PART ONE: THE ACCIDENT

¶Chapter 1 relates the history of the Space Shuttle Program before the Challenger accident. With the end looming for the Apollo moon exploration program, NASA unsuccess- fully attempted to get approval for an equally ambitious (and expensive) space exploration program. Most of the proposed programs started with space stations in low-Earth orbit and included a reliable, economical, medium-lift vehicle to travel safely to and from low-Earth orbit. After many failed attempts, and finally agreeing to what would be untenable compromises, NASA gained approval from the Nixon Administration to develop, on a fixed budget, only the transport vehicle. Because the Administration did not approve a low-Earth-orbit station, NASA had to create a mission for the vehicle. To satisfy the Administrationʼs requirement that the system be economically justifiable, the vehicle had to capture essentially all space launch business, and to do that, it had to meet wide-ranging requirements. These

¶sometimes-competing requirements resulted in a compromise vehicle that was less than optimal for manned flights. NASA designed and developed a remarkably capable and resilient vehicle, consisting of an Orbiter with three Main Engines, two Solid Rocket Boosters, and an External Tank, but one that has never met any of its original requirements for reliability, cost, ease of turnaround, maintainability, or, regrettably, safety.

¶Chapter 2 documents the final flight of Columbia. As a straightforward record of the event, it contains no findings or recommendations. Designated STS-107, this was the Space Shuttle Programʼs 113th flight and Columbiaʼs 28th. The flight was close to trouble-free. Unfortunately, there were no indications to either the crew onboard Columbia or to engineers in Mission Control that the mission was in trouble as a result of a foam strike during ascent. Mission management failed to detect weak signals that the Orbiter was in trouble and take corrective action.

¶Columbia was the first space-rated Orbiter. It made the Space Shuttle Programʼs first four orbital test flights. Because it was the first of its kind, Columbia differed slightly from Orbiters Challenger, Discovery, Atlantis, and Endeavour. Built to an earlier engineering standard, Columbia was slightly heavier, and, although it could reach the high-inclination orbit of the International Space Station, its payload was insufficient to make Columbia cost-effective for Space Station missions. Therefore, Columbia was not equipped with a Space Station docking system, which freed up space in the payload bay for longer cargos, such as the science modules Spacelab and SPACEHAB. Consequently, Columbia generally flew science missions and serviced the Hubble Space Telescope.

¶STS-107 was an intense science mission that required the seven-member crew to form two teams, enabling round- the-clock shifts. Because the extensive science cargo and its extra power sources required additional checkout time, the launch sequence and countdown were about 24 hours longer than normal. Nevertheless, the countdown proceeded as planned, and Columbia was launched from Launch Complex 39-A on January 16, 2003, at 10:39 a.m. Eastern Standard Time (EST).

¶At 81.7 seconds after launch, when the Shuttle was at about 65,600 feet and traveling at Mach 2.46 (1,650 mph), a large piece of hand-crafted insulating foam came off an area where the Orbiter attaches to the External Tank. At 81.9 seconds, it struck the leading edge of Columbiaʼs left wing. This event was not detected by the crew on board or seen by ground support teams until the next day, during detailed reviews of all launch camera photography and videos. This foam strike had no apparent effect on the daily conduct of the 16-day mission, which met all its objectives.

¶The de-orbit burn to slow Columbia down for re-entry into Earthʼs atmosphere was normal, and the flight profile throughout re-entry was standard. Time during re-entry is measured in seconds from "Entry Interface," an arbitrarily determined altitude of 400,000 feet where the Orbiter begins to experience the effects of Earthʼs atmosphere. Entry Interface for STS-107 occurred at 8:44:09 a.m. on February 1. Unknown to the crew or ground personnel, because the data is recorded and stored in the Orbiter instead of being transmitted to Mission Control at Johnson Space Center, the first abnormal indication occurred 270 seconds after Entry Interface. Chapter 2 reconstructs in detail the events leading to the loss of Columbia and her crew, and refers to more details in the appendices.

¶In Chapter 3, the Board analyzes all the information available to conclude that the direct, physical action that initiated the chain of events leading to the loss of Columbia and her crew was the foam strike during ascent. This chapter reviews five analytical paths – aerodynamic, thermodynamic, sensor data timeline, debris reconstruction, and imaging evidence – to show that all five independently arrive at the same conclusion. The subsequent impact testing conducted by the Board is also discussed.

¶That conclusion is that Columbia re-entered Earthʼs atmosphere with a pre-existing breach in the leading edge of its left wing in the vicinity of Reinforced Carbon-Carbon (RCC) panel 8. This breach, caused by the foam strike on ascent, was of sufficient size to allow superheated air (probably exceeding 5,000 degrees Fahrenheit) to penetrate the cavity behind the RCC panel. The breach widened, destroying the insulation protecting the wingʼs leading edge support structure, and the superheated air eventually melted the thin aluminum wing spar. Once in the interior, the superheated air began to destroy the left wing. This destructive process was carefully reconstructed from the recordings of hundreds of sensors inside the wing, and from analyses of the reactions of the flight control systems to the changes in aerodynamic forces.

¶By the time Columbia passed over the coast of California in the pre-dawn hours of February 1, at Entry Interface plus 555 seconds, amateur videos show that pieces of the Orbiter were shedding. The Orbiter was captured on videotape during most of its quick transit over the Western United States. The Board correlated the events seen in these videos to sensor readings recorded during re-entry. Analysis indicates that the Orbiter continued to fly its pre-planned flight profile, although, still unknown to anyone on the ground or aboard Columbia, her control systems were working furi- ously to maintain that flight profile. Finally, over Texas, just southwest of Dallas-Fort Worth, the increasing aerodynamic forces the Orbiter experienced in the denser levels of the atmosphere overcame the catastrophically damaged left wing, causing the Orbiter to fall out of control at speeds in excess of 10,000 mph.

¶The chapter details the recovery of about 38 percent of the Orbiter (some 84,000 pieces) and the reconstruction and analysis of this debris. It presents findings and recommendations to make future Space Shuttle operations safer.

¶Chapter 4 describes the investigation into other possible physical factors that may have contributed to the accident. The chapter opens with the methodology of the fault tree

¶analysis, which is an engineering tool for identifying every conceivable fault, then determining whether that fault could have caused the system in question to fail. In all, more than 3,000 individual elements in the Columbia accident fault tree were examined.

¶In addition, the Board analyzed the more plausible fault scenarios, including the impact of space weather, collisions with micrometeoroids or "space junk," willful damage, flight crew performance, and failure of some critical Shuttle hardware. The Board concludes in Chapter 4 that despite certain fault tree exceptions left "open" because they cannot be conclusively disproved, none of these factors caused or contributed to the accident. This chapter also contains findings and recommendations to make Space Shuttle operations safer.