What Happened Here? The Space Shuttle Challenger - What Happened Here?, #1

On January 28th, 1986, the world witnessed one of the most stunning tragedies in the history of space exploration. Worse yet, they witnessed it live on television, and many of those witnesses were children wanting to see a teacher go to space. The depth of the tragedy of the Shuttle Challenger seemed bottomless, even moreso when people learned the whole truth. That this tragedy could have been prevented.
That mistakes made years before that frigid morning in Florida ended up being the catalyst for devastation. The question is, what happened?