Nasa astronauts begin second mission spacewalk

Nasa astronauts from the shuttle Endeavour began a spacewalk to replace one of the International Space Station's steering gyroscopes yesterday while engineers in Houston examined images of a deep gouge in the orbiter's belly.

The US space agency said it had not decided whether the gouge needed a repair in space to ensure the ship's safe return to Earth from its visit to the space station. Shuttle astronauts used a robot arm to scan the damage with a laser on Sunday.

"The teams on Earth are still looking at the information gathered on Sunday and are expected to decide by tomorrow if more tests are needed," said Nasa spokesman Debbie Nguyen.

"If a repair is needed it will probably take place on one of the two remaining spacewalks still planned. And if we do need to do a repair we have all the tools needed to do that," she said.

The damage was caused by a chunk of foam that fell off the shuttle's fuel tank about a minute after lift off from the Kennedy Space Centre in Florida on Wednesday.

During atmosphere re-entry, temperatures at the rear of the ship where the damage is located can reach 1,260 degrees Celsius.

The damage revived concerns that the shuttle fuel tanks, which were twice redesigned after the fatal 2003 Columbia accident, may need more work before Nasa will clear future missions for flight.

Columbia was destroyed because of heat shield damage caused by falling foam insulation during launch that hit the ship's wing. The shuttle broke apart sixteen days later as it plowed through the atmosphere for landing, killing all seven astronauts aboard.

Yesterday's spacewalk was scheduled to last six-and-a-half hours and is the second of four planned spacewalks during Endeavour's mission.

American astronaut Richard "Rick" Mastracchio and his Canadian colleague Dafydd "Dave" Williams from Endeavour began their spacewalk at 11:32 EDT (1532 GMT).

The gyroscope that the astronauts are replacing is about the size of a washing machine and is one of four used to control the space station's orientation.

They keep the station properly positioned without the use of gas-guzzling rocket thrusters.