[fgeiger]

Maybe I misunderstand your point of spherical vs parabolic, but doesn't this paragraph explain it?

> The concept turns part of the inside surface of an inflated sphere into a parabolic antenna. A section comprising about a third of the balloon’s interior surface is aluminized, giving it reflective properties.

The balloon is approximately spherical but probably not exactly (actually, when looking closely, hardly any beachballs are spherical either). What is parabolic is the part of the balloon which is aluminized.

Edit: fixed a typo

[persnickety]

This references the problem, but doesn't explain the big question: how do they turn a section of a sphere into a section of a parabola?

Beach balls might not be spherical, but my bet would be on ovoid rather than parabolic.

[denton-scratch]

Yeah; I was wondering how they get the mirrored part of the balloon to take on a parabolic shape, rather than spherical; is that done by manipulating the balloon material somehow? Or are they settling for spherical as a good-enough approximation?