  Let $G$ be a simply connected, almost simple group over an algebraically
closed field $\mathbf k$, and $P$ a maximal parabolic subgroup corresponding to
omitting a cominuscule root. We construct a compactification
$\phi:T^*G/P\rightarrow X(u)$, where $X(u)$ is a Schubert variety corresponding
to the loop group $LG$. Let $N^*X(w)\subset T^*G/P$ be the conormal variety of
some Schubert variety $X(w)$ in $G/P$; hence we obtain that the closure of
$\phi(N^*X(w))$ in $X(u)$ is a $B$-stable compactification of $N^*X(w)$. We
further show that this compactification is a Schubert subvariety of $X(u)$ if
and only if $X(w_0w)\subset G/P$ is smooth, where $w_0$ is the longest element
in the Weyl group of $G$. This result is applied to compute the conormal fibre
at the zero matrix in any determinantal variety.
