Chernobyl.
April/26/1986.

-At least 4,000 died from radiation poisoning and cancer.

- Cities, like Pripyat, with over a 1/4 million people, became
abandoned relics.

- I know one of you Zoners who has or had distant or not-so-distant relatives
within lethal range of that radioactive fallout.

-And, to make it even more personal; everyone of you reading this has
at least a literal handful [single digit's worth] of radioactive atoms
from that event in your body right now.

Nuclear power suffered understandable setbacks on earth and in space
from that event.

Example: Prior to Chernobyl, the Soviets were seriously designing and on the verge
of developing a nuclear-powered "space-tug" that would have made lunar bases
feasible by now...But Chernobyl sucked the enthusiasm away from such proposed
space technology.
Maybe the nuclear space initiative by President Bush could revive things.