HOUSTON - The heat shield that protects the
space shuttle Discovery from the searing temperatures of reentry has a clean
bill of health, NASA mission managers said Sunday.
Final
analysis of a protruding bit of ceramic cloth and two dinged thermal blanket
patches yielded no concerns over Discovery's ability to bring its six-astronaut
crew home safely, shuttle officials said.
"Not only
did the team pound these issues flat, they put a dimple in the board when it
was all said and done," said Steve Poulos, NASA's orbiter project manager,
during a briefing here at the Johnson Space Center. "We are absolutely clear
and ready to bring this vehicle home whenever the mission is accomplished."
The
announcement comes four days after Discovery's STS-121 crew made their first
inspection of their spacecraft's heat shield, and two days after a second
look at six areas
of interest chosen by a team of analysts.
"That is
great news, that's fantastic," Discovery's commander Steven
Lindsey told flight controllers today after hearing the news. "To get all
that done by Flight Day 6 when we did focused inspections on Flight Day 4 is
amazing."
Poulos said
that detailed analysis of a small,
ceramic cloth gap filler jutting from between tiles on the mid-aft region
of Discovery's belly have shown that - in a worst case scenario of maximum
heating - the added stress it could cause during reentry would not exceed the
thermal or structural limitations of the surrounding shuttle tiles or
spacecraft structure. The heating would also not affect the eight shuttle
subsystems that are positioned inside the orbiter near that area of the
vehicle, he added.
Similarly,
engineers conducted pull tests on test articles, and then NASA's space
shuttle Endeavour, to determine that a paid of small thermal blanket
patches on Discovery's nose should not rip off as the vehicle reenters the
Earth's atmosphere. Additional debris transport analysis - using computer
models to determine whether any bits could damage Discovery if they did break
free - also found no issues, NASA said.
Poulos said
STS-121 mission managers have taken the lessons learned from the heat shield studies
of NASA's first post-Columbia mission, July 2005's STS-114 mission also aboard
Discovery, to streamline the process of evaluating the shuttle's thermal
protection system.
"What we
found was that a lot of the team members were spinning their wheels waiting on
people to hand off data," Poulos said of the STS-114 effort, adding that new
systems are in place to cut down on that time. "Basically, all the data is
available simultaneous to everybody."
Lindsey and
his STS-121 crew launched toward the International Space Station (ISS) on July 4,
and are nearing the midpoint of their 13-day
mission in orbit. Their shuttle mission is NASA's second orbiter test flight
since the 2003 Columbia accident,
and is aimed at resupplying the ISS, ferrying a third crewmember to the orbital
lab, and testing shuttle heat shield repair tools and techniques.
In addition
to completing NASA's post-Columbia return to flight goals - which includes developing
the hardware and methods to fix damaged shuttle heat shield tiles and panels - Discovery's
STS-121 mission is delivering
more than 5,000 pounds (2,267 kilograms) of cargo, 2,000 pounds (907
kilograms) of ISS equipment and European astronaut Thomas
Reiter to the orbital space station.
Reiter, a
native of Germany and the first European Space Agency (ESA) astronaut to take a
long-duration post aboard the ISS, has joined the station's Expedition
13 crew and will stay on through the beginning of Expedition
14 before returning to Earth aboard Discovery in December.
"This has
really been two missions for us," said John Shannon, NASA's deputy shuttle
mission manager and chief of the STS-121 Mission Management Team. "The other
piece of it, which is just as important, is what we have done for the station."
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