Space Station Life Support Loop (ECLSS)

Crew & Hardware

Crew size 4 people

Electrolyzer power (O₂ generation) 60%

CO₂ scrubber capacity 55%

Sabatier water-recovery efficiency 70%

Nominal — loop balanced

Cabin Atmosphere

Cabin O₂

21.0%

Cabin CO₂

400 ppm

Water reserve

150 L

Loop closure

Mission elapsed

0.0 h

O₂ output

0.00 kg/h

How it works

A real Environmental Control and Life Support System (ECLSS, as flown on the ISS) closes three linked loops around the crew's metabolism:

Electrolysis (OGA):  2 H₂O → 2 H₂ + O₂
Sabatier reaction:   CO₂ + 4 H₂ → CH₄ + 2 H₂O
Crew metabolism:     O₂ (in) → CO₂ (out), ≈1:1 by mole (RQ ≈ 0.83)

Each simulated hour: the crew draws O₂ from the cabin and exhales CO₂. The CO₂ scrubber (CDRA) pulls CO₂ out of the cabin air and feeds it to the Sabatier reactor together with the hydrogen by-product from the electrolyzer. The reactor recovers a fraction of that CO₂ + H₂ back into liquid water (set by the "efficiency" slider) — the rest is lost as vented methane. Recovered water refills the tank the electrolyzer draws from to keep making O₂, which is what makes the loop "closed": run it well and water use asymptotes toward a small make-up trickle instead of draining the tank.

dO₂/dt   = OGA_rate·(H2O available) − crew·O2_consumption
dCO₂/dt  = crew·CO2_production − scrubber_rate
dH2O/dt  = Sabatier_recovery − OGA_water_use
Sabatier_recovery = η · (36/44)·min(CO₂_in, H₂_in·44/(4·2))

Crew size — more people, proportionally more O₂ consumed and CO₂ produced.
Electrolyzer power — sets the target O₂ production rate; throttles itself automatically if the water tank runs dry.
CO₂ scrubber capacity — how much CO₂ per hour the CDRA can pull from the cabin air.
Sabatier efficiency — the fraction of scrubbed CO₂ and by-product H₂ that gets converted back into water instead of vented as methane; this is the number that determines whether the loop is genuinely closed or slowly consumes the water reserve.

Cabin O₂ and CO₂ are tracked as mass fractions of a fixed ~465 kg of cabin air (≈400 m³ at sea-level density), the same order of magnitude as the ISS cabin.

O₂ CO₂ H₂O H₂ CH₄ (vented)

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