Space Shuttle Columbia disaster-Mobile



he Space Shuttle Columbia disaster occurred on February 1, 2003, when the Space Shuttle Columbia disintegrated over Texas during re-entry into the Earth's atmosphere, with the loss of all seven crew members, shortly before it was scheduled to conclude its 28th mission, STS-107.

The loss of Columbia was a result of damage sustained during launch when a piece of foam insulation the size of a small briefcase broke off the Space Shuttle external tank (the main propellant tank) under the aerodynamic forces of launch. The debris struck the leading edge of the left wing, damaging the Shuttle's thermal protection system (TPS), which protects it from heat generated with the atmosphere during re-entry. While Columbia was still in orbit, some engineers suspected damage, but NASA managers limited the investigation on the grounds that little could be done even if problems were found

NASA's Shuttle safety regulations stated that external tank foam shedding and subsequent debris strikes upon the Shuttle itself were safety issues that needed to be resolved before a launch was cleared, but launches were often given the go-ahead as engineers studied the foam shedding problem without a successful resolution. The majority of Shuttle launches recorded such foam strikes and thermal tile scarring in violation of safety regulations. During re-entry of STS-107, the damaged area allowed the hot gases to penetrate and destroy the internal wing structure, rapidly causing the in-flight breakup of the vehicle. A massive ground search in parts of Texas, Louisiana and Arkansas recovered crew remains and many vehicle fragments.

Mission STS-107 was the 113th Space Shuttle launch. It was delayed 18 times over the two years from its original launch date of January 11, 2001 to its actual launch date of January 16, 2003. (It was preceded by STS-113.) A launch delay due to cracks in the shuttle's propellant distribution system occurred one month before a July 19, 2002 launch date. The Columbia Accident Investigation Board (CAIB) determined that this delay had nothing to do with the catastrophic failure six months later.

The Columbia Accident Investigation Board's recommendations addressed both technical and organizational issues. Space Shuttle flight operations were delayed for two years by the disaster, similar to the Challenger disaster. Construction of the International Space Station was put on hold, and for 29 months the station relied entirely on the Russian Federal Space Agency for resupply and crew rotation until Shuttle flights resumed with STS-114.

Debris strike during launch
Approximately 82 seconds after launch, a suitcase-size piece of thermal insulation foam broke off the External Tank (ET), striking Columbia's left wing Reinforced Carbon-Carbon (RCC) panels. As demonstrated by ground experiments conducted by the Columbia Accident Investigation Board, this likely created a 6 to 10 in diameter hole, allowing hot gases to enter the wing when Columbia later reentered the atmosphere. At the time of the foam strike, the orbiter was at an altitude of about 66000 ft, traveling at Mach 2.46 (1870 mph). The foam fragment was about 1.2 lb in mass and impacted the wing at roughly 800 ft/s.

The Left Bipod Foam Ramp is an approximately three-foot (one-meter) aerodynamic component made entirely of foam, as opposed to being a metal structure 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. The shuttle's main fuel tank is covered in foam as an insulator, to avoid ice forming on it when full of liquid hydrogen and oxygen, which itself could damage the shuttle when shed during lift-off. The bipod ramp (having left and right sides) was originally designed to reduce aerodynamic stresses around the bipod attachment points at the external tank, but it was proven unnecessary in the wake of the accident and was removed from the external tank design for tanks flown after STS-107. (Another foam ramp along the liquid oxygen line was also later removed from the tank design to eliminate it as a foam debris source, after complex analysis and tests proved this change safe.)

Bipod Ramp insulation had been observed falling off, in whole or in part, on many previous flights- STS-7 (1983), STS-27 (1988), STS-32 (1990), STS-50 (1992), plus subsequent flights (STS-52 and -62) showing partial losses. In addition, Protuberance Air Load (PAL) ramp foam has also shed pieces, plus spot losses from large-area foams. At least one previous strike caused no serious damage. NASA management came to refer to this phenomenon as "foam shedding." As with the O-ring erosions that ultimately doomed the Challenger, NASA management became accustomed to these phenomena when no serious consequences resulted from these earlier episodes. This phenomenon was termed "normalization of deviance" by sociologist Diane Vaughan in her book on the Challenger launch decision process.

Video taken during lift-off of STS-107 was routinely reviewed two hours later and revealed nothing unusual. The following day, higher-resolution film that had been processed overnight revealed the foam debris striking the left wing, potentially damaging the thermal protection on the Space Shuttle. At the time, the exact location where the foam struck the wing could not be determined due to the low resolution of the tracking camera footage.

Flight risk management
In a risk-management scenario similar to the Challenger disaster, NASA management failed to recognize the relevance of engineering concerns for safety. Two examples were failures to honor engineer requests for imaging to inspect possible damage, and failure to respond to engineer requests about the status of astronaut inspection of the left wing. Engineering made three separate requests for Department of Defense (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 CAIB recommended subsequent shuttle flights be imaged while in orbit using ground-based or space-based Department of Defense assets.

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 that 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. The investigation report in particular singled out NASA manager Linda Ham for exhibiting this attitude.

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 (RCC) leading-edge panels. (The TPS includes a third category of components, thermal insulating blankets, but damage predictions are not typically performed on them. Damage assessments on the thermal blankets can be performed after an anomaly has been observed, and this has been done, at least once after the Return to Flight following Columbia's loss.)

Damage-prediction software was used to evaluate possible tile and RCC damage. The tool for predicting tile damage was known as "Crater", described by several NASA representatives in press briefings as not actually a software program but rather a statistical spreadsheet of observed past flight events and effects. The "Crater" tool predicted severe penetration of multiple tiles by the impact if it struck the TPS tile area, but NASA engineers downplayed this. The engineers believed that results showing that the model overstated damage from small projectiles meant that the same would be true of larger Spray-On Foam Insulation (SOFI) impacts. The program used to predict RCC damage was based on small ice impacts the size of cigarette butts, not larger SOFI impacts, as the ice impacts were the only recognized threats to RCC panels up to that point. 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 rationale to reduce predicted damage of the RCC panels from possible complete penetration to slight damage to the panel's thin coating.

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 Defense images.

Crew

 * 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 (STS-96).
 * 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.

Destruction during re-entry
The following is a timeline of Columbia's re-entry. The shuttle was scheduled to land at 9:16 a.m. EST.
 * 2:30 a.m. EST, Saturday, February 1, 2003 – The Entry Flight Control Team began duty in the Mission Control Center.
 * The Flight Control Team had not been working on any issues or problems related to the planned de-orbit and re-entry of Columbia. In particular, the team had 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 Center.


 * 8:00 – Mission Control Center Entry Flight Director LeRoy Cain polled the Mission Control room for a GO/NO-GO decision for the de-orbit burn.
 * All weather observations and forecasts were within guidelines set by the flight rules, and all systems were normal.


 * 8:10 – The Capsule Communicator (CAPCOM) notified the crew that they are GO for de-orbit burn.
 * 8:15:30 (EI-1719) – Commander Husband and Pilot McCool executed the de-orbit burn using Columbia’s two Orbital Maneuvering System engines.
 * The Orbiter was upside down and tail-first over the Indian Ocean at an altitude of 175 mi when the burn was executed. The de-orbit maneuver was performed on the 255th orbit, and the 2-minute, 38-second burn slowed the Orbiter from 17500 mph 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 maneuvered Columbia into a right-side-up, forward-facing position, with the Orbiter's nose pitched up.


 * 8:44:09 (EI+000) – Entry Interface (EI), arbitrarily defined as the point at which the Orbiter enters the discernible atmosphere at 400000 ft, occurred 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 2500 F during the next six minutes. (As former Space Shuttle Program Manager Wayne Hale stated in a press briefing, the majority--about 90%--of this heating is the result of compression of the atmospheric gas caused by the orbiter's supersonic flight, rather than the result of friction.)


 * 8:48:39 (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, which is similar in concept to a flight data recorder, and was not telemetered to ground controllers or displayed to the crew.


 * 8:49:32 (EI+323) – Columbia executed a pre-planned roll to the right. Speed: Mach 24.5.
 * Columbia began a banking turn to manage lift and therefore limit the Orbiter's rate of descent and heating.


 * 8:50:53 (EI+404) – Columbia entered a 10-minute period of peak heating, during which the thermal stresses were at their maximum. Speed: Mach 24.1; altitude: 243000 ft.


 * 8:52:00 (EI+471) – Columbia was approximately 300 mi west of the California coastline.
 * The wing leading-edge temperatures usually reached 2650 F at this point.


 * 8:53:26 (EI+557) – Columbia crossed the California coast west of Sacramento. Speed: Mach 23; altitude: 231600 ft.


 * The Orbiter's wing leading edge typically reached more than 2800 F at this point.


 * 8:53:46 (EI+597) – Signs of debris being shed were sighted by people out to watch. Speed: Mach 22.8; altitude: 230200 ft.
 * The superheated air surrounding the Orbiter suddenly brightened, causing a streak in the Orbiter's luminescent trail that was quite noticeable in the pre-dawn skies over the West Coast. Observers witnessed another four similar events during the following 23 seconds. Dialogue on some of the amateur footage indicates the observers were aware of the abnormality of what they were filming.


 * 8:54:24 (EI+613) – 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." In Mission Control, re-entry had been proceeding normally up to this point.
 * "Off-scale low" is a reading that falls below the minimum capability of the sensor, and it usually indicates that the sensor has faulted (stopped functioning, due to internal or external factors), rather than that the quantity it measures is actually below the sensor's minimum response value.
 * The Entry Team continued to discuss the failed indicators.


 * 8:54:25 (EI+614) – Columbia crossed from California into Nevada airspace. Speed: Mach 22.5; altitude: 227400 ft.
 * Witnesses observed a bright flash at this point and 18 similar events in the next four minutes.


 * 8:55:00 (EI+651) – Nearly 11 minutes after Columbia re-entered the atmosphere, wing leading-edge temperatures normally reached nearly 3000 F.
 * 8:55:32 (EI+683) – Columbia crossed from Nevada into Utah. Speed: Mach 21.8; altitude: 223400 ft.
 * 8:55:52 (EI+703) – Columbia crossed from Utah into Arizona.
 * 8:56:30 (EI+741) – Columbia initiated a roll reversal, turning from right to left over Arizona.
 * 8:56:45 (EI+756) – Columbia crossed from Arizona to New Mexico. Speed: Mach 20.9; altitude: 219000 ft.
 * 8:57:24 (EI+795) – Columbia crossed just north of Albuquerque.
 * 8:58:00 (EI+831) – At this point, wing leading-edge temperatures typically decreased to 2880 F.
 * 8:58:20 (EI+851) – Columbia crossed from New Mexico into Texas. Speed: Mach 19.5; altitude: 209800 ft.
 * At about this time, the Orbiter shed a Thermal Protection System tile, the most westerly piece of debris that has been recovered. Searchers found the tile in a field in Littlefield, Texas, just northwest of Lubbock.


 * 8:59:15 (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.
 * 8:59:32 (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.
 * 9:00:18 (EI+969) – Videos made by observers on the ground revealed that the Orbiter was disintegrating. In Mission Control, while the loss of signal was a cause for concern, there was no sign of any serious problem.
 * 9:05 – Residents of north central Texas reported a loud boom, a small concussion wave, smoke trails and debris in the clear skies above the counties southeast of Dallas.
 * 9:12:39 (EI+1710) – After hearing of reports of the shuttle being seen to break apart, the NASA flight director declared a contingency (events leading to loss of the vehicle) and alerted search and rescue teams in the debris area. He told the Ground Controller to "lock the doors", and two minutes later put Mission Control contingency procedures into effect. Nobody was permitted to enter or leave the room, and flight controllers had to preserve all the mission data for later investigation.

Response from the President
At 14:04 EST (19:04 UTC), President George W. Bush addressed the United States:

Recovery of debris
More than 2,000 debris fields, including human remains, were found in sparsely populated areas southeast of Dallas from Nacogdoches in East Texas, where a large amount of debris fell, to western Louisiana and the southwestern counties of Arkansas. 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. Because of the widespread area, volunteer amateur radio operators accompanied the search teams to provide communications support.

A group of small (1 mm adult) Caenorhabditis elegans worms, living in petri dishes enclosed in aluminium canisters, survived re-entry and impact with the ground and were recovered weeks after the disaster. They were part of a Biological Research in Canisters experiment designed to study the effect of weightlessness on physiology.

Debris Search Pilot Jules F. Mier Jr. and Debris Search Aviation Specialist Charles Krenek died in a helicopter crash that injured three others while they were contributing to the ground search effort.

Some Texas residents recovered some of the debris, ignoring the warnings, and attempted to sell it on the online auction site eBay, starting at $10,000. The auction was quickly removed, but auctions for Columbia merchandise such as programs, photographs and patches, went up dramatically in value immediately following the disaster, creating a surge of Columbia-related listings.

On May 9, 2008 it was reported that data from a disk drive on board Columbia survived the shuttle accident. The drive was used to store data from an experiment on the properties of shear thinning. Although part of the 340MB drive was damaged, the area that contained the data was unharmed. Because the computer using the drive on board Columbia was running a DOS filesystem, all of the data had been written to the drive in sequence; whereas a modern-day operating system might have scattered the information around the drive for performance reasons.

Onboard video
One item recovered from the debris field was a videotape recording made by the astronauts during the start of re-entry. The video recording lasts for thirteen minutes and shows the flight crew astronauts conducting routine re-entry procedures and joking with each other, none of them giving any indication of a problem. The video shows the flight-deck crew putting on their gloves and passing the video camera around in order to take footage of plasma and flames visible outside the windows of the orbiter (a completely normal occurrence), and ends approximately four minutes prior to the start of the shuttle's disintegration. On normal flights, the recording would have continued through landing. According to the online introduction given by Scott Altman, the remainder of the tape was destroyed in the accident.

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 investigation focused 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. Tile damage had also been traced to ablating insulating material from the cryogenic fuel tank in the past. The composition of the foam insulation had been changed in 1997 to exclude the use of freon, a chemical that is suspected to cause ozone depletion; while NASA was exempted from legislation phasing out CFCs, the agency chose to change the foam nonetheless. This led to many accusations of environmental pressures leading to the foam strikes. STS-107 used an older "lightweight tank" (a design that was succeeded by the "superlightweight tank", both being upgrades from the original space shuttle external tank) where the foam was sprayed on to the larger cylindrical surfaces using the newer freon-free foam. However, the bipod ramps were manufactured 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. In any case, the original formulation had shown frequent foam losses, as discussed earlier in this article.

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

Rescue
Normally a rescue mission is not possible, due to the time required to prepare a shuttle for launch, and the limited consumables (power, water, air) of an orbiting shuttle. However, Atlantis was well along in processing for a March 1 launch, and Columbia carried an unusually large quantity of consumables due to an Extended Duration Orbiter (EDO) package. The CAIB determined that 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.

Repair
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 Canadarm, or 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 maneuvering 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 could destroy the orbiter upon re-entry, requiring an emergency EVA to close them manually. Similar methods could have reached the shuttle left wing for inspection or repair.

For the repair, the CAIB determined the 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.

Columbia Accident Investigation Board
Simulation of known and possible conditions of the foam impact on Columbia's final launch, showed brittle failure of RCC.

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, Texa] 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. After the initial Shuttle test-flights were completed, the recorder was never removed from Columbia and was still functioning on the crashed flight. 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 breakup. Investigators could often use the loss of signals from sensors on the wing to track how the damage progressed. This was correlated with forensic debris analysis conducted at Lehigh University and other tests to obtain a final conclusion about the probable events.

On July 7, 2003 foam impact tests were performed by Southwest Research Institute, wich used a compressed air gun to fire a foam block of similar size and mass to that which struck Columbia and at same estimated speed. To represent the leading edge of Columbia's left wing, RCC panels from orbiter Enterprise and from NASA stock, along with fiberglass mock-up panels, were mounted to a simulating structural metal frame. Over many days, tens of these blocks of foam were shot at the wing leading edge model at various angles, aimed at different specific RCC panels, most of which produced only cracks or surface damage to the RCC. In the final round of testing, a block fired at the side of an RCC panel created a hole 41 by in the protective RCC panel

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 and 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 safe, 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 mission-compromising consequences. One of those was the conflict between a design specification stating the thermal protection system was not designed to withstand significant impacts and the common occurrence of impact damage to it during flight. The board made recommendations for significant changes in processes and organizational culture.

On December 30, 2008 NASA released a further report entitled Columbia Crew Survival Investigation Report produced by a second commission, the Spacecraft Crew Survival Integrated Investigation Team (SCSIIT). NASA had commissioned this group, "to perform a comprehensive analysis of the accident, focusing on factors and events affecting crew survival, and to develop recommendations for improving crew survival for all future human space flight vehicles." Among other conclusions the report found that, "The Columbia depressurization event occurred so rapidly that the crew members were incapacitated within seconds, before they could configure the suit for full protection from loss of cabin pressure. Although circulatory systems functioned for a brief time, the effects of the depressurization were severe enough that the crew could not have regained consciousness. This event was lethal to the crew."

Fears of terrorism
Despite some initial fears after announcement in the news that Columbia suffered explosion over Palestine, Texas and that the addition of the first Israeli astronaut to the crew had made the Columbia a more likely target for terrorists, there is no evidence to support any theory that terrorism was involved. In any case, security surrounding the launch and landing of the space shuttle had been increased to ward off any potential terrorist attack The Merritt Island launch facility, like all sensitive government areas, had increased security measures put in place in the wake of the September 11 attack. Gordon Johndroe, spokesman for the United States Department of Homeland Security, stated: "There is no information at this time that this was a terrorist incident."

Purple streak image
The San Francisco Chronicle reported that an amateur astronomer had taken a five-second exposure that appeared to show "a purplish line near the shuttle" during re-entry.