  The effect of the expanding universe on planetary motion is considered to
first order in the Hubble constant H. Orbital elements are shown to be
unaffected, but there is a small change in the connection between planetary
proper time and coordinate time. This can produce an apparent anomalous
acceleration in velocities inferred from echo-ranging, but the effect is too
small by many orders of magnitude to account for the Pioneer 10/11 anomaly.
