NASA's space shuttle Challenger accident was a devastating tragedy that killed seven astronauts and shocked the world on Jan. 28, 1986. Killed in the accident were Challenger commander Dick Scobee, pilot Michael Smith, mission specialists Judy Resnik, Ronald McNair and Ellison Onizuka, payload specialist Gregory Jarvis and Christa McAuliffe, who was set to become the first teacher in space.
Here's a look at how the Challenger accident occurred:
An inspection of the launch pad revealed large quantities of ice collecting due to unusually cold overnight Florida temperatures. NASA had no experience launching the shuttle in temperatures as cold as on the morning of Jan. 28, 1986. The coldest temperature of a previous launch was 20 degrees warmer.
Morton Thiokol, the builder of the solid-rocket boosters, advised NASA that they believed the O-ring seals in the solid-rocket boosters would perform adequately in the cold.
To make each solid-rocket booster, the Morton Thiokol factory built four hull segments filled with powdered aluminum (fuel) and ammonium perchlorate (oxidizer).
At the launch site, the fuel segments were assembled vertically. Field joints containing rubber O-ring seals were installed between each fuel segment.
The O-rings were never tested in extreme cold. On the morning of the launch, the cold rubber became stiff, failing to fully seal the joint.
As the shuttle ascended, one of the seals on a booster rocket opened enough to allow a plume of exhaust to leak out. Hot gases bathed the hull of the cold external tank full of liquid oxygen and hydrogen until the tank ruptured.
At 73 seconds after liftoff, at an altitude of 9 miles (14.5 kilo- meters), the shuttle was torn apart by aerodynamic forces.
The two solid-rocket boosters continued flying until the NASA range safety officer destroyed them by remote control.
The crew compartment ascended to an altitude of 12.3 miles (19.8 km) before free-falling into the Atlantic Ocean.