The U.S. space agency NASA is to decide later Thursday whether it will carry out another spacewalk to repair an insulation blanket on the shuttle Discovery.

Engineers are concerned that a torn thermal blanket below the shuttle commander's cockpit window could rip off during re-entry into Earth's atmosphere and strike Discovery. 

Earlier Thursday, the crew of Discovery held a ceremony to pay tribute to seven Colombia astronauts who died in 2003.  The shuttle Colombia disintegrated on re-entry into Earth because of damage to the heat-resistant ceramic tiles that protect the spacecraft during re-entry.

On Wednesday, Discovery astronaut Steve Robinson successfully completed a spacewalk to remove two pieces of fabric dangling from between some of the shuttle's tiles on its underside.

Some information for this report provided by Reuters and AP.