We present an analytic study of an optimal boundary control problem for the diffusive
$SP_{1}$-system modeling radiative heat transfer. The cost functional is of tracking-type and the
control problem is considered as a constrained optimization problem, where the constraint is given
by the nonlinear parabolic/elliptic $SP_{1}$-system. We prove the existence, uniqueness and regularity of
bounded states, which allows for the introduction of the reduced cost functional. Further, we show
the existence of an optimal control, derive the first-order optimality system and analyze the adjoint
system, for which we prove existence, uniqueness and regularity of adjoint states.