S-Scale (Solar Radiation Storm Scale)

The official 1-to-5 scale NOAA's Space Weather Prediction Center uses to rate solar radiation storms, based on the flux of high-energy solar protons reaching Earth's vicinity. S1 storms have minimal real-world impact; S5 extreme storms can force high-altitude polar flights to reroute, expose astronauts to radiation levels requiring shelter in more shielded spacecraft compartments, and degrade satellite solar panels.