It was a failed o-ring from launching in too cold of temperatures that caused the Challenger disaster though, not a failure of the rocket fuel. The engineers that understood the danger to the o-rings objected to the launch and would not sign off on it, but they were overruled by NASA's broken management culture at the time and the rest is history. There was a thorough investigation and it placed the blame squarely on NASA management for the root cause of launching under conditions that were dangerous to the shuttle design.
This was the investigation largely carried out by Richard Feynman, who ignored much of the other investigators to actually get to the root of the issue.
And because the Shuttle had two launch sites, one on either coast. And because the different segments had different propellant profiles for different stages of flight. And because inspection and manufacturing in segments is a lot easier.
