(CNN) -
35 years ago, NASA suffered a tragedy when the Challenger space shuttle disintegrated shortly after its launch.
All seven of the crew on board died in the incident.
On taking off from Kennedy Space Center in Cape Canaveral, Florida, cold weather conditions that morning, combined with a design flaw, caused the main booster rocket to fail and caused a structural collapse.
LOOK: "Challenger: The Final Flight" addresses the explosion of the space shuttle, 73 seconds after its takeoff in 1986
The external fuel tank collapsed due to a leak, releasing liquid hydrogen and liquid oxygen, generating a giant fireball that made the Challenger appear to have exploded.
Allan McDonald, director of the Space Shuttle Solid Rocket Engine Project for engineering contractor Morton Thiokol, declined to sign a launch recommendation for the Challenger the night before for safety reasons.
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The Challenger disintegrated 73 seconds after launch at approximately 11:40 a.m. ET on January 28, 1986.
The launch and subsequent explosion were broadcast live on CNN and seen in US classrooms that morning.
NASA installed a special satellite broadcast for schools across the country to see what was supposed to be a historic moment.
Christa McAuliffe, a high school teacher from New Hampshire, was supposed to be the first civilian and American teacher in space.
It was selected as part of the Teachers in Space program.
He would join Major Francis R. Scobee;
pilot Michael J. Smith;
payload specialist Gregory Jarvis;
and mission specialists Ronald McNair, Ellison Onizuka and Judith Resnik to form the crew of Mission STS-51L.
Each year NASA celebrates a "Remembrance Day" to honor fallen astronauts.
It began after the Columbia space shuttle disaster, which claimed the lives of its seven-member crew during its return to Earth on February 1, 2003.
