ruptures on the surface of the seal. Space Shuttle Challenger disaster The failure of an O-ring seal was determined to be the cause of the Space Shuttle Challenger disaster on January 28, 1986. A crucial factor was cold weather prior to the launch. This was famously demonstrated on television by Caltech physics professor Richard Feynman, when he placed a small O-ring into ice-cold water, and subsequently showed its loss of flexibility before an investigative committee. The material of the failed O-ring was FKM, which was specified by the shuttle motor contractor, Morton-Thiokol. When an O-ring is cooled below its glass transition temperature Tg, it loses its elasticity and becomes brittle. More importantly, when an O-ring is cooled near (but not beyond) its Tg, the cold O-ring, once compressed, will take longer than normal to return to its original shape. O-rings (and all other seals) work by producing positive pressure against a surface, thereby preventing leaks. On the night before the launch, exceedingly low air temperatures were recorded. Due to this, NASA technicians performed an inspection; the ambient temperature was within launch parameters, and the launch sequence was allowed to proceed. However, the temperature of the rubber O-rings remained significantly lower than that of the surrounding air. During his investigation of the launch footage, Feynman observed a small out-gassing event from the Solid Rocket Booster at the joint between two segments in the moments immediately preceding the disaster. This was blamed on a failed O-ring seal. The escaping high-temperature gas impinged upon the external tank, and the entire vehicle was destroyed as a result. Since the accident, rubber production companies have enacted changes. Many O-rings now come with batch and cure date coding, as is done in medicine production, to precisely track and control distribution. For aerospace and military applications, O-rings are usually individually packaged and labeled with the material, cure date, and batch information. O-rings can, if needed, be recalled off the shelf. Furthermore, O-rings and other seals are routinely batch-tested for quality control by the manufacturers, and often undergo quality assurance testing several more times by the distributor and ultimate end-users. As for the boosters themselves, NASA and Morton-Thiokol redesigned them with a new joint design, which now incorporated three O-rings instead of two, with the joints themselves having onboard heaters that can be turned on when temperatures drop below . No O-ring issues have occurred since Challenger, and