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  Controls the momentum in a spacecraft using solar pressure. 
  Uses a PI controller and a two degree of freedom gimbal at the end of the 
  solar array. The solar pressure flap is a perfect mirror.
  The available torque is first mapped over a range of angles. Then a
  controller is designed and simulated. Note that the array can only provide
  torques in X and Z.
  See also SolarF.
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