Low-Thrust Eccentricity-Constrained Orbit Raising

The problem of zero-eccentricity-constrained orbit raising in circular orbit in the presence of shadowing is analyzed using both numerical and analytical methods. Given the shadow arclength, piecewise constant pitch angles are selected analytically, and the location along the orbit where the pitch angle switches is optimized to effect the largest change in semimajor axis per revolution. Two strategies yielding near-optimal performance are presented, differing in whether or not a pitch reorientation maneuver is carried out inside the shadow arc. These analytic results are also compared with the exact eccentricity-constrained numerical solutions, which use optimally varying continuous pitch profiles to maximize the change in semimajor axis after each revolution. The suboptimal analytic strategies are almost as effective as the optimal strategy, especially in higher orbit. These strategies remove the need for continuously reorienting the spacecraft attitude in pitch, providing robust real-time on-board guidance capability for electric orbit transfer vehicle orbit raising applications. (Author)