page_title: Trans-lunar injection
section_title: Free return
hierarchical_section_title: Trans-lunar injection / Theory / Free return
caption_attribution_description: English: A sketch of a circumlunar free return trajectory (not to scale). Created by myself based on NASA's Apollo mission profiles (http://www.hq.nasa.gov/alsj/a410/A08_MissionReport.pdf).
context_page_description: A trans-lunar injection is a propulsive maneuver used to set a spacecraft on a trajectory that will cause it to arrive at the Moon.
context_section_description: In some cases it is possible to design a TLI to target a free return trajectory, so that the spacecraft will loop around behind the Moon and return to Earth without need for further propulsive maneuvers.
  Such free return trajectories add a margin of safety to human spaceflight missions, since the spacecraft will return to Earth "for free" after the initial TLI burn. The Apollos 8, 10 and 11 began on a free return trajectory, while the later missions used a functionally similar hybrid trajectory, in which a midway course correction is required to reach the moon.
caption: Sketch of a circumlunar free return trajectory (not to scale)
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