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Life Support in Space - Closed Systems

Above Image: NASA Environmental Control and Life Support System © James E. Scarborough, Wikimedia Commons

Life Support in Space: Working Toward a Closed System

People need air, water and food to survive. On Earth, different parts of ecosystems provide these basic needs. For example, because plants add essential oxygen to the atmosphere and remove toxic carbon dioxide, they help keep our air breathable. Drinking water comes from lakes, rivers and groundwater. Soil feeds the crop plants that are harvested to feed people.

With respect to the matter that makes up air, water and food, the Earth is a closed system. Matter is not added to the Earth from space, or lost to space from the Earth. All the matter is recycled within the global ecosystem.

American flag

On the ISS, the American ECLSS manages the atmosphere (air quality, humidity, temperature and pressure), water (waste water treatment and drinking water production), emergency services (such as detecting and controlling fires and toxic spills), and waste (collection and storage).

The International Space Station (ISS) orbits Earth 400 kilometres above the planet’s surface. Astronauts on the ISS need air, water and food, but there are no ecosystems in space to provide these basic needs. The ISS life support systems generate and recycle some, but not all, oxygen and water. All food is sent from Earth. Because the ISS is dependent on Earth for its full life support needs, it is an open system.

NASA’s Environmental Control and Life Support System (ECLSS) is a system of interconnected and interdependent machines that provide breathable air and pure drinking water for astronauts on the ISS . Machines built by the Russian Federal Space Agency (Roscosmos) also provide some ISS life support.

Air on the ISS

Breathable air contains oxygen and very little carbon dioxide. The Oxygen Generating Assembly (OGA) of ECLSS makes oxygen by separating liquid water into hydrogen and oxygen gas, using electricity from the ISS solar panels. ECLSS removes toxic carbon dioxide from inside the ISS using filters.

Russian Flag

The Russian Elektron system makes oxygen by water electrolysis, just like the ECLSS. Vozdukh is the Russian system that removes carbon dioxide from the ISS air.

Waste carbon dioxide, along with waste hydrogen from the OGA, used to be vented into space. In 2010, the addition of the Carbon Dioxide Reduction System, also called the Sabatier System, was a big step towards a closed oxygen recycling system. The Sabatier System uses the waste carbon dioxide and hydrogen gases to make water, which is eventually returned to the OGA to make oxygen again. (Methane gas is a second product of the Sabatier reaction; it is vented into space.)

The Sabatier System is not perfectly efficient; about half of the oxygen can be recovered from the waste carbon dioxide. NASA is working to improve this efficiency. In the meantime, tanks of oxygen are sent from Earth on resupply vehicles, and the ISS is stocked with special emergency back-up candles that release oxygen when they are burned.

Water on the ISS

Russian Flag

The Russian Condensate Water Processor (SRV-K) reclaims water vapour from the ISS air (humidity from sweating), but does not recycle urine like ECLSS.

ECLSS reclaims around 90% of the water used by astronauts and purifies it into clean drinking water. The Water Processor Assembly (WPA) collects water from the Sabatier System, used water from washing, condensed water vapour from the air (humidity from sweating), and even urine. The WPA produces pure water for drinking, meal preparation, hand washing, showering, and oxygen production in the OGA.

Some containers of water are still sent from Earth on resupply vehicles, but water recycling by the ECLSS is approaching a closed system. NASA’s goal is to improve the ECLSS so that the air and water systems are completely integrated and function as a closed loop, recycling or regenerating all the air and water that astronauts need.

Food on the ISS

Everything that astronauts eat on the ISS is sent from Earth, so this is a completely open system. Currently, most space food is ready-to-eat or pre-cooked. Resupply vehicles bring a limited amount of fresh fruit and vegetables, which are a delicious dietary treat for the astronauts.

NASA is learning how to grow fresh produce in space using its Vegetable Production System, dubbed Veggie. ISS astronauts tasted space-grown lettuce for the first time in August 2015. More recent Veggie experiments involved growing zinnias – not edible, but a good test for other plants, such as tomatoes, that must flower for fruit production.

Space Food: Feeding Astronauts on the ISS and Beyond

Being able to grow some fresh fruits and vegetables in space will be important for future long-term missions, like a voyage to Mars. In theory, plants can also help maintain air quality on spacecraft through photosynthesis (plants take in carbon dioxide and produce oxygen). Currently, this is not a significant contribution because only a few plants can be grown at a time.

Waste on the ISS

Solid waste on the ISS includes packaging, containers, trash (such as plastic bags, hygiene wipes, used clothing), and fecal waste. All waste is gathered and stored until is it put into an empty resupply vehicle after cargo delivery. When the waste-filled spacecraft enters Earth’s atmosphere, everything – including the vehicle – burns up. Waste management is an open system because all waste is sent back toward Earth.

NASA is trying to reduce the amount of waste by using less packaging and developing ways to repurpose packaging material in space. For example, some packaging could be reused as-is or melted into tiles for building shelters. This will be most important for future long-term missions, like going to Mars.

Fully Closed Life Support – MELiSSA is Working on it

Canadian flag

The University of Guelph in Ontario is one of the international partners for MELiSSA, with expertise in growing plants in closed environments.

The European Space Agency (ESA) is coordinating an international research project called the Micro-Ecological Life Support System Alternative, or MELiSSA. The goal is a completely closed life support system that could be used for future space travel. MELiSSA is an artificial ecosystem, modeled on an aquatic ecosystem. A functioning MELiSSA would use plants and algae to recover food, water and oxygen from human waste and carbon dioxide, using light energy for photosynthesis. This complete integration of air, water, food and waste is still in the experimental phase.

Long-term space missions will probably happen before a fully closed life support system, like MELiSSA, is ready to go. For the trip to Mars, the “Reduce, Reuse, Recycle” philosophy will be important for designing a life support system that is as closed as possible.

Glossary

Closed system

For the purpose of this backgrounder, a closed system is a system that does not exchange matter with its surrounding – matter is recycled within the system. A broader definition includes the exchange of energy (see Open system).

Ecosystem

An interacting community of living organisms and their non-living environment. An ecosystem can be small, such as a pond (including fish, bacteria, algae, plants, water, sediment) or large, such as the Earth (including plants, animals, microbes, water, soil, air).

Open system

For the purpose of this backgrounder, an open system is a system that exchanges matter with its surroundings - matter can leave and enter the system. A broader definition includes the exchange of energy. The Earth is a closed system with respect to matter, but an open system with respect to energy (light energy enters from the sun to replace the heat energy lost during biochemical reactions in plants and animals).

Photosynthesis

The process used by plants to change light energy into biochemical energy (sugar). Light energy is used to turn carbon dioxide and water into oxygen and sugar.

System

A group of parts that are interconnected and interdependent and work together as a complex whole. Examples include the human body, an aquatic ecosystem, the Earth, the International Space Station (including astronauts).

References

ECLSS Infographic

Source (person graphic): Pixabay

References: Infographic adapted from Reference Guide to the International Space Station, Utilization Edition, NASA, 2015; ISS Environmental Control and Life Support System (ECLSS) Future Development for Exploration, NASA, 2013