This story was updated at 9:44 a.m. EDT.
CAPE
CANAVERAL, Fla. - Six
astronauts and NASA's shuttle
Atlantis will have to wait at least one more day before launching toward the International Space
Station (ISS) while engineers puzzle a fuel cell glitch aboard the spacecraft.
Atlantis'
launch is now reset for no earlier than Thursday at 12:03:03 p.m. EDT (1603:03
GMT) as shuttle specialists tackle a voltage issue with one of three fuel cells
which generate the electricity to power the shuttle during its 11-day ISS
construction mission. The shuttle's launch window closes Friday.
"We were
ready to go," NASA spokesperson Bruce Buckingham said here at the Kennedy Space
Center (KSC), where Atlantis stands poised to launch at Pad 39B. "We were just
waiting."
NASA
mission managers held off fueling Atlantis' 15-story external tank with cryogenic
liquid oxygen and liquid hydrogen propellant - originally slated for 2:30 a.m.
EDT (0630 GMT) - while discussing the fuel cell glitch, which first appeared as
engineers powered up the shuttle before 1:30 a.m. EDT (0530 GMT) this morning. Atlantis
was slated
to launch its STS-115 mission at 12:28:46 p.m. EDT (1628:46 GMT) today.
"We held
off as long as we could," Buckingham said. "We're going to troubleshoot this,
see if we can understand what happened and when we can rectify it."
A
voltage spike in the alternating current of Fuel Cell 1 prompted the concern,
NASA officials said, adding that the short occured in a coolant motor for that unit. According to NASA flight rules, all three of Atlantis' fuel cells must be functioning properly before the shuttle can launch. Engineers are drawing up options to work around, repair or replace the hardware, shuttle officials said.
Shuttle managers scrubbed Atlantis' Wednesday launch for at least
24 hours to give engineers more time to study the fuel cell issue. The shuttle
had a 70
percent chance of favorable launch weather today and is expected to have
the same odds over the next two days.
Shuttle managers will gather at 1:00 p.m. EDT (1700 GMT) today during a Misison Management Team meeting to discuss Atlantis' options. A press briefing is expected to follow that discussion.
By calling
off today's launch attempt before loading Atlantis' shuttle fuel tank with its
526,000 gallons of super-cold fuel, NASA does avoid the typical $600,000 cost
of a scrub after tanking is complete, Buckingham added.
Atlantis' STS-115
mission - commanded by veteran
shuttle astronaut Brent Jett - is aimed at delivering a $371.8
million pair of massive portside trusses and two new solar arrays to the
ISS. The spaceflight will mark NASA's first dedicated ISS construction effort
since the 2003 Columbia
accident and follows two
return to flight test missions.
The last
major piece of ISS hardware - the Port 1 (P1)
truss - launched aboard NASA's Endeavour orbiter during the STS-113
mission in late 2002. Atlantis' Port 3/Port 4 (P3/P4) trusses are destined
to be installed at the end of their P1 cousin.
Today's scrub follows several delays for Atlantis' STS-115 mission, following a lightning strike to the shuttle's launch pad and storm threats from a tropical depression last month.
Fuel
cell puzzle
Each NASA
space shuttle is powered by three fuel cells tucked beneath its cargo bay. The
reusable, restartable fuel cells weigh about 255 pounds and run 45 inches long,
15 inches wide and about 14 inches high, according to manufacture
specifications.
While the
shuttle carries three fuel cells, only one is required to power the spacecraft,
according to builder UTC Power. They use liquid hydrogen and liquid oxygen to
produce a steady 12-kilowatt supply of power each, can put out 16 kilowatts for
short periods, and generate heat and water - used for drinking by astronaut
crews - as byproducts.
If
extensive repairs - such as a fuel cell replacement - are needed Atlantis would
likely miss its current STS-115
launch window, which closes on Sept. 8. NASA's current daylight launch
restrictions for Atlantis actually allow for a launch up to Sept. 13, but
shuttle officials will stand down Friday to avoid conflicts
with the planned Sept. 18 launch of a Russian Soyuz spacecraft that will ferry
a new crew and one space tourist to the ISS.
Wayne Hale,
NASA's space shuttle program manager, said earlier this week that a study is
currently underway to reevaluate
the daylight launch rules for Atlantis' STS-115 mission. Those restrictions
were in place to evaluate fuel tank modifications, but may not be relevant when
the next lighted launch window opens on Oct. 26, Hale has said.
If a
well-lit launch is not required, Atlantis could rocket toward the ISS sometime
after Sept. 29, when Russia's ISS crew change mission concludes, Hale has said.
NASA officials said fuel cell
glitches have afflicted several shuttle missions in the past, including: Columbia's STS-2
flight in 1981, Discovery's STS-42 mission in 1992, Endeavour's STS-69 flight
in 1995, Columbia's STS-83 spaceflight in 1997 and Atlantis'
STS-98 in 2001.
The STS-69 glitch
also prompted NASA shuttle managers to scrub their attempted launch before
loading Endeavour's external tank propellant, NASA records show. The space agency
actually re-launched the STS-83 mission as STS-94 after a fuel cell issue prompted
cut the planned 16-day flight down to three days. Erratic readings were seen in
one of Endeavour's fuel cells before flight and developed into a full-blown
problem once in orbit.
The planned
five-day STS-2
mission aboard Columbia was also shortened to three days due to a fuel cell
failure in flight.
It took
NASA about one week to replace a fuel cell after scrubbing the planned Aug. 31,
1995 launch Endeavour's STS-69 mission, just over 11 years before Atlantis' current
problems. STS-69 launched on Sept. 7 of that year.
NASA's post-MMT press briefing on Atlantis' launch scrub is expected to begin no earlier
than mid-afternoon. The briefing will air live on NASA TV, and you are invited to follow the event via SPACE.com's NASA TV feed by clicking here.
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