Workers keep check on the closing payload bay doors on Space Shuttle Discovery.

Workers keep check on the closing payload bay doors on Space Shuttle Discovery. Inside are the two elements to be added to the International Space Station on mission STS-92. At top is the third Pressurized Mating Adapter; below it is Integrated Truss Structure Z-1, the cornerstone truss of the Station. Making the 100th Space Shuttle mission launched from Kennedy Space Center, Discovery also will be making its 28th flight into space. On the 11-day mission, the crew of seven will be making four space walks to attach the hardware to the Station