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the Columbia Accident

The The Space Shuttle Columbia disaster was the disintegration of the Space Shuttle Columbia over Texas on February 1, 2003, during re-entry into the Earth's atmosphere on its 28th mission, STS-107. The entire seven-member crew died.

The loss of the Columbia was caused by damage sustained during launch when most of the left bipod foam ramp (see below) broke off the main propellant tank under the aerodynamic forces of launch and struck the orbiter's left wing leading edge. A thermal protection system (TPS) panel on the wing was damaged, which allowed the hot gasses of re-entry to penetrate and weaken the wing structure, ultimately causing it to fail. The vehicle became uncontrollable and was destroyed by the extreme heat of re-entry.

Some engineers suspected damage to the thermal protection, but NASA managers limited the investigation, feeling that nothing could be done even if damage was found.

U.S. manned space flights did not resume until over two years later, but the foam shedding problem continued. Despite these setbacks, the International Space Station continues to operate with a skeleton crew transported and supplied by Russian space vehicles.

There have now been two such losses of a space shuttle and crew. The first was the Challenger disaster in 1986.


The crew of STS-107 on launch day

Commander: Rick D. Husband, a US Air Force colonel and mechanical engineer, who piloted a previous shuttle during the first docking with the International Space Station.
Pilot: William C. McCool, a US Navy commander
Payload Commander: Michael P. Anderson, a US Air Force lieutenant colonel and physicist who was in charge of the science mission.
Payload Specialist: Ilan Ramon, a colonel in the Israeli Air Force and the first Israeli astronaut.
Mission Specialist: Kalpana Chawla, an Indian-born aerospace engineer on her second space mission.
Mission Specialist: David M. Brown, a US Navy captain trained as an aviator and flight surgeon. Brown worked on a number of scientific experiments.
Mission Specialist: Laurel Clark, a US Navy captain and flight surgeon. Clark worked on a number of biological experiments.

Debris strike during launch

Close-up of the Left Bipod Foam Ramp that broke off and damaged the Shuttle wing.

STS-107 had been delayed 18 times over the course of two years (despite its designation as the 107th mission, it was actually the 113th mission launched) from its original launch date of 11 January 2001 to its actual launch date of 16 January 2003. A well-publicized launch delay due to cracks in the shuttle's propellant distribution system occurred one month before a 19 July 2002 launch date, but the Columbia Accident Investigation Board (CAIB) determined that this delay had nothing to do with the catastrophic failure six months later.

Columbia lifting off on its final mission. The light-coloured triangle visible at the base of the strut is the Left Bipod Foam Ramp.

The Left Bipod Foam Ramp is an approximately three-foot (one-metre) piece made entirely out of foam, as opposed to being a metal ramp that is merely coated with foam. As such, the foam, not normally considered to be a structural material, is required to bear some aerodynamic loads. Because of these special requirements, the casting-in-place and curing of the ramps may be performed only by a senior technician. Apparently, even the best technical servicing available could not compensate for this fatal design flaw.

Bipod Foam Ramps had fallen off on at least three previous Shuttle flights, with at least one previous Shuttle strike but no serious damage. The euphemism used by NASA management to refer to this phenomenon was "foam shedding." As with the O-ring erosions that ultimately doomed the Challenger Shuttle, NASA management seemed to grow complacent and accustomed to these phenomena when no serious consequences resulted from these earlier episodes.

Video taken during lift-off was routinely reviewed two hours after the launch and revealed nothing unusual. The following day, higher-resolution film that had been processed overnight revealed that a piece of insulation foam fell from the external fuel tank 81.9 seconds after launch and appeared to strike the shuttle's left wing, potentially damaging the thermal protection on the Space Shuttle. The exact location where the foam struck the wing could not be determined due to the low resolution of the tracking camera footage.

Launch to Landing

In a risk-management scenario similar to the Challenger disaster, NASA management failed to recognize the relevance of engineering concerns for safety. Two examples of this were failure to honour engineer requests for imaging to inspect possible damage, and failure to respond to engineer requests about status of astronaut inspection of the left wing.

Engineering made three separate requests for Department of Defence (DOD) imaging of the shuttle in orbit to more precisely determine damage. While the images were not guaranteed to show the damage, the capability existed for imaging of sufficient resolution to provide meaningful examination. In fact the Columbia Accident Investigation Board (CAIB) recommended subsequent shuttle flights be imaged while on orbit using ground-based or space-based Department of Defence assets [1]. NASA management did not honour the requests and in some cases intervened to stop DOD from assisting.

NASA's chief thermal protection system (TPS) engineer was concerned about left wing TPS damage and asked NASA management whether an astronaut would visually inspect it. NASA managers never responded.

Throughout the risk assessment process, senior NASA managers were influenced by their belief nothing could be done even if damage was detected, hence this affected their stance on investigation urgency, thoroughness and possible contingency actions. They decided to conduct a parametric "what-if" scenario study more suited to determine risk probabilities of future events, instead of inspecting and assessing the actual damage.

Much of the risk assessment hinged on damage predictions to the thermal protection system. These fall into two categories: damage to the silica tile on the wing lower surface, and damage to the reinforced carbon/carbon leading edge panels.

Boeing-developed damage prediction software was used to evaluate possible tile and reinforced carbon/carbon (RCC) damage. The software predicted severe penetration of multiple tiles by the impact, but Boeing engineers downplayed this. They believed that results showing that the software overstated damage from small projectiles meant that the same would be true of larger foam (SOFI) impacts. The program used to predict RCC damage was based on small ice impacts, not larger SOFI impacts. Under 1 of 15 predicted SOFI impact paths, the software predicted an ice impact would completely penetrate the RCC panel. Engineers downplayed this, too, believing that impacts of the less dense SOFI material would result in less damage than ice impacts. In an e-mail exchange, NASA managers questioned whether the density of the SOFI could be used as justification for reducing predicted damage. Despite engineering concerns about the energy imparted by the SOFI material, NASA managers ultimately accepted the rational to reduce predicted damage of the RCC panels from complete penetration to slight damage to the panel's thin coating.

NASA managers assumed a rescue or repair was impossible, so there was no point in trying to inspect the vehicle for damage while on orbit. However the CAIB determined either a rescue mission or on-orbit repair, though risky, might have been possible had NASA verified severe damage within five days into the mission.

Ultimately the NASA Mission Management Team felt there was insufficient evidence to indicate that the strike was an unsafe situation, so they declared the debris strike a "turnaround" issue (not of highest importance) and denied the requests for the Department of Defence images.

Destruction during re-entry

At 2:30 a.m. EST on February 1, 2003, the Entry Flight Control Team began duty in the Mission Control Centre. The Flight Control Team was not working on any issues or problems related to the planned de-orbit and re-entry of Columbia. In particular, the team indicated no concerns about the debris impact to the left wing during ascent, and treated the re-entry like any other. The team worked through the de-orbit preparation checklist and re-entry checklist procedures. Weather forecasters, with the help of pilots in the Shuttle Training Aircraft, evaluated landing-site weather conditions at the Kennedy Space Centre. At the time of the de-orbit decision, about 20 minutes before the initiation of the de-orbit burn, all weather observations and forecasts were within guidelines set by the flight rules, and all systems were normal.

Shortly after 8:00 a.m., the Mission Control Centre Entry Flight Director polled the Mission Control room for a GO/NO-GO decision for the de-orbit burn, and at 8:10 a.m., the Capsule Communicator notified the crew they were GO for de-orbit burn.

As the Orbiter flew upside down and tail-first over the Indian Ocean at an altitude of 175 statute miles (282 km), Commander Husband and Pilot McCool executed the de-orbit burn at 8:15:30 a.m. using Columbia’s two Orbital Manoeuvring System engines. The de-orbit manoeuvre was performed on the 255th orbit, and the 2-minute, 38-second burn slowed the Orbiter from 17,500 mph (7.8 km/s) to begin its re-entry into the atmosphere. During the de-orbit burn, the crew felt about 10% of the effects of gravity. There were no problems during the burn, after which Husband manoeuvred Columbia into a right-side-up, forward-facing position, with the Orbiter’s nose pitched up.

Entry Interface, arbitrarily defined as the point at which the Orbiter enters the discernible atmosphere at 400,000 feet (120 km), occurred at 8:44:09 a.m. (Entry Interface plus 000 seconds, written EI+000) over the Pacific Ocean. As Columbia descended from space into the atmosphere, the heat produced by air molecules colliding with the Orbiter typically caused wing leading-edge temperatures to rise steadily, reaching an estimated 2,500 degrees Fahrenheit (1400 °C) during the next six minutes. As superheated air molecules discharged light, astronauts on the flight deck saw bright flashes envelop the Orbiter, a normal phenomenon.

At 8:48:39 a.m. (EI+270), a sensor on the left wing leading edge spar showed strains higher than those seen on previous Columbia re-entries. This was recorded only on the Modular Auxiliary Data System, and was not telemetered to flight controllers or displayed to the crew.

At 8:49:32 a.m. (EI+323), travelling at approximately Mach 24.5, Columbia executed a roll to the right, beginning a pre-planned banking turn to manage lift, and therefore limit the Orbiter’s rate of descent and heating.

At 8:50:53 a.m. (EI+404), travelling at Mach 24.1 and at approximately 243,000 feet (74 km), Columbia entered a 10-minute period of peak heating, during which the thermal stresses were at their maximum. By 8:52:00 a.m. (EI+471), nearly eight minutes after entering the atmosphere and some 300 miles (500 km) west of the California coastline, the wing leading-edge temperatures usually reached 2,650 degrees Fahrenheit (1450 °C). Columbia crossed the California coast west of Sacramento at 8:53:26 a.m. (EI+557). Travelling at Mach 23 and 231,600 feet (70.6 km), the Orbiter’s wing leading edge typically reached more than an estimated 2,800 degrees Fahrenheit (1540 °C).

Columbia at approximately 0857. Debris is already starting to come off from the left wing.

On crossing California, the Orbiter appeared to observers on the ground as a bright spot of light moving rapidly across the sky. Signs of debris being shed were sighted at 8:53:46 a.m. (EI+577), when the superheated air surrounding the Orbiter suddenly brightened, causing a noticeable streak in the Orbiter’s luminescent trail. Observers witnessed another four similar events during the following 23 seconds, and a bright flash just seconds after Columbia crossed from California into Nevada airspace at 8:54:25 a.m. (EI+614), when the Orbiter was travelling at Mach 22.5 and 227,400 feet (69.3 km). Witnesses observed another 18 similar events in the next four minutes as Columbia streaked over Utah, Arizona, New Mexico, and Texas.

Columbia debris (in red, orange, and yellow) detected by National Weather Service radar over Texas and Louisiana

In Mission Control, re-entry appeared normal until 8:54:24 a.m. (EI+613), when the Maintenance, Mechanical, and Crew Systems (MMACS) officer informed the Flight Director that four hydraulic sensors in the left wing were indicating “off-scale low,” a reading that falls below the minimum capability of the sensor. As the seconds passed, the Entry Team continued to discuss the four failed indicators.

At 8:55:00 a.m. (EI+651), nearly 11 minutes after Columbia had re-entered the atmosphere, wing leading-edge temperatures normally reached nearly 3,000 degrees Fahrenheit (1650 °C). At 8:55:32 a.m. (EI+683), Columbia crossed from Nevada into Utah while travelling at Mach 21.8 and 223,400 ft (68 km). Twenty seconds later, the Orbiter crossed from Utah into Arizona.

At 8:56:30 a.m. (EI+741), Columbia initiated a roll reversal, turning from right to left over Arizona. Travelling at Mach 20.9 and 219,000 feet, Columbia crossed the Arizona-New Mexico state line at 8:56:45 (EI+756), and passed just north of Albuquerque at 8:57:24 (EI+795).

Columbia debris (in red, orange, and yellow) detected by National Weather Service radar over Texas and Louisiana. Around 8:58:00 a.m. (EI+831), wing leading-edge temperatures typically decreased to 2,880 degrees Fahrenheit (1580 °C). At 8:58:20 a.m. (EI+851), travelling at 209,800 feet (64 km) and Mach 19.5, Columbia crossed from New Mexico into Texas, and about this time shed a Thermal Protection System tile, which was the most westerly piece of debris that has been recovered. Searchers found the tile in a field in Littlefield, Texas, just northwest of Lubbock. At 8:59:15 a.m. (EI+906), MMACS informed the Flight Director that pressure readings had been lost on both left main landing-gear tires. The Flight Director then told the Capsule Communicator (CAPCOM) to let the crew know that Mission Control saw the messages and was evaluating the indications, and added that the Flight Control Team did not understand the crew’s last transmission.

At 8:59:32 a.m. (EI+923), a broken response from the mission commander was recorded: “Roger, uh, bu - [cut off in mid-word] …” It was the last communication from the crew and the last telemetry signal received in Mission Control. Videos made by observers on the ground at 9:00:18 a.m. (EI+969) revealed that the Orbiter was disintegrating.

At about 9:05 (14:05 UTC), residents of north central Texas reported a loud boom, a small concussion wave and smoke trails and debris in the clear skies above the counties southeast of Dallas. More than 2,000 debris fields, as well as human remains, were found in sparsely populated areas southeast of Dallas from Nacogdoches in East Texas, where a lot of debris fell, to western Louisiana and the south-western counties of Arkansas. This debris included live C. elegans worms from a science package that survived the re-entry. NASA issued warnings to the public that any debris could contain hazardous chemicals, that it should be left untouched, its location reported to local emergency services, or government authorities and that anyone in unauthorized possession of debris would be prosecuted.

Shortly after being told of reports of pieces of the shuttle being seen to break away, the NASA flight director declared a contingency (events leading to loss of the vehicle) and alerted search and rescue teams in the area. He told the ground controller to "lock the doors", which is the code phrase that a contingency is in effect, nobody can enter or leave the room, and flight controllers should preserve all the mission data for later investigation.

Initial investigation

NASA Space Shuttle Program Manager Ron Dittemore reported that "The first indication was loss of temperature sensors and hydraulic systems on the left wing. They were followed seconds and minutes later by several other problems, including loss of tire pressure indications on the left main gear and then indications of excessive structural heating". Analysis of 31 seconds of telemetry data which had initially been filtered out because of data corruption within it showed the shuttle fighting to maintain its orientation, eventually using maximum thrust from its reaction control system jets.

The focus of the investigation centred on the foam strike from the very beginning. Incidents of debris strikes from ice and foam causing damage during take-off were already well known, and had actually damaged orbiters, most noticeably during STS-45, STS-27, and STS-87 [8]. Tile damage had also been traced to ablative insulating material from the solid rocket motors in the past. The composition of the foam insulation had been changed in 1997 to exclude the use of Freon, a chemical that causes ozone depletion; while NASA was exempted from legislation phasing out CFCs, the agency chose to change the foam nonetheless. This led to many statements linking the foam strike to environmental pressures. STS-107 used an older "lightweight tank" where the foam was sprayed on to the larger cylindrical surfaces using the newer no freon foam. However the bipods were manufacture red from BX-250 foam which was excluded from the EPA regulations and did use the original Freon formula. The composition change did not contribute to the accident.

Was rescue or repair possible?

Had NASA management acted in time, two possible contingency procedures were available: A rescue mission by shuttle Atlantis, and an emergency spacewalk to attempt repairs to the left wing thermal protection.

The CAIB determined a rescue mission, though risky, might have been possible provided NASA management took action soon enough.

Normally a rescue mission isn't possible, due to the time required to prepare a shuttle for launch, and the limited consumables (power, water, air) of an orbiting shuttle. However in this case Atlantis was well along in processing for a March 1 launch. Also Columbia carried an unusually large quantity of consumables due to an Extended Duration Orbiter (EDO) package. This would have allowed Columbia to stay in orbit until flight day 30 (February 15). NASA investigators determined that Atlantis processing could have been expedited with no skipped safety checks for a February 10 launch. Hence if nothing went wrong there was a five day overlap for a possible rescue.

NASA investigators determined on-orbit repair by the shuttle astronauts was possible but risky, primarily due to the uncertain resiliency of the repair using available materials.

Columbia did not carry the Remote Manipulator System which would normally be used for camera inspection or transporting a spacewalking astronaut to the wing. Therefore an unusual emergency EVA would have been required. While there was no astronaut EVA training for manoeuvring to the wing, astronauts are always prepared for a similarly difficult emergency EVA – to close the external tank umbilical doors located on the orbiter underside. During launch these doors are open for the propellant feed lines from the external tank to supply the main engines in the orbiter tail. If they fail to close after jettisoning the external tank, it constitutes a thermal protection breach which would destroy the orbiter upon re-entry. This requires an emergency EVA to close them manually. Similar methods could have reached the shuttle left wing for inspection or repair.

For the repair, astronauts would have to use tools and small pieces of titanium, or other metal, scavenged from the crew cabin. These heavy metals would help protect the wing structure and would be held in place during re-entry by a water-filled bag that had turned into ice in the cold of space. The ice and metal would help restore wing leading edge geometry, preventing a turbulent airflow over the wing and therefore keeping heating and burn-through levels low enough for the crew to survive re-entry and bail out before landing. Because the NASA team could not verify that the repairs would survive even a modified re-entry, the rescue option had a considerably higher chance of bringing Columbia's crew back alive.

The Columbia Accident Investigation Board

Following protocols established after the loss of Challenger, an independent investigating board was created immediately following the accident. The Columbia Accident Investigation Board, or CAIB, consisted of expert military and civilian analysts who investigated the accident in great detail.

Columbia's flight data recorder was found near Hemphill, Texas on March 20, 2003. Unlike commercial jet aircraft, the space shuttles do not have flight data recorders intended for after crash analysis. Rather the vehicle data is transmitted in real time to the ground via telemetry. However since Columbia was the first shuttle, it had a special flight data OEX (Orbiter Experiments) recorder, designed to help engineers better understand vehicle performance during the first test flights. Even after these were completed, the recorder was never removed from Columbia, and was still functioning. It records many hundreds of different parameters and contained very extensive logs of structural and other data which allowed the CAIB to reconstruct many of the events during the process leading to break-up. Investigators could often use the loss of signals from sensors on the wing to track how the damage progressed. This was correlated with analysis of debris and tests to obtain a final conclusion about the probable events.

On July 7, 2003 foam impact tests were performed by Southwest Research Institute, which used a foam block of similar size, mass and speed to that which struck Columbia, and it created a hole 41 cm by 42.5 cm (16.1 inches by 16.7 inches) in the protective RCC panel. The tests clearly demonstrated that a foam impact of the type Columbia sustained could seriously breach the protective RCC panels on the wing leading edge.

On August 26, the CAIB issued its report on the accident. The report confirmed the immediate cause of the accident was a breach in the leading edge of the left wing, caused by insulating foam shed during launch. The report also delved deeply into the underlying organizational and cultural issues that led to the accident. The report was highly critical of NASA's decision-making and risk-assessment processes. It concluded the organizational structure and processes were sufficiently flawed that compromise of safety was expected no matter who was in the key decision-making positions. An example was the position of Shuttle Program Manager, where one individual was responsible for achieving safety, timely launches and acceptable costs, which are often conflicting goals. The CAIB report found that NASA had accepted deviations from design criteria as normal when they happened on several flights and did not lead to fatal consequences. One of those was the conflict between a design specification stating the thermal protection system was not designed to withstand significant impact damage and the common occurrence of impact damage to it during flight. The board made recommendations for significant changes in processes and culture.

In late July 2003, an Associated Press poll revealed that Americans' support for the space program remained strong, despite the tragedy. Two-thirds believed the space shuttle should continue to fly and nearly three-quarters said that the space program was a good investment. On the question of sending humans to Mars, 49% thought it was a good idea, while 42% opposed it. Support slipped for sending civilians like teachers into space with 56% supporting the idea and 38% opposed.

Grid on the floor of the Reusable Launch Vehicle (RLV) Hangar where workers in the field bring in pieces of Columbia's debris. The Columbia Reconstruction Project Team attempted to reconstruct the bottom of the orbiter as part of the investigation into the accident.