Spaceship based telescopes

[Fred Brackin]

Originally Posted by David L Pulver

If I may ask again, could you follow up more on the scaling factor?

Considering only the mirror (and big modern telescopes are almost exclusively reflectors rather than refractors) I believe mirror weight might actually go up by the cube and not the square of an increase in diameter.

If you make your mirror wider you need to make the backing material thicker to keep it stiff under gravitational or inertial loads. There are thermal issues too.

The Keck design with its' geometric array of smaller mirrors might be a way around the "one big mirror" limit but it's not obvious that what you save in total weight from thinner mirrors you don't make up in the gear to finely control them.

It's hard to say much about competing mirror designs for large astronomical instruments. Every blessed one of them is a prototype. There are no production models and whatever design gets chosen is in the hands of whoever raised the money and set up the fabrication shop. The choice selected probably represents that person's individual preferences and experience.

Still, as a mirror gets bigger it would have to increase in weight by the square as a minimum and more likely the cube.