Roger Boisjoly

Simplified cross section of the joints between solid rocket booster segments; outside at left.
Legend:
A – steel wall 0.5 inches (12.7 mm) thick
B – base O-ring,
C – backup O-ring,
D – Strengthening-Cover band,
E – insulation,
F – insulation,
G – carpeting,
H – sealing paste,
I – fixed propellant

Boisjoly wrote a memo in July 1985 to his superiors concerning the faulty design of the solid rocket boosters that, if left unaddressed, could lead to a catastrophic event during launch of a Space Shuttle. Such a catastrophic event occurred six months later resulting in the Space Shuttle Challenger disaster.

This memo followed his investigation of a solid rocket booster (SRB) from a shuttle flight in January 1985. During his investigation, he discovered that the first of a system of two O-rings had failed completely and that damage had been caused to the second O-ring.

The O-rings were two rubber rings that formed a seal between two sections of the SRBs. The sections of the boosters were joined using tang and clevis joints and the rings were intended to seal the joint while allowing for the inevitable movement between the sections under flight conditions. By design, pressure from within the booster was to push a fillet of putty into the joint, forcing the O-ring into its seat. The system never functioned as designed. The rings were supposed to sit in a groove and seal the joint between the sections of the booster. It was found, however, that flight dynamics caused the joints in the SRBs to flex during launch, opening a gap through which rocket exhaust could escape. As the joints flexed, the rings would come out of their grooves and move to a new position in the joint, a process called extrusion. The extruded ring would form a seal in this new position, but during the time it took for the ring to shift, the joint was unsealed and hot gases could escape, a process called blow-by. These hot gases damaged the rings until the seal was achieved.

Boisjoly's investigation showed that the amount of damage to the O-ring depended on the length of time it took for the ring to move out of its groove and make the seal, and that the amount of time depended on the temperature of the rings. Cold weather made the rubber hard and less flexible, meaning that extrusion took more time and more blow-by took place. He determined that if the O-rings were damaged enough they could fail.

If the second O-ring had failed, the results would almost certainly have been catastrophic with an almost instantaneous explosion of gargantuan proportions, resulting in the complete loss of the shuttle, the crew and the launch pad facilities seemingly the only outcome. His investigation found that the first O-ring failed because the low temperatures on the night before the flight had compromised the flexibility of the O-ring, reducing its ability to form a seal. The temperature at launch had been only 10 °C (50 °F), the coldest on record (until January 28, 1986). The first rubber O-ring had formed a partial seal, not a complete one; but the second O-ring had held.

Boisjoly sent a memo describing the problem to his managers, but was apparently ignored.[8] Following several further memos, a task force was convened to investigate the matter, but after a month Boisjoly realized that the task force had no power, no resources, and no management support. In late 1985, Boisjoly advised his managers that if the problem was not fixed, there was a distinct chance that a shuttle mission would end in disaster. No action was taken.

Following the announcement that the Challenger mission was confirmed for January 28, 1986, Boisjoly and his colleagues tried to stop the flight. Temperatures were due to fall to −1 °C (30 °F) overnight. Boisjoly felt that this would severely compromise the safety of the O-ring and potentially the flight.

The matter was discussed with Morton Thiokol managers, who agreed that the issue was serious enough to recommend delaying the flight. NASA protocols required all shuttle sub-contractors to sign off on each flight. During the go/no-go telephone conference with NASA management the night before the launch, Morton Thiokol notified NASA of their recommendation to postpone. NASA officials strongly questioned the recommendations, and asked (some say pressured) Morton Thiokol to reverse its decision.

The Morton Thiokol managers asked for a few minutes off the phone to discuss their final position again. The management team held a meeting from which the engineering team, including Boisjoly and others, were deliberately excluded. The Morton Thiokol managers advised NASA that their data was inconclusive. NASA asked if there were objections. Hearing none, NASA decided to launch the STS-51-L Challenger mission.

Historians have noted that this was the first time NASA had ever launched a mission after having received an explicit no-go recommendation from a major contractor, and that questioning the recommendation and asking for a reconsideration was highly unusual. Many have also noted that the sharp questioning of the no-go recommendation stands out in contrast to the immediate and unquestioning acceptance when the recommendation was changed to a go.

The concerns of Boisjoly proved correct.[9] Initially, Boisjoly was relieved when the flight lifted off, as he had predicted that the SRB would explode before lift-off.

Upon ignition, the O-ring was burned to ash, which formed a weak seal in the joint. At 58 seconds after launch, the shuttle was buffeted by high-altitude winds, the ash seal collapsed, and hot gases streamed out of the joint in a visible blowtorch-like plume that burned into the external hydrogen tank. At about 73 seconds, the adjacent SRB strut gave way, the right rocket booster crashed into the external fuel tank and the vehicle quickly disintegrated.