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
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 required to maintain this trajectory.
A number of manned missions were also proposed 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.
* ^ "The launch and mission trajectory". Apollo 13 Mission Report. Spaceflight Now. Retrieved 2009-06-30. * ^ Turnhill, Reginald. " Apollo 13 on Free Return Trajectory". Spaceflight Now. Retrieved 2009-06-30. * ^ Wade, Mark. "Manned Circumlunar". Encyclopedia Astronautica . Retrieved 2015-02-11.
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