Space shuttle Endeavour's crew completed an inspection of the shuttle's thermal protection system the morning of May 26, NASA reported. The crew began the inspection early and used the 50-foot-long Orbiter Boom Sensor System to conduct a high fidelity, three-dimensional scan of areas of the shuttle that experience the highest heating during entry - the wing leading edges and nose cap.
The late inspection occurred earlier in the mission than normal, prior to undocking. As a consequence, the risk of re-entering with undetected micrometeoroid debris is increased but deemed acceptable.
Managers and engineers in Mission Control will review the data to validate the heat shield's integrity and assure it has suffered no significant micrometeoroid and orbital debris damage, the space agency reported.
The inspection is a routine precautionary check for any damage that may have occurred during the docked phase of the mission, although this is usually done after undocking. Because the orbiter boom will be left on the space station, it is necessary to perform the inspection while the two vehicles are still mated.
During the mission's fourth and final spacewalk scheduled for May 27, the boom will be left at the space station to extend the robotic reach. Mike Fincke and Greg Chamitoff will prepare it for its stay by replacing its grapple fixture with a power data grapple fixture to enable its use as the new International Space Station Boom Assembly. Once on station without power and in the extended exposure to the vacuum of space, the boom's imagery sensors will cease functioning.
Endeavour Mission Specialists Drew Feustel and Mike Fincke installed a power and data grapple fixture on the Russian Zarya module during a 6-hour, 54-minute spacewalk early May 25, bringing the International Space Station's Canadarm2 closer to having a new base of operation, giving it access to much of the orbiting laboratory's Russian segment.
The arm can "inchworm" its way to the new base by grasping it and then releasing the hand holding the old base to become the new end effector. A cable to provide power to that new operating base is on the to-do list for the fourth spacewalk of the mission. The spacewalkers also installed a video signal converter on Zarya and ran power cables from the U.S. segment to Zarya, which provides a backup for transmission of power from the solar arrays to the Russian segment.
Feustel and Fincke used a new procedure to prepare astronauts for spacewalks. They breathed oxygen for an hour, then put on spacesuits and did "light exercise" for 50 minutes, standing and doing slow intermittent movements. The procedure avoids the overnight stay in the Quest airlock that had become standard, according to a mission overview provided by NASA.
The spacewalk brought the total time spent for station assembly construction and maintenance to 995 hours and 13 minutes during 158 spacewalks. The mission's fourth spacewalk is expected to break the 1,000-hour mark. It will also be the last spacewalk by space shuttle crewmembers. A spacewalk during the program's final mission, STS-135, is to be conducted by space station residents.