Work is underway to install Discovery's Reinforced Carbon-Carbon panels.
Space Shuttle Discovery passed a major Return to Flight milestone March 15.
Work began to install Reinforced Carbon-Carbon, or RCC panels, on the leading edges of the orbiter's wings.
When the orbiter returns to Earth from space, the RCC panels help protect the vehicle from the 3,000 degree heat of re-entry.
During the course of Return to Flight preparations, workers have used several ways to inspect and test the panels without damaging them.
Some of these non-destructive testing methods include computer-aided CAT scans, X-rays and flash thermography.
There are 22 RCC panels on each of the orbiters' wings.
The light gray carbon composite is also used in other areas, such as the nose cap and chin panel.
Discovery is being prepared for STS-114, NASA's Return to Flight mission.