The crew from the space shuttle Endeavour got a little bit of a scare over the weekend when a camera inspection revealed damage to part of the space shuttle's thermal protection system.

However, after a thorough inspection, NASA engineers have cleared Endeavour's thermal protection system, or heat shield, for reentry, quelling concerns of a repeat of the Columbia disaster. In 2003, the space shuttle Columbia disintegrated on reentry when a piece of foam from the shuttle's external tank broke off and damaged some of the ceramic tiles that cover the skin of the shuttle.

The original problem was a damaged tile on the shuttle's heat shield. The tile is one thousands that protect the shuttle's structure from high temperatures. The heat shield can withstand temperatures of 2,000 degrees Fahrenheit, whereas the underlying structure can only withstand temperatures of 350 degrees before it is damaged.

An inspection by the International Space Station's robotic arm revealed there was damage to one of the tiles. NASA technicians used Endeavour's and the station's robotic arm to get digital camera views and scans with a laser camera system to get a closer look. What they found was damage that won't have any affect on Endeavour's reentry and no cause for alarm, which is much different from what happened with Columbia.

On Columbia, a piece of foam broke off the external tank and created a hole in one of the leading edge wing panels, which allowed hot gas to enter inside the wing and ultimately resulted in the disintegratation of Columbia, a NASA spokesperson said. In this case, they believe a piece of ice from the external tank came off and created a cavity in one of the thousands of tiles on the underside of space shuttle. It damaged the tile but it didn't put a hole in it. After carefully assessing it, experts determined this was not significant issue and that is safe to reenter.

After the heat shield concerns were addressed, Endeavour mission specialists Drew Feustel and Mike Fincke conducted the second spacewalk of the mission. During the eight hour, seven minute spacewalk, the sixth longest in history, the astronauts refilled one of the station's cooling loops with ammonia and lubricated one of the station's massive solar alpha rotary joints. A third spaceawalk is scheduled for Wednesday and the final one is set for Friday.

Meanwhile the crew from the Endeavour shuttle waved to their Russian space brethren, as the three astronauts from Soyuz Expedition 27 headed back to earth. Hatches were closed between Russia's Soyuz TMA-20 and the International Space Station, signifying the end of that shuttle's time in space. Expedition 27 Commander Dmitry Kondratyev, NASA Flight Engineer Cady Coleman and European Space Agency Flight Engineer Paolo Nespoli have undocked and will return to Earth at 10:26 p.m. Eastern time.

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