The science case and challenges of space-borne sub-millimeter
  interferometry
  Ultra-high angular resolution in astronomy has always been an important
vehicle for making fundamental discoveries. Recent results in direct imaging of
the vicinity of the supermassive black hole in the nucleus of the radio galaxy
M87 by the millimeter VLBI system Event Horizon Telescope and various
pioneering results of the Space VLBI mission RadioAstron provided new momentum
in high angular resolution astrophysics. In both mentioned cases, the angular
resolution reached the values of about 10-20 microrcseconds. Further
developments toward at least an order of magnitude "sharper" values are
dictated by the needs of astrophysical studies and can only be achieved by
placing millimeter and submillimeter wavelength interferometric systems in
space. A concept of such the system, called Terahertz Exploration and
Zooming-in for Astrophysics (THEZA), has been proposed in the framework of the
ESA Call for White Papers for the Voayage 2050 long term plan in 2019. In the
current paper we discuss several approaches for addressing technological
challenges of the THEZA concept. In particular, we consider a novel
configuration of a space-borne millimeter/sub-millimeter antenna which might
resolve several bottlenecks in creating large precise mechanical structures.
The paper also presents an overview of prospective space-qualified technologies
of low-noise analogue front-end instrumentation for millimeter/sub-millimeter
telescopes, data handling and processing. The paper briefly discusses
approaches to the interferometric baseline state vector determination and
synchronisation and heterodyning system. In combination with the original ESA
Voyage 2050 White Paper, the current work sharpens the case for the next
generation microarcsceond-level imaging instruments and provides starting
points for further in-depth technology trade-off studies.
