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Station astronauts begin another spacewalk BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: February 4, 2007 Astronauts Mike Lopez-Alegria and Sunita Williams switched their spacesuits to internal battery power today at 8:38 a.m., officially kicking off their second spacewalk in less than a week to finish switching the lab complex to its permanent cooling system. "Good luck, guys. Be careful," cosmonaut Mikhail Tyurin radioed from inside the lab complex. On Wednesday, Lopez-Alegria and Williams tied the lab's low-temperature systems to ammonia coolant loop A and today they plan to finish the job by switching moderate-temperature avionics and computer systems to coolant loop B. A third spacewalk is planned for Feb. 8 to remove thermal shrouds from a segment of the station's main solar array truss on the left side of the lab complex and to deploy two external cargo stowage platforms. This is the 79th spacewalk devoted to station assembly and maintenance since assembly began in 1998, the eighth overall for Lopez-Alegria and the third for Williams. Going into today's excursion, 65 astronauts, cosmonauts and international fliers from Japan, Canada, Germany, France and Sweden had logged 477 hours and 54 minutes in station spacewalk time. After Wednesday's spacewalk, Lopez-Alegria ranked fourth in the world in cumulative EVA time with 47 hours and 31 minutes over two shuttle missions and the current space station expedition. During a shuttle visit in December, spacewalking astronauts and ground controllers carried out a complex mission to switch the station's electrical system from a temporary configuration, used during the initial stages of construction, to its permanent system. They also powered up two big pumps in the main solar array truss and began circulating ammonia through coolant loops A and B. Electrical components in the station are mounted on cold plates that use circulating water to carry heat away. Heat exchangers, in turn, transfer that heat to external ammonia coolant loops. Up until now, lab systems have been cooled by an interim cooling system, which used radiators on the P6 solar array truss, extending up from the Unity module, to dissipate heat to space. Most of the work two hook up coolant loops A and B requires work in the so-called "rat's nest," a confined area between the Destiny laboratory module, the Unity connecting module and the Z1 truss that extends upward and supports the P6 solar array that provided the station's interim power. NASA planners initially considered having the shuttle Discovery's crew handle the required plumbing changes during the December mission to activate the station's permanent electrical system. But given the complexity of the electrical work, the cooling system re-plumbing was passed on to Williams and Lopez-Alegria. Along with hooking up coolant loop B, the spacewalkers also will:
If all goes well, the P6 array will be moved to the left end of the station's main solar truss in September and the wings will be re-extended.
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