On 28 January 1986, the 25th Space Shuttle mission (STS-51L) ended in tragedy 73 sec after launch. The Challenger Orbiter was destroyed and its seven-member crew killed. A presidential commission set up to investigate the accident concluded that a failure had occurred in the joint between the two lower segments of the right Solid Rocket Booster (SRB). The rubber seal, or O-ring, had hardened overnight in freezing weather and failed when the boosters ignited at launch. The escaping flame breached the External Tank, and the vehicle broke apart as the propellants ignited. The commission also concluded that there were flaws in the Shuttle program. Many changes in the SRB and Orbiter design, as well as in management, were made to improve safety.
Countdown to catastrophe
Objectives of mission STS-51L were to launch a new Tracking and Data Relay Satellite, fly a module to observe Halley's comet, and carry out a number of experiments, including the Fluid Dynamics Experiment, the Comet Halley Active Monitoring Program Phase Partitioning Experiment, and three Shuttle Student Involvement Program experiments. A first-time activity was the lesson-from-orbit that classroom teacher Christa McAuliffe planned to teach. As well as McAuliffe, the other crew members were Francis R. Scobee, commander; Michael J. Smith, pilot; mission specialists Judith A. Resnik, Ellison Onizuka, and Ronald E. McNair; and non-NASA payload specialist Gregory Jarvis, an employee of Hughes Aerospace.
The launch, originally scheduled for 22 January 1986, had been postponed six times because of bad weather and mechanical problems. When the decision was made to launch, the air temperature was 36°F (2°C), cold for Florida, even in January. Launch finally took place at 11:38 am Eastern Standard Time.
Photographic data later revealed that the first indication of a problem occurred at 0.678 seconds into the flight, when a strong puff of gray smoke spurted from the vicinity of the aft field joint on the right solid rocket booster. The vaporized material streaming from the joint indicated the absence of complete sealing action within the joint. Quickly, observers saw eight distinctive puffs of increasingly blacker smoke. At just under a minute into the flight, the first flickering flame would be detected on image-enhanced film on the right solid rocket booster, and one film frame later, the flame was visible without image enhancement. It rapidly grew into a continuous, well-defined plume that was directed onto the surface of the massive external tank, which held the fuel for the main engines.
At 64 seconds came the first visual indication that the swirling flames from the right solid rocket booster had breached the external tank. Within 45 milliseconds of the breach, a bright, sustained glow developed on the black-tiled underside of the Challenger between it and the external tank. Less than 10 seconds later, at an altitude of 46,000 ft (14,325 m), the Challenger was totally engulfed in an explosive burn. At 73 sec after liftoff, it exploded, claiming the crew and vehicle while millions watched in horror on their televisions.
Moments after the explosion, all mission data, flight records, and launch facilities were impounded. Within an hour, NASA's associate administrator for space flight, Jesse Moore, named an expert panel to investigate the disaster.
On 3 February, President Ronald Reagan announced the formation of a presidential commission to investigate the accident. The commission was headed by former secretary of state and attorney general William P. Rogers and consisted of people not connected with the mission. The commission immediately began a series of hearings that dealt with all areas of the Space Shuttle program. In all, the commission interviewed more than 160 individuals and held more than 35 formal panel investigations, generating almost 12,000 pages of transcript. Almost 6,300 documents, totaling more than 122,000 pages and hundreds of photographs were examined and became part of the commission's permanent database and archives.
Early in its investigations, the commission began to learn of the troubled history of the solid rocket motor joint and seals. Commission members discovered the first indication that the manufacturer of the solid rocket booster, Morton Thiokol, had initially recommended against launch the night before because of concerns regarding the effects of the low temperature on the joint and seal. Following further testimony, Chairman Rogers issued a station noting that "the process [leading to the launch of Challenger] may have been flawed."
The commission released its report and findings on the cause of the accident on 9 June 1986. The consensus of the commission and participating investigative agencies was that the loss of Challenger was caused by a failure in the joint between the two lower segments of the right solid rocket motor. The specific failure was the destruction of the O-ring seals that were intended to prevent hot gases from leaking through the joint during the propellant burn of the rocket motor. The evidence assembled by the commission indicated that no other element of the Space Shuttle system contributed to this failure.
In addition to this primary cause, the commission identified a contributing cause of the accident relating to the decision to launch. The commission concluded that failures in communication resulted in launch decision based on incomplete and sometimes misleading information. Further, engineering data and management judgments conflicted and NASA's management structure permitted internal flight safety problems to bypass key Shuttle managers. Neither concerns regarding the low temperature and its effect on the O-ring nor the ice that formed on the launch pad had been communicated adequately to senior management or been given sufficient weight by those who made the decision to launch. In addition, the heavy emphasis on maintaining the schedule of Shuttle launches and an ambitious flight rate diluted the resources available for a single mission and very likely compromised quality.
The problem with the Space Shuttle's Solid Rocket Booster joint began with its faulty design and increased as both NASA and Thiokol management first failed to recognize the problem, then failed to fix it, and finally treated it as an acceptable flight risk. NASA minimized the growing problem in its management briefings and reports, and Thiokol's stated position was that "the condition is not desirable but is acceptable." At no time did management either recommend a redesign of the joint or call for the Shuttle's grounding until the problem was solved.
The findings of the commission determined that the genesis of the Challenger accident-the failure of the joint of the right solid rocket motor-began with decisions made in the design of the joint and in the failure by both Thiokol and NASA to understand and respond to facts obtained during testing.
In its report to the President, the commission unanimously adopted nine recommendations. These ranged from the obvious redesign of the solid rocket booster joints to recommendations relating to management, communications, and safety. The commission also recommended that NASA slow the pace of its launches. Although critical of the agency, the commission also urged that the country continue to support NASA as a "national resource" and applauded the agency's achievements.
Return to flight
At the same time that the commission was meeting, NASA was working on defining and implementing the actions it would take that would allow resumption of Shuttle flights. This included redesign of the solid rocket motor that eliminated the weakness that had led to the accident. The agency also reviewed every element of the Shuttle system and added features to improve safety including a drag-chute system and upgrades of the orbiters' tires, brakes, and nose-wheel steering mechanism. A crew escape system that would allow astronauts to parachute from the orbiter under certain conditions was also added. Finally, a new, streamlined management team was also put in place that included experienced astronauts.
NASA selected the orbiter Discovery for the "return to space" mission, designated STS-26. On September 29, 1988, it blasted off from Kennedy Space Center, carrying a new Tracking and Data Relay Satellite identical to the one that had been destroyed two and a half years before. The Shuttle had returned to the skies, a much safer program. And never again would any Shuttle launch be considered "routine."
1. Vaughan, Diane. The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA. Chicago: University of Chicago Press, 1997.
Source: U.S. Centennial of Flight Commisssion