SPACE CENTER, Houston – As Discovery's astronauts paused Thursday to honor their seven colleagues who died while returning to Earth in 2003, NASA (search) officials pondered whether another space walk was needed to fix a problem with the space shuttle.
Mission Control is weighing whether a fourth spacewalk will be needed to deal with a torn thermal blanket below a cockpit window.
The concern is that a roughly 1-foot section of the blanket could rip away during re-entry, whip backward and slam into the shuttle, perhaps causing grave damage. Engineers expect to know by Thursday afternoon whether the danger is real and whether any blanket trimming is required.
"I think in the old days we would not have worried about this nearly so much," deputy shuttle program manager Wayne Hale said. "I am very hopeful that we will be able to put this issue at rest."
Investigators determined a 1.67-pound chunk of foam fell from Columbia's external fuel tank when it launched and tore a hole in its left wing. The superheated gases of re-entry melted the wing from the inside out and caused Columbia to disintegrate over Texas as it headed to Florida's Kennedy Space Center (search) on Feb. 1, 2003.
Based on the tragedy, Discovery's astronauts have spent a majority of their test flight mission inspecting their ship, making repairs and testing out new repair techniques.
Discovery's astronauts were finishing work early Thursday loading items that Discovery will ferry back from the international space station. Three of the astronauts also planned to test out a proposed repair method for small holes in the carbon panels that line the shuttle's wings in Discovery's mid-deck.
That repair technique — a patch for small holes in carbon panels developed in the wake of Columbia — was the last of three set to be tested on orbit by Discovery's crew.
On Wednesday, Discovery astronaut Stephen Robinson removed two worrisome pieces of filler material from the shuttle's belly with a gentle tug — an unprecedented space repair job that drew a big sigh of relief from NASA (search).
Discovery's crew honored their fallen colleagues Thursday by talking about space exploration, its costs and remembered those who didn't make it home.
"We choose to do these things not because they are easy, but because they are hard," astronaut Wendy Lawrence said. "And certainly, space exploration is not easy and there has been a human price that has been paid."
Astronaut Charles Camarda said Columbia's loss in 2003 reaffirmed the need for those who explore to be vigilant about the risks involved.
"In that accident, we not only lost seven colleagues, we lost seven friends," Camarda said. "They believed in space exploration. They knew the risks, but they believed in what they were doing. They showed us that the fire of the human spirit is insatiable."
A picture of the seven Columbia astronauts has been displayed on Discovery's flight deck since it lifted off last week.
Meanwhile, a newspaper report published Thursday raised questions about NASA's actions. The New York Times quoted from an internal NASA memo, written in December, that said problems remained in the way foam was being applied to the fuel tank. The memo warned "there will continue to be a threat of critical debris generation."
A NASA spokesman told the Times that officials had a response to the memo but would not release it because of of confidentiality rules.
The Associated Press contributed to this report.