Semi-analytical approach for computing near-optimal low-thrust transfers to geosynchronous orbit

In this paper, a novel semi-analytical approach is developed for solving minimum-time and minimum-fuel low-thrust transfers to geosynchronous orbit. The proposed method is mainly based on two intuitive control strategies, with one focusing on the instantaneous variation of orbit elements, and the other concerning the cumulative effect of thrust force. By optimizing the objective functions of the two strategies, analytical thrust-steering laws are derived for each case. With the use of a refined efficiency factor, thrust arc locations can also be optimized during the transfer. In addition, selection of weights and other parameters further improves the performance of the resulting trajectories. Finally, two examples of transfers are presented. The computed trajectories are very close to, or even better than the optimal results obtained from the traditional direct and indirect techniques. Due to its simplicity and good performance, the proposed method would be particularly useful for preliminary mission analysis.