US astronauts complete risky spacewalk outside ISS

By Barry Eitel

SAN FRANCISCO

Two American astronauts on Friday completed a spacewalk outside the International Space Station that lasted nearly eight hours and required the pair to dodge highly toxic ammonia particles leaking from a cooling system.

Scott Kelly and Kjell Lindgren were originally scheduled to fix the cooling and plumbing systems of the ISS during a 6.5-hour spacewalk.

But several minor disruptions including the leak and minor glove damage caused Kelly and Lindgren to remain outside the station for 7 hours and 48 minutes. The delays meant that the spacewalkers were unable to finish repairs on a spare radiator.

“The astronauts restored the port truss ammonia cooling system to its original configuration, the main task for today’s spacewalk,” NASA said in a statement. “They also returned ammonia to the desired levels in both the prime and back-up systems.”

Mending the leak in the cooling system completed repairs on a leak that began causing problems in 2012. While part of the faulty system was replaced in 2013 in a makeshift repair, NASA wanted to reconnect the original thermal system. To do that, the astronauts successfully topped off ammonia coolant levels and retracted a backup radiator.

NASA claimed that the astronauts reported seeing flakes of ammonia fly out of the leak but did not find any on their spacesuits after an inspection. Ammonia crystals are highly toxic and can easily cling to spacesuits. To avoid carrying the substance into the ISS, astronauts had to wait outside for up to 30 minutes to allow the sun to bake off the crystals.

Kelly and Lindgren conducted a similar spacewalk to fix other systems less than two weeks ago.

Friday’s excursion was the 190th spacewalk in the station’s history.

The ISS – the most expensive object ever built – recently celebrated its 15th anniversary of continual human habitation.

Crew members have spent almost 1,200 hours working outside the station.