Two US astronauts aboard the Atlantis orbiter have completed a spacewalk to deploy new solar panels on the International Space Station (ISS).
The operation was delayed for several hours when four gyroscopes that keep the ISS steady became overloaded.
Atlantis docked with the ISS on Sunday, after a back flip so its heatshield systems could be photographed.
A section of thermal blanket was seen to be peeled back and Nasa is now considering what action to take.
Damage to the shuttle Columbia's heat-protection tiles in 2003 during its launch led to the vehicle's disintegration as it returned to Earth, killing all seven crew.
A decision on whether to conduct another spacewalk to fix the blanket will be made in the next few days, the US space agency said.
The 10cm (4in) section is near the shuttle's tail and is assumed to have lifted up during Saturday's launch from the Kennedy Space Center in Florida.
Nasa said it did not consider the damage to be significant. A spokesman said: "We do not see any cause for concern right now."
Monday began with the space station's robotic arm attaching a new 16-tonne (35,000lb) segment to the ISS containing a pair of new solar panels.
The spacewalkers then set about connecting power, data and cooling cables ready for the new solar array to be deployed.
The astronauts returned to the ISS after a total of six hours and 15 minutes working outside.
The damage to the blanket is sited at the rear of the orbiter
The solar panels will increase the station's power generation capacity, paving the way for Europe's Columbus module to join the station later this year.
Two more spacewalks, on Wednesday and Friday, are planned to finish the installation work and, if necessary, attempt repairs to the thermal blanket.
This was supposed to be the second shuttle mission in 2007, but a freak storm over the Florida launch site in late February caused hail damage to the shuttle and delayed the mid-March flight.
Despite the delays, managers are confident they will be able to complete the ISS before the shuttles' 2010 retirement date.
Nasa plans to fly 15 more missions to the station to deliver large components, spare parts and other supplies. In addition, one final servicing call to the Hubble Space Telescope is planned for September 2008.