Spacewalkers Mike Fossum and Ron Garan completed their first task, moving a failed pump module from a temporary storage site on the outside of the space station to the cargo bay of space shuttle Atlantis. Returning the module, which failed last year and disabled half of the station’s cooling system, is a key objective of the STS-135 mission. Engineers will diagnose what caused the failure so they can take steps to mitigate future pump module failures.