Lunar cycler at apogee. Computer artwork of a Lunar cycler (centre) at its furthest orbital point (apogee) from the Earth (upper right), rounding the far side of the Moon (lower left) to begin its fall back towards Earth. Lunar cyclers (or Earth-Moon cyclers) are hypothetical spacecraft that are potentially useful for transporting people or materials using little propellant. Instead, they rely on gravity assist manoeuvres to keep them going. At apogee the lunar cycler is about 300 thousand miles from the Earth and 50 thousand miles beyond the orbit of the Moon (further from Earth than any human has yet ventured).