NASA's Black Week

It's an oddity of history that all three major tragedies of NASA's human spaceflight efforts-- the Apollo 1 training fire that killed three astronauts, and the Challenger and Columbia accidents that killed seven each-- all occurred within one calendar week.  There is no factor connecting all three events that could explain the timing.  Whether humans want to believe it or not, coincidences do happen.

The tragedies created turning points.  The Apollo 1 fire led to an overhaul of the innards of the Apollo command module and a much more capable spaceship.  Challenger marked the high point in the frequency of space shuttle launches.  After that, NASA acknowledged the shuttle could not be the space truck sold to Congress, and Columbia led to the end of the shuttle program.