On Friday, two American astronauts took a marathon spacewalk. They spent about eight hours outside the International Space Station on a truly exceptional plumbing job. NASA astronauts Scott Kelly and Kjell Lindrgren spent 7 hours and 48 minutes working outside the station, performing the essential maintenance on their spacecraft.

It was the duo's second spacewalk in nine days. In the first-ever spacewalk of the astronauts past week, headed by Kelly, the duo was on distinct tracks while performing a number of long-term maintenance tasks outside the station.

This time it was commanded by Lindgren, they worked together, coordinating their moves to reconfigure and add ammonia to the port-side station cooling systems, 'high-flying plumbing, as called by NASA officials through Twitter.

It has marked the 190th spacewalk outside the station, totaling over 1,192 hours of spacewalking time.

The astronauts started early, firstly removing a thermal cover from a part of the external ammonia station before getting separated to synchronize the disconnection of the cooling systems, each from a distinct location.

The ultimate mission of the astronauts was to undo work that was done during a 2012 spacewalk by astronauts Suni Williams and Akihiko Hoshide, wherein the astronauts rerouted ammonia away from the main radiator of the port-side cooling system to the backup system in an attempt to halt an ammonia leak. Later the source of leak was identified as a faulty cooling pump, which was replaced by astronauts Chris Cassidy and Tom Marshburn in 2013 while they were on a last-minute spacewalk with only two days of planning.