The untold story behind the devastating mission. The CNN Original Series Space Shuttle Columbia: The Final Flight premieres Sunday, April 7 at 9p ET/PT on CNN. | CNN

The NASA space shuttle Challenger exploded 40 years ago, on January 28, 1986, just 73 seconds after liftoff. The disaster claimed the lives of all seven astronauts aboard, including Christa McAuliffe, a teacher from New Hampshire who would have been the first civilian in space. “The crew of the space shuttle Challenger honored us by the manner in which they lived their lives,” President Regan said in an address to the nation that night. “We will never forget them, nor the last time we saw them,

REMEMBERING COLUMBIA: On February 1, 2003, these brave astronauts lost their lives in the Space Shuttle Columbia tragedy. Today, we honor and remember them. Where were you when it happened? http://at.wftv.com/2kW1ZV1 | WFTV Channel 9