Alow-energy transfer, or low-energytrajectory, is a route inspace that allowsspacecraft to changeorbits using significantly less fuel than traditional transfers.[1][2] These routes work in theEarth–Moon system and also in other systems, such as between themoons of Jupiter. The drawback of such trajectories is that they take longer to complete than higher-energy (more-fuel) transfers, such asHohmann transfer orbits.
Low-energy transfers are also known asweak stability boundary trajectories, and includeballistic capture trajectories.
Low-energy transfers follow special pathways in space, sometimes referred to as theInterplanetary Transport Network. Following these pathways allows for long distances to be traversed for little change in velocity, ordelta-v.
Missions that have used low-energy transfers include:
On-going missions that use 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 spacecraftHiten, 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 theJet 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 forHiten 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 temporary lunar orbit using zerodelta-v, but required five months instead of the usual three days for a Hohmann transfer.[8]
From low Earth orbit to lunar orbit, thedelta-v savings approach 25% on the burn applied after leaving low Earth orbit, compared to the retrograde burn applied near the Moon in the traditionaltrans-lunar injection, and allow for a doubling of payload.[9]
Robert Farquhar has described a 9-day route from low earth orbit to lunar capture that takes 3.5 km/s.[10] Belbruno's routes from low Earth orbit require a 3.1 km/s burn for trans lunar injection, a delta-v saving of not more than 0.4 km/s. However, the latter require no large delta-vchange after leaving low Earth orbit, which may have operational benefits if using an upper stage with limited restart or in-orbit endurance capability, which would require the spacecraft to have a separate main propulsion system for capture.[11]
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.[12]
