The August 1972 Superstorm — an Apollo-Era Astronaut Radiation Near-Miss

What happened

An X9-class flare produced one of the fastest-ever recorded Sun-to-Earth coronal mass ejection transit times, arriving in roughly 14.6 hours. The resulting geomagnetic storm reached Kp 9 (G5) and induced currents that caused an outage on AT&T's L4 transcontinental telephone cable, tripped protective relays on Canadian power grids, and is documented to have triggered the accidental detonation of multiple US magnetic-influence naval sea mines near Haiphong, North Vietnam. The event fell between the Apollo 16 and Apollo 17 missions — had it occurred during either flight, NASA's own later analyses concluded the radiation dose could have been life-threatening to the crew.