Astronauts took another spacewalk at the international space station Saturday, this time to lighten the workload for future crews.

Steven Swanson and Joseph Acaba loosened bolts on batteries, hooked up an antenna and photographed a pair of radiators. But they were stymied by a protruding pin that prevented them from setting up equipment storage platforms.

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It was the second spacewalk in three days for the crew of shuttle Discovery. On Thursday, Swanson and another astronaut installed the final pair of solar wings at the orbiting outpost. The panels were unfurled Friday.

Saturday's 6 1/2-hour excursion, though just as busy, lacked the drama associated with the multimillion dollar, high-priority solar wings. NASA was still basking in that success, telling the astronauts in a wake-up message that the space station "now looks like the artist renderings that we've been seeing for years. A day to celebrate!"

As soon as they floated outside, Swanson and Acaba, a former Florida schoolteacher making his first spacewalk, made their way all the way to the end of the space station's power-grid framework. They loosened bolts holding down batteries that will be replaced on the next shuttle visit in June.

A space station alarm went off as the spacewalkers wrapped up that job. The gyroscopes that were maintaining the position of the station-shuttle complex became overloaded from the astronauts' work on the end of the truss. Discovery quickly assumed control with its thrusters.

"Nothing to worry about," Mission Control assured the astronauts.

The astronauts later had trouble deploying an equipment storage platform. Mission Control ordered them to give up and move on to other tasks: installing a Global Positioning System antenna and using an infrared camera to photograph a pair of radiators, one of which has a peeling cover.

By then, there was no time to set up any equipment shelving on the opposite side of the station. Before going back inside, Swanson tied down the troublesome platform so it wouldn't flap around.

Some of the spacewalking chores had been added just this past week.

The GPS antenna work on the Japanese laboratory, for instance, was supposed to occur on a later spacewalk that ended up being canceled because of shuttle Discovery's repeated launch delays. That antenna will be needed when Japan launches a new space station cargo carrier this fall.

The astronauts' to-do list kept being changed, even as the spacewalk was in progress.

"We sure appreciate the hard work you did for our beautiful space station." space station commander Mike Fincke said when it was all over. "You guys proved that flexibility is definitely key."

Inside the space station, meanwhile, Fincke and others conducted a dry run of the new urine processor that was delivered by Discovery. It's part of a recycling system for turning urine and condensation into drinking water. The original urine processor broke.

One more spacewalk is planned Monday during Discovery's mission.

The shuttle will depart the space station Wednesday, eight days after arriving, and return to Earth next Saturday.