  In order to extend the direct observation of high-energy cosmic rays up to
the PeV region, highly performing calorimeters with large geometrical
acceptance and high energy resolution are required. Within the constraint of
the total mass of the apparatus, crucial for a space mission, the calorimeters
must be optimized with respect to their geometrical acceptance, granularity and
absorption depth. CaloCube is a homogeneous calorimeter with cubic geometry, to
maximise the acceptance being sensitive to particles from every direction in
space; granularity is obtained by relying on small cubic scintillating crystals
as active elements. Different scintillating materials have been studied. The
crystal sizes and spacing among them have been optimized with respect to the
energy resolution. A prototype, based on CsI(Tl) cubic crystals, has been
constructed and tested with particle beams. Some results of tests with
different beams at CERN are presented.
