Lunar Reference Frames (ACR24 white paper)¶

Document: Lunar Reference Frames, a five-page white paper headed "2024 Moon to Mars Architecture" and footed "2024 Moon to Mars Architecture Concept Review". No date is printed beyond the year; the download path is 2024/12. Files: text sources/text/docs/2024-12-acr24-lunar-reference-frames.txt; raw sources/raw/docs/2024-12-acr24-lunar-reference-frames.pdf (fetched 2026-10-01T07:22:46Z from https://www.nasa.gov/wp-content/uploads/2024/12/acr24-lunar-reference-frames.pdf, per sources/manifest.csv). Page numbers: the printed numbers match the PDF pages and the text file's [page N] markers. Pages 1–4 were checked against the PDF; p. 5 is references only.

Which paper this is. NASA's White Papers web page lists it under "2024 Architecture Concept Review": "Offers considerations for developing an architecture that supports multiple reference frames to meet diverse positioning, navigation, and timing needs" (White Papers page, fetched 2026-10-01). ADD Rev C cites it: "For more information about lunar reference frame considerations, see the associated 2024 Moon to Mars Architecture white paper" (ADD Rev C, p. 66, footnote 21). It is 2024 context.

Summary. NASA has long used two body-fixed lunar frames, Mean Earth and Principal Axis, and the same point on the surface can differ "by as much as 875 meters" between them (p. 2). A NASA working group set up in 2024 recommended an architecture that supports more than one frame, with transformations between them, and endorsed Mean Earth "as the standard for initial surface operations, including planning and user location data exchange". It set no orbital standard (p. 3). The content is on C&PNT Systems.

Contents¶

Page	Section	Wiki home
1	Introduction (the objective and the 2022 national strategy); Figure 1; What is a Reference Frame?	C&PNT Systems
2	Mean Earth; Principal Axis; Key Considerations (accuracy and safety, collaboration and consensus, backwards compatibility, architectural flexibility, Artemis continuity)	same
3	Recommendations (the 2024 working group)	same
4	Key Takeaways	this page
5	References 1–15	this page

What the PDF shows that the text layer loses¶

Figure 1 (p. 1), captioned "Figures 1: Simplified diagram highlighting differences between lunar reference frames." Titled "Lunar Reference Frames: Comparing Mean Earth and Principal Axis". It draws Earth and the Moon with the "Lunar Orbit Plane", the "Ecliptic Plane (Earth's Orbit Around the Sun)" and "Earth's Equator", and the Moon's "Mean Earth" and "Principal Axis" X, Y and Z axes, which point in slightly different directions. It carries the angles 27.44°, 6.68°, 1.53° and 5.14°, which the text doesn't discuss, and the note "Simplified Diagram for Illustrative Purposes Only". The text layer keeps only the caption.
Emphasis. Bold in the PDF: "Accurate and precise lunar navigation data improves safety, enhances planning, and enables crewed and robotic missions to achieve agency goals" and the paper's statement of purpose (p. 1); the working group's recommendation of a multi-frame architecture, its endorsement of Mean Earth, and its decision not to endorse an orbital standard (p. 3).

Key takeaways (p. 4)¶

"Accurate and precise lunar navigation data improves safety, enhances planning, and empowers science for crewed and robotic missions; lunar reference frames are a critical component of a navigation architecture."
"There are two primary lunar reference frames in use: Mean Earth and Principal Axis. Neither frame meets the needs of every stakeholder; each frame is better suited to a different set of specific disciplines and scientific communities. Availability of relevant transformation data allows for conversion between frames."
"Establishing a consensus approach to lunar reference frames requires NASA to consider the needs of individual Artemis exploration assets and its industry, academic, and international partners."
"It would be impractical and disruptive to establish a single reference frame for all lunar activities. A flexible architecture supporting multiple, complementary reference frames will benefit diverse users."
"Adopting a Mean Earth reference frame for initial surface operations, including planning and user location data exchange, will meet current needs identified for missions while on the lunar surface. The working group did not endorse a corresponding orbital standard, understanding the need for mission-driven flexibility."
"NASA will use the Architecture Concept Review cycle to evaluate and implement reference frame updates. This evaluation must include all relevant stakeholders and should quantify impacts to all stakeholders."

What changed by Rev C¶

These comparisons are the wiki's.

Rev C states the need, not the choice. Its SCaN section says "NASA must define, adopt, and implement lunar reference systems (including reference frames) in the early stages of architecture development", and "U.S. policy on these topics is available and international coordination is underway", citing White House policy files, the IAU's "2024 Resolutions II and III", and this paper (ADD Rev C, pp. 65–66; SCaN Networks). Rev C never names Mean Earth or Principal Axis (search of its text). So the sources read don't say whether the working group's endorsement of Mean Earth was adopted.
The objective is unchanged. The paper quotes the lunar infrastructure goal "Develop a lunar position, navigation and timing architecture capable of scaling to support long term science, exploration, and industrial needs" (p. 1). The December 2025 lunar decomposition carries the same words as LI-03 L (Lunar objectives).
Frames, not time. The paper deals with reference frames. Rev C's C&PNT description also asks for "a coordinated lunar time standard traceable to Earth's Coordinated Universal Time" (ADD Rev C, p. 41), and FN-C-205 L is "Provide a coordinated lunar time scale" (C&PNT Systems; Lunar functions). The paper doesn't discuss a lunar time scale.
Accuracy. The paper says both frames are accurate "to about the meter level, which is about 10% of the navigation accuracy budget for Artemis missions" (p. 2), without giving the budget. Gap #0101's target is absolute real-time localization "to within 10m, 3 sigma" (tech gaps spreadsheet). The two sources don't relate these figures.

References that are other architecture documents¶

The paper cites 15 references (p. 5). Those that are Moon to Mars documents or pages, as printed:

Ref.	Title, as printed	Among the wiki's sources?
1	NASA's Moon to Mars Objectives	yes, Moon to Mars Objectives (2022) (same file name in the link)
3	NASA's Moon to Mars Architecture	yes, source page
4	Architecture Definition Document	the ADD documents web page, source page
15	Architecture Concept Review	yes, source page

The others: the National Cislunar Science & Technology Strategy (2022); the IAU's Nomenclature for Fundamental Astronomy glossary; two papers on lunar coordinates (Apollo landers; the Lunar Reconnaissance Orbiter); and pages on GNSS (UN Office for Outer Space Affairs), WGS 84, the National Geospatial-Intelligence Agency, Galileo, reference frames in GNSS (ESA Navipedia), the Space Frequency Coordination Group and the ITU.

Oddities¶

As printed, PDF checked:

"Figures 1" for a single figure (p. 1).
"the selection and implementation of or lunar reference frames" (p. 1).

C&PNT Systems · SCaN Networks · #0101 · ACR25 FE C&PNT white paper · RT-7 Interoperability · Lunar objectives · Architecture definition process