Low-energy transfer

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A low-energy transfer, or low-energy trajectory, is a route in space that allows spacecraft to change orbits using very little fuel.[1][2] These routes work in the EarthMoon system and also in other systems, such as traveling from Earth to Mars or between the satellites 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 expenditure of delta-v.

Missions that have used low-energy transfers include:

Proposed missions using low-energy transfers include:

History

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 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.[1] This course would result in the probe being captured into lunar orbit using zero delta-v, but required five months instead of the usual three days for a Hohmann transfer.[6]

Delta-v savings

From low Earth orbit to lunar orbit, the delta-v savings approach 25% and allow for a doubling of payload.[7]

For rendezvous with the Martian moons, the savings are 12% for Phobos and 20% for Deimos. Rendezvous is targeted because the stable pseudo-orbits around the Martian moons do not spend much time within 10 km of the surface.[8]