US astronauts face shuttle repairs as spacewalk begins

Two astronauts began a spacewalk today to replace equipment on the international space station as Nasa experts calculated whether the shuttle Endeavour’s crew would need to repair a gouge on the ship’s belly.

A chunk of insulating foam hit the Endeavour at lift-off last week in an unlucky ricochet off the fuel tank.

The unevenly shaped gouge – which straddles two side-by-side thermal tiles and the corner of a third – penetrates all the way through the thermal shielding on the ship’s underside.

Former teacher Barbara Morgan and other crew members spent much of yesterday using a laser boom attached to the shuttle’s robot arm to create 3-D images of the gash and a few other damaged areas that Nasa officials say pose no threat.

Mission managers expect to decide later today, or tomorrow at the latest, whether to send astronauts out to patch the gouge.

Engineers are trying to determine whether the marred area can withstand the searing heat of atmospheric re-entry at flight’s end and heating tests will be conducted on similarly damaged samples.

Space shuttle Columbia was destroyed and its seven crew members killed in 2003 when hot atmospheric gases seeped into a hole in its wing and melted the wing from the inside out. A foam strike at lift-off caused the gash.

John Shannon, chairman of the mission management team, said: “We have really prepared for exactly this case, since Columbia.

“We have spent a lot of money in the programme and a lot of time and a lot of people’s efforts to be ready to handle exactly this case.”

In space, astronauts Dave Williams and Rick Mastracchio began the mission’s second spacewalk, floating out of the 100 billion dollar (£50 billion) space station to replace one of the four gyroscopes that help control the orbiting outpost’s orientation.

The astronauts will replace the broken gyroscope with equipment they brought aboard Endeavour.

The gyroscope that broke in October will be stored at the station so it can be brought back to Earth during a later mission.

Astronauts plan to conduct two more spacewalks on Wednesday and Friday, and they could add the gouge repairs to their to-do list. Depending on the extent of the damage, astronauts can apply protective paint, screw on a shielding panel, or squirt in filler.

The damaged thermal tiles are near the right main landing gear door and beneath the aluminium framework for the right wing, which would offer extra protection during the ride back to Earth.

The foam came off a bracket on the external fuel tank 58 seconds after Wednesday’s launch. It fell down onto a strut on the tank, then bounced up, right into Endeavour’s belly.

Ice apparently formed before lift-off near the bracket, which helps hold the long fuel feed line to the tank, and caused the foam to pop off when subjected to the vibrations of launch.

It is possible some ice was attached to the foam, which would have made the impact even harder. The debris that came off is believed to have been grapefruit-sized.

Mr Shannon said these brackets have lost foam in previous launches and were a concern for Nasa.

A switch to titanium brackets, eliminating foam, will not occur before next year.

Mr Shannon said he did not know whether the recurring foam problem would delay the next shuttle flight, currently scheduled for October.

Endeavour has been docked at the space station since Friday.