ATSA: a cold, active telescope for Space Astronomy

The National Academies’ Decadal Survey telescope studies have produced mission design concepts that plot pathways into the future to follow on from Hubble, Spitzer, JWST and NGRST. Considering the results of the LUVOIR and HabEx studies in particular, it is clear that segmented mirrors will eventually be needed to provide very large apertures in space and that this architecture presents both a scientific opportunity and an engineering challenge. Furthermore, while HabEx and LUVOIR cover a great deal of spectrum, both fall short of the mid-IR region where general astronomy and astrophysics can be undertaken that would be impossible from terrestrial observatories and where there also exist spectral features of interest in the search for life. A telescope with similar capabilities to Habex/LUVOIR but also capable of exoplanet work in spectral regions up to 5 μm would largely bridge the gap between those proposals and TPF-I (which would have operated from about 7 μm upwards), and is therefore worthy of study. The Active Telescope for Space Astronomy (ATSA) design study presents a possible architecture and is moderately sized (6 m) to enable the use of both starshade and coronagraph technologies. While the segment gaps of a segmented primary mirror present a challenge for coronagraphy, the architecture does allow direct wavefront control at each segment of that mirror, enabling a great degree of control at the primary source of contrast degradation. While active systems (for example, deformable mirrors on WFIRST CGI) are being incorporated into telescope designs today, a fully active mirror system needs further development for a future mission. With this concept in mind, and intending to build on the LUVOIR and HabEx studies, we discuss the elements of a cooled telescope design enabling both general astrophysics and exoplanet studies from the near UV through to the near-IR.