But he may have to go out again to fix yet another trouble spot.

Robinson was barely back inside the shuttle and out of his spacesuit on Wednesday when Mission Control informed the crew there was a chance that a fourth spacewalk may be needed on Friday to deal with a torn thermal blanket below a cockpit window.

The concern is that a roughly 30-cm section of the blanket could rip away during re-entry, whip backward and slam into the shuttle, perhaps causing grave damage.

Engineers expect to know by Thursday afternoon whether the danger is real and whether any blanket trimming is required.

Few seconds job

It took Robinson just seconds to pull out each short dangling strip of ceramic-fibre cloth, which engineers had feared might cause the shuttle to overheat during its descent through the atmosphere and lead to another Columbia-type disaster.

"That was the ride of the century!"

Astronaut Stephen Robinson

"That was the ride of the century!" Robinson exclaimed. "Steve, we trained for four years. You're going to spend the next four years signing autographs," said his spacewalking partner, Soichi Noguchi.

Space station flight director Mark Ferring said he could hear "a palpable change in the tone" of the astronauts' voices after the task was completed.

The spacewalk ended after six hours. Robinson and Noguchi also installed a massive toolbox filled with spare parts on the space station.

Nasa had spent four days analysing the potential threat of the so-called thermal tile gap fillers and what to do about them.
Officials said it was absolutely safe to simply remove the fillers.

The filler was apparently ripped by debris during the 26 July liftoff, the first shuttle flight since Columbia disintegrated on re-entry two and a half years ago.

Damning report

Meanwhile, an internal Nasa report last December warned of deficiencies in the way insulating foam was being applied to sections of the fuel tank to be used on the shuttle Discovery's current mission, The New York Times reported on Thursday.

The report was provided by a person outside the space agency who is part of an informal network of people concerned about shuttle safety, and it did not recommend against launching the Discovery, the paper said. 

Nasa said in a secret report that
falling foam was still a problem

But it delivered a harsh critique of the quality control and practices at the Michoud Assembly Facility in New Orleans.

While the National Aeronautics and Space Administration spent some $200 million to address foam problems after the Columbia disaster, they resurfaced on 26 July with the launch of Discovery. 

According to the report, even after two years of effort to correct the foam debris problem, "there will continue to be a threat of critical debris generation", the Times quoted the report as saying.

"This variable could reasonably be eliminated," the report continued, "and yet it continues".

The 23-page document was initially sent to safety managers by email and came to be distributed more broadly.

The person who provided it to The Times did so on condition of anonymity, saying he had not been authorised to read it.