<h2>AAS  96-197</h2><h2>OPTIMAL CONTINUOUS THRUST ORBIT TRANSFERS</h2><h4>J. D. Thorne and C. D. Hall, Air Force Institute of Technology</h4><h2> Abstract </h2>To solve the minimum time, circle-to-circle orbital transfer problem under continuous thrust, initial values of the Lagrange costates are required in the calculus of variations formulation.  Expressions are developed for the approximate values of the optimal initial costates, which are then used as starting guesses for the associated two-point boundary value problem.  The optimal initial costates are modeled as functions of the thrust and final radius in canonical units.  Examples are provided for coplanar and non-coplanar orbital transfers.  A dynamic step limiter is also presented which improves convergence in the shooting method.<br><br>