Variable Speed Control Moment Gyroscopes for Reorientation Maneuvers of Rigid Spacecraft
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Variable Speed Control Moment Gyroscopes for Reorientation Maneuvers of Rigid Spacecraft1 Giulio Avanzinf and Guido de Matteis' Abstract Feedforward steering laws for variable speed control moment gyroscopes are designed using an inverse simulation method based on a constrained optimization algorithm. The technique fully exploits torque actuator redundancy provided by the system to efficiently avoid singular states and to deal with the issues of position/rate saturation and/or gimbal mechanical failure. Rest-to-rest slew maneuvers are specified in terms of time evolution of Euler angles or rotation angle about the eigenaxis. System performance is improved by taking advantage of wheel speed variation with limited increment of required power. Real-time implementation of the algorithm may be problematic due to the complexity of the dynamical model and the high number of constraints.
Introduction A command generation technique based on the local optimization approach is proposed for reorientation maneuvers of a rigid spacecraft model featuring variable speed control moment gyroscopes (VSCMG) as internal torque actuators. Momentum exchange devices such as single gimbal CMGs (SGCMG) and reaction wheels (RW) are effective and widely used systems for attitude control during either station keeping or reorientation maneuvers, when a prescribed trajectory is to be precisely tracked. The principal characteristics of the two systems can be summarized in short when one recalls that RWs, where control torque is generated along the rotor spin axis, have the advantage of a rather simple mechanization and dynamics because
'Presented as paper AAS 2002-168 at the 2002 AAS/ AIAA Spaceflight Mechanics Meeting, San Antonio, TX, January 27-30,2002. 2Assistant Professor, Department of Aeronautical and Space Engineering, Politecnico di Torino, corso Duca degli Abruzzi 24, 10129 Turin, Italy. 3professor, Department of Mechanics and Aeronautics, Universita di Roma "La Sapienza," via Eudossiana, 18, 00184, Rome, Italy.
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only a variation of relative velocity between rotor and spacecraft is involved [1]. On the other hand, SGCMGs, where the control torque is perpendicular to both the gimbal and wheel spin axes, present the relevant feature of the well-known torque amplification property [2]. However, successful design and implementation of an attitude control system using SGCMG can be a difficult task because of the complex dynamics resulting from gyroscopic effects and the issue of singular gimbal configurations. In the latter situation, the commanded gimbal rate becomes very high because output torque is zero about a particular axis [3, 4]. In recent times, the combined use of RW and SGCMG control modes in VSCMG devices where the flywheel speed can be varied in a narrow range has been proposed [5, 6] as a very effective means for dealing with SGCMG singularities. The major advantage of the variable speed system stems from the higher degree of redundancy of the control actuators, because in singularity avoi
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