A: There is no one ‘best’ way to reach the moon because space travel always trades off between time, fuel, and payload mass.

If a mission carries a human crew, mission designers will prioritise speed to minimise the astronauts’ exposure to space radiation, at the expense of burning more fuel. Conversely, a robotic cargo mission can take a longer, more winding path to save fuel and carry more mass. Missions have different goals and budgets, so the ‘best route’ depends on what the spacecraft is carrying and how quickly it needs to travel.

A recent study by researchers from Brazil, France, and Portugal, published in Astrodynamics, has reported a new ‘best’ route while reducing fuel use. Using a mathematical tool called theory of functional connections (TFC), they used the L1 Lagrangian point — a strategic point located between the earth and the moon — as the route’s midpoint.

Then they designed a trajectory where a spacecraft would flyby the moon to reach an orbit around the L1 point, before making a final descent to the moon’s surface. To move the spacecraft, the team took advantage of invariant manifolds, which are like natural gravitational currents in space. Using TFC, the team was able to evaluate tens of millions of potential paths to find the most efficient one.

According to the team’s results, the new route can reduce fuel use by at least 58.8 m/s compared to previous options. On the other hand, it takes nearly 32 days to get to the moon.