Cryogenic Propellant Loading Control

Loading Sequence

STANDBY

Controls

Target O/F mass ratio 6.0 : 1

Max valve flow rate 60 kg/s

Ambient heat leak 2.0×

Relief valve setpoint 260 kPa

Readouts

LOX loaded

0 / 0 kg

LH2 loaded

0 / 0 kg

LOX ullage P

0 kPa

LH2 ullage P

0 kPa

Elapsed

0.0 s

Total flow

0 kg/s

How it works

A ground control loop meters two cryogenic propellants — liquid oxygen (LOX, 90 K) and liquid hydrogen (LH2, 20 K) — into the vehicle's tanks, driving each toward a target mass split by the mixture ratio r you set:

m_LOX(target) = M·r/(r+1)
m_LH2(target) = M/(r+1)
flow_i = clamp(k·(target_i − loaded_i), 0, maxFlow)

Each tank's ullage — the vapor space above the liquid — obeys the ideal gas law. As liquid rises, the headspace volume V shrinks and pressure climbs even with no added gas; ambient heat leak also boils off a trickle of liquid into vapor, adding moles n over time:

P·V = n·R·T   (R = 8.314 J/mol·K)
P = n·R·T / V_headspace

A relief valve automatically vents vapor the instant P crosses your setpoint, holding pressure near that ceiling — exactly the safety behaviour described for real launch-pad fueling systems. Loading stops the moment each tank reaches its target mass; the sequence is READY only once both propellants are topped off and pressures have settled.

Target ratio — sets how the total propellant budget splits between oxidizer and fuel.
Max flow rate — the valve's capacity; higher values fill faster but overshoot pressure spikes more.
Heat leak — how fast ambient warmth boils liquid into ullage vapor.
Relief setpoint — the pressure at which the automatic vent fires.

LOX flow LH2 flow Venting

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