isanameaname

isanameaname t1_ivx9d88 wrote

They had been partially failing since early testing but that partial failure was deemed acceptable because they failed in a way which was thought to be within acceptable levels of risk:

https://en.wikipedia.org/wiki/Space_Shuttle_Challenger_disaster?wprov=sfla1

Fun fact: it wasn't.

> Evaluations of the proposed SRB design in the early 1970s and field joint testing showed that the wide tolerances between the mated parts allowed the O-rings to be extruded from their seats rather than compressed. This extrusion was judged to be acceptable by NASA and Morton Thiokol despite concerns of NASA's engineers. A 1977 test showed that up to .052 inches (1.3 mm) of joint rotation occurred during the simulated internal pressure of a launch. Joint rotation, which occurred when the tang and clevis bent away from each other, reduced the pressure on the O-rings which weakened their seals and made it possible for combustion gases to erode the O-rings.

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