  Anderson, et al., find the measured trajectories of Pioneer 10 and 11
spacecraft deviate from the trajectories computed from known forces acting on
them. This unmodelled acceleration can be accounted for by non-isotropic
radiation of spacecraft heat. This explanation was first proposed by Murphy,
but Anderson, et al. felt it could not explain the observed effect. This paper
includes new calculations on the expected magnitude of this effect, based on
the relative emissivities of the different sides of the spacecraft, as
estimated from the known spacecraft construction. The calculations indicate the
proposed effect can account for most, if not all, of the unmodelled
acceleration.
