KENNEDY SPACE CENTER, FLA. - Inside the payload changeout room on Launch Pad 39B, STS-121 Mission Specialist Michael Fossum looks closely at part of the payload for the mission. He is dressed in a clean room suit, appropriate for the environmentally clean or "white room" condition in which the payload resides before being transferred to the shuttle's payload bay. At lower left is the multi-purpose logistics module Leonardo, which is carrying supplies and equipment for the International Space Station. The payload also includes the lightweight multi-purpose experiment support structure carrier and the integrated cargo carrier. Crew members are at NASA's Kennedy Space Center for Terminal Countdown Demonstration Test activities, which include equipment familiarization and a simulated launch countdown. Mission STS-121 is scheduled for launch on Space Shuttle Discovery on July 1.