The board investigating the Columbia space shuttle disaster issued its first recommendations to NASA yesterday, saying that the agency's existing methods of inspecting the crucial heat-shielding on the leading edges of the shuttles' wings are "not adequate."
In urging a more thorough and scientifically advanced inspection of the carbon composite on the leading edges, the board was reflecting its prevailing belief about the event that triggered the Feb. 1 destruction of the Columbia: that a breach in the left wing's heat shield allowed superheated gas to penetrate and caused the craft to disintegrate as it reentered the atmosphere, killing its seven crew members.
The board also criticized NASA's recent agreement with a government spy satellite agency to capture detailed satellite images of orbiting space shuttles whenever the opportunity presents itself. The board urged that imaging of orbiting shuttles be a "standard requirement."
Some board members, including former astronaut Sally Ride, have expressed bafflement that NASA managers refused to seek photographs of the space shuttle in orbit after the left wing was struck by foam debris during launch Jan. 16. NASA engineers discovered the incident while reviewing videotapes a day later, but NASA managers, relying on a computer analysis of Boeing Co. engineers that concluded there was no flight risk, opted not to seek satellite or ground-based photographs of the shuttle.
Last month, NASA officials attempted to anticipate the board's recommendation on imaging by entering into an agreement with the National Imagery and Mapping Agency "to employ NIMA assets during targets of opportunity," without NASA having to request the imaging each time. But board members want assurances that every shuttle flight will be photographed in orbit to detect problems, and offered a recommendation yesterday to strengthen the NASA-NIMA agreement, a board source said.
The requirement could place an added constraint on NASA's scheduling of shuttle launches, depending on how the final memorandum of understanding with NIMA is worded, NASA and board officials said.
Yesterday's pronouncements were the first in a series of recommendations that the 13-member Columbia Accident Investigation Board is expected to issue for improving the safety of the three remaining shuttles, which were grounded after the Columbia accident. The board, headed by retired Adm. Harold W. Gehman Jr., hopes to complete a preliminary report by late June or early July pinpointing the probable causes of the breakup and recommending changes in shuttle design and program management.
In its assessment of NASA's program for inspecting the Reinforced Carbon-Carbon (RCC) compound shielding the leading edges, the board concluded that "current inspection techniques are not adequate to assess structural integrity of RCC, supporting structure and attaching hardware."
NASA Administrator Sean O'Keefe has pledged to implement all of the board's recommendations as quickly as possible in a bid to speed the resumption of the shuttle missions, which are critical to servicing the International Space Station.
However, in a speech to the National Press Club yesterday, O'Keefe stressed that the board would give NASA broad leeway in determining the technical details of how to revamp the shuttle program and resume operations. "They aren't going to prescribe what the solutions need to be," he said.
Judging from what is known about problems that must be fixed, O'Keefe said the shuttles could resume flights by the end of the year at the earliest.
He said it is clear from the results of the investigation so far that NASA must improve its ability to track and analyze trends involving recurring hardware problems. "We should do a better job of trying to really analyze what that trend may be telling us about future problems."
The bigger challenge of the two recommendations is the call for NASA to develop modern methods of nondestructive testing of the heat-shield panels on the leading edges. Ideally, such tests, conducted between shuttle flights, would detect subsurface defects without engineers having to tear apart the components.
But Michael Greenfield, NASA's top technology official and a leader of its preparations to resume shuttle flights, said no such tests have proven viable on this particularly complex composite material.
He said it could take months to certify such a test, which might include X-ray or ultrasonic techniques.
In addition to developing new testing methods, NASA is leaning toward requiring that all the wing panels be removed and inspected on all sides after every flight. Such a procedure is not adopted casually, engineers said, because anytime they detach and install parts they risk introducing a problem.
The wings' leading-edge shielding, along with its attachment hardware and support structure, has no backup system. NASA lists it among the critical items whose failure can lead to the loss of vehicle and crew. In recent years, inspectors have found several instances of significant postflight damage to the area.
NASA up to now has relied on visual inspections, manually tapping and feeling for soft spots. Since the accident, tests commissioned by the investigation board have found that these methods missed defects in the wing panels attributed to aging of the composite material.
After about every eight flights, when the shuttles go into dry dock for refurbishment, "we take the vehicle virtually apart and replace things which had environmental problems" such as corrosion, Greenfield noted. This process includes an examination of the heat-shield panels on the wings. "Those that need to be reworked are sent back to the factory."
On Columbia's left wing, he said, all of the carbon fiber panels were originals, more than two decades old, but eight to 10 of them had been sent back to the factory for refurbishment. The rest were deemed to be "in good shape."
Even before the loss of Columbia, repeated leading-edge damage had prompted NASA to begin work on at least one kind of nondestructive testing. Since the breakup, NASA's Leading Edge Structural Subsystem Problem Resolution Team, relying on experts at NASA's Langley Research Center in Hampton, Va., and in the industry, has accelerated efforts to develop such tests.
Investigators are focusing not only on the panels themselves, but also on the sealers between them and other attached hardware as possible sources of the breach in the wing.