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Grades 9–12 · Systems

How can a space station keep reusing air and water?

Space-station life support combines several processing routes rather than treating air and water as endlessly reusable supplies. Cabin air is circulated through equipment that removes exhaled carbon dioxide and other unwanted substances. Ventilation matters because a clean gas supply is useful only if it reaches the places where people live and work.

S63 visual explanationStation life support removes carbon dioxide and trace contaminants from circulating air. Wastewater and cabin moisture are processed and checked before water is stored for reuse. Electrolysis of some water supplies oxygen. In a supplied 100 L water batch with 98 percent recovery, 98 L is recovered and 2 L remains outside the recovered stream. The example is not a station-wide material balance. Operation still needs power, food and replacement supplies; the loop is not perfectly closed.Station life support recirculates air and recovers waterAIR: remove CO₂ and other unwanted substancesCabin airClean the airRemove CO₂ReturnWATER: collect, purify, check and storeWastewaterPurify +checkStoreSplitting some water supplies breathing oxygen.Reuse reduces supplies without closing every loop.Recovery needs power and replacement supplies.

In the diagramStation life support recirculates air and recovers waterAIR: remove CO₂ and other unwanted substancesCabin airClean the airRemove CO₂ReturnWATER: collect, purify, check and storeWastewaterPurify +checkStoreSplitting some water supplies breathing oxygen.Reuse reduces supplies without closing every loop.Recovery needs power and replacement supplies.

Air recirculation and water recovery are distinct routes; splitting some treated water also supplies oxygen.

The water route collects wastewater and moisture condensed from cabin air, including water from breath and sweat. Processing separates and removes contaminants through several stages. Sensors check the treated water; water that does not pass the checks can be processed again. Accepted water enters storage for later use.

Air and water processing also connect chemically. Electrolysis splits some water into oxygen and hydrogen. Oxygen is supplied to the cabin. In another process, hydrogen can react with captured carbon dioxide to produce water and methane; the methane is released. These transfers recover useful materials, but they do not reconstruct every input without loss.

Water left in concentrated waste is one reason recovery is incomplete. Additional brine processing can reclaim more of it, reducing how much water must be supplied from elsewhere. Even a high recovery percentage describes one material stream rather than the entire habitat. The station still needs power, food, replacement equipment and replenishment of consumables. Recovery reduces the supply burden without making the whole habitat a perfectly closed loop.

About this explanation

Starting knowledge: Understand conservation of matter, gas mixtures, filtration, chemical change and percentages.

Sources

  • NASA — Environmental Control and Life Support Systems
  • NASA — NASA Achieves Water Recovery Milestone on International Space Station
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