Also, what would the effect of the atmosphere be in such a large telescope? would a bigger mirror increase or decrease the effects of Earth's atmosphere for these kind of observations?
Why not a 100 Meter Telescope? Cost and engineering. With these retro reflectors getting so big, you have to worry a lot about thermal expansion and differential levels of it across the whole surface. Also, the structure to hold it has to be monitored really closely in real time to make sure the calculations are accurate. It's not easy. Also, with modern adaptive optics, you'll have apply all the little piezo-motors across the entire surface which goes as the square of the radius, so costs go up geometrically (plus about 15% more for each doubling in surface area due to cabling, power issues, larger facilities with thicker steel beams, more janitors, etc.). If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius.
The Thirty Meter Telescope cost $1 billion. So the 100 Metre Overwhelmingly Large Telescope would cost ~$15 billion using your ~15x multiplier. That's large, but for perspective: The F-35 fighter jet program cost $168 billion.
Like with the Large Hadron Collider, if the extra cost means the difference between being able to crucially measure the atmospheric spectra of nearby exosolar planets and not being able to, then the extra cost is worth it.
I'll take getting definite answers to humanity's most pressing questions, over new tools for killing people, any day.
https://en.wikipedia.org/wiki/Realism_(international_relatio...
15 billion (as per a sibling comment) sounds like a lot, but relative to other, IMO not so important things like said plane, it's not that much.
However I wonder if it would be worth it or if that money would be better spent creating a Hubble replacement for example.