NASA's space shuttle Challenger completed 10 missions before it broke apart during a launch in 1986, killing seven astronauts.

Because a teacher was going to space, millions of schoolchildren watched the Challenger lift off on Jan. 28, 1986. It exploded 73 seconds later.

Forty years ago, Americans were shocked when the space shuttle Challenger exploded 73 seconds after it launched on a chilly day in Florida.