A question about radiotelescope construction

[Keatah]

How do they make the surfaces of the parabola to stay permanently in shape? After reading -- http://www.space.com/20128-most-powerful-radio-telescope-facts.html -- it states that the parabolic shape doesn't deviate more than 20 micrometers from optimal.

How the hell they do that in an Earthbound telescope subjected to temperature swings. And what about weather & wind, shifting gravity as the telescope moves around. Birds could crash into it. All sorts of things. And these dishes are big too.

What'm I not getting here?

 

[MaverickSawyer]

The same technique used to keep optical telescopes in optimal shape: adaptive optics (or reflectors in this case).
Also, at the wavelengths that most radio telescopes operate at, the "optimal" shape is pretty flexible (pun not intended )

As for the wind, most large telescopes are made from a mesh, with the spacing determined by the wavelength of the highest frequency they want to observe. If the gap is too big, the signal goes through like water through a sieve.