Washington: Astronauts from the
International Space Station today conducted a third spacewalk
to replace a busted cooling unit on the orbiting outpost, NASA
Spacewalkers Doug Wheelock and Tracy Caldwell Dyson began
their work on installing a spare ammonia pump module on the
ISS at 6:20 am (local time) according to the US space agency,
which said the spacewalk would last a total of about six and a
Flight Engineer Shannon Walker assisted the effort from
inside the ISS by operating the station`s robotic arm.
Space officials said Wheelock carefully positioned the
spare pump so that it could be securely bolted into place by
Caldwell Dyson and that four and a half hours into the
spacewalk, all fluid lines on the new unit were successfully
connected, with no detectable ammonia leaks.
The cooling unit`s nearly 800-pound (360 kilo) ammonia
pump failed unexpectedly on July 31 and was removed from the
USD 100-billion orbiting station during a spacewalk last
The pump is critical to keep the station from
overheating. The six-member crew has relied on a single backup
since the malfunctioning pump failed during a power surge.
The incident set off alarms onboard the station, although
officials have said that crew of three Russians and three
Americans were never seriously in danger.
A first spacewalk to begin repairs on the malfunctioning
cooling system took place on August 7 and lasted a record
eight hours, three minutes, with a follow-up second spacewalk
on August 11.