(AP) -- Two astronauts who were teaching math and science to middle school students just five years ago went on a spacewalk together Monday, their path cleared of dangerous orbiting junk that had threatened the space station and shuttle. On Sunday, the linked shuttle-station complex had to move out of the way of a 4-inch piece of debris that had been projected to come perilously close during the spacewalk.
Astronauts Joseph Acaba and Richard Arnold II had no luck trying to free up a jammed equipment storage shelf at the international space station, one of their main tasks.
Using a hammer, they managed to loosen a pin that Acaba and another astronaut accidentally inserted upside down on the platform during Saturday's spacewalk. But the shelf mechanism would not extend into the proper position, despite repeated efforts.
"Three, two, one, go," Arnold called out as they tugged with all their might. "Negative."
Mission Control instructed the spacewalkers to tie the platform down using sturdy tethers.
It was the first time two former schoolteachers took a spacewalk together, and was the third and final spacewalk for shuttle Discovery's mission.
It also was the second time out the hatch for both Acaba and Arnold. Their previous outings were with another astronaut, and they took pleasure in sharing this one together. Both in their 40s, they were teaching when NASA picked them as educator-astronauts in 2004.
"Take your time, enjoy it and do good work. We're counting on you," the space station's skipper, Mike Fincke, called out.
The jammed storage platform is located on the left side of the space station framework that holds the solar wings. The platform is supposed to secure big spare parts that will be needed once NASA's shuttles stop flying in 2010.
Similar shelving is on the opposite side of the framework and also needs to be extended. But Mission Control told the spacewalkers to skip that because of all the trouble with the first platform.
The spacewalkers did move a crew and equipment cart from one end of the space station to the other, and unhooked some clamps on a hose.
"You've left the space station in much better shape ... and we heartily thank you," Mission Control radioed as the 6 1/2-hour spacewalk ended.
As for space junk, it's becoming a growing concern for the 220-mile-high space station. Earlier this month, space station residents had to seek shelter in their emergency getaway capsule because of debris. Last week, the station almost had to dodge another piece of junk.
Discovery's astronauts said Sunday they don't think about space junk when they're outside. They said there are enough things to worry about, like keeping themselves and their tools tethered and getting the job done. There's always a risk tiny pieces of debris that can't be tracked from the ground could come zooming by.
The two crews will part Wednesday, and Discovery will aim for a touchdown back at NASA's spaceport Saturday.
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