Monday, July 27, 2009

Live In Orbit: Shuttle Crew Set For 5th Spacewalk

The Endeavour astronauts will complete construction today of the Japanese wing of the International Space Station while equalling the record for spacewalking work at the orbiting outpost.

Shuttle mission specialists Chris Cassidy and Tom Marshburn will set up two television cameras outside the $1 billion Japanese Kibo science research facility, capping an assembly job carried out over three shuttle missions in the past 16 months.

The venture outside will be the fifth for the Endeavour crew, tying the record for the most extravehicular excursions on a station assembly mission.

"This is a very aggressive mission, and, obviously, it's a very long mission. And the crew has just done a fantastic job," NASA flight director Brian Smith said Sunday.

But Endeavour mission commander Mark Polansky said this is no time to rest on laurels.

"I think we're all keenly aware that (spacewalks) carry some risks with them, and so we're going to be very, very deliberate and careful about the last (spacewalk) because in my book, the last one you do is the one you have to watch out for the most."

Cassidy and Marshburn have a hodge-podge of assignments.

The first will be to rewire an electrical panel that routes power to the station's four dome-shaped gyroscopes, devices that help keep the outpost properly oriented in orbit.

Two of those 800-pound American gyroscopes now are fed electricity over the same power channel. The failure of that single channel, as a result, could knock out both gyroscopes. The rewiring work will put the two gyroscopes on separate power channels.

Cassidy, a former Navy SEAL, and Marshburn, a former emergency room doctor, also plan to readjust multi-layer thermal insulation on a two-armed Canadian robot known as Dextre. And they aim to deploy a mechanism upon which a spare parts carrier will be mounted later this year.

The TV camera work will wind up Kibo construction, which began in March 2008 with the delivery of an attic-like logistics module. Five spacewalks were done on that flight, too.

The cylindrical warehouse now is fixed atop the 37-foot-long Kibo laboratory module, which arrived at the station in June 2008.

The Endeavour astronauts installed the third and final Kibo segment: an external platform that serves as a porch for science experiments outside the outpost.

They also outfitted the porch with an x-ray astronomy observatory, a space environment experiment and a communications system that will link Kibo with Japan's Mission Control Room outside Tokyo.

"I know JAXA (Japan Aerospace Exploration Agency) is very pleased, and we're very pleased for them," Smith said. "They've got an incredible laboratory both inside and outside now."

The Endeavour astronauts this week are entering the home stretch of their mission. The shuttle is set to depart the station Tuesday and land at Kennedy Space Center at 10:52 a.m. Friday.

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