Current status and preliminary design of the High-Energy Ray Observatory (HERO) are presented. The HERO is planned to be launched onboard a heavy satellite. This experiment is based on the application of a deep and wide aperture ionization calorimeter with mass from 10 to 70 tonns. The effective geometrical factor of the observatory varies from 12 to 62 m2sr respectively, depending on the mass of the calorimeter. Under the 5-7 years exposure, this mission will allow to measure the cosmic ray composition and energy spectra of nuclei around the knee and up to 10^17 eV with high precision and to solve the most actual problems of high energy astrophysics. Stages of development are presented; details of technical realization are discussed.