Extra battery work for astronauts on spacewalk 4

CAPE CANAVERAL -- Astronauts are aiming for an extra-long spacewalk Friday to give the international space station more fresh batteries.

This time, astronaut Christopher Cassidy will head out to the work site more slowly. NASA cut short Wednesday's spacewalk because of rising carbon dioxide levels in his suit. NASA officials say the former Navy SEAL was moving so fast at the start of Wednesday's spacewalk that his air-cleansing canister did not work as efficiently as it should have.

Cassidy and Thomas Marshburn will attempt to install four new batteries during the planned seven-and-a-half-hour spacewalk. Two of those batteries should have been plugged in Wednesday.

It will be the fourth spacewalk for Endeavour's visiting crew.