컬럼비아호 사고조사위원회( http://www.caib.us/default.asp)는 24일 오후 1시(미국 동부시각) 기자회견을 통해 이번 사고를 일으켰으리라 짐작되는 기체손상부분을 찾아냈다고 밝혔다. 수집된 잔해를 조사한 결과, 이번 추락에 결정적인 역할을 한 손상부위는 그림에서와 같이 왼쪽 날개 시작 부분의 8번째 강화 카본 카본(Reinforced Carbon Carbon) 패널이라는 것. 이러한 사실은 근처 다른 패널 안의 금속구조물은 그대로 존재하는데 반해 8번 패널 속의 금속구조물만 없어졌다는 점에 근거를 두고 있다.

이와같은 결과가 나옴에 따라 컬럼비아호 폭발사고 원인 규명은 외부연료탱크에서 떨어진 발포단열재가 어떻게 손상을 주게 되었는지를 밝혀내는 실험에 주안점을 두게 될 것으로 보인다. 최근에 행해진 충격 실험에서 발포단열재가 실제 쓰였던 패널에 균열을 일으킬 수 있다는 점이 밝혀진 바 있다(첨부된 사진 참조). 사고조사위원회는 한달 후에 최종 사고조사 결과보고서를 발표할 예정이다. 출처: 뉴욕타임즈 06/25/2003

강화 카본 카본 패널 관련 자료: http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html#sts-rcc






June 25, 2003
Shuttle Board Determines Likely Site of Fatal Damage
By MATTHEW L. WALD


WASHINGTON, June 24 — The Columbia Accident Investigation Board today located within inches the spot on the shuttle's left wing that was damaged by foam on liftoff on Jan. 16 and said the wing came apart at that point 16 days later in the shuttle's re-entry from space.

The spot, the board said, was on the eighth of 22 panels on the leading edge of the wing, probably on its lower side.

Two board members described the evidence for fatal damage at Panel 8 as "compelling."

"We've been trying to line up all the Swiss cheese holes," one board member, Roger E. Tetrault, said, elaborating on the evidence. "I think those holes have lined up pretty good."

Mr. Tetrault also said that foam was "the most probable cause" of the disintegration of the shuttle, adding that it was the first time he had made such a statement.

While the board has not made any formal finding yet, and the chairman said its 13 members would not agree on what word to use to describe their degree of certainty about the cause of the accident, members said the damage caused by foam was clear from several independent sources, including the debris from the crash, pictures from liftoff, the pattern of data loss on re-entry and a series of laboratory tests still being performed.

Panel 8, which is U-shaped, is about 28 inches wide and 25 inches high on each side. On the Columbia, it was the widest of the panels and was not supported in the middle. It has a complex shape because the wing of the V-winged orbiter begins to swing away from the fuselage there.

One piece of evidence supporting Panel 8 as the site of the damage is that so much of the metal hardware behind the panel is missing because the hardware had melted and re-solidified. The metal hardware appears to be intact on adjacent pieces.

In addition, pieces of the panel were found over a large area, indicating that part of it broke off with the left wing, which was found generally to the west of the rest of the wreckage, while part of it stayed with the main body of the shuttle until its final breakup over Texas.

But board members have been able to draw only limited conclusions based on the location of shuttle debris. All the pieces, including those that came off in chunks and then broke up again on their way down, flew with a different glide path because each had its own ratio of lift to mass.

As a result, the order in which pieces were found under the shuttle's path does not precisely coincide with their order of breaking off the orbiter.

Investigators have given up trying to determine precisely how each part of the debris flew.

As they near the completion of their report, expected in about a month, the investigators are still finding other areas that puzzle them. They determined, for example, that foam fell from a connector to the external fuel tank in seven launchings. Five of those involved the Columbia, and a sixth occurred with the Challenger, which exploded shortly after liftoff in 1986. The seventh was the Atlantis, three months before the Columbia's fatal launching.

"I wish I had an answer for that," said Adm. Harold W. Gehman Jr., the board chairman.

Admiral Gehman said investigators had looked without success at the names of the technicians who made those parts, the humidity when they were fabricated in a Louisiana factory and the angles at which the shuttles were sent into orbit, among other factors.

It was clear today that other factors might never be explained. For example, Scott Hubbard, a board member, described in a briefing today tests that are now being carried out at the Southwest Research Institute in San Antonio, where technicians are using a gun with a 30-foot barrel to fire pieces of foam at a test structure at about 500 miles an hour.

In recent tests, they have varied the part of the block of foam that hits the wing — sometimes using a corner and sometimes an edge — and have found that this makes a substantial difference in the way that the wing panels are damaged.

They estimate that during the launching, the debris was rotating about 18 times a second, so they have no idea how it hit.

The investigators are planning a test early next month using the same kind of material, reinforced carbon carbon, that was on the leading edge of the Columbia's wing. In fact, some of it will be actual shuttle material, borrowed from the shuttle Discovery because carbon carbon parts are in short supply.

Replacing the panel taken from the Discovery will take about six months, Admiral Gehman said, a time frame that meshes with the earliest time that NASA is likely to fly a shuttle again.

As it continues to deal with other material from the Columbia's wreckage, NASA today released video images and photographs of the crew salvaged from the 85,000 pounds of debris found.

Also today, Admiral Gehman laid out other recommendations the board is likely to make to NASA. One is a reduction in foam shedding, especially of large pieces, and another focuses on the orbiter's ability to withstand hits. A third centers on the ability to repair the orbiter in space.

Admiral Gehman said that he favored the creation of an escape system for the crews but that the board would not delve into that area.

In addition, Admiral Gehman said his board would recommend that NASA more urgently pursue the successor to the shuttle. NASA should be further along with a design, he said, but now is simply circulating conceptual diagrams.