<h2>AAS 97-180</h2>
<h2>ON-OFF CONTROL TO DESPIN AND RETRIEVE A TETHERED ARTIFICIAL  GRAVITY SPACECRAFT INCLUDING PASSIVE DAMPING                                        </h2>
<h4> S. I. Saeed and J. D. Powell, Stanford University                                                                                                                        </h4>
<h2> Abstract </h2>
 This paper develops optimal on-off thrusting profiles to despin and retrieve a  tethered artificial gravity spacecraft.  A nonlinear on-off thrusting optimization  is performed on a simple 3-DOF system.  Fuel usage for on-off thrusting is compared  to a continuous thrusting case and found to be slightly better compared to previous  results.  The nonlinear optimized thrusting profile is applied to a three segment  tether model with constant passive damping and found to be unstable during  retrieval.  By increasing the retrieval time and stopping thrusting for low tether  tensions, the tether retrieval is stabilized for tether lengths greater than 25  meters.