Cassidy and Marshburn carried out three previous EVAs during a July 2009 space shuttle ISS assembly mission. Two of the excursions, carried out as a team, took the two astronauts to the P-6 solar power module for a scheduled replacement of the power storage batteries.
In addition, the leak troubleshooting is ranked as one of the “Big 12” ISS maintenance tasks that U.S. crewmembers train extensively for before they lift off.
Hadfield, an experienced spacewalker who has also trained for the Big 12, would choreograph the EVA from inside the station if ISS managers give final approval.
Early May 10, the station’s three Russian cosmonauts joined in the efforts to pinpoint the source of the leak, with one noting a seepage of “frozen drops” 1-3 cm in diameter coming from the area of the P-6, 2B radiator panel. The cosmonauts also transmitted a photo of a suspicious “mark” on the solar module to ground controllers for evaluation.
On Nov. 1, previous ISS crewmembers Sunita Williams and Akihiko Hoshide carried out a near 7-hr. spacewalk to install jumper cabling in an effort to circumvent a persistent, low-rate coolant leak in the same region of the station’s far port-side solar power truss. The source was never pinpointed by the repair work, which included re-activation of a radiator panel that had been active during the station’s early assembly phase.
The P-6 is the oldest of the station’s four big solar power modules. Launched in late 2000, it was mounted in a temporary position on the station to serve as a solar power source during initial assembly. The 30,000-lb. truss piece with its twin solar panels was re-located to its current position during a late 2007 shuttle ISS assembly mission.
The departing crewmembers are scheduled to be replaced on May 28 by cosmonaut Fyodor Yurchikhin, NASA astronaut Karen Nyberg and European Space Agency astronaut Luca Parmitano. They are scheduled to launch aboard the Soyuz TMA-09M at 4:31 p.m. EDT, on an expedited transit that would have them dock at 10:17 p.m. EDT.