The 10 astronauts aboard Discovery and the space station face the most challenging construction tasks ever attempted in a single mission.
They may get a little more time to tackle their to-do list because engineers have not spotted any significant problems with the shuttle's thermal shield.
The crew has set aside several hours Saturday for a focused inspection of any trouble spots, but mission management team chairman John Shannon said that examination probably won't be necessary.
NASA has made damage inspections a priority since the disintegration of the shuttle Columbia in 2003.
A piece of foam broke off Columbia's external fuel tank during liftoff and gashed a wing, allowing hot gases to penetrate the spacecraft during its return to Earth. All seven of its astronauts were killed.
Further analysis is needed before NASA can say for sure that Discovery suffered no significant launch damage. But given all the construction work on this mission, "We are extremely lucky that we have a vehicle that is in such incredible shape," Shannon said.
During Friday's spacewalk, Parazynski and Wheelock are to remove a broken antenna from the station and pack it aboard Discovery for its return to Earth, and prepare a space station girder for relocation later in the flight.
"It's going to be a very interesting day. A lot of folks have been looking forward to this for a long time," Shannon said, referring to Harmony's installation.
___
On the Net:
NASA:http://spaceflight.nasa.gov
