(Top) A 10-cm gap in the thermal blanket on Atlantis and Sunita Williams inside the Space Station. (AP)

Houston, June 11 (Reuters): Astronauts on space shuttle Atlantis prepared for a walk in space today to add a giant new piece to the International Space Station, and Nasa engineers pondered whether a bump in the ship’s heat protection system needs repair.

Atlantis crew members Jim Reilly and Danny Olivas were to make a seven-hour spacewalk to install a 14-metre long, 16,183-kg aluminum structure that will become part of the station’s exterior backbone and includes solar panels to generate more electricity.

Atlantis docked with the station yesterday 354 km above the Earth and handed the $367 million module in its cargo bay to the station’s robot arm.

Once the unit is in place, Reilly and Olivas will hook it to the station; tomorrow the solar array will be deployed.

The panels will add a net 14 kilowatts of electricity to the international space station, which will be needed as upcoming shuttle flights add new sections. Nasa plans 12 more shuttle missions to complete the $100 billion station, a project of 16 nations, before the ageing shuttle fleet is retired in 2010. Another mission is planned for maintenance on the Hubble Space Telescope.

Reilly and Olivas were preparing for low pressure during their spacewalk by sleeping overnight in an airlock with reduced air pressure. Atlantis’ crew is scheduled to perform two more spacewalks during its week-long station visit to retract an old solar array and possibly repair a thermal blanket that peeled back slightly during Friday’s launch.

The blanket protrusion exposed a few inches of underlying layers of the shuttle, which could lead to damage during the heat of re-entry, deputy shuttle manager John Shannon said.

He said the size and location of the problem meant any damage would not be catastrophic, but could require repair once Atlantis returns from its scheduled 11-day mission. “I would just like to avoid that scenario altogether and tuck that blanket back down,” Shannon said.

Fixing the bump would be a simple chore that could be incorporated if time permits into the third spacewalk, scheduled for Friday. If not, it would mean a fourth spacewalk.