MOSCOW, August 13 (RIA Novosti) - NASA has prolonged the Endeavour shuttle's visit to the International Space Station, where it has been docked since Friday, until August 20, the agency's Web site said.

"Mission managers decided Sunday to extend the STS-118 mission by three days. The decision came after the successful operation of the new Station-to-Shuttle Power Transfer System (SSPTS)," NASA said.

The new power transfer system brought by Endeavour reroutes power from the space station to the shuttle during docked operations, allowing the orbiter to conserve materials needed to generate power and spend more time in space.

Endeavour is now scheduled to undock from the orbital station August 20 and land August 22. In addition to the extra time at the orbital outpost, managers added a fourth spacewalk scheduled for August 17, NASA said.

NASA is now calculating whether risky spacewalk repairs are needed after a close-up inspection Sunday revealed that a nine-centimeter-long gouge penetrates the thermal shielding on the shuttle's belly, the Associated Press reported Monday.

A chunk of insulating foam hit the Endeavour at liftoff last week in an unlucky ricochet off the fuel tank. Engineers are trying to determine whether the damaged area can withstand the searing heat of atmospheric re-entry at the end of the flight. Actual heating tests will be conducted on similarly damaged samples, the AP reported.