NASA astronauts Scott Kelly and Kjell Lindgren spent a total of seven hours and 48 minutes working outside the International Space Station on a spacewalk (extra vehicular activity) to fix the port truss (P6) ammonia cooling system back to its original configuration. They also returned ammonia to the desired levels in both the prime and back-up systems. The spacewalk was the second for both astronauts. The crew started their spacewalk at 1022 GMT on 6 November 2015.