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A multiple-team organization for decentralized guidance and control of formation flying spacecraft

In recent years, formation flying has become an enabling technology for several mission concepts at both NASA and the Department of Defense. In most cases, a multiple-satellite approach is required in order to accomplish the large-scale geometries imposed by the sensing objectives. In general, the paradigm shift of using a multiple-satellite cluster rather than a large, monolithic spacecraft has also been fueled by the objectives of increased robustness, greater flexibility, and reduced cost. However, the operational costs of monitoring and commanding a large fleet of close-orbiting satellites is likely to be unreasonable unless the onboard software is sufficiently autonomous, robust, and reconfigurable. This paper presents the prototype of a system that addresses these objectives – a decentralized guidance and control system that is distributed across spacecraft using a multipleteam framework. The system is designed to provide a high-level of autonomy, to support clusters with large numbers of satellites, to enable the number of spacecraft in the cluster to change post-launch, and to provide for on-orbit software modification. The real-time distributed system will be implemented in C++ using the MANTA environment (Messaging Architecture for Networking and Threaded Applications). In this architecture, tasks may be remotely added, removed or replaced post-launch to increase mission flexibility and robustness. This built-in adaptability will allow significant or simple software modifications to be made on-orbit in a robust manner. The prototype system, which is implemented in Matlab, emulates the task-based and message-passing features of the MANTA software. In this paper, the multiple-team organization of the cluster is described, and the relative dynamics in circular and eccentric reference orbits is reviewed. Families of periodic, relative trajectories are identified and represented with static geometric parameters. An analytic solution for impulsive maneuvering is used for whole orbit-period control in circular orbits, and linear programming techniques are used to find time-weighted, minimum-fuel control solutions. Finally, the decentralized guidance law design is presented, with a comparison between the optimal and a sub-optimal assignment algorithm.