Challenger Disaster

ON JANUARY 28, 1986, only 73 seconds after launching of Mission 51-L, seven crewmembers including a schoolteacher, Christa McAuliffe, died in the explosion of the space shuttle Challenger. A subsequent investigation by the President's Commission on the space shuttle Challenger Accident (the Rogers Commission) concluded that the cause of the Challenger explosion was the failure of the O-ring pressure seal in the spacecraft's right solid rocket booster.

O-ring seals are designed to prevent hot gases from leaking through the joint during the propellant burn of the rocket motor. However, almost immediately after takeoff the O-ring seals were destroyed allowing hot gases to leak through the right solid rocket motor field joint. In the process, the struts linking the solid booster and the external tank began to weaken. Eventually, the solid rocket booster was allowed to rotate freely and impact the intertank structure and the lower part of the liquid oxygen tank. Continuous structural failure to the hydrogen tank released large amounts of liquid hydrogen. This combination of events created an enormous oxygen-hydrogen explosion that engulfed the Challenger within seconds.

The commission's report stated that gray and black smoke emitted from the right solid rocket booster was an indication that grease, joint insulation, and rubber O-rings in the joint seal were being burned and eroded by hot gases. Beyond the technical cause of the explosion, the commission and other scholars maintain several factors contributed significantly to the tragedy including pressure placed on the National Aeronautics and Space Administration (NASA) to sustain a busy launch schedule (15 launches were scheduled for 1986 and another 19 for 1987). Faulty design of the spacecraft, weather temperatures, and a lack of organizational communication also contributed to the crash.

The space shuttle Challenger, named after the British Naval vessel HMS Challenger, was the second orbiter to become operational at Kennedy Space Center. During the 1960s, NASA enjoyed unlimited political support and financial resources. However by the 1970s, budget constraints and a lack of political and public support dramatically affected NASA's ability to design a fully comprehensive reusable spacecraft. As a result, NASA made several compromises in its spacecraft design, often in favor of cheaper but more dangerous parts. For instance, instead of using safer liquid-fueled engines, NASA used the more volatile solid-fueled rockets. By the 1980s, the Ronald Reagan Administration placed tremendous pressure on NASA to[Page 154] accelerate the use of the space program for commercial, military, and scientific purposes. This emphasis on a fully operational space shuttle program meant that NASA had to further compromise shuttle designs in order to meet political desires and demands for a rapid launch schedule. The result was a hybrid design of the space shuttle that generally overlooked some safety issues.

As early as 1978, several engineers at NASA's Marshall Space Flight Center expressed concern about Morton Thiokol's design of the field joint. Thiokol was the primary private business contracted by NASA to build the solid rocket booster. Marshall engineers agreed that Thiokol's faulty design could lead to hot gas leaks that would essentially cause catastrophic failure. Indeed, Marshall classified the O-ring seals as “criticality 1” meaning they did not meet space shuttle requirements for adequate failsafe standards. Further tests confirmed Marshall engineers' fears that the secondary Orings were dysfunctional and subject to extreme erosion and damage. Despite this evidence, Marshall continued to define the problems with the Orings as an acceptable risk. The Challenger was also designed with several used parts. Two of the solid rocket motors had been previously used and had grown in terms of diameter. Consequently, the Orings designed to prevent seepage or gas leaks did not completely seal the opening.

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