This story was updated at 11:36 a.m. EST.
NASA engineers are pondering the source of
a day-long power loss aboard the International Space
Station (ISS) Sunday that temporarily shut down science and communications
equipment.
At 1:00 a.m. EST (0600
GMT) Sunday, a power channel in the station's
Port 4 (P4) solar array electrical system shut down due to a glitch with an
electrical distribution device known as a direct current switching unit, NASA
officials said [image].
"The station's three crew
members were not in any danger, but it did turn an off-duty day into a full
work shift," the space agency said in a statement.
The power drop led to a
temporary loss of ISS communications and the shutdown of heating units, some
science equipment and one of three operating U.S. gyroscopes used for attitude
control.
"Flight controllers
restored power to nearly all affected systems and equipment by Monday morning,"
NASA officials said. "They are still investigating what caused the glitch, but
believe it was an isolated event."
NASA officials said it
took about 31 hours for flight controllers and the space station's Expedition
14 crew to restore ISS systems to normal.
"I wanted to
congratulate you on a really well done job," Expedition 14 commander Michael
Lopez-Alegria told flight controllers in a message
rebroadcast on NASA TV after power was restored. "Hats off to
you guys and thanks."
The ISS did fly in a
two-gyroscope mode for attitude control, the minimum required to orient the
station without consuming propellant for Russian thrusters, during the glitch.
The space station has a total of four 620-pound (281-kilogram) Control
Moment Gyroscopes, though one - CMG-3 - was powered
down in October due to excessive vibration.
At no point did the ISS
experience any loss of attitude control during the power loss, NASA said.
Delivered
to the ISS in September
2006, the P4 solar
arrays are the newest power-generating components aboard the orbital
laboratory, and began
feeding station systems in December during NASA's STS-116
shuttle flight to the orbital laboratory.
The arrays consist of
two solar wings that reach out in opposite directions from their base on the P4
truss for a total wingspan of about 240 feet (73 meters). The arrays rotate to
track the Sun and route electrical power
through direct current switching units to the station's main bus switching
units for distribution to ISS systems.
Each of the two P4 solar
wings is designed to produce about 32.8 kilowatts of direct current power and
together generate enough electricity to supply about 30 non-air conditions
homes, according to a NASA description.
An older solar array
segment, the Port
6 power module, currently extends above the ISS from atop the outpost's
Unity node. Only one of that segment's two solar wings - the starboard array -
is deployed. The port-reaching array was retracted during the STS-116 mission.
NASA's next shuttle
mission - STS-117
aboard Atlantis - is slated to launch on March 15 to deliver the third of
four solar arrays, part of its Starboard 3/Starboard 4 (S3/S4) payload, to the
ISS.
When complete, the ISS
will rely on four sets of U.S. solar arrays and eight power channels to supply
space station systems with about 84 kilowatts. The final configuration will
employ eight direct current switching units routing power through the station's
four main bus switching units for distribution to power-hungry systems.
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