[Videos below of President Regan’s speech, and footage of explosion] Today marks the 25th anniversary of the Challenger explosion. Seven people, one of them a school teacher, died in a tragedy that unfolded in front of a television audience at a time, 1986, when that type of experience was, to say the least, uncommon.

On January 28, 1986, nothing was supposed to be different. Space Shuttle Challenger, NASA’s second Space Shuttle orbiter, had already completed nine missions after making its maiden flight nearly three years earlier; Challenger flew 85 percent of all Space Shuttle missions in 1983 and 1984 and became known as the workhouse of NASA’s prized fleet. But 73 seconds after launch, which was broadcast live for the country to see, Challenger exploded. All seven crew members were killed and the entire shuttle fleet was grounded for more than two years while NASA engineers worked to figure out what went wrong. We know now that a booster failure resulted in the explosion that stunned a nation and cut mission STS 51-L short.

A quarter-century later, NASA continues to do important work, but the Space Shuttle system is scheduled to be retired from service later this year after 135 launches.