Aug 25 2007 4:31PM | Permalink | Email this | Comments (1) |
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It’s hard to believe that anything could have been done cheaply to save costs on the NASA space shuttle. Yet that appears to be exactly the case with the insulation problems that have been plaguing recent flights. On Friday, cracked installation was found on all three of the fuel tanks scheduled for upcoming flights. And the cracks have probably been there a while.

Cracks are appearing in foam-covered cork insulation that is applied to aluminum alloy brackets. The brackets, which are 17 inches long and four inches wide when foamed, support the liquid oxygen feedline on the external fuel tank. The cork prevents ice from forming on the brackets. Super-cold fuel is inside the tank. Engineers are now finally developing a better solution—replacement of the aluminum alloy with titanium. For the next shuttle flight, the foam and high-density cork insulation will be removed and replaced with foam only.  The titanium parts will be ready by spring.

Bad materials engineering has been one of the banes of the space shuttle program. And the problems have not exactly been rocket science. The most famous, or course, was the O-ring failure that lead to the disintegration of the Challenger in 1986. It was well known that the fluoroelastomeric materials in the O-rings had extremely poor low-temperature capabilities.  Once compressed, very cold O-rings take time to return to their normal shape. Temperatures were very cold the night before the Challenger launch, but temperatures at launch time were within allowable guidelines.  Because of poor communications, the problems with the O-ring materials' properties were not adequately known, and the launch proceeded. O-ring joints now have on-board heaters that are turned on when temperatures drop below 50F.

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