Amid increasing human activities on the Moon, there's a growing consensus on the necessity of establishing a standardized lunar time. In March 2023, the European Space Agency announced that space agencies worldwide had put setting lunar time on the agenda, contemplating how to proceed.
On April 2, 2024, the White House directed the National Aeronautics and Space Administration (NASA) to establish unified time standards for the Moon and other celestial bodies. According to Reuters, amidst the intensifying lunar competition among nations and private enterprises, the U.S. move aims to set international norms in space.
Discrepancies between Earth and Lunar Time
A memorandum from the White House Office of Science and Technology Policy (OSTP), led by Arati Prabhakar, indicates that NASA, in collaboration with other U.S. government agencies, is tasked with developing Coordinated Lunar Time (LTC) by the end of 2026.
According to Einstein's theory of relativity, time elapses differently on the Moon compared to Earth. For instance, approaching a black hole would significantly slow down time—or at least the perception of it—due to the intense gravitational pull. Although the difference in the passage of time between the Moon and Earth is minuscule, over time, these discrepancies accumulate.
Diverse gravitational forces and potential other factors on the Moon and other celestial bodies result in different perceptions of time compared to Earth. Moreover, coordinating lunar time will provide timing benchmarks for lunar spacecraft and satellites that require extremely high precision for mission execution.
The White House memorandum suggests that for individuals on the Moon, clocks based on Earth time seem to lose an average of 58.7 microseconds per Earth day. Additionally, with other cyclical variations, the deviation between lunar and Earth time will further increase. A previous report in Nature magazine stated that if humans on the Moon were to use regular clocks for timing, they would be completely out of sync with Earth time.
As part of the Artemis program, NASA aims to send astronauts to the Moon in the coming years and establish a scientific lunar base to lay the groundwork for future Mars missions. This endeavor involves dozens of agencies and various spacecraft.
An unnamed official from the White House Office of Science and Technology Policy stated that without a unified lunar time standard, ensuring secure data transmission between spacecraft would be challenging, as would synchronizing communication between Earth, lunar satellites, bases, and astronauts.
The official noted that temporal discrepancies could also lead to errors in executing mapping and positioning tasks on the lunar surface and in lunar orbit.
"Imagine if clocks around the world weren't synchronized to the same time, the disruption it would cause, and how challenging everyday life would be."
Possible International Agreement with 36 Countries
Kevin Coakley, head of space communications and navigation at NASA, stated in an interview, "The clocks we use on Earth run at a different speed on the Moon. Think about the atomic clocks at the U.S. Naval Observatory (located in Washington, D.C.). They're the nation's timekeepers, syncing everything. You'd definitely want a timekeeper on the Moon too."
The operation of most clocks on Earth and the division of time zones are based on Coordinated Universal Time (UTC). This internationally recognized standard relies on a vast network of atomic clocks spread across the globe. These atomic clocks measure changes in atomic states and produce an average, ultimately forming an accurate time.
According to an official from the White House Office of Science and Technology Policy, it may be necessary to deploy atomic clocks on the lunar surface. The official also stated that as commercial activities expand to the Moon, a unified time standard is crucial for coordinating operations, ensuring transaction reliability, and managing lunar commercial logistics.
In January 2024, NASA announced plans to send four astronauts on a flyby mission around the Moon and return them to Earth by September 2025, with a goal to complete the first crewed lunar landing since the end of the Apollo program in the 1970s by September 2026.
It's worth noting that the White House directive is not without precedent. Last year, the European Space Agency opened applications to external companies to assist in developing standardized lunar clocks. As early as 2019, NASA introduced the Deep Space Atomic Clock (DSAC) to enable spacecraft to navigate more effectively independently of Earth.
The aforementioned memorandum states, "A standard defined by the United States will benefit all spacefaring nations, achieving the required accuracy and resilience in the challenging lunar environment."
The memorandum emphasizes that determining how to implement Coordinated Lunar Time will require a series of international agreements through "existing standard-setting bodies." This will necessitate reaching international agreements with the 36 countries that have signed the Artemis Accords.
An official from the White House Office of Science and Technology Policy stated that Coordinated Universal Time may also influence the implementation of Coordinated Lunar Time. The International Telecommunication Union of the United Nations has defined Coordinated Universal Time as an international standard.
While the United States has so far been the only country to send astronauts to the Moon, other nations are also planning lunar missions. Countries worldwide are interested in the potential mineral resources on the Moon, and establishing lunar bases can also support future missions to explore Mars and other celestial bodies.
In 2023, India successfully landed a spacecraft near the lunar South Pole and announced plans to send astronauts to the Moon by 2040. In January 2024, Japan became the fifth country to send a spacecraft to the Moon.
