  The Hubble Space Telescope (HST) has been the most impactful science-driven
mission ever flown by NASA. However, when HST reaches the end of its life,
there will be a void due to the loss of some of the science capabilities
afforded by HST to astronomers world-wide. The previous 2010 Decadal Survey
(DS) noted this void, arguing for the need for a successor to HST with UV
capabilities in three separate places in the main report (pp. 190, 203, and
220). The large strategic missions that will follow HST, namely JWST and
WFIRST, will continue to spark the interest of the public in space-based
astronomy. In order to ensure continued US preeminence in the arena of large
space-based astrophysics missions, and a seamless transition after WFIRST, a
future flagship mission must be waiting in the wings. Anticipating this need,
NASA initiated four large strategic mission concept studies (HabEx, LUVOIR,
Lynx, and Origins), which have mature designs, including detailed technology
assessments and development plans. Two of these concepts, HabEx and LUVOIR, are
responsive to the recommendations of the previous DS regarding a UV-capable
mission. Both are more powerful successors to HST, with UV-to-optical
capabilities that range from significant enhancements to orders-of-magnitude
improvement. At the same time, technological and scientific advances over the
past decade only now make it feasible to marry such a mission with one that can
search for life outside the solar system. Acknowledging that the constraints
that the Astro2020 DS must consider may be difficult to anticipate, the HabEx
and LUVOIR studies present eleven different variants, each of which enable
groundbreaking science, including the direct imaging and characterization of
exoplanets. The HabEx and LUVOIR mission studies offer a full suite of options
to the Astro2020 DS, with corresponding flexibility in budgeting and phasing.
