MINIMUM-TIME LOW-EARTH ORBIT TO HIGH-EARTH ORBIT LOW-THRUST TRAJECTORY OPTIMIZATION

The problem of many revolution low-thrust Earth-orbit trajectory optimization is considered. The objective is to transfer a spacecraft from a parking orbit to a de-sired terminal orbit in minimum time. The minimum-time orbital transfer problem is posed as a nonlinear optimal control problem, and the optimal control problem is solved using a direct transcription variable-order Gaussian quadrature collocation method. It is found that the thrust-to-mass ratio holds a power relationship to the transfer time, final mass, and final true longitude. Using these power relationships obtained through regression on the collected results, it is possible to estimate the performance of a given thrust-to-mass ratio without solving for the optimal trajec-tory. In addition, the key structure of the optimal orbital transfers are identified. The results presented provide insight into the structure of the optimal performance for a range of small thrust-to-mass ratios and highlight the interesting features of the optimal solutions. Finally, a discussion of the performance of the variable-order Gaussian quadrature collocation method is provided