HOUSTON--The
space shuttle Discovery was given a clean bill of health to return home Monday
after mission managers declared a fourth spacewalk would not be needed to
repair a damaged thermal blanket on the orbiter's hull.
"We have cleared
Discovery to reenter," said Wayne Hale, NASA's deputy shuttle program manager,
during a briefing here Thursday at Johnson Space Center (JSC). "We believe the
chances of anything untoward happening with this piece of fabric is remote."
The
announcement came after a night of wind tunnel tests which proved that sizeable
chunks of the small thermal blanket--damaged on launch and puffing out from just
below the orbiter's leftmost flight deck window--would likely not rip off and
smash into a vulnerable section of Discovery. The blanket clearance was the
last piece needed to clear Discovery for landing. Its heat-resistant tiles and
reinforced carbon carbon (RCC) panels were cleared
during earlier inspections, shuttle officials said.
Hale said
that after wind tunnel tests of three concluded this morning, engineers
believed there was only a 1.5 percent chance a piece of the blanket could
detach from its mooring at time it could cause the worst damage--while the
Discovery was locked in supersonic flight between Mach 6 and Mach 1, about 10
minutes before landing. In that worst case scenario, a piece of the blanket
about eight-tenths of an inch long could pull free and hit a critical area,
such as the orbiter's tail.
"I will not
tell you that there is zero risk," Hale said. "Even if this blanket were in
pristine shape, there is not zero risk."
However, the
risk of landing with the damaged blanket was much less than the risk of once
more suiting up Discovery's two spacewalkers, STS-114 mission specialists
Stephen Robinson and Soichi Noguchi, and sending them
on a repair job.
This could
have potentially created more debris that could harm the orbiter or astronauts'
spacesuits, Hale said. Similarly, deciding to leave Discovery's crew on orbit
to be retrieved by a rescue shuttle--a remote case that would call for the
launch of Atlantis orbiter--also carries more risk than landing as there are
still concerns about external tank foam shedding during liftoff, Hale said.
The
damaged blanket
measures about 20 inches (50 centimeters) long and 3.8 inches wide (9.6 centimeter), though only about an eight-inch (20-centimeter) section puffed
up during launch.
Flight
controllers alerted Discovery's astronaut crew of the good news before mission
managers had concluded their daily meeting Thursday, NASA officials said.
"Soichi we have good news," astronaut Julie Payette, serving
as Discovery's CAPCOM. "The blanket is safe for return...so no EVA four."
"That's, I
would say, good news," Noguchi replied.
Noguchi and
Robinson have successfully conducted three spacewalks during their STS-114
mission, the latest including a first-ever repair of the orbiter's tile-lined
belly. During that repair, Robinson pulled two space-filling strips of
ceramic-lined cloth jutting out from between the heat tiles underneath the
orbiter's nose.
Meanwhile,
the entire STS-114 crew has completed their primary cargo transfer work,
loading tons of fresh supplies into the International Space Station (ISS) and
transferring still more tons into a cargo pod for return to Earth, shuttle
officials said.
The shuttle
is scheduled to land at NASA's Kennedy Space Center on Aug. 8.
"This
flight has been conducted flawlessly," Hale said. "It is a thing of beauty."
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