The Need for Lunar Time Standardization
As dozens of missions to the moon are planned for the coming decade, including efforts to establish permanent human presence, the need for a unified timekeeping system has become apparent. Historically, each lunar mission has operated on the time zone of the nation managing it, all of which are linked to Earth-based Coordinated Universal Time (UTC). However, this approach becomes impractical and imprecise as the number and complexity of lunar activities grows.
Precise timekeeping and synchronization are critical for navigation, communication, and coordination between various spacecraft, rovers, and eventually, human explorers on the moon. Even tiny discrepancies can lead to significant problems. Clocks on the moon gain about 56 microseconds per Earth day compared to terrestrial clocks, a difference that would compound over time. The rate of this divergence also varies based on location, with clocks ticking differently on the lunar surface compared to orbit.
Without a common lunar time standard, it would become increasingly challenging to ensure that data transfers between Earth, lunar satellites, moon bases and astronauts are all in sync. Discrepancies could lead to errors in guidance systems and the tracking of objects in cislunar space (the area under the gravitational influence of the Earth and moon). As commercial activities expand to the moon, a unified time will also be essential for coordinating operations, conducting commerce, and managing lunar infrastructure and resources.
Defining a Lunar Time Standard
The White House has tasked NASA to work with other government agencies to devise a plan by the end of 2026 for establishing what it calls Coordinated Lunar Time (LTC). However, many technical and political hurdles remain in defining and implementing this new time system for the moon.
One key question is whether lunar time should be kept independent and asynchronous from Earth time, or if it should remain synced to terrestrial UTC. Clocks on the moon run faster, so some adjustment would be needed to keep the two in alignment over the long term. Lunar time could potentially be allowed to diverge, although this may be impractical for mission operations coordinated from Earth.
Another consideration is whether a single space agency or international organization should be responsible for setting and maintaining lunar time, similar to how the International Bureau of Weights and Measures currently handles UTC on Earth. Decisions will also need to be made on the technical implementation, such as whether to deploy a network of atomic clocks on the lunar surface and in lunar orbit to maintain the time standard.
Some have proposed dividing the moon into time zones, as is done on Earth, to account for the position of the sun. However, a lunar day lasts 29.5 Earth days, with 14 days of continuous sunlight followed by 14 days of darkness. Basing timekeeping on this cycle may not be practical for astronauts living and working on the moon. A single, non-solar based time system will likely be needed.
Ultimately, the definition and implementation of lunar time will require international agreements and coordination between space agencies and the private sector. NASA is collaborating with space programs in Europe, Japan, Canada and other nations as part of the Artemis Accords. However, major spacefaring countries like China and Russia have not signed on to this U.S.-led initiative, which could complicate the global adoption of a common time system.
Geopolitical Implications
The U.S. government views its leadership in establishing a standardized lunar time as important for more than just practical mission needs. Influence over this fundamental aspect of lunar operations is also seen as a matter of national power and prestige in the renewed international competition to explore and utilize the moon.
Throughout history, the ability to set and control time has been a significant source of authority. In the 19th century, the standardization of time and selection of the Prime Meridian passing through Greenwich, England provided immense benefits to the British Empire. The current Earth time standard, UTC, is governed by an international body, but still retains vestiges of this colonial legacy.
Some observers worry that if the U.S. or other major spacefaring nations are seen as unilaterally imposing a lunar time system, it could be interpreted by other countries as an overreach or even a step towards asserting sovereignty and enabling lunar colonialism. Broad international participation and transparency in the selection of lunar time standards will be important for securing global legitimacy and buy-in.
Technical Hurdles
Defining a standardized time system for the moon is not just a political challenge, but a technical one as well. Clocks behave differently on the moon than on Earth due to the effects of general relativity. The moon’s weaker gravitational field causes clocks on its surface to run faster than terrestrial clocks, gaining about 56 microseconds per Earth day. This rate also differs between the lunar surface and orbit.
On Earth, the global satellite navigation systems that we rely on for precise positioning, such as GPS, depend on extremely accurate atomic clocks. For the GPS system, timing is so critical that an error of just a few nanoseconds can throw off positioning by meters. A similar satellite navigation network is planned for the moon, which will require even more stringent timekeeping to account for relativistic effects.
Atomic clocks used as time standards are also sensitive to environmental factors like temperature and radiation. The harsh conditions on the moon, with its long day/night cycles and exposure to solar radiation and cosmic rays, will pose additional technical hurdles for deploying a reliable network of lunar clocks.
Looking Ahead
NASA plans to land the first astronauts back on the moon by 2026 as part of the Artemis program, with the goal of establishing a permanent human presence. Other nations, including China, Russia, Japan and India, also have ambitions for crewed lunar missions in the coming decades. In the longer term, the moon is seen as a proving ground for technologies that will eventually enable human missions to Mars and beyond.
As humanity extends its reach in the solar system, the challenges of timekeeping will only grow more complex. The moons of Mars and other worlds will have their own unique “tempos” based on their gravitational and orbital properties. Some scientists have even proposed a universal time system that would work anywhere in the solar system, accounting for both gravitational time dilation and the relative motions of planets and moons.
Establishing a workable lunar time standard now is an important step in preparing for this future. As NASA’s chief of communications and navigation Kevin Coggins explains, “Think of the atomic clocks at the U.S. Naval Observatory (in Washington). They’re the heartbeat of the nation, synchronizing everything. You’re going to want a heartbeat on the moon.”
The White House’s directive for NASA to develop a plan for Coordinated Lunar Time reflects the necessity and urgency of setting common standards as the world embarks on a new era of lunar exploration and development. As with other aspects of space activity, success will depend on balancing competition and cooperation between nations. Thoughtful, inclusive leadership will be needed to establish governance frameworks that promote the responsible and equitable use of the moon and its resources for the benefit of all humankind.
The standardization of lunar time may seem like a small technical matter compared to the immense challenges of returning humans to the moon and establishing a permanent presence. But as the history of timekeeping on Earth demonstrates, the ability to define and synchronize time confers real economic, social and political power. Decisions made now about lunar time will have far-reaching implications as humanity takes its next steps in the exploration of the solar system and beyond.
