Challenger Disaster Synopsis (Based on Texas A&M University, Dept. of M.E., website) On January 28, 1986, seven astronauts were killed when the space shuttle they were piloting, the Challenger, exploded just over a minute into flight. The failure of the solid rocket booster O-rings to seat properly allowed hot combustion gases to leak from the side of the booster and burn through the external fuel tank. The failure of the O-ring was attributed to several factors, including faulty design of the solid rocket boosters, insufficient low temperature testing of the O-ring material and the joints that the O-ring sealed, and lack of communication between different levels of NASA management. Organization and People Involved Marshall Space Flight Center - in charge of booster rocket development Larry Mulloy - challenged the engineers' decision not to launch Morton Thiokol - Contracted by NASA to build the Solid Rocket Booster Alan McDonald - Director of the Solid Rocket Motors Project Bob Lund - Engineering Vice President Robert Ebeling - Engineer who worked under McDonald Roger Boisjoly - Engineer who worked under McDonald Joe Kilminster - Engineer in a management position Jerald Mason - Senior Executive who encouraged Lund to reassess his decision not to launch. Key Dates 1974 - Morton-Thiokol awarded contract to build solid rocket boosters. 1976 - NASA accepts Morton-Thiokol's booster design. 1977 - Morton-Thiokol discovers joint rotation problem. November 1981 - O-ring erosion discovered after second shuttle flight. January 24, 1985 - shuttle flight that exhibited the worst O-ring blow-by. July 1985 - Thiokol orders new steel billets for new field joint design. August 19, 1985 - NASA Level I management briefed on booster problem. January 27, 1986 - night teleconference to discuss effects of cold temperature on booster performance. January 28, 1986 - Challenger explodes 72 seconds after liftoff. Background NASA managers were anxious to launch the Challenger for several reasons, including economic considerations, political pressures, and scheduling backlogs. Unforeseen competition from the European Space Agency put NASA in a position where it would have to fly the shuttle dependably on a very ambitious schedule in order to prove the Space Transportation System's cost effectiveness and potential for commercialization. This prompted NASA to schedule a record number of missions in 1986 to make a casefor its budget requests. The shuttle mission just prior to the Challenger had been delayed a record number of times due to inclement weather and mechanical factors. NASA wanted to launch the Challenger without any delays so the launch pad could be refurbished in time for the next mission, which would be carrying a probe that would examine Halley's Comet. If launched on time, this probe would have collected data a few days before a similar Russian probe would be launched. There was probably also pressure to launch Challenger so it could be in space when President Reagan gave his State of the Union address. Reagan's main topic was to be education, and he was expected to mention the shuttle and the first teacher in space, Christa McAuliffe. The shuttle solid rocket boosters (or SRBs), are key elements in the operation of the shuttle. Without the boosters, the shuttle cannot produce enough thrust to overcome the earth's gravitational pull and achieve orbit. There is an SRB attached to each side of the external fuel tank. Each booster is 149 feet long and 12 feet in diameter. Before ignition, each booster weighs 2 million pounds. Solid rockets in general produce much more thrust per pound than their liquid fuel counterparts. The drawback is that once the solid rocket fuel has been ignited, it cannot be turned off or even controlled. So it was extremely important that the shuttle SRBs were properly designed. Morton Thiokol was awarded the contract to design and build the SRBs in 1974. Thiokol's design is a scaled-up version of a Titan missile whichhad been used successfully for years. NASA accepted the design in 1976. The booster is comprised of seven hollow metal cylinders. The solid rocket fuel is cast into the cylinders at the Thiokol plant in Utah, and the cylinders are assembled into pairs for transport to Kennedy Space Center in Florida. At KSC, the four booster segments are assembled into a completed booster rocket. The joints where the segments are joined together at KSC are known as field joints (See Figure 1). These field joints consist of a tang and clevis joint. The tang and clevis are held together by 177 clevis pins. Each joint is sealed by two O rings, the bottom ring known as the primary O-ring, and the top known as the secondary O-ring. (The Titan booster had only one O-ring. The second ring was added as a measure of redundancy since the boosters would be lifting humans into orbit. Except for the increased scale of the rocket's diameter, this was the only major difference between the shuttle booster and the Titan booster.) The purpose of the O-rings is to prevent hot combustion gasses from escaping from the inside of the motor. To provide a barrier between the rubber O-rings and the combustion gasses, a heat resistant putty is applied to the inner section of the joint prior to assembly. The gap between the tang and the clevis determines the amount of compression on the O-ring. To minimize the gap and increase the squeeze on the O-ring, shims are inserted between the tang and the outside leg of the clevis. Launch Delays The first delay of the Challenger mission was because of a weather front expected to move into the area, bringing rain and cold temperatures. Usually a mission wasn't postponed until inclement weather actually entered the area, but the Vice President was expected to be present for the launch and NASA officials wanted to avoid the necessity of the Vice President's having to make an unnecessary trip to Florida; so they postponed the launch early. The Vice President was a key spokesperson for the President on the space program, and NASA coveted his good will. The weather front stalled, and the launch window had perfect weather conditions; but the launch had already been postponed to keep the Vice President from unnecessarily traveling to the launch site. The second launch delay was caused by a defective micro switch in the hatch locking mechanism and by problems in