At Launch Pad 39A workers wait to begin replace Shuttle Atlantis' Power Drive Unit (PDU.

At Launch Pad 39A, workers wait to begin replace Shuttle Atlantis' Power Drive Unit (PDU), which is attached to the crane (center). The PDU controls the rudder/speed brake on the orbiter. Atlantis is scheduled to lift off April 24 at 4:15 p.m. EDT on mission STS-101, the third flight to the International Space Station. The primary mission is to carry logistics and supplies to the Space Station, plus the crew will be preparing the Station for the arrival of the Zvezda Service Module, expected to be launched by Russia in July 2000