ARCHITECTURE CONCEPT 

REVIEW 2022 White Paper

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National Aeronautics and 

Space Administration

SYSTEMS ANALYSIS OF ARCHITECTURE 

DRIVERS

Analysis of a space systems architecture can be reflected in a six-sided trade space, shaped 

by the answers to six key questions: Who, What, Where, When, Why, and How? (Figure 1). In 

laying out a Mars architecture decision roadmap, it is critically important for decision-makers 

to understand how these key drivers relate to each other and how the architecture can change 

depending on the order in which these decisions are made. 

The Apollo program was famously characterized by the mandate of “landing a man on the Moon 

and returning him safely to Earth” before the end of the decade. This prioritized “when?” (within 

the decade) over other considerations. NASA successfully achieved the goal, but because 

the resulting architecture was optimized to meet a tight implementation schedule, it was not a 

particularly extensible architecture, with implications to sustained human exploration of the Moon.

Figure 1. Key architecture drivers
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The Apollo Program serves as a cautionary tale for Mars: if the focus is on “when?” as an anchoring decision 

(architecting from the right in Figure 2), and the answer is a date that doesn’t permit enough time to develop 

new technologies, then the answer to “how?” will default to heritage or heritage-derived systems. If the 

specified date is too soon to develop and certify both a new transportation system and new descent, ascent 

and surface systems, then the schedule compromise may be an orbital-only or fly-by first mission, followed 

by surface missions in later years. This affects not just “how?” but cascades to “what?” and “why?” If instead 

of a particular date, “when?” is indexed to another event—for example, the timeline of a particular technology 

development or an agency funding profile—then certain technologies or assets from other Programs may be 

prescribed, again influencing both “how?” and “what?” If the answer to “when?” specifies both a “boots on 

Mars” date and a “boots back on Earth” date (in other words, a total crewed mission duration) that will define 

whether new high-tech, high energy transportation systems capable of shorter mission durations must be 

developed. As shown in Figure 2, architecting from the right by starting with “when?” potentially makes the 

answers to “why?” “where?” and “who?” reliant on the answers to “how?” and “what?”

With few architecture decisions mandated thus far, human Mars exploration offers a unique opportunity to 

take an objectives-based exploration architecture development approach.

NASA’s new Moon to Mars Blueprint Goals and Objectives for Exploration initiative1 provides such a framework. 

In contrast to a capabilities-based approach, an objectives-based approach focuses on the big picture, the 

“what?” and “why?” of what NASA should be doing in terms of deep space exploration before prescribing the 

“when?” or “how?”

As shown in Figure 3, NASA’s exploration blueprint identifies many answers to the question of “Why?” Any 

single answer is unlikely to satisfy all stakeholders, but each answer is important to one or more stakeholders. 

Starting with “why?” will help anchor the development process, but architecture choices may still vary widely 

depending on how the many different answers to “why?” are prioritized. Must the first human Mars mission 

check off every item in the “Why?” Venn diagram, shown in Figure 3, or is it sufficient to establish a firstmission architecture that meets the highest priority items, and is extensible to meet lower priorities during 

subsequent missions. 

Figure 2. Architecture decision flow if starting with “when?”

INFLUENCES HOW 

TO GO & RETURN

Do we have time to develop advanced 

technologies? (Orbital only if no time to 

develop lander/surface systems?)

What Program assets/tech 

have to be assumed?

Shorter duration drives 

architecture selections

INFLUENCES WHY GO

To beat a deadline

Mission pull for current programs or

technology development

Expand human spaceflight experience

INFLUENCES WHERE TO GO 

Go where we can get to fastest

Go where our heritage 

assets are best suited

Go where we can get back fast

INFLUENCES WHO WILL BE INVOLVED 

Number of crew based on time 

available to develop systems

Number of crew based on

heritage systems

Faster fewer crew

By a particular date?

Index to another 

program or technology 

development timeline?

Get there and back

within a limited 

total duration? 

WHEN TO GO

WHAT CAN BE DONE IN THE TIME

AVAILABLE THERE? 

Stay in orbit if no time to develop 

lander/ascent/surface systems

Architecture limited to indexed assets

Limited surface stay

means limited operations
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For example, prioritizing Science on the first human Mars mission will influence “where?” the landing site is 

selected if the specific science objective of interest requires access to a particular region or feature; this may 

require mission elements (the “how?”) tailored to that particular science discipline. If that priority science 

location is difficult to reach or lacks the resources for sustained human presence, a lighter exploration footprint 

may be desired for the first mission, and crew selection may be heavily influenced by science expertise. 

Conversely, if Inspiration, in the form of sustained human presence is the priority goal, then a landing site 

offering abundant resources or ease of access may be desired, with the first mission elements laying the 

groundwork for a heavier, permanent infrastructure at a single location, able to support a larger number of 

crew, possibly selected for their engineering expertise. As shown in Figure 4, again architecting from the right, 

different priorities within “why?” will cascade through the other questions.

These sample decision structures illustrate an important point: the Mars architecture depends on which 

decisions are prioritized, and which are allowed to “float” to enable the highest priorities first. In practice, the 

Mars architecture decision flow is likely to be iterative rather than linear. To minimize disruption, rework and 

cost or schedule changes, understanding the minimum goals and priorities for the first mission, as well as the 

longer-term goals for subsequent missions, can aid in establishing a flexible and sustainable architecture. The 

answer to any one of these questions is less important than whether the answers to all six complement one 

another as a set and can be balanced to establish an architecture that is achievable, affordable, and adaptable.

Figure 3. “Why?” Explore

Investigations in deep space, 

on the Moon, and on Mars will 

enhance our understanding 

of the solar system, the Earth, 

the human body, and how to 

perform new operations while 

we are out there exploring.

Accepting audacious 

challenges and succeeding 

through perseverance 

and tenacity in the face of 

adversity motivates current 

and future generations to 

dare mighty things.

What we choose to do, how we 

do those things, and who we 

do them with greatly impacts 

our place in the world today, 

our quality of life, and our 

possibilities for the future.

BENEFITS TO 

HUMANITY

Why We Explore
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KEY TAKE-AWAYS 

Mars architecture will be shaped by the answers to six questions: Who, What, Where, When, Why, and 

How? It is critically important for decision-makers to understand how these key decisions relate to each 

other and how the architecture varies depending on the order in which these decisions are made, or how 

different facets are prioritized within a given aspect. The answer to any one of these questions is less 

important than whether the answers to all six complement one another as a set and meet the agency’s 

overall exploration objectives.

This white paper was developed as part of NASA’s 2022 strategic analysis cycle to address topics of frequent discussion. For 

the latest white papers or other architectural documents related to human missions to the Moon and Mars, please visit:

www.nasa.gov/MoonToMarsArchitecture. 

Figure 4. Architecture decision flow from “why?”

WHEN WILL WE ACHIEVE 

LUNAR OBJECTIVES? 

Multi-decadal campaign

Support annual cadence of crewed missions

Development of permanent infrastructure

Expansion of economic sphere to the Moon

WHO DOES THIS 

APPROACH INCLUDE? 

NASA

U.S. Government

Industry

International Partners

Academia

Public

WHY EXPLORE? 

WHAT FOUNDATIONAL 

CAPABILITIES ARE NEEDED? 

Long-duration microgravity systems

Partial gravity destination platforms

Low Earth Orbit assets and infrastructure

WHERE SHOULD SYSTEMS BE? 

Ensure access to the lunar South Pole

Capability for non-polar expeditions

HOW WILL WE GET THERE 

AND RETURN? 

Lunar Microgravity staging in NRHO

Earth NRHO Lunar surface

Surface mobility

—SCIENCE—

Understand the universe

Direct observations

—INSPIRATION—

“Artemis Generation”

Overcome challenges

Succeed with hard work

—NATIONAL POSTURE—

Enrich lives on Earth

Technology development

International partnerships