This
story was updated at 10:20 p.m. EST.
NASA has
delayed the planned Feb. 12 launch of the space shuttle Discovery by at least a
week to allow extra time to evaluate vital fuel valves on the spacecraft,
agency officials said late Tuesday.
Discovery
was slated
to launch toward the International Space Station on Feb. 12 to deliver the
last set of U.S.-built solar arrays to the orbiting laboratory. The mission is
now scheduled to blast off no earlier than Feb. 19 at about 4:41 a.m. EST (0941
GMT), but an official launch target will be determined at a later date.
"By looking
at it right now, we think it's about a week delay, but we're not going to put
pressure on the team," said John Shannon, NASA's space shuttle program manager,
in a briefing at the agency's Kennedy Space Center in Florida. "We'll just let
the information drive us."
The delay
is necessary to allow engineers time to be sure that pieces of Discovery's flow
control valves won't chip off and damage vital plumbing between the
spacecraft's main engines and its 15-story external tank. The valves are used
to keep the space shuttle's hydrogen propellant tank pressurized as the orbiter
rockets spaceward.
The valves
were replaced on Discovery after engineers discovered damage to a similar valve
that flew aboard its sister ship Endeavour last November.
During Endeavour's
Nov. 14 launch, a piece of one of three flow control valves chipped off,
apparently from high-cycle fatigue, Shannon said. The valve functions much like
a pop-up lawn sprinkler to funnel hydrogen gas from a shuttle's main engine
back into its external tank to maintain proper pressure levels, he added.
Shannon
said the damaged valve on Endeavour caused no serious harm during that
shuttle's November launch and NASA officials want to be sure the same will be
true for Discovery when it flies.
"We don't
expect there to be a problem, but we don't have the proof in hand," Shannon
said. "We want to have that proof in hand before we commit to go fly."
Shuttle
officials announced Discovery's flight delay late Tuesday after a day-long
meeting to discuss the orbiter's launch readiness.
NASA
engineers plan to perform a series of tests to evaluate what effects valve
debris could cause during ascent. Top shuttle officials are expected to discuss
the results from those tests next week before setting an official new launch
target.
Michael
Leinbach, NASA's launch director, said his team of shuttle workers is currently
in a holding pattern until a new launch date is set.
"Once we're
given a launch date, we'll get back into our processing," Leinbach said.
Commanded
by veteran spaceflyer Lee Archambault, Discovery's
STS-119 mission will launch seven astronauts toward the space station to
deliver the outpost's last set of U.S. solar arrays. Four spacewalks are
scheduled during the two-week spaceflight. The mission will also ferry Japanese
astronaut Koichi Wakata to the space station, where he will replace NASA
spaceflyer Sandra Magnus as a member of the outpost's three-person crew.
Space
station mission managers, meanwhile, are tackling several issues to prepare the
outpost for Discovery's arrival this month and the planned shift to a larger,
six-person crew later this year. They range from a recent
vibration event associated with a Jan. 14 thruster firing to ongoing, but
not insurmountable, glitches with new life support equipment.
NASA space
station program manager Mike Suffredini said he is confident the glitches will
be resolved and the station ready to support the first six-person crew in late
May as planned.
Suffridini
said that while the vibrations on Jan. 14, which occurred during a routine
Russian thruster firing to boost the space station's orbit, were
stronger than the acceptable limits, they did not cause any structural damage to
the outpost. During the two-minute, 22-second engine burn, the space station's
current skipper Michael Fincke of NASA reported that the outpost shook more
than he'd ever seen in his two increments aboard, but he did not hear creaks or
groans from the structure, he added.
A video
from a camera inside the station showed items shaking back and forth.
"You can
see things were moving around pretty good," Suffredini said.
But despite
the shaking, the event did not impact the space station's 15-year design lifetime,
he added.
Earlier
today, space station managers in Russia and at NASA's Mission Control in Houston
canceled another planned thruster firing planned Wednesday. The next maneuver may take place sometime in March, Suffredini said.
Discovery's
STS-119 mission is NASA's first of up to six planned shuttle flights for 2009.
They include one final flight to overhaul
the Hubble Space Telescope and a series of space station construction
missions.
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