Spaceflight Now

Detailed failure scenario released by Columbia board
Posted: July 11, 2003

The Columbia Accident Investigation Board today released a definitive scenario detailing the doomed shuttle's countdown, launch and re-entry, a scenario that merges all available telemetry from the orbiter, recorded data, debris analysis and complex computer simulations. The result is the most complete picture yet showing how a foam strike during launch punched a catastrophic hole in the shuttle's left wing that led to the ship's destruction during re-entry Feb. 1.

  Hole Dimensions Dimensions of the hole punched during an impact test this Monday. Photo: CAIB.
Board member Scott Hubbard also presented additional data from a dramatic test last Monday that lends additional credence to the updated scenario. In the test, a chunk of external tank foam insulation was fired at a wing leading edge mockup at the Southwest Research Institute in San Antonio under conditions that simulated the actual foam strike known to have occurred 82 seconds after Columbia's launching Jan. 1.

Along with blasting a 16-by-17-inch-wide hole in reinforced carbon carbon panel No. 8 - the same carbon composite panel believed to have been struck during Columbia's liftoff - the impact also broke an internal lug fitting and caused severe cracks in the surrounding material.

Hubbard said two large fragments of RCC material were blown into the breach by the impact. Dramatic high-speed camera footage shot inside a cavity behind the leading edge panels showed the fragments blowing inward with extraordinary violence. Hubbard said a similar fragment, having a surface area of 90 square inches or more, is perhaps the best explanation for a mysterious object detected by ground radar systems the day after launch that was seen slowly separating from the shuttle. The idea is a large fragment could have lodged in the breach during launch and then floated free after a day of maneuvering in orbit.

  Inside view A camera behind the RCC panel capture the moment a block of foam smashes through during Monday's impact test. Photo: CAIB.
On top of that, cracking similar to that seen around the breach in the wing mockup likely led to debris shedding during re-entry. Amateur shuttle watchers on the ground filmed what appeared to be flaming debris falling away from the descending orbiter well west of Texas. Finally, the broken lug fitting observed after Monday's test would have provided a way for a so-called T-seal between RCC panels 8 and 9 to rock open and closed during entry, providing just the sort of intermittent heating needed to explain heat damage that, until now, had defied explanation.

"The board felt this testing was very, very important because it will help us, it will determine how strong a word we use to equate the foam strike, which we know happened, to the creation of some kind of damage that was pre-existing prior to the entry," CAIB chairman Harold Gehman said Friday. "This allows us now to use a word, which we haven't agreed to yet, but use a word that expresses high confidence, a very high degree of confidence that we have indeed found the cause here."

Board member James Hallock said the actual breach probably was in the six- to 10-inch-wide range. A larger hole would have let so much heat into the wing during the initial stages of re-entry that Columbia probably would not have survived all the way to Texas.

But figuring out the mechanical failure mode is only part of the CAIB's goal. The board's final report, now expected around Aug. 26, will focus just as strongly on management issues and shortcomings.

"We started off with kind of a hierarchy of factors," said Gehman. "We had the direct, mechanical thing and then below that, we had contributing factors. We've now decided that these things are equal. That's why we're being so cautious and so careful about the management sections and the safety sections and all those kinds of things. Because the way the report is going to characterize these things is we have what we're now calling the physical, or mechanical failure, and then we have the systemic failures and we're now giving them equal weight. It would be premature to go much further than that because we're writing that section."

But Gehman made it quite clear the board views the space shuttle as an experimental spacecraft as opposed to an operational vehicle. He has said that before, but today he gave a bit more background on how the board views the shuttle system.

"In the case of an operational vehicle, like a commercial airliner or something like that, the events that you use the vehicle for - takeoff and landing and transporting people and then also the turnaround in between flights - if it's an operational vehicle, you expect each one of these events will be nearly identical and repeatable," he said. "And therefore, it's easy and it's logical and it's prudent to contract that out because you essentially want repeatability, you want the thing to happen exactly the same way each time and you expect the same results each time.

"If, on the other hand, it's a developmental vehicle, your expectation is it will not be the same every time. You are always on the lookout for little, tiny little differences, your suspicious of little tiny little differences and also you demand extraordinarily accurate and intrusive instrumentation so you can detect little variances in how the thing operates.

"And you also don't have an expectation that when the thing lands that you can turn it around and get it back in the air again quickly," he said. "There is no expectation that you can do that and there's no expectation you can do that economically. To me, those are the big differences. I cannot emphasize too strongly how much the board is impressed with how deeply and how broadly the differences translate themselves into practical applications. ... We consider it to be truly significant."

Asked if NASA had to be able to repair RCC holes 16 inches across in order to resume shuttle flights, Gehman said "they have to be able to repair holes in RCC caused by debris."

"If they can't stop the debris, they've got to be able to fix the hole," he said. "If they can stop the debris to where it's tiny little pieces of debris and it causes tiny little holes, then they can have a tiny little hole fixer."

Columbia, of course, was struck with the largest piece of foam debris on record, a 1.8-pound suitcase-sized chunk that broke away from the so-called bi-pod ramp area where one of two large struts attaches the nose of the shuttle to the external fuel tank. NASA engineers now plan to launch future shuttles without any such foam insulation, using heaters instead to prevent ice buildups before launch.

  Admiral Gehman Admiral Hal Gehman, chairman of the Columbia Accident Investigation Board. Photo: Rick Stiles CAIB.
"No shuttle is going to fly with a bi-pod ramp again, so you're not going to see this happen again, I don't think," Gehman said. "And I mentioned this before in press conferences and it's in our interim recommendations, that we view this as a system. NASA has to cut down on the amount of debris that comes off, they have to toughen the orbiter, they have to be able to inspect and repair the orbiter and then they've also got to give the crew a better chance to survive. All four of these contribute to safer operations and no any one of them, in my view, is a fix."

Whether NASA can address all such factors before next summer is an open question. Most insiders still believe NASA will have a hard time launching the next mission before the middle of next summer at the earliest, but agency leaders continue to hold out hope for a return to flight next spring.

While Gehman said he still believes NASA can make the necessary fixes in time for a flight six to nine months from now, he also said "the board is convinced that coming and going into orbit remains an enormously dangerous task."

"And even if you had the world's best engineers and world's best managers working on this thing, there's still a high degree of risk in what we're doing here. It's still not flying in a commercial airliner, it's not like taking a drive in your car. It's dangerous. It's very dangerous, and it will remain that way.

"So under that rubric, you could say that even if we had the best managers and best engineers in the world, you're in a business where something can still cause you to have a tragedy like this.

"On the other hand, when looking into this particular accident, we think we have found some issues, some practices, some managerial, budgetary kinds of things, which we believe could be done better even if we had not had this accident. I mean, if they had (formed) this panel to look at NASA for five months, seven days a week like we have, I suspect we would come up with probably the same set of recommendations even if the Columbia had not been lost."

While the mechanical cause of the accident seems clear, the CAIB report will not be 100 percent conclusive. Engineers simply cannot rule out a space debris impact of some sort or even impact by debris from a possibly faulty "bolt catcher" in the booster-external tank separation system.

As for management issues, Gehman declined to comment other than to toss out a few hints.

"We are not consciously saving up things for the report," he said. "But there are some parts of the report that really we have not said a whole lot about. ... The board is still wrestling with some of the words and some of the findings. That part is not very mature yet. ... And also, you haven't seen all of this written down on one piece of paper yet.

"We've talked about a thing here and a thing there, we've talked about inspections this and quality assurance that and testing of this and these things. But when you see it all written down, the tone may be something we haven't come across yet. ... There may be some news value in the tone of the report."

That might rank as one of the greater understatements of the investigation, which Gehman said likely will cost $15 million to $20 million when all is said and done.

"If you agree with me that we have not perfected, we have not learned everything we need to know yet about routinely going into space and coming back out of space, then even if you have a situation where you have a tragedy like this, your obligation to learn as much as you possibly can," Gehman said.

"And the fact that we've allowed cameras and range instrumentation and on-board instrumentation and all kinds of things like that to kind of gracefully atrophy over the years leads me to bring this issue up that there are some signs that it's been considered a routine operation or an operational vehicle rather than a test vehicle."

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