Posted on 02/14/2003 3:51:25 PM PST by jpthomas
The shuttle orbiter Columbia's left wing was increasingly compromised by the penetration of 2000F reentry plasma starting over the Pacific Ocean 400 mi. off the coast of California, early in the hottest phase of its disastrous reentry Feb. 1, according to new data released by NASA. p This information provides more detail on sensor readings and when they occurred relative to the orbiter's ground track during the reentry, which ended in the loss of Columbia and her seven crewmembers over north central Texas.
One critical finding is that a breach in the left wing-along its leading edge, its landing gear door or seals-would had to have occurred for temperatures in the left wheel well to rise as they did in the final seconds before breakup began, according to data developed by a NASA thermal analysis team. The data were provided to the independent Columbia Accident Investigation Board headed by Adm. (ret.) Harold Gehman.
The analysis is extremely important because it indicates that missing thermal tiles alone on the wheel well door would not cause a temperature rise like that detected before breakup, officials in Houston said.
Sources outside the board noted that it is increasingly likely the breach in the wing structure was not specifically in the wheel well area, although sensors in the wheel well and on the trailing edge of the wing provided some of the first signs of trouble.
They said the nexus of data from the accident continue to implicate the impact of insulation from the Lockheed Martin-built external tank on the left wing as part of a chain of events that could have resulted in a breach of wing structure.
The Boeing debris impact analysis highlighted both the leading edge of the wing and an area on the gear door as significant impact areas.
How the breach occurred and its location remain key questions for the board. But "additional analysis is underway looking at various scenarios in which a breach of some type, allowing plasma into the wheel well or elsewhere in the wing could occur," according to a statement from the board.
It specifically noted that there are no data to support a premature deployment of the left landing gear, contrary to widespread media reports late last week.
If debris had damaged the wing's leading edge reinforced carbon-carbon structures or deeply gouged tiles, allowing hot plasma to penetrate and erode the underlying aluminum, an increasingly larger path for the plasma to enter the wing could have been created (AW&ST Feb. 10, p. 22).
As part of its research, the thermal analysis team studied what thermal effects inside the wheel well would have been if all of the numerous tiles on the door's exterior had been removed.
The engineers found that radiant heating alone would not increase the temperatures in the wheel well like those recorded by sensors before breakup. The role that may have been played by any potential prelaunch deficiencies in shuttle thermal protection tiles and reinforced carbon-carbon leading edge materials and seals is also being examined intensively.
Michael Mott, Boeing vice president and general manager of NASA systems, told Aviation Week & Space Technology he knows of no unusual tile or leading-edge problems found during Columbia's modification period at Palmdale, Calif., in 1999, or after its only other flight before the accident-a 2002 mission to service the Hubble Space Telescope.
Both Mott and top NASA managers last week continued to assert faith in the debris analysis that involved more than 100 managers and engineers.
However, e-mails between Johnson Space Center and Langley Research Center engineers indicate there were ongoing concerns among some at Houston, even after Boeing analysis showed no safety implications from the tank debris impact.
Those concerns were significant enough to spark flat-tire landing simulation tests at the large landing simulation rig at Ames Research Center in Mountain View, Calif., after the Boeing analysis had been completed and the mission was still aloft. By chance, the Ames facility was temporarily configured for shuttle work anyway.
The Johnson/Langley exchanges began by phone and were completed by e-mails between David Lechner, a United Space Alliance member of the Mission Control's Maintenance, Mechanical and Crew Systems office and Robert Daugherty, a shuttle tire/landing gear expert at Langley near Hampton, Va. The discussions involved up to a dozen personnel, said Milt Heflin, who heads the Johnson Flight Director's office. Both Heflin and Columbia's lead reentry flight director, Leroy Cain, said last week that the discussions were typical "what-if-types" between good engineers.
The Langley engineer cited numerous worst-case scenarios. They were centered on the potential for Columbia's tires to explode or otherwise be flattened, along with landing gear damage-if the findings of the Boeing debris analysis were faulty and thermal damage occurred in the wheel well but the vehicle had survived. "I do not really think things are as bad as I am getting ready to make them out," Daugherty said in his e-mail exchange, before he cited serious tire consequence from any serious heat penetration of the wheel well.
In his reply, Lechner noted, "Like everyone we hope the debris impact analysis is correct and all of this discussion is mute [sic]."
NASA also continues to investigate the potential for damage the day after launch by any space debris that hit on the shuttle's left wing.
But as of Feb. 12, shuttle orbiter data are "unable to substantiate" that any such event occurred," Cain said. Gehman noted that members of his team have investigated a total of 50 accidents-among them the loss of Challenger at launch in 1986. "But almost every one of us has had an experience where following the hottest lead and working on the hottest theory turned out to be completely wrong. So we are very careful not to fall in love with any particular scenario."
Nevertheless, at the request of NASA, major tests and computer analysis are getting underway at Ames and Langley to reassess the Boeing analysis and potential for life-threatening damage from the external tank debris striking the left wing. NASA has asked Langley for support with both computational and wind tunnel debris related analysis.
The new data timeline shows Columbia was only about 90 sec. into the hottest phases of the reentry at Mach 23.5, and 236,791 ft. over the Pacific when a left main line landing gear brake line temperature began to rise, the first sign of trouble. This was at 7:52:17 a.m. CST, heading toward a planned Kennedy landing at 8:16 a.m. CST. Temperature increases and data dropouts related to lines compromised by temperature increases multiplied until breakup.
The revised timeline shows the first flight control system action to counteract increased drag-from what analysis now indicates was a damaged left wing-occurred at 7:54:20 a.m. CST as Columbia passed over eastern California.
At Mach 20.2 and 216,000 ft. near the New Mexico/Texas border, "sharp" elevon trim motions were recorded at 7:58:03 CST as the control system further tried to counteract drag.
At 7:59:30 a.m. CST, about 3 sec. before breakup, two right firing yaw jets ignited to assist the elevons in holding the proper attitude. One second later the elevons swept through their largest motions to that point; a second after that, all data were lost.
As the accident board is beginning its work, dozens of truckloads of Columbia debris from Texas and Louisiana are arriving from Barksdale AFB, La., at a specialized Kennedy hangar. Built in 2001 ironically as a "Reusable Launch Vehicle Hangar" to support flight-test vehicles for shuttle replacement studies, the facility sits by the threshold for Kennedy Runway 33, where Columbia was to land.
Parts of the leading edge of Columbia's left wing, believed to be a less critical outboard section, were found last week in a section of the main debris field around Lufkin, Tex. Gehman said investigators continue to be interested in debris west of Fort Worth. As of Feb.13, none had been recovered.
Imagery of the reentry remains vital to the investigation, Gehman said. "We are building a great mosaic, combining various video products [to mold] the exact timeline of the video, telemetry and radar observations into a sophisticated audio-visual and telemetry reconstruction from the time Columbia crossed the coast until we lost signal."
Aviation Week reported last week that a "high-resolution" image taken from an Air Force tracking camera " in the southwest" showed serious structural wing damage to the inboard leading edge of Columbia's left wing. USAF Maj. Gen. (ret.) Michael Kostelnik, NASA deputy associate administrator for space station and shuttle, said the image is "consistent with telemetry."
NASA subsequently released an image it said came from the Starfire facility at Kirtland AFB, N.M. Technicians there later said it was taken with an off-the-shelf telescope and computer hardware.
NASA and other engineers remain extremely interested in the released image-especially the jagged feature on the left wing and the significantly different flow pattern off its trailing edge.
Civilian imagery analysts, using their own software programs to assess the image, have contacted Aviation Week. They generally support the significance of the leading edge feature, although one program indicates that it could be a thermal ab-normality resulting from structural damage rather than damage itself, while another made the feature disappear altogether.
The analysis reviewed here agrees on the significance of the left trailing edge plume compared with the right. Image analyst John Warner, who has processed different types of imagery for both NASA and Defense Dept., applied multiple software runs to the image. He said data from several of those runs indicate the left wing trailing edge plume could contain structural particulate matter in addition to unusually concentrated flow. Warner has sent that analysis to NASA. He also generated a simpler histographic analysis.
That analysis used the center of the trailing edge plume to generate a vector forward-which overlays precisely the leading edge feature, a possible indication that the leading edge feature is generating the disturbed hypersonic flow behind the left wing.
I find it hard to viualize a piece of urethane foam at 200 mph causing this kind of damage. 18,000 mph space junk ?
If this area of the wing is so critical, why is it made of aluminum? The really crtical parts of the wing should have been made of titanium. Sure titanium is exepensive, but so is the catastrophic loss of an orbiter.
I doubt it. That would take energy to boost the shuttle back up to orbital velocity. There's no fuel for the main engines to put it back into orbit. The whole point of re-entry is to dissipate the kinetic energy of the orbiting shuttle. Once the shuttle starts travelling through the atmosphere, friction starts converting the shuttle's kinetic energy into heat. I think it would be a violation of the second law of thermodyamics to be to reverse the process and go back up to orbit.
Unless there had been some way to patch the damaged heat shield, or program a different protocol for steering the shuttle to favor the other side, the only way I can think the shuttle could have been saved would have been to abort the launch and land at Cape Canaveral or Senegal Africa. Unfortunately the no one knew about the foam impact till two days after launch.
Here's a schematic cross-section that shows how the shuttle leading edge panel is bolted onto the wing structure:
Notice the flat leading edge spar behind it and the insulation stuffed inside? That flat spar is made of aluminum. Plasma that gets into a breach between the leading edge panels would burn into that spar like a blow torch.
With current materials science technology, much of the structure could probably be designed as a "hot structure", with load-bearing materials that could also withstand the temperatures of reentry. The leading edges and other "hot spots" would still require special reinforced carbon materials.
Implies that radiant heat [due to missing tiles] isnt what created the specific breach. Something created the breach and missing tiles is a prime candidate. The Shuttles wing didnt spontaniously combust from the inside out.
The article says "One critical finding is that a breach in the left wing- 1. along its leading edge, 2. its landing gear door or 3. seals-would had to have occurred for temperatures in the left wheel well to rise as they did..."
It doesnt say for certain that a breach occured along the leading edge, only that it is one of the neccesary areas of breach to produce the results they are gleening from the data. In my completely unqualified opinion I would think that tile[s] loosened as a result of the intitial debris that struck the Left Wing during liftoff probably facilitated the breach and subsequent removal of tile[s] [upon reentry] which then gave way to the Shuttle's inability to maintain structural integrity.
?
Well, they fire their small engines for about 2.5 minutes which only changes the shuttle velocity 176mph. But by the time they get into the atmosphere about 25 minutes later, they are being slowed down even more by the air drag. By the time the very first indication of anything odd, they'd lost about 2000 mph of velocity, about 10% of their total velocity. Clearly the main fuel tank and the boosters were not available and you can see that 10% of that capacity is no small thing. Re-orbit at that point, first sign of anything unusual, was out of the question.
Also, how do you think a stainless steel spar would have stood up to the heat? {Weight penalty of course}.
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