Case Study #$1$: Space Shuttle Challenger

How could this happen in a program where money was almost no object and the prestige of a nation depended on its success? The world was watching as the fatal chain of events came together.

$1977-$ During the test firings of the solid rocket booster, Thiokol engineers discovered that casing joints were expanding instead of tightening as they were designed. Thiokol persuaded NASA that this was not desirable but acceptable. They also noted that one of the two O$-$ring joint seals frequently became unseated, thus failing to provided the backup for which it was designed.

$1981-$ NASA planned two lightweight versions of the boosters in order to increase the payload. One was to be of steel, while the other was made of carbon filament. Hercules submitted an improved design for the latter, which incorporated a lip at the joint to prevent the O$-$ring from unseating $($termed a capture feature$).$ Thiokol continued to use unmodified joints for its steel boosters.

Nov. $81-$ Maintenance personnel reported erosion $($or scorching$)$ on one of the primary $O-$rings. This was the same joint that was to fail in the Challenger.

Dec. $82-$ As a result of the report, NASA upgraded the critical rating on the joints to $1,$ which meant that the failure of this component could cause the loss of both crew and spacecraft.

April $83-$ Some NASA engineers attempt to adapt the Hercules "capture feature" into the new thinner boosters. The proposal was shelved and the old joints continued to fly.

Feb. $84-$ Just prior to the ${10}^{th}$ shuttle launch, high pressure air tests were carried out on the booster joints. On return, an inch long scorch was found on one of the primary O$-$rings. Despite the critical $-1$ rating, Marshall Space Center reported that no remedial action was required. No connection was noticed between the high pressure testing and the scorching, although maintenance observed pinholes in the insulating putty.

April $84-$ On the ${11}^{th}$ flight, one of the primary O$-$rings was found breached altogether. This was still regarded as acceptable. No connection was made between the high pressure air testing and the scorching, even though the latter was found on the $10$ of the subsequent $14$ shuttle flights.

Jan. $85-$ Breaches $($blowbys$)$ were found on $4$ of the booster joints. The weather at the launch time was the coldest to date: $51$ degrees F$..$ No connection was noted.

April $85-$ On the ${17}^{th}$ shuttle mission, maintenance discovered the primary O$-$ring in the nozzle joint had failed to seal. Scorching was found all the way around the joint.

July $85-$ After another flight with $3$ blowbys, NASA booster project manger