This
story was updated at 8:28 p.m. EST.
CAPE
CANAVERAL, Fla. -- NASA's shuttle Atlantis and its seven-astronaut crew will
have to wait until Saturday to rocket toward the International Space Station
(ISS) with a new European laboratory after a sensor glitch thwarted a Thursday
launch attempt.
Faulty
readings in two of four hydrogen fuel gauge sensors prevented Atlantis
from launching from NASA's Kennedy Space Center here at 4:31 p.m. EST (2131
GMT). NASA flight rules call for three operational sensors in order to launch.
"Preliminary
indications are that we have an open circuit there," said NASA shuttle launch
director Doug Lyons after the scrub, adding that more analysis is required to
determine if that is the case and the circuit's location. "Once we isolate
that, we can determine the appropriate corrective action."
Atlantis
and its STS-122 astronaut crew are now set to launch spaceward Friday at 3:43
p.m. EST (2043 GMT), with weather forecasts predict an 60 percent chance
favorable conditions at launch time.
Known as Engine
Cut-Off (ECO) sensors, the instruments sit on the bottom of Atlantis'
15-story external tank and serve as liquid hydrogen fuel gauges that ensure a
shuttle's three main engines shut down before their hydrogen supply runs dry
after liftoff. NASA shuttles consume more than 500,000 gallons (1.9 million
liters) of super-chilled liquid hydrogen and liquid oxygen propellant during
the 8.5-minute flight into space.
"It is a redundant system,"
Lyons said of the fuel sensors, adding that Atlantis' onboard computer should
automatically shut down the shuttle's engines before the cut off sensors are
required. "But it is a system that's critical to us, so we certainly want them
to operate so we can go fly."
While fueling Atlantis'
tank, engineers found that two of the four hydrogen sensors failed a standard
test while covered in liquid hydrogen. The test, which commanded the sensors to
falsely read dry while awash in propellant, determines whether the sensors are
functioning properly. Similar glitches have delayed
several shuttle flights over the last two years, beginning with STS-114 -
the agency's first post-Columbia accident flight - in July 2005.
Commanded
by veteran shuttle flyer Stephen Frick, Atlantis' planned 11-day
mission will deliver the European Space Agency's Columbus
laboratory to the International Space Station (ISS) and swap out one member
of the outpost's three-astronaut crew. At least three spacewalks are planned during
the mission to install Columbus and upgrade the ISS.
Set to
launch spaceward aboard Atlantis with Frick are STS-122 pilot Alan Poindexter,
mission specialists Rex Walheim, Leland Melvin, Stanley Love and European Space
Agency astronauts Hans Schlegel and Leopold Eyharts.
The shuttle
mission will mark NASA's fourth ISS construction flight of 2007 and the second
to add a new pressurized room to the orbital laboratory this year.
NASA must
launch Atlantis by Dec. 13 while the angles between the space station's solar
arrays and the sun are favorable to generate enough power while the orbiter is
docked. If the shuttle cannot launch by the window's close, NASA will likely
stand down until no earlier than Jan. 2 for another attempt, mission managers
have said.
"The team
remains in good spirits," Lyons said. "And we are really confident that we can
work our way through this and get a few launch attempts in this window."
If Atlantis
is unable to launch Friday, a third attempt is possible on Saturday at 3:43
p.m. EST (2043 GMT). The launch time for NASA's STS-122 mission occurs slightly
earlier each day as the flight window progresses in order to keep the shuttle
on target to meet the ISS in orbit.
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