Airlock Pressure Equalization Cycle (2D)

Cycle Direction

Chamber sealed at habitat pressure

Valve & Target

Valve conductance 1.00×

Habitat set-point 101.3 kPa

Simulation speed 1.00×

Pump-back gas recovery

Chamber Readouts

0 kPa (vacuum)105 kPa

Chamber pressure

101.3 kPa

Cycle time

0.0 s

Gas vented to space

0.0%

Gas recovered

0.0%

How it works

An airlock is a small sealed chamber between the pressurized habitat (≈101.3 kPa) and vacuum. Crew cycle it in two directions: depressurize before an EVA egress, repressurize after ingress. For a fixed chamber volume and temperature, pressure is proportional to trapped gas mass (ideal gas law), and for subsonic flow through a valve/orifice the mass flow rate is closely proportional to the pressure differential across it — the same "fluid RC circuit" approximation used for quick valve-sizing estimates:

dP/dt = -k · (P - P_target)
P(t)  = P_target + (P₀ - P_target) · e^(-k·t)
k = valve conductance C (this sim's slider, s⁻¹)

Depressurizing vents toward vacuum (P_target = 0 kPa); repressurizing pulls toward the habitat set-point. With pump-back recovery enabled, a mechanical pump moves the vented gas into a habitat storage tank instead of dumping it overboard — the pressure curve is identical (same k), but the tracked gas-loss stat drops to zero and the recovered-gas stat rises instead, reflecting the real trade every station design makes between air-loss mass and pump hardware/energy cost.

Valve conductance — scales k: a wider/more open valve reaches the target pressure faster (shorter, noisier cycle); a narrower one is slower but gentler on seals and eardrums.
Habitat set-point — the pressure repressurization drives toward, matching the article's 97–105 kPa operational band for crewed pressure control.
Simulation speed — scales how fast simulated time advances per real second, so you can watch a full slow cycle without waiting, or slow it down to see the curve's early steep drop.
Gas vented / recovered — integrates the mass actually lost from the closed habitat-airlock system versus mass captured by the recovery pump, as a percentage of the chamber's full gas load.

Real hardware (ISS Quest airlock, Shuttle airlocks) uses exactly this recovery trick — a Pressure Control Pump — to cut consumable oxygen/nitrogen loss across thousands of EVA cycles. Drag inside the chamber view to tilt the cutaway and see the molecule field from a different angle.

Mode
Idle

drag to tilt view

Air molecule (simulated) Habitat hatch Space hatch

Pressure vs. time (kPa)