Re: Shuttle ET foam shedding fix?



paisley2@xxxxxxxxxxxxxx wrote:

I'm aware of that, but i'm wondering if the paint has some effect by
shielding the foam from the atmosphere? Or is that not the problem
here?

P


The basic problem with the foam was the extremely cold temperatures of the Shuttle's propellants caused air to liquefy if it was trapped under the foam (unfortunately, the insulation works both ways- it keeps the cold in, and prevents ice from forming on the outside of the tank's insulation, but it also means that the metal skin of the tank itself is extremely cold where it comes into contact with the foam). The liquefied air turns back into gas under the heat of ascent and the lowering air pressure as the Shuttle ascends through the atmosphere, and can cause the the foam above it to be ripped free from the tank's surface by gas pressure, and fall off in bigger and smaller pieces. the very small pieces are referred to as "popcorning" and due to their very low weight can't cause cause severe damage to the Shuttle, although they can ding its tiles and make them need to be repaired or replaced.
The problem is where you get thick pieces of foam on the tank that my have a sizable bubble under them that occurred accidentally when the foam was being applied- this can create enough gas that it will push a sizable section of foam away from the tank, and the thickness of the foam means that a good-sized piece can break off due to it 's structural strength and lack of porosity when it's applied that thickly.
One solution to the problem was to perforate the foam with tiny pinholes in a regular pattern so that the gas would have a path to escape from it if there was some liquefied air between it and the tank's skin.
Unfortunately, putting holes in the foam brings the threat that rain could possible get into it and solidify into ice, adding to the tank's overall weight, while at the same time making any pieces that fall off of it heavier and more damaging.
Maybe the paint wasn't a bad idea- if you could make the foam's surface completely airtight, there would be less opportunity for air to get under it and liquefy in the first place, and the rain problem would be removed.

Pat
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