Article Posted on : - Aug 11, 2010

The International Space Station.

WASHINGTON (BNS): NASA astronauts Doug Wheelock and Tracy Caldwell Dyson on Tuesday completed all tasks ahead of their second spacewalk Wednesday to replace the failed ammonia coolant of the International Space Station (ISS).

NASA has decided to begin Wednesday's spacewalk an hour later than originally planned.

The additional time will allow teams to fine-tune robotic procedures and get some extra rest, the space agency said.

To facilitate the spacewalk, ground controllers overnight activated the Pressure Regulator Valve (GPRV) for the Loop A Nitrogen Tank Assembly, lowering the overall pressure in the plumbing for the inactive cooling loop.

The GPRV's pressure reduction will help in the closure of quick disconnect valves at the S0/S1 truss interface when the two astronauts will remove the fourth and final line connector holding the inactive pump module, NASA said.

The lowered pressure will also facilitate the reconnection of all fluid lines once the new pump is installed.

A third spacewalk is scheduled for Sunday to install the new pump.