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This report describes the on-orbit performance evaluation of the NAVSTAR 6 cesium clock. Time domain measurements, taken between the NAVSTAR 6 spacecraft and the Vandenberg GPS monitor station, by a spread spectrum receiver, have been collected for about 100 days and analyzed to estimate the long term frequency stability of the NAVSTAR 6 cesium clock. The results indicate a combined clock/ephemeris frequency stability of 1.3 x 10 to the minus 13th power, or less, for sample times varying from 1 to 10 days. Future work will include analysis of other orbiting GPS cesium and rubidium clocks. (Author)

Since the launch of the first Navigation Technology Satellite (NTS) in 1974, international time-transfer experiments have been performed as part of the concept validation phase of the Global Positioning System (GPS). Time-transfer results from both NTS-1 and NTS-2 are presented, including recent measurements from receivers located in South America, Germany, Japan, and the United States. A time link to the DOD Master clock allows submicrosecond intercomparison of UTS (USNO, MC1) with clocks in the respective countries via the NTS link. Work is progressing toward a retrofit conversion of existing NTS receivers (located at NASA and foreign observatories) into GPS time-transfer receivers. Initial results are presented on the long-term rubidium frequency stability as measured from the GPS NAVSTAR-4 space vehicle (SV). Analysis has been performed for sample times varying from 1 to 10 days. Using a 154-day data span starting on day 36, 1979, data was collected from the four GPS monitor stations located at Vandenberg, Guam, Alaska, and Hawaii. A time domain estimate for the NAVSTAR-4 SV clock off-set is obtained for each SV pass over the GPS monitor sites, using a smoothed reference ephemeris, with corrections for ionospheric delay, tropospheric delay, earth rotation, and relativistic effects. Conversion from the time domain to the frequency domain is made using the two-sample Allan Variance; sigma-tau plots are used to identify the noise processes. Estimates of flicker and white frequency noise for the NAVSTAR-4 rubidium frequency standard are obtained.

During May through September 1978 a six nation cooperative experiment was performed to intercompare time standards of major laboratories at the submicrosecond level using NTS satellites. NTS time transfer receivers, which were developed for use with the NTS series of satellites, were installed at the Division of National Mapping (DNM), Australia; in Japan at the Radio Research Laboratories (RRL) and the National Research Laboratory of Metrology (NRLM); National Research Council (NRC), Canada; Royal Greenwich Observatory (RGO), England; Bureau International de l'Heure, France (BIH); Institute for Applied Geodesy (IFAG), West Germany; and in the U.S. at the Goddard Space Flight Center (GSFC), National Bureau of Standards (NBS), Naval Research Laboratory (NRL), and the Naval Observatory (USNO). The results obtained by satellite were compared to those obtained by portable clocks. At all stations the differences were less than 0.75 microseconds. The RMS of the data from nine stations is less than 0.4 microseconds. (Author)

This paper describes the on-orbit frequency stability performance analysis of the GPS NAVSTARs 3 and 4 rubidium clocks, and the NAVSTARs 5 and 6 cesium clocks. Time-domain measurements, taken from the four GPS monitor sites, have been analyzed to estimate the short- and long-term frequency stability performance of the NAVSTAR clocks. The data analyzed includes measurements from 1981, 1982, and the first 100 days of 1983. Short- and long-term results are presented for data collected during 1982. The Allan variance was used as the measure of frequency stability performance in the time domain. (Author), This article is from 'Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (15th) Held at Washington, DC on 6-8 December 1983,' AD-A149 163, p171-209.

This report describes the on-orbit frequency stability performance analysis of the Global Positioning System (GPS) NAVSTARs 3 and 4 rubidium clocks and the NAVSTARs 5 and 6 cesium clocks. Time domain measurements, taken from the four GPS monitor sites, have been analyzed to estimate the short- and long-term frequency stability performance of the NAVSTAR clocks. The data presented include measurements from 1981, 1982, and the first 100 days of 1983.

The Timation (Time Navigation) technique of passive ranging is a concept that could be expanded to provide a worldwide navigation service. Passive ranging is accomplished by measuring the time difference between electronic clocks located within the satellite and in the navigator's receiver. The Timation technique uses a highly stable, synchronized clock in the satellite; however, the navigator's clock stability may vary considerably, depending on the navigator's equipment and vehicle dynamics. One-hundred and seven satellite constellations are discussed in terms of their influence on earth coverage and navigation fix accuracy. The recommended configuration derived is comprised of three planes with nine satellites (3 x 9) each in 8-hour circular orbits at a 53 deg inclination. (Author)

The TIMATION (Time Navigation) technique of passive ranging can be employed to provide a worldwide navigation and time-transfer service. Passive ranging is accomplished by measuring the time difference between electronic clocks located within the satellite and the navigator's receiver. Navigation results were obtained with a prototype system consisting of the TIMATION 2 satellite and four ground stations. The results indicate a CEP position-fixing capability of 33 meters (100 feet) using dual-frequency range measurements. The analysis of the data includes ionospheric refraction, instrumentation error, and the effect of satellite trajectory position error in both the observed and predicted regions. (Author)

The Timation II satellite is an experimental model of a range and doppler measurement satellite navigation system sponsored by the Naval Air Systems Command. In this report the satellite is described briefly, along with the ranging concept and the range and doppler measuring equipment. The basic navigation equations for range, doppler, and simultaneous range and doppler measurements are developed, along with several alternate techniques depending upon the user equipment. An analytical expression is developed for experimentally determining the range error due to first-order ionospheric refraction. The system biases are identified with clock difference (range bias) and frequency difference (doppler bias). An error analysis is performed to determine the influence of geometry and system noise upon navigation accuracy. (Author)

A worldwide satellite navigation system (TIMATION) has been proposed that will yield instantaneous and continuous position fixes by suitable satellite configurations and navigator equipment. The TIMATION project is conducted by NRL under the sponsorship of the Navy Space Project Office (PM-16) and the Naval Air Systems Command. This report addresses the instantaneous position-fixing results obtained by using range and doppler measurements obtained with the TIMATION II satellite and a navigation receiver employing a relatively precise frequency standard. The results are corrected for first-order ionospheric refraction and indicate a two-dimensional position-fixing capability of 105 m RMS (60 m CEP). (Author)