Gehman reported that at one point upwards of 5,300 people have been engaged in the on-going search for Columbia wreckage, along with a dozen fixed-wing aircraft and helicopters.
In addition, over 200 submerged targets have been detected by sonar at the bottom of two Texas lakes. Possibly awaiting recovery by Navy diving teams are Columbias main engines, Gehman said.
Bad weather, including snow in eastern Texas, has prevented some crucial pieces of debris to be found. "Were hoping that when people get outdoors, farmers plow their fields, and snow meltsthat more interesting debris further west will start to emerge," Gehman said.
Following the foam
CAIB member, Major General Kenneth Hess, said that an image taken by the militarys Starfire optical range in New Mexico during Columbias plunge to Earth remains inconclusive as to whether or not the picture shows a damaged space plane.
"Its important now to enhance that photo as much as can be done, without adjusting the facts behind the photo," Hess said.
"Were following the foam", said Major General John Barry, a CAIB member, noting that particular attention is being paid to the leading edge of Columbias left wing, as well as falling foam or ice or combination of the two seen cascading off the shuttle systems huge external fuel tank.
Detailed photo analysis has found that three pieces of material came off the external tank at the same time. These pieces appear to hit on the underside of the Columbias left wing, striking panels of reinforced carbon-carbon (RCC) material used on the leading edges of Columbias wings.
But after the debris jets by the left wing, ground photography taken during the shuttles climb skyward shows no missing tiles or obvious damage.
"Once again, we have these tantalizing little pieces of evidence that dont fit together," Gehman added.
Stress, strain and old age
Gehman said that foam striking an older Columbia -- one that has seen wear and tear from multiple liftoffs and reentries -- is being reviewed. " That might have been a normal event that she could have survived at age 10 ... maybe she couldnt survive it at (a later age)," he added.
Barry said that CAIB team members are focusing on inspection issues for RCC materials, noting that pin holes and voids underneath the surface of the reentry panels have been found in other space planes that arent detected by visual scrutiny alone.
One new finding has surfaced regarding Columbia's ascent into orbit.
Barry reported that at 62 seconds after liftoff, there was an additional stress load on the left-hand side of the space plane. This type of stress, while not beyond engineering specifications, had been noted on two earlier flights of Columbia. Those flights roared off the launch pad and headed for a 39-degree inclination and both used lightweight external tanks, the same as on the shuttle's last mission.
"We're trying to identify if there's any commonality there," Barry said, in regards to transient stresses on Columbia that may have played a role in its reentry problems. "It's a detective story," he said.
What happened first?
Sheila Widnall, an MIT aerodynamic expert and CAIB member, said that the recovered fragments of Columbia offer a wealth of information on heating and aerodynamic loads experienced by the orbiter.
While not wanting to speculate, Widnall said it appears that the vehicle came coasting into the thickening atmosphere with some type of heat-related damage, then rapidly suffered a dramatic aerodynamic event.
Board members remain perplexed as to what appears to be a significant disturbance much earlier along Columbias path to destruction. The space planes onboard guidance and navigation systems were trying to compensate for unexpected side-to-side motion.
"Things were happening earlier in the reentry than we previously had been given to understand," Gehman said. He further added: "Which started first? Did the thermal event cause loss of tiles and thereby these aerodynamic forces? Or did we lose an aerodynamic surface first, which then allowed the heat to start unzipping this aircraft?"
"Every time Ive got it figured out, I get a piece of data that changes my mind," Gehman said.
Pilot error, not ruled out
Gehman told SPACE.com that pilot error as a cause for Columbias breakup has yet to be discounted.
"One of our investigation road maps includes flight crew performance. It is too early to rule that out right now. We have no indication of that, but we are not ruling it out," he said.
Based on reconstructed reentry data, there is indication that a command was given to override Columbias autopilot, or perhaps one of the shuttle pilots accidentally hit the manual control stick.
"Weve looked into that in great detail, Gehman said. "That happened even before the tape endedwhich makes it like eight minutes before reentry. The orbiter was back in a nominal reentry at that time," he said.
Columbia-Challenger contrasts
Outside the CAIB press briefing, there is some speculation as to the condition of the crew cabin. It is now known that the space planes forward, mid, and aft fuselage were still intact late into the overall disintegration of the vehicle.
Some NASA insiders are wondering whether the Columbia breakup may have followed a similar pattern like that observed in the January 1986 disaster involving the Challenger.
As Challenger broke up at some 46,000 feet after launch it was traveling at Mach number of 1.92 much slower than the incoming Columbia space plane.
But like Columbia, the Challenger underwent extreme aerodynamic loads, breaking into several large sections. One of those sections was the crew compartment, tossed free from a fireball of burning fuel. Close photographic inspection of the Challenger pieces shooting through the sky identified the crew-carrying segment, trailing various lines torn free of the ill-fated space planes cargo bay.
Minute by minute, piece by piece
Whether or not Columbias cabin survived while space plane superstructure fell away from behind the seven-person crew, piece by piece, is not known.
Those investigating the 1986 Challenger catastrophe later reported that some of the crew had survived the space planes breakup. Emergency-escape air packs were found to have been activated while the crew compartment plummeted toward the sea.
Challengers cabin was estimated to have struck the water at some 200 miles per hour.
At the Florida hanger where recovered Columbia pieces are being placed on a floor grid, cabin wreckage is being assembled in a special area, out of public view.
advertisement
