HOUSTON - NASA engineers have cleared the space shuttle Atlantis' heat
shield of any concern pending one last inspection by the orbiter's
six-astronaut crew, mission managers said Tuesday.
John
Shannon, NASA's deputy shuttle program manager, said engineering teams cleared
two final issues prompted by orbital photography
and a detailed
inspection of Atlantis' heat-resistant tiles, wing edges and nose cap.
"We were
able to clear all of the thermal protection system in 60 hours [and] my best estimate
was always five days, about 120 hours," Shannon, who also chairs Atlantis'
STS-115 Mission Management Team, told reporters in a briefing here at NASA's
Johnson Space Center. "So we did it in half the time."
Atlantis is
docked at the International
Space Station (ISS), where its six-astronaut crew delivered a massive
pair of trusses and new solar arrays in a spacewalk
earlier today. The mission is NASA's first ISS construction flight since late
2002.
The only
two shuttle heat shield issues of any note included a slightly puffed thermal
blanket on the dome of Atlantis' starboard - or right - Orbiter Maneuvering
System (OMS) pod and a bright bit of orange plastic known as shim stock.
The thermal
blanket represented no debris or excessive heating threat to Atlantis on
reentry and the plastic
shim - once thought to be a ceramic
cloth gap-filler - will melt well before the orbiter experiences its
maximum heating during landing.
Shuttle
tiles withstand temperatures of about 2,300 degrees Fahrenheit (1,260 degrees Celsius)
at the peak of atmospheric reentry. The plastic shim will soften at just 200
degrees Fahrenheit (93 Celsius) and melt completely at 450 degrees (232
Celsius), Shannon said.
One last inspection, to scan for any damage by orbital debris or micrometeorites, is scheduled once Atlantis undocks from the ISS next week.
The fact
that NASA engineers cleared Atlantis' heat shield on Flight Day 4 of the shuttle's
mission, rather than one or two days later as seen on the last two shuttle
flights, is a sign that the engineering teams are streamlining and improving
their processes, Shannon added.
ISS Additions
Also Doing Well
In addition
to Atlantis, the space station's new $372
million trusses and solar arrays are also doing well after a swift spacewalk
today.
John
McCullough, NASA lead ISS flight director for Atlantis' STS-115
mission, said some systems aboard the still-unpacked
solar arrays and a 45-foot
(13-meter) pair of massive trusses were powered up following the spacewalk
by astronauts Joseph
Tanner and Heidemarie
Stefanyshyn-Piper.
The
astronauts attached 15 critical power and data lines, as well as two fluid
lines, to bring the 17.5-ton Port 3/Port 4 (P3/P4) trusses into the ISS fold.
The solar array boxes were poised in position to deploy their power-generating
panels on Thursday morning, ISS Mission Management Team chairman Kirk Shireman
said.
Flight
controllers sent 1,631 commands to the ISS in a careful choreography with the spacewalking
crew, more than eight times the standard 200 commands of any given eight hours
aboard the station, Shireman said.
The only hitch
in the orbital construction job was the loss of a small 1.5-inch (3.8-centimeter)
bolt, which lost a restraining washer and popped off a thermal cover Tanner
removed from a motor lock on the P3 element's Solar
Alpha Rotary Joint (SARJ). Located between the P3 and P4 trusses, the SARJ
is a motor-driven wheel that will rotate P4 and future outboard segments so
their solar arrays can track the Sun for maximum power generation.
"It's
pretty trivial," McCullough said, adding that the bolts are likely no hazard to
the station, Atlantis or future spacecraft.
"I just
hope that bolt is on its way to Mother Earth right now and not anywhere around the
SARJ," Tanner said after today's spacewalk.
Shireman
said a second STS-115 spacewalking team - mission specialists Daniel
Burbank and Steven
MacLean of the Canadian Space Agency - are camping out in the space station's
Quest airlock tonight to purge their bodies of nitrogen for their mission's
second spacewalk on Wednesday.
That
planned 6.5-hour spacewalk calls
for Burbank and MacLean to remove 14 remaining launch locks on SARJ, where
they will now keep an eye on all bolts in use, station managers said, adding
that the Atlantis crew's ISS construction work is a welcome challenge.
"I felt
that this is what NASA is supposed to do," McCullough said after overseeing the
spacewalk. "Everything we do on the space station teaches us more about what to
do to reach the Moon and Mars."
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