Thursday, December 30, 2010

NASA Wraps Up Discovery X-ray Scans with Hope

By Mark Carreau

Technicians at NASA’s Kennedy Space Center in Florida wrapped up X-ray scans of the shuttle Discovery’s external tank (ET) on Dec. 29, a day ahead of schedule, in troubleshooting that has so far not detected additional stringer cracks as a result of a Dec. 17 launch pad tanking test.
Four cracks surfaced on two adjacent 21-foot-long aluminum lithium stringers during a Nov. 5 launch scrub, stalling efforts to send Discovery on the orbiter’s final flight, an 11-day assembly mission to the International Space Station.
Shuttle program managers were to meet Dec. 30 to decide whether to equip the stringer section of the 154-foot-long tank with a radial block, a modification that would further strengthen regions on either side of two thrust panels. The two ET thrust panels face Discovery’s solid rocket boosters and shoulder critical launch loads.
“So far, we’ve seen nothing out of the ordinary,” NASA spokesman Allard Beutel said, as the X-ray analysis that began three days earlier was winding down. The imagery was being scoured by experts at other NASA installations.
Additional testing of sample stringers that might confirm suspicions of an assembly problem as the root cause of the cracks also is under way.
Discovery was returned to Kennedy’s Vehicle Assembly Building (VAB) after the Dec. 17 tanking test at Launch Pad 39A. During the test, the ET’s stringer section was fitted with 89 strain gauges and temperature sensors to help determine the cause of cracks that formed as cyrogenic hydrogen and oxygen flowed into the tank and determine the potential for further damage. The VAB permitted X-ray scans of all 108 stringers, which separate internal ET hydrogen and oxygen propellant containers.
The scrub was blamed on an unassociated hydrogen leak that was repaired with the replacement of the ET’s Ground Umbilical Carrier Plate.
If shuttle managers approve the radial block modification, work would begin Jan. 3, 2011. The work schedule would permit Discovery to return to Launch Pad 39A in mid-January, in time for launch attempts during a Feb. 3 through Feb. 10 window.
A crew of six astronauts has trained to deliver and equip the station with a storage module and an external platform to secure spare parts.

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