Sketch of a circumlunar free return trajectory (not to scale), plotted on the rotating reference frame rotating slightly faster than a sidereal month.

A cycler is a potential spacecraft on a closed transfer orbit that would pass close to two celestial bodies at regular intervals. Cyclers could be used for carrying heavy supplies, life support and radiation shielding.

Free return trajectory

A free-return trajectory is a symmetrical orbit past the Moon and Earth that was first analysed by Arthur Schwaniger[1]

Lunar cycler

Main article: Lunar cycler

A lunar cycler or Earth–Moon cycler is a cycler orbit, or spacecraft therein, which periodically passes close by the Earth and the Moon, using gravity assists and occasional propellant-powered corrections to maintain its trajectories between the two. If the fuel required to reach a particular cycler orbit from both the Earth and the Moon is modest, and the travel time between the two along the cycler is reasonable, then having a spacecraft in the cycler can provide an efficient and regular method for space transportation.[2]

Mars cycler

Main article: Mars cycler

A Mars cycler or Earth–Mars cycler is a spacecraft trajectory that encounters the Earth and Mars on a regular basis, or a spacecraft on such a trajectory

Interstellar cycler

Main article: Interstellar cycler

An interstellar cycler or Schroeder cycler, a theoretical spacecraft trajectory that encounters two or more stars on a regular basis, or a spacecraft on such a trajectory


  1. ^ Schwaninger, Arthur J. (1963). Trajectories in the Earth-Moon Space with Symmetrical Free Return Properties. Technical Note D-1833. Huntsville, Alabama: NASA / Marshall Space Flight Center.
  2. ^ Kenneth D. Mease; Benjamin F. Villac; Josep M. Mondelo; et al. (Jordi Casoliva Rodon) (June 2008). Economical Space Transportation Routes Between Earth, Moon, and Beyond (PDF) (Report). University of California. p. 2. Archived from the original (PDF) on 2014-09-08.