Run completes mission
Run stockouts
Mean ± 1σ envelope
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Life-support engineers can't test a hardware failure margin on a real crew, so they lean on Monte Carlo modeling: sample the uncertain inputs — consumption variability, leak rate, regenerator efficiency loss — hundreds or thousands of times, integrate the same mass-balance ODE for every draw, and look at the spread of outcomes rather than a single number. This simulator does exactly that for a spacecraft oxygen reserve buffer: pick a crew size, mission length and uncertainty band, run a batch, and watch a 3D cloud of trajectories fan out from a full reserve toward the mission end, colored by whether each one keeps enough O₂ in the tank or hits zero first. Live readouts report the mean margin, the probability of a stockout, and which stochastic input — consumption, leak, or regenerator degradation — is actually driving the risk, the same one-at-a-time sensitivity ranking used to decide which subsystem gets the next round of hardware margin.