Lunar laser ranging in infrfared at hte Grasse laser station

For many years, lunar laser ranging (LLR) observations using a green wavelength have suffered an inhomogeneity problem both temporally and spatially. This paper reports on the implementation of a new infrared detection at the Grasse LLR station and describes how infrared telemetry improves this situation. Our first results show that infrared detection permits us to densify the observations and allows measurements during the new and the full Moon periods. The link budget improvement leads to homogeneous telemetric measurements on each lunar retro-reflector. Finally, a surprising result is obtained on the Lunokhod 2 array which attains the same efficiency as Lunokhod 1 with an infrared laser link, although those two targets exhibit a differential efficiency of six with a green laser link

Tests with a Carlina-type diluted telescope; Primary coherencing

Studies are under way to propose a new generation of post-VLTI interferometers. The Carlina concept studied at the Haute- Provence Observatory is one of the proposed solutions. It consists in an optical interferometer configured like a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed cospherical segments, a helium balloon (or cables suspended between two mountains), carries a gondola containing the focal optics. Since 2003, we have been building a technical demonstrator of this diluted telescope. First fringes were obtained in May 2004 with two closely-spaced primary segments and a CCD on the focal gondola. We have been testing the whole optical train with three primary mirrors. The main aim of this article is to describe the metrology that we have conceived, and tested under the helium balloon to align the primary mirrors separate by 5-10 m on the ground with an accuracy of a few microns. The servo loop stabilizes the mirror of metrology under the helium balloon with an accuracy better than 5 mm while it moves horizontally by 30 cm in open loop by 10-20 km/h of wind. We have obtained the white fringes of metrology; i.e., the three mirrors are aligned (cospherized) with an accuracy of {\approx} 1 micron. We show data proving the stability of fringes over 15 minutes, therefore providing evidence that the mechanical parts are stabilized within a few microns. This is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or under a balloon. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named diluted telescopes.Comment: 18 pages, 17 figures, A&A, accepte

Phylogenetic analyses indicate independent recruitment of diverse gene cassettes during assemblage of the 2,4-D catabolic pathway

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Télémétrie laser pour le vol en formation: Vers des mesures de haute exactitude des distances kilométriques dans l?espace

International audienceLa mesure de longue distance à haute précision est essentielle pour les missions spatiales de vol en formation: les missions d'observation par synthèse d'ouverture nécessitent la connaissance des distances absolues et de la géométrie de la formation, avec une très haute précision. Les deux télémètres laser développés sont basés sur l'utilisation d'un faisceau modulé en amplitude à haute fréquence qui parcourt une voie de référence de longueur constante et la voie de mesure. Le premier télémètre (T2M) ne fait aucune utilisation de l'interférométrie. La phase du faisceau de retour est détectée, d'une manière qui rejette les erreurs cycliques dues aux diaphonies optique et électro-nique. La distance est tirée de la valeur de la fréquence pour laquelle les deux signaux détectés (référence, mesure) sont en phase. Une résolution meilleure que 10 nm a été obtenue avec ce système simple. Le deuxième télémètre (ILIADE) doit fournir une résolution sub-nanométrique, au prix d'une procédure plus compliquée, qui implique à la fois des mesures de temps de vol (collab. avec E. Samain, OCA, labo GéoAzur) et des mesures d'interférométrie à deux modes, que nous présenterons

Characterization of an ultra stable quartz oscillator thanks to Time Transfer by Laser Link (T2L2, Jason-2)

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Temperature, radiation and aging analysis of the DORIS Ultra Stable Oscillator by means of the Time Transfer by Laser Link experiment on Jason-2

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Time Transfer by Laser Link: Data analysis and validation to the ps level

International audienceThe Time Transfer by Laser Link (T2L2) is a very high resolution time transfer technique based on the recording of arrival times of laser pulses at the satellite. T2L2 was designed to achieve time stability in the range of 1 ps over 1000 s and an accuracy better than 100 ps. The project is in operation onboard the Jason-2 satellite since June 2008. The principle is based on the Satellite Laser Ranging (SLR) technology; it uses the input of 20–25 SLR stations of the international laser network which participate in the tracking. This paper focuses on the data reduction process which was developed specifically to transform the raw information given by both space instrument and ground network: first to identify the triplets (ground and onboard epochs and time of flight of the laser pulse), second to estimate a usable product in terms of ground-to-space time transfer (including instrumental corrections), and thirdly to produce synchronization between any pair of remote ground clocks. In describing the validation of time synchronizations, the paper opens a way for monitoring the time difference between ultra-stable clocks thanks to a laser link at a few ps level for Common View passes. It highlights however that without accurately characterizing the onboard oscillator of Jason-2 and knowing the unavailability of time calibrations of SLR stations generally, time transfer over intercontinental distances remain difficult to be accurately estimated