Going to the moon is expensive. Each kilogram of fuel carried by a spacecraft has to be picked up from Earth, burning more fuel. That’s why aerospace engineers and orbital mechanics researchers spend so much time looking for the smallest potential for how a spacecraft travels. A reduction of a few meters per second here and there could save millions of dollars per mission. Now, an international team of researchers says they have precisely found a more efficient route between Earth and the Moon, calculated using advanced computer modelling, and it was hidden in plain sight the whole time.
How gravity powers spacecraft through interplanetary transportation networks for free
To understand why this discovery matters, it helps to understand how spacecraft actually move. Engines burn only for a short period of time. For most of the journey, spacecraft rely on the gravitational pull of the planets, moons, and Sun to take them on natural routes through the solar system. These gravity-determined routes are often referred to as interplanetary transportation networks, and they run through the solar system like invisible highways. Using them is, in fact, free propulsion.So, finding a cheaper route to the Moon has a lot to do with gravity, specifically the gravitational pull of both the Earth and the Moon. Researchers studying these paths create what are called “variates”, natural trajectories that lead a spacecraft toward a desired orbit without the need for constant engine thrust. The question is always which part of diversity to enter and from which direction.
Counter-intuitive discovery that turns traditional lunar navigation upside down
This is where this new research took an unexpected turn. Conventional thinking held that the most logical approach was to enter lunar orbit at its closest point to Earth, which was the obvious, intuitive choice. But researchers found that it’s actually better to approach that diversity from the opposite direction. “Instead of assuming that it is easy to choose the part closest to Earth, we can use systematic analysis with fast methods to find non-trivial solutions,” said study co-author Vitor Martins de Oliveira, a postdoctoral researcher at the University of Sao Paulo in Brazil. In other words, turning around proves to be more efficient than going straight.
How 30 million simulations led researchers to a more fuel-efficient moon route
The method behind the discovery is rooted in the theory of functional connections, a mathematical framework that reduces the computational load required to run complex orbital simulations. Using this approach, the team simulated 30 million different routes to the Moon, with 280,000 simulations referenced in their published study. That scale of analysis would have been much more difficult to conduct using older methods, which is why this particular pathway had never been identified before. The newly reported route consumes 58.80 meters per second less fuel than the previous cheapest known route. It may not sound dramatic, but in orbital mechanics, delta-v, the measure of velocity change required from the spacecraft’s engines, is the currency of mission planning. Lower delta-v means less fuel, less mass at launch, and lower costs at every stage of the mission.
Why does this new lunar trajectory also eliminate communication blackouts in space?
Efficiency gains aren’t the only benefit. The orbit the researchers propose also maintains uninterrupted communication with Earth, which existing routes do not always guarantee. “For example, the Artemis 2 mission lost contact with Earth for a period of time because it was directly behind the Moon,” Oliveira said. The new trajectory avoids that problem entirely, keeping the spacecraft in constant contact with ground stations throughout the journey.
What the discovery of the lunar route means for the future of lunar space missions
The researchers are careful to present this as a start rather than a final answer. Their modeling took into account only the gravity of the Earth and the Moon. Future research could include additional variables such as the Sun’s gravitational influence, potentially leading to even more cost-effective trajectories.“The systematic analysis we applied in our work could be more widely adopted going forward,” said Alan Cardec de Almeida Jr., a researcher at the University of Coimbra in Portugal and lead author of the study.The study was published in the journal Astrodynamics in April. As agencies and private companies plan an ambitious slate of lunar missions in the coming decade, the value of the equipment that makes those trips cheaper and more reliable will only increase. It, it turns out, was always there just waiting to be found on the other side.