LOW-THRUST TRANSFERS WITH EARTH-SHADOW AND POWER-DEGRADATION EFFECTS

Optimizing low-thrust Earth-orbit transfers is a challenging problem due to the low control authority of the electric thrusters, and consequently the long transfer times. This already challenging problem is exacerbated when real environmental effects associated with operating electric-propulsion spacecraft, such as Earth-shadow eclipses (zero thrust) and solar-cell degradation (due to trapped radiation), are included. In many cases, mission analysts need to perform preliminary trade studies in order to determine the general trend among various electric-propulsion system parameters. This paper presents a new low-thrust trajectory program that can easily accommodate both Earth-shadow and power-degradation effects. The new method utilizes Edelbaum's analytic solutions for continuous-thrust, quasi-circular transfers, and hence does not require numerical integration of the system dynamics. Furthermore, the method does not rely on an iterative search, so non-convergence is not an issue. Several numerical trials are presented in order to demonstrate the utility of the new low-thrust trajectory program as a useful tool for rapidly performing mission analyses and trade studies.