<h2>AAS 97-149</h2>
<h2> DETERMINATION OF OPTIMAL SPACECRAFT TRAJECTORIES USING A  STEP-BY-STEP LINEARIZATION METHOD                                                     </h2>
<h4> S. H. Pourtakdoust, M. A. Jalali and J. R. Saberian, Sharif University of Technology, Iran                                                                               </h4>
<h2> Abstract </h2>
 A new step-by-step linearization method is developed to solve the nonlinear optimal  control problems.  The total process time is divided into equally-spaced time  intervals.  At each segment linearized equations are used to model the system  evolution and explicitly solved to relate dependent variables at start and terminal  points of each segment.  This gives a mapping rule in recursive form which by  iteration over all segments leads to a system of nonlinear algebraic equations for  unknown state and costate variables at the initial and final times of the process.   This technique has been shown to be robust and efficient.