A group of astronomers last year proposed a 11.7 meter diameter multi-mirror space telescope that could image planets around other stars: From Cosmic Birth to Living Earths (See also the detailed study in the AURA report (pdf))

The High Definition Space Telescope (HDST) would be sensitive to light at UV through near-infrared wavelengths, viewing the universe from the second Earth-Sun Lagrange point (L2), one million miles from the Earth. Its segmented mirror would be folded into either a current or future heavy-lift rocket, before being launched and deployed at its final home.

In its mission to discover and study Earth-like planets orbiting Sun-like stars, HDST will directly image exoplanets — including planets that may be as much as 10 billion times fainter than their host star — by carefully suppressing the star’s light. HDST’s exquisite image quality at visible wavelengths (with more than 25 times the resolving power of the Hubble Space Telescope) and high sensitivity all the way into the ultraviolet part of the spectrum (100 times more sensitive than Hubble), combined with a versatile set of imaging and spectroscopic instruments, will trigger profound breakthroughs in astrophysics.

Like Hubble and JWST, HDST would operate as a general observatory, supporting a broad range of investigations beyond its core exoplanet mission.

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The HDST mirror array in comparison to the Hubble space telescope mirror and the James Webb Space Telescope

HDST‘s primary goal is to find and characterize dozens of Earth-like exoplanets. A sample of dozens of exoEarths opens up the opportunity to identify truly Earth-like worlds with rocky surfaces and oceans, amidst a complex zoo of other varieties of terrestrial planets.

With this large sample, observing telltale signs of life in the planets’ atmospheres becomes possible. If life is rare, HDST will take us from our current complete ignorance of the occurrence rate of inhabited worlds to a first constraint, potentially showing how remarkable our own existence is. 

 If life is common, a large sample of terrestrial worlds with highly unusual atmospheric chemistry will secure our belief that life of some kind exists beyond the Earth, regardless of possible false positives. Whatever the outcome, HDST will change how we see our place in the Universe.

A view of the telescope folded up inside the fairing of a Delta IV Heavy rocket:

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A folded 11 m primary mirror, constructed with 54 1.3 m segments, is shown inside a Delta 4-H shroud.