75% of its normal power capacity, requiring minor limitations of normal operations until the issue was addressed. A second EVA to tighten the balky bolt, to complete the installation of the replacement MBSU-1 in an attempt to restore full power, was scheduled for Wednesday, 5 September. Yet in the meantime, a third solar array wing went offline due to some fault in that array's Direct Current Switching Unit (DCSU) or its associated system, further reducing ISS power to just five of the eight solar array wings for the first time in several years. On 5 September 2012, in a second, 6 hr, EVA to replace MBSU-1, astronauts Suni Williams and Aki Hoshide successfully restored the ISS to 100% power. 2012 – Failure of primary Carbon Dioxide Removal Assembly (CDRA) The ISS has two rack sized CDRAs (Carbon Dioxide Removal Assemblies) for redundancy with the Lab CDRA primary and the Node 3 CDRA as a powered off backup because of issues with sticking valves in the Node 3. It can step in as a backup if necessary but is not the preferred CDRA because of the problems with the sticking Air Selector Valves (ASVs). The Russian segment has its own carbon dioxide scrubbers but they are not sufficient for the whole of the ISS. On 16 June 2012 the lab CDRA suddenly shut down. This problem was traced to a failure of the second of three temperature sensors (the first one had failed previously) and it was quickly restored. However it soon shut down again, on 20 June due to erratic data from the one remaining temperature sensor. ISS decided to put the Lab CDRA into standby and activate the Node 3 CDRA instead, even with its valve sticking issues. 2013 – Ammonia Leak and CDRA issues again On 9 May 2013, at around 10:30 a.m. CDT, the ISS crew reported seeing small white flakes floating away from the Station’s truss structure. Analysis of the crew reports and images captured by external cameras confirmed a leak of ammonia coolant. Two days later a spacewalk was undertaken in order to inspect and possibly replace a pump controller box suspected of leaking. In early September one of the Air Selector Valves in the CDRA was removed and replaced, but problems with sticking valves persisted, and Node 3 had to be restarted several times. The ISS at this point had no new ASVs to