Here is a recent SETI Institute seminar in which three scientists each presented a different proposal for a next-generation space observatory: SETI Talks The Future of NASA Space Telescopes – What to Look for in the Next Generation
Three of those space telescopes got the attention of the SETI Institute because of their potential to answer the question, “Are We Alone?”
The Origins Space Telescope (Origins) is a large cooled infrared space telescope with higher sensitivity and better angular resolution than any prior observatory accessing similar wavelengths. Among its many science objectives covering the first stars to life, Origins could help scientists understand the abundance and availability of water for habitable planets and could look for biosignatures on potentially habitable worlds transiting low-mass stars.
The Large UV Optical Infrared Surveyor (or LUVOIR) is a general-purpose observatory; its key science goal is to characterize a wide range of exoplanets, including those that might be habitable and orbiting a range of stellar types.
The Habitable Exoplanet Imaging Mission (HabEx) is a space telescope, optimized to search for and image Earth-sized exoplanets in the habitable zones around sun-like stars, where liquid water might exist. HabEx would also have a suite of general astrophysics science capabilities.
Each of these concepts has pros and cons, as well as other technological, cost, and risk challenges. These mission concepts will be described in detail in their final study reports, which will be delivered to the National Academy of Sciences for the Astro 2020 Decadal Survey later this year. It is still unknown whether the Decadal Survey will prioritize none, one, or even all of these concepts, but the several hundred scientists and engineers involved in these mission concept studies for the past three years are confident that we are now capable of building these telescopes, and that the science that they can deliver will be compelling and change again our view of the cosmos, just as the Hubble Space Telescope has done for the past 3 decades.