It may sound like the setup for a lame joke, but "What time is it on the Moon?" will soon be a valid question. The White House has instructed NASA to devise a system for Coordinated Lunar Time (LTC) that will provide official reference time for future lunar missions. The executive branch aims to fully implement LTC by the end of 2026, just in time to help coordinate a flurry of activity as humanity returns to the lunar surface.
The memo (PDF) instructs NASA to work with the Departments of Commerce, Defense, State, and Transportation to develop the system. This would provide an alternative to the mishmash of UTC and local times used to time space missions. With space around the Moon about to get much busier, the government feels it's the right time to standardize time measurement in space.
The memo, issued by Arati Prabhakar of the Office of Science and Technology Policy, sets out overarching principles that agencies should use to create new time zones for space. The effort will begin with LTC, but the Office of Science and Technology Policy intends to use the same approach to create time zones for other celestial objects.
When creating LTC, the memo instructs NASA to build in four key properties. LTC should be traceable to UTC for easy conversions. It should also be accurate enough to support precision navigation and science operations. LTC must also be resilient enough to survive the loss of contact with Earth, although NASA is experimenting with orbits to eliminate communication blackouts. Finally, the new lunar time zone has to be scalable to space environments beyond the Earth-Moon system.
Setting up LTC isn't as simple as deciding on a number and syncing it with Earth's atomic clocks. Space exploration often involves traveling at high speeds, which can affect how we perceive time, thanks to general relativity. For example, to someone on Earth, a clock on the lunar surface would appear to lose 58.7 microseconds per Earth day. Scientists must consider this effect when developing LTC to ensure it is precise enough for navigation and coordination with Earth. Timekeepers on Earth rely on highly advanced atomic clocks, and the Moon may need something similar.
Even if the project is done within the current deadline, NASA's next few Artemis missions will have to head to the Moon without the benefit of Coordinated Lunar Time. Artemis II is now on the books for 2025, and the Artemis III crewed landing is set for 2026. If all the current players continue lunar operations, the late 2020s and early 2030s will be a cosmic traffic jam. China, Russia, India, and others are planning to expand their presence on and around the Moon.
