A future network for lunar navigation could be located in one of the most unforgiving lunar locations. Scientists are evaluating the potential of using extremely stable lasers placed in the permanently shadowed craters of the lunar south pole to serve as timing standards for spacecraft, rovers, and astronaut missions. This concept aims to resolve one of the fundamental issues facing deep space operations: while the moon lacks a satellite constellation that would allow the implementation of GPS, the upcoming activity on the surface of the moon would have to be considerably autonomous compared to the capabilities of Earth-based tracking.
According to NASA, the ability to navigate precisely is required for safe operations, precise landing, synchronization of scientific experiments, and efficient movement on the moon. What makes permanently shadowed craters attractive is the physics of the phenomenon.
Due to the tilt of the moon axis, there is no direct sunlight inside some craters located near the lunar south pole. The result is very low temperature inside the crater, reaching about minus 370 degrees Fahrenheit, making these places inhospitable for humans and convenient for precision instrumentation. Typically, a highly stable laser operation requires special cooling systems, such as cryogenics, and protection from vibrations. But lunar craters could provide natural ways of implementing these technologies through extremely low temperature, low pressure, and lack of environmental disturbances compared to terrestrial laboratories.
The proposed device uses a silicon optical cavity, which is responsible for keeping laser light confined to the specified wavelength with extremely high accuracy by maintaining the distance between its walls constant. Any discrepancy in distance causes changes in the frequency of the laser. Maintaining the stability of distance leads to highly accurate timing reference used in navigation. In the case of the proposed method published in Proceedings of the National Academy of Sciences, the cooling process would reduce the temperature to about 16 kelvins.
This is crucial since navigation relies on time, which needs to be kept extremely accurate at a scale unattainable by ordinary devices like clocks and radios. “As soon as I understood what the permanently shadowed regions can offer, I felt that this would be the most ideal environment for a super-stable laser.”
The timing issue is particularly relevant at the south lunar pole, as planned by Artemis program scientists, where many valuable science and operational activities could occur. The area has rugged terrain and poor lighting, and the resulting shadows complicate movement and navigation. The description of the Artemis surface planning called the area “torturous terrain”, reminding that maps do not guarantee good navigation. Improved timing standards could help implement beacon networks, orbital navigation equipment, and later even synchronized lunar timekeeping for various devices operating simultaneously.
Laser placement is not the only solution being studied. For example, NASA tested a variety of methods for navigating based on orbital systems like Lunar GNSS Receiver Experiment, which demonstrated that signals from navigation satellites can be received at the moon. Also, some research focused on using smaller satellites on the moon to achieve this purpose using ephemerides reversal method. The distinguishing feature of the laser concept lies in taking into account the harshness of lunar environment instead of considering it as a hindrance. In addition to helping rovers navigate the terrain, this laser would help build a network of optical clocks on the moon, closing the gap between the means of space exploration and the actual settlement of the natural satellite.