OPTIMAL EARTH-MOON TRAJECTORIES USING COMBINED CHEMICAL-ELECTRIC PROPULSION

Minimum-fuel, three-dimensional Earth-moon trajectories are obtained f or spacecraft using both chemical and electric propulsion stages. The problem involves maximizing the final spacecraft mass delivered to a c ircular, polar midlunar orbit, The mission definition involves a chemi cal-stage boost from low-Earth orbit into a coasting ballistic traject ory followed by a lunar capture trajectory performed by the electric p ropulsion stage. For this analysis, the ballistic orbit transfer and t he powered orbit transfer to a circular orbit within the lunar sphere of influence are modeled by the dynamics of the classical restricted t hree-body problem, and two body-centered coordinate frames are utilize d, The subsequent descending three-dimensional spiral trajectory to ci rcular polar midlunar orbit is computed via Edelbaum's analytic equati ons in order to eliminate the need to numerically simulate the numerou s near-circular lunar orbits, Two classes of current-term electric pro pulsion thrusters are utilized (arcjet and plasma thrusters) along wit h current-term launch vehicle configurations, Numerical results are pr esented, and the optimal chemical-electric propulsion transfers exhibi t a substantial reduction in trip time compared to Earth-moon transfer s using electric propulsion alone.