Challenger

Challenger was one of five National Aeronautics and Space Administration (NASA) space shuttle orbiters to fly in space, and the only shuttle as of 2002 lost in an accident. The shuttle was named after a nineteenth-century naval vessel that explored the Atlantic and Pacific Oceans. The orbiter flew in space nine times between 1983 and 1985 on a number of missions. On its tenth flight, STS-51-L on January 28, 1986, a problem with a solid rocket booster led to an explosion that destroyed Challenger and killed its seven crewmembers. The disaster and resulting investigation grounded the shuttle fleet for more than two and a half years, and led to a number of safety improvements to the shuttle fleet.

Early History

Challenger's development began in the mid-1970s as a structural test article. The vehicle was not originally planned to fly in space, but instead was meant to allow engineers to study how orbiters would handle the stresses of flight. During these and other tests, NASA concluded that some modifications would be needed to the structure of the shuttle. NASA had planned to refit Enterprise, a shuttle orbiter built for landing tests, to fly in space, but found it would be less expensive to modify Challenger instead. Challenger's conversion into a space-rated orbiter was completed in 1982.

Challenger entered service for NASA in April 1983 on the sixth shuttle flight and the first flight by any shuttle other than Columbia, the first shuttle to fly in space. Challenger completed nine successful flights through November 1985. A summary of those flights is listed in the accompanying table.

Mission 51-L

The tenth flight of Challenger was mission STS-51-L, scheduled for January 1986. This mission attracted considerable pre-launch attention because

CHALLENGER SHUTTLE MISSIONS
Mission	Launch	Landing	Highlights
STS-6	1983 April 4	1983 April 9	• First mission
			• Deployed TDRS-1 communications satellite
			• First spacewalk from shuttle
STS-7	1983 June 18	1983 June 24	• First flight into space by an American woman (Sally Ride)
			• Deployed Anik C-2 and Palapa-B1 communications satellites
STS-8	1983 August 30	1983 September 5	• First flight into space by an African-American (Guion Bluford Jr.)
			• Deployed Insat-1B communications and weather satellite
STS-41-B	1984 February 3	1984 February 11	• First untethered spacewalks
			• Deployed Westar-VI and Palapa-B2 communications satellites
			• First shuttle landing at Kennedy Space Center
STS-41-C	1984 April 6	1984 April 13	• Retrieved and repaired the Solar Max satellite
			• Deployed Long Duration Exposure Facility
STS-41-G	1984 October 5	1984 October 13	• Deployed Earth Radiation Budget satellite
			• First spacewalk by an American woman (Kathryn Sullivan)
STS-51-B	1985 April 29	1985 May 6	• Spacelab-3 tested materials processing and fluid mechanics in weightlessness.
STS-51-F	1985 July 29	1985 August 6	• Shuttle main engine #1 shut down 5 minutes, 45 seconds after launch, forcing "abort to orbit"
			• Spacelab-2 performed a number of astronomy and life sciences experiments
STS-61-A	1985 October 30	1985 November 6	• German Spacelab D-1 mission performed experiments on materials science, life science, and technology
			• Crew included two German and one Dutch astronauts

its seven-person crew included a civilian—Christa McAuliffe, a New Hampshire teacher who had been selected from more than 10,000 applicants to become the first teacher in space. The mission also featured the deployment of the TDRS-2 communications satellite as well as studies of Comet Halley.

The launch of Challenger on STS-51-L was originally scheduled for January 22, 1986, but postponed until January 28 because of the delayed launch of the previous shuttle mission, bad weather, and technical glitches. The morning of January 28 was very cold at Kennedy Space Center in Florida, with temperatures well below freezing. The launch was delayed two hours to allow ice on the launch pad to melt as well as to fix an unrelated technical problem. Challenger finally lifted off at 11:38 A.M. Eastern Standard Time. The launch appeared to be flawless until an explosion took place 73 seconds after liftoff, destroying the shuttle and its external fuel tank, and raining debris over the Atlantic Ocean. The two solid rocket boosters (SRBs) attached to the external tank flew free from the explosion for several seconds before launch controllers issued self-destruct commands to prevent them from crashing into populated areas. Challenger and its seven astronauts were lost in the accident, the worst in the history of the space program.

In February 1986 U.S. President Ronald Reagan established a presidential commission to investigate the disaster and recommend changes to prevent such occurrences from happening again. The commission was led by William Rogers, former secretary of state, and included a number of past and present astronauts, engineers, and scientists. The commission concluded that the disaster was caused by the failure of a rubber O-ring in a joint in one of the SRBs. The O-ring was designed to act as a seal and prevent hot gases from escaping, but the O-ring lost its flexibility in the cold temperatures the night before launch and failed to fit properly, allowing hot gases to escape. The hot gases formed a plume that, 72 seconds after launch, caused a strut connecting the SRB to the external tank to fail. A second later, this led to the structural failure of the external tank, igniting the liquid hydrogen and oxygen it carried into a fireball. The fireball itself did not cause the destruction of Challenger; instead, severe aerodynamic loads created by the external tank explosion broke the shuttle apart.

The commission recommended a number of changes to the shuttle program to improve the safety of future launches. First and foremost, the SRBs were redesigned with improved joints to prevent hot gas from leaking from them during a launch. Other improvements were made to the shuttle's main engines and brakes, and an escape system was installed that would allow astronauts to leave the shuttle while in flight in some cases. NASA also changed how it managed the shuttle program, and improved communications between engineers and managers.

The Challenger disaster grounded the shuttle fleet for more than two and a half years while the required improvements were made to the remaining orbiters. The shuttle program returned to flight with the launch of Discovery on mission STS-26 on September 29, 1988.

SEE ALSO CHALLENGER 7 (VOLUME 3); HISTORY OF HUMANS IN SPACE (VOLUME 3); HUMAN SPACEFLIGHT PROGRAM (VOLUME 1); SOLID ROCKET BOOSTERS (VOLUME 3); SPACE SHUTTLE (VOLUME 3); TEACHER IN SPACE PROGRAM (VOLUME 3); WOMEN IN SPACE (VOLUME 3).

Jeff Foust

Bibliography

Jenkins, Dennis. Space Shuttle: The History of Developing the National Space Transportation System. Indian Harbour Beach, FL: Jenkins, 1996.

Vaughan, Diane. The Challenger Launch Decision. Chicago: University of Chicago Press, 1996.

Internet Resources

NASA Kennedy Space Center. "51-L Shuttle Mission." <http://www-pao.ksc.nasa.gov/kscpao/shuttle/missions/51-l/mission-51-l.html>.

Wade, Mark. "STS-51-L." <http://www.astronautix.com/details/sts51l.htm>.