Scientists Map Most Cost-Effective Route to the Moon Out of 24 Million Possibilities

New math finds a cheaper Earth-to-moon route, but it takes patience.

In spaceflight, every kilogram matters. Each item you bring along increases fuel consumption, which means the spacecraft can’t go as far. But the mass of the fuel itself also matters. A spacecraft that carries less fuel can carry more hardware. A mission that needs fewer heavy propellants can become cheaper, more flexible, or easier to launch.

Much of the cost savings of spaceflight, focus on mass and fuel. Now, a new study suggests that another way to cut the cost of lunar travel may be to take a less obvious path.

Researchers used a mathematical method to search tens of millions of possible routes between Earth orbit and lunar orbit. The most optimal path first swings close to the moon, then enters a looping orbit around the Earth-moon L1 Lagrange point, a gravitational balance region between the two worlds, before later dropping into lunar orbit.

Looping Path to Savings

The savings look tiny on paper: 58.80 meters per second less than comparable routes. But spacecraft missions are measured in hard trade-offs. A little less fuel can mean a lighter launch, a cheaper mission, or room for extra instruments and cargo.

“When it comes to space travel, every meter per second equates to a massive amount of fuel consumption,” Allan Kardec de Almeida Júnior, a researcher at the University of Coimbra and lead author of the study.

The route is not built for speed. During Artemis 2, the Orion spacecraft followed a roughly 10-day free-return path, flying around the far side of the moon before returning home. The route proposed in the new study is much slower. It takes about 32 days to go from Earth orbit to lunar orbit because the spacecraft first passes through a looping orbit near the L1 point. But that detour is the point: it trades speed for much lower fuel use and perhaps a useful stopover.

As such, the route may be better suited for cargo than crews. But after the moon and its lunar space become permanently settled by humans, such routes will likely be preferred for most resupply missions.

Flying Through Gravitational Corridors

The new study focuses on a family of natural paths in the Earth-moon system known as invariant manifolds. These mathematically defined routes shaped by gravity. Mission designers sometimes describe related low-energy pathways as part of the “Interplanetary Transportation Network,” a loose web of routes where spacecraft can trade speed for efficiency.

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The researchers used the theory of functional connections, or TFC, to reduce the computational cost of searching these paths. In simple terms, the method lets scientists build key mission constraints directly into the equations before running the search. That made it easier to scan a far larger range of options.

Previous work cited used about 280,000 simulated trajectories. Almeida’s team evaluated tens of millions. For the first leg alone, from Earth to the stable manifold leading toward L1, the researchers examined 24 million trajectories before refining the best candidates further. The paper reports a best first-leg cost of 3,342.96 meters per second, reached after a 3.69-day transfer where the spacecraft enters the stable gravitational path toward the L1 Lyapunov orbit.

The surprising part was where the best path entered the gravitational route.

Most earlier approaches assumed the cheaper option would be to enter the manifold from the branch closer to Earth. The new search found the opposite. The spacecraft saves fuel by looping closer to the moon and entering from the other side.

“Instead of assuming it’s easier to choose the part of the variate closest to Earth, we can use systematic analysis with faster methods to try to find nontrivial solutions,” Vitor Martins de Oliveira, a postdoctoral researcher at the University of São Paulo and a co-author of the study, said in the press release.

A Stopover Between Earth and Moon

The proposed route uses L1 as a kind of gravitational rest stop.

In the researchers’ model, the spacecraft leaves a 167-kilometer-altitude Earth parking orbit, performs two engine burns, and uses a lunar flyby to enter a Lyapunov orbit around L1. Later, it leaves that region and transfers to a 100-kilometer lunar orbit. The complete transfer costs 3,991.60 meters per second, plus fuel for station-keeping and control, and takes about 31.9 days in the modeled scenario.

That is slow compared with Apollo/Artemis-style direct trips, which took only a few days. For astronauts, the longer journey would mean more food, water, radiation exposure and life-support demands. For cargo, however, time often matters less than mass and cost. A slow route that saves fuel could be useful for sending equipment, supplies or robotic infrastructure to the moon.

The L1 stopover also offers a communications advantage. A spacecraft behind the moon can temporarily lose contact with Earth. But a spacecraft near Earth-moon L1 can maintain a more favorable geometry.

“The Artemis 2 mission, for example, lost communication with Earth for a while because it was directly behind the moon. The orbit we propose is a solution that maintains uninterrupted communication,” Oliveira said.

That could make L1 valuable as cislunar space becomes busier. NASA’s Artemis program, the planned Gateway station, China’s lunar ambitions, commercial landers and future communications networks all point toward a moon that is no longer visited only occasionally after 2030.

Not the Fastest Route, and Not the Final Word

The new route is not necessarily the cheapest Earth-to-moon path in every sense. The researchers compared it with direct transfers that do not stop near L1. Some of those routes use less velocity change overall, including one 31-day direct transfer that costs about 66.66 meters per second less than the new L1 route. But those direct routes do not provide the same benefits: a lunar close approach, a possible stay near L1, and a final transfer from that region to lunar orbit at a cost very close to the theoretical minimum.

The simulations considered the gravity of Earth and the moon, but not the sun or other bodies. That makes the route useful as a general mission-design result rather than a final flight plan. In other words, in practice, the most efficient, cost-effective path may look a bit different.

Adding the sun’s gravity could produce even cheaper paths, but only for specific dates. The geometry of Earth, moon and sun changes constantly, so a route optimized for one launch day may not work for another.

“It’d be necessary to run the simulation for a specific position of the sun. For example, if we simulate the mission’s launch date as December 23, we’ll obtain results valid only for a mission launched on that date,” Almeida said.

Real missions would need to account for launch site geometry, orbital inclination, spacecraft control, station-keeping around L1, navigation errors and perturbations from bodies outside the Earth-moon pair.

Still, the method may prove useful beyond this one route. The central claim is not only that the team found a cheaper lunar transfer, but that it found a way to search the landscape of possible transfers more systematically.

“The systematic analysis we applied in our work is something that could be adopted more widely going forward,” Almeida said.

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As the moon becomes a destination for more than flags and footprints, that kind of efficiency may become increasingly important. The next era of lunar exploration will need rockets, landers and habitats. But it will also need better maps of the invisible roads between worlds.

The findings appeared in the journal Astrodynamics.