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Tests affirms foam theory { July 8 2003 } Original Source Link: (May no longer be active)
http://www.washingtonpost.com/wp-dyn/articles/A23721-2003Jul7.htmlhttp://www.washingtonpost.com/wp-dyn/articles/A23721-2003Jul7.html
The Shuttle's 'Smoking Gun'
Test Affirms Theory That Foam Damaged Wing, Panel Says
By Kathy Sawyer
Washington Post Staff Writer
Tuesday, July 8, 2003; Page A01
SAN ANTONIO, July 7 -- With a resounding thwack, a 500 mph foam bullet today blew a ragged hole the size of a stop sign in a section of a space shuttle wing, effectively shattering any remaining doubts about what destroyed Columbia and its crew Feb. 1.
"We have found the smoking gun," said Scott Hubbard, a member of the Columbia Accident Investigation Board, who supervised the testing. It was the last of seven impact tests and came closest to duplicating exactly an incident that occurred during Columbia's Jan. 16 launch, when a suitcase-size chunk of foam insulation from the external tank broke free and slammed into the leading edge of the left wing.
The damage was so severe today that the small crowd of observers gasped in amazement. It also showed dramatically how badly engineers for NASA and its contractors had miscalculated the vulnerabilities of the leading edge, which they had never tested in this manner.
Grabbing his stomach, Hubbard said his initial response was "in here, a visceral reaction," and then, "Oh, my god!" Although "such a dramatic punch-through" was completely unexpected, he said, the size of the hole is on the order of one that investigators concluded had to exist on Feb. 1.
As the five-month investigation progressed, multiple lines of evidence pointed with growing clarity at a single section of the wing -- the eighth of 22 panels on the leading edge -- as the site of a fatal breach that allowed superheated gases to penetrate and destroy the shuttle wing during reentry. The panels are made of a carbon fiber material called RCC, for Reinforced Carbon Carbon, which is designed to withstand temperatures up to 3,000 degrees.
Hubbard declined to comment on whether a high-powered national security satellite could have detected a hole of this size while the shuttle was in orbit. In what the board has called a serious mistake, NASA officials countermanded a request by lower-level engineers to seek such images during Columbia's flight.
One of the 16 cameras that monitored the test showed a target's-eye view as the 1.67-pound foam rectangle, 11.5-by-20 inches, exploded into the wing cavity like an incoming warhead. The impact drove big shards of heat-shielding into the wing, damaged a camera and left sensors hanging by wires, Hubbard said. The hole was about 16 inches by 16 inches.
Today's test was the culmination of the board's effort to "connect the dots" between the Jan. 16 foam impact and the Feb. 1 tragedy by proving that the lightweight foam -- lighter than Styrofoam -- traveling at high speed could have delivered enough force to blow open the required hole in the heat shielding.
"I've now got a direct connection between foam-shedding creating a hole that's the same order of magnitude as what must have been there when Columbia came home," Hubbard said.
"I was surprised, I was very surprised" at the outcome, he added. "I feel gratified that after months of work we were able to demonstrate this connection . . . but I know it was a source of tragedy, so that makes me feel very sad."
Engineers for Boeing, a shuttle contractor, concluded during the mission that such an impact would do nothing more than scuff the carbon fiber material and that there was no threat to the safety of the vehicle or crew.
Hubbard said the test also appeared to explain what he called "one of the mysteries" of this investigation -- the identity of an object observed on radar floating away from the orbiting shuttle on the second day of the doomed mission. The mystery object could be a section of RCC shielding such as the ones that today fell into the wing cavity like scattered pieces of a jigsaw puzzle.
One piece, retrieved right after the test and displayed for reporters, was 11 inches long and 3 to 4 inches wide, with rough, torn edges and a split near the middle. "I would say . . . we've also established that [the mystery piece] could very likely be part of the carbon panel itself," Hubbard said.
The board already issued preliminary recommendations calling on NASA to treat the shuttle as an experimental vehicle, to obtain spy-satellite imagery routinely in orbit and beef up its system of launch-monitoring cameras. It has also urged NASA to develop ways to repair the heat shielding and minimize the threat from debris impacts on shuttle surfaces.
However, Hubbard said, "I don't know personally of any way you can patch a hole this big."
Hubbard noted that it is unlikely that any of the cameras positioned along the Florida launch range would have been able to detect a dark hole, even of this conspicuous size, against the dark background of the heat shielding during the turbulent launch.
Today's hole is on the edge of the resolving power of the camera with the best view of the impact point, he said. The cameras could see details as small as about 1-by-2 feet, he said.
"But you're looking at black on black," he said.
The tests used a compressed-gas cannon with a 35-foot-long barrel to fire foam at a million-dollar mockup of the shuttle wing. Today's test was only the second using actual shuttle components. The target leading-edge panel, No. 8, was taken from the orbiter Atlantis and had flown 27 flights -- comparable to the hardware on Columbia. Panels 9 and 10 were taken from the orbiter Discovery.
Shuttle officials had resisted giving up the heat-shield panels. Each is custom-made, costs about $800,000 and takes about eight months to manufacture.
In preparation for the tests, the board had engineers build a full-scale mockup of the shuttle's leading edge and install it here at the Southwest Research Institute. The total cost of the hardware in today's test was about $3.4 million, Hubbard said.
The earlier test on actual leading-edge hardware and five others using fiberglass mockups had produced serious cracking and dislocation, but nothing approaching today's damage.
There were key differences between this test and earlier ones, Hubbard noted. The target point on Panel 8 was lower on the wing, and the foam was fired so it struck along the length of its 11.5-inch edge, rather than on one of its corners, in order to more accurately reflect the estimated force of the launch-day impact.
He emphasized that the test was not a "worst-case scenario" but one involving mid-range impact, using averages of the lowest and highest possible velocity and other measurements of the observed launch-day impact.
Bill Parsons, the newly installed shuttle program manager, today directed that NASA continue the testing as shuttle engineers try belatedly to understand the characteristics of leading-edge heat-shield system.
"I would think that before return to flight," Hubbard said, "you'd need to know a lot more about what I call the 'damage threshold.' I don't know, and I don't know that anybody knows, what that threshold is for RCC."
© 2003 The Washington Post Company
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