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Time for GIOVE-A: the onboard rubidium clock experiment / J. Hahn in GPS world, vol 18 n° 5 (May 2007)

Public [article]  inGPS world > vol 18 n° 5 (May 2007) . - pp 64 - 69 Titre : Time for GIOVE-A: the onboard rubidium clock experiment Type de document : Article/Communication Auteurs : J. Hahn, Auteur ; D. Navarro-Reyes, Auteur ; F. Gonzalez, Auteur ; et al., Auteur Année de publication : 2007 Article en page(s) : pp 64 - 69 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Satellites artificiels [Termes IGN] GIOVE (satellite) [Termes IGN] horloge atomique [Termes IGN] temps universel [Termes IGN] test de performance Résumé : (Editeur) Apart from the ability to launch satellites, what was the single greatest technological development which has made global navigation satellite systems possible? Time's up (that should give you a hint). It is the atomic clock. GNSS receivers work by accurately timing how long it takes signals to travel from the satellites' antennas to the receiver's antenna and converting the time delays to ranges using the speed of light. Each delay is essentially the difference between the time a particular signal transition was received, as measured with the receiver's clock, and the time that same transition left a satellite, as measured with the satellite's clock. The delays must be measured very accurately since a timing error of just 10 nanoseconds is equivalent to a ranging error of about 3 meters. One of the clocks must be a highly stable reference clock. The demands on the timekeeping ability of the other clock is much less since its timing error can be estimated from measurements. The only practical approach for a GNSS is to place reference clocks in the satellites, permitting receivers to operate with a low-cost clock whose error is estimated along with the receiver's coordinates from the simultaneous measurements made on four or more satellites. Only atomic clocks have the required accuracy and stability to be used as reference clocks. Scientists have developed three basic kinds of atomic clock, each based on a different element ; cesium, rubidium, and hydrogen. The GPS Block II and IIA satellites each carried four clocks: two cesium and two rubidium whereas the Block IIR and IIR-M satellites each carry three rubidium clocks. GLONASS satellites carry three cesium clocks. The European Galileo system will also use redundant atomic clocks onboard its satellites. One candidate clock for the future Galileo satellites is the European Rubidium Atomic Frequency Standard. Two of these clocks are flying onboard the GIOVE-A test satellite which was launched on December 28, 2005. In this month's column, the GIOVE clock experiment team discusses the tests which have been conducted to assess the performance of the satellite's active clock and their future plans for onboard clock assessment including the passive hydrogen maser to be flown on GIOVE-B. Copyright Questex Media Group Inc Numéro de notice : A2007-223 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28586 [article]

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