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Discovery to launch despite safety concerns |
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Written by Derek Kessler on
Friday, 12 October 2007
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 In spite of small cracks that have appeared in the leading edge of the Space Shuttle Discovery's wings, NASA still intends to launch the shuttle on October 23 without repair. According to shuttle program manager Wayne Hale, the defects are too small to allow passage to the super-heated plasma created by air friction on reentry, and that studies of the wing after each flight indicate that no significant growth in the cracks has occured since 2003.
On Wednesday, the independent NASA Engineering and Safety Center advisory panel recommended that NASA pull Discovery off the launch pad and repair the wing panels, a process that would delay the planned launch at least two months. While there was no indication that the degredation of the panels posed an immediate danger, they thought it prudent to replace them anyway.
The panels in question are thre of a total of forty foutl leading edge caps on the wings, composed of silicon carbide. The manufacturing process for the panels involves heat in excess of 3000 F, and as the panels cool small cracks develop. They are typically filled with a sealant. New testing procedures impemented after the loss of the Space Shuttle Columbia in 2003 apply heat to the wing panels, stressing them as if they were undergoing a reentry (with out the high speeds and super-heated plasma, of course), and during those tests some of the sealed cracks have reopened. Removal of the panels has revealed enough damage inside to warrant the replacement of other panels on previous occassions.
NASA has yet to determine the cause behind the cracks, and because of the uncertainty the Engineering and Safety Center has advised them to delay launching Discovery so the panels can be replaced, as well as replacing and panels on the other two shuttles (Atlantis and Endeavour) that exhibit the same damage.
After Discovery is launched the heat shield will be scanned by lasers and undergo an intense visual inspection by the shuttle crew and the crew of the International Space Station upon their arrival. If it is discovered that the cracks have changed, the crew will have several options to repair the shield, or will be able to wait in space while docked to the ISS until NASA can scramble a shuttle launch to rescue the crew. Discovery would then be undocked and piloted remotely from the ground, or if the damage is too severe to risk a landing, the shuttle could be ditched over the Pacific Ocean and burned up in the atmosphere. NASA seems to be confident that will not be the case.
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