  We construct a complete conformal scattering theory for Maxwell fields in the
static exterior region of a Reissner-Nordstr{\o}m-de Sitter black bole
spacetime. This is done using uniform energy decay results that we obtain in a
separate paper, to show that the trace operators are injective and have closed
ranges. We then solve the Goursat problem (characteristic Cauchy problem) for
Maxwell fields on the null boundaries showing that the trace operators are also
surjective.
