Spaceflight Now

CAIB recommends extensive leading edge inspections
Posted: April 17, 2003

As expected, the Columbia Accident Investigation Board today released its first two interim recommendations to NASA, calling for routine spy satellite imagery of shuttles in orbit and detailed pre-flight inspections of the protective panels on the leading edges of the shuttle's wings. A breach in a reinforced carbon carbon (RCC) panel on Columbia's left wing is believed to have triggered the shuttle's breakup during re-entry Feb. 1.

An agreement to make classified on-orbit imagery a routine requirement during shuttle flights is already in work by NASA and the National Imagery and Mapping Agency, or NIMA. But what might be required to implement the board's other recommendation - extensive pre-flight tests of the shuttle's leading edge panels - and how long such tests might take to complete is not yet clear.

"This recommendation was issued because of the board's finding that current inspection techniques are not adequate to assess structural integrity of RCC, supporting structure, and attaching hardware," the board said.

During Columbia's launching Jan. 16, a chunk of external tank foam insulation broke off 81 seconds after liftoff and slammed into the left wing leading edge, at 450 mph, one second later. NASA managers decided not to request satellite imagery of the shuttle's wing after concluding the orbiter could safely land as is. That decision has faced criticism and second guessing in the aftermath of the disaster and the accident investigation board has concluded such imagery should be routine for future flights.

"Prior to return to flight, NASA should modify its Memorandum of Agreement with National Imagery and Mapping Agency (NIMA) to make on-orbit imaging for each Shuttle flight a standard requirement," the board stated today.

The interim recommendation included three supporting facts: A) The U.S. government has the capability to image the shuttle on orbit; B) a Memorandum of Agreement exists between NASA and NIMA regarding on-orbit imaging of the shuttle; and C) "during the flight of STS-107, there were no on-orbit images taken of sufficient resolution to assess the orbiter's condition."

But the board's primary recommendation was for NASA to implement non-destructive evaluation, or NDE, to determine the heath of the RCC leading edge panels before shuttles are cleared for launch.

"Prior to return to flight, NASA should develop and implement a comprehensive inspection plan to determine the structural integrity of all Reinforce Carbon-Carbon (RCC) system components," the board wrote. "This inspection plan should take advantage of advanced non-destructive inspection technology."

The board noted that the RCC panels are a non-redundant, "crit 1" system, meaning a failure results in the loss of the vehicle and its crew. During initial manufacturing, the carbon-carbon composite is tested at various stages in the assembly process "by physical tap, ultrasonic, radiographic, eddy current, weight gain, and visual tests."

"In addition, a flat plate control panel made in parallel with the production piece is destructively tested at various points in the production process," the board wrote. The projected lifetime of the panels assumes the material and its support hardware are free of any internal defects.

Going into Columbia's mission, "visual external inspections and tactile checks" were the only tests required to assure the RCC panels were safe to fly unless visually obvious problems results in replacement.

But in the wake of the Columbia disaster, "non-destructive testing of some post-flight RCC components has shown indications of RCC material defects not previously identified by visual inspection methods currently employed," the board wrote, recommending the implementation of routine NDE of the leading edge.

A major question mark, however, is what technology is needed to implement such tests and inspections and how long it might take to thoroughly examine the 44 RCC panels on each orbiter. And the board did not specifically state whether such inspections are required before return to flight or before every flight.

Hubble Calendar
NEW! This remarkable calendar features stunning images of planets, stars, gaseous nebulae, and galaxies captured by NASA's orbiting Hubble Space Telescope.

Hubble Posters
Stunning posters featuring images from the Hubble Space Telescope and world-renowned astrophotographer David Malin are now available from the Astronomy Now Store.

Earth Calendar
NEW! This amazing 2003 calendar features stunning images of mountain ranges, volcanoes, rivers, and oceans obtained from previous NASA space shuttle missions.