Spacewalk to Replace Aging Batteries
Astronauts David Wolf and Christopher Cassidy switched their spacesuits to battery power at 10:32 a.m. EDT to officially kick off a challenging spacewalk to replace four massive solar array batteries.
CBS News space analyst Bill Harwood reports that Wolf and Cassidy will first head to the newly-installed Japanese Exposed Facility on the front left side of the International Space Station to remove insulation from experiments that will be mounted on the platform Thursday. Wolf also will install handrails to assist future spacewalkers.
The astronauts then will make their way to the far left end of the station's main power truss to change out four of six batteries used by the lab's oldest set of solar arrays.
The spacewalkers will be working far from the safety of the airlock - several hundred feet - manually swapping out 375-pound batteries.
"There's no way to get back quick," Wolf said in a NASA interview about EVA 3. "The robot arm will place these large solar array batteries reasonably near where they will be installed. But we'll be handling these heavy batteries, each the size of a small refrigerator, each with rows of delicate cooling fins on the back.
"And we will pull those out of the Vertical Cargo Carrier, hand them back and forth until we get them in position and mate those fins with the opposing fins on the space station. Those are cooling fins so those batteries won't overheat in use. We'll do four of those batteries on EVA-3. We'll do two more [on] EVA-4, and we consider this one of the highest critical pieces of work to do on this mission."
The final two P6 batteries will be replaced during a spacewalk Friday by Cassidy and Thomas Marshburn.
This will be the 128th EVA devoted to station assembly and maintenance since construction began in 1998, the ninth so far this year and the third of five planned by Endeavour's crew. It will be the seventh spacewalk for Wolf and the first for Cassidy, a former Navy Seal.
For identification, Wolf will be wearing a spacesuit with solid red stripes around the legs while Cassidy will use a suit with diagonal stripes.
"P6 is the truss segment that's been up there the longest and the batteries are therefore the oldest, so those batteries need to be changed out and there's six of them total," Cassidy said in a NASA interview. "We've learned in our training that it's unrealistic to get six completed in one spacewalk. So Dave and I will tackle four and they need to be done in pairs. You know, when you read the instructions on your flashlight and it says, 'Don't mix an old one and a new one together,' I never knew why. Well, the same thing applies to space batteries. You want the pairs to be both new batteries. We can't mix old ones and new ones.
"So consequently if we do two and we try to do the third, we're committed to the fourth. I think we could probably do five in one EVA, but it doesn't make sense from a hardware perspective. They're done in sets. So we're doing these first four batteries."
Each nickel-hydrogen battery measures 40-by-36-by-18 inches and weighs 375 pounds. Two batteries in series can store 8 kilowatts of power. The batteries have a design life of 6.5 years and can endure more than 38,000 charge/discharge cycles.
"P6 is a long ways away from the airlock," Cassidy said. "I think it's the farthest you could get from the airlock hatch because the airlock's on the starboard side. We're going port, and it's way out there. We have safety tethers that allow us to go 55 or 85 feet. There's two different sizes and so we have to stack ... some together to give us twice the distance.
"The task in and of itself, of physically pulling out a battery and putting it in, is not necessarily the hard part," Cassidy said. "The hard part is the choreography with the folks moving the arm, Doug (Hurley) and Julie (Payette). As we grab the battery, they'll guide the pallet, the ICC-VLD, away from us, essentially pulling the battery out of the carrier. And then Dave and I have to ... do a series of hand offs. He grabs it and then I move and then I'll grab it and he lets go and then he moves and we kind of do this hopping motion until we get to the spot where the battery's going to go."
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