Antarctic balloon-borne detector of high-energy cosmic rays (SPHERE project)

The experiment SPHERE is based on a A.E. Chudakov's suggestion to use a new method for investigations of the energy spectrum of ultrahigh-energy primary cosmic rays. A small device lifted up off a snowed surface of the Earth detects Cherenkov light of an extensive air shower that is reflected from the surface. A contemporary status of the experiment SPHERE, a description of the method, the first measurements of the background night starlight in the region of the Russian Antarctic station Novolazarevskaya are presented. A relatively simple detector SPHERE-2 including a spherical mirror of the diameter 1.5 m and a 100-pixel retina is developed for Antarctic balloon-borne measurements of the cosmic ray spectrum. A long-time winter flight makes it possible to measure the spectrum above 1020eV. A comparison with satellite and ISS projects of the nearest future shows that efficiency of this detector is sufficiently high.