Ultrastable lasers could enable lunar navigation, precision timekeeping and more

A new scientific proposal outlines how placing ultrastable lasers inside the permanently shadowed craters of the Moon could transform space exploration

These lasers, positioned in some of the coldest and darkest regions of the solar system, could establish a master time signal, provide GPS-like navigation for lunar spacecraft, and enable highly precise measurements to detect exotic physics phenomena like ripples in space-time.

The research, published in the Proceedings of the National Academy of Sciences, demonstrates how the unique environment of the lunar south pole provides the perfect conditions for stabilising advanced laser systems.

The advantage of lunar silicon cavities

To build a highly stable laser, scientists rely on a component called an optical silicon cavity. This device is a block of silicon with mirrors on each end that permits only certain frequencies of light to bounce back and forth. For the laser to remain stable, the distance between these two mirrors must not change.

While the Moon is already an excellent location for an optical cavity due to its lack of air and low vibrations compared to Earth, permanently shadowed craters provide a much greater technical advantage.

Achieving perfect thermal stability

The craters at the lunar south pole maintain a natural temperature of about 50 Kelvin (50 degrees above absolute zero). This extreme cold drastically reduces the random jitter of the mirrored surfaces inside the device. Additionally, these deep craters feature a higher vacuum than the open lunar surface, which eliminates vibrations caused by stray particles or sound waves striking the mirrors.

By venting any remaining heat from the device directly into outer space, the system can be passively cooled even further to a temperature of 16 Kelvin. At 16 Kelvin, silicon possesses a unique physical property: it neither expands nor contracts when exposed to small temperature changes. This ensures that the light entering the cavity always travels the exact same distance between the two mirrors, creating a completely unwavering frequency.

Supporting lunar infrastructure and science

Once the optical silicon cavity is lowered into a crater, a commercially available laser placed nearby on the rim or inside the shadow can lock its light to the cavity’s resonant frequency. This process ensures the laser emits light of a single, unchanging colour.

This stabilised light can then serve as a navigation signal to help guide spacecraft to safe landings, particularly in the dimly lit regions near the lunar south pole. By syncing this laser light with atomic clocks on orbiting satellites, scientists can establish the first optical atomic clock on an extraterrestrial surface, matching the timekeeping precision of advanced laboratories on Earth.

Furthermore, if astronauts install a network of these stable lasers, the instruments can measure distances across the Moon with extreme accuracy. This precision would allow the network to function as a detector for gravitational waves, which are ripples in space-time that slightly alter the distance between objects as they pass by.

Deployment and mission timeline

The silicon optical cavity is small enough to fit inside a standard spacecraft and would be fully assembled on Earth. During deployment on the Moon, its radiative cooling panels would unfold, and astronauts would use a remote or mechanically controlled lunar rover to lower the device into the crater.

These permanently shadowed regions are high-priority targets for long-term space exploration because they contain water-ice and other vital resources required to sustain a human presence. Researchers estimate that the technology could be demonstrated in low-Earth orbit within two years, deployed on the lunar surface within three to five years, and eventually installed inside a dark crater through multiagency collaboration.