Friday, May 11, 2007

Troublesome Tanks of Foaminess


As we all know, the latest shuttle launch was delayed due to a hail storm pitting the foam on the external tank. In the photo above, you can see the little white dents that the hail stones left behind. In the latest news from NASA, the tank is ready to go -- having been refoamed in several spots -- if a bit homely in appearance.

Apparently, the insulating foam is orange because of natural aging when exposed to UV. It actually starts out white and changes color over time. When Atlantis launches, the external tank's complexion is going to be a complex palette of white, off-white, and orange bits. Two things come up regarding this news: 1) Would a coat of white or reflective paint prevent the UV aging and general unsightliness (although who cares about unsightliness over safety)? 2) Does exposing the foam to UV and the raw elements present any risk of moisture absorbtion and thus potential foam separation during launch?

The reason I bring up the moisture issue is because there was some speculation that the foam separation that's happened before may be due to moisture getting between the tank and the foam. When the LOX and LH2 are added to the tank the theory is that the moisture turns into ice, which separates the foam from the tank. When it's stressed during launch, the foam at that spot breaks off. I can imagine that in a place like Florida (KSC) or Louisiana (Michoud), humidity has to be a constant problem, and since the external tank is hauled by barge along the Gulf and Atlantic coasts to KSC, it is a wonder that the tank isn't soaking wet by the time it gets to the launch pad.

So it occurs to me that sealing the surface of the foam with a moisture repellent barrier (paint) would be a good thing. Additionally, I was thinking that that one of the ways to ensure that the foam wouldn't pop off of the external tank was to embed mist net or a carbon fibre equivalent material into the outer surface of the foam. Mist nets are made of super fine nylon fibers with 2cm or a bit smaller sized square holes. If a tank-sized mist net were put over the tank (or at least the front of the tank), then any foam that was compelled to leave would first be held in place by the net, and if it still managed to come off, it would have to pass through the net's webbing; to be cut into harmless sugar-cube sized bits.

These are two ideas that I think NASA should consider. At the very least, they should at least leave feedback.

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