Good explaination. Too many people think the cold launch day and NASA culture that allowed a launch on such a day was the only issue. It's less widely known that the design was fucked from the start and wasn't working properly for any of the Shuttle launches.
Also, there was another very poor decision by NASA that the article does not mention. The summer before the Challenger launch, Thiokol, at the urgent request of its engineers, sent NASA a memo stating that the SRB O-rings were not sealing properly and recommending that all Shuttle flights be stopped until the issue was understood and fixed. NASA's response was to reclassify the SRB O-rings as a Criticality 1 flight risk instead of Criticality 1R--1R means the issue could cause loss of vehicle and loss of crew if it happens, but there is a redundant backup, whereas 1 means no redundant backup, which means the Shuttle should indeed have been grounded--and then waived the risk so the Shuttle could continue flying. So NASA not only put a very poor design into use, they kept on using it even after their own flight risk procedure told them they should stop.
You're mixing up events. The reclassification happened in 1980 (correction: 1982, I can't math), ~4 years prior:
"A second major event regarding the joint seal occurred in the summer of 1982. As noted before, in 1977-78, Leon Ray had concluded that joint rotation caused the loss of the secondary O-ring as a backup seal. Because of May 1982 high pressure O-ring tests and tests of the new lightweight motor case, Marshall management [126] finally accepted the conclusion that the secondary O-ring was no longer functional after the joints rotated when the Solid Rocket Motor reached 40 percent of its maximum expected operating pressure. It obviously followed that the dual O-rings were not a completely redundant system, so the Criticality 1R had to be changed to Criticality 1.53 This was done at Marshall on December 17, 1982. The revised Critical Items List read (See pages 157 and 158)"
Also, the issues with the o-rings not sealing properly were known from the very beginning. Thiokol's seal design was extremely unorthordox, NASA engineers objected before the contract selection, testing showed substantial leakage during both static pressure testing and actual firings. NASA management ignored all this, and Thiokol insisted it wasn't a problem and re-wrote the pass/fail standards in terms of leakage.
There were numerous problems; the o-rings were glued instead of molded as they had been on the Titan, the boosters were assembled horizontally (something that had never been done before - certainly not on the largest solid rocket motor ever built), the o-ring assemblies were not inspected for voids...the list of incompetence just goes on and on.
Actually, the reclassification happened in December 1982, according to the Rogers Commission report that you reference. (The original classification as 1R happened in 1980; the reclassification that removed the "R" happened in 1982.) Which I agree is not the summer prior to the Challenger launch; I was misremembering that part. But the rest of what I said--Thiokol recommending to NASA that the Shuttle be grounded until the O-ring issue was fixed, and NASA refusing--did happen the summer prior to the Challenger launch (summer 1985).
> the issues with the o-rings not sealing properly were known from the very beginning
The fact that the design was unorthodox was known, yes. The extent to which that design would lead to actual events in actual flights was not. The Thiokol engineers only gradually learned what the extent of the actual flight risk was as they analyzed flight data. A good account, which includes a brief description of how the design was flawed, the efforts made by the Thiokol engineers to analyze flight data and to obtain test data on the O-rings, the information sent by Thiokol to NASA in the summer of 1985, and and an account of the conference call the night before the Challenger launch, is given in this paper co-authored by Roger Boisjoly:
To be clear, none of this means the design should have been accepted in the first place; clearly it shouldn't have been. I am simply pointing out that the article under discussion in this thread leaves out further points in the process, besides the original design choice and the conference call the night before the launch, where NASA was given strong indications that they should change their minds, and they never did.
Yes, what I found excellent about this explanation is how the system is actually dynamic, but NASA treated it as static.
In the reference good design, the single O-Rings must dynamically seat against the outermost surface from the forces in the initial leak test, and that seating is reinforced by the actual flight pressures. This also relies upon the free path of hot gasses from the hot pressurized combustion side to apply equal pressure around the ring and compress the now-hot air against the ring and steel walls, which act as a heat sink, and achieve 1/1-million failure rates.
In contrast, it looks like NASA treated it as a static system, just adding more "sealant" and O-Rings to the system, which actually forked-up the dynamics, forcing a single-point breakthru of the O-ring. And worse yet, they magnified the problem in the "fix", and the only reason it didn't happen again is they never launched in such cold temps again.
Also particularly sad to see the failure obvious in Pic #4, with hot gasses expelling from the SRB side even before it leaves the pad. They were already doomed. And even if someone somehow saw that failure happening on the pad, could anything have been done? A way to separate them from the main structure early and abort? Separate the shuttle from the main tank and abort?
SLS uses improvements made late in the Shuttle program. Lower temp materials and some larger diameters. Presumably that exact problem is fixed. Others? Who knows.
