A combination of faulty design of the solid rocket booster segment joints and deliberate progressive relaxation of launch safety procedures by NASA officials and the weather (the temperature that morning was the coldest of any shuttle launch ever).
The design error was to use rubber O-rings to attempt to seal a joint that expands significantly during normal operation, rubber O-rings should only be used where they can be kept constantly in compression. Also at the temperature on the morning of the launch the rubber became hard, losing all elasticity and thus had no ability to expand when the joints flexed.
NASA had documented cases of charred O-rings from hot gasses in the solid rocket boosters escaping past the O-rings and out the joints, yet they ignored this instead of trying to address it and fix the problem.
On the day of the launch of the Challenger, as there was the teacher Christa Mcauliffe was in the crew it was a "prestige flight" and very important and NASA officials deliberately ignored several safety warnings that would have required a launch delay!
Note: Unlike what most people think there was no explosion involved in the Challenger disaster, the vehicle was torn apart by flight stresses that exceeded design limits as the solid rocket booster crushed into the top of the external tank while the main engines gimbaled to their limits to try to keep the vehicle on course in response to uneven thrust from the two solid rocket boosters. The photos that appear to show a "fireball" engulfing the vehicle is just a condensing water vapor cloud (produced by burning of hydrogen and oxygen escaping from the damaged external tank) illuminated by sunlight.
The events of the launch leading to the disaster were:
It blew up.
Space shuttle Challenger exploded on the 28th of January 1986.
1986
An O-ring failure.
A lot of people get this wrong but the real answer, the truth is that Challenger 7 blew up on January 29, 1986.
See: how did the astronauts die in the Challenger disaster.
1986
It blew up.
Faulty O ring
Space shuttle Challenger exploded on the 28th of January 1986.
An O-ring failure.
1986
A lot of people get this wrong but the real answer, the truth is that Challenger 7 blew up on January 29, 1986.
no, space shuttle atlantis didn't blow up, the shuttles that blew up were columbia and challenger.
The Space shuttle Challenger disaster occurred on January 28, 1986.
Space Shuttle Challenger disaster happened on 1986-01-28.
The space shuttle Challenger disaster occurred on January 28, at 11:39am