After four successful spacewalks, the 10 astronauts aboard the orbiting complex formed by space shuttle Endeavour and the International Space Station are preparing the fifth and final spacewalk of the STS-123 mission.

According to the schedule, the STS-123 crew performed the final inspection of space shuttle Endeavour’s heat shield using the shuttle’s robot arm and the Orbiter Boom Sensor System (OBSS).

Commander Dominic Gorie, Pilot Gregory H. Johnson, and Mission Specialist Takao Doi surveyed the orbiter’s wings and nose cap to ensure that no damage had occurred to the tiles that protect Endeavour from the heat of reentry.

The space shuttle Endeavour passed an earlier inspection, which was focused on finding heat shield damage from impact from launch debris.

Mission Specialists Robert L. Behnken and Mike Foreman will begin the fifth spacewalk at 5:23 p.m. EDT Saturday.

Behnken and Foreman will stow the OBSS on the station’s main truss. With Linnehan as intravehicular officer, they will also release launch locks on Harmony’s left and Earth‐facing common berthing mechanisms and perform other tasks including installation of Trundle Bearing Assembly 5 in starboard Solar Alpha Rotary Joint (SARJ) and more SARJ inspection work. The STS-124 crew aboard space shuttle Discovery, set to launch in May, will pick up the OBSS.

"That sensor boom is going to be left on station because the following mission is going to deliver the next portion of the Japanese laboratory," said spacewalker Robert Behnken in a NASA interview. "That module is a very large module and there's actually not room in the shuttle payload bay to launch both that module and this sensor boom on the same shuttle flight.”

The fourth spacewalk, during which Michael Foreman and Robert Behnken have tested a new method of repairing damaged heat shield tiles in orbit, was considered also a success by NASA mission managers.

Astronauts aboard the International Space Station performed a six-and-a-half hour spacewalk during which they tested a special foam dispenser and the technique to repair holes in the space shuttle's vital heat shield.

"Endeavour, we are absolutely captivated by what you guys are doing here," said astronaut Steve Robinson from Mission Control to the space shuttle. "It's like brain surgeons up there."

Astronauts Michael Foreman and Robert Behnken squeezed out a special goo-like material into damaged test tiles and then flattened the composite material with a special brush. Everything worked as expected, to their great relief. NASA engineers will take another look at the tiles when the space shuttle comes back to Earth. The shuttle's high-speed re-entry into our planet's atmosphere generates temperatures up to 1,500 degrees Celsius on some of the thermal tiles that line its underbelly.

The primary purpose of the detailed test objective was to evaluate the Shuttle Tile Ablator-54 (STA-54) material and a tile repair ablator dispenser in a microgravity and vacuum environment for their use as a space shuttle thermal protection system repair technique. Spacewalkers Robert Behnken and Mike Foreman have performed the test on the outside of the Destiny lab.

According to space station flight director Dana Weigel, the goo performed just as NASA thought it would. There was a small amount of expansion, but not as much as expected, she added.

Much of flight day 14’s morning will be off-duty time for shuttle crew members. Later they’ll also hold the joint crew news conference, wrap up equipment and logistics transfers between the station and shuttle and check out rendezvous tools. Highlighting flight day 15 are crew farewells, hatch closings, undocking, Endeavour’s fly-around of the station with pilot Johnson at the controls, and departure.

Landing preparations, including checkout of the flight control system and the reaction control system, are the focus of flight day 16. The crew members will stow items in the cabin and hold a deorbit briefing just before bedtime. Deorbit preparations, and landing at the Kennedy Space Center (KSC) on flight day 17 (Wednesday) wind up Endeavour’s lengthy and demanding STS-123 mission to the ISS.