This is the 2D companion to the 3D ECLSS station-ring simulator, computed independently from the same real Environmental Control and Life Support System model flown on the ISS, not a flattened render of the 3D scene. It 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 (in practice capped by how much CO₂ is actually present in the cabin at any instant, so a scrubber sized well above crew output simply keeps CO₂ pinned low instead of "banking" spare capacity).
- 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.
- Drag to pan, scroll/pinch to zoom the flow diagram; the strip below the map is a live history of O₂%, CO₂ and water reserve over mission time — a genuinely 2D-native diagnostic the 3D version has no room to show.
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.