You are confusing the o-ring issue with the brake away foam which caused the second disaster. The foam had been changed due to environmental concerns to a foam that tended to break away in larger chunks. BTW, I designed a small piece of the shuttle in about 1976.
The foam had been changed due to environmental concerns to a foam that tended to break away in larger chunks.
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IIRC, the foam that broke away had nothing to do with any EPA rule changes. I think Rush Limbaugh perpetuated the myth.
The bottom line is the Shuttle was always an unsafe design starting with the Orbiter being place on the side instead of the top.