The winged orbiter, the best-known symbol of the nation's space program, is built by Rockwell International Inc. in Palmdale, Calif., 60 miles north of Los Angeles.
The twin rocket boosters, consisting of a solid fuel booster atop a small engine, come from Brigham, Utah, and are manufactured by Morton-Thiokol Inc.
The third element, the external fuel tank, is the large brown backdrop to the white orbiter and powers the shuttle after the boosters' fuel is consumed. It comes from Michoud, La., and is made by Martin Marietta Corp.
All three are shipped to the Kennedy Space Center for final assembly before launch. The tank and rocket boosters represent less than one-twentieth of the shuttle's total cost of between $1.1 billion and $1.3 billion.
''A good rule of thumb is about $1 billion for just the winged orbiter,'' said Marc Vaucher, a space analyst with the Center for Space Policy, a private Cambridge, Mass., consulting company. ''It's very difficult to replace one of those.''
Spokesmen for Martin Marietta and Morton-Thiokol said there had been no earlier problems with their fuel systems.
Rockwell built the first shuttle in 1976, the now-retired Enterprise, and the other four -- Columbia in 1979, Challenger in 1982, Discovery in 1983 and Atlantis last summer.
Although three companies build the most visible parts of the shuttle, thousands of individual companies are subcontractors.
Vaucher focused early speculation on the external fuel tank as the cause of the explosion. The $20 million tank is used only once. Its 385,265 gallons of liquid hydrogen, and 143,351 gallons of liquid oxygen are spent in the first eight minutes of launch, and then the tank is jettisoned over the Indian Ocean.
The twin fuels are highly volatile and are kept in two separate tanks, with the smaller liquid oxygen tank on top. Lines feed the fuels to the shuttle's three main engines, which are built by the Rocketdyne division of Rockwell. The oxygen, cooled to-297 degrees Fahrenheit, and the hydrogen, cooled to -423 degrees, are added at Kennedy Space Center.
''It's two individual tanks inside a bigger one,'' Vaucher said. ''It's a flying bomb. When you put them together, they almost always ignite.''
Propelling the shuttle into its first moments of orbit are the twin solid rocket boosters, which use a plastics-based fuel that has the consistency of a ''gray ink eraser,'' said Morton-Thiokol spokesman Rocky Raab.
Each 12 feet in diameter and 138 feet long, the two boosters provide ''80 to 85 percent of thrust for the first two minutes,'' Raab said. They cost about $25 million a pair, he said.
The used boosters are recovered by ship about 120 to 130 miles out into the Atlantic Ocean, Raab said. The parts are broken down and then mixed together for use in future shuttle missions.
Burning at 6,000 degrees Fahrenheit, the boosters and external tank fuel provide enough thrust to lift the shuttle into orbit, although the spacecraft uses its own engines for precise steering in the final pre-orbit moments.
The external tank is made of several materials, including aluminum, titanium and steel. ''The brown color that you see is an insulation,'' said Art Koski, spokesman for Martin Marietta's Denver Aerospace operations, which oversees all space business for the company.
Last October, Martin broke out its external tank group into the Michoud Aerospace division, which employs about 5,000 people in the New Orleans area. Evan McCollum, a company spokesman who saw the launch, said Martin Marietta had delivered 34 fuel tanks up until Tuesday's launch. The company has had the business since 1973, McCollum said, though the most recent contract, for $390 million, dates back only to mid-1984.