NASA has pinned
down the apparent location of an erratic fuel tank sensor glitch that foiled
two launch attempts of the space shuttle Atlantis, the agency said Tuesday.
Engineers tracked
the glitch to an oversized electrical socket that bridges the interior and
exterior of Atlantis' 15-story external tank after fueling the vessel with more
than 500,000 gallons (1.9 million liters) of its super-chilled rocket fuel in a
test.
"I'm just
pleased as punch that we know it's in the connector and not some other place in
these 100 feet or so of wiring and sensors and electronics boxes," said Wayne
Hale, NASA's space shuttle program manager, after the test. "So we know in what
area to concentrate our efforts."
NASA staged
Tuesday's fueling test on Atlantis' Pad 39A launch site at the Kennedy Space Center in Cape Canaveral, Fla., in hopes of recreating the same type of engine
cutoff sensor malfunctions that prevented mission managers from launching the STS-122 construction
flight to the International Space Station (ISS) earlier this month.
Known as
engine cutoff (ECO) sensors, the fuel gauge-like devices serve as a backup
system to shut down a shuttle's three main engines before the orbiter's fuel
tank runs dry. If the engines continue to fire without fuel, they could cause
catastrophic damage, NASA has said.
NASA flight
rules call for at least three of the four liquid hydrogen sensors to work
properly in order to lift off, but Atlantis' fuel gauges suffered
repeated failures during standard countdown tests for Dec. 6 and Dec. 9
launch attempts. Similar glitches have plagued NASA since the agency resumed
shuttle flights in 2005 following the Columbia accident, prompting mission
manager to delay the STS-122 mission to no
earlier than Jan. 10 to settle the glitch once and for all.
"We gleaned
quite a bit of data today, I'm happy to say," Hale said of Tuesday's test. "The
data is indicating that we have a problem in what we call a feed-through
connector."
The
connector is about 1.5 inches (3.8 cm) wide, 4 inches (10 cm) long and composed
of three major segments: an interior electrical socket, a series of metal pins
set in glass, and an exterior electrical socket that allows cables to run from
the external tank to electronics boxes inside Atlantis.
Engineers
used a tool similar those used by telephone and cable television companies to
track breaks in their wiring to find open circuits at Atlantis' feed-through
connector, Hale said, adding that the glitch appears to be associated with the
cryogenic temperatures of the shuttle's liquid hydrogen and liquid oxygen
propellant.
"These
things are not showing up at normal, everyday temperatures when the tank is
warming back up or is empty," Hale said.
Engineers
will meet on Wednesday to go over potential modifications and other fuel tank
troubleshooting work to address the shuttle fuel tank sensor glitch. Any
repairs will depend on exactly where the problem resides. Engineers could spend
up to 10 days replacing the connector's exterior socket and other hardware, but
would have to stand down for a much longer period should the glitch be tracked to
the interior socket, which can only be reached from inside the shuttle fuel
tank, Hale said.
The
technical data and repair method will determine whether Atlantis will be ready
to haul the European-built Columbus lab to the ISS on Jan. 10 or will have to
wait a bit longer, he added.
"We don't
need to go fly if it's not safe," Hale said. "What we need to do is take it one
step at a time and do it right, right now."
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