Three International Space Station crew members, including the orbiting lab’s first Canadian commander, are scheduled to depart for Earth late Monday, following a whirlwind spacewalk over the weekend by two U. S. astronauts to stem a sudden leak in the ammonia cooling system.
Chris Hadfield first Canadian spacecraft commander. Photo Credit/NASA TV
Canadian Chris Hadfield and one of the spacewalkers, Tom Marshburn, are to join cosmonaut Roman Romanenko in a Soyuz crew transport scheduled to depart the station shortly after 7 p.m., EST. The capsule should be on the ground in southern Kazakhstan at 10:31 p.m., EST, ending a 146 day mission for the three men.
Hadfield, a two time NASA space shuttle veteran, assumed command of the station’s Expedition 35 in March, becoming only the second non-American, non Russian to lead activities aboard the six-person research installation. His objectives were to keep his five crew mates safe, protect the station and make good use of its research facilities.
“I can proudly say that all three of those have been accomplished,” said Hadfield in a ceremony Sunday to mark the change of command that will accompany the Soyuz departure. “The crew is healthy and happy, and I think any of us would come back given the opportunity.”
Pavel Vinogradov, a veteran Russian cosmonaut, will assume command.
Hadfield’s command ended with a flurry of activity.
On Saturday, Marshburn joined Chris Cassidy for a 5 1/2 hour spacewalk to replace a pump and flow control system (PVCS) assembly electronics box on the oldest segment of the station’s long solar power system truss. Two days earlier, Vinogradov spotted snowy flakes streaming from the segment that anchors two of the station’s eight solar panels.
Chris Cassidy, left, and Tom Marshburn address ammonia leak during space station spacewalk. Photo Credit/NASA TV
That triggered a rush by International Space Station mission managers and the NASA flight control team tomountspacewalkrepairs as coolant levels dropped low enough to force a thermal control system loop and power channel off line. Cassidy and Marshburn, both trained in the procedures, had shared a spacewalk at the same worksite during a July 2009 space shuttle station assembly mission.
Marshburn and Cassidy inspected the leak site during their spacewalk but were unable to pinpoint the source of the seepage. But as per the plan, they replaced the PVCS box and stood by as the new hardware was activated and the flow of ammonia coolant was re-initiated. Again, there was no sign of a leak, leading ground controllers to conclude the old PVCS box was the most likely ammonia leak source.
However, NASA flight control teams plan to closely monitor the cooling system in the coming weeks for further indications of a leak that might require additional repairs.
”I will tell you we are happy, very happy,” said Joel Montalbano, NASA’s deputy space station program manager, in a post spacewalk news briefing. “We did not see any obvious signs of a leak, but it’s going to take some time, weeks perhaps months, to evaluate the system to make sure we did indeed stop the leak.”
Vinogradov, Cassidy and cosmonaut Alexander Misurkin remain behind on the station as Hadfield, Marshburn and Romanenko depart for Earth. The holdovers are scheduled to be joined on May 28 by new U.S., European and Russian station crew members Karen Nyberg, Luca Parmitano and Fyodor Yurchikhin.
If further cooling system spacewalk repairs become necessary, they will likely be assigned to Cassidy and Parmitano.