Two American astronauts currently residing in the International Space Station had a lengthy stay outside the station Friday as they completed an eight-hour spacewalk to service part of the ISS’s plumbing system.
The celestial plumbing job was carried out by NASA astronauts Scott Kelly and Kjell Lindgren, who spent a total of seven hours and 48 minutes in space today performing the necessary maintenance. This was the pair’s second space walk in just nine days, their previous one being their first as a duo.
While their first spacewalk together last week involved maintenance tasks performed autonomously by the two astronauts under Kelly’s command, this recent one saw the two working together in a synchronous fashion, with Lindgren at the helm. Their mission was to reconfigure and add ammonia to the station’s port side cooling system, an act NASA referred to as “high-flying plumbing.”
The spacewalk also happened to be a mild milestone, being the 90th spacewalk outside of the International Space Station, with all 190 adding up to more than 1192 hours of extra vehicular activity around the ISS.
The necessity for maintenance on the cooling systems came about after work was done to them in 2012 by astronauts Suni Williams and Akihiko Hoshide, who needed to perform a spacewalk to re-route the ammonia away from the main port side cooling system’s radiator and into the backup system to avoid an ammonia leak. The leak was then sourced back to a faulty cooling pump, which was fixed in a last minute spacewalk in 2013 by astronauts Chris Cassidy and Tom Marshburn, who remarkably only had two days to plan their mission.
Now, with the mission of getting everything back in working order, Kelly and Lindgren got an early start, first removing the thermal cover from the external ammonia station, then splitting up to disconnect the cooling systems. This required coordination, since different systems have different locations on the outside of the station.
Next, great care needed to be taken as the isolated systems were cleared of excess ammonia. Ammonia is toxic to humans, and as such cannot be taken back into the station. Any residue that remains on their suits has to be evaporated off in space so as to not contaminate the living and working quarters on board. Lindgren noticed a few flakes of ammonia while at work isolating the prime cooling system from its backup, which warranted a close inspection from his teammate, and vice versa, before entering the airlock at the end of the mission.
With the fill lines of the isolated systems clear of an excess ammonia, it was time for NASA’s ground control to step in, remotely controlling a valve and initiating the filling of the back up systems ammonia coolant. While the 20-minute process was underway, Kelly stood by, ready to manually shut the valve down in the event of any leakage. Luckily, this was not the case. After that, the process was repeated on the primary system, with the same success. All in all, the backup system received 3 kilograms (6.8 pounds) of ammonia added to its 41-kilogram (90 pound) reservoir, with the primary receiving 3.4 kilograms (7.5 pounds) into its 24-kilogram (4 pound) tank.
After the filling, Lindgren retracted the backup radiator, docking it in its out-of-use position before starting on the final task in the mission: venting leftover ammonia from the plumbing lines that had been used in the re-configuring process. This excess ammonia was stored in a back on the outside of the ISS. One additional part of the mission, cinching the backup radiator in place along the side of the station and adding a protective cover, was not able to be completed. This, however, poses no risk to the crew of the station, according to NASA engineers.
After cleanup, it was time to head in. It was determined that the astronauts had been in sunlight long enough to evaporate off any traces of ammonia that might have tried to hitch a ride on their suits. Once inside, Japanese astronaut Kimiya Yui and Russian Cosmonaut Sergey Volkov help the pair our of their EVA suits and the two started a well deserved half day break before getting back to work.
Lindgren is almost at the end of his very first mission to the International Space Station, while Kelly is 225 days into his year long stay in space.