As NASA prepares for a sustainable human presence on the Moon under the Artemis program, the agency has been tasked by the White House with a unique timekeeping challenge: developing an official lunar time standard for coordinate future Moon walking missions.
The presidential directive, first reported by Reuters, instructs NASA to establish a “lunar coordinated time” (LTC) system by the end of 2026 to support the ambitions of the Artemis program and maintain American leadership in space exploration.
The need for dedicated lunar time arises from the effects of Einstein’s theory of relativity. Due to subtly different gravitational forces, time passes slightly faster on the Moon than on Earth. Over short periods of time, this variation is negligible, but it could cause significant desynchronization issues for future lunar crews and spacecraft that rely on Earth-based timing systems.
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NASA must establish lunar time
Currently, lunar missions communicate simply using Coordinated Universal Time (UTC), the primary civilian timekeeping standard derived from Earth’s highly precise atomic clocks. However, experts estimate that a lunar clock would gain about 56 microseconds per Earth day due to relativity.
Although seemingly infinitesimal, these microseconds could quickly add up to whole seconds of disparity, making UTC unsuitable for the coordinated operations required for Artemis crewed moon landings and the establishment of the lunar outpost planned for the end of this decade.
NASA is no stranger to grappling with the effects of relativity on precision timekeeping. In 2019, the agency launched its Deep Space Atomic Clock (DSAC) experiment to test nuclear timekeeping decoupled from Earth to improve spacecraft navigation.
For its part, the European Space Agency has also been exploring standardized concepts of “lunar time,” issuing tenders last year for companies to develop lunar clocks to support its own robotic and human missions to come.