Shuttle Lost Parts Over Calif. (finally confirming what amateur skywatchers from Day One said)

SPACE CENTER, Houston - Space shuttle Columbia began losing pieces over the California coast well before it disintegrated over Texas, the accident investigation board reported Tuesday, finally confirming what astronomers and amateur skywatchers have been saying from Day One.

But board member James Hallock, a physicist and chief of the Transportation Department's aviation safety division, said the fragments were probably so small they burned up before reaching the ground.

He said the conclusion that the space shuttle was shedding pieces a full six minutes before it came apart over Texas was based on images of the doomed flight. Astronomers and amateurs on the West Coast photographed and videotaped the shuttle's final minutes.

"Obviously, it would be very important to understand what those pieces are, particularly the ones that started falling off at the very beginning," because they would shed light on the earliest stages of the breakup, he said.

However, Hallock said the pieces that came off early did not seem to be very big, judging from the light reflected off them.

"For us to find something that far back along the path, I think it's going to have to be a pretty substantial piece of the shuttle itself," he said.

Moreover, he added: "That's a lot of area to be looking. ... We have the Grand Canyon area and all of the areas of Southern California, the mountainous area and stuff like this, that even if we could home in on some of these things, it's going to be very difficult to find it. But we sure would like to see it."

In their second news conference in as many weeks, the board members also said they are not convinced the debris that hit the left wing shortly after liftoff on Jan. 16 was insulating foam from the external fuel tank. It is possible the debris was actually ice or much heavier insulating material behind the foam, they said.

Hallock said the suspected breach in Columbia's left wing had to have been bigger than a pinhole, in order to allow the superheated gases surrounding the ship to penetrate the hull.

_ The board said it hopes to hold its first public hearing next week, possibly on Feb. 27, to listen to non-NASA (news - web sites) experts who have theories about what destroyed the shuttle. The hearing will be held somewhere in the Houston area. The board has been criticized by some U.S. lawmakers as being too closely tied to NASA.

"We will invite experts who are not associated with any U.S. government program who have theories or hypothesis, who have written to us or provided research documents, to express to us their opinions," said board chairman Harold Gehman Jr., a retired Navy admiral. "That way we get input ... not by any government agency."

_ The board split into three teams Tuesday — materials, operations and technology — and began delving into what may have caused a breach in the shuttle's left wing.

_ An Air Force telescope in Maui took pictures of Columbia as the shuttle orbited overhead during its mission. Gehman said the images were being analyzed and it was too soon to know whether they may hold clues to the shuttle's demise.

_ An external fuel tank identical to the one used by Columbia has been impounded at the Michoud Assembly Facility in New Orleans and will be tested. If any destructive testing is performed, engineers need to be careful because "we only get one shot at it," Gehman said.

_ Nearly 4,000 pieces of debris have been shipped to Florida's Kennedy Space Center (news - web sites), of which 2,600 have been identified and cataloged, Gehman said. Investigators hope to partially assemble the pieces to help them figure out what happened to the space shuttle. An additional 10,000 pieces are headed to Barksdale Air Force Base in Louisiana and Kennedy.

It is impossible to calculate how much of Columbia the recovered pieces represent, the board said. In terms of weight, it represents only a tiny portion because so much of the wreckage is small, like fragments of insulation.

In the more than two weeks since the tragedy, the NASA-appointed board has publicly put forth just one hypothesis: that the superheated gases surrounding the spaceship during its descent through the atmosphere penetrated the left wing.

Still a major focus of the investigation is the supposed 2 1/2-pound chunk of rigid insulating foam that broke off Columbia's external fuel tank shortly after liftoff and slammed into the left wing at more than 500 mph.

NASA concluded while Columbia was still in orbit that any damage caused by the foam was slight and posed no safety threat. But engineers are now redoing their analysis to see if they made a mistake or missed something.

Air Force Maj. Gen. John Barry, a member of the investigating board, identified four previous launches, as far back as 1983, in which foam from the same part of the fuel tank struck a shuttle's thermal tiles. "We've got some backtracking to do," he said.

The board has yet to order any foam or thermal tile impact tests, Gehman said. Over the years, NASA has shot .22-caliber bullets, BB pellets and even ice at tiles, and the board wants to read up on this "enormous library of testing" first, he said.

"Before we go ordering NASA to do things, the first thing we're doing is getting smart," Gehman said.

The board began its work within hours of Columbia's breakup on Feb. 1. The shuttle was traveling at 18 times the speed of sound and was just minutes away from a Florida touchdown when contact was lost. All seven astronauts aboard were killed.

The newest member of the 10-person panel, former Air Force Secretary Sheila Widnall, will join her colleagues later this week. Additional members are being sought to include more scientific experts and quell criticism from members of Congress who contend the board is not independent enough of NASA.

07:00 p.m., 02/18/03, Update: Shuttle breach described; additional telemetry revealed; board members comment
Engineers dissecting telemetry from the shuttle Columbia and videotape of its fiery re-entry now believe eyewitness accounts of debris falling away from the spacecraft as it passed above California, well before its ultimate breakup high above Texas. At the same time, investigators believe the breach that let hot gas eat its way into the shuttle's left wing probably was located at or near the leading edge of the wing or perhaps at or near a seal in the left main landing gear door.
While no options have been ruled out, many NASA insiders favor the leading edge theory as the best explanation of the telemetry released to date. Wherever the breach occurred, a member of the independent Columbia Accident Investigation Board said today it must have been fairly large to explain the resulting catastrophe.

"When you're flying in this superheated air area, what's forming around the spacecraft itself is actually called a shock front," said board member James Hallock. "It's creating a boundary layer so it's not that you have a little tiny pinhole, you need something bigger than just a pinhole for something to actually be able to penetrate within that area.

"But once it gets in there, then it starts off as being a very small thing and then it would propagate. And it becomes much like, I guess, an arc welder's torch."

While the media will no doubt focus on that description, Hallock agreed later that calling a plasma intrusion a 'jet' or "torch" was misleading. An aerodynamicist with expertise in re-entry physics said in an email "there is no such thing as 'plasma jet' inside the wing or inside the landing gear well."

"Once the plasma in the shock layer of the external flow enters into the wing structure passages, the electrons and ions recombine at very high rate due to the high pressure (larger than 1 pound per square foot), and to the catalytic effect of the walls," he wrote. "The air inside is just at low pressure and very hot."

Hot enough to eat through sensor wiring, raise temperatures in the shuttle's left main landing gear wheel well and, ultimately, to affect the aerodynamic characteristics and structural integrity of the left wing itself. Hallock said the accident board has not ruled out anything in its search for what caused the fatal breach. Among the more likely suspects are impact by high-velocity space debris; impact by a micrometeoroid; damage caused by foam insulation from Columbia's external tank that fell off during launch and struck the underside of the left wing; or some combination of these and other factors.

On another front, engineers are slowly but surely coaxing additional data from the telemetry beamed down from Columbia just before it broke apart.

In the days following the disaster, shuttle program manager Ronald Dittemore said ground systems recorded sporadic telemetry from Columbia for up to 32 seconds after commander Rick Husband's final transmission at 8:59:32 a.m. Additional analysis has now extended the time Columbia was known to be intact by five seconds or so beyond Husband's final call, showing two more right-firing rocket thrusters were commanded to fire in a futile bid to prevent aerodynamic drag on the left wing from pulling the spacecraft into a fatal "sideslip" orientation.

In addition, sources say a "roll reference message" generated by Columbia's flight computers at some point midway through that 32-second period also was seen in the telemetry. The message got as far as a computer buffer but it never reached the crew's cockpit displays. By that point, the astronauts undoubtedly knew something was amiss.

While he did not confirm the roll reference message, Hallock said "we continue to dig data out of that 32-second period of time."

Columbia was in a left bank at the time, descending at Mach 18 over northwest Texas at an altitude of more than 200,000 feet. While the exact timing is still unclear, time-stamped video from an Apache helicopter flying near Fort Hood, Texas, shows multiple contrails by 9:00:30 a.m., indicating Columbia broke completely apart less than a minute after the last valid data frame was downlinked.

Already released telemetry from the shuttle shows whatever went wrong went wrong early in the descent, with unusual temperature increases beginning just a minute and 24 seconds after the shuttle reached the region of maximum heating while approaching the coast of California.

While this page has generally avoided the "competitive speculation" fueling many media accounts of the tragedy, a fair number of agency insiders now suspect that a breach at or near the leading edge of the left wing in front of the wheel well is a reasonable explanation for the telemetry released to date.

Telemetry shows the first clear signs of elevated temperatures in the left main landing gear wheel well while Columbia was still off the coast of California. As the shuttle's descent proceeded, additional wheel well sensors either failed or recorded high temperatures while other skin temperature and hydraulic sensors positioned near the back of the wing simply failed. Wiring from those sensors was routed around the left side of the landing gear wheel well and then directly in front of it before entering Columbia's fuselage. A plasma intrusion near the wheel well could have affected the rear-wing sensor wiring as well as the sensors in the unpressurized wheel well.

"When you look at how the wires are set up within the craft itself, it leads you directly towards the wheel well, there's no question," Hallock said. "The wires that lead to those sensors that we're talking about go right in front of the wheel well. Then when you look where the temperature sensors are and you get a sense of how they're reading, you can almost triangulate (to where the problem is). That's what we're trying to do."

NASA engineers familiar with the shuttle's constru?tion say a plasma intrusion directly into the wheel well, perhaps from a breach in a landing gear door seal, would have wreaked more immediate havoc than the relatively modest temperature increases seen in Columbia's telemetry. But a wheel well breach has not yet been ruled out.

Video shot by amateurs along Columbia's path shows what appear to be pieces of debris breaking away from the shuttle well before Husband's final transmission. The accident investigation team has asked the public for help locating any such debris, which could include reinforced carbon carbon leading edge panels or heat shield tiles. Investigators also are seeking FAA and military radar tapes and checking into widespread reports of sonic booms over California and Nevada. Such booms would be consistent with the passage of high-velocity debris.

Outside experts have been asked to evaluate the trajectory of any debris that might have broken free of Columbia over California and the southwest to help search teams narrow the potential debris "footprint." So far, no such debris has been located.

But there is little doubt that Columbia was shedding some sort of debris well before its breakup. Numerous witnesses reported seeing what appeared to be debris falling away from the orbiter or hearing muffled rumbling that may have been caused by torn-off shuttle components falling along the spacecraft's ground track.

"We have been poring over the films," said Hallock. "From the timing I've seen right now, it does look like things were beginning to come from the shuttle as it approached, right about California. So it's not something that was close in, it began way out in that area.

"People are looking at the pieces (on film), we're trying to get a sense by looking at them where we have these films and trying to extract from them what we think the mass would be and then how it's moving. Some people here at (the Johnson Space Center) are trying to extrapolate that to the point of where it might land so we can pick some places and try to find it. Obviously, it would be very important to understand what those pieces are, particularly those that started falling off at the very beginning."

Near town of Twain Hart, Calif., 4,000 feet above sea level in the foothills of the Sierra Mountains, Glen Caldwell and his daughter got up early to watch Columbia fly overhead. A veteran of two previous shuttle re-entries, Caldwell knew what to expect and told his grown daughter the view would be worth the early morning effort.

The weather was excellent and "it's right on time, coming out of the west, and when it gets pretty darn high in the sky for us, we see a little, like a fireball, like a Roman candle or a fire come off this thing," Caldwell, an insurance broker, said today in a telephone interview. "Then a second later or so, we see it again. I commented at that time to my daughter, 'it looks like that thing is falling apart.'" Walking back to his house, Caldwell watched the remainder of Columbia's entry on NASA's satellite television channel, which he was recording. All too soon, the projected ground track of the shuttle, visible on a projection TV screen in mission control, stopped updating over Texas.

"I see the ground track stop and I'm getting a little bit concerned and starting to put two and two together," Caldwell said. He later calculated that Columbia's ground track must have passed about 15 miles north of his location, giving him a good, high-elevation view of the ship's fiery path across the sky. For scale, he said imagine holding an almond at arm's length.

Relative to that almond, "what we saw come off the side of this thing were two pieces the size of a BB," he said. "The orbiter is very, very bright, very iridescent when it comes in and these two pieces when they came off were the same color and intensity. They were very, very bright, very easily discernible and very clearly separate from the orbiter. From our perspective, they disappeared very quickly into the (shuttle's plasma) trail and disappeared."

Unlike video of Columbia's debris falling over Texas, in which different pieces of wreckage fell together, "what I saw was kind of the opposite," Caldwell said. "They peeled off and the orbiter raced away from them."

Mike Dambacher, who was taking a morning walk Feb. 1 and saw the shuttle pass over by accident, did not see any signs of debris falling away. But he heard a rumbling that might have been sonic booms triggered by the passage of unseen debris.

"I'm watching this ball of flame going over," he said in a telephone interview. "I'm watching for probably 15 seconds. My first thought was, I'm watching a falling star, except it's not falling."

A few moments later, he heard a boom and "I'm thinking is that a sonic boom? We hear sonic booms occasionally because they do test flights over here. This was a very muffled sound. There as such a delay, I couldn't tie that to what I saw fly over."

Watching news reports in his home a few minutes later, Dambacher realized he had just seen the shuttle fly over. Comparing notes later with other witnesses, he said some people heard two booms, others heard one.

"The sonic boom is not heard when something goes subsonic!" the re-entry expert said in another email. "Every time a supersonic body flies over an ear at ground level, its bow shock will excite the ear with what we call a 'sonic boom.' The sonic boom is influenced by atmospheric effects, body size, rigidity, acceleration, etc. They all contribute to what we call the 'signature of the sonic boom.'"

Large craft like the space shuttle and the Concorde produce double sonic booms caused by bow shock and wake shock.

"A cluster of supersonic bodies will produce a very complicated sonic boom. Anything can happen, but it will sound more like a long thunder, like a rumble, as the cluster of bodies continues to break down. The shock waves coalesce and form a complicated acoustic pulse."

Small bodies a few inches across - including shuttle tiles - would not produce sonic booms," he said. And while higher Mach numbers yield stronger booms, higher altitudes tend to weaken the boom.

"You will not hear a sonic boom from one tile," he said. "You may from a cluster of tiles (about 20) if they go off simultaneously. But you will hear an alteration of the vehicle's 'nominal' signature if a non-structural member starts to flutter."

For example, one of the insulation blankets on the side of the shuttle.

"The human ear is very good at signature analysis of broad band noise," the physicist continued. "The abnormal noise people heard could have been related to the shedding off of (an insulation blanket)."

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