All parts here: This spacewalk took place 01 Nov 2012. Video will show only the helmet camera ISS external cameras views. There will be no Mission Control views.ISS Spacewalkers deploy Thermal Control Radiator to bypass Ammonia Leak.International Space Station Crew Members Suni Williams and Aki Hoshide successfully completed US EVA-20 on Thursday, reconfiguring one of the Space Station's Photovoltaic Thermal Control System Channels to take care of an ammonia leak. The ammonia leak on the P6 Integrated Equipment Assembly 2B Channel Photovoltaic Thermal Control System has been known since December 2006. The leak was rather small and the system lost about 0.7 Kilograms per year requiring periodic refills of the system to keep the total amount of NH3 above the critical limit to keep the system up and running. During Space Shuttle Mission STS-134 in May 2011, the 2B PVTCS system was refilled and teams assumed that another refill would be needed 4 years after that, assuming leakage remained constant. Recently, leakage started trending up to about 2.5kg per year and the system was approaching its limit much quicker than expected with quick-look assessments indicating that this threshold would be hit in late December 2012 or early January 2013. Each PVTCS channel holds about 25 Kilograms of ammonia in its nominal condition and channel 2B had been trending down until being replenished in 2011, followed by an increase in leak rate in 2012. ISS Mission Managers decided to perform the EVA as soon as possible to take advantage of the current spacewalking crew of Suni Williams and Aki Hoshide as long as they are still aboard ISS. This EVA featured a very experienced spacewalking team, both, inside Mission Control and aboard the Station. Suni Williams started this EVA as the leading female spacewalker with six EVAs and 44 hours and 2 minutes of total EVA time. More importantly, Suni Williams had past experience working on the P6 Truss and its PVTCS System. She and Michael Lopez-Alegria performed three spacewalks in 2007 to work on an Early Ammonia Servicer on P6 and associated cooling lines. She performed the stowage of the EETCS Radiator that was deployed on this EVA, so she already has hands-on experience with the actual hardware in orbit. Aki Hoshide started this ISS Expedition as Spacewalking Rookie, but performed two challenging EVAs with Williams in August and September to remove and replace a failed Main Bus Switching Unit on the Station's power system, so he has had the opportunity of gaining extensive EVA experience, becoming the leading Japanese Spacewalker with 14 hours and 45 minutes of EVA time.The spacewalking team was supported by fellow ISS resident Kevin Ford who was in charge of EMU configuration and airlock operations. The IV-Crew Member choreographing this EVA from Mission Control was Mike Fincke, a very experienced spacewalker with previous experience working with the PVTCS 2B System on STS-134 to re-fill the loop. Behind him was an experienced EVA team with EVA-Lead Allison Bolinger who was supported by MCC Backroom Personnel and hardware specialists.SOURCE FULL STORY:
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