The primary task of the fifth spacewalk conducted by Robert L. Behnken and Mike Foreman was to attach an inspection boom to the outside of the ISS to enable the next shuttle crew to check their spacecraft for heat shield damage.
The next space shuttle Discovery crew will blast off to the ISS in late May to deliver Japan's Kibo laboratory to the ISS. The lab is so big that it will leave no room in the shuttle for the orbiter boom sensor system. Once the Kibo lab is installed on the station, the shuttle Discovery crew will detach the boom from its temporary location outside the ISS and use it to perform inspections and bring it home.
NASA began paying particular attention to thermal shield damages after the space shuttle Columbia exploded on re-entry into Earth's atmosphere in 2003, killing the crew of seven. A piece of isolating foam, which had peeled off from an external fuel tank and punctured one of the wings on liftoff, was later established as the cause of the tragedy.
The current shuttle mission - STS-123 - is the longest to the ISS and involved a record five spacewalks.