When the gleaming white space orbiter Discovery moved onto the launch pad at the Kennedy Space Center in Florida early last month, it became both a soaring symbol and a thorny trial for NASA. On one hand, the 122-ft.-tall orbiter represented the agency's successful recovery from the tragic explosion 2 1/2 years ago of Challenger, the last manned U.S. space mission. Discovery was also a test: Could NASA, operating this time around with extraordinary caution and under intense scrutiny, pull off an A-O.K., on-time launch? That question has caused growing frustration in the space agency.
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