C. A. Bartholomew

Peer Reviewed

Abstract: Satellite Frequency standards have progressed from quartz oscillators used in Navy Navigation Satellite System (NNSS) satellites and early TIMATION launches to rubidium units used in the NTS-1 of NAVSTAR GPS, cesium units in NTS-2, and hydrogen maser units projected for NTS-3. The reasons that a large NRL effort has been made is that the character of satellite navigation systems has changed. The NNSS operates on a navigation technique suitable for objects having well known velocities. The parameter used is frequency; the satellites operate at low altitudes so the passes last only for 15 minutes or so. The frequency stability of the satellite clock must be such that the change in frequency does not introduce appreciable error in position fix. The NAVSTAR GPS is designed to give positions continuously in three dimensions. To do so it uses satellites in much higher altitudes than NNSS. At these altitudes continuous fixes by means of frequency measurement is impractical so ranging is used instead. Since a further requirement is that the user be passive the ranging measurement is obtained by having all satellites have clocks that are synchronized so the user can make measurements on enough satellites that he can determine the clock synchronization parameters. The problem of clock synchronization without near continuous updating of the satellite clocks has determined the search for better satellite clocks, programming through quartz, rubidium, cesium and now hydrogen maser standards.
Pages: 113 - 120
Cite this article: Bartholomew, C. A., "SATELLITE FREQUENCY STANDARDS (SPACE SEGMENT)", NAVIGATION, Journal of The Institute of Navigation, Vol. 25, No. 2, Summer 1978, pp. 113-120.
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