There is a hidden shortcut even on the way from Earth to the moon. Instead of flying straight along the shortest distance, you can save fuel by following a trajectory that uses the gravity of Earth and the moon.
A team of international researchers recently analyzed tens of millions of lunar transfer paths by computer and, in the end, found a new route to the moon that uses less fuel than before while keeping communications with Earth intact. The team said the result shows that lunar exploration expense can be lowered through orbit design that leverages gravity alone.
◇ Going to the moon along the "hidden route" made by gravity
How do we find a route to the moon? First, researchers convert the positions, velocities, and gravities of Earth and the moon, and the spacecraft's departure conditions, into mathematical equations. Then they repeatedly compute, by computer, what trajectory the spacecraft will take depending on which direction it heads and how fast it goes. That is because even slight changes to the departure angle or speed can significantly alter the spacecraft's path. So, when designing an actual mission, they calculate countless candidate routes and choose one that uses less fuel while meeting safety, communications, and scheduling requirements.
One key metric here is "delta-v." Delta-v refers to the amount of velocity change a spacecraft needs to alter its trajectory or direction during a mission. The smaller the delta-v, the less propellant is required, which can reduce launch expense or increase payload margin.
In particular, spacecraft move by using "gravity," a kind of free thrust. The scientific community looks for paths along the flow of gravity that allow spacecraft to move naturally. In the solar system, such paths are woven like a spider web, sometimes called the "interplanetary transport network."
There are natural paths created by gravity between Earth and the moon as well. Especially near certain points where the two bodies' gravities interlock, spacecraft can remain in orbit or shift to another trajectory with relatively little energy. This is why scientists calculate complex curved trajectories rather than simple straight-line routes when designing lunar transfer paths.
◇ Found after 30 million computations… a "cheaper route" to the moon
An international team led by the University of Coimbra in Portugal calculated Earth–moon routes using a mathematical method called the "function consolidation theory." The function consolidation theory reduces the computational burden of complex trajectory calculations. Based on this, the team simulated about 30 million Earth–moon transfer paths.
What the team found upended conventional intuition. Many existing models assumed it was efficient for a spacecraft, once it departs Earth, to enter its target trajectory directly from the near-Earth side. It looks similar to choosing the nearest on-ramp when getting onto a highway.
However, the calculations showed that having the spacecraft first approach close to the moon, change its speed and direction using lunar gravity, and then merge into the target trajectory actually reduced delta-v. It may look like a detour on the surface, but the path that rides the flow of gravity better proved more economical.
The new route lowered delta-v by 58.80 meters per second compared with the most economical lunar route known so far. The team also explained that this route is advantageous for maintaining communications with Earth. When a spacecraft goes behind the moon, direct communication with Earth can be cut off, but the new trajectory shows the possibility of avoiding such communication gaps.
The team said, "This calculation considered only the gravities of Earth and the moon," and added, "If we include more variables such as the sun's gravity going forward, even more efficient routes may emerge. The analysis method used this time can be applied more widely in the future."
References
Astrodynamics (2026), DOI: https://doi.org/10.1007/s42064-025-0297-x