The roots of polynomial $ p(s) $ are:
$$ \begin{aligned}s_1 &= 1.4656\\[1 em]s_2 &= -0.2328+0.7926i\\[1 em]s_3 &= -0.2328-0.7926i \end{aligned} $$Polynomial $ 2s^3-2s^2-2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.