National Aeronautics and

Space Administration

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

Background

The International Space Station is the world’s 

preeminent orbital microgravity platform. 

For more than 20 years, scientists have used 

the space station to conduct research into 

biological, physical, biomedicine, materials, 

and Earth and space science. Technology 

demonstrations aboard the space station 

have advanced state-of-the-art applications 

with benefits both on Earth and in space. The 

space station’s redundant systems enable the 

crew to test multiple environmental systems 

simultaneously, creating a unique testbed for 

life support and environmental technology 

that will enable future exploration. Sensors 

deployed on the space station have validated 

climate models and contributed to host of new 

information about Earth’s changing climate, 

while space science instruments on the orbiting 

laboratory have advanced our knowledge of 

phenomena like neutron stars and dark matter. 

International Space Station crews have also 

been part of a critical experiment, volunteering 

themselves as test subjects for research into 

human adaptation to microgravity. These longduration demonstrations and experiments 

into the joint human-and-vehicle system are 

enabling future human exploration of the solar 

system. The station will operate through 2030, 

continuing to offer benefits to humanity while 

paving the way for commercial industry to meet 

NASA’s needs in low-Earth orbit and beyond.

The International Space Station has five major 

goals and has realized significant advances in 

each: 

• Enable deep space exploration.

• Conduct research to benefit humanity.

• Foster a U.S. commercial space industry.

• Lead and enable international collaboration.

• Inspire humankind.

Exploration Lessons from the 

International Space Station 

Figure 1. This mosaic depicts the International Space Station pictured from the SpaceX Crew 

Dragon Endeavour during a fly around of the orbiting lab that took place following its undocking 

from the Harmony module’s space-facing port on Nov. 8, 2021.
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The station’s first decade was dedicated to on-orbit 

assembly. Its second was devoted to research and 

technology development and learning how to conduct 

these activities most effectively in space. The station is 

now in its third and most productive decade, continuing to 

advance research, create commercial value, and bolster 

global partnerships. During this period, NASA will test and 

validate exploration and human research technologies 

to support deep space exploration, continue to return 

medical and environmental benefits to humanity, and 

lay the groundwork for a commercial future in low-Earth 

orbit.

The space station offers a unique platform for 

demonstrating new technology in space, including the 

technologies needed for the Artemis missions to the 

Moon and future missions to Mars. Exploration-focused 

research and development on the station includes 

environmental control and life support systems (ECLSS), 

navigation, food storage systems, extravehicular activity 

(EVA) suits, and human research, among others. This 

white paper details how technology developed on the 

station and lessons learned from station operations 

enable future exploration missions.

Fly-Off Plans

The International Space Station program tracks the key 

technologies and human health mitigations needed for 

deep space exploration through a series of “fly-off” plans. 

These plans ensure that NASA completes all research that 

must be done in the low-Earth orbit environment before 

the end of the station’s operational life, planned for 2030. 

The plans also account for technology demonstrations 

that may be started on the space station but concluded 

on commercial low-Earth orbit destinations after the 

station’s retirement.

Environmental Control and

Life Support Systems

Since 2009, the regenerative ECLSS aboard the 

International Space Station has been tested and 

upgraded into the Exploration ECLSS, intended to 

support long-duration missions beyond low-Earth orbit. 

The system-level redundancy of the U.S. and Russian 

segments, which can maintain critical functions in the 

event of failures, make the station an ideal testbed for 

this upgraded system. 

The initial ECLSS was an open-loop, non-regenerative 

system. The Exploration ECLSS is a regenerative air 

and water system. Ongoing upgrades will continue to 

improve reclamation of water and air and overall system 

reliability. 

The Water Recovery System provides clean water 

for astronaut use by recycling urine; cabin humidity 

condensate from crew sweat, respiration, and hygiene; 

and water recovered from the Air Revitalization System. 

The Urine Processor Assembly, part of the Water Recovery 

System, was designed for 85 percent water recovery 

from crew urine. Over the last year, that performance 

has improved to 87 percent thanks to analysis that 

showed there was still a margin against calcium sulfate 

precipitation. 

The combined water recycling system on the International 

Space Station has now reached a theoretical 98 percent, 

Mars-class efficiency thanks to another new device being 

tested on board — the Brine Processor Assembly, which 

demonstrates the ability to recover additional water from 

crew urine and reduce water waste. Special membranes 

in the system retain contaminates and pass water vapor 

into the cabin’s atmosphere, where it is captured and 

delivered to a water processing system. 

The Air Revitalization System has also evolved, with 

additional upgrades planned to launch in the near term. 

A new generation Carbon Dioxide Removal Assembly, 

known as the 4-bed CO2 scrubber, has demonstrated 

improved performance and reliability over its 

predecessor. This improved performance has enabled 

lower carbon dioxide levels, improving crew health, and 

has reduced crew time for maintenance. 

The original Oxygen Generation Assembly is also 

being upgraded into the Advanced Oxygen Generation 

Assembly, which will fly to the space station in FY25. This 

new system will feature a more robust cell stack design 

that reduces mass and maintenance of replacement 

parts, which NASA estimates will save hundreds of 

pounds in spares for future long-duration missions. 

A redesigned Sabatier carbon dioxide reduction system, 

which produces methane from CO2 and hydrogen, will 

also fly to the station in FY25. This will be a redesigned 

reflight of a previous Sabatier system that failed because 

of catalyst bed contamination and degradation. 

When integrated together, the Exploration ECLSS air 

systems will recover approximately 50 percent of the 

oxygen from carbon dioxide. In addition, NASA has 

been working on advanced carbon dioxide reduction 

technologies that will potentially recover more than 75 

Figure 2. 

Environmental 

Control and Life 

Support Subsystem 

Diagram
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percent of oxygen from carbon dioxide. Those technology 

demonstrations are planned for late in the decade, either 

on the space station or follow-on commercial low-Earth 

orbit destinations. 

Equally important — if not more important than ECLSS 

loop closure — is ECLSS system reliability. One of the 

major lessons learned from ECLSS on the space station 

is that no matter how much systems are ground tested, 

new issues are discovered when they are integrated in 

the space environment. Even after operating regenerative 

ECLSS for over 14 years, NASA is still learning. 

While the proximity of low-Earth orbit enables relatively 

easy launch of replacement components, long-duration 

missions beyond low-Earth orbit must have either a highly 

reliable ECLSS or the ability to launch with thousands of 

pounds of spare parts. The ECLSS evolution and testing 

that has occurred and is still planned on the space station 

has already improved system reliability, measured in 

spares mass required for a Mars mission, by more than 

35 percent. Additional testing on the orbiting laboratory, 

coupled with ground testing, will continue to improve our 

understanding of these systems and their reliability. 

Navigation

The Orion spacecraft uses an optical navigation system 

called OpNav to voyage to and from the Moon. OpNav 

uses images of the Moon and Earth, looking at their sizes 

and positions to determine Orion’s angle and distance 

from these bodies, to keep Orion on course. The system 

also can help Orion autonomously return home if the 

spacecraft loses communication with Earth. 

The International Space Station is demonstrating the 

effectiveness of this approach by testing OpNav. The 

station investigation uses two cameras mounted on a 

plate and offset by about 20 degrees. The plate is installed 

in the station’s cupola, a seven-windowed observation 

module, with the cameras pointing out one of the 

windows. One camera captures images of stars and the 

other takes photos of specified views of the Moon. OpNav 

software then analyzes these images and determine the 

station’s position in space. Since the station’s position is 

always known, and the time at which a particular photo 

was taken is also known, NASA engineers can compare 

the OpNav algorithm results with the actual location to 

judge the system’s accuracy.

The Sextant Navigation for Exploration Missions focuses 

on stability and star sighting opportunities in microgravity. 

Astronauts have demonstrated that the handheld sextant 

intended for use on future Orion exploration missions can 

successfully be used as a backup navigation capability in 

a microgravity environment. 

Another, more modern sextant technology on the 

space station is also contributing to future navigation 

capabilities. The external Neutron-star Interior 

Composition Explorer (NICER) external payload studies 

the composition of neutron stars and pulsars deep in 

the universe, adding to humanity’s understanding of 

astrophysics. The Station Explorer for X-ray Timing and 

Navigation Technology (SEXTANT), a NICER experiment, 

detected pulsars’ repeated, consistent flashes of 

radiation to demonstrate X-ray navigation for the first 

time in space. X-ray navigation uses the specific timing of 

pulsars to determine position, just as a GPS reciever on 

Earth uses the timing supplied by GPS satellites. When 

developed to an operational capability, X-ray navigation 

could allow precision navigation anywhere in the solar 

system.

Food Storage Systems

The eXposed Root On-Orbit Test System (XROOTS) 

experiment uses aeroponic and hydroponic systems to 

grow fresh food without space-consuming growth media. 

XROOTS grows plants in the microgravity environment 

and evaluates nutrient delivery and recovery techniques 

over the course of a full plant growth cycle, from 

germination to maturity. The system uses multiple 

independent growth chambers in parallel to evaluate 

alternative methods and configurations; the results could 

lead to large-scale food production systems. This would 

offer reductions in the weight requirements for such 

systems and fresh food produced in situ, allowing more 

room for other valuable cargo. 

Figure 3. Astronaut Frank Rubio checks tomato plants 

growing inside the International Space Station for the 

XROOTS space botany study.
Extravehicular Activities

Extravehicular activities, or spacewalks, have been critical 

to the assembly and maintenance of the International 

Space Station. Similarly, spacewalks will be essential to 

establishing and expanding our presence in cislunar 

space and on the lunar surface. To date, NASA astronauts 

aboard the station have performed more than 85 

spacewalks, contributing to our understanding of working 

outside in the vacuum of space. 

As we look forward to cislunar and lunar exploration, the 

station is also playing an important role in demonstrating 

technologies that will enable astronauts to work outside 

the Gateway lunar space station and on the lunar surface. 

These efforts include testing active thermal control 

components and demonstrating the functionality of nextgeneration spacesuits, as well as determining whether 

crew members can complete certain suit maintenance 

tasks in microgravity that would otherwise require 

returning parts of the suit to the ground for evaluation 

and testing.

Human Research

Crew health and performance are critical to successful 

human exploration beyond low-Earth orbit. NASA’s 

Human Research Program investigates and mitigates 

the biggest risks to human health and performance, 

providing essential countermeasures and technologies 

for human space exploration using the International 

Space Station’s unique capabilities. Those risks include 

physiological effects from radiation, microgravity, and 

planetary environments, as well as unique challenges in 

medical treatment, human factors, and behavioral health 

support. The Human Research Program is responsible 

for understanding and mitigating these risks to astronaut 

health and performance to ensure crew members remain 

healthy and productive during long-term missions 

beyond low-Earth orbit.

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Key Take-Aways

For more than 20 years, scientists have used the International Space Station to conduct 

research into biological, physical, biomedicine, materials, and Earth and space science. 

The International Space Station offers a unique platform for demonstrating new technology 

in space, including the technologies needed for the Artemis missions to the Moon and future 

missions to Mars.

Crew members aboard the International Space Stations have been a critical part of the 

experiments, volunteering as test subjects for research into human adaptation to microgravity.

Exploration-focused research and development on the space station includes navigation, 

environmental control and life support systems, food storage systems, extravehicular activities, 

spacesuits, and human research.