HOUSTON-NASA's space shuttle Discovery is
closing in on a scheduled
December launch towards the International Space
Station (ISS), where astronauts plan to deliver a new piece of the outpost
and rewire its power grid, mission managers said Monday. The spaceflight may
even launch a day early, they added.
"We
are working ahead of schedule well enough that the team thinks we might even
advance the launch day an additional day, to Dec. 6," Wayne Hale, NASA's
shuttle program manager, said in a preflight briefing here at the agency's Johnson
Space Center.
Discovery
and its STS-116
astronaut crew are currently poised to blast off on Dec. 7, about a week
earlier than initially planned. The launch will mark NASA's first night launch in four years,
a welcome milestone since night launches are essential to the agency's plan to help
complete the ISS by the orbiter fleet's 2010 retirement.
"I am
extremely proud of the work our crew did at the Kennedy Space Center," Hale said of NASA's shuttle spaceport of Cape Canaveral, Florida. "I cannot,
in the entire history of the shuttle program, remember a time where we advanced
the launch date by a week within the last couple of months of preparation."
Discovery's
speedy turnaround since its last flight-NASA's STS-121
mission in July-cleared the path for the STS-116 spaceflight, which many in
the agency described as the most difficult to date.
"Every mission says that theirs is the most challenging and complicated to
date," said NASA's Tony Ceccacci, the mission's lead shuttle flight
director. "Well, that's no different for STS-116."
Discovery's
seven-astronaut crew, commanded by veteran
shuttle flyer Mark Polansky, is slated to deliver the spacer-like Port 5
(P5) truss segment to portside edge of the station's metallic backbone during
the first of three planned spacewalks to rewire the orbital laboratory's power
grid.
The station
has relied primarily on a pair of solar arrays attached to its mast-like Port 6
(P6) truss, but the arrangement was always meant to be temporary since that
segment must be moved in the future. STS-116 spacewalkers will shift the ISS
power systems from the P6 arrays to the solar panels on the station's recently
installed Port 3/Port 4 (P3/P4) truss delivered in September.
As part of
the STS-116 rewiring process, one of the P6 solar arrays must be folded away to
allow the newer solar panels to rotate and track the Sun. The folding procedure
has never been tried before, and both P6 solar arrays have been in space since
2000, experiencing drastic temperature changes that range from minus 200
degrees Fahrenheit (minus 129 Celsius) to plus 200 degrees Fahrenheit (93 Celsius)
every 45 minutes.
There are, however, backup
plans in place in case the solar arrays fail to retract automatically.
"They've built in a
lot of contingency devices into the design," said STS-116
mission specialist Robert Curbeam. "We'll go up there and if it doesn't
retract, we'll retract it by hand using a pistol grip tool or a cordless drill
if that's necessary. We'll latch it if that's necessary...One way or another,
we're going to get it retracted."
A bigger worry, Curbeam
said, is the possibility that some ISS equipment will not work after the rewiring.
Equipment has to be turned off prior to rewiring, and then turned back on
again. Some of the equipment is vital to the operation of the station and the
crew's life support, so if they don't function properly after rewiring, the
spacewalkers will have to undo everything and do it again.
"That's my biggest
worry, if things don't power up correctly," Curbeam said.
In addition to Curbeam and
Polansky, the seven-member STS-116 crew includes shuttle pilot William
Oefelein and mission specialists Joan
Higginbotham, Nicholas
Patrick, Sunita
Williams and Swedish spaceflyer Christer
Fuglesang, of the European Space Agency (ESA). Williams will relieve ESA
astronaut Thomas Reiter, of Germany, who has served aboard the space
station since July.
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