US standards body proposes atomic clocks in lunar orbit to keep Moon time

Knowing precise time on satellite essential if we want accurate GPS-like system for exploration

Researchers at the US National Institute of Standards and Technology (NIST) have come up with a proposal for keeping track of time on the Moon – an essential for lunar navigation tools.

While the Apollo-era astronauts rarely ventured far from their Lunar Module during the precious few days they spent on the lunar surface, NASA's Artemis program aims to establish a sustained human presence on the Moon, which will require accurate timekeeping for a GPS-like navigation system for lunar exploration.

The problem is well known. Atomic clocks on the Moon's surface tick faster than those on Earth by approximately 56 microseconds per day (other sources put the average as 58.7 microseconds). Initially, this is not a problem… unless accurate landings and decent bandwidth for communicating with Earth are required.

In April, NASA was directed to implement a Coordinated Lunar Time (LTC) for the Moon, which would be traceable to Coordinated Universal Time (UTC). However, there was precious little detail on how the standard might be implemented.

NIST's approach is to implement a "highly precise network of clocks at specific locations on the Moon’s surface and in lunar orbits."

According to NIST: "These precise atomic clocks in lunar orbit would function as the 'satellites' of the lunar GPS network, providing accurate timing signals for navigation."

The system will result in a lunar time that accounts for the Moon's gravitational environment and provides a master 'Moon Time' that will serve a similar purpose to Coordinated Universal Time (UTC) on Earth.

NIST physicist Bijunath Patla said: "It's like having the entire Moon synchronized to one 'time zone' adjusted for the Moon's gravity, rather than having clocks gradually drift out of sync with Earth's time."

Accurate timing signals mean a lunar GPS is possible, which means more efficient exploration. Patla said the eventual goal was to get accuracy within just a few meters when landing spacecraft.

NASA has footed part of the bill for the work, and a longer-term goal is to apply the lessons learned to timekeeping on missions farther afield.

"The proposed framework underpinning lunar coordinate time could eventually enable exploration beyond the Moon and even beyond our solar system," said Patla.

"Once humans develop the capability for such ambitious missions, of course," he added. ®