CAPE
CANAVERAL, Fla. – NASA is working feverishly to launch the shuttle Discovery before
the end of the month, even as engineers struggle to identify and fix a fuel
sensor anomaly that scrubbed the orbiter’s attempted space shot last week,
mission managers said Monday.
“We’re
still looking for the problem,“ NASA’s shuttle program manager Bill Parsons
said during an evening press conference. “This team is trying everything it can
to launch in the July window.”
Discovery
will not launch any earlier than July 26, which is the first opportunity
engineers will have to fill its external tank with the super-chilled liquid
hydrogen and liquid oxygen propellant used during liftoff, shuttle officials
said. But whether shuttle engineers will try and launch day, or simply fill the
external tank with fuel to check its performance, is undecided, they added.
“Hopefully,
in the next 24 to 48 hours we will find the glitch that’s got us all confused,”
said Wayne Hale, deputy shuttle program manager, during the briefing. ”But I
think Tuesday [July 26] is probably the earliest we’d be looking for launch
even in that optimistic case.”
Discovery’s
STS-114 commander Eileen Collins and her STS-114 astronaut crew will leave KSC
this week and return to NASA’s Johnson Space Center (JSC) in Houston, Texas for
a day of ascent and reentry training, but they should return the same days once
the exercise is completed, NASA officials said.
The STS-114
mission is NASA’s first attempt at shuttle flight since the 2003 Columbia
disaster, and was poised to launch on July 13 when flight controllers received an
errant signal from an engine cut-off sensor (ECO) during a standard countdown
test.
Launch officials
scrubbed the launch attempt after the sensor, one of four liquid hydrogen fuel gauges,
failed to respond accurately to a test signal from launch control. Under
current flight rules, all four hydrogen sensors – and four others that track
liquid oxygen levels – must perform perfectly in order to launch.
For nearly
a week, shuttle engineers have struggled and failed to identify exactly what
went wrong with the fuel sensor system to cause the errant signal. On Sunday,
they attached an external tank simulator to the sensor box aboard Discovery
responsible for processing the external tank fuel gauge information to see if
it performed as expected, and still found nothing out of the ordinary, shuttle
officials said. Earlier today, engineers checked to make sure there were no
loose wires in the orbiter’s sensor system, they added.
“Our goal
is to figure out a path to go find the problem and then obviously try to
correct the problem,” said Ed Mango, deputy director of orbiter projects at
JSC, in the briefing.
Shuttle
managers are considering a few approaches leading up to July 26, including a
full blown fueling test of the Discovery’s external tank, a less extreme test
folded into a launch countdown and a flight rule change that would set launch
requirements to need only three of the four fuel gauge sensors to operate
nominally in order to lift off, NASA officials said.
Before the
1986 Challenger accident, only three of the four sensors were required to
perform properly, but the rule was changed when engineers realized that a power
failure in the system could cripple two sensors at once, shuttle officials
said. During the preparation of Discovery, that sensor power system has been modified
to prevent such a failure, they added.
Mission
managers at KSC and JSC studying whether to extend Discovery’s STS-114 launch
window into early August, though the much-sought after lighting conditions to
photograph the shuttle’s external tank separation gradually worsen after the
July 31 deadline. But caution, especially given the risk of human spaceflight,
is paramount, they said.
“A few days
delay to figure out what is going on and make sure we’re safe is always the
right answer,” Hale said. “It is a business where you have to have patience.”
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