I. Introduction

Key elements of NASA’s Moon to Mars Objectives 

for expanding humanity’s presence beyond 

low-Earth orbit will require surface-based, 

partial-gravity extravehicular activities (EVAs). 

Surface EVA needs affect many aspects of the 

exploration architecture, including EVA suit 

subsystems, such as suit or pressure garment 

mobility, the portable life support system, and 

the informatics system; and external systems, 

such as habitation modules and surface mobility 

platforms. 

Lunar surface missions take place in harsh 

environments with additional challenges, 

including limited resources/consumables 

resupply, communications delays, navigation, 

and lighting, depending on landing location 

and terrain. Suited activity on the Moon 

introduces multiple factors that drive the 

broader architecture, including dust intrusion, 

partial gravity, atmospheric pressures, 

logistics, pressurized volumes, site planning, 

contingencies, and human access to and 

from the lunar surface from various habitable 

elements. This paper highlights several 

key considerations related to lunar surface 

exploration EVAs that will be addressed in the 

Moon to Mars Architecture.

2. Dust (Regolith) Mitigation

An integrated strategy for lunar dust mitigation 

should include testing on Earth using simulants 

and the use of lunar experiments to characterize 

dust properties and build an understanding 

of polar regolith behavior. Dust in the polar 

region will be impacted by the unique natural 

environment: electrostatic charging can cause 

dust to adhere to surfaces, dust particles take 

longer to settle than on the Earth, and stirring/

movement can remobilize dust particles. 

Ground testing faces environmental limits. 

Convective flows typically dominate non-vacuum 

ground testing, making it difficult to replicate 

expected polar region electrostatic behaviors. 

Ground testing also typically requires multiple 

simulants, since no one simulant captures all 

the properties of lunar soil or the variety of soil 

compositions that astronauts might encounter. 

National Aeronautics and

Space Administration

2023 Moon to Mars Architecture Concept Review 1white paper 2023 Moon to Mars Architecture

Surface EVA

Architectural Drivers

Figure 1. Conceptual Rendering 1
2023 Moon to Mars Architecture Concept Review 2

Most of the dust that poses a danger to system hardware 

and human health will also not be visible to the naked 

eye. 

A successful mitigation strategy will both minimize dust 

intrusion and control dust at the interface with critical 

systems (including human dust exposure).[1] While human 

lungs are the most sensitive organs to dust exposure, 

dust can also have ocular and skin effects. NASA used 

research findings to derive a permissible exposure limit 

that defines acceptable lunar dust exposures and size 

fractions of physiological concern. Lunar dust adherence 

and transport into the habitable environment by EVA 

suits, tools, equipment, and payloads is difficult to 

predict. The amounts vary depending on the method of 

ingress/egress and mitigation methods/tools available to 

the crew. 

Mechanical components of environmental control and 

life support systems, including vents, fans, intakes, and 

louvers, must be designed with dust intrusion in mind. 

Crew cabin systems and EVA systems adversely affected 

by dust include food preparation, medical implements, 

hygiene, filters, vacuum cleaners, seals, crew time, 

cameras, windows, lights, quick disconnects/connecters, 

switches, hatch seals, and more. 

During the Apollo Program, the Lunar Module had direct 

crew access, with no intermediate airlock volume. Apollo 

crews complained of dust intrusion into the Lunar Module 

in almost all Apollo missions, and in some cases, dust was 

observed within the Command Module after on-orbit 

docking. The Artemis missions will develop operations 

to reduce dust intrusion, develop mitigation methods to 

reduce dust adherence and clean up/filter intruded dust, 

learn from the implementation of this development, and 

evolve as the missions progress.

3. Partial Gravity

Performing EVAs with differently sized crewmembers 

in partial gravity influences the design of the suits and 

accompanying architectures (especially sizing, mobility, 

and mass), science and logistics payloads that must be 

operated by crewmembers, and tools for performing 

geological/maintenance activities.[2] Some tasks will 

require the crew to navigate up and down slopes, traverse 

into and out of craters, and deploy surface payloads. 

Tasks beyond collecting geological samples could include 

vehicle maintenance, cargo/logistics transfer, and other 

physically demanding activities. Tasks to be performed 

by the EVA crew — such as riding in a rover, hammering, 

or climbing — drive specific interfaces and suit mobility 

features. 

The suit architecture and interfaces with surface elements 

must accommodate a wide range of crewmember 

sizes. These requirements drive the design of the suit 

and attached hardware, vehicle interfaces, the types of 

crew actions and motions during EVAs, direct physical 

interactions with the lunar surface, and the total number 

of EVAs. Finally, systems will have to accommodate 

different prebreathe protocols than Apollo or microgravity 

prebreathe.[3]

4. Atmospheric Pressures

A fundamental limitation of human physiology when 

preparing for and conducting EVAs is the potential for 

acute and chronic injury from decompression sickness 

caused by pressure transitions. It is necessary to control 

the transition from the habitable volume’s saturation 

atmosphere to the EVA suit’s pressure, which is set lower 

to improve the crewmember’s ability to operate and 

maneuver in the suit. This transition is managed in part 

by an oxygen prebreathe using a combination of the 

vehicle’s atmosphere and the suit’s pressure. 

The amount of time necessary for this prebreathe is 

directly proportional to the difference between vehicle 

saturation and EVA pressures. While physiologically 

necessary, crew time spent engaged in prebreathe affects 

EVA operations and the risk of decompression sickness 

and can affect the duration of the EVA itself. Prebreathe 

studies help minimize prebreathe durations, allowing 

for increased utilization and completion of objectives 

performed by the crew during EVAs. 

This choice of alternative atmospheric parameters 

in the vehicle (as opposed to relying on the suit and 

implementations thereof) may pose significant issues, 

including vehicle design challenges, such as reduced 

effectiveness for atmosphere-based avionics cooling, 

increased flammability, and more.[4] The suit and 

supporting architectures will also have the capability to 

perform decompression sickness treatment functions 

during the EVA if they are required for crew safety.

5. Commodities and Logistics

Elements that provide EVA capability include the 

architecture to recharge suit consumables (e.g., power, 

oxygen, water, CO2 removal) and the ability to reserve suit 

consumables while connected to the vehicle via umbilical 

during activities such as prebreathe, suit checkouts, and 

pre- and post-EVA. The interfaces between the suits and 

the vehicles/elements must use common hardware to 

ensure compatibility and reduce astronaut training time 

and vehicle reconfiguration time.

Given the constraints for landed surface mass, different 

exploration architecture solutions will have varied impacts 

on commodity usage (such as the amount of air required 

to repressurize the habitable volume, depending on the 

ingress/egress method), in addition to the quantities 

used in the EVAs themselves. Suit maintenance must take 

place in a habitable pressurized environment. 

Transferring logistics and consumables from logistics 

landers to habitable elements also presents a major 

challenge. The presence or absence of existing lunar
2023 Moon to Mars Architecture Concept Review 3

surface infrastructure, such as hardware for logistics

transfer, is also an architecture driver since the EVA 

system may have to make up for any shortcomings in 

existing assets. The goal is to minimize logistics transfer 

in EVA timelines and maintain utilization objectives during 

EVAs.

6. Habitation and Pressurized Volumes

For both mobile and permanently emplaced surface 

habitation, layout and volume are important factors in 

the acceptability of the cabin interior. Crewmembers 

will require adequate internal size, in terms of both 

volume and surface area, to perform mission tasks safely 

and efficiently. This includes sufficient space to allow 

crewmembers to don/doff the suits in parallel, perform 

maintenance, volume for spares/logistics, and gather 

items needed to perform the EVA objectives. 

For example, rear-entry suits require volume above the 

helmet to allow crewmembers to climb into their suits. 

Once suited, acceptable volume will be needed for EVA 

airlock hatches to swing open and closed, creating keepout zones. Both mobile and permanently emplaced 

elements must also be designed for EVA compatibility. 

This includes access to any worksites, hatch sizes, sharp 

edges, thermal touch temperatures, and other factors. 

7. Variations in Architectural 

Solutions for Ingress/Egress

An airlock could provide a separate volume from the 

main cabin to facilitate surface access. As such, airlocks 

provide a significant opportunity to control or propagate 

backward and forward contamination.[4,5] While other 

ingress/egress architecture solutions could help with dust 

intrustion, consumables, and other drivers listed in this 

paper, they also pose significant challenges to vehicles 

and suit architectures such as mass and volume.[6]

8. Enabling Suited Crew Decision-Making

Distributing work functions among Earth-based assets 

and mission assets, enabling an Earth-independent 

architecture, will be a profound architectural driver. 

Earth independence starts by giving crew members, 

particularly during EVA, the capacity to make informed 

decisions by interacting with and acting upon locally 

sourced information. Achieving this feat will not only 

be a technological accomplishment that advances suit 

capabilities but would also establish a fundamentally new 

medium of communication and information exchange 

between mission assets and Earth-based support.[7,8,9] 

Earth-independent crew decision-making currently 

faces multiple challenges, such as establishing a highly 

integrated network of data-sharing among mission 

assets (from different vendors); rendering a variety of 

data in meaningful and contextually useful ways for 

crew consumption, interaction, and understanding; and 

aligning the broader flight operations structure (across 

NASA and service vendors) with the appropriate function 

allocation.[10,11]

Figure 2. Conceptual Rendering 2
2023 Moon to Mars Architecture Concept Review 4

9. Communications, Navigation, and Lighting

Communications between EVA crewmembers may be 

limited by distance and/or line of sight to each other 

and other surface assets during certain periods of initial 

surface missions because of architecture constraints 

and the potential for contingencies/walk-back scenarios. 

Surface mobility assets and other surface elements 

with Earth communications capabilities will allow the 

crew to explore further from the landing site, increasing 

utilization destination options. 

Early missions will mainly utilize orienteering for 

navigation. Guidance and navigation systems, displayed 

via informatics and mobility assets, will help crew 

members get to destinations and back, guiding them to 

targets specifically designated by the science team. 

The crew will experience persistent long shadows near 

the lunar South Pole, while also having the Sun directly 

in their field of view. To traverse safely and effectively 

across lunar terrain and slopes and into shadowed 

regions, the crew will use lighting sources (e.g., helmet 

lights and lights strapped/mounted to a crewmember or 

placed near the worksite), which can drive power needs. 

Thermal control performance in dark shadows will also 

affect EVA duration. 

10. Site Planning

While missions to the lunar South Pole are being planned, 

design reference missions also include the capability to 

perform missions globally. Performing multiple missions 

to the South Pole and different regions of interest within 

range of each other will require strategic site planning. 

Several factors, such as ability to navigate difficult terrain 

while in a spacesuit, interactions required between 

surface elements, and safety will affect the integrated 

arrangement and configuration of surface elements to 

accomplish mission objectives. Mission designs will also 

need to address environmental factors (e.g., terrain, 

illumination, distance, plume) in concert with surface 

asset capabilities (e.g., rovers, habitats, landers, driving 

range, charging) and EVA capabilities (e.g., walk-back 

distance, vision), all while protecting the EVA crew. 

Lunar surface selection of the site location of the surface 

elements must, of course, accommodate EVAs to 

perform science and utilization, maintenance, logistics, 

observations, and traversing during short-term missions, 

long-term stays, and sustained operations. This requires 

monitoring surface operations effects and management 

of habitation. 

EVA ranges must be considered when planning distances 

between stationary elements to provide the crew 

access to a pressurized safe haven within the limits of 

emergency consumables in the event of a suit failure 

or medical event. Along with other considerations (i.e., 

landing accuracy, plume/surface interaction), distances 

the mobility elements can be driven or teleoperated 

before requiring charging affects the mission’s mass 

requirements and must be balanced with operational 

needs such as EVA preparation, EVA duration, crew time, 

and crew sleep. 

11. Contingencies and Operations

Ensuring crew safety is the most important aspect of 

planning human space missions. Risks such as system 

complexity, suit exposure, dust intrusion, EVA overhead 

times, vehicle failures, distance from a safe haven, and 

more can factor into the possible loss of crew or mission 

and must be considered in capability assessments. A 

vehicle/suit failure could result in scenarios where crew 

must walk back to a safe haven.

Hardware and human failures can lead to contingencies 

or incapacitation on the lunar surface, ultimately 

requiring assistance during EVA. Incapacitation requiring 

continuous full assistance is a risk that may need 

additional loading, transport, and lift capabilities, all of 

which affect suit design. 

12. Conclusions

Surface EVA exploration has a significant number of 

architectural drivers that differ from microgravity. These 

differences include dust, the challenge of operating 

in partial gravity, mobility and habitation architecture, 

site planning, and contingency scenarios. Architectural 

challenges for surface EVAs result from limitations to 

mass, power, volume, the environment, and physical 

operations that occur on the Moon and, to even greater 

extent, on Mars.
2023 Moon to Mars Architecture Concept Review 5

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Figure 3. Conceptual Rendering 3