  While the energy density of the Cosmic X-ray Background (CXB) provides a
statistical estimate of the super massive black hole (SMBH) growth and mass
density in the Universe, the lack, so far, of focusing instrument in the 20-60
keV (where the CXB energy density peaks), frustrates our effort to obtain a
comprehensive picture of the SMBH evolutionary properties. HEXIT-SAT (High
Energy X-ray Imaging Telescope SATellite) is a mission concept capable of
exploring the hard X-ray sky with focusing/imaging instrumentation, to obtain
an unbiased census of accreting SMBH up to the redshifts where galaxy formation
peaks, and on extremely wide luminosity ranges. This will represent a leap
forward comparable to that achieved in the soft X-rays by the Einstein
Observatory in the late 70'. In addition to accreting SMBH, and very much like
the Einstein Observatory, this mission would also have the capabilities of
investigating almost any type of the celestial X-ray sources. HEXIT-SAT is
based on high throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality
(15 arcsec Half Power Diameter) multi-layer optics, coupled with focal plane
detectors with high efficiency in the full 0.5-70keV range. Building on the
BeppoSAX experience, a low-Earth, equatorial orbit, will assure a low and
stable particle background, and thus an extremely good sensitivity for faint
hard X-ray sources. At the flux limits of 1/10 microCrab (10-30 keV) and 1/3
microCrab (20-40 keV) (reachable in one Msec observation) we should detect ~100
and ~40 sources in the 15 arcmin FWHM Field of View respectively, thus
resolving >80% and ~65% of the CXB where its energy density peaks.
