Blogger Note: Today's spacewalk is slated to begin at 10:58 a.m. EDT.
Spacewalking astronauts will venture outside the International Space Station today to replace batteries that have been powering the outpost during swings around the dark side of Earth since December 2000.
Easier said than done.
"It's somewhat similar to the work you would do in your garage or your home. But in a lot of ways it's different," NASA space station flight director Brian Smith said Tuesday.
Astronauts work in pressurized spacesuits in a vacuum environment where a tear on a sharp object could lead to certain death. The suits are so bulky its akin to trying to swap out a car battery while wearing boxing gloves.
"It looks easy," Smith said. "(But) don't let that mislead you...It is complicated and you have to be extremely careful."
Endeavour mission specialists Dave Wolf and Chris Cassidy will set out today to replace four nickel-hydrogen batteries that have outlived their 6.5-year design. Each weighs 375 pounds and cost $3.6 million. Two more will be replaced on a fourth spacewalk on Friday.
Getting to their work site will be a hand-over-hand hike. Wolf and Cassidy will crawl from handrail to handrail to the far left end of the station's central truss - a point half a football field away from the station's U.S. Quest airlock.
All the while they'll have to make certain two braided steel safety tethers keep them hooked onto handrails. Both astronauts will be outfitted with small jet backpacks in case they somehow become untethered and float free.
But in the 127 spacewalks performed since 1998 to build the $100 billion station, none of nearly 90 assembly workers from the U.S., Russia, Canada, Japan, Germany, France and Sweden have had to use the jetpacks.
All added up, spacewalkers have tallied 792 hours and 31 minutes - the equivalent of 33 days - assembling the 340-ton station, so far without serious incident.
The Endeavour astronauts spent part of the day Tuesday doing prep work for today's spacewalk. Their tasks included moving a carrier holding the batteries to the far left end of the central truss.
The astronauts also took time to answer questions posted on YouTube. Dawn from Indianapolis wanted to know what spacewalkers do if they have to sneeze in their spacesuits.
"Aim well," said Wolf, a veteran of six spacewalks. Keep it off the helmet's faceplate. "It can mess up your view and there is no way to clear it."
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