  The Sasa-Satsuma equation with $3 \times 3 $ Lax representation is one of the
integrable extensions of the nonlinear Schr\"{o}dinger equation. In this paper,
we consider the Cauchy problem of the Sasa-Satsuma equation with generic
decaying initial data. Based on the Rieamnn-Hilbert problem characterization
for the Cauchy problem and the $\overline{\partial}$-nonlinear steepest descent
method, we find qualitatively different long time asymptotic forms for the
Sasa-Satsuma equation in three solitonic space-time regions:
  (1)\ For the region $x<0, |x/t|=\mathcal{O}(1)$, the long time asymptotic is
given by
  $$q(x,t)=u_{sol}(x,t| \sigma_{d}(\mathcal{I})) + t^{-1/2} h + \mathcal{O}
(t^{-3/4}). $$
  in which the leading term is $N(I)$ solitons, the second term the second
$t^{-1/2}$ order term is soliton-radiation interactions and the third term is a
residual error from a $\overline\partial$ equation.
  (2)\ For the region $ x>0, |x/t|=\mathcal{O}(1)$, the long time asymptotic is
given by
  $$ u(x,t)= u_{sol}(x,t| \sigma_{d}(\mathcal{I})) + \mathcal{O}(t^{-1}).$$
  in which the leading term is $N(I)$ solitons, the second term is a residual
error from a $\overline\partial$ equation.
  (3) \ For the region $ |x/t^{1/3}|=\mathcal{O}(1)$, the Painleve asymptotic
is found by
  $$ u(x,t)= \frac{1}{t^{1/3}} u_{P} \left(\frac{x}{t^{1/3}} \right) +
\mathcal{O} \left(t^{2/(3p)-1/2} \right), \qquad 4<p < \infty.$$
  in which the leading term is a solution to a modified Painleve $\mathrm{II}$
equation, the second term is a residual error from a $\overline\partial$
equation.
