Getting to the moon is expensive, so even a small cut in fuel use matters.

An international team of researchers says it has found a more efficient route between Earth and the moon using advanced computer modeling. The method is based on the theory of functional connections, which reduces the compute needed to run complex models.

The researchers simulated 30 million different routes to the moon, and 280,000 simulations are referenced in their newly published study. The route they identified was hidden within the gravity-driven pathways that spacecraft can use through the solar system.

Spacecraft use fuel only part of the time. Gravity is often the preferred method of propulsion because it is free. These gravity-determined routes are often referred to as the Interplanetary Transportation Network.

The team said the cheap route to the moon depends on the gravitational pulls of both Earth and the moon. In spaceflight, a variate refers to a natural trajectory leading to a certain orbit.

The researchers found that instead of using the branch of the lunar-orbit variate closest to Earth, it is better to enter that variate from the opposite 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,” study co-author Vitor Martins de Oliveira, a postdoctoral researcher at the University of São Paulo in Brazil, said in a statement.

The team said the hidden path offers more free gravity-based propulsion. The newly reported route uses 58.80 metres per second less fuel consumption than the previous cheapest known route.

The researchers also said the route would avoid interruptions in communication with Earth.

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

The researchers said this is not the final word on low-cost travel between Earth and the moon. Their modeling included gravity from only Earth and the moon. Future research could add other variables, including gravity from the sun, which could lead to even more cost-effective trajectories.

“The systematic analysis we applied in our work is something that could be adopted more widely going forward,” study lead author Allan Kardec de Almeida Júnior, a researcher at the University of Coimbra in Portugal, said in the same statement.

The study was published April 10 in the journal Astrodynamics.

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