### Trajectory Optimization

The trajectory optimization program is based upon the matched conic model of the solar system; that is, heliocentric trajectories are computed under the assumption that the sun is the only attracting body. Once the terminal heliocentric velocities are known from the solution to Lambert’s Problem, the velocities relative to the terminal body are evaluated and equated to planetocentric conditions at infinity. This method is alternatively referred to as "matched asymptotes" or "zero sphere of influence patched conic". It is generally regarded as sufficiently accurate for purposes of preliminary mission analysis and for propulsion system sizing and selection.

Trajectory optimization is achieved with the indirect techniques of the ordinary calculus. While the solution to the boundary value problem that results with this approach is considered by many to be overly difficult, the robust iterator that is used in the program normally renders the solution routine. Advantages of indirect techniques are that convergence tends to be quadratic in the neighborhood of the solution and that convergence assures that the solution is locally stationary.