For the first time in a shuttle mission, the astronauts used Discovery's robotic arm to scan the wing's heat shield for potential micrometeorite impacts as it circled the Earth attached to the ISS.
The inspection, which wasn’t crucial to the mission, was nearly cancelled because it was running 45 minutes late.
The delay was caused by technical problems earlier with the ISS's robotic arm, which two astronauts guided to move a container from the orbiting laboratory into Discovery's payload bay.
The astronauts will inspect the shuttle's right wing and nose cap after Discovery undocks from the ISS later today.
Earlier, lead flight director Tony Ceccacci said that shuttles had been hit by space debris in the past without consequence.
The odds of catastrophic damage from space debris were one in 221, while the inspection lowered the risk to one in 282, he said.
NASA officials have already cleared Discovery free of damage that could have been caused by debris during the July 4 liftoff.
The astronauts will bid farewell to the orbiting laboratory's three crew members today and leave on a two-day journey back to the Kennedy Space Centre in Cape Canaveral, Florida.