Every 10 years, about two dozen of this country's top astronomers and astrophysicists get together under the auspices of the National Research Council and make a wish list. The list has on it the new telescopes these astronomers would most like to see built. At the last gathering, they said, in essence, "We most want the Large Synoptic Survey Telescope."
Here's why. A synoptic survey is a comprehensive map of every square inch of the night sky. The Large Synoptic Survey — LSST — will do that multiple times.