How long would a Mars mission last?
This depends on the trajectory taken to Mars, i.e. whether an opposition-class or conjunction-class mission is chosen. In both missions, Earth to Mars transit time is roughly 180 days. However, since the two planets must also be aligned properly for the return flight from Mars to Earth, this is where their similarity ends. In an opposition-class mission, astronauts would stay on Mars for 30 days, followed by a 430-day return mission that would swing by Venus for a gravity assist, for a total round-trip of 640 days. In a conjunction-class mission, astronauts would spend 550 days on Mars, followed by a another 180-day return leg along roughly the same route as Earth to Mars, for a total round-trip of 910 days. While on the surface a shorter round-trip time might seem safer, because the astronauts on an opposition-class mission actually spend more time in interplanetary space (610 days vs. 360 days for a conjunction-class mission), hazards associated with a zero-gravity environment and co
