A solar particle event (SPE) sends a burst of high-energy protons past the station. The unshielded ("free-space") dose rate is modeled with a rise-and-decay pulse shaped like the real thing — fast onset, slower decay:
Ḋ_free(t) = Ḋ_bg + Ḋ_peak · (t/t_p) · e^(1 − t/t_p)
t_p = time to peak
Ḋ_peak = peak dose rate above background
Ḋ_bg = steady galactic-cosmic-ray background
Consumable stores (drinking-water tanks, food packaging, even trash) stacked around a shelter core add mass without adding launch payload. Areal density x (g of material per cm² of wall) attenuates the beam exponentially, same law as any shielding slab:
Ḋ_shelter(t) = Ḋ_free(t) · e^(−x_eff(t) / λ)
λ ≈ 18 g/cm² (attenuation length, water-equivalent)
x_eff(t) = x · min(1, t_since_alarm / t_delay)
The crew doesn't teleport into the shelter — x_eff ramps linearly from 0 to the full stacked thickness over the "time-to-shelter" delay, so a slow move to shelter costs real dose even with thick walls waiting. Cumulative dose is the running integral D = ∫ Ḋ_shelter dt, checked against the 250 mGy 30-day skin-dose limit used for ISS-class missions.
- Trigger Storm — starts an SPE pulse on top of the steady background; the mission clock keeps running either way.
- Shield areal density — how much water/food mass is stacked into the shelter walls; doubling it does not halve the dose rate — the exponential means every extra λ (≈18 g/cm²) cuts the surviving flux by another factor of e.
- Time-to-shelter delay — how long the crew takes to reach the shelter and finish stacking it; this is often the dominant term in total dose during a fast-rising storm.
This 2D rebuild replaces the 3D station model with two linked panels drawn on one canvas: a rotatable cutaway of the shelter core with its four shield walls and incoming/absorbed/leaking protons (drag to rotate the view), and a live strip chart of the free-space vs. shelter dose rate so you can see the pulse shape and the attenuation gap open up in real time.