[the_matrix_walker]

Spoiler:  

Note: Vassarious does not become foam that expands. They turn from a metal hemisphere into a less dense construction foam-like material at full size.

IMO... The movement speed of the outer surface is whatever the maximum distance is to be to the new outer perimeter over 10 seconds it takes to shapeshift, as they are not really moving, just shifting. There should be no bubbles unless they are able to damage the surface as it expands, and the density of the wall shifts as it gets bigger... in the first few seconds of shapeshifting when the rocket hits, only a limited amount of durability would be lost, (a 10% shift per second seems most appropriate ). Of course, it works however you say, but just my 2 cents.

.... Ok, I guess there is nothing left for V to do but hopefully survive and see how it turns out.