This story was updated at 8:00 p.m. EDT.
NASA will
try to squeeze in a launch attempt for the space shuttle Endeavour on Wednesday,
just days ahead of a different rocket also set to send two unmanned probes to
the moon this week, mission managers said Sunday.
The NASA
moon probes were previously scheduled to fly on June 17, but the agency would
delay their mission in order to get one more chance to launch
Endeavour after a potentially dangerous hydrogen gas leak prevented a
Saturday liftoff. A final decision on which mission will launch first will be
made Monday afternoon.
"From a
priority standpoint, what we are trying to do in the agency is maximize our
launch opportunities," said LeRoy Cain, NASA's deputy shuttle program manager,
in a Sunday briefing at NASA's Kennedy Space Center in Florida.
A Wednesday
launch for Endeavour would occur at 5:40 a.m. EDT (0940 GMT) from a seaside pad
the Cape Canaveral, Fla.-based spaceport with favorable weather expected. NASA's two new
moon probes - the Lunar Reconnaissance Orbiter and a smaller spacecraft
that will intentionally crash into the moon to look for water ice - could then
launch on Friday, Cain said.
The schedule is tight. If foul weather delays any work on Endeavour or its
launch pad by even a few hours, the shuttle may not be ready to launch on
Wednesday. If a delay occurs soon enough, such as overnight tonight or early
Monday, NASA could swap launch days with the moon mission and try to loft
Endeavour on June 20.
"The schedule
that we're moving toward is very tight," said NASA launch director Pete
Nickolenko. "But it is achievable."
Gas leak
repairs
Endeavour
was slated to launch early Saturday from the Cape Canaveral, Fla., spaceport
and begin a grueling 16-day space station construction flight. The shuttle's seven-astronaut
crew plans to deliver an external experiment porch for the station's $1
billion Japanese Kibo lab. Five spacewalks and a one-man swap for the station's
new six-person crew were also planned.
But a leak
of gaseous hydrogen forced NASA to postpone the launch attempt since the
extremely flammable gas posed an explosion risk to both Endeavour and the seven
astronauts aboard. Repairs to the vent line leaking the hydrogen should be
complete by early Monday.
The leak is
similar to one that delayed the launch of Endeavour's sister ship Discovery
earlier this year during NASA's STS-119 mission in March. Shuttle technicians
replaced the hydrogen vent pipe that siphons excess gas away from the Discovery's
15-story external tank and the mission successfully lifted off after a four-day
delay.
While NASA
is confident a similar fix will work for Endeavour, shuttle managers remain perplexed
by the gas leak. Engineers suspect temperature changes caused by a shuttle's
super-chilled cryogenic fuel may lead to gaps in the vent pipe, but they still
do not know for sure.
"We'll
change it out. It will either work or it won't," Cain said of the vent line
repair. "If it doesn't, then we certainly aren't going to go launch."
Endeavour's
mission is NASA's third shuttle flight of 2009 and the second this year
dedicated to space station construction. A May mission by the shuttle Atlantis
flew to the Hubble Space Telescope.
Commanded
by veteran spaceflyer Mark Polansky, Endeavour's six-man, one-woman crew is the
first to the visit the
space station since the outpost doubled its population up to six people
last month. The astronauts are remaining in quarantine to avoid getting sick
while NASA decides their launch plan.
When
Endeavour docks, 13 people - the highest
number ever - will be living and working aboard the station at the same
time.
Launch
date toss-up
The
difficulty surrounding Endeavour's launch date revolves around an overlapping
schedule on the Eastern Range, a rocket launch range that extends eastward out
over the Atlantic Ocean. NASA shares the range with the nearby Cape Canaveral
Air Force Station, which is where an unmanned Atlas 5 rocket is poised to
launch the two moon probes.
Typically,
the Eastern Range requires at least two days to switch between a shuttle flight
out of the Kennedy Space Center and an unmanned rocket launch from the Air
Force station. Clouding the issue even more are the different launch windows for
Endeavour and the unmanned moon probes.
Endeavour's
window to launch toward the space station closes on June 20, when sun angles
and heating conditions become unfavorable for a shuttle linked to the outpost.
NASA could extend that window to the June 21, but that would require shortening
Endeavour's busy flight by a day and cutting one of the five spacewalks in
order to leave the station in time, Cain said.
The Atlas 5
rocket, meanwhile, has a parallel four-day window (June 17-20) in order to
launch on a trajectory that would allow its Lunar Reconnaissance Orbiter
payload to arrive at the moon four days later. The orbital mechanics line up
every two weeks, but the lunar mission's launch has already been delayed
several times since October 2008.
If Endeavour cannot launch this week, NASA's next opportunity to launch the
shuttle would come on July 11, when sun angles and heating conditions at the
space station, mission managers said. That slip should not seriously impact
NASA's plans to launch eight more missions before retiring the shuttle fleet in
2010 to make way for its capsule-based Orion successor, but NASA remains
hopeful the shuttle can fly on Wednesday.
"A lot of
things have to go our way," Cain said.
SPACE.com
is providing continuous coverage of STS-127 with Staff Writer Clara Moskowitz
and Senior Editor Tariq Malik in New York. Click here for mission
updates and SPACE.com's live NASA TV video feed.
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