400px|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  spacecraft on a closed transfer orbit that passes close to two celestial bodies at regular intervals. Cyclers are intended to be used for carrying heavy supplies, life support and radiation shielding.
400px|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.
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