Fundamental Limitations to Optical Doppler Measurements for Space Navigation

Theoretical consideration is given to the problem of optical Doppler velocity determination of the high accuracy (about 1 ft/sec) required to be useful for space navigation. From the physical theory of line-broadening and -shifting mechanisms in stellar atmospheres, it is concluded that an intrinsic variability of ±200 ft/sec may be expected in the measurement of an observer's Doppler velocity. Examination of the current state of the art in measuring equipment suggests that it does not set the limits on accuracy.