  Here is presented the current state of the SPHERE-2 balloon-borne experiment.
The detector is elevated up to 1 km above the snow surface and registers the
reflected Vavilov-Cherenkov radiation from extensive air showers. This method
has good sensitivity to the mass-composition of the primary cosmic rays due to
its high resolution near the shower axis. The detector consists of a 1500 mm
spherical mirror with a 109 PMT cluster in its focus. The electronics record a
signal pulse profile in each PMT. In the last 2 years the detector was
upgraded: time resolution of pulse registration was enhanced up to 12.5 ns,
channel sensitivity was increased by a factor of 3, a new LED-based relative
PMT calibration method was introduced, and new hardware and etc. was installed.
