An international team of researchers has identified a new fuel-efficient route between Earth and the Moon that also avoids the kind of communications blackout the Artemis II crew experienced when their spacecraft slipped behind the lunar far side in April. The trajectory, published in the journal Astrodynamics by a group led by Allan Kardec de Almeida Júnior at the University of Coimbra, uses roughly 58.80 metres per second less change in velocity than the most efficient previously known route, and parks the spacecraft at the L1 Lagrange point as an intermediate waypoint with continuous line-of-sight to Earth.
The savings sound modest set against the roughly 3,343 m/s total budget of the journey. They are not. In rocketry, every metre per second of delta-v translates exponentially into propellant mass at launch, which is why mission planners spend years hunting for fractional improvements in trajectory design.
A hidden branch on a well-mapped highway
Spacecraft rarely fire their engines for long. Most of a deep-space journey is coasting along gravitational contours that physicists collectively call the Interplanetary Transport Network — a web of low-energy pathways that connect orbits around planets, moons and Lagrange points. The underlying mathematics treats gravity as nearly free propulsion, with thrusters needed mainly to nudge a vehicle from one natural trajectory to the next.
Within that network, what mission designers call a “variate” is a natural trajectory leading into a target orbit. Conventional wisdom said the cheapest entry point onto the lunar-orbit variate was the branch closest to Earth. The new analysis flips that assumption. As co-author Vitor Martins de Oliveira, a postdoctoral researcher at the University of São Paulo, put it in a statement issued by Brazil’s FAPESP research agency, the team’s systematic search showed it was better to enter the variate from the opposite side, closer to the Moon, rather than from the Earth-facing branch most prior models had favoured.
An answer to the problem Artemis II just lived through
The trajectory carries a second advantage that connects directly to an experience NASA’s Artemis II crew had only weeks ago. On flight day five of their mission, Orion passed behind the Moon for roughly 40 minutes, during which radio contact between the Deep Space Network and the spacecraft was cut by the Moon itself. NASA had planned for the blackout, similar ones occurred during Artemis I and Apollo, and the crew used the time to make close-range observations of the lunar far side. But for crewed missions in general, any minutes spent out of contact change the calculus of medical emergencies, navigation anomalies and abort decisions.
The blackout is not a hardware failure that can be patched. It is geometry: the Moon itself sits between the spacecraft and any Earth-based antenna. Workarounds have historically meant relay satellites, costly trajectory tweaks, or simply accepting the silence. The Almeida group’s proposed trajectory side-steps the problem by routing the spacecraft to the L1 Lagrange point, between Earth and the Moon, where it can remain in an intermediate orbit indefinitely and never lose line-of-sight with mission control. As Oliveira told FAPESP, citing Artemis II by name: “The orbit we propose is a solution that maintains uninterrupted communication.”
The math behind the discovery
What sets the new approach apart is the sheer breadth of its search. The team used a technique called the theory of functional connections, which sharply reduces the computational cost of modelling complex orbital dynamics. That let them simulate around 30 million possible trajectories — compared with roughly 280,000 in earlier studies — and pull out solutions that local optimisation methods would never find.
The trajectory itself is split into two segments. The first carries the spacecraft from a 167-kilometre Earth parking orbit onto a stable manifold leading to L1. The second departs L1 along an unstable manifold and transitions into lunar orbit. The non-trivial choice is in the second segment: instead of entering the lunar-orbit variate from the branch closest to Earth, the optimum entry is from the Moon-facing side, where the gravitational structure of the system offers more free assistance.
What the model leaves out
Trajectories calculated using the team’s model account only for Earth and the Moon. Real spacecraft also feel the Sun’s pull, smaller perturbations from other bodies, and radiation pressure. Adding the Sun’s gravity could reveal even more efficient routes — but it would tie a given trajectory to a specific launch date, narrowing the launch window. As Almeida noted in the FAPESP release, simulating with the Sun’s position fixed produces results valid only for that one date.
This is how trajectory design has always advanced. The low-energy transfer that saved Japan’s Hiten probe in 1991, and later delivered NASA’s GRAIL twins to lunar orbit, emerged from exactly this kind of incremental mathematical exploration of multi-body problems. In Hiten’s case the savings were not theoretical: the probe reached lunar orbit on a propellant budget that would have been impossible under a conventional Hohmann transfer.
What the savings buy
The deeper story here is not a single number. It is that the lunar transportation problem, treated by most observers as a solved engineering exercise since Apollo, still has hidden structure that systematic computation can reveal. Half a century after Apollo 11, the cheapest known way to get to the Moon was apparently not the cheapest way at all.
For a cislunar economy that, on current plans, will see dozens of crewed and uncrewed flights to lunar orbit and the lunar surface across the next decade, the implications extend well beyond one paper. Almeida’s stated hope is that the method itself, not just this one trajectory, gets adopted more widely. If systematic search through 30-million-route solution spaces generalises to other destinations — Mars transfers, asteroid rendezvous, outer-planet flybys — mission architectures built on conventional optimisation may all be sitting on similar hidden savings.
