Black Hole Shadow Observations with Space-Ground Interferometers
  We consider the black hole (BH) shadow images which can be restored by data
processing and image recovery procedures in future space Very Large Baseline
Interferometry (VLBI) missions. For Kerr BHs with masses and coordinates of
SgrA*, M87* and M31*, illuminated by light source behind them, we consider
three kinds of observation: the ground-based interferometer (similar to the
Event Horizon Telescope), space-ground interferometer with a satellite in
geocentric orbit and space-ground interferometer with a satellite located in
Lagrange point $L_2$. The significant difference between the images produced by
the ground-based telescope alone and the one of the space VLBI with an added
low-orbit satellite is caused by both the increased baseline and the improved
of (u,v) coverage. The near-Earth configuration of the radio interferometer for
the observation of BH shadows is the most preferable for the BH shadow
observations among considered cases. With further increasing the orbit radius
up to the Lagrange point $L_2$ the density of the (u,v) filling decreases and
the results appear less reliable. Model images for all the cases are presented.
