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Recently, the sensors ability of remote sensing satellites are offering much better resolution, higher quality, etc. [1] The gathered data size by the satellite has become larger. However, generally, downlink transfer capacity from the satellite to a ground station using RF (Radio Frequency) communication is limited, due to the internal balance of resources (power consumption, size capacity, mass, placement, etc.) in the satellite, and allocation of bandwidth by frequency regulation arrangement.

In recent years, the performance of observation equipment mounted on satellites has improved to such levels that it can obtain significant amount of data from a single observation [1]. Radio waves are used as a method for transmitting large volumes of data acquired by satellites to the ground. However, currently operational radio frequencies make it difficult to improve the communication speed, owing to interference problems and the carrier frequency. Space optical communication is expected to be a solution to this problem.

Optical Satellite Downlinks have gathered increasing attention in the last years. A number of experimental payloads have become available, and downlink experiments are conducted around the globe. One of these experimental systems is SOTA, the Small Optical Transponder, built by the National Institute of Information and Communications Technology (NICT). This paper describes the downlink experiments carried out from SOTA to the German Aerospace Center’s Optical Ground Stations located in Oberpfaffenhofen, Germany. Both the Transportable Optical Ground Station (TOGS) as well as the fixed Optical Ground Station Oberpfaffenhofen (OGS-OP) are used for the experiments. This paper will explain the preparatory work, the execution of the campaign, as well as show the first results of the measurements.

In collaboration between CNES, NICT, Geoazur, the first successful lasercom link between the micro-satellite SOCRATES and an OGS in Europe 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. Downlink & Uplink budgets are analyzed, the theoretical estimation matches well to measured power levels. 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. We also show the comparison between the expected and measured BER distributions.

Research and development of space optical communications is conducted in the National Institute of Information and Communications Technology (NICT). The NICT developed the Small Optical TrAnsponder (SOTA), which was embarked on a 50kg-class satellite and launched into a low earth orbit (LEO). The space-to-ground laser communication experiments have been conducted with the SOTA. Atmospheric turbulence causes signal fadings and becomes an issue to be solved in satellite-to-ground laser communication links. Therefore, as error-correcting functions, a Reed-Solomon (RS) code and a Low-Density Generator Matrix (LDGM) code are implemented in the communication system onboard the SOTA. In this paper, we present the in-orbit verification results of SOTA including the characteristic of the functions, the communication performance with the LDGM code via satellite-to-ground atmospheric paths, and the link budget analysis and the comparison between theoretical and experimental results.

A first free space optical communication campaign was established during June-October 2015 between the NICT SOTA [1], [2] (Small Optical TrAnsponder) instrument flying on the Low Earth Orbit satellite SOCRATES and the Optical Ground Station (OGS) MeO belonging to Observatoire de la Cote d’Azur (OCA) – GeoAzur. Several links at 10 Mbps have been done at 1549 and 976 nm. The main objectives of this experiment are the study of the laser beam propagation through the atmosphere and the design of all the sub-systems constituting the OGS. This experiment has been developed in the framework of an agreement signed between the Japan’s National Institute of Information and Communications Technology (NICT) and the French space agency (CNES). The development of the OGS and the measurement campaign were conducted in collaboration with NICT, CNES, ONERA and OCA. The OGS was specially designed for that optical link with SOTA from the existing MeO laser station (primary devoted to satellite and Moon laser ranging). We will first give a global presentation of the whole OGS with some details on the transmitter, the telescope, the receiver bench and the dedicated instrumentation used to monitor the link. We will then give an overview of some results obtained during that campaign.

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.

NICT initiated R&D effort of Small Optical TrAnsponder (SOTA) for LEO satellites to demonstrate the laser communication via satellite-to-ground atmospheric path links. SOTA is the payload on a 50-kg class microsatellite called Space Optical Communication Research Advanced Technology Satellite (SOCRATES), launched on 24th of May, 2014. Several international partners were interested in joint collaboration and NICT has initiated the international experiment campaign using SOTA with other agencies to perform laser communication experiments between SOTA and different international Optical Ground Stations (OGSs). In this paper, we describe the interface and link establishment protocol that had to be considered in the different OGS and the preliminary results in the international experiment campaign using SOTA.

Remoteley sensed images are useful for assessing damage caused by large-scale disasters. However, observation data recorded using aircraft are currently transmitted after the plane has landed using a terrestrial network, as inflight satellite communication links are inadequate. Therefore, the process of obtaining data is time-consuming. In this respect, the National Institute of Information and Communicaitons Technology (NICT) have developed an aeronautical earth station for the Wideband InterNetworking test and Demonstration Satellite (WINDS), wherein the remote sensing data observed from the aircraft can be transmitted via satellite links. NICT established the aeronautical earth station onboard an aircraft (Gulfstream II). A test flight was then conducted tomeasure the antenna teacking performance. Results confirmed that the tracking performance was good and that the interlock function worked when the drive angle was at limited values.

International audience; For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.; La turbulence atmosphérique est la principale cause de dégradation des liens laser sol satellite. Les perturbations de phase induites le long du cana de propagation conduisent à de la scintillation dans le plan du récepteur et peuvent sévèrement compromettre le couplage du flux dans un récepteur de petite dimension. Pour résoudre ces problèmes, différentes stratégies dédiées doivent être développées. Cela nécessite une compréhension précise de l'origine des perturbations. Les modèles de propagation de faisceau ont démontré leur capacité à reproduire les caractéristiques statistiques des perturbations optiques affectant un lien laser satellite sol pour des élévations descendant à 20°. Pour des élévations plus petites des mesures réalisées sur étoiles ont démontrées toutefois les limites de ces approches analytiques et l'intérêt de modèles de type Monte-Carlo. Nous faisons état ici des premières mesures sur un canal de propagation établi avec un microsatellite LEO grâce à un analyseur de Shack Hartmann. Le faisceau laser à 976nm est fourni par le terminal optique SOTA et analysé grâce à un Shack Hartmann situé au foyer coudé d'une station française (télescope MéO de 1.55m) en juillet 2015. Les caractéristiques du front d'onde et les structures de scintillation enregistrées avec l'analyseur sont analysées et comparées aux modèles de perturbation de la turbulence atmosphérique alimentés par les mesures in situ des paramètres atmosphériques tels que fournis par un GDIMM.

Increased performance of onboard sensors has greatly increased the amount of communications data from satellites. The data rates from Earth observation satellites are also increasing, but communication rates of several tens of gigabits per second will inevitably be required for data download. This cannot be achieved using radio communications, but is possible using optical communications. Many demonstrations have been conducted to verify the usability of sophisticated optical communications equipment in orbit. The technology readiness level for space-based optical communications has reached seven, so the time has come to develop spacebased optical communications for use in operational environments. However, the influence of terrestrial weather conditions remains as a problem to be solved. One potential solution is site diversity, where several ground stations are used. The National Institute of Information and Communications Technology (NICT), is investigating a terrestrial free-space optical communications network for future

Current development status of the small optical transponder (SOTA) to be installed into a small satellite is described, where the breadboard model, the engineering model and the protoflight model are respectively introduced. The tracking performance is estimated to show that the angular error is low enough in comparison to the divergence angle of the transmitted beam.

Since 2006, ground-to-satellite laser communication experiments have been successfully performed using intensity modulation/direct detection (IMDD) between the National Institute of Information and Communications Technology (NICT) optical ground station located in Tokyo and a low earth orbit (LEO) satellite. With the advent of coherent binary phase-shift keying (BPSK) receivers in orbit by a German satellite, it is now absolutely imperative to establish interoperability between the different optical communications systems. At NICT, an optical receiver that can demodulate both IMDD and coherent optical signals for free-space laser communications has been developed that can recover the carrier phase after homodyne detection by means of digital signal processing (DSP). A transportable optical ground station has also been developed for site-diversity purposes in order to increase accessibility between terrestrial and space systems. A new NICT mid-term research plan has started since April 2011 and this paper presents research and development in free-space laser communications technologies at NICT.

50kg-class satellites can reduce production cost and time compared to larger satellites. On the other hand, the communication capacity in radio frequency for 50 kg-class satellites is limited, however it can be improved by using optical communications. The National Institute of Information and Communications Technology (NICT) has begun to develop a Small Optical TrAnsponder (SOTA) onboard a 50kg-class satellite, which project is called the Space Optical Communications Research Advanced Technology Satellite (SOCRATES). We will introduce the experiment plan for SOTA onboard the 50 kg-class small satellite.