Architecture framework: segments and sub-architectures¶
Summary. The ADD splits the Moon to Mars Architecture two ways. Segments are portions of the architecture in order of "increasing operational complexity and objective satisfaction". Sub-architectures are groups of "tightly coupled" elements, functions and capabilities. NASA chose this split over a design fixed up front, so that new systems and technologies can be added each year. This page gives NASA's definitions. The segments, sub-architectures and elements themselves (ADD Section 2) have their own pages: Segments, Sub-architectures and Elements.
What NASA means by "architecture"¶
"An architecture is the high-level, unifying structure that defines a system. It provides a set of rules, guidelines, and constraints that define a cohesive and coherent structure consisting of constituent parts, relationships, and connections that establish how those parts fit and work together" (ADD Rev C, p. 11). The definition is from the NASA Systems Engineering Handbook (p. 11, footnote 3), and the ADD repeats it in its framework key terms (p. 18).
The objectives documents' definition is different. The 2022 Moon to Mars Objectives and the 2023 Strategy and Objectives Development document define it as "A set of functional capabilities, their translation into elements, their interrelations and operations. The architecture enables the implementation of various mission scenarios that achieve a set of given goals and objectives" (Moon to Mars Objectives, p. 12; Strategy and Objectives Development, PDF pp. 6, 33, which adds a comma after "interrelations"). The 2023 document adds a near-synonym, "wireframe": "An architectural structure that connects projects, programs, and entities in a meaningful way toward achievable goals, with purpose toward the near-term endeavor and long-term vision. Wireframe can be used interchangeably with Architecture" (PDF p. 6). Rev C uses the Handbook definition and doesn't use "wireframe" (the wiki's search of its text). As the wiki reads them, the two definitions don't conflict but stress different things: capabilities turned into elements, against rules for how parts fit together.
The ADD calls the campaign "the agency's most complex systems engineering effort to date", with programs and systems that "will span decades, agencies, countries, cultures, and a variety of commercial, academic, and other types of contributors". The document "establishes a common language, framework, and process to communicate and chronicle the evolution of the Moon to Mars Architecture" (p. 11).
Why a framework instead of a fixed design¶
"In a traditional systems engineering process, NASA would fully establish an architecture up front, define requirements and concept of operations, and begin execution through associated programs and projects. This method — if applied to an architecture of this scale — would require the agency to select mission profiles, technologies, and development schedules up front, biasing the architecture toward mature solutions and capabilities that exist today" (ADD Rev C, p. 18).
Instead, "to realize an evolutionary architecture that responds to the changing technological landscape, NASA's iterative Moon to Mars Architecture framework divides the architecture into the sub-architectures and segments discussed in Section 2" (p. 18). The framework "embraces systems engineering processes that empowers incremental advancements, infusion of new innovations, incorporation of partnerships, and systematic fulfillment of objectives" (pp. 17–18). "This framework allows the architecture to add new systems over time. NASA may also add or reassign functions to systems as they mature, reflecting new capabilities and maximizing objective satisfaction" (p. 18).
Key terms¶
NASA's definitions (ADD Rev C, p. 18):
| Term | Definition |
|---|---|
| Segments | "Portions of the architecture, identified by one or more notional missions or integrated use cases, illustrating the interaction, relationships, and connections of the sub-architectures through progressively increasing operational complexity and objective satisfaction." |
| Sub-Architecture | "A group of tightly coupled elements, functions, and capabilities that perform together to accomplish architecture objectives." |
The running text says the same more briefly: "Sub-architectures group tightly coupled systems, needs, and capabilities that function together to accomplish objectives. The segments define portions of the architecture with increasing operational complexity and objective satisfaction" (p. 18). Section 2 repeats both definitions word for word in its own key-terms table (p. 21) and adds three more terms (Element, Exploration Asset, Utilization Payloads and Equipment), defined on the elements index. There it calls segments "broad phases of exploration" (p. 21).
In the objective decomposition figure, use cases carry the label "Segments" and functions the label "Sub-architectures" (p. 16); see Objective decomposition.
Shorter versions, 2023 and 2024. The two executive overviews print a seven-term box with plainer definitions: a segment is "A portion of the architecture that integrates sub-architectures and progressively increases in complexity and objective satisfaction", and a sub-architecture "A group of tightly coupled elements, functions, and capabilities that work together to accomplish one or more objectives" (2023 overview, PDF p. 3; 2024 overview, PDF p. 20). Architecture is "The unified structure that defines a system, providing rules, guidelines, and constraints for constituent parts and establishing how they fit and work together", a short form of the Handbook definition above. The full comparison is on the 2024 overview's source page. ADD Appendix F defines the same terms again, mostly in the body's words; it makes "Segments" singular ("A portion of the architecture", p. 301). All three sets are compared on the Glossary. Both overviews also say what the architecture is not: "It isn't a mission, a manifest, or a set of requirements" (2023, PDF p. 3; 2024, PDF p. 20). The ADD's own list of what it is not is on its source page.
The four segments, by name¶
From the ADD contents (ADD Rev C, p. 5), Section 2.1 "Segments" (p. 22):
| Segment | Starts on | Wiki page |
|---|---|---|
| Human Lunar Return | p. 24 | segments/human-lunar-return |
| Foundational Exploration | p. 27 | segments/foundational-exploration |
| Sustained Lunar Evolution | p. 33 | segments/sustained-lunar-evolution |
| Humans to Mars | p. 37 | segments/humans-to-mars |
There is also a placeholder for "Future Segments" (p. 23). Overview, element-by-segment table and gap counts: Segments.
Segments are not Moon Base phases. The Moon Base was announced after Rev C, and no source maps ADD segments onto Moon Base phases: none of the 2026 documents, decks or Moon Base pages names a segment beside the Moon Base (Moon Base phases).
Sub-architectures¶
ADD Section 2.2 (pp. 40–44) lists 12 sub-architectures, each with a one-letter "Decomposition Abbreviation" used in the objective decomposition (p. 40): Autonomous Systems and Robotics (A); Communications and Positioning, Navigation, and Timing Systems (C); Data Systems and Management (D); Habitation Systems (H); Human Systems (X); Infrastructure Support (G); In-situ Resource Utilization Systems (I); Logistics Systems (L); Mobility Systems (M); Power Systems (P); Transportation Systems (T); Utilization Systems (U). The tech-gap spreadsheet uses the same 12, and the Moon Base Users Guide groups its Phase 1 functional gaps under seven of them (Users Guide, p. 9). See Sub-architectures.
Elements¶
ADD Section 2.3 (pp. 45–68) describes 15 elements, the "major systems and hardware that enable exploration" (p. 45). The overview and the element-to-segment and element-to-sub-architecture tables are on Elements, which links one page per element (ADD pp. 47–68).
Related pages¶
Objective decomposition · Architecture definition process · ADD Rev C source page · Segments · Sub-architectures · Elements · Gaps index · Data gaps index · NASA's Components web page
Sources¶
ADD Rev C, pp. 3, 5, 11, 16–18, 21, 23, 40, 45, 301 · Users Guide, p. 9 · Moon Base hub (for the segment-to-phase point) · Moon to Mars Objectives (2022), p. 12 · Strategy and Objectives Development (2023), PDF pp. 6, 33 · 2023 executive overview, PDF p. 3 · 2024 executive overview, PDF p. 20