CAPE
CANAVERAL, Fla. - NASA is back on the trail of an erratic fuel sensor glitch
that forced the agency to delay launch plans for the space shuttle Atlantis
until early January, mission managers said Sunday.
The failure
of a fuel gauge-like sensor in Atlantis' 15-story external tank during a
countdown test today forced NASA to call off a planned
afternoon launch for the second time. Engineers will now scour the
sensor system in hopes of pinning down the malfunction in time for a potential
Jan. 2 launch attempt.
"In this
case, with the vehicle and the system at the pad, we feel like we need to find
root cause," said LeRoy Cain, head of Atlantis' mission management team, after
the launch attempt here at the agency's Kennedy Space Center spaceport. "And
we're going to make every effort to do that."
Cain said
an engineering team is expected to draw up possible troubleshooting efforts
while Atlantis is on the launch pad and present a preliminary plan to mission
managers on Tuesday.
Known as engine
cut-off sensors, the fuel gauges monitor the levels of super-chilled liquid
hydrogen and liquid oxygen propellant in Atlantis' external tank. They serve as
a backup system to shut down the shuttle's three main engines during flight before the fuel
tank runs dry.
During a
Thursday launch attempt, two of the four engine cut-off sensors monitoring
Atlantis' liquid hydrogen supply failed a standard countdown test, with a third failing later. NASA flight
rules require at least three working sensors to launch.
Because the
sensors have behaved erratically in the past, working sometimes then failing at
others, NASA tightened its launch rules to require all four suspect units to
function properly before Atlantis could fly. Mission
managers also cut the shuttle's five-minute launch window to just a single minute to
conserve fuel as an extra safety measure in case the sensors failed during
liftoff.
"We gave it
a good try," said Doug Lyons, Atlantis' STS-122 launch director. "I think the
team is disappointed, but highly motivated to go help this [engineering] team
to track this problem."
NASA has been plagued
by intermittent glitches with shuttle engine cut-off sensors sine 2005,
when the space agency resumed orbiter flights following the Columbia accident. If the engines continue to
fire with a dry tank, they could rip apart and cause catastrophic damage,
though several other failures in addition to the sensor glitch must occur for
that possibility, NASA has said.
Engineers,
last year, switched to new engine cut-off sensors and attached additional
instruments to monitor their performance, only to see the issues resurface
aboard Atlantis.
"I think
this has been sort a cloud that has always been over us," said William
Gerstenmaier, NASA's associate administrator for space operations. "We thought
we had it fixed when we changed out the engine cut-off sensors before."
Gerstenmaier
said there is currently enough padding in NASA's flight schedule to hunt for
the glitch and launch Atlantis' mission before the planned Feb. 14 liftoff of
the shuttle Endeavour to carry part of Japan's Kibo laboratory to the ISS
next year. But with up to 12 more shuttle missions on tap to complete the ISS,
plus one more to service the Hubble Space Telescope, NASA hopes to settle the
fuel sensor glitch once and for all in order to avoid more delays.
The agency
plans to retire its aging three-shuttle fleet by September 2010 once space
station construction is complete.
"So this
can be a huge advantage to us to get this understood and move forward,"
Gerstenmaier said.
Commanded
by veteran shuttle flyer Stephen Frick, Atlantis' seven-astronaut crew planned
to haul the European Space Agency's Columbus
laboratory to the International Space Station (ISS) to mark NASA's fourth
construction flight of the year. The shuttle's STS-122
mission was slated to run about 11 days and include at least three
spacewalks to attach the 1.4 billion Euro ($2 billion) Columbus lab to the ISS.
NASA had a
slim, week-long window that closes Thursday in which to launch Atlantis due to
the angles between the sun and the ISS while the shuttle is docked at the space
station. While the window reopens around Dec. 30, mission managers have said
they would wait until Jan. 2 to avoid software concerns with flying during the
year-end change.
"We want to
thank everyone who worked so hard to get us into space this launch window,"
Frick and his STS-122 crewmates said in a group statement. "We were ready to
fly, but understand that these types of technical challenges are part of the
space program."
The
astronauts will depart for NASA's Johnson Space Center in Houston at
5:00 p.m. EST (2200 GMT) and resume training for their space station
construction flight.
"We hope
everyone gets some well-deserved rest, and we will be back to try again when
the vehicle is ready," the astronauts said.
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