CAPE
CANAVERAL, Fla. - After one false start, NASA’s shuttle Atlantis and seven astronauts
will again attempt to launch toward the International Space Station (ISS) today
despite suspect fuel tank sensors that have delayed the mission for days.
Shuttle commander Stephen Frick and his STS-122 crewmates
are poised to
launch spaceward at 3:20:59 p.m. EST ((2020:59 GMT) to haul the space station’s new Columbus laboratory into orbit for the European Space Agency (ESA). But the space shot will only blast off if a set of erratic fuel tank sensors perform properly.
“The team is in great spirits,” Doug Lyons, shuttle launch
director for Atlantis’ STS-122 mission. “They’ve got the pad
and the vehicle ready to go make an attempt [Sunday] and we’re looking
forward to getting off the pad and starting the mission.”
Mission managers called off a planned
Thursday launch for Atlantis and its crew after two of the four engine
cut-off sensors in the liquid hydrogen portion of the shuttle’s
15-story fuel tank failed a countdown check. A third sensor also returned
erroneous readings after the tank was drained.
NASA flight
rules call for at least three of the four sensors to be in working order for
launch, though mission managers tightened them to require all four of the
sensors and their monitoring equipment to be online before liftoff.
“If
everything works perfectly, as we would expect from our past history, we’ll
go fly,” said Wayne Hale, NASA’s shuttle program manager, told
reporters Saturday. “If we have any other anomalies, or a repeat anomaly,
then we think it would be worthwhile to stand down and troubleshoot.”
Atlantis
also has a one-minute launch window, instead of the traditional five-minute
target, to launch. The shorter window will allow the shuttle to conserve
precious fuel during liftoff as an extra safety measure to assure that its
external tank still has propellant in case the engine cut-off sensors fail
during launch.
NASA has
wrestled with intermittent
fuel tank sensor glitches since 2005, when it resumed shuttle flights
following the Columbia
tragedy. Then, shuttle flight rules also called for all four sensors to work
before a planned launch, but loosened the restriction to three of four after months
of failing to isolate the problem’s source.
After two
days of analysis, mission managers opted to reinstitute the four-sensor rule
for Atlantis’ current mission only. Current weather forecasts predict an
80 percent chance of good weather at launch time.
The STS-122
astronauts are slated to install the ESA’s 1.4
billion Euro ($2 billion) Columbus lab to the ISS during at least three
spacewalks planned for their 11-day mission. If the shuttle’s power
supply holds out, NASA could extend the flight by two days to allow an extra
spacewalk to inspect a balky solar array joint on the station’s starboard
side.
Set to
launch spaceward with Frick are shuttle pilot Alan Poindexter; mission
specialists Leland Melvin, Rex Walheim, Stanley Love and ESA astronauts Hans
Schlegel and Leopold Eyharts. A veteran French astronaut, Eyharts will replace U.S. astronaut Dan Tani as a space station
flight engineer and help christen Europe’s Columbus lab during the STS-122 mission.
NASA has a
slim window that closes on Thursday, with a possible one-day extension, in
which to launch Atlantis before sun angles become unfavorable for the shuttle’s
mission.
The shuttle’s
launch would mark NASA’s fourth shuttle flight of 2007 and the second
this year carrying a new orbital room bound for the space station.
NASA is
broadcasting Atlantis' STS-122 mission’s Sunday launch live on NASA TV
beginning at 6:00 a.m. EST (1100 GMT). Click here for SPACE.com's shuttle mission coverage and NASA TV feed.
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