This paper introduces a method for spacecraft rotation and translation control by on-off thrusters with guaranteed Lyapunov-stable tracking of linear dynamic models. In particular, the proposed control method switches on, at each time step, only those thrusters needed to maintain stability. Furthermore, the strategy allocates the configuration so that the minimum number of actuators is used. One of the benefits of the proposed method is that it substitutes both the thruster mapping and the pulse modulation algorithms typically used for real-time allocation of the firing thrusters and for determining the duration of the firing. The proposed approach reduces the computational burden of the onboard computer versus the use of classical thruster mapping algorithms, which typically involve iterative matrix operations. The paper presents analytical demonstrations, numerical simulations on a six-degree-offreedom spacecraft, and experimental tests on a hardware-in-the-loop three-degree-of-freedom spacecraft simulator floating over air pads on a flat floor. The method proves to be effective and easy to implement in real time.Received 21 September 2009; revision received 10 March 2010; accepted for publication 12 March 2010. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0731-5090/10 and $10.00 in correspondence with the CCC.

This paper deals with the problem of spacecraft time-optimal reorientation maneuvers under boundaries and path\ud constraints. The minimum time solution with keep-out constraints is proposed using the particle swarm optimization\ud technique. A novel method based on the evolution of the kinematics and the successive obtainment of the control law is\ud presented and named as inverse dynamics particle swarm optimization. It is established that the computation of the\ud minimum time maneuver with the proposed technique leads to near-optimal solutions, which fully satisfy all the\ud boundaries and path constraints

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This paper focuses on the fuel-minimum in-plane spacecraft reconfiguration maneuver in 2 perturbed near-circular orbits. The reconfiguration problem is posed as a nonlinear optimal control problem and it is solved by two techniques, namely the Mixed-integer Linear Programming and the Particle Swarm Optimization. The control is assumed to be a piecewise constant function and a linear dynamics model based on relative orbit element parameterization is used to derive the fueloptimal solution. Simulation results demonstrate the efficiency of both proposed methods, pointing out the performance in terms of computing time and accuracy.

A novel approach for minimum-time reconfiguration of satellite formations is proposed considering the perturbation forces as control variables. Planning appropriate attitude maneuvers for each satellite, the atmospheric drag and of the solar radiation pressure are properly controlled, and the formation is given the appropriate inputs to achieve the imposed reconfiguration. Limits and advantages of the presented maneuvers are examined considering low Earth orbits, medium Earth orbits, and geostationary orbits. The recent inverse dynamics particle swarm optimization is involved; the integration of the attitude dynamics is avoided, thus reducing the computational effort, and satisfied attitude constraints at the initial and final time instants are guaranteed. B-spline curves approximate the attitude kinematics, variable time mesh points are introduced, and adaptive decreasing tolerances are considered for the imposed constraints. The evolution of the configuration is simulated with a high-fidelity orbital simulator considering all the perturbations that can affect the maneuver. Two test cases are taken into account, one involving a circular formation reconfiguration and the other an along-track reconfiguration

At Low Earth Orbits differentials in the drag force between spacecraft can be used for controlling their relative motion in the orbital plane. Current methods for determining the drag force may result in errors due to inaccuracies in the density models and drag coefficients. In this work, a methodology for relative maneuvering of spacecraft based on differential drag, accounting for uncertainties in the drag model is proposed. A dynamical model composed of the mean semi-major axis and argument of latitude is utilized for describing long range maneuvers. For this model, a Linear Quadratic Regulator is implemented, accounting for the uncertainties in the drag force.The actuation is the pitch angle of the satellites, considering saturation. The control scheme guarantees asymptotic stability of the system up to a certain magnitude of the state vector, which is determined by the uncertainties. Numerical simulations show that the method exhibits consistent robustness to accomplish the maneuvers, even in presence of realistic modeling of density fields, drag coefficients, the co-rotation of the atmosphere and zonal harmonics up to J 8 .

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