Perverse ${\mathbb{F}}_p$-sheaves on the affine Grassmannian

For a reductive group over an algebraically closed field of characteristic $p

0$weconstructtheabeliancategoryofperverse$$\mathbb{F}$_p$-sheaves on the affine Grassmannian that are equivariant with respect to the action of the positive loop group. We show this is a symmetric monoidal category, and then we apply a Tannakian formalism to show this category is equivalent to the category of representations of a certain affine monoid scheme. We also show that our work provides a geometrization of the inverse of the mod $p$ Satake isomorphism. Along the way we prove that affine Schubert varieties are globally $F$-regular and we apply Frobenius splitting techniques to the theory of perverse ${\mathbb{F}}_p$-sheaves.