  High-rate satellite communications among hundreds and even thousands of
satellites deployed at low-Earth orbits (LEO) will be an important element of
the forthcoming sixth-generation (6G) of wireless systems beyond 2030. With
millimeter wave communications (mmWave, ~30GHz-100GHz) completely integrated
into 5G terrestrial networks, exploration of its potential, along with
sub-terahertz (sub-THz, 100GHz-300GHz), and even THz (300GHz-3THz) frequencies,
is underway for space-based networks. However, the interference problem between
LEO mmWave/THz satellite cross-links in the same or different constellations is
undeservedly forgotten. This article presents a comprehensive mathematical
framework for modeling directional interference in all key possible scenario
geometries. The framework description is followed by an in-depth numerical
study on the impact of cross-link interference on various performance
indicators, where the delivered analytical results are cross-verified via
computer simulations. The study reveals that, while highly directional mmWave
and, especially, THz beams minimize interference in many cases, there are
numerous practical configurations where the impact of cross-link interference
cannot be neglected and must be accounted for.
