Mission to Mars

The orbital alignments of the planets Mars and Earth in their paths around the sun create windows of opportunity for transfer between these two planets once every two years. Due to the inclination of their elliptical orbits, the closest distance betw een Mars and Earth, during each launch window, varies through a 15-year cycle as illustrated below in Figure 2.2-1. The minimum distance can vary between 0.4 AU at th e best opportunities to nearly 0.7 AU at the worst. Any Earth-Mars transportation system s hould be designed to operate at the worst-case condition.