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.