CAPE CANAVERAL, Fla. -- Shuttle Discovery's spacewalkers scaled the International Space Station twice this week, experiences that one of the astronauts likened to mountaineering or, better yet, being a high-rise window washer.
Carrying out some station construction work, Daniel Barry and Patrick Forrester clambered up and down the 17-story outpost on their first sortie, mounting coolant tanks and suitcase-sized science packages to the exterior of the complex.
Then acting as orbital electricians, the two rigged up power cables on the outer hull of the $1.4 billion U.S. Destiny science laboratory during another spacewalk aimed at readying the outpost for new construction work next year.
And during the course of the two forays, the astronauts got a good feel for the enormity of the complex while working near the top of the towering station, which now stretches 171 feet (52 meters) from end to end.
"Just the sheer size of it is magnificent," Barry told SPACE.com's Andrew Chaikin in a space-to-ground interview Sunday.
"The chance to move that far away from our shuttle (and) up into the sky, looking down on all that structure, you truly feel that you are climbing a mountain, or right up the side of a building. And that is just spectacular."
Launched Aug. 10 from Kennedy Space Center, Discovery and its four astronauts ferried a new crew and some 7,400 pounds (3,330 kilograms) of food, clothing, research apparatus and science experiments to the station.The two spacewalks came amid a scramble to unpack all the gear from a shuttle-borne shipping container and then load it back up for Discovery's upcoming return to Earth.
Heading home on the shuttle: Outgoing station commander Yuri Usachev and flight engineers Susan Helms and Jim Voss, who boarded the outpost in March and have already spent 164 days in space.
Such lengthy stays in the weightless space environment tend to have a debilitating effect on the human body, weakening the skeletal and immune systems as the heart, lungs and other major organs.
Blood and body fluids also tend to pool in the head and upper torso in weightlessness, rushing back toward the legs and feet upon a reentry into normal Earth gravity - a phenomenon that causes returning astronauts to feel woozy.
Leg muscles also are apt to be weak from a lack of use, so a seemingly simple walk can be difficult for homebound station crews.
Nevertheless, Barry -- who is a medical doctor and a physical rehab specialist -- said he thinks Usachev, Helms and Voss will fare well upon their return to terra firma.
The reason: The trio has spent two hours a day for the past five-and-a-half months working out in a station health clinic outfitted with a zero gravity treadmill and a resistive exercise machine -- training specifically designed to counteract the effect of long stays in weightlessness.
"I think that they have maintained their physical conditioning in a rigorous manner. It's very clear that they've worked hard on it. It's a priority for them," Barry told Chaikin. "And so I think all of that hard work is going to really pay off for them when we hit the ground."
In fact, Barry wishes he were in such good shape.
"I got a chance to try some of their exercise devices. I ran on their treadmill, and I used their resistive exercise device," he said.
"I was sweating and huffing and puffing and sort of just barely getting along, and I had been watching Yuri and Jim and Susan every day, sprinting along on that treadmill."
Consequently, Barry isn't likely to challenge the trio to a race once they return home.
"I suspect, at least based on the comparison of me on their treadmill and them on their treadmill, that when we get back they may be running miles faster than I will be," he said.
With the so-called Expedition Two crew in tow, Discovery and its crew are slated to depart the station about 10:52 a.m. EDT (1452 GMT) Monday, capping an eight-day stay at the outpost.
The shuttle and the returning station crew are due back at Kennedy Space Center at 12:48 p.m. EDT (1648 GMT) Wednesday. New station skipper Frank Culbertson and his two cosmonaut colleagues -- Vladimir Dezhurov and Mikhail Turin -- will remain in space until Dec. 9.
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