What was the fatal flaw that caused the Space Shuttle Challenger disaster?
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So on the Space Shuttle the Solid Rocket Boosters (SRBs) go through thermal loads, and as a result they expand over the course of the flight. In order to keep them together while simultaneously allowing them to expand, the outer shell of the SRBs is actually a number of separate pieces, with O-rings at the joints made of Viton to allow them to expand and contract as needed over the launch sequence.
The problem was that the O-rings have a temperature range where they expand optimally, and the day of the launch the temperatures were very cold and below the optimal range of the Viton material. As a result, when the shuttle launched, the O-rings didn’t seat correctly into the wall of the right SRB. However, by happenstance, the aluminum oxides produced by combustion in the SRB itself sort of plugged the leak, allowing the initial stages of the launch to proceed normally until around a minute into the flight. At this point, high wind shear dislodged the oxide material, at which point a plume of hot exhaust gas started exiting the side of the right SRB, and was pointed straight at one of the struts holding the SRB to the rest of the shuttle, and also burning into the liquid hydrogen portion of the external fuel tank.
Around 72 seconds in, the strut failed, causing the load to shift in the external fuel tank and basically throwing it forwards, all of which caused the orbiter to twist off of it’s normal heading, and at close to Mach 2 the resulting aerodynamic forces tore the shuttle apart.
NASA absolutely knew of the potential for failure of the O-rings, and had been warned by the manufacturer’s engineers, but proceeded with the launch anyway.
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