Space Shuttle Challenger launch decision

A view of Space Shuttle Challenger shortly before launch. Evidence of ice buildup is visible in the foreground.

The Space Shuttle Challenger launch decision was the decision-making process that led to the launch of the Space Shuttle Challenger on January 28, 1986 despite inclement weather conditions and the warnings of many engineers working both for NASA and for NASA contractors Morton Thiokol and Rockwell International. The Shuttle was destroyed as a consequence of the failure of one of the O-ring joints in its right solid rocket booster (SRB). After the loss of Challenger, the engineering decisions, organizational problems and inadequate safety culture that led to its launch were criticized by the Rogers Commission and by the U.S. House Committee on Science and Technology, as well as by independent commentators such as Edward Tufte.

Background

As originally designed by Thiokol, the O-ring joints in the Shuttle's SRBs were supposed to close more tightly due to forces generated at ignition. However, a 1977 test showed that when pressurized water was used to simulate the effects of booster combustion, the metal parts bent away from each other, opening a gap through which gases could leak. This phenomenon, known as "joint rotation," caused a momentary drop in air pressure. This made it possible for combustion gases to erode the O-rings. In the event of widespread erosion, an actual flame path could develop, causing the joint to burst—which would have destroyed the booster and the shuttle.

Engineers at the Marshall Space Flight Center wrote to the manager of the Solid Rocket Booster project, George Hardy, on several occasions suggesting that Thiokol's field joint design was unacceptable. For example, one engineer suggested that joint rotation would render the secondary O-ring useless. However, Hardy did not forward these memos to Thiokol, and the field joints were accepted for flight in 1980.

Evidence of serious O-ring erosion was present as early as the second space shuttle mission, STS-2, which was flown by Columbia. However, contrary to NASA regulations, the Marshall Center did not report this problem to senior management at NASA, but opted to keep the problem within their reporting channels with Thiokol. Even after the O-rings were redesignated as "Criticality 1"—meaning that their failure would result in the destruction of the Orbiter—no one at Marshall suggested that the shuttles be grounded until the flaw could be fixed.

By 1985, Marshall and Thiokol realized that they had a potentially catastrophic problem on their hands. They began the process of redesigning the joint with three inches (76 mm) of additional steel around the tang. This tang would grip the inner face of the joint and prevent it from rotating. However, they did not call for a halt to shuttle flights until the joints could be redesigned. Rather, they treated the problem as an acceptable flight risk. For example, Lawrence Mulloy, Marshall's manager for the SRB project since 1982, issued and waived launch constraints for six consecutive flights. Thiokol even went as far as to persuade NASA to declare the O-ring problem "closed". Donald Kutyna, a member of the Rogers Commission, later likened this situation to an airline permitting one of its planes to continue to fly despite evidence that one of its wings was about to fall off.