Low-low, satellite-to-satellite Doppler tracking, aimed at performing an accurate survey from orbit of the Earth gravity field, with a radio link that operates in the frequency band 50 to 100 GHz, has been under consideration for some time. It is therefore of interest to discuss the upper bound in Doppler measurement accuracy imposed by the effects of ionospheric turbulence. With recent technological advances in EHF equipment, ionospheric turbulence may indeed be the remaining most important contributing factor to the uncompensated, uncorrectable, measurement error.