Investigation Summary
The disaster was rooted in a phenomenon later termed the normalization of deviance, where technical anomalies were repeatedly accepted as manageable risks rather than signals of impending failure. Engineers at Morton Thiokol, the contractor for the SRBs, had observed O-ring erosion and "blow-by" (gas escaping past the primary seal) in previous missions. On the night before the launch, these engineers warned that the predicted temperature of 36°F was far below the 53°F threshold they considered safe for the O-rings to remain resilient. However, under significant schedule pressure and a desire to maintain the shuttle's reputation as an operational vehicle, NASA managers pressured Morton Thiokol to reverse their recommendation. The launch proceeded, and the cold-stiffened O-rings failed to seat properly at ignition. A plume of flame eventually breached the external tank, leading to the aerodynamic breakup of the orbiter at an altitude of approximately 46,000 feet.
Final Conclusions
The Presidential Commission on the Space Shuttle Challenger Accident (Rogers Commission) concluded that the loss was caused by a failure in the joint between the two lower segments of the right Solid Rocket Booster. The specific failure was the destruction of the seals (O-rings) that were intended to prevent hot gases from leaking. The commission also cited a flawed decision-making process at NASA, where safety concerns raised by engineers were not effectively communicated to the managers responsible for the launch decision.
Photographic Evidence (1)
Video Analysis
What Caused the Space Shuttle Challenger Explosion — A detailed look at the technical and organizational failures that led to the 1986 breakup of the Space Shuttle Challenger.
If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Solid Rocket Booster (SRB) Field Joint
The connection points between the four segments of the SRB, sealed by two rubber O-rings and zinc chromate putty to prevent the escape of 5,000°F combustion gases.
O-rings
Viton rubber seals designed to expand and fill the gap in the SRB joints during ignition; cold temperatures caused them to harden and lose their ability to seal quickly.
Personal Egress Air Packs (PEAPs)
Emergency breathing apparatuses intended for ground egress; their activation proved some crew members survived the initial breakup.
Interesting Facts
- 01The temperature at launch was 36°F, the coldest ever for a shuttle mission.
- 02At least three Personal Egress Air Packs (PEAPs) were found to have been manually activated by the crew after the breakup.
- 03Recovered wreckage showed that several electrical switches on Pilot Michael J. Smith's panel had been moved and lever locks manipulated, indicating conscious attempts to restore power after cabin separation.
- 04The crew cabin remained largely intact until it struck the ocean surface.
- 05The Kerwin Report concluded that crew consciousness was possible but not certain, likely depending on whether the cabin remained pressurized during the descent.
- 06The Rogers Commission included Nobel physicist Richard Feynman, who famously demonstrated O-ring loss of elasticity using a glass of ice water.
Safety Actions & Advisories
SRB Redesign
Source ↗The Solid Rocket Motor was redesigned as the Redesigned Solid Rocket Motor (RSRM), featuring a new 'capture feature' in the field joints to prevent O-ring rotation and improved insulation to ensure seal integrity.
Crew Escape System
Source ↗NASA implemented a telescoping escape pole system that allowed the crew to slide out of the side hatch and clear the orbiter's wing during a controlled glide, though this system would not have saved the STS-51L crew during the initial breakup.
Organizational Restructuring
Source ↗NASA established the Office of Safety, Reliability, and Quality Assurance, reporting directly to the NASA Administrator, to ensure that safety concerns were no longer bypassed by mission management.
Known Controversies & Unanswered Questions
Morton Thiokol Management Pressure
Reference ↗Engineers were told by their managers to 'take off their engineering hats and put on their management hats' to approve the launch despite known safety risks.