MIAMI:- Two US astronauts embarked Tuesday on the second spacewalk this month to make much-needed repairs to the International Space Station’s robotic arm, NASA said. Expedition 53 Commander Randy Bresnik is leading the outing, accompanied by Nasa flight engineer Mark Vande Hei. The spacewalk formally began when the duo switched their spacesuits to battery power at 7:56 am (1156 GMT), then floated out into the vacuum of space, Nasa said. On their spacewalk Thursday, the pair replaced the latching end of the 57-foot-long (18-meter) Canadian-made arm, called Canadarm2.