<h2>AAS 95-413</h2><h2>Detumbling and Reorienting Underactuated Rigid Spacecraft</h2><h4>V. Coverstone-Carroll, University of Illinois at Urbana-Champaign, Champaign, IL</h4><h2> Abstract </h2>Control algorithms that detumble and reorient underactuated spacecraft are discussed.  Underactuated spacecraft have control torques about only two of the principal axes.  Variable structure control is used to detumble the spacecraft.  This technique requires that a switching surface, a surface which defines the desired dynamic relationship between state variables, be constructed.  Control algorithms are designed to drive the system to the switching surface.  Exponential decay of the angular velocity results once the surface is reached.  After the spacecraft is detumbled, a series of at most three rotations about the two active axes is used to reorient the spacecraft.  An example of a detumbling and reorientation maneuver is presented.
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