This
story was updated at 2:49 p.m. EST (1949 GMT).
Two
spacewalking astronauts brought the International Space Station (ISS) a step
closer to full power Wednesday after replacing a broken motor at the base of
one of their orbiting lab's wing-like solar arrays.
Taking
great care to avoid electrical shocks, station commander
Peggy Whitson and flight engineer Dan Tani successfully restored the vital
electricity-producing wing to full operations during their seven-hour
spacewalk.
"It's an
important step for us to get that power generation back up to where it's
optimized," Whitson said before the repair.
The space
station's power grid has been afflicted by a pair of major glitches centered on
its starboard side since last fall. In late October, Tani discovered metal
debris contaminating a massive, 10-foot (3-meter) wide gear that rotates the
outpost's starboard solar wings like a paddlewheel to maximize power production
by continuously track the sun.
The second
malfunction, which station astronauts fixed today, occurred in early December
when a garbage can-sized motor that pivots its solar
wing on a different axis than the larger gear suffered three different
electrical failures. The new motor, known as a Bearing Motor Roll Ring Module,
successfully performed 360-degree test spin during today's spacewalk.
"Yay, it works!" cheered
Whitson as she and Tani watched the solar wing turn. "Excellent,
outstanding...isn't that cool?"
Without the
new motor, the station could support NASA's
next shuttle mission — set to launch a European lab to the ISS on Feb. 7 —
but not much more, space station managers said. But the motor's successful
activation should allow the station to host shuttle flights delivering new European
and Japanese lab modules through this summer.
"We had
clean sweep today," said Expedition 16 flight director Kwatsi Alibaruho after
the repair. "The [spacewalk] went flawlessly."
NASA hopes
to launch up to five shuttle flights to the ISS this year to add European and
Japanese laboratories and prepare the station for larger, six-person crews.
In addition
to the motor repair, Whitson and Tani also performed another inspection — the
fourth so far — of the station's starboard Solar Alpha Rotary Joint, the gear
contaminated with metal debris. The spacewalkers evaluated damage from the
debris and collected samples from areas previously unseen.
Alibaruho
said the new debris samples will help shape future repair plans for the larger
gear later this year. They will be shipped back to Earth along with the broken
solar wing motor aboard one of the next NASA shuttles to fly, he said.
Wednesday's spacewalk began
at 4:56 a.m. EST (0956 GMT) and marked the fifth excursion of the station's
current Expedition 16 mission, as well as the sixth career excursion for both
Whitson and Tani.
A communications glitch
left the spacewalkers without direct contact to Mission Control in Houston
briefly, but a backup system worked fine during the seven-hour, 10-minute
excursion. Russian cosmonaut and flight engineer Yuri Malenchenko remained
inside the ISS during the spacewalk and served as a go-between during the short
glitch.
Risky
repair
Whitson and
Tani used extra caution during today's spacewalk because of the added risk of
electrical shock near the starboard solar wing.
Each U.S.
solar wing extends produces about 160 volts when awash in sunlight and feeds
power through the so-called beta gimbal assembly that houses the motor replaced
in today's orbital work. To avoid shocks and electrical arcs, Whitson and Tani
worked only in safe, 33-minute periods of darkness as the station orbited the
Earth.
"This is an
incredibly tricky box that has to be changed out," said Keith Johnson,
Expedition 16's lead spacewalk officer, of the 200-pound (90-kg) motor. "Never
was it considered a task that a station-based team would do."
Because of
the tight timing, most mission planners assumed a heavily trained shuttle-based
spacewalking team would be required, he added.
Whitson,
who squeezed inside the station's starboard truss girder to swap out the broken
motor, said there was also the risk of accidentally disconnecting vital latches
that anchor the 115-foot (35-meter) solar wing to the space station.
"That would
lose us a whole lot of style points," Whitson said before the spacewalk, though
the actual repair appeared go smoothly.
Wednesday's
excursion marked the final planned spacewalk of the Expedition 16 mission and
the 101st dedicated to space station assembly and maintenance. The spacewalk
also marked the sixth career excursions for both Whitson and Tani, who
repeatedly commented on view of Earth and space.
"It's
beautiful," Tani said as the station passed over South Africa. "Reds, blacks ...
such colors."
Tani also
beamed an orbital good morning call down to his wife Jane and two daughters,
Keiko and Lilly, on what he expected to be the last spacewalk of his mission.
He is scheduled to return to Earth next month with the STS-122 crew
aboard NASA's Atlantis shuttle.
The
spacewalk was Tani's first since the unexpected death of his 90-year-old mother
Rose in a car accident before Christmas last month. ISS flight controllers said
Tani has coped with the tragic loss admirably and that it has not affected his
work.
Whitson,
who holds the world record for most spacewalking time by a female astronaut,
closed the excursion with a new total 39 hours and 46 minutes. Tani, meanwhile,
concluded with 39 hours and 11 minutes of spacewalking time under his belt.
Together, Whitson and Tani rank 15th and 16th among the world's most
experienced spacewalkers.
"Five
spacewalks in three months, that's been fantastic," said Tani, as he thanked
flight controllers and engineers on Earth for their help planning today's
spacewalk. "It's been a great run here."
advertisement
