Doug Wheelock, poised on space station robot arm, pulls failed cooling system pump from space station. Tracy Caldwell Dyson, right, assists Photo Credit/NASA TV
NASA astronauts Doug Wheelock and Tracy Caldwell Dyson will float outside the International Space Station for a third time on Monday in a bid to wrap up repairs to the orbiting laboratory’s external cooling system.
Half of the system that circulates ammonia coolant through outstretched radiators to cool the station’s life support systems, science experiments and other vital electronics has been crippled since July 31 by an electrical short in a pump motor assembly.
On Wednesday, Wheelock and Caldwell Dyson managed to extract the damaged pump from its resting place on the station’s long solar power truss with some careful planning and assistance from Mission Control and NASA engineers.
Just four days earlier, the spacewalkers were thwarted in the efforts to remove the bulky pump by the leak of toxic ammonia in one of the four coolant lines they had to detach from the damaged motor first.
When they embark on Monday’s spacewalk, the two astronauts will retrieve a spare pump assembly attached to a stowage platform on their airlock and install it in place of the old motor. The task will not be complete until they re-attach the four coolant lines and five electrical cables.
“Our goal is to get the pump installed and hooked up,” said Mike Suffredini, NASA’s space station program manager. “That will be a stretch goal. But I think we can get there.”
The seven hour spacewalk is scheduled to begin just before 7 a.m., EDT.
Ground control teams expect to devote several days to the re-activation of the crippled cooling system.
However, NASA has not ruled out the need for a fourth spacewalk to stow the damaged pump and perhaps carry out other cooling system work.