Space Shuttle Discovery Launch Further Delayed, Tank Work Continues

Discovery's long-delayed launch is pushed back again as NASA officials address cracks in the space shuttle's external tank.

NASA managers are evaluating potential launch dates for space shuttle Discovery in late February and working to see if International Space Station orbit operations would allow a launch as early as Feb. 24.

The space agency said more would be known next week and managers hope to set a launch date by the end of next week. Agency officials said progress continues to be made in understanding the most probable cause of cracks discovered on Discovery's external tank mid-section, known as the intertank, where small cracks developed during the Nov. 5, 2010, launch attempt.
Four additional small cracks were found during thorough X-rays of the backside of the tank in early December after Discovery was returned to the Vehicle Assembly Building, a NASA release confirmed.
The shuttle program also reviewed the plan to modify as many as 32 additional stringers with radius blocks, which will provide added structural support in areas known to carry much of the structural load of the external tank. These radius blocks essentially fit over existing stringer edges through which the securing rivets are installed to provide additional structural support.
"The radius block modification is a known and practiced structural augmentation technique used extensively on the intertank," a NASA release explained. "This work should begin as soon as the repairs to the three stringers with the four additional small cracks have been completed, likely in the next day or so, and the modification of the additional 32 stringers is expected to be complete next week."
NASA said program managers would also meet with space shuttle program officials on Monday to review the progress to date and the forward plan, and a determination of the need and viability for the installation of additional radius blocks on all remaining stringers will be made sometime next week.
"With the work remaining, the potential for additional modifications yet to be defined, and further reviews pending, the decision was made Thursday to allow the teams additional time and delay the targeted launch date out of the early February launch window," the release said. "Launch dates for Discovery and Endeavour will be discussed at next Thursday's Space Shuttle Program Requirements Control Board meeting."

When Discovery heads to the International Space Station on its final mission, it will be taking with it two key components-the Italian-built Permanent Multipurpose Module and Express Logistics Carrier 4-that will provide spare parts and storage capacity to the orbiting complex. Discovery also will deliver Robonaut 2, which will become the first humanoid robot in space.

Discovery was NASA's third space shuttle orbiter to join the fleet at Kennedy Space Center and is currently the oldest orbiter in service. Early in its career, Discovery provided a base so astronauts could retrieve satellites, test new technologies and conduct two-week-long experiments in microgravity. NASA turned twice to Discovery for Return-to-Flight missions after accidents with shuttles Challenger and Columbia, and it launched the agency's landmark observatory, the Hubble Space Telescope.