Oct 14 2000
From The Space Library
Despite unexpected problems, astronauts aboard Space Shuttle Discovery installed a 9-ton (8,200-kilogram or 8.2-tonne) structural truss on the Unity module of the ISS, completing one of the major objectives of the mission. The Z1 truss held four mass gyroscopes and the station's main Ku-band and S-band communications antennas. In addition, the truss provided a temporary attachment point for a set of solar arrays scheduled to arrive during a December Shuttle mission. The astronauts faced several obstacles during the installation process. A short in the Shuttle's payload circuitry disabled the computerized camera system needed to orient the truss for attachment, causing a 2%-hour delay. However, the astronauts were able to wire a backup computer into an alternate power source, restoring power to the Space Vision System, which NASA had programmed to "determine the truss's precise location and orientation with respect to the station by measuring the locations of the targets on its surface as viewed from different payload bay cameras." The astronauts had to delay their work again when the Space Vision System failed to generate reliable data during certain orbital lighting conditions, requiring astronaut William S. McArthur to recalibrate the system.
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