Low-energy transfer

A low-energy transfer, or low-energy trajectory, is a route in space that allows spacecraft to change orbits using very little fuel. These routes work in the Earth–Moon system and also in other systems, such as between the moons of Jupiter. The drawback of such trajectories is that they take longer to complete than higher-energy (more-fuel) transfers, such as Hohmann transfer orbits.

Low-energy transfers are also known as weak stability boundary trajectories, or ballistic capture trajectories.

Low-energy transfers follow special pathways in space, sometimes referred to as the Interplanetary Transport Network. Following these pathways allows for long distances to be traversed for little change in velocity, or delta-v.

Missions that have used low-energy transfers include:

Proposed missions using low-energy transfers include:

Low-energy transfers to the Moon were first demonstrated in 1991 by the Japanese spacecraft Hiten, which was designed to swing by the Moon but not to enter orbit. The Hagoromo subsatellite was released by Hiten on its first swing-by and may have successfully entered lunar orbit, but suffered a communications failure.

Edward Belbruno and James Miller of the Jet Propulsion Laboratory had heard of the failure, and helped to salvage the mission by developing a ballistic capture trajectory that would enable the main Hiten probe to itself enter lunar orbit. The trajectory they developed for Hiten used Weak Stability Boundary Theory and required only a small perturbation to the elliptical swing-by orbit, sufficiently small to be achievable by the spacecraft's thrusters. This course would result in the probe being captured into temporary lunar orbit using zero delta-v, but required five months instead of the usual three days for a Hohmann transfer.

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