Live In Orbit: Spacewalkers Haul Spare Cooling Pump

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Spacewalking astronauts aim to move a spare cooling system pump to a storage pallet outside the International Space Station after successfully fixing a spare communications antenna to the same external platform.

Endeavour mission specialists Dave Wolf and Tom Marshburn are about midway through what is expected to be a 6.5-hour excursion -- the second of five planned during the shuttle's stay at the station.

Wolf is anchored to a portable foot restraint he attached to the end of the station's 57-foot robot arm, which is being operated by Canadian Space Agency astronaut Julie Payette and Endeavour pilot Douglas Hurley.

Wolf has been having a little trouble positioning himself in the foot restraint, but the astronaut nonetheless hauled a huge communications antenna with a six-foot dish from a shuttle-launched cargo carrier to an external stowage platform on the port side of the station's central truss.

The antenna work was delayed a bit when Marshburn lost track of his 85-foot safety tethe. He remained safely attached to station structure by his shorter, 55-foot tether.

NASA safety rules call for astronauts to two braided steel tethers to anchor astronauts to the station or the shuttle cargo bay at all times. Spacewalkers are equipped with small jet backpacks just in case they somehow become untethered and float free.

Now Wolf just removed a cooling system pump from the cargo carrier, which was hauled up on Endeavour and temporarily stowed on the top of the station's Mobile Transporter rail cart.

The Pump Module Assembly is part of the system that provides cooling to internal and external station electronics as well as station payloads and its crew members.

The station has two coolant independent coolant loops. The external loops use an ammonia-based coolant and the internal loops use water. The pump module is the heart of the system. It pumps ammonia through external loops to provide cooling and also plays a role in carrying heat to station radiators so it can be dissipated.

The Boeing-made pump weighs 780 pounds and measures approximately 5 1/2 feet long by 4 feet wide by 3 feet high.