HOUSTON - The space shuttle Discovery's astronauts are safe to come home without further repairs to the ship's heat shielding, NASA managers decided yesterday.
Engineers had debated whether to have the crew perform the mission's fourth spacewalk to deal with a torn thermal blanket beneath a window outside Discovery's flight deck. The concern was that parts of the woven ceramic material might break free during the latter stages of the shuttle's return to Earth and hit another part of the orbiter.
Analyses concluded that a damaged piece of the blanket, weighing less than an ounce, had a 1.5 percent chance of coming off at a critical time and causing structural damage. A unanimous mission management team determined that was a "negligible concern" not worth the risk of another spacewalk and cleared Discovery for landing.
"Our indications are that nothing will come off. Or at least, if it does come off, it will be very small, a few threads, a few little pieces of the blanket," said N. Wayne Hale, deputy manager of the shuttle program.
Hale characterized the management team's deliberations as "eerie" at times because of the memories they evoked of discussions during Columbia's final flight. The difference, he said, was that a wide array of improved policies and procedures led to a far better understanding of technical issues during Discovery's mission.
"It's just a night-and-day difference," Hale said. "We have a much larger team invested in evaluating all these things. We have independent reviewers that are part of every step of the way, so that alternative thoughts are brought into this. And finally, I guess the most profound thing is we put the orbiter under a microscope."
In orbit, Discovery's seven astronauts expressed confidence about their safe homecoming, scheduled for 4:46 a.m. Monday at Kennedy Space Center in Florida.
The crew had a mostly restful day yesterday after transferring unneeded items from the International Space Station into a 21-foot-long cargo canister that will be brought back to Earth aboard the shuttle.
During Wednesday's spacewalk, astronaut Steve Robinson easily removed two dangling pieces of fabric from the tile-covered underside of Discovery. Engineers had worried that the fabric might cause excessive heating of the shuttle as it re-entered the atmosphere.
Memorial for Columbia
The astronauts took time yesterday for a memorial to the crew of Columbia and others who have died in the pursuit of space exploration.
Wearing red shirts embroidered with Columbia's logo, the astronauts took turns honoring the astronauts who died in 2003 when their shuttle broke apart as it flew over Texas 16 minutes before landing.
"In that accident, we lost seven friends," astronaut Charles 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."
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