Abstract <p>The High Energy Ray Observatory (HERO) is a project for a space experiment based on an ionization calorimeter to measure the spectrum and composition of cosmic rays. The effective geometric factor of the installation is not less than 12 m² sr for protons and not less than 16 m² sr for nuclei and electrons. During ~5–7 years of exposure, this mission will measure the element-by-element spectra of cosmic rays in the energy range 10¹² –10¹⁶ eV/particle with a high energy resolution. A Monte Carlo simulation of the experiment using a borated scintillator as a part of the calorimeter is presented.</p>