CAPE
CANAVERAL, Fla. - The clock is once more ticking
down to a Sept. 8 launch for NASA's space shuttle Atlantis after engineers all
but cleared a fuel
cell issue aboard the spacecraft, mission managers said late Thursday.
Atlantis is now set to launch six
astronauts - commanded by veteran shuttle
flyer Brent Jett - towards the International Space
Station (ISS) at 11:40:32 a.m. EDT
(1540:32 GMT) and deliver a new set of solar
arrays and two massive trusses to the orbital laboratory.
Only one final analysis stands
between Atlantis and a Friday launch attempt here at the Kennedy Space Center
(KSC), though shuttle officials expect a favorable result.
"We have had to stand down two days
to make sure we are safe to fly, we have gone the extra mile," NASA shuttle
program manager Wayne Hale told reporters, adding that the risk of launching
Atlantis is less than replacing the fuel cell in question. "I don't feel like
we're not racing to the end of the [launch] window."
The announcement, which was not
entirely unanimous among shuttle managers, comes one day after an electrical
short in Fuel Cell 1 - one of the three units that produce the electricity for
all of Atlantis' systems - forced mission managers to scrub
a Wednesday launch attempt so engineers could track the problem.
The short stifled one of three
alternating current (AC) power phases for the fuel cell's vital coolant pump
motor, which prevent the generator from overheating in flight. While the other
two phases continued to function perfectly, engineers wanted to make sure they
wouldn't fail during Atlantis' 11-day flight and force the shuttle's STS-115
astronauts to come home early without completing all their objectives - known
as a minimum duration mission.
Steve Poulos, NASA's orbiter projects
manager, said the problem likely lies in thin wire for the Phase
A power loop in Fuel Cell 1's vital coolant motor. The phase will be switched
off to avoid future shorts during Atlantis's launch, but engineers will not
know for sure what prompted the failure until they dissect Fuel Cell 1.
"Until we take the fuel cell out, we
won't know exactly. It's a detective story," Hale said. "There is always the
element that we could be wrong."
Poulos said the Fuel Cell 1 cooling pump
last flew aboard NASA's Columbia orbiter during its STS-93
mission, which experienced an electrical short during launch due to wiring
issues. However, the fuel cell was found to be unaffected from that flight.
Replacing the 255-pound fuel cell aboard Atlantis, especially at the launch
pad, is no small order and runs a higher risk of causing more damage to the
orbiter than launching the spacecraft, he added.
"We're good to go fly, we're ready
to support this mission," Poulos
said. "I don't have a concern that we're going to lose this fuel cell going
uphill or during the mission."
Atlantis' STS-115 mission is set to
install the $371.8 million Port 3/Port 4 (P3/P4) trusses and wing-like solar
panels to the port side of the ISS during a series of complicated robotics
tasks and three spacewalks. The spaceflight is NASA's first dedicated ISS
construction mission since late 2002 and the third shuttle launch since the
2003 Columbia tragedy.
The spaceflight has been in a pinch
of sorts.
Launch lighting rules are in place to
allow cameras to scan Atlantis' external tank for any signs of falling foam
insulation - a debris hazard similar to that which doomed Columbia and its crew in 2003 - during
launch. The resulting footage would be used to guide future external tank
modifications.
While NASA's full window to launch
Atlantis extended through Sept. 13, the space agency has also promised Russia's Federal Space Agency that it
would stand down after Sept. 8 to allow the liftoff of a Soyuz spacecraft
carrying a new
crew to the ISS.
The shuttle was expected to undock
from the ISS on Sept. 17, with the Soyuz to launch towards the station one day
later.
NASA ISS program manager Mike Sufferdini said that
Atlantis can now launch on Sept. 9 and undock on Sept. 18 within hours of the
Soyuz liftoff. This will maintain the much-needed buffer time for the space
station's three-astronauts to jettison an unmanned Russian Progress cargo ship
on Sept. 19 and be ready for the arrival of the Soyuz on Sept. 20.
"We have kind of a choreography
to do," Sufferdini said. "We have all these
vehicles flying around, coming and going at the space station."
Should Atlantis remain grounded
Friday, Sufferdini
will meet with his Russian counterparts to review the Sept. 9 launch plan.
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