This Friday, January 28, is the twenty-fifth anniversary of the shuttle orbiter Challenger which broke up 73 seconds after liftoff, bringing a devastating end to the spacecraft’s tenth mission. The disaster claimed the lives of all seven astronauts aboard, including Christa McAuliffe, a teacher from New Hampshire who had been selected to join the mission and teach lessons from space to schoolchildren around the country. It was later determined that two rubber O-rings, which had been designed to separate the sections of the rocket booster, had failed due to cold temperatures on the morning of the launch. The tragedy and its aftermath received extensive media coverage and prompted NASA to temporarily suspend all shuttle missions.
The primary goal of the shuttle orbiter Challenger was to launch the second Tracking and Data Relay Satellite. It also carried the Spartan Halley spacecraft, a small satellite that was to be released by Challenger and picked up two days later after observing Halley’s Comet during its closest approach to the Sun.
Greatest visibility among the crew went to teacher-in-space Christa McAuliffe of Concord, N.H., the winner of a national screening begun in 1984. McAuliffe was to conduct at least two lessons from orbit and then spend the following nine months lecturing students across the United States. The goal was to highlight the importance of teachers and to interest students in high-tech careers. Other members of the crew were Commander Francis (Dick) Scobee, pilot Michael Smith, mission specialists Ellison Onizuka, Judith Resnik, Ronald McNair, and Hughes Aircraft engineer Gregory Jarvis.
The original launch was postponed for several days, partly because of delays in getting the previous shuttle mission back on the ground. On the night before the launch, central Florida was swept by a severe cold wave that deposited thick ice on the launch pad. On launch day, January 28, liftoff was delayed until 11:38 AM. All appeared to be normal until after the vehicle emerged from “Max-Q,” the period of greatest aerodynamic pressure. Mission Control told Scobee, “Challenger, go with throttle up,” and seconds later the vehicle disappeared in an explosion just 73 seconds after liftoff, at an altitude of 14,000 meters (46,000 feet). Tapes salvaged from the wreckage showed that the instant before breakup Smith said “Uh-oh,” but nothing else was heard. Debris rained into the Atlantic Ocean for more than an hour after the explosion; searches revealed no sign of the crew.
The incident immediately grounded the shuttle program. An investigation by the national Aeronautics and Space Administration (NASA) and a commission appointed by U.S. President Ronald Reagan and chaired by former secretary of state William Rogers followed. Other members of the commission included astronauts Neil Armstrong and Sally Ride, test pilot Chuck Yeager, and physicist Richard Feynman. What emerged was an appalling pattern of assumptions that the vehicle could survive minor mishaps and be pushed even further. The ill-fated launch brought to the floor the difficulties that NASA had been experiencing for many years in trying to accomplish too much with too little money.
The immediate cause of the accident was suspected within days and was fully established within a few weeks. The severe cold reduced the resiliency of two rubber O-rings that sealed the joint between the two lower segments of the right-hand solid rocket booster. Under normal circumstances, when the shuttle’s three main engines ignited, they pressed the whole vehicle forward, and the boosters were ignited when the vehicle swung back to centre. On the morning of the accident, an effect called “joint rotation” occurred, which prevented the rings from resealing and opened a path for hot exhaust gas to escape from inside the booster. Puffs of black smoke appeared on the far side of the booster in a spot not visible to most cameras.
As the vehicle ascended, the leak expanded, and after 59 seconds a 2.4-meter (8-foot) stream of flame emerged from the hole. This grew to 12 meters (40 feet) and gradually eroded one of three struts that secured the booster’s base to the large external tank carrying liquid hydrogen and liquid oxygen for the orbiter engines. At the same time, thrust in the booster lagged slightly, although within limits, and the nozzle steering systems tried to compensate. When the strut broke, the booster’s base swiveled outward, forcing its nose through the top of the external fuel tank and causing the whole tank to collapse and explode.
The Challenger broke up in the explosion, but the forward section with the crew cabin was severed in one piece. It continued to coast upward with other debris, including wings and still-flaming engines, and then plummeted to the ocean. It was believed that the crew survived the initial break up, but the loss of cabin pressure rendered them unconscious within seconds since they were not wearing pressure suits. Death probably resulted from oxygen deficiency minutes before impact.
The Rogers Commission report, delivered on June 6 to the president, faulted NASA as a whole, and its Marshall Space Flight Center in Huntsville, Ala., and contractor Morton Thiokol, Inc., in Ogden, Utah, in particular, for poor engineering and management. Marshall was responsible for the shuttle boosters, engines, and tank, while Morton Thiokol manufactured the booster motors and assembled them at the Kennedy Space Center at Cape Canaveral, Fla.
