Not only did Gregg Easterbrook's article describe the dangers that would eventually lead to the demise of the Challenger and the Columbia, but he also mentions

Not only did Gregg Easterbrook's article describe the dangers that would eventually lead to the demise of the Challenger and the Columbia, but he also mentions a third failure mode: the Space Shuttle Main Engines. Could easily have failed catastrophically and taken out a third Shuttle. Instead, all the failures of the SSME turned out to be survivable. We just got really lucky. From "Mr. Feynman Goes to Washington": http://calteches.library.caltech.edu/3570/ http://calteches.library.caltech.edu/3570/ > NASA was claiming that the engines were in the regular range of engineering, but they're not; the engines had many difficulties that the guys at JPL told me about. (I found out later that the people who worked on the engines always had their fingers crossed on each flight, and the moment they saw the Shuttle explode, they were all sure it was the engines. But of course, the TV replay showed a flame coming out of one of the solid rocket boosters.)