Mark Kelly and Stephanie Wilson are joined by two shuttle technicians as they examine the orbiter boom sensor system in Discovery's bay.

In NASA Kennedy Space Center's Orbiter Processing Facility bay 3, STS-121 Pilot Mark Kelly and Mission Specialist Stephanie Wilson are joined by two shuttle technicians as they examine the orbiter boom sensor system in Discovery's payload bay. The crew is at Kennedy to take part in the crew equipment interface test, which provides hands-on experience with equipment to be used on-orbit. Launch of Space Shuttle Discovery on mission STS-121, the second return-to-flight mission, is scheduled no earlier than May.