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

As soon as they floated outside, Steven Swanson and Joseph Acaba 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.

It was the second spacewalk in three days for the astronauts.