 [email protected] exploration. Where human exploration is desired, robotic ABSTRACT—This paper describes the Remote Agent flight precursors can help identify and map candidate landing experiment for spacecraft commanding and control. In the sites, find resources, and demonstrate experimental Remote Agent approach, the operational rules and technologies. constraints are encoded in the flight software. The software may be considered to be an autonomous “remote agent” of Current spacecraft control technology relies heavily on a the spacecraft operators in the sense that the operators rely relatively large and highly skilled mission operations team on the agent to achieve particular goals. that generates detailed time-ordered sequences of commands or macros to step the spacecraft through each The experiment will be executed during the flight of desired activity. Each sequence is carefully constructed in NASA’s Deep Space One technology validation mission. such a way as to ensure that all known operational During the experiment, the spacecraft will not be given the constraints are satisfied. The autonomy of the spacecraft is usual detailed sequence of commands to execute. Instead, limited. the spacecraft will be given a list of goals to achieve during the experiment. In flight, the Remote Agent flight software This paper describes a flight experiment which will will generate a plan to accomplish the goals and then demonstrate the Remote Agent approach to spacecraft execute the plan in a robust manner while keeping track of commanding and control. In the Remote Agent approach, how well the plan is being accomplished. During plan the operational rules and constraints are encoded in the execution, the Remote Agent stays on the lookout for any flight software and the software may be considered to be an hardware faults that might require recovery actions or autonomous “remote agent” of the spacecraft operators in replanning. the sense that the operators rely on the agent to achieve particular goals. The operators do not know the exact In addition to describing the design of the remote agent, this conditions on the spacecraft, so they do not tell the agent paper discusses technology-insertion challenges and the exactly what to do at each instant of time. They do, approach used in the Remote Agent approach to address however, tell the agent exactly which goals to achieve in a these challenges. period of time as well as how and when to report in. The experiment integrates several spacecraft autonomy The Remote Agent (RA) is formed by the integration of technologies developed at NASA Ames and the Jet three separate technologies: an on-board planner-scheduler, Propulsion Laboratory: on-board planning, a robust multi- a robust multi-threaded executive, and a model-based fault threaded executive, and model-based failure diagnosis and diagnosis and recovery system. recovery. This Remote Agent approach is being designed into the 1. INTRODUCTION New Millennium Program’s Deep Space One (DS1) mission Robotic spacecraft are making it possible to explore the as an experiment. The spacecraft (see Figure 1) will fly by other planets and understand the dynamics, composition, an asteroid, Mars, and a comet. and history of the bodies that make up our solar system. These spacecraft enable us to extend our presence into The New Millennium Program is designed to validate high- space at a fraction of the cost and risk associated with payoff, cutting-edge technologies to enable those human exploration. They also pave the way for human technologies to become more broadly available for use on other NASA programs. The experiment is slated to be Tens of Minutes exercised in October of 1998. Early Notice Later Planned interesting Replan Replanned Observation region Observation Spacecraft Trajectory Figure 2. Fast replanning based on new information Similarly, on the Mars Pathfinder mission, the science team requested the ability for the meteorology instrument, when it senses that a dust devil is passing, to tell the camera to Figure 1. DS1 Spacecraft take unplanned images aimed at the departing dust devil. It is difficult to see how this capability could coexist with Section 2 discusses the benefits to the spacecraft time-tagged command sequences for the imaging planned community from increased spacecraft autonomy and the for the rest of the day. motivation for this work. Section 3 outlines some of the challenges to acceptance of spacecraft autonomy and Reducing Spacecraft Operations Costs Section 4 introduces the Remote Agent design approach Our funding sources are insisting that means be found to and architecture. Section 5 covers the particulars of the DS1 reduce operations costs. A fixed amount of funding is Remote Agent experiment. Section 6 discusses the available from NASA for solar system exploration including functioning of each of the three technology components of spacecraft development and operations. When operations the Remote Agent. Section 7 describes how the Remote costs are reduced, more resources become available for Agent software is integrated into the separately-developed developing a wider variety of interesting solar system Deep Space One flight software. Section 8 describes how exploration missions. Development of detailed spacecraft the Remote Agent experiment is tested prior to flight. sequences accounts for the largest expenditure in operations Section 9 summarizes the paper and describes plans for budgets. future Remote Agent development. By commanding spacecraft at a higher level of abstraction, 2. NEED FOR AUTONOMY ON SPACECRAFT much of the sequence development task becomes the responsibility of the flight software, reducing ground The desire to increase the level of spacecraft autonomy operations costs. Some of the savings come from a change comes from at least three separate objectives of spacecraft in how we think about operations planning. The old customers: taking good advantage of science opportunities, approach was that all spacecraft activities needed to be reducing spacecraft operations costs, and handling predicted and approved by ground controllers. The new uncertainty—including ensuring robust operation in the thinking is that the ground controllers do not (always) need presence of faults. to know the low-level details of spacecraft activities but Taking Advantage of Science Opportunities only the capabilities of the spacecraft and the high-level goals. Our science customers would like the spacecraft to be able to modify its sequence of actions more quickly based on Ensuring Robust Operation in the presence of late-breaking information available on the spacecraft. uncertainty For example, an ultraviolet spectrometer on a comet flyby Our customers still require high reliability and the ability to mission might identify a region of particular interest for respond to problems in flight. For existing spacecraft, the intense scrutiny. With current technology, scientists have fault protection system often represents the most to make do with whatever pre-planned sequence of autonomous system on-board. Robust operation is desired observations has been stored on-board and cannot in the presence of hard faults, degraded performance, and reprogram any of those to examine more closely the newly operator errors. identified region of interest. With a future RA, plans may Traditional spacecraft, even in conservative designs, be revised based on this new information hours or minutes generally provide some minimal level of fault protection out before flyby. With ground-based control, a turnaround time of necessity. Otherwise, any major problem with attitude of hours is impractical and a turnaround time of minutes is control, power, or antennas could by itself prevent ground physically impossible due to the speed of light. See Figure controllers from diagnosing or correcting the problem. The 2. Remote Agent is able to go a step further: after recovering from a fault, it can continue the mission, even if it involves replanning for degraded capability. Another advantage of the Remote Agent derives from the Some additional techniques are required. These are nominal and failure modeling used by the fault diagnosis described in the testing section of this paper. engine. For hard-coded fault protection designs, the domain knowledge is implicit rather than explicit. This The concern about early definition may be valid depending means that we rely on the fault protection algorithm on how much of the spacecraft behavior we choose to build developers to understand the system, and abstract from that into the flight software before launch. With the traditional understanding a design for which symptoms to look for and sequence development approach, many sequences are what responses to take when they show up. In contrast, with developed after launch, so there is no opportunity to model-based fault diagnosis, the fault protection software observe full end-to-end behavior in a test environment. engineers explicitly model how the system behaves in With an on-board planner, we now have the opportunity to nominal and failure cases. Fault diagnosis then becomes a design and test the behavior before hand. It should be search for likely diagnoses given observed symptoms. pointed out that this is an opportunity and not a Since the spacecraft designers understand the details of the requirement. For example, the Project may choose to delay system behavior, there is an advantage to having them final design of flyby scenarios until after launch.

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