DIY work on damaged space shuttle will not delay its return to Earth, says Nasa

The Japanese astronaut Soichi Noguchi and his American colleague Stephen Robinson left the relative safety of the space shuttle Discovery at 11am GMT to test new repair techniques on a six-and-a-half-hour space walk. The methods, involving an oversized putty knife and a huge sealant gun, have been developed in the past two years to repair cracks in the delicate carbon panels that line shuttles' wings.

The astronauts stepped out yesterday morning as the shuttle floated 222 miles above the Earth. Their walk was carefully timed to coincide with the least extreme temperatures of the day. When the sun is shining on the outside of the shuttle, temperatures can reach 121C. In the dark, astronauts would be working at about minus 157C. Emerging from the shuttle's airlock and looking down on central Asia, Noguchi remarked: "What a view." Robinson responded: "There are just no words to describe how cool this is."

The astronauts had previously worked side by side in Discovery's open cargo bay, applying the experimental material to sample tiles. The repair technique was developed after the damaged Columbia space shuttle disintegrated on its re-entry to the Earth's atmosphere two and a half years ago, killing the seven astronauts on board. It is hoped the new material will be capable of repairing cracks of up to 5cm in length and half a millimetre wide - not as large as those that destroyed Columbia. That shuttle was damaged when a 751g chunk of foam hit its wing on take-off.

Nasa officials say the damage is not "major" and the shuttle will return to Earth on 7 August as planned.