of tests to determine what caused shuttle Columbia to break up on re-entry on February 1, killing all seven aboard. The remaining three shuttles have since been grounded.
Because engineers worried that pieces of foam insulation from the shuttle's massive external fuel tank may have damaged the orbiter during launch, the independent investigators probing the Columbia disaster test-fired similar foam at high speed against a piece of a space shuttle wing.
Pictures of the sample wing, released by O'Keefe at a briefing with reporters, show hairline cracks extending several inches (centimetres) inside and outside the wing.
"You've got to put your face about 2 to 3 inches (5 to 7.6 cm) away in order to see that crack," O'Keefe said. He stressed that the independent Columbia Accident Investigation Board, which is to convene in Washington on Thursday, has drawn no conclusions from this test.
However, he noted that if this is the kind of damage caused to Columbia, NASA will have to put an "extremely meticulous" inspection plan in place before all future shuttle flights and all launches would have to be in daylight.
The space agency had concluded that future launches should "be conducted during daylight so that we can have multiple cameras and examine every single facet that may have occurred during launch so we can get as much data as we possibly can," O'Keefe said.
He said astronauts on future shuttles may make more space walks while orbiting or while docked at the International Space Station to inspect possible damage. NASA is considering structural changes, including putting hand- and foot-holds on shuttles to let astronauts get close to any damaged areas.
As he has before, O'Keefe acknowledged there was no fail-safe inspection plan on such an inherently risky venture as space flight. But he was insistent that keeping the shuttles grounded indefinitely was not an option.
He said the pictures of the hairline cracks were sobering but added the space exploration program must go on and rejected any suggestion of giving up. "If we give up we ought to just go back to the caves. ... Build fires in caves and call it quits, because we're afraid of everything," he said.
"That's not the nature of human experience, and it sure isn't the instinct and motivation and drive of the astronaut corps," he said.
Shuttles could return to flight as soon as December or early in 2004, O'Keefe said. All future flights except one will dock at the International Space Station, which should make damage inspection easier. The exception is a mission to repair the orbiting Hubble Space Telescope, expected next year.
While the shuttles are grounded, Russian vehicles are ferrying supplies to the space station, and a robotic Russian Progress vehicle docked at the orbiting outpost on Wednesday.
Meanwhile, on Capitol Hill, US-Russian space cooperation came under question by Henry Sokolski, executive director of the Nonproliferation Policy Education Center.
"Conventional wisdom has it that the more we and our allies cooperate with Russia on civilian space projects and show them that they can profit from peaceful trade, the less they will be inclined or need to sell this sensitive technology to nations that would use it for military purposes," Sokolski told a House Science panel.
However, he said Russia's most important incentives to proliferate have nothing to do with profit, but rather with a desire to have leverage with such states as Iran and China, and to maintain its outsize space and missile sector.