Challenger joined NASA fleet of reusable winged spaceships in July 1982. It flew nine successful Space Shuttle missions. On January 28, 1986, the Challenger and its seven-member crew were lost 73 seconds after launch when a booster failure resulted in the breakup of the vehicle.
Challenger started out as a high-fidelity structural test article (STA-099). The airframe was completed by Rockwell and delivered to Lockheed Plant 42 for structural testing on 02/04/78. The orbiter structure had evolved under such weight-saving pressure that virtually all components of the air frame were required to handle significant structural stress. With such an optimized design, it was difficult to acurately predict mechanical and thermal loading with the computer software available at the time. The only safe approach was to submit the structural test article to intensive testing and analysis. STA-099 underwent 11 months of intensive vibration testing in a 43 ton steel rig built especially for the Space Shuttle Test Program. The rig consisted of 256 hydraulic jacks, distributed over 836 load application points. Under computer control, it was possible to simulate the expected stress levels of launch, ascent, on-orbit, reentry and landing. Three 1 million pound-force hydraulic cylinders were used to simulate the thrust from the Space Shuttle Main Engines. Heating and thermal simulations were also done.
Rockwell's original $2.6 billion contract had authorized the building of a pair of static-test articles (MPTA-098 and STA-099 and two initial flight-test vehicles (OV-101 and OV-102. A decision in 1978 not to modify Enterprise from her Approach and Landing Test (ALT) configuration would have left Columbia as the only operational orbiter vehicle so on 1/29/79 NASA awarded Rockwell a supplemental contract to convert Challenger (STA-099) from a test vehicle into a space-rated Orbiter (OV-099).
STA-099 was returned to Rockwell on 11/7/79 and it's conversion into a fully rated Orbiter Vehicle was started. This conversion, while easier than it would have been to convert Enterprise, still involved a major disassembly of the vehicle. Challenger had been built with a simulated crew module and the forward fuselage halves had to be separated to gain access to the crew module. Additionally, the wings were modified and reinforced to incorporate the results of structural testing and two heads-up displays (HUD's) were installed in the cockpit. Empty Weight was 155,400 lbs at rollout and 175,111 lbs with main engines installed. This was about 2,889 pounds lighter than Columbia