article image

Unscheduled spacewalk set to fix space station leak

Paul Sutherland, Feature writer
May 10, 2013, 7:00 UTC

Sen—Astronauts on board the International Space Station are preparing for an unscheduled spacewalk today (Saturday) after the orbiting outpost began leaking ammonia.

NASA stressed the six astronauts on board were in no danger, following the observation that the gas was escaping from a port-side section of the truss on Thursday.

The ammonia is used as a coolant for power channels that provide electricity to the space station’s systems. As mission managers discussed the leak with the crew, work began to reroute power.

The station continued normal operations on Friday while the astronauts used handheld cameras to take pictures to download for analysis and described what they could see outside. They were then asked to close shutters all windows not in use to avoid them being contaminated by the ammonia.

ISS Expdition 35 commander Chris Hadfield told mission control he had been watching from a docking compartment and saw “a very steady stream of flakes or bits” escaping as the truss holding the solar array rotated.

Flight controllers at Houston examined photos taken by the crew together with pictures from external cameras fitted to the ISS and other data and confirmed that the amount of ammonia leaking from that section of the cooling system had increased.

Crew members Chris Cassidy and Tom Marshburn began preparing for a possible spacewalk by checking out their NASA spacesuits. Each of them has made three previous spacewalks on an earlier trip, the STS-127 mission by the shuttle Endeavour to the ISS in 2009.

Flight controllers on the ground gave the final go-ahead for the spacewalk late on Friday. Cassidy and Marshburn will exit the Quest airlock to inspect the area of truss labelled P6 from which the leak appeared to be coming. They will examine and possibly replace a pump controller box that is thought to be to blame for the leaking ammonia.

The spacewalk, which is due to begin at around 8.15am EDT, is expected to last 6.5 hours and will be broadcast live on NASA TV.

Commander Hadfield, who will assist with the spacewalk from within the station, seemed quite unfazed by the drama. He tweeted yesterday: “Good Morning, Earth! Big change in plans, spacewalk tomorrow, Chris Cassidy and Tom Marshburn are getting suits and airlock ready. Cool!”

Then he added: “The whole team is ticking like clockwork, readying for tomorrow. I am so proud to be Commander of this crew. Such great, capable, fun people.”

Each of the eight arrays of solar panels on the ISS has its own independent cooling loop. The loop that is giving trouble is the same one where spacewalkers attempted to troubleshoot a leak in November last year, though it is not certain that the leak is in the same place. The loop was expected to have lost all its ammonia before any spacewalk.

The P6 truss is one of the oldest parts of the ISS's structure. It was carried into space by Endeavour on the STS-97 mission in November 2000, then moved from its original installation position during the STS-120 mission of the shuttle Discovery in October/November 2007.

The other astronauts currently aboard the ISS are Tom Marshburn, Roman Romanenko, Pavel Vinogradov and Alexander Misurkin. Hadfield, Marshburn and Romanenko are due to return to Earth on Monday.