A Minimal Space Interferometer Configuration for Imaging at Low Radio
  Frequencies
  The radio sky at lower frequencies, particularly below 20 MHz, is expected to
be a combination of increasingly bright non-thermal emission and significant
absorption from intervening thermal plasma. The sky maps at these frequencies
cannot therefore be obtained by simple extrapolation of those at higher
frequencies. However, due to severe constraints in ground-based observations,
this spectral window still remains greatly unexplored. In this paper, we
propose and study, through simulations, a novel minimal configuration for a
space interferometer system which would enable imaging of the radio sky at
frequencies well below 20 MHz with angular resolutions comparable to those
achieved at higher radio frequencies in ground-based observations by using the
aperture-synthesis technique. The minimal configuration consists of three
apertures aboard Low Earth Orbit (LEO) satellites orbiting the Earth in
mutually orthogonal orbits. Orbital periods for the satellites are deliberately
chosen to differ from each other so as to obtain maximum (u, v) coverage in
short time spans with baselines greater than 15000 km, thus, giving us angular
resolutions finer than 10 arcsec even at these low frequencies. The sensitivity
of the (u, v) coverage is assessed by varying the orbit and the initial phase
of the satellites. We discuss the results obtained from these simulations and
highlight the advantages of such a system.
