NASA is targeting
an early June launch for its space shuttle Atlantis and will complete repairs
to the orbiter's hail-battered external fuel tank rather than replace the
15-story vessel with a pristine one, mission managers said late Tuesday.
Atlantis
and its six-astronaut crew are now slated to launch towards the International
Space Station (ISS) no earlier than June 8 to deliver new starboard solar
arrays and girders to the orbital laboratory.
"As of
right now we're going to stay with the tank," said NASA shuttle program manager
Wayne Hale of Atlantis' pockmarked fuel tank during a teleconference late
Tuesday. "The entire team unanimously agreed that progress was being made to do
that."
Hale said
that the ongoing
repair work to Atlantis' fuel tank would allow the orbiter to leave the
cavernous Vehicle Assembly Building at NASA's Kennedy Space Center (KSC) in
Florida and return to its launch pad around May 6, but that would not allow the
orbiter and its STS-117 crew to launch within the limited flight window that
closes on May 21.
Since the
repair work was making progress, and replacing the Atlantis' fuel tank with a
new one would push the orbiter's launch date to no earlier than June 19, mission
managers opted to keep the current fuel tank, Hale added.
The new
launch window stretches from June 8 to about July 18, with the next flight
opportunity occurring around Aug. 5, NASA officials said.
Atlantis' STS-117
mission has
been delayed since Feb. 26, when a severe thunderstorm battered the
orbiter's fuel tank with golf ball-sized hail at its launch pad just weeks shy
of a planned March 15 liftoff. The hail gouged more than 2,600 dings in the
vital foam insulation covering the fuel tank.
Since that
freak February storm, which appeared to occur right over Atlantis' Pad 39A
launch site, engineers have been hard at work sanding the tank's surface and
filling in divots with new foam, while another team analyzes the fixes to
ensure they are sound.
Repair
work underway
John
Honeycutt, head of NASA's external tank project, said there are some 2,664
damaged areas on Atlantis' external tank. About 700 of them require workers to
pour new foam insulation into the divots, a task that is about half complete,
he added. Other areas will require a sand and blend approach, while still others
may require a spray technique.
Shuttle
workers are also removing the Atlantis' three main rocket engines to inspect
its propellant lines for silicone contamination akin to that found in the
propellant lines of Atlantis' sister ship Discovery, NASA officials said, adding
that the work is not expected to affect the orbiter's launch date.
Commanded
by veteran shuttle flyer Rick Sturckow, Atlantis' six-astronaut crew is gearing
up to install the 17.5-ton Starboard 3/Starboard 4 trusses and twin solar
arrays during three
spacewalks planned for their 11-day mission. He and his crew have used
their extra time on Earth to continue their mission training and spend time
with family and friends.
"They're
taking it in good spirits," Hale said of the STS-117 crew. "They want to have a
good safe launch vehicle."
Atlantis'
launch delay does mean that one NASA astronaut, spaceflyer
Sunita Williams currently aboard the ISS, will have to wait a bit longer to
return to Earth.
Williams
was scheduled to return home aboard NASA's Endeavour orbiter during the STS-118
mission in July. Atlantis' launch slip to June pushes Endeavour's planned
liftoff to early August, though Williams remains on schedule to return to Earth
with the STS-118 crew.
"Right now
we're staying with the current scenario," William Gerstenmaier, NASA's
associate administrator for space operations, told reporters.
Williams
could conceivably come home earlier aboard Atlantis, which would then bring NASA astronaut Clayton Anderson as a replacement, if the STS-118 flight slipped
deep into fall, Gerstenmaier added, but stressed that it is not the current
plan.
An eye
on foam
The layers
of foam insulation covering a shuttle's external tank prevent the vessel's
super-cold load of liquid hydrogen and liquid oxygen propellant from building
up ice on its aluminum exterior, NASA officials have said. Some foam at the
tank's nose provides protection from aerodynamic stresses during launch, they
added.
The foam's
integrity has been a prime concern since the 2003, when an errant chunk of tank
foam fell free during the launch of NASA's Columbia orbiter, piercing its left
wing leading edge heat shield and leading to the loss of the shuttle and its
seven-astronaut crew as they reentered the Earth's atmosphere.
NASA has
since made a series of modifications to shuttle fuel tanks to eliminate foam
where possible and limit the amount of material shed during launch. Shuttle and
ISS astronauts also perform meticulous robotic and photographic inspections of
an orbiter's heat shield while in space.
Atlantis'
STS-117 mission is expected to be the first of about four planned NASA shuttle
missions to continue ISS assembly in 2007. NASA hoped to squeeze in a fifth
shuttle flight during December, though mission managers have said that
spaceflight will likely slip to 2008. Even launching four shuttle flights this
year may prove challenging, they added.
"I would say
that flying four flights is not outside the realm of possibility," Hale said. "But
we want to do this in a safe and orderly manner."
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