CAPE CANAVERAL, Fla. – NASA will
restart the countdown for the
space shuttle Discovery
Saturday, with plans to launch
the orbiter spaceward on July 26
after more than week of work to
pin down a fuel sensor glitch,
mission managers said late
Wednesday.
“Right now we think we have
eliminated all the common
causes,” shuttle program manager
Bill Parsons said of the glitch
during a press briefing here at
NASA’s Kennedy Space Center (KSC).
“We believe we’ve done
everything we possible could on
the vehicle.”
Discovery’s STS-114 mission,
NASA’s first shuttle flight
since the 2003 Columbia
disaster, is now set to launch
at 10:39 a.m. EDT (1439 GMT) on
July 26.
Wednesday’s announcement comes
after more than a week after
launch controllers
scrubbed Discovery’s
attempted July 13 space shot
when a fuel sensor, one of four
that monitor liquid hydrogen
levels inside the shuttle’s
external tank, failed a standard
countdown test. Known as engine
cut-off (ECO) sensors, the
sensor system is designed to
track fuel levels during launch
and ensure Discovery’s three
main engines shut down properly
before the external tank runs
dry. If the engines keep firing
without fuel, it would prove
disastrous for the orbiter and
its crew.
“This has been a very, very
thorough effort that we’ve been
through,” said John
Muratore,
manager of shuttle systems
engineering and integration,
during the briefing. “We’ve used
every kind of analysis technique
and test technique that we can
find.”
Shuttle engineers
investigating the anomaly
believe that electromagnetic
interference from existing or
new hardware, such as additional
cameras or heaters attached to
the bipod fitting that connects
Discovery to its external tank,
and a
small grounding issue with
sensor wiring may be the
culprit.
Additional tests over the next
48 hours should address those
areas, with the launch countdown
set to begin at about 12:00 p.m.
EDT (1600 GMT) Saturday, Parson
said.
But engineers have only a
limited time to complete their
troubleshooting efforts inside
Discovery’s aft compartment,
where the electronics box that
processes ECO sensor readings
resides.
“About 20 hours into the
countdown is when you do the
cryogenic loading for the
[shuttle’s] fuel cells,” said
Michael Wetmore, director of
space shuttle processing at KSC.
“We’d absolutely have to be out
of there by then.”
While all four hydrogen ECO
sensors are required to perform
properly under current flight
rules, shuttle officials said
they could make an “exception”
for Discovery on launch day if
they see a glitch that they
fully understand.
“We expect to have four of four
sensors,” Parsons said. “If we
can understand that failure and
it was a known failure that we
expected…then we might very well
be willing to go fly with three
of four sensors, there’s good
flight rationale behind it.”
If shuttle officials see a
sensor failure that they do not
expect then they’d have to
reassess the situation, which
could take more than 24 hours or
push the launch outside
of
July entirely, Parsons added.
Discovery’s launch window runs
through July 31, with the next
flight opportunity opening on
Sept. 9.
New launch protocols instituted
after the Columbia accident call
for optimum lighting levels for
the myriad of still and video
cameras watching the shuttle’s
ascent, as well as good lighting
for the STS-114 crew when they
photograph the external tank
just after it separates from the
orbiter. Still more daylight is
needed during Discovery’s
International Space Station (ISS)
rendezvous, where station
crewmembers will photograph its
tile-lined belly to record and
transmit its condition to
ground-based engineers.
Columbia disintegrated during
atmospheric reentry, killing its
seven-astronaut crew, on Feb. 1,
2003.
Launch officials said that if
nothing bars a July 26 space
shot, flight controllers should
have at least four opportunities
to launch Discovery. Additional
dates for the flight – should it
fail to fly Tuesday – include
the 27th, 29th
and 31st of July.
“We’ve got a great amount of
work in front of us,” Parson
said. “But we’ve all agreed this
work is doable, and that it all
takes us to a launch.”
