4-Bed Molecular Sieve CO2 Scrubber

Crew & Cabin

Crew size 4

4-Bed Molecular Sieve

Bed switch interval 8 min

Desorption heater temp 204°C

Bed Status

Bed AADSORBING

Bed BDESORBING

Cabin Readout

ppCO2 (cabin)

3.8 mmHg

CO2 fraction

0.50%

Next auto-swap

4:00

Removal rate

— g/hr

How it works

A spacecraft 4-bed molecular sieve (4BMS) CO2 scrubber runs two zeolite beds in antiphase: one adsorbs cabin CO2 while the other is heated and vented to vacuum to desorb the CO2 it captured on the previous cycle, then the roles swap. Adsorption follows Langmuir kinetics — uptake slows as a bed fills:

dθ/dt =  k_ads · p(CO2) · (1 − θ)      (active bed, loading θ ∈ [0,1])
dθ/dt = −k_des · θ · (T_bed / T_ref)    (regenerating bed, vented to space)

The cabin itself is a mass balance between crew metabolic production and scrubber removal:

d(ppCO2)/dt = [ N_crew · m_CO2 − k_ads · p(CO2) · (1 − θ_active) · Q_bed ] / V_cabin

An adult astronaut produces roughly 1.0 kg of CO2 per day at rest (more under exercise). NASA's spacecraft maximum allowable concentration is about 5.3 mmHg (~0.7% at 1 atm); the nominal ISS target sits near 3–4 mmHg, matching the <0.5% target this sim's source article cites.

Crew size — scales metabolic CO2 production, the only source term in the mass balance.
Bed switch interval — how long a bed stays in adsorption mode before the 4BMS valve sequencer swaps it to desorption; too long and the active bed saturates (θ→1) and stops removing CO2.
Desorption heater temp — higher temperature drives k_des up, so the regenerating bed empties faster and is ready sooner for its next adsorption cycle.
Auto / manual swap — Auto swaps on the timer above; turn it off and press "Swap Beds Now" yourself to see what happens if the sequencer is late (cabin ppCO2 climbs while both beds are the wrong phase).

CO2 molecule Adsorbing bed (cool) Desorbing bed (hot)

Cabin ppCO2
3.8 mmHg

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