The next decade will see a resurgence of lunar exploration, including dozens of missions and plans to establish permanent bases on the Moon. The efforts pose myriad challenges. Among them is a subtle but fundamental question that metrologists around the world are working to answer-how to tell time on the Moon.
“We’re just beginning to figure that out,” said Cheryl Gramling, an aerospace engineer who leads the position, navigation and timing team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Moon does not currently have an independent time scale.
Each lunar mission uses its own time scale that is linked through its handlers on Earth to Coordinated Universal Time, or UTC, the standard against which the planet’s clocks are set. But this method is relatively inaccurate, and spacecraft exploring the Moon do not synchronize time with each other. The approach works when the Moon hosts a handful of independent missions, but will be a problem when there are multiple craft working together.
Space agencies will also want to track them using satellite navigation, which relies on precise timing signals. It is not obvious what form a universal lunar time would take. Official lunar time could be based on a clock system designed to synchronize with UTC, or it could be independent of Earth time.
Representatives of space agencies and academic organizations from around the world met in November 2022 to begin drafting recommendations on how to define lunar time at the European Space Agency’s (ESA) European Space Research and Technology Center in Noordwijk, the Netherlands.
“Decisions need to be made soon,” said Patrizia Tavella, who heads the Time Department at the International Bureau of Weights and Measures in Sèvres, France.
“If an official lunar time is not established, space agencies and private companies will find their own solutions. This is why we want to sound an alarm now, showing that we can work together to make a common decision.”