One day after climbing aboard the International Space Station (ISS), the Discovery crew guided the shuttle's robotic arm to take a new set of photographs that will help determine if they can safely fly back to Earth in 10 days.
NASA said it could take a day longer to learn if Discovery was seriously damaged by debris during liftoff in just the second mission since the Columbia tragedy of February 2003.
The Discovery and ISS crews had already taken hundreds of pictures of the shuttle's heat shield in the last three days.
NASA has described the vessel as "clean" and the Discovery astronauts have appeared satisfied with the state of their ship.
The vessel will get another checkup at the end of the mission before getting the all-clear to fly home.
For the first time ever, the shuttle will be inspected for possible in-orbit damage caused by micrometeorites.
NASA has said the astronauts could take refuge inside the ISS while waiting for a rescue mission if the shuttle suffered irreparable damage.
The US space agency hopes the mission will show that flight safety has increased dramatically in order to resume regular shuttle missions.
NASA has taken several measures to improve safety and two astronauts will venture into space Saturday to test equipment for potential in-orbit repairs.
British-born US astronaut Piers Sellers and his colleague Mike Fossum will climb on the shuttle's robotic arm and simulate repairs to test the feasibility of using it to fix the spacecraft.
NASA has also announced that it has extended the mission to 13 days, adding one day in order to perform a third spacewalk to try out other repair techniques.
The shuttle is now scheduled to return on July 17.
Earlier, Discovery mission specialists Lisa Nowak and Stephanie Wilson used the ISS's robotic arm to pull an Italian-made container from Discovery's payload bay and berth it to the ISS.
The astronauts will transfer equipment and supplies to the ISS over the next few days.