35 YEARS LATER: On this day in 1986, the Space Shuttle Challenger exploded after liftoff, killing all seven astronauts on board. The Challenger broke apart at 11:39 a.m., falling into the Atlantic Ocean. Investigators would later discover the disaster was caused by the failure of an “O ring” seal in one of the two solid-fuel rockets. As a result of the horrific accident, NASA did not send astronauts into space for more than two years as it redesigned a number of space shuttle features for improv

This week, as we remember those lost in the pursuit of space exploration, take a look back at the tragic aftermath of the Columbia Space Shuttle's explosion over Texas in 2003. Learn more Sunday 9/8c on The Strange Truth. | National Geographic TV

The Columbia disaster revealed critical safety failures hidden within NASA. | The History Archives