HOUSTON - The crew of the space shuttle Discovery will commemorate their lost Columbia astronaut comrades today, but fear communications problems may cut their service short, the shuttle's commander told reporters today.

Veteran astronaut Eileen Collins, commander of Discovery's STS-114 mission, would not shed light on plans for the commemorative video downlink, to be broadcast live on NASA Television at 8:04 a.m. EDT (1204 GMT), but expressed confidence in the health of their spacecraft now docked at the International Space Station (ISS)

"I wouldn't fly this flight if I didn't think it was a safe thing to do,'' Collins told the Associated Press, adding that a spacewalk repair to the orbiter's tile-lined belly Wednesday has boosted her confidence in the shuttle. "When I saw Steve pull the gap-filler out, I started clapping and we were cheering in the flight deck."

During the spacewalk, Robinson pulled two gap-fillers - ceramic fiber cloth - jutting from between the heat-resistant tiles along the forward section of Discovery's belly. He is the first astronaut ever to be positioned on the underside of the orbiter, let alone perform a repair. Gap-fillers are used to fill excess space between shuttle tiles and prevent the heat-resistant blocks from bumping against one another.

"Nobody has done this before," Robinson's spacewalking partner Soichi Noguchi, of the Japanese Aerospace Exploration Agency (JAXA), told Japanese students and officials today of the repair. "It was an achievement...it was a team effort."

Collins has said that today's commemorative service, which will also include the crew of the International Space Station, is aimed at honoring all astronauts, including the seven astronauts who died aboard Columbia when it broke apart over Texas during reentry on Feb. 1, 2003.

"It is something we put together to remember the crews who've gone before us, including the Columbia crew," Collins said Tuesday during a joint shuttle-ISS news conference. "We have a picture of the Columbia crew on the flight deck of Discovery."

In 2003, investigators found that a briefcase-sized chunk of foam insulation fell from Columbia's external tank and pierced the heat shield lining its left wing leading, which ultimately allowed hot atmospheric gases to enter and destroy the vehicle during landing. Discovery's STS-114 crew has conducted an extensive survey of spacecraft's own heat shield using new tools and methods developed by NASA to enhance shuttle flight safety in response to the accident.

Engineers are still examining a damaged thermal blanket just under the left window on Discovery's forward section. While not a heating concern for reentry, engineers want to be sure pieces of the small blanket won't rip off and pose a potential hazard to the rest of the orbiter downstream. Should the blanket need to be removed, spacewalk planners are drawing up plans for the potential repair and Discovery's crew was notified of the possibility at the end of their work day Wednesday.

"I'm less interested today in determining what causes this problem, than in making sure it is safe for reentry," Wayne Hale, NASA's deputy shuttle program manager, said Wednesday.

Discovery and its STS-114 astronaut crew are scheduled to return to Earth on Aug. 8 and land at NASA's Kennedy Space Center in Cape Canaveral, Florida.

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