(Updates with details, quotes)
* Problem leaves space station without one power unit
* Astronauts likely to return soon to attempt repair
* Spacewalk was NASA's first since last year
By Irene Klotz
CAPE CANAVERAL, Fla., Aug 30 NASA on Thursday
halted attempts to replace a power distributor on the
International Space Station after spacewalking astronauts were
repeatedly stymied by a jammed bolt, officials said.
NASA astronaut Sunita Williams and Japan's Akihiko Hoshide,
both station flight engineers, had planned to spend 6.5 hours
outside the orbital outpost to work on its power system and
install electrical cables for a new Russian module expected to
arrive next year.
The astronauts ran into problems after removing the
station's balky 220-pound (100-kg) power-switching unit, one of
four used in a system that distributes electrical power
generated by the station's solar array wings. The old unit could
supply power to the station, but could not be commanded.
"We uncovered this problem some months ago and had been
living with it ever since," station program manager Mike
Suffredini told reporters during a press conference on Thursday.
"We waited to conduct the (spacewalk) until we were ready and
had every thing in place."
But problems surfaced as soon as Hoshide tried to remove
the old unit. Once it was finally wrested free of its housing,
Williams reported finding metal shavings on one of its bolts and
around the housing.
As a precaution, astronauts used a canister of nitrogen gas
to blow away shavings in the housing before attempting to
install the new unit, but problems mounted.
Repeated attempts to attach the new device failed when a
bolt jammed, preventing astronauts from hooking it up into the
station's power grid.
"We're kind of at a loss of what else we can try," astronaut
Jack Fischer at NASA's Mission Control Center in Houston told
the crew after more than an hour of trouble-shooting. "If you
guys have any thoughts or ideas or brilliant schemes on what we
can do, let us know."
Hoshide suggested using a tool that provides more force on
bolts, but NASA engineers were reluctant to try anything that
could make the situation worse.
As the spacewalk slipped past seven hours, flight
controllers told the astronauts to tether the unit in place,
clean up their tools and head back into the station's airlock.
"We're going to figure it out another day," Fischer said.
The loss of one power distributor cuts the amount of
electricity available for station operations and science
experiments by 25 percent, though managers said they expect to
be able to minimize impacts by carefully juggling schedules.
"We have to do a balancing act," said NASA flight director
Ed Van Cise.
Managers said another attempt to install the power
distributor could come as early as next week if engineers can
figure out what to do to fix the stuck bolt.
The eight-hour, 17-minute spacewalk, NASA's first since the
final space shuttle mission in July 2011, turned out to be one
of the longest in the agency's history.
Thursday's outing followed a six-hour Russian spacewalk on
Aug. 20 by cosmonauts Gennady Padalka and Yuri Malenchenko to
relocate a crane, launch a small science satellite and install
micrometeoroid shields on the station's Zvezda command module.
The station, a $100-billion project of 15 countries, is an
orbiting laboratory used for medical and basic science
experiments, microgravity research and technology development.
Williams was able to finish most of the work to install
electrical lines for the new Russian laboratory. But the
astronauts were unable to get to a third task replacing a camera
on the station's robot arm.
(Editing by Eric Walsh)