Astronauts Finish ISS Battery Changeout
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By Frank Morring, Jr.
Spacewalkers Chris Cassidy and Tom Marshburn were able to finish replacing the oldest set of batteries on the International Space Station July 24, catching up on a task that was halted abruptly on July 22 when the carbon dioxide level in Cassidy's spacesuit started rising during the third extravehicular activity (EVA) of the STS-127 mission.
As a result, planners rewrote the timeline for the fourth EVA to accommodate the work left undone. Originally Cassidy and astronaut Dave Wolf were to have replaced four of the six batteries in the P6 truss element on July 22, leaving only two more for the July 24 spacewalk.
Although Cassidy's carbon dioxide level rose slightly as the latest EVA drew to a close, it did not appear to be heading for unacceptable levels and he was allowed to continue working. Experts at Mission Control Center-Houston speculated that Cassidy overtaxed his lithium hydroxide scrubber early in the first EVA of his career on July 22, and counseled him to take it a little easier on his second trip out of the airlock, according to Holly Ridings, lead ISS flight director for the mission.
Cassidy and Marshburn returned to the July 22 worksite at the far port end of the truss and picked up where the third EVA left off. They pulled the old batteries out of the P6 truss, temporarily stowed them out of the way while they retrieved fresh units from the integrated cargo carrier (ICC) that carried the hardware to orbit, and then stowed the old batteries in the empty spaces on the ICC.
Once the work was completed, the station robotic arm pulled the ICC out of the way, and the two spacewalkers gathered their tools and headed back to the Quest airlock on the U.S. side of the station. In all they spent seven hours, 12 minutes on the EVA, which ended at 5:06 p.m. EDT.
On July 22, Cassidy and Wolf were ordered to leave most of their tools on the P6 element so Cassidy could get back onto station life support as quickly as possible.
Meanwhile, as the astronauts worked outside the station, controllers at Mission Control Center-Moscow guided the Progress 34P resupply capsule toward the station. The robotic spacecraft lifted off from the Baikonur Cosmodrome in Kazakhstan at 6:56 a.m. EDT July 24, loaded with 2.5 tons of food and other supplies for the six-person station crew. It is scheduled to dock with the ISS at 7:11 a.m. EDT July 29.
Endeavour is scheduled to undock from the station on July 28 to make way for the Progress vehicle, which will loiter in orbit until then, in keeping with flight rules prohibiting its docking while an orbiter is present at the station. Endeavour, which launched late because of weather at Kennedy Space Center, is leaving the station earlier than originally planned because of the conflict with the Russian vehicle.
Some packing and other work that normally would have been done in the orbiter before the hatches close will be shifted until after undocking to accommodate the early departure.
Photo of extravehicular activity: NASA
