Design and Control of Libration Point Spacecraft Formations

The article of record as published may be located at http://dx.doi.org/10.2514/6.2004-4786Proceedings of AIAA Guidance, Navigation, and Control Conference ; Paper no. AIAA 2004-4786, Providence, Rhode Island, Aug. 16-19 2004We investigate the concurrent problem of orbit design and formation control around a libration point. The problem formulation is based on a framework of multi-agent, nonlinear optimal control. The optimality criterion is fuel consumption modeled as the L1-norm of the control acceleration. Fuel budgets are allocated by isoperimetric constraints. The nonsmooth optimal control problem is discredited using DIDO, a software package that implements the Legendre pseudospectral method. The discretized problem is solved using SNOPT, a sequential quadratic programming solver. Among many, one of the advantages of our approach is that we do not require linearization or analytical results; consequently, the inherent nonlinearities associated with the problem are automatically exploited. Sample results for formations about the Sun-Earth L2 point in the 3-body circular restricted dynamical framework are presented. Globally optimal solutions for relaxed and almost periodic formations are presented for both a large separation constraint (about a third to half of orbit size), and a small separation constraint (a few hundred km or about 5_10_6 of orbit size).N

Model-Based Systems Engineering in Concurrent Engineering Centers

Concurrent Engineering Centers (CECs) are specialized facilities with a goal of generating and maturing engineering designs by enabling rapid design iterations. This is accomplished by co-locating a team of experts (either physically or virtually) in a room with a focused design goal and a limited timeline of a week or less. The systems engineer uses a model of the system to capture the relevant interfaces and manage the overall architecture. A single model that integrates other design information and modeling allows the entire team to visualize the concurrent activity and identify conflicts more efficiently, potentially resulting in a systems model that will continue to be used throughout the project lifecycle. Performing systems engineering using such a system model is the definition of model-based systems engineering (MBSE); therefore, CECs evolving their approach to incorporate advances in MBSE are more successful in reducing time and cost needed to meet study goals. This paper surveys space mission CECs that are in the middle of this evolution, and the authors share their experiences in order to promote discussion within the community

Design and Control of Libration Point Spacecraft Formations

The article of record as published may be located at http://dx.doi.org/10.2514/1.18654We investigate the concurrent problem of orbit design and formation control around a libration point. Concurrency implies that the design and control problem are simultaneously investigated. Separating the two problems is both unnecessary and ill-advised. The full problem can be naturally cast as a multi-agent, nonlinear, constrained optimal control problem. The optimality criterion is fuel consumption because the engineering feasibility of a formation design is dominated by the amount of propellant required to maintain a formation. Contrary to popular belief, quadratic costs do not measure fuel consumption; consequently, we take a direct measure of fuel consumption given by the L1 norm of the control acceleration. Fuel budgets to individual spacecraft are allocated by isoperimetric constraints. As with most nonlinear problems, the resulting problem does not have closed-form solutions. The full problem is solved by a Legendre pseudospectral method implemented in DIDO. DIDO exploits SNOPT, an active-set sequential quadratic programming solver, and generates quick solutions to facilitate redesign, an important requirement during the early stages of formation design. This approach does not use linearizations in modeling the dynamics, nor does it require analytical results; rather, the inherent nonlinearities associated with the problem are automatically exploited. Furthermore, we take advantage of a true distributed system architecture that does not rely on designing a leader–follower system. Sample results for formations about the sun–Earth and Earth– moon L2 point in the three-body circular restricted dynamical framework are presented. Optimal solutions for relaxed and almost periodic formations are presented for both a large separation constraint (about a third to half of orbit size), and a small separation constraint (about a millionth of orbit size)