  Very-high-energy and ultra-high-energy neutrinos are messengers of energetic
sources in the universe. Sub-orbital and satellite-based neutrino telescopes
employ detectors of the atmospheric Cherenkov emission from extensive air
showers (EASs) generated by charged particles. These Cherenkov detectors can be
pointed below or above the Earth's limb. Cherenkov emissions produced from
directions below the limb are from upward-going EASs produced in the atmosphere
sourced by Earth-skimming neutrinos. When the Cherenkov telescope is pointed
slightly above the Earth's limb, signals from EASs are initiated by cosmic ray
interactions in the atmosphere. For sub-orbital detectors, muons produced from
cosmic rays in the atmosphere can directly hit the Cherenkov telescope. Using a
semi-analytic technique with cascade equations for atmospheric particle fluxes,
we quantify the atmospheric muon flux that reaches sub-orbital telescopes like
Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2). We
assess this potential background to the EAS signals. The calculation technique
may also provide an understanding of the evolution of the muon content in
individual EAS.
