For Andy Cline, the guide for the National Outdoor Leadership School (NOLS) who both worked and played with Rick Husband's crew, the morning of Saturday 1 February 2003 brought a peculiar and inexplicable sense of dread. Alone in his cabin in Wyoming, he got up early, aware that his seven friends were returning to Earth and eager to check if they had begun their descent. However, in his head, he instinctively knew that something was not quite right.

"My wife had gotten up early to go into the mountains for some work,'' he told BBC journalist Leo Enright a few months later, the emotion of that terrible day still raw in his voice, "and I was lying in bed thinking that the Columbia crew was about to land. It was one of those uncanny moments when I realised that something was... desperately wrong. I put on my clothes and started running down the path to the road. My wife was just in the process of driving back into the driveway and she told me about the [accident].''

For Evelyn Husband and her two children, on the other hand, that Saturday started with great joy as they awaited the return of their husband and father from his 16-day flight. Like the other STS-107 family members, they were at the KSC viewing site waiting to be reunited with their loved ones. At 2:05 pm GMT, with 11 minutes to go before Columbia was scheduled to touchdown on the 5-km-long runway, a photographer snapped Evelyn and her children in front of the countdown clock as it ticked away the final seconds, little realising that the Shuttle had already disintegrated . . .

For at least two other people, the awareness that something was wrong had already appeared days earlier. One was Laurel Clark's 8-year-old son Iain, who repeatedly begged his mother not to fly: he had cried on the morning of Columbia's launch and complained to her about leaving at each space-to-ground video conference. It could have been due to the near-fatal air crash that he and his parents suffered in December 2002, but to his father it was "something more than typical separation anxiety. What do kids know that we don't know? What do they see that we don't see?''

In the following months, Jon Clark would wonder if it would have been better for all three of them to have died in that air crash; perhaps then, he rationalised, his family could have remained together, the STS-107 launch would have been delayed, and the lives of the other six astronauts might have been saved. Perhaps. On the other hand, the root cause of the Columbia disaster might have remained undetected, uncorrected and would have lain in wait for another unlucky Shuttle crew . . .

Speculation had arisen immediately after launch that a briefcase-sized chunk of foam insulation had fallen from the External Tank and hit the Shuttle's left wing; film footage showed a spectacular shower of particles, although it remained unclear if these were from the foam itself or fragments of shattered tiles from Columbia's wing. If it was the latter, it did not bode well: for the Reinforced Carbon Carbon (RCC) protected her from the brunt of near-3,000-Celsius temperatures during reentry. Senior NASA managers, however, doubted that the foam could cause such severe damage to the panels and concluded it was not a 'safety-of-flight' issue.

Nonetheless, lingering doubts remained. On 31 January, in a chilling preview of what would unfold, an engineer named Kevin McCluney gave a hypothetical description to colleagues in JSC's flight control team of the kind of 'signature' they might see if a large hole had been punched through one of Columbia's tiles, allowing super-heated plasma to enter. ''Let's surmise,'' he began, ''what sort of signature we'd see if a limited stream of plasma did get into the [main landing gear] wheel well, roughly from entry interface until about 200,000 feet; in other words, a 10- or 15-minute window.

"First would be a temperature rise for the tyres, brakes, strut actuator and the uplock actuator return ..."

At 1:52:17 pm GMT on 1 February, nine minutes after entry interface - the point at which the Shuttle begins to encounter the uppermost traces of the atmosphere -Flight Director Leroy Cain and his team saw unusual data on their monitors. Cain had begun his shift that morning with ''Let's go get 'em, guys,'' before giving Husband the green light to fire Columbia's OMS engines. Most of the re-entry profile was conducted under GPC control, as was the normal procedure, but with 23 minutes to go before touchdown, Maintenance, Mechanical, Arm and Crew Systems (MMACS) officer Jeff Kling spotted something strange.

In what flight controllers refer to as an 'off-nominal' event, Kling noted that two downward-pointing arrows had appeared next to readings from a pair of sensors deep inside Columbia's left wing. They were designed to measure hydraulic fluid temperatures in lines leading back to the elevons; a few seconds later, two more sensors also failed. The attention of Kling and two other engineers was instantly riveted on the quartet, which showed all the signs of having had their wiring cut. They tried vainly to identify some common 'thread' to explain the fault.

''FYI, I've just lost four separate temperature transducers on the left side of the vehicle,'' he told the flight director. ''Hydraulic return temperatures. Two of them on system one and one in each of systems two and three.''

''Four hyd return temps?'' asked Cain.

''To the left outboard and left inboard elevon.'' Cain's thoughts were following a similar pattern to Kling's own: he wondered if there was a common root cause for the four failures to have occurred in such close proximity. When the mechanical

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Taken at 2:15 pm GMT on 1 February 2003, precisely when Columbia should have been landing in Florida, this photograph shows a tense Mission Control in Houston.

systems officer told him that there was "no commonality" between them, he was perplexed. Immediately, his thoughts returned to his own words to journalists the previous afternoon, in which he confirmed that the foam impact to Columbia's left wing during launch posed absolutely no concern for re-entry. Were these four sensor failures linked, in fact, to the foam strike?

Cain was nervous and admitted later that he thought at that moment that hot gas may have found its way through a hole in the wing and was gradually wreaking havoc on the internal sensors, cables and systems. However, upon checking with Guidance, Navigation and Control (GNC) officer Mike Sarafin, he was assured that Columbia's performance as she passed high above the California-Nevada state line at 22.5 times the speed of sound was normal. Cain checked with Kling that all other hydraulic systems were functioning normally and was assured that there were no other problems.

"... Tyre pressure would rise, given enough time, and assuming the tyre[s] don't get holed,'' continued Kevin McCluney's chilling hypothesis from a day earlier, "the data would start dropping out as the electrical wiring is severed ... ''

Suddenly, at 1:58 pm, Rick Husband made his first radio call since entry interface a quarter of an hour earlier. He started to call Houston, but his transmission was abruptly cut off. A few seconds later came a loss of temperature and pressure data for both the inboard and outboard tyres of the landing gear in the left well. If Columbia's tyres were holed or losing pressure, it would be a bad day: she was already heavier-than-normal with the Spacehab module and FREESTAR pallet in her payload bay and many doubted a 'wheels-up' belly landing would be survivable.

"... Data loss would include that for tyre pressures and temperatures, brake pressures and temperatures," McCluney had concluded.

After hearing Kling's report, Capcom Charlie Hobaugh - who was scheduled to fly Columbia on her next mission, STS-118 - called Husband to inform him of the tyre pressure messages and ask him to repeat whatever he had tried to say. There was no reply. Meanwhile, Cain was pressing Kling for answers on whether the messages were due to faulty instrumentation, but was advised all of the associated sensors were reading 'off-scale low'; in other words, they had simply stopped working. Seconds later, at 1:59:32 pm, Husband tried again to contact Mission Control. They were the last words ever spoken from Columbia.

''Roger,'' he said, presumably in acknowledgement of Hobaugh's earlier tyre pressure call, ''uh ... buh ... '' At that point, his voice was cut off in mid-sentence, together with all data flowing from the ship. Communications were never restored. Thirty-two seconds after Husband's partial transmission, a ground-based observer equipped with a camcorder shot video footage of multiple debris contrails streaking across the Texan sky . . .

With the flow of telemetry broken, the situation in Mission Control was becoming increasingly uncomfortable, with Kling telling Cain that there was no common thread between the tyre pressure messages and the earlier hydraulic sensor failures and adding that other instrumentation for monitoring the positions of the nose and main landing gear had also been lost. As the seconds of radio silence drew longer, Cain asked Instrumentation and Communications Officer (INCO) Laura Hoppe how long she expected intermittent communications to last. She admitted that she expected some 'ratty' communications, but was puzzled by how protracted and 'solid' the silence was.

''Columbia, Houston, comm check,'' radioed Hobaugh at 2:03 pm, checking to see if the crew was experiencing communication difficulties with Mission Control. His words were greeted only by static.

A minute later, he repeated the call. Again, there was no reply.


Half a continent away, in Florida, astronauts Jerry Ross and Bob Cabana were chatting outside the convoy commander's van at the Shuttle runway when they heard communications had been lost. At first, they were unconcerned - at least, that is, until they were informed that powerful radars near KSC, which were supposed to lock onto the incoming spacecraft at 2:04 pm and track its final approach, saw nothing coming over the horizon. In Leroy Cain's words, ''that was the absolute black-and-white end. If the radar is looking and there is nothing coming over the horizon, the vehicle is not there."

Unlike an aircraft, which can adjust its flight profile to make a second approach to a runway, the Shuttle falls from orbit with the aerodynamic grace of a brick and has only one shot at landing. Throughout re-entry, its enormous velocity of 25 times the speed of sound is gradually slowed by a series of sweeping turns to such a point that it touches down at 220 mph. Its trajectory through the atmosphere can thus be plotted very precisely and reliably and, as soon as the OMS engines have fired, its touchdown time can be predicted to the second.

"We're a 220,000-pound glider coming in," said Digger Carey, who flew as Pilot on Columbia's previous mission in March 2002. "We actually enter the Earth's atmosphere over the Indian Ocean and we have enough speed to glide halfway around the world and land in Florida."

The assembled crowds at KSC were following the countdown clock as it ticked towards a scheduled 2:16 pm landing. They confidently expected to hear the trademark double sonic boom, announcing Columbia's arrival in Florida airspace, and the sight of a small, rapidly descending black-and-white speck on the horizon. It never came. Astronaut Steve Lindsey, who had the important job of taking care of the families of the STS-107 crew, was on hand and recalled hearing people innocently remark "They're always late'' when the countdown clock reached zero and began ticking back upwards.

Lindsey, by now a three-flight veteran, knew better: returning Shuttles were never late. They were always exactly on time. When the sonic booms did not reverberate across the marshy Florida landscape, when Columbia did not appear over the horizon, and when she did not settle onto the runway at 2:16 pm, he instinctively knew that something was terribly wrong.

So too did Bill Readdy, another veteran astronaut who had been NASA's Associate Administrator for Space Flight since the summer of 2002. He was standing next to Administrator Sean O'Keefe, who later described the former fighter pilot and three-time Shuttle flier as ashen-faced and visibly trembling. Jerry Ross, meanwhile, was a few months into his new job as the agency's chief of vehicle integration and his first act upon learning that tracking had been lost was to say a brief prayer. Then he set to work instructing his staff to secure KSC and round up the crew's families.

By this time, Texan police were being inundated with 911 calls, reporting bright flashes in the sky, loud explosions and falling debris; CNN quickly picked up on the stories and began reporting them. In Mission Control, however, televisions were not tuned in to outside broadcasts. Many flight controllers, including Leroy Cain, suspected the worst but prayed for the best. It was an off-duty NASA engineer named Ed Garske, who was watching Columbia pass overhead from the roadside south of Houston, who phoned colleague Don McCormack in Mission Control with the devastating news.

"Don, Don, I saw it!'' Garske yelled, clearly out of breath. "It broke up!"

"Slow down,'' McCormack replied. "What are you telling me?''

"I saw the orbiter. It broke up!"

Sitting behind Cain, at around the same time, veteran flight director Phil Engelauf received a telephone call from off-duty flight director Bryan Austin - who had supervised Columbia's previous mission, STS-109 - and heard first-hand testimony of the Shuttle disintegrating in the skies above Texas. By this time, although no one in Mission Control had actually seen the ship's destruction, they had resigned themselves to it. Already, at 9:05 am, Cain had asked Flight Dynamics Officer (FDO) Richard Jones when he expected tracking data from the radars in Florida -and was told it should have happened at least a minute earlier ...

Now, as Engelauf relayed Austin's emotional report to Cain, the flight director slowly shook his head, composed himself and turned to the now-silent control room to declare an emergency. At 2:12 pm, he instructed Ground Control (GC) officer Bill Foster to ''lock the doors'' - a de facto admission that all hope was gone - and ordered flight controllers not to leave the building, but to begin preserving their data and writing up their logbook notes for use in the subsequent investigation. After checking with Jones that no further tracking data had been acquired, Cain referred his team to their emergency plans.

''Okay,'' he told them, ''all flight controllers on the flight loop, we need to kick off the FCOH [Flight Control Operations Handbook] contingency plan procedure, FCOH checklist page 2.8-5.'' He then proceeded to talk them through the required actions: preserving their logbook notes and display printouts, communicating only on the flight loop and restricting outside telephone calls and transmissions.

Fifteen hundred kilometres to the east, at KSC, the families of Columbia's astronauts had been shepherded from the viewing site to the crew quarters by 2:30 pm. It was left to Bob Cabana to tell them the dreadful news. Mission Control, he said, had not picked up any radio beacon signals that would have been activated had the crew managed to bail out of their disintegrating ship and that, at an altitude of more than 60 km and a velocity of 23,600 km/h, it was extremely unlikely that anyone could possibly have survived.

Later that morning, Clark Barnett spotted something while driving through Sabine County in eastern Texas; he gave it no more thought until he received a call from his friend Mike Gibbs, who told him about Columbia. The two men decided to investigate and found an astronaut's charred torso, thigh bone and skull with front teeth intact. ''I wouldn't want anybody seeing what I saw,'' Gibbs said later. ''It was pretty gruesome.'' Elsewhere in Texas, near Hemphill, Roger Coday found some human remains, said a quiet prayer and built a small wooden cross by the roadside.


On the evening of 18 March 2003, Florida firefighter Art Baker prayed for success. One of thousands of volunteers searching a vast area of Texas for debris from Columbia, he had just heard that a single find could shed light on exactly why the spacecraft disintegrated during its descent six weeks earlier. Suspicions that 'the foam did it' were in most people's minds, although Shuttle manager Ron Dittemore and others doubted that such an ''inconsequential'' debris strike could have brought down a $2-billion national asset. Even Sean O'Keefe feared the root cause might never been found.

''Was it something that happened after launch? Was it something that happened

The recovered Orbiter Experiments (OEX) recorder: battered, but in one piece. It was to provide key evidence for what had happened to Columbia in her final minutes.

during the re-entry? Or was it something that happened during ascent and we didn't see it? Those are all possibilities,'' Dittemore had told a press conference on 5 February. ''It just does not make sense to us that a piece of debris would be the root cause for the loss of Columbia and its crew. There's got to be another reason.''

The definitive answer might come, however, from a square, breadbox-sized metal device called the Orbiter Experiments (OEX) recorder - part of Columbia's Modular Auxiliary Data System (MADS) and essentially the ship's 'black box' - which stored readings from more than 570 sensors scattered throughout the fuselage. In fact, as NASA's oldest orbiter, Columbia was the only member of the fleet to have such a device; it had been fitted for her first four test flights and, although some sensors had been removed, most were still operational by the time STS-107 lifted off.

One of the cruellest ironies was that, had any of the other Shuttles been lost in the same manner as Columbia, investigators might never have found the technical cause with absolute certainty. Only with the discovery of the OEX recorder by Art Baker as he trudged hilly terrain near Hemphill on 19 March could they begin piecing together the ship's final moments. The recorder's location was pinpointed by carefully plotting the discovery of other debris - including boxes originally mounted either side of the recorder, which had been mangled or torn to shreds - and it was found, miraculously, in near-pristine condition.

"We're obviously excited that it has been found,'' said Tyrone Woodyard, a spokesman for the newly formed Columbia Accident Investigation Board (CAIB), which was under presidential directive to find the cause of the disaster. "We're cautious, because we don't know what the data is going to be like. In other words, we don't know how intact that information is going to be.'' Late on 21 March, NASA shipped the recorder to data-storage-tape specialist Imation Corporation in Minnesota, which began the painstaking task of cleaning and stabilising it. Next, it returned to KSC for copying and then to JSC for engineering analysis.

Although the tape had broken between its 'supply' and 'take-up' reels inside the device and a portion had been stretched or 'wrinkled', Imation specialists described it as being in surprisingly good condition. It was hand-cleaned - repeatedly immersed in a filtered, de-ionised water bath, dried with lint-free cloth and nitrogen and wound back onto its original hub with new flanges - and returned to KSC on 25 March. Analysis revealed a strong signal and valid data lasting until 2:00:18 pm GMT, almost a full minute after Rick Husband's final radio transmission and 14 seconds after Texas skywatchers videotaped the first debris contrails.

After that, when Columbia's fuselage broke apart and electrical power to the OEX was severed, the tape had stopped running.

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