As I have noted in my predictions if we can combine hypertelescope concepts (very large space arrays), new worlds imaging ideas (satellites that null the light from stars so that their planets can be seen) and magnetic inflation of really big space and cheap space structures then we could make telescopes with nano-arc second resolution (hypertelescope) and have kilometer size mirror elements (using magnetic inflation). This can be further enhanced with molecular nanotechnology (massive increase in production capabilities and reduction of the costs for getting into space) and metamaterials (we are developing the capability for superlens able to focus to 1/20th the wavelength of light). I think that an advanced realization of that grand project is possible in the 20-30 year range, but that some very useful precursors could be started immediately.
A giant telescope with a mirror up to 60 metres wide is being planned by the European Southern Observatory. The telescope would be able to detect Earth-like planets around other stars and spot the universe's first galaxies. ESO aims to put the E-ELT on a fast track. Their goal is to build it for €750 million ($950 million) and have it ready to observe by 2015.
Two other groups are also pushing forward with plans for giant telescopes. A US-Australian consortium is planning a 24.5-metre instrument called the Giant Magellan Telescope (GMT) to be built by 2016 (see World's largest telescope begins with a spin). And a US-Canadian group is planning the Thirty Meter Telescope (TMT), also to be built by 2016.
While space-based telescopes enjoy crystal-clear views, ground-based telescopes have their own advantages. "For a given budget, ground-based telescopes can be much larger than telescopes in space," says GMT project manager Matt Johns of the Carnegie Institution of Washington's Observatories in Pasadena, California, US.
The giant ground-based telescopes will have vision roughly four times sharper than the James Webb Space Telescope (JWST) that will replace Hubble.
As supporting technology such as adaptive optics improves, the new telescopes could eventually analyse the gases in the atmospheres of other Earth-like planets.
Magnetic inflation could make really big space based telescopes cheaper
Other interesting space ideas from NIAC (Nasa Institute for Advanced Concepts
Blimp based telescopes planned
Promising space technology
Article about no fermi paradox. Part way through links to hypertelescope concept and New worlds imager