  By invoking the relativistic spectral radiance, as derived by Lee and Cleaver
[1], the drag radiation pressure of a relativistic planar surface moving
through an isotropic radiation field, with which it is in thermal equilibrium,
is determined in inertial and non-inertial frames. The forward- and
rearward-directed emission radiation pressures are also derived and compared. A
fleeting (inertial frames) or ongoing (some non-inertial frames) Carnot cycle
is shown to exist as a result of an intra-surfaces temperature gradient. The
drag radiation pressure on an object with an arbitrary frontal geometry is also
described.
