  We present the last version of {\scshape{Hyperion}} (HYdrodynamic Ppm
Explosion with Radiation diffusION), a hydrodynamic code designed to calculate
the explosive nucleosynthesis, remnant mass and light curve associated to the
explosion of a massive star. By means of this code we compute the explosion of
a subset of red supergiant models, taken from the database published by
\cite{lc18}, for various explosion energies in the range $\rm \sim
0.20-2.00~10^{51}~erg$. The main outcomes of these simulations, i.e., remnant
mass, $\rm ^{56}Ni$ synthesized, luminosity and length of the plateau of the
bolometric light curve, are analyzed as a function of the initial parameters of
the star (mass and metallicity) and of the explosion energy. As a first
application of {\scshape{Hyperion}} we estimated the mass and the metallicity
of the progenitor star of SN 1999em, a well studied SN IIP, by means of the
light curve fitting. In particular, if the adopted distance to the host galaxy
NGC 1637 is $\rm 7.83~Mpc$, the properties of the light curve point toward a
progenitor with an initial mass of $\rm 13~M_\odot$ and a metallicity
[Fe/H]=-1. If, on the contrary, the adopted distance modulus is $\rm 11.7~Mpc$,
all the models with initial mass $13\leq M/M_\odot\leq 15$ and metallicities
$\rm -1\leq [Fe/H] \leq 0$ are compatible with the progenitor of SN 1999em.
