This morning workers reestablished access to the replaced PDU and reconnected the hydraulic lines. Mechanical and electrical connections will conclude today and this afternoon engineers will begin preliminary leak checks and compressibility tests. Because of the PDU change-out, a full hydraulic system test for Shuttle main engines and aerosurfaces is scheduled Saturday. Subsequent data review will confirm the system's readiness for flight.

Concurrent with other Shuttle processing efforts, technicians are replacing an electronic control box located in the orbiter's aft compartment today. The box amplifies the electrical signal transmitted from a multiplexer/demultiplexer to the orbiter's aerosurfaces. Technicians are also replacing a leaky hydraulic fluid discharge hose on the main pump for auxiliary power unit (APU) No. 1. Replacement of the flex hose requires an APU hot fire Sunday afternoon. Engineers are also evaluating two minor dings on two separate liquid hydrogen lines in the aft compartment. The known dings were previously documented and engineering analysis will confirm their acceptability for flight.

Atlantis' payload bay doors were closed for flight late Tuesday and the astronaut space suits have been installed in the orbiter and checked. SPACEHAB early stow operations are in work today and flight crew equipment stowage begins Monday. The remaining work schedule still supports an April 24 launch date and managers plan to begin the launch countdown at 7 p.m. on April 21.