OSTP Celestial Time Standardization memo (2024)

In plain language

On 2 April 2024 the White House Office of Science and Technology Policy issued a policy memorandum on celestial time standardization ^[1]Official. It gives the proposed lunar standard a name, Coordinated Lunar Time (LTC), and it tells NASA to work out how to build it.

The memorandum is policy, not metrology. It defines no time scale, publishes no scale, and names no clocks. It states a requirement, assigns the work, and puts dates on the work.

It also quotes a rate. A clock in a lunar frame gains about 58.7 microseconds per Earth-day on a clock keeping Terrestrial Time on Earth ^[1]Official. That pair of scales is not the pair behind the 56.02 µs/day of the peer-reviewed literature ^[4], and 56 vs 58.7 microseconds sets the two pairs side by side. Every lunar value we show is a model value ^[3].

What it decides

• It names the standard. The memorandum calls the proposed scale Coordinated Lunar Time and abbreviates it LTC ^[1]Official. The name spread from this document into everything written since; what Coordinated Lunar Time is follows that trail.
• It requires traceability to UTC. The lunar standard has to stay tied to Coordinated Universal Time, so that a lunar reading can be converted to a terrestrial one ^[1]Official.
• It assigns the lead. NASA leads the work, in coordination with the Departments of Commerce, Defense, State and Transportation ^[1]Official.
• It rules out simply using UTC on the Moon. A clock on the lunar surface does not tick at the rate at which the SI second is realized on Earth, so applying UTC unchanged would break the units ^[1]Official.
• It puts dates on the work. Three directives, three dates, listed verbatim below ^[1]Official.

What it leaves open

• The realization. How LTC is computed, from which clocks, on what schedule and by whom — none of it is in the memorandum ^[1]Official.
• The clock ensemble. No agency is named as the keeper of the clocks, and none has announced that it will be ^[5]Official.
• Offsets for individual sites. Whether a base at the south pole would keep the same reading as one on the near side is not addressed; will the Moon have time zones collects what has been proposed ^[1]Official.
• The tie to the IAU definitions. This memorandum is dated 2 April 2024; the IAU defined Lunar Coordinate Time later the same year ^[6]Official. How the operational standard sits on top of that coordinate time is not written down anywhere yet.
• The reference systems. A companion OSTP memorandum of 18 December 2024 covers lunar reference systems and carries its own 2026 deadline ^[7]Official.

Key passages

The memorandum carries three directives with three different dates. Two of them fall in 2024 and are almost never quoted; the third is the one the press reported ^[8].

Deliverable	Deadline	Verbatim wording in the memorandum	Source
Finalized strategy to the Executive Office of the President	31 December 2026	NASA will, in coordination with the Departments of Commerce, Defense, State, and Transportation, provide a finalized strategy to the Executive Office of the President to implement lunar timing standardization no later than December 31, 2026.	[1]Official
LTC considered in the annual Moon-to-Mars Architecture Concept Review cycle	31 December 2024	NASA will also include consideration of Coordinated Lunar Time (LTC), as described in this memorandum, as part of its annual Moon-to-Mars Architecture Concept Review cycle no later than December 31, 2024.	[1]Official
Milestone-based approach delivered to OSTP	31 December 2024	NASA will provide OSTP with a milestone-based approach to establish LTC in line with this guidance no later than December 31, 2024.	[1]Official

The OSTP press release of the same day repeats the 2026 deadline and only that one ^[2]Official. It is a secondary source here: the primary record for all three dates is the memorandum itself.

This policy directs NASA to work with the Departments of Commerce, Defense, State, and Transportation to deliver a strategy for the implementation of LTC no later than December 31, 2026.

Reporting followed the press release, so a single date entered circulation ^[9]. The next dated milestone that we can verify is still the 2026 strategy: the standards tracker follows it, and the timeline places this memorandum beside the other decisions of 2024 to 2026 ^[1]Official.

The international counterpart to this national deadline is Draft Resolution D of the 28th CGPM, which is on the agenda for October 2026 ^[10]Official.