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What To Expect: NASA’s 2023 Architecture Concept Review

The year 2024 is set to be a crucial one for NASA’s lunar ambitions. Several commercial lunar payloads will attempt a landing this year under the CLPS initiative, while the buildup for Artemis II progresses towards its historic crewed flight. While these missions set their sights on the Moon, NASA is preparing to launch even more forward-looking plans this month: products from the 2023 Architecture Concept Review. Set for release on January 22nd, these highly-anticipated documents will provide key insights into NASA’s overarching Moon to Mars exploration strategy, including new details in its vision for sending humans to Mars.

Space Scout previously introduced NASA’s Moon to Mars Architecture in the article Anatomy of a Deep Space Transport. With updates to these plans coming later this month, we’ll be taking a closer look at the rationale and process for developing the architecture, and exploring what we can expect to learn from the upcoming product release.

NASA’s Architecture Process

In the context of systems engineering, architecture refers to the framework that relates a system’s components and the functions they perform to its overall objectives. The architecture for a project allows engineers and planners to work “backwards” from their highest-level goals, then distill those down into the capabilities and elements needed to accomplish them. Since end goals are often visualized on the right side of a timeline, this process is called “architecting from the right.”

NASA’s Moon to Mars Architecture represents an application of this concept on a much larger scale. Rather than covering a single mission, the architecture instead organizes NASA’s human spaceflight ambitions at the highest level. Its constituent elements are themselves entire missions and programs, ranging from robotic precursors to human explorers.

This is a relatively new approach for NASA, which has had previous spaceflight plans fail to materialize due to a perceived lack of direction. Vehicles without a clear purpose are vulnerable to political criticism, and can hinder a program’s ambitions by restricting its capabilities. By architecting from the right, NASA instead seeks to outline the “big picture” first, to understand the capabilities they will need before initiating any new development programs. Then, when the architecture identifies a gap in capabilities, NASA can begin to formulate an element to play this role.

At NASA, The Exploration Systems Development Mission Directorate (ESDMD) is responsible for defining and managing the overall development of its Moon to Mars plans, including the ongoing Artemis Program. The Strategy and Architecture Office (SAO) is the division of ESDMD which continuously develops the architecture itself, maintaining a current baseline and incorporating feedback from relevant stakeholders in science, policy, and industry. This takes the form of a Strategic Analysis Cycle, which repeats every year as the SAO refines the Moon to Mars Architecture.

Crucially, this process culminates in an annual Architecture Concept Review (ACR), where NASA pools together the work of the past year and presents a unified plan across the agency. The first such review, ACR22, was conducted in late 2022, with its products released in April of 2023. Future reviews occur annually in November, with product release targeted for the early months of the following year. The most recent review, ACR23, was held from November 14th through 16th, with release targeted for January 22nd of 2024.

A flowchart illustrating the Strategic Analysis Cycle.
Credit: NASA

The architecture itself is described by the Architecture Definition Document, or ADD. The ADD contains detailed coverage of all facets of the architecture, and will receive regular updates as the analysis process continues. Additionally, each ACR produces a number of “White Papers,” shorter documents which each highlight a specific feature of the architecture. Six of these were released alongside the initial ADD in 2022. Current and previous versions of these products are available at

The Moon to Mars Architecture

The first Architecture Concept Review laid out the foundation of NASA’s approach to its Moon to Mars ambitions. Fundamentally, the architecture seeks to answer the Who, What, When, Where, Why, and How of human space exploration. Unlike previous programs, NASA has chosen to emphasize “Why” as the key driver for all other decisions: to seek new scientific knowledge, to inspire the next generation of explorers, and to reinforce the United States’ national posture.

A diagram depicting the objective decomposition process.
Credit: NASA

These guiding principles drove the formulation of sixty-three objectives that the architecture must accomplish at its highest level. Each is relevant to the Moon, Mars, or both. The objectives are then “decomposed” into a set of specific use cases and functions that the architecture must address, such as the delivery of crew and cargo to the lunar surface. Related use cases and functions can then be grouped together and assigned to a particular element, such as a lander, rover, or spacesuit. This process ensures traceability within the architecture: individual elements are linked to a clearly-defined set of needs which can be followed all the way up the hierarchy to NASA’s fundamental goals.

The Moon to Mars Architecture is organized into a series of four segments, each of which roughly corresponds to a different phase in the program. Each segment incrementally addresses a subset of the goals, functions, and use cases of the larger architecture, representing an evolving set of capabilities over time. In approximately chronological order, these are Human Lunar Return, Foundational Exploration, Sustained Lunar Evolution, and Humans to Mars.

The four Moon to Mars Architecture segments.
Credit: NASA

The first segment, Human Lunar Return, is currently underway, and comprises the realization of initial capabilities needed to send humans back to the Moon for the first time since the Apollo program. The first few Artemis missions and landings fall under this segment. The functions and use cases addressed by this segment are already defined, and the elements they are associated with are either operational, such as the Space Launch System and Orion spacecraft, or in development, such as Gateway and the Human Landing System. This portion of the architecture received the most attention during ACR22, and is now largely in the execution phase, though details may still be revised as needed.

The second segment, Foundational Exploration, encompasses the expansion of capabilities needed to conduct scientific research on the Moon and demonstrate technologies in support of future Mars missions. Foundational Exploration generally corresponds to Artemis missions in the near future, after an initial presence has been established. Newer capabilities include both pressurized and unpressurized surface mobility, as well as the ability to support long-term habitation on the lunar surface. Here, the relevant use cases and functions have been defined, but their association with specific elements was not detailed under ACR22.

The third segment, Sustained Lunar Evolution, will see NASA and its partners working towards a steady cadence of regular human presence on and around the Moon, supporting long-term science as well as economic opportunities. In the ADD, NASA calls this the “broad, undefined end state” for lunar exploration, and notes that specific use cases and functions are not yet associated with this segment. Objectives like expanded power generation, in-situ resource utilization, and advanced transportation systems are understood to be relevant, but NASA expects this segment to develop more organically as the previous segments are executed. As such, this area is not expected to be a major focus in the near future.

The fourth segment, Humans to Mars, addresses capabilities needed for the first crewed missions to Mars, while supporting future exploration missions. Though this vision is straightforward, the architecture process for this segment was the least developed as of ACR22. Although the Moon-focused objectives had been fully decomposed, the Mars-focused ones had not, and specific functions and use cases were not formally defined in the ADD. The challenge for NASA’s architecture team is to identify the most significant problems that must be solved and understand what solutions are available. Products from ACR22 therefore focused on describing some of the basic trade spaces under consideration, including deep space transportation, Mars landing systems, Mars surface systems, and crew health and support.

Looking Forward: ACR23 Products

For NASA, ACR22 effectively served as a shakedown of the architecture review process, in addition to developing the architecture itself. This first review focused heavily on documenting the Human Lunar Return segment, which is currently being implemented through NASA’s first Artemis missions. Both the initial ADD and White Papers reflect this focus, while Mars studies are relatively underdeveloped.

The most recent review, ACR23, focused primarily on the Humans to Mars segment. At the conclusion of ACR23, Catherine Koerner, Associate Administrator for ESDMD, explained that the review “focused on identifying the foundational decisions needed for a crewed mission to Mars,” among other architecture goals. Details about these decisions, and insights into how NASA will resolve them, will appear in an updated version of the Architecture Definition Document, called ADD Revision A. In particular, we can expect to see the decomposition of Mars-focused objectives into more detailed use cases and functions, helping NASA to understand what problems need to be solved to accomplish early Mars missions.

While the SAO maintains Mars reference missions as a baseline, we are not likely to see a complete mission architecture in ADD Revision A, as NASA is still evaluating the best path forward. However, the product release will also include twelve new White Papers, five of which are focused on exploring the unique challenges of a crewed Mars mission, including abort considerations, surface power generation, and human health and performance. While many hard decisions remain in the future of Mars planning, we can expect these documents to yield an inside look at NASA’s options and preferences.

The twelve White Papers produced during ACR23.
Credit: NASA

In addition to Humans to Mars, ACR23 also worked on updating the Moon-focused architecture segments, with an emphasis on Foundational Exploration. Notably, many of the functions and use cases here have been assigned to mature elements, and we can expect to see definitions of these in ADD Revision A. These include systems like the Lunar Terrain Vehicle, Pressurized Rover, future human-class landers, and several new Gateway components. Six of the twelve new White Papers discuss challenges for the near future of lunar exploration, such as precision landing, EVA systems, logistics, and communications. The ideas expressed in these papers will likely be implemented in the next few years, as the Artemis program works to evolve beyond its first small steps.

The road to Mars is long, and success is predicated on our ability to make informed decisions about the future. Each iteration of the Moon to Mars Architecture brings NASA and its partners one step closer to achieving sustainable exploration throughout the solar system. With the release of these planning documents just a week away, Space Scout looks forward to continuing its coverage of NASA’s long-term human spaceflight ambitions.

Edited by Derek Newsome and Nik Alexander

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