Each crew member exhales roughly 1.0 kg CO₂/day and needs about 0.84 kg O₂/day. The chemical loop scrubs CO₂ with LiOH canisters (≈1.09 kg LiOH per kg CO₂, from 2LiOH + CO₂ → Li₂CO₃ + H₂O) and replenishes O₂ from stored tanks — both are consumables that must be carried and resupplied, so their mass grows linearly with mission length. The bioregenerative loop instead cycles CO₂ and O₂ through algae/plant photosynthesis: nearly closed-loop and self-sustaining once running, but its output scales with light intensity and it ramps up over roughly two weeks rather than responding instantly.
covered_by_bio = bioShare × (light / 100)
shortfall = bioShare − covered_by_bio (made up by chemical backup)
chem_fraction = 1 − covered_by_bio
daily_mass = chem_fraction × crew × (1.09×CO2 + O2)
- Bioregenerative share — how much of the crew's CO₂/O₂ load is routed to the algae/plant reactor instead of chemical consumables.
- Light availability — photosynthesis rate; below 100% the bioreactor can't cover its assigned share, and the gap falls back onto chemical consumables.
- Crew size — scales daily CO₂ production and O₂ demand directly.
- Mission duration — the chemical loop's mass keeps climbing for the whole mission; the bioregenerative loop's steady-state coverage does not, once it has ramped up.
Real-world relevance: this is the core trade behind ISS-style LiOH/tank systems (fast, simple, but a resupply burden) versus MELiSSA/BIOS-3-style bioregenerative research loops (near-closed mass balance, but slower and light/nutrient dependent) — exactly the trade a long-duration mission has to size in advance.