Discovery’s crew is set to install the first of two major components that it carried to the Space Station today – a unique piece of hardware called the Z1 truss. The truss is an exterior framework that houses gyroscopes and communications equipment and later will serve as a mounting platform for large solar arrays that will provide power to the International Space Station.
Earlier this morning, space station flight controllers in Houston successfully activated and checked out controllers and power sources for Unity’s common berthing mechanism, preparing it for the Z1 installation. Discovery’s robot arm will be powered up at 7:37 a.m. by NASDA astronaut Koichi Wakata and Mission Specialist Mike Lopez-Alegria. Wakata will maneuver the arm to the Z1 truss in Discovery’s payload bay, grappling the box-like frame about 8:20 a.m.
A series of capture latches that secures the truss in place will be commanded open and Wakata will gently raise the Z1 out of the payload bay. With the truss firmly in its grip, the arm will be maneuvered to a position called low hover and will remain during a final inspection to ensure that all seals and petals on the common berthing mechanism are properly aligned for the final installation. Commander Brian Duffy will maneuver Discovery into the proper orientation for installation as the Z1 is moved to its capture position. A series of four “ready to latch” indicators are the signal for Discovery’s crew to issue the final capture command, and the Z1 truss should be attached to the Space Station shortly after 10 a.m. today.
Using a laptop computer, Pilot Pam Melroy will command 16 bolts to tighten in a four-stage process to secure the Z1 truss to the Unity module, as Wakata releases the Shuttle’s robot arm and moves it back to its cradled position alongside the payload bay. Final connections and outfitting work for the Z1 truss will be accomplished by space-walking astronauts Bill McArthur, Leroy Chiao, Jeff Wisoff and Mike Lopez-Alegria. Sunday, during the first of four scheduled spacewalks for this flight, McArthur and Chiao will connect a series of power cables, an S-band communications assembly, install a Space to Ground Antenna and boom assembly and install an EVA tool stowage box on the port side of the structure.
With the Z1 installation complete, the astronauts will enter the Zarya module to transfer equipment and supplies for the first resident crew expected to arrive later this month. McArthur and Chiao will configure Discovery’s middeck in preparation for Sunday’s spacewalk, staging some of the tools, tether and hardware they will use during their planned 6½-hour EVA.
The next Mission Control Center status report will be issued at 7 p.m. CDT or as events warrant.
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