In the way of major new instruments for ground-based optical astronomy, maximizing the science favors a large
hypertelescope. If equipped with adaptive optics and a laser guide star, it can provide direct high-resolution images of
faint extra-galactic and cosmological sources. The signal/(photon noise) ratio is theoretically higher than with
interferometer schemes relying upon aperture synthesis, using a few large apertures to reconstruct images. The crowding
limit on complex objects, the direct-imaging field, and the dynamic range are also improved with many small apertures.
The adaptive phasing of hypertelescopes, achievable on bright stars with modified wave sensing techniques such as
"dispersed speckle" analysis, is also achievable on very faint sources with a modified version of a laser guide star. This
makes large hypertelescopes capable of observing cosmological deep fields of faint galaxies. Pending space versions,
the size of which can in principle reach hundreds and thousands of kilometers, terrestrial hypertelescopes limited in size
to one or two kilometers can be built at suitable sites and used efficiently from ultra-violet to millimeter wavelengths.
Some sites can allow the coupling of a hypertelescope with an ELT, an alternate option which can also be efficient for
imaging deep fields with a high-resolution.