Circumlunar trajectory
In orbital mechanics, a circumlunar trajectory, trans-lunar trajectory or lunar free return is a type of free return trajectory which takes a spacecraft from Earth, around the far side of the Moon, and back to Earth using only gravity once the initial trajectory is set. History. The first spacecraft to fly a circumlunar trajectory was Luna 3. Circumlunar trajectories were also used by Apollo missions prior to lunar orbit insertion, to provide a free return to Earth in the event of a propulsion system malfunction on the way to the Moon. This was used on Apollo 13 , when an oxygen tank rupture necessitated return to Earth without firing the Service Module engine, although a number of course corrections using the Lunar Module descent engine were used to refine the trajectory. A number of manned missions were also proposed but not flown to intentionally conduct circumlunar flybys, including the Soviet Soyuz 7K-L1 or Zond programme, and several US proposals, including Gemini-Centaur and an early Apollo proposal. Planned. The "#dearMoon" project is planned as a 2023 circumlunar flight using the SpaceX Starship to carry approximately 10 tourists on a multiday flight to the Moon and back. Circumlunar