  Over the past 16 years, NASA's Chandra X-ray Observatory has provided an
unparalleled means for exploring the universe with its half-arcsecond angular
resolution. Chandra studies have deepened our understanding of galaxy clusters,
active galactic nuclei, galaxies, supernova remnants, planets, and solar system
objects addressing almost all areas of current interest in astronomy and
astrophysics. As we look beyond Chandra, it is clear that comparable or even
better angular resolution with greatly increased photon throughput is essential
to address even more demanding science questions, such as the formation and
subsequent growth of black hole seeds at very high redshift; the emergence of
the first galaxy groups; and details of feedback over a large range of scales
from galaxies to galaxy clusters. Recently, NASA Marshall Space Flight Center,
together with the Smithsonian Astrophysical Observatory, has initiated a
concept study for such a mission named the X-ray Surveyor. This study starts
with a baseline payload consisting of a high resolution X-ray telescope and an
instrument set which may include an X-ray calorimeter, a wide-field imager and
a dispersive grating spectrometer and readout. The telescope would consist of
highly nested thin shells, for which a number of technical approaches are
currently under development, including adjustable X-ray optics, differential
deposition, and modern polishing techniques applied to a variety of substrates.
In many areas, the mission requirements would be no more stringent than those
of Chandra, and the study takes advantage of similar studies for other large
area missions carried out over the past two decades. Initial assessments
indicate that such an X-ray mission is scientifically compelling, technically
feasible, and worthy of a high rioritization by the next American National
Academy of Sciences Decadal Survey for Astronomy and Astrophysics.
