How did weather contribute to the Challenger disaster?

Answer 1

The primary cause of the Challenger disaster was the failure of O-rings in the solid rocket boosters ( SRB'S) to properly seal due to the extremely cold temperatures experienced on the launch morning.

This problem had not gone unforeseen. The already-delayed mission was scheduled to launch when unusually low temperatures and cool clear weather were forecast - 23 degrees F overnight preceding the launch. This especially concerned the engineers at Thiokol, the company responsible for the manufacture of the SRB's. The seals had only been tested down to a minimum temperature of 53F, with a projected baseline of 40F. Beyond that, no guarantees could be made. They calculated the temperature at the expected time of launch would compromise the seal's ability to remain elastic enough to seal in the gases and heat. Some NASA officials placed pressure on Thiokol to approve the launch, and although the engineers refused to give in, they were over-ridden by the Thiokol management and launch was approved by them. In a series of mis-communications where those responsible for the final decision to launch did not hear about the concerns expressed, NASA ultimately approved the delayed launch.

On the launch morning, the ice team worked through the night to clear ice from the orbiter and surrounding structures. Some icicles were 16 inches long, and a single ice sheet extended down several levels of the gantry. The ice-team gave the green light to launch officials when the ice was seen to be melting, as launch was delayed for an hour to allow the temperature to rise slightly.

A factor which compounded the problems with the temperature around the booster was the super-cooled air which flowed down from the External Fuel Tank. This is a normal occurance, but on this particular morning, the wind direction blew the air in a way which caused it to settle around the aft-joint in which the O-rings are situated. This compounded the already low temperatures of the structure.The ice team are said to have measured the temperature in the region of the O-ring at 8 F, but this was never passed on to higher level NASA officials.

At launch, the Thiokol engineer's worst fears were realized as the rings failed to move enough to completely seal, as evidenced by the black smoke puffs visible as soon as 0.678 seconds after ignition. The rings vaporized due to the leaking hot gases, and subsequent flame that emerged from the breach. This led to a chain of events until the external fuel tank ruptured and disintegrated, and the orbiter itself was pulled apart by aerodynamic forces.

A final influence of the weather on the disaster was the wind shear experienced seconds before the final break-up of the shuttle stack. This wind shear was the worst ever experienced during a shuttle launch and occurred at the point of maximum stress on the vehicle (max Q). When the O-rings had failed to seal, a temporary seal had been formed by melted aluminum oxide leaking into the joint. This seal shattered in the wind shear, and many feel that had the wind force not been so violent, it may have been sufficient to last until booster separation (although the shuttle would probably not have reached orbital height).