  INTEGRAL IBIS/ISGRI 18-60 keV observations of SS433 performed in 2003-2011
enabled the hard X-ray phase-resolved orbital and precessional light curves and
spectra to be constructed. The spectra can be fitted by a power-law with photon
index $\simeq 3.8$ and remain almost constant while the X-ray flux varies by a
factor of a few. This suggests that the hard X-ray emission is produced in an
extended quasi-isothermal hot 'corona' surrounding central parts of a
supercritical accretion disc. A joint analysis of the broadband 18-60 keV
orbital and precessional light curves was performed in the model assuming a
significant Roche lobe overfilling by the optical star, up to its filling the
outer Lagrangian surface enabling mass loss through the outer Lagrangian L$_2$
point. From this modeling, the relativistic-to-optical component mass ratio
$q=M_x/M_v\gtrsim0.4\div 0.8$ is estimated. An analysis of the observed
long-term stability of the orbital period of SS433 with an account of the
recent observations of SS433 by the VLTI GRAVITY interferometer enabled an
independent mass ratio estimate $q>0.6$. This estimate in combination with the
radial velocity semi-amplitude for stationary He II emission, $K_x=168\pm 18$
km/s (Hillwig et al 2004) suggests the optical component mass in SS433 $M_v>12
M_\odot$. Thus, the mass of the relativistic component in SS433 is $M_x>7
M_\odot$, which is close to the mean mass of black holes in X-ray binaries
($\sim 8 M_\odot$). The large binary mass ratio in SS433 allows us to
understand why there is no common envelope in this binary at the secondary mass
transfer evolutionary stage and the system remains semi-detached (van den
Heuvel et al. 2017). We also discuss unsolved issues and outline prospects for
further study of SS433.
