A solar-proximity probe like Parker Solar Probe doesn't survive the Sun by resisting heat — it survives by hiding from it. Its carbon-composite heat shield stays pointed straight at the Sun and reaches roughly 1,400°C on its sun-facing side, while the instruments and electronics sit just centimeters behind it, inside the narrow cone of shadow the shield casts. Because the shield is a poor conductor and the shadow blocks essentially all direct flux, the shielded body stays near room temperature indefinitely — for years and dozens of close passes, not the few minutes a re-entry heat shield has to survive.
The entire strategy depends on keeping the spacecraft body inside that shadow cone at every instant. Tilt the shield even slightly and the body swings sideways out of the cone while the cone itself stays locked to the Sun-line — the exposed sliver receives raw solar flux intense enough to destroy unshielded hardware in seconds, not the gentle warming you'd expect from "slightly off-angle."
- Pointing error — how far the shield's axis has drifted from dead-on alignment with the Sun; past the tolerance line the shadow cone no longer fully covers the body.
- Distance to Sun — closer perihelion passes mean more intense flux on the shield and a much less forgiving margin: any given pointing error uncovers the same area, but that area is bathed in far higher flux and heats to failure far faster, so mission rules tighten the allowed pointing error as perihelion approaches.
- Auto perihelion pass / auto pointing drift — animate a full close approach or a slow attitude drift so you can watch the safe window narrow and the exposure threshold get crossed in real time.