A cycler is a potential spacecraft on a closed

transfer orbit {{Astrodynamics Orbits Astrodynamics In orbital mechanics, a transfer orbit is an intermediate elliptical orbit that is used to move a spacecraft in an orbital maneuver from one circular, or largely circular, orbit to another. There are several ...

that would pass close to two celestial bodies at regular intervals. Cyclers could be used for carrying heavy supplies, life support and

radiation shielding Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposur ...

Free return trajectory

free-return trajectory In orbital mechanics, a free-return trajectory is a trajectory of a spacecraft traveling away from a primary body (for example, the Earth) where gravity due to a secondary body (for example, the Moon) causes the spacecraft to return to the primar ...

is a symmetrical orbit past the moon and Earth that was first analysed by Arthur Schwaniger

Lunar cycler

A ''lunar cycler'' or ''Earth–Moon cycler'' is a cycler orbit, or

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

therein, which periodically passes close by the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, using

gravity assist In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...

s 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.

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

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

References

Space Spacecraft {{spacecraft-stub fr:Cycler