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In collaboration between CNES, NICT, Geoazur, the first successful lasercom link between the micro-satellite SOCRATES and a non-Japanese OGS has been established. This paper presents some results of telecom and scintillation first data analysis for 4 successful links in June & July 2015 between SOTA terminal and Meo optical ground station (OGS) at Caussols France. The telecom and scintillation data have been continuously recorded during the passes by using a detector developed at the laboratory. An irradiance of 190 nW/m² and 430 nW/m² has been detected for 1549 nm and 976 nm downlinks at 35° elevation. Spectrums of power fluctuation measured at OGS are analyzed at different elevation angles and at different diameters of telescope aperture to determine fluctuations caused by pointing error (due to satellite & OGS telescope vibrations) and caused by atmospheric turbulence. Telecom signal forms and bit error rates (BER) of 1549 nm and 976 nm downlink are also shown at different diameters of telescope aperture. BER is 'Error Free' with full-aperture 1.5m telescope, and almost in 'good channel' with 0.4 m sub-aperture of telescope.

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INTRODUCTIONOptical transmissions between earth and space have been identified as key technologies for future high data rate transmissions between satellites and ground. CNES is investigating the use of optics both for High data rate direct to Earth transfer from observation satellites in LEO, and for future telecommunications applications using optics for the high capacity Gateway link. In order to assess the feasibility of these future systems, several studies have been initiated for investigating the propagation channel and its impact on the data transmissions. The aim is to define the more appropriate physical layer, in terms of choice of modulations, coding and interleaving, so that to obtain a robust data link. In order to design future optical transmission systems, field measurements are necessary to confront models with real conditions. The DOMINO project, which stands for "Demonstrator for Optical transMission at hIgh data rate iN Orbit)", aims at performing field measurements with international partners.

INTRODUCTIONThe problem of the time to first fix (TTFF) of a spaceborne global navigation satellite system (GNSS) receiver is crucial. The high Doppler range of data collected by a GNSS receiver on a low earth orbiter (LEO) makes it difficult to achieve the conditions classically required to achieve a fix (i.e., the presence of four simultaneous emitters), in particular when the number of receiver channels is small; when the configuration of the antenna is not optimal; or when the sensitivity of the receiver is poor, which is the case during cold starts. On a geostationary earth orbit (GEO) satellite, the problem of the TTFF is even more difficult, since the conditions of four simultaneous emitters are rarely met. This paper begins by presenting three detailed algorithms based on the three main configurations that have been studied: LEO orbit with two emitters, LEO orbit with three emitters, and GEO orbit with one emitter. Then, results of tests using actual TOPEX data are presented; these results are in the 100 km error range when two emitters are present and in the 10 km error range when three emitters are present. The GEO orbit algorithm has been tested with simulated data, collected during the qualification campaign of the Alcatel TOPSTAR 3000 GNSS receiver. The results are in the 100 km error range. In all of these configurations, the resultant position is precise enough to improve the TTFF, to reduce the acquisition thresholds of the receiver, or to initialize an orbital navigator. The enhancement of the TTFF is then reviewed, based on a characterization of the algorithms of the TOPSTAR 3000 receiver, on which theses techniques will be implemented in the near future. THE CLASSICAL POSITION FIXThe classical position fix is well known [1,2]: It requires the use of four or more simultaneous pseudorange measurements. The four unknown quantities are the three coordinates of the position of the receiver; b, the clock bias between GPS time and the time of the receiver.