  In this work we investigate the orbital distribution of interstellar objects
(ISOs), observable by the future wide-field National Science Foundation Vera C.
Rubin Observatory (VRO). We generate synthetic population of ISOs and simulate
their ephemerides over a period of 10 years, in order to select those which may
be observed by the VRO, based on the nominal characteristics of this survey. We
find that the population of the observable ISOs should be significantly biased
in favor of retrograde objects. The intensity of this bias is correlated with
the slope of the size-frequency distribution (SFD) of the population, as well
as with the perihelion distances. Steeper SFD slopes lead to an increased
fraction of the retrograde orbits, and also of the median orbital inclination.
On the other hand, larger perihelion distances result in more symmetric
distribution of orbital inclinations. We believe that this is a result of the
Holetschek effects, which is already suggested to cause observational bias in
orbital distribution of long period comets. The most important implication of
our findings is that an excess of retrograde orbits depends on the sizes and
the perihelion distances. Therefore, the prograde/retrograde orbits ratio and
the median inclination of the discovered population could, in turn, be used to
estimate the SFD of the underlying true population of ISOs.
