National Aeronautics and Space Administration

NASAfacts

Environmental Control and Life Support Systems

Sustaining Life Offworld – from the International Space Station 

to the Moon, Mars, and Beyond

Earth’s atmosphere and planetary resources provide 

life-sustaining air, water, and conditions that support 

life, but the same natural, self-perpetuating bounty 

isn’t available to explorers pursuing deep-space 

missions to distant moons or planets – and resupply shipments from Earth are neither practical nor 

cost-effective. 

NASA’s Marshall Space Flight Center in Huntsville, 

Alabama, with contributions by other NASA centers, is responsible for the design, construction, and 

testing of regenerative life support hardware for the 

International Space Station, including cutting-edge air 

and water reclamation and recycling systems which 

have made possible two decades of continuous crew 

operations on the orbiting science platform.

Now Marshall teams and their commercial partners 

are refining and enhancing these advanced Environmental Control and Life Support Systems (ECLSS) 

to serve new Artemis-era lunar missions and future 

exploration of Mars – the first extended human 

journeys of discovery into the deep solar system.

Providing Clean Water and Air to ISS Crews

The three largest ECLSS systems are the Water 

Recovery System, the Air Revitalization System, and 

the Oxygen Generation System. The first rack of air 

revitalization equipment was deployed in 2001 and 

has been active aboard the station ever since. The 

rest of the regenerative ECLSS racks were added 

in 2008, and the entire system has been kept in 

constant, synchronized use on station since then.

The systems were jointly designed and tested by 

Marshall and industry partners including Boeing, 

Lockheed Martin, Honeywell, Inc., and the former 

UTC Aerospace Systems, which became Collins 

Aerospace when UTC and Rockwell-Collins merged 

in 2018, and in 2020 merged with Raytheon to 

become a division of Raytheon Technologies Co. The 

hardware is packed into four refrigerator-sized racks 

in the station’s U.S. Tranquility module. A second Air 

Revitalization System is housed in the U.S. Destiny 

Laboratory. 

The Water Recovery System provides clean water by 

reclaiming cabin humidity condensate – including crew 

perspiration and respiration moisture – and wastewater 

including water reclaimed from crew members’ urine. 

Each astronaut needs about a gallon of water per 

day for consumption, food preparations and hygiene, 

including teethbrushing and shaving, but recovered 

water must meet stringent purity standards before 

it can be used to support crew, extravehicular and 

payload activities.

The Job of ECLSS

The space station’s ECLSS system performs several functions: 

• Provides oxygen for breathing 

• Provides potable water for consumption, food preparation 

and hygiene 

• Purifies recycled water from multiple sources back 

to potable water

• Removes carbon dioxide from the cabin air 

• Recovers and recycles oxygen from carbon dioxide 

to resupply the crew 

• Filters particulates and microorganisms from the cabin 

air and maintains cabin pressure, temperature, and 

humidity levels 

• Removes volatile organic trace gases, such as ethanol, 

that are colorless, odorless, and can build up over time 

• Distributes cabin air between each station module

Expedition 63 Commander Chris Cassidy installs the Urine 

Processing Assembly’s upgraded distillation assembly on 

the station in September 2020. (NASA)
ECLSS Stats

• The Oxygen Generator Assembly produced approximately 1,664 

pounds of oxygen annually between 2008-2021. One person needs 

about 1.83 pounds of oxygen per day.

• The ECLSS system recovered some 6,600 gallons of water – more 

than 55,000 pounds – from crew urine between 2008-2021. That’s 

enough to fill a 5-foot-by-15-foot pool.

• The Water Processing Assembly purified more than 13,414 gallons 

of water between 2008-2021 – or the equivalent of filling up 

319 standard bathtubs to the rim.

• Since activation of the Trace Contaminant Control subassembly in 

2001, it has processed the space station’s complete cabin volume 

some 2,978 times. That cabin volume is about 31,780 feet cubed 

– which means the system has scrubbed the equivalent air inside 

5,915 ordinary suburban homes over the past 20 years.

• The Carbon Dioxide Removal Assembly has processed 6,615 complete station cabin volumes between 2001-2021 – or the equivalent 

of 13,139 ordinary houses.

• Approximately 85% of the water in crew urine can be recovered 

and purified for reuse by the station crew. The technologies behind 

such leaps in water purification and wastewater recycling have been 

adapted on Earth to help provide water for communities in arid or 

remote locations or areas devastated by natural disasters.

Water reclaimed by the urine processor is combined with 

other wastewater and delivered to the water processor for 

treatment, where it goes through a series of multifiltration 

beds, catalytic oxidization, and ion exchange resins for 

purification. Water purity is stringently checked by electrical conductivity sensors in the systems; any water deemed 

unacceptable for use is reprocessed. Clean water is sent 

to a storage tank, ready for crew use. Currently, the Water 

Recovery System is capable of recovering and recycling 

more than 90% of the water on station, dramatically slashing 

resupply requirements from Earth. 

The Air Revitalization System is dedicated to cleaning the circulating air in the space station’s living quarters, laboratories, 

and connecting corridors. The process scrubs the air of carbon dioxide, exhaled by the crew during normal respiration, 

as well as trace contaminants produced by electronics, plastics and human off-gassing. Carbon dioxide is removed using 

molecular sieves, materials which selectively trap and separate gases based on their molecular size. Trace contaminants 

are removed by flowing cabin air through three separate units: 

an activated charcoal bed, a catalytic oxidizer and a lithium 

hydroxide bed. Additional carbon dioxide removal and trace 

contaminant control capability is provided by NASA’s Russian 

partners on the station.

The Oxygen Generation System, which produces breathable oxygen for the crew, consists of the Oxygen Generation 

Assembly (OGA) and the Carbon Dioxide Reduction Assembly 

(CDRA). The OGA is composed of cell stacks, which electrolyze – or break apart – water provided by the Water Recovery 

System, capturing oxygen and hydrogen as byproducts. The 

NASA astronaut Kjell Lindgren brews a cup of coffee using the station’s Capillary Beverage Cup. ECLSS technology on station helps 

recycle the fundamental necessities for living and working in space 

– including water to make coffee. (NASA)

European Space Agency astronaut Samanta Cristoforetti exercises 

on the space station’s Cycle Ergometer with Vibration Isolation and 

Stabilization (CEVIS). As astronauts sweat and generate carbon 

dioxide, the ECLSS system recycles both into usable water and 

breathable air. (NASA)

oxygen is delivered to the cabin atmosphere for reuse. The 

hydrogen is vented into space or fed to the CDRA, which 

combines it with carbon dioxide exhaled by the crew in a 

Sabatier reactor. 

Based on technology developed by Nobel prize-winning 

French chemist Paul Sabatier, the reactor converts the carbon dioxide and hydrogen into methane – which is vented into 

space – and water to be repurposed for crew use once it has 

been recycled. NASA’s Russian space station counterparts 

maintain a second oxygen generator as well, further reducing 

requirements for oxygen supplies to be ferried up from Earth. 

Together, these complex, innovative systems create a nearly 

closed loop for the reclamation and recycling of water, oxygen, 

and carbon dioxide.
Taking ECLSS Beyond Earth Orbit

Marshall engineers and their partners across NASA and 

industry are constantly developing ways to improve ECLSS 

systems, making the assemblies more reliable and easier to 

maintain, working to refine system reliability, and ensuring 

future deep space missions have the right complement of 

spare parts to keep those systems at peak function.

In 2020, for example, a newly upgraded distillation assembly for the urine processor was delivered by Marshall and 

flown to the station. A significant upgrade to the assembly 

addresses a persistent issue with drive belt stretching and 

slipping, particularly when exposed to condensed steam. 

ECLSS engineers partnered with Marshall’s Materials and 

Processes Laboratory to explore 3D printing options for a 

more durable belt drive pulley to accept a new toothed belt 

design. Several other component upgrades were addressed, 

effectively increasing hardware runtime from approximately 

1,400 hours to more than 4,300 hours without parts replacement. Similar refinements are continuously being developed 

for assemblies across the ECLSS system.

The space station also offers a proving ground to develop 

next-generation life support hardware, maximizing water 

and oxygen recycling in an effort to develop still more robust 

systems capable of further reducing resupply needs – and 

demonstrating technologies that will help future lunar and 

planetary explorers harvest breathable air and potable water 

in situ. These advances will enable humans to travel farther 

into space than ever before, and live and work successfully 

on worlds other than our own.

Such technologies are already undergoing testing on the 

station. A new Brine Processor Assembly, enabling the 

reclamation of even more recyclable water from crew urine 

using a sophisticated filtering bladder, was integrated into the 

ECLSS system in early 2021. Developed by Paragon Space 

Development Corp. of Tucson, Arizona, in cooperation with 

Marshall and NASA’s Johnson Space Center in Houston, the 

new technology could recover up to 98% of usable water. 

Marshall also delivered to the station a new air filtration technology – the 4-Bed Carbon Dioxide Scrubber – which uses 

state-of-the-art commercial adsorbent materials to more 

efficiently filter carbon dioxide out of the station’s air. The new 

scrubber unit, to be tested on orbit for up to four years, offers 

better component stability and lifespan and will introduce 

a first-of-its-kind, magnetic bearing air blower to push air 

through its adsorption beds.

National Aeronautics and Space Administration

George C. Marshall Space Flight Center

Huntsville, AL 35812

www.nasa.gov/marshall

www.nasa.gov

FS-2021-08-39-MSFC

G-583661