NASA's Mission Control has re-integrated a series of crucial internal heat exchangers with the external thermal control system of the six person International Space Station, following a pair of recent U.S. spacewalks to deal with the Dec. 11 failure of a flow control valve in one of two external ammonia cooling loops.
Heat exchangers that allow internal water loops to cool electronics in the U.S. Destiny lab and Harmony and Tranquility nodes; the European Space Agency's Columbus lab module; and the Japanese Aerospace and Exploration Agency's Kibo experiment module were successfully re-activated on Dec. 25, according to Judd Frieling, NASA's lead flight director for the activities.
"That's all up and running," Frieling said in a Dec. 26 NASA update.
U.S. astronauts Rick Mastracchio and Mike Hopkins successfully replaced an external pump module, which included a new flow control valve, on the station's starboard solar power truss with spacewalks on Dec. 21 and 24. The exchangers permit heat from the electronics in the U.S., European and Japanese lab modules as well as the connecting nodes to move from water-based internal cooling lines to the Loop A ammonia thermal control loop.
The heat exchangers were taken off line following the Dec. 11 valve failure to prevent ultra-cold ammonia from freezing water at the exchangers. If damaged, the water thermal control apparatus could have permitted ammonia, a toxic substance, into the station's habitable volume.
Flight control teams expect to dedicate several days to re-integrating electrical systems that were taken off line back into the thermal control system, according to NASA. The valve issue interrupted a range of scientific activities underway aboard the station.
The re-integration process of electrical systems in the Columbus lab had not begun Dec. 26 and was awaiting the arrival of ESA experts, according to Frieling.
Following the valve failure, NASA's flight control team shut down non-essential electronics and shifted some thermal control duties to the station's Loop B cooling apparatus. The dual-loop ammonia system dissipates heat from external as well as internal sources through radiators that extend from the station's solar truss.
Meanwhile, the ISS mission management team offered formal approval on Dec. 26 for cosmonauts Oleg Kotov and Sergey Ryazanskiy to embark on a previously scheduled Dec. 27 spacewalk for the installation of two commercial Canadian Earth observing cameras outside the station's Russian segment as well as for the servicing of external experiments.
The 11th ISS excursion of 2013 is scheduled to begin at 8 a.m. EST.