How Life Support Systems Work on the International Space Station

A life support system in space flight is the onboard technology that keeps astronauts alive by addressing their survival needs including food, water, and air.

The typical astronaut crewmember of usual body size requires a combined 11 pounds of food, water, and air per day; an almost identical weight is expelled from the body in the form of carbon dioxide, and liquid and solid waste. Any and all life support systems must address these needs, supplying the necessary intake and disposing of the consequential outputs.

At its most basic level, life support systems must address seven core human needs. The necessary components of a life support system address:

1. 1. Potable water supply trough water reclamation
2. 2. Food supply
3. 3. Breathable cabin air supply (oxygen generation system)
4. 4. Air pressure control (maintained at 101.kPa)
5. 5. Air temperature regulation through a heat exchanger
6. 6. Human waste management and waste disposal
7. 7. Fire detection and suppression

Beyond these core needs, additional life support systems might also address shielding the human body from external factors such as radiation and micrometeorites. This is particularly important in the space suits astronauts wear when performing extravehicular activities such as spacewalks. Learn more about spacewalks here.

To address the above needs, the current NASA ECLSS system standards include the following components of a life support system:

• Crew compartment cabin pressurization
• Cabin air revitalization
• Water coolant loop system
• Active thermal control system
• Supply and wastewater
• Water collection system
• Wastewater tank
• Airlock support
• Extravehicular mobility units
• Crew altitude protection system
• Radioisotope thermoelectric generator cooling and gaseous nitrogen purge for payloads

Life support systems ideally will recycle supplies shuttled up from Earth. Water, for example, is recycled with a water processor utilizing wastewater and water vapor:

• It is reclaimed from a urine processor and humidity control unit
• Water is cleaned, and given right back to astronauts for drinking
• This loop system still requires an additional amount of water input but are increasingly efficient based on chemical reactions but will have to be 100% efficient for future space travel including missions to Mars
• The systems that carry out this reclamation are a critical component of the onboard life support system

Recycling and reclaiming, however, is not always possible.

• Food, for example, cannot (yet) be produced efficiently in space
• Food must always be shuttled up to the space station to feed astronauts
• The systems that address the human solid waste that comes from metabolizing food is also a part of the life support system

Space is a hostile environment in which humans were not meant to survive; life support systems have thus been necessary from the very beginning of human space exploration.

Yet though human needs have not evolved, the systems utilized to address them have become increasingly advanced and integrated as long-duration spaceflight missions became. For example, early space crafts utilized a 100% oxygen environment; later space shuttle missions have come to mimic the earth’s atmosphere, with 22% oxygen and 78% nitrogen.

The ISS utilizes a life support system called the Environmental Control and Life Support System (ISS ECLSS).

Learn more about the ISS here.

Astronauts living aboard the ISS use a combination of supplies brought up from Earth, including oxygen and water, and onboard technology that regenerates them. To explore further into space, we’ll need to develop reliable equipment that will allow us to eventually wean ourselves from Earth resupply entirely.

Much of what the life support equipment does on the ISS mimics what happens naturally on Earth:

• Processors purify the astronauts’ air, filtering trace gases and removing their exhaled carbon dioxide. Where possible, the oxygen is extracted and released back into the cabin, but the small losses are supplemented with stored oxygen.
• Water is similarly recycled from urine and dehumidifiers, typically with about 90% efficiency. That’s better than ever, but every cargo ship still carries air and water to the ISS—we need to get to virtually 100% recycling before we can venture with confidence to Mars.
• Food is even more difficult to recycle, as farming is a multi-stage process, growing seasons take time, and a balanced diet is essential. For simplicity and reliability, the ISS receives virtually all of the astronauts’ food via regular deliveries from Earth. To ensure long shelf life and to minimize the chance of food poisoning, meals are dehydrated, irradiated, thermo-stabilized and/or canned. Preparation is kept simple, with a water dispenser and warming ovens. Only rarely, as a kindness from the support team, can a few items of fresh fruit or vegetables be sent to the crew, added as late stowage on a resupply ship.

For missions further into space, bringing prepared food will become less practical. There are currently experiments on the ISS to explore how to grow crops, testing things such as what direction a plant grows without gravity, how to pollinate, and what types of hydroponic soil are best.

Future space exploration, like a Mars mission or to asteroids, will require even more efficient life support systems.

Whether you’re a budding astronautical engineer or simply want to become more informed about the science of space travel, learning about the rich and detailed history of human space flight is essential to understanding how space exploration has advanced. In Chris Hadfield’s MasterClass on space exploration, the former commander of the International Space Station provides invaluable insight into what it takes to explore space and what the future holds for humans in the final frontier. Chris also talks about the science of space travel, life as an astronaut, and how flying in space will forever change the way you think about living on Earth.

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