Wednesday, July 22, 2009

Live In Orbit: Astronauts Take Hand-Over-Hand Hike

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Blogger Update, 1:28 p.m.: One down, three to go. The first of the four new batteries now has been successfully installed on the P6 truss.

Spacewalking astronauts are heading out on a hand-over-hand hike to the far left end of the International Space Station's central truss -- a point more than half a football field away from the U.S. Quest airlock and safety.

Endeavour mission specialists Dave Wolf and Chris Cassidy aim to remove and replace four of six batteries on the P6 truss segment, which serves as a mounting point for massive American solar wings.

The wings collect solar energy that is stored in the batteries and used to power the station when it is flying on the dark side of Earth.

About the size of small refrigerators, the 375-pound batteries have been charging and discharging since the P6 truss was delivered to the station in December 2000. They each cost $3.6 million and have a design life of 6.5 years.

The new batteries are mounted on a shuttle-launched carrier now mounted to the top of the station's Mobile Transporter rail cart.

Built by the Canadian Space Agency, the cart runs on rails atop the central truss and can move the station's robot arm or large payloads from work site to work site. The transporter now is station at Work Site 8 -- the one closest to the far left end of the truss.

Here's how they plan to do the battery swap:

The old batteries -- numbered 1 through 6 -- will be unbolted from their housing on the P6 truss by Cassidy. Then he'll hand it off to Wolf, move closer to his colleague, and then take hold of the battery.

Wolf will move a bit further back toward the shuttle-launched carrier and then once again take a battery hand-off from Cassidy. The astronauts call this process "shepherding" the batteries, and it will sort of look like they are inch-worming the old and new batteries back and forth between the truss and the battery carrier.

The new batteries are lettered A through F.

The exchange is expected to take about four-and-a-half hours to complete.

The final two batteries will be swapped out by Cassidy and Endeavour mission specialist Tom Marshburn during the fourth of five spacewalks planned during the shuttle's stay at the station. That excursion is set to take place on Friday.

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