CAPE
CANAVERAL, Fla. - NASA engineers are attempting to root out the cause of a
sensor glitch that scrubbed Wednesday's launch of the space shuttle Discovery.
Pad
engineers drained Discovery's fuel-filled external tank of its super-chilled
liquid propellant late Wednesday after a sensor sent errant signals to flight
controllers during a countdown check.
"All I can
say is shucks," said Wayne Hale, NASA's deputy shuttle program manager, during
a press briefing after the failed launch. "We came out here all ready to go
here today...and we incurred a problem."
Discovery's
launch, slated for today at 3:50:53 p.m. EDT (1950:53 GMT), is now delayed
until Saturday, July 16 at 2:40 p.m. EDT (1840 GMT) at the earliest, NASA
officials said.
"That's
probably the very best case scenario," Hale said.
Earlier,
NASA chief Michael Griffin told reporters that Discovery's STS-114 spaceflight -
the space agency's first attempt to resume shuttle operations since the Columbia disaster - could slip to Monday if not later.
Unsolved
anomaly
At 1:30
p.m. EDT (1730 GMT) today, launch controllers conducted a test of four external
tank fuel sensors required to function properly before the orbiter can lift off.
The sensors
are designed to monitor the fuel levels inside Discovery's external tank during
launch in order to shut down the shuttle's main engines before propellant runs
out. If one sensor fails, the shuttle could keep firing its engines on an empty
tank, which is a hazardous situation, NASA officials said.
During
Discovery's countdown, launch controllers directed the sensors - which read 'wet'
with a full fuel tank - to read 'dry' as if the tank was empty. But one sensor
inside the liquid hydrogen section continued to read 'wet,' violating launch
restrictions that call for four, fully functioning sensors.
"It was
clearly a violation of our launch commit criteria," Hale said. "It took us five
minutes to decide [to scrub]."
NASA has
had problems with Discovery's tank sensors before during an April test on a
completely different external tank, an anomaly which engineers still cannot
fully explain.
With a
second occurrence, which cropped up long after Discovery's external tank was
filled with fuel, shuttle engineers hope to put the glitch to rest.
"This is an
intermittent problem," Griffin said in the later briefing. "When we can explain
it, we will."
The fault,
shuttle officials said, could lie anywhere between the sensor electronics box
aboard Discovery, which processes the data, and the actual tank-bound sensor itself.
"It could
be an open circuit beyond the box in the external tank," said Steve Poulos,
orbiter project manager, during a press briefing on the failed launch.
Launch
director Michael Leinbach said pad engineers will shroud Discovery with its
protective rotating service structure late tonight or early Thursday morning to
gain access to the orbiter.
Safeguarding
Discovery's external tank to allow the work will take about 21 hours, meaning pad
crews will be able to begin work on the shuttle by 3:00 p.m. (1900 GMT)
Thursday.
Downtime
for crew
Astronaut
David Wolf, a veteran of three shuttle launches and three launch scrubs, said
that while it's disappointing that Discovery remains Earthbound, there is one
benefit from the scrubbed launch.
"Once you
come down from the excited state of launch, you get relaxed and look around,"
Wolf told SPACE.com. "At that time you could really use a break that you couldn't
get planned."
Discovery's
STS-114 crew, commanded by veteran astronaut Eileen Collins, is remaining at
KSC for the time being, though could fly back to Johnson Space Center (JSC) in Houston, Texas if their mission suffers an extended delay, NASA officials said.
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