Monday, November 19, 2007

Why is the external tank not painted?

I found a student web site with a lot of interesting data of the space shuttle's external tank. While the site was set up as a think-tank for the student project, it provides generally useful information.

I'd like to quote one section that I found especially interesting:

Why doesn't NASA apply paint, a cover, or net over the tank? One might remember that we painted the first couple of External Tanks with white paint in the early 1980's. In both cases, we had a significant amount of foam loss during ascent. Although at face value applying a net or some other foam entrapping method to the External Tank sounds easy, it is not without concern. After careful examination of this approach, NASA's conclusion is that portions of the net could become in itself an undesirable debris source. Depending on the material used (Kevlar, aluminum, etc.), the density of the netting material would present a more critical debris source than foam to the Orbiter Thermal Protection System. Through a rigid certification process, we would also have to understand if and when the netting material could come off and in what quantities or mass that the netting material could present. Our assessment is that the process of certifying a netting material for flight would take several years and would not be available until late in the Space Shuttle Program life. NASA's goal remains to eliminate the potential for critical debris from all sources, including the External Tank foam.
At Kennedy Space Center, I was always told to the weight of the paint was the reason that the tank is no longer painted. That sounded logical to me (and for sure is part of the reason). It was so logical that I never thought about it any further. It now makes perfectly sense to me that paint can also be a major source of debris - it may hold loose parts together, forming an even greater lump that could come off.

Thanks to Nicole Sharp for putting this all together.

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