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Celestial tracking systems employed in the navigation of military vehicles in the atmosphere of the earth have the capability of tracking a large number of stars in the daytime. In daytime tracking, the quantum efficiency of the detector, as well as additional sensitivity gain through electronic charge storage, is of primary importance. Theoretical formulas for the signal-to-noise ratios of four detectors are presented: the photoelectric photomultiplier, image dissector, vidicon and the image orthicon. The photomultiplier and image dissector require the use of very slow scanning velocities, narrow detection bandwidths, and the resultant time required for star acquisition is in the order of minutes. The image orthicon, due to target saturation, is restricted to the observation of only bright stars. The vidicon, with sensitivity gain through electronic charge storage, is used with rapid scanning velocities, and star acquisition is accomplished in less than one second of time. In interplanetary or nighttime navigation, with a low level of background radiation, the salient detector characteristics are sensitivity, gain through either storage or photomultiplication, and dark current. The image dissector rates first among the detectors considered, followed by the photomultiplier, image orthicon and the vidicon. Field test data are presented in this work in substantiation of the analysis of the several detector types.
Aerospace and Navigational Electronics, IEEE Transactions on (Volume:ANE-10 , Issue: 3 )
Date of Publication: Sept. 1963