Towards Lunar Synchronization: NASA's Standard Time for the Moon

In September 2025, NASA's four-member Artemis crew is planned to fly around the moon in preparation for the space organization's main goal to arrive on the moon again. To boost such scientific missions, the White House Office of Science and Technology Policy (OSTP) on April 2, coordinated its space agency, the National Aeronautics and Space Administration (NASA), to lay out a Coordinated Lunar Time (LTC) to standardize cislunar tasks with the universal time followed on Earth.

OSTP Delegate Director for National Security Steve Welby said, "A reliable meaning of time among operators in space is critical to successful space situational awareness capacities, navigation, and communications."

Time seems to elapse slowly where gravity is stronger, as close to celestial bodies. Subsequently, the length of a second on Earth is different for an observer under various gravitational conditions, like on the moon.

The LTC will be the standard to measure cislunar operations and space activities between the moon and Earth with Coordinated Universal Time (UTC), the global time used to regulate time on Earth. Roping in federal offices like the U.S. Departments of Commerce, Defence, State, and Transportation, the White House has set a deadline of December 31, 2026, for NASA and its global partners to convey a system to carry out LTC.

The project falls under the current administration's National Cislunar Science and Technology Strategy. NASA has coordinated to draw in with the 39 countries who have marked the Artemis Accords for this project. It is expected to introduce its thought of the LTC by December 31, 2024, as a part of its Moon-to-Mars Architecture Concept Review cycle.

What is Coordinated Lunar Time (LTC)?

In 2023, the European Space Agency (ESA) sent off a project called 'Moonlight' to design satellites for astronauts and robotic explorers, which will be utilized to help NASA's moon mission 'Artemis.' While dealing with the project, questions emerged on setting a solitary time region for the moon and how to go about it.

On Earth, we use a 24-hour day based on the planet's rotation. However, the moon rotates much more leisurely every 29.5 Earth days. Because of its slow rotation, it would be practical to have less than Earth's 24 time zones ideally, a single time zone for the moon would be natural and featuring that this would be like the Coordinated Universal Time (UTC).

The idea for the UTC was formed during the 1960s. Atomic clock devices that measure time-based on the vibration of atoms are known for their extreme accuracy in measuring time. In the meantime, solar time, calculated by measuring the rotation of Earth on its axis relative to the Sun, is variable. A weighted average of hundreds of atomic clocks produces the International Atomic Time (TAI).

The UTC was planned as a way to accommodate the contrast between solar time and atomic time and is kept within 0.9 seconds of solar time to follow Earth's rotation variations and within a definite number of seconds of the TAI. At present, moon missions follow the time of the country that operates the spacecraft, while the International Space Station (ISS) runs on the UTC. However, a standardized time for space and the moon isn't followed.

It will conflict with the moon's light and dark periods (because of its slow rotation, the moon faces away or towards the Sun for long periods), and it wouldn't be reasonable to have a weeks-long "day" followed by a weeks-long "night."

The White House's Celestial Time Standardization policy looks to assign a time standard to each celestial body and its surrounding space climate, first focusing on the lunar surface and missions working in cislunar space. It frames the four features such a time standard must possess:

1. Traceability to UTC: Lunar Time is similar to Terrestrial Time on Earth (TAI+ 32.184 seconds). Like Terrestrial Time, Lunar Time might be set through an ensemble of clocks on the moon. This time standard, i.e., LTC may employ or distribute the UTC offsets expected to maintain both local time and UTC within tolerance limits.

2. Scalability beyond the Earth-Moon system: Conversion of LTC to UTC for operations including associations with Earth will be possible by utilizing the above approach to set the LTC. This approach is also extensible to space environments past the Earth-Moon systems (for instance, for Mars).

3. Accuracy for precision navigation and science: The LTC will give users in cislunar space a reference time standard near the gravitational environment in which they operate. Space resources can synchronize with one another with accuracy for navigation.

4. Resilience to loss of contact with Earth: The reference time LTC should survive independently when contact with Earth is lost.

Why is LTC required?

Past moon missions included astronauts visiting the lunar surface, finishing their work, and flying home. Notwithstanding, with space offices across the world intending to lay out an extremely durable human presence on the moon, LTC is required. Up to now, when you have a mission on the moon, you would continuously synchronize with a time region on Earth. However, presently we will have numerous missions in the future, and having a typical reference time is truly required.

The pressing need for LTC is because of the arrangement to make a dedicated global satellite navigation system (GNSS) for the moon by 2030. This system will work similarly to how the Global Positioning System (GPS) and other navigation networks work on Earth.

Commercial operations on the lunar surface including transactions and logistics will be more dependable with the LTC.

Issues in characterizing and carrying out LTC

The method involved with defining lunar time is complicated by the impact of the moon's gravitational pull. According to relativity theory, because of the weaker gravitational pull of the moon, a clock on the moon would run quicker than one on Earth, explains Patrizia Tavella, Head of the Time department at the International Bureau of Weights and Measures in Sèvres, France. "A clock's speed would change relying upon its position on the lunar surface, due to the moon's revolution," she adds.

NASA aerospace engineer Cheryl Gramling estimates that any clock on the moon would acquire 56 microseconds more than 24 hours. Per an estimate by The Scientific American, at least three master clocks that tick at the moon's natural pace should be installed. The result of these three clocks combined with a calculation is supposed to produce a more precise time standard.

In particular, lunar time will have to be practical for astronauts there (ISS). Each lunar day endures as long as 29.5 Earth days. With the Artemis Program going for the lunar landing as soon as 2026, it requirements to consider how to adjust to this challenge for a long-duration stay.

In November 2022, the requirement for a unified lunar time was voiced worldwide by space agencies and academic organizations at an ESA meeting in Noordwijk, the Netherlands. Most participants settled on "a common lunar reference time," however discussed if a single organization should set and keep up with time on the moon.

Aside from the US, a few nations have lunar ambitions. China has expressed that it will put its astronauts on the moon by 2030, while India intends to land in 2040. In January, Japan became the fifth country to land a spacecraft on the moon, after the US, Russia, India, and China. However, India is the main one to land a spacecraft close to the lunar south pole.

"U.S. leadership in characterizing a reasonable standard will help all spacefaring countries," the OSTP stated. Getting consensus on LCT should be easier for the U.S. because of the inclusion of the Artemis Accord countries. However, two of its greatest space rivals - China and Russia - have not signed the agreements, posing obstacles.