I would agree that the best environment for a telescope is to keep it in constant sunlight, but how does the HST handle going through the Earth’s shadow orbit after orbit and still get very crisp photos? It’s orbit is only about 350 miles above the Earth.
The 30m/100 foot primary mirror is divide up into 492 hexagonally-shaped pieces that are each 1.4m (4.6 feet) across. The fairings on an Atlas 5 are four and five meters in diameter which is more than large enough to carry such mirrors.
http://en.wikipedia.org/wiki/Thirty_Meter_Telescope
HST has very sophisticated thermal control. Of course this can be done on a larger scale, but it can’t be done for $1 billion.
Launching 492 pieces would require hundreds of launches. Probably $100 billion. Not to mention the structure that holds them all together.
Then you have the issue on on-orbit assembly, which would make the launch issue seem like child’s play and pocket change.
Next comes the issue of a spacecraft to control the telescope. More on-orbit assembly, and lots of complexity. The angular momentum of such a large spacecraft would require unprecedented slewing mechanisms.
We might be able to put a 100 meter telescope into orbit, but look for a 10 year time frame and at least $1 trillion.