Challenger being prepared in 1985 for its second-to-last flight STS-61-A
Because of the low production of orbiters, the Space Shuttle program decided to build a vehicle as a Structural Test Article, STA-099, that could later be converted to a flight vehicle. The contract for STA-099 was awarded to North American Rockwell on July 26, 1972, and its construction was completed in February 1978. After STA-099's rollout, it was sent to a Lockheed test site in Palmdale, where it spent over 11 months in vibration tests designed to simulate entire shuttle flights, from launch to landing. In order to prevent damage during structural testing, qualification tests were performed to a factor of safety of 1.2 times the design limit loads. The qualification tests were used to validate computational models, and compliance with the required 1.4 factor of safety was shown by analysis. STA-099 was essentially a complete airframe of a Space Shuttle orbiter, with only a mockup crew module installed and thermal insulation placed on its forward fuselage.
NASA planned to refit the prototype orbiter Enterprise (OV-101), used for flight testing, as the second operational orbiter, but design changes made during construction of the first orbiter, Columbia (OV-102), would have required extensive work. Because STA-099's qualification testing prevented damage, NASA found that rebuilding STA-099 as OV-099 would be less expensive than refitting Enterprise. Work on converting STA-099 into Challenger began in January 1979, starting with just the crew module (the pressurized portion of the vehicle) as the rest of the orbiter was still used by Lockheed. STA-099 returned to the Rockwell plant in November 1979, and the original unfinished crew module was replaced with the newly constructed model. Major portions of STA-099, including the payload bay doors, body flap, wings and vertical stabilizer, also had to be returned to their individual subcontractors for rework. By early 1981, most of these components had returned to Palmdale and were reinstalled on the orbiter. Work continued on the conversion until July 1982.
Challenger (and the orbiters built after it) had fewer tiles in its Thermal Protection System than Columbia, though it still made heavy use of the white LRSI tiles on the cabin and main fuselage compared to the later orbiters. Most of the tiles on the payload bay doors, upper wing surfaces, and rear fuselage surfaces were replaced with DuPont white Nomex felt insulation. These modifications as well as an overall lighter structure allowed Challenger to carry 2,500 lb (1,100 kg) more payload than Columbia.Challenger's fuselage and wings were also stronger than Columbia's despite being lighter. The hatch and vertical stabilizer tile patterns were also different from that of the other orbiters. Challenger was also the first orbiter to have a head-up display system for use in the descent phase of a mission, and the first to feature Phase I main engines rated for 104% maximum thrust.
Challenger broke apart during launch in 1986, killing all crew on board.
After its first flight in April 1983, Challenger quickly became the workhorse of NASA's Space Shuttle fleet, flying far more missions per year than Columbia. In 1983 and 1984, Challenger flew on 85% of all Space Shuttle missions. Even when the orbiters Discovery and Atlantis joined the fleet, Challenger flew three missions a year from 1983 to 1985. Challenger, along with Discovery, was modified at Kennedy Space Center to be able to carry the Centaur-G upper stage in its payload bay. If flight STS-51-L had been successful, Challenger's next mission would have been the deployment of the Ulysses probe with the Centaur to study the polar regions of the Sun.
Challenger flew the first American woman, African-American, and Canadian into space; three Spacelab missions; and performed the first night launch and night landing of a Space Shuttle. Challenger was also the first space shuttle to be destroyed in an accident during a mission. The collected debris of the vessel is currently buried in decommissioned missile silos at Launch Complex 31, Cape Canaveral Air Force Station. From time to time, further pieces of debris from the orbiter wash up on the Florida coast. When this happens, they are collected and transported to the silos for storage. Because of its early loss, Challenger was the only space shuttle that never wore the NASA "meatball" logo, and was never modified with the MEDS "glass cockpit". The tail was never fitted with a drag chute – it was fitted to the remaining orbiters in 1992.
Challenger's rollout from Orbiter Processing
Facility (OPF) to the Vehicle Assembly Building (VAB). Photo 1983-8-25 courtesy of NASA.
Challenger while in service as structural test article STA-099.