I was watching a video about new NASA space telescopes & how light the mirror assembly had to be (one of them is made of beryllium (!). One of the problems of any large telescope is how to build a mirror that is a very rigid structure, but also very light. Ignoring the problem of "active mirrors" for ground-based telescopes for the moment, isn't there some _fractal_ structure which can be both extremely light and yet extremely rigid that could be built using a 3D printer? I'm assuming that the face of the mirror is still a paraboloid, but the structure behind it has to be rigid & light, so that it can optimally resist deformation under gravity at a wide variety of angles. Just as important as the mirror itself is the rigidity of the structure holding the sensor (nowadays almost always a silicon chip). I would imagine that small versions of such structures could be built out of plastic at home using hobbyist 3D printers.