HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450 nm to 2450 nm with resolving powers from 3500 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. HARMONI is a work-horse instrument that provides efficient, spatially resolved spectroscopy of extended objects or crowded fields of view. The gigantic leap in sensitivity and spatial resolution that HARMONI at the ELT will enable promises to transform the landscape in observational astrophysics in the coming decade. The project has undergone some key changes to the leadership and management structure over the last two years. We present the salient elements of the project restructuring, and modifications to the technical specifications. The instrument design is very mature in the lead up to the final design review. In this paper, we provide an overview of the instrument's capabilities, details of recent technical changes during the red flag period, and an update of sensitivities.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. The IAC, as an institution participating in the consortium responsible for the design and manufacturing of HARMONI, is in charge of the pre-optics system. This large-scale subsystem requires a cryogenic test bench capable of accommodating it. At this point, the HIPOTEC cryostat comes into play. A Beckhoff PLC automates this large-scale cryostat. A Touchscreen panel or web browser carried out the operation, allowing for remote control. This system utilizes the TwinCAT PLC HMI Web Server. This PLC automates all the control processes of the cryostat, allowing the cryogenic cycle to perform automatically with just one click. It carries out this entire process safely using a state machine capable of bringing the system into operation.
The High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI) is planned as a first light instrument for the Extremely Large Telescope (ELT). The Instrument Control Electronics (ICE) subsystem plays a vital role in HARMONI, housing all control devices and ensuring they function optimally. However, limited space within the instrument necessitates a unique design approach for the electronic cabinets. This paper details the design of these bespoke cabinets, emphasizing the thermal analysis and insulation technologies implemented to maintain proper operating temperatures for the electronics within the compact instrument volume.
HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope. It covers a large spectral range from 470nm to 2450nm with resolving powers from 3300 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes (including a High Contrast capability) - or with Non Adaptive Optics. The project is preparing for Final Design Reviews. In this paper, we present the optical design of the Pre-Optics for Final Design Reviews, the pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. This involves many functions, mainly relaying the light from the telescope focal plane to the integral field unit focal plane via a set of interchangeable scale changing optics. The pre-optics also provides components including a focal plane mask wheel, cold pupil masks, spectral order sorting filters, a fast shutter, and a pupil imaging capability to check telescope/instrument pupil alignment.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It will use an image slicer to provide spectra over a single contiguous area, providing fields of view on the sky of 9.3x6.3”, 4.2x3.1”, 2.1x1.5” and 0.84x0.62” with increasing spatial resolution (i.e.- 60x30, 20x20, 10x10 and 4x4 mas2) and magnification 2, 3/6, 6/12 and 15/30 respectively. The anamorphic magnifications in 20x20, 10x10 and 4x4 scales are implemented using two toroidal mirrors in each optical path. In this paper, we present a complete tolerance analysis for the anamorphic stages and a compensation procedure to ensure the requirements of the system.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. In this paper, we present a complete stray light analysis of the HARMONI pre-optics including scattering from optical surface roughness and coatings, unwanted light from mechanical mounts and mechanisms, ghost reflections and scattering from particulate contaminants. Several solutions to reduce this unwanted light are proposed.
HARMONI is the first light, adaptive optics assisted, integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). A work-horse instrument, it provides the ELT’s diffraction limited spectroscopic capability across the near-infrared wavelength range. HARMONI will exploit the ELT’s unique combination of exquisite spatial resolution and enormous collecting area, enabling transformational science. The design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, and provide a summary of the instrument’s design. We also include recent changes to the project, both technical and programmatic, that have resulted from red-flag actions. Finally, we outline some of the simulated HARMONI observations currently being analyzed.
HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope (ELT). It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The IFS Pre-Optics (IPO), sub-system under the responsibility of the Institute of Astrophysics of the Canary Islands (IAC), contains 30 opto-mechanical mounts working at cryogenic temperatures and are classified into three types depending on the mirror shape: [1] - Sprung kinematic mount for flat mirrors: By spring loading, the mirror is constrained radially against a Vee-groove. - Thermally compensated kinematic sprung mount for power mirrors: It is similar to the previous mount but the radial pads compensate mirror radial movement. - Bonded mount for toroidal mirrors: The mirror is bonded to a rear invar pad, which serves as an interface to the support. This work describes the designs developed for the opto-mechanical modules of the Instrument IPO in order to comply with the sub-system requirements. We also present the prototypes developed to prove some of the adopted concepts in the design.
HARMONI is the first light visible and near-IR integral field spectrograph for the Extremely Large Telescope (ELT). This instrument covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. The Pre-Optics (sub-system under the responsibility of the IAC) contains five mechanisms working at cryogenic temperatures. Three types of mechanisms are needed to provide full functionality: wheels (2), turrets (2) and shutter (1). The wheels and turrets, supported by a series of radial and axial bearings, are driven by stepper motors through a system of gears that provide mechanical reduction. In addition, the focal plane mask wheel has a detent system to improve repeatability to within +/- 2.5 microns. Finally, the shutter consists in two masks with three clover shape blades mounted on a stepper motors. The work describes the main IPO mechanisms requirements and the design developed for every module. We also present some of the prototypes developed to proof the concepts adopted in the design..
This article summarizes the results of a system engineering approach to the design of a Transportable Optical Ground Station (TOGS) intended to be used for quantum key distribution in a number of scenarios. Key requirements are listed and a product breakdown is proposed, identifying parts, which are specific to a particular scenario and others, which are common to many of them, and thus will allow their implementation to be shared. We are proposing the use of Adaptive Optics (AO) for compensation of the effects of the atmospheric turbulence, in order to improve the efficiency of the signal coupling to a Single-Mode Fiber.
HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.
Inter-satellite and ground to satellite optical communications have been successfully demonstrated over more than a decade with several experiments, the most recent being NASA’s lunar mission Lunar Atmospheric Dust Environment Explorer (LADEE). The technology is in a mature stage that allows to consider optical communications as a high-capacity solution for future deep-space communications [1][2], where there is an increasing demand on downlink data rate to improve science return. To serve these deep-space missions, suitable optical ground stations (OGS) have to be developed providing large collecting areas. The design of such OGSs must face both technical and cost constraints in order to achieve an optimum implementation. To that end, different approaches have already been proposed and analyzed, namely, a large telescope based on a segmented primary mirror, telescope arrays, and even the combination of RF and optical receivers in modified versions of existing Deep-Space Network (DSN) antennas [3][4][5]. Array architectures have been proposed to relax some requirements, acting as one of the key drivers of the present study. The advantages offered by the array approach are attained at the expense of adding subsystems. Critical issues identified for each implementation include their inherent efficiency and losses, as well as its performance under high-background conditions, and the acquisition, pointing, tracking, and synchronization capabilities. It is worth noticing that, due to the photon-counting nature of detection, the system performance is not solely given by the signal-to-noise ratio parameter.
To start with the analysis, first the main implications of the deep space scenarios are summarized, since they are the driving requirements to establish the technical specifications for the large OGS. Next, both the main characteristics of the OGS and the potential configuration approaches are presented, getting deeper in key subsystems with strong impact in the performance. The different configurations are compared from the technical point of view, taking into account the effect of atmospheric conditions. Finally a very preliminary cost analysis for a large aperture OGS is presented.
This paper reviews the EDiFiSE (Equalized and Diffraction-limited Field Spectrograph Experiment) full-FPGA (Field Programmable Gate Array) adaptive optics (AO) system and presents its first laboratory results. EDiFiSE is a prototype equalized integral field unit (EIFU) spectrograph for the observation of high-contrast systems in the Willian Herschel Telescope (WHT). Its AO system comprises two independent parallel full-FPGA control loops, one for tip-tilt and one for higher order aberrations. Xilinx's Virtex-4 and Virtex-5 FPGA's fixed point arithmetic and their interfacing with the rest of the AO components and the user have been adequately dealt with, and a very deterministic system with a negligible computational delay has been obtained. The AO system has been recently integrated in laboratory and verified using the IACAT (IAC Atmosphere and Telescope) optical ground support equipment. Closed loop correction bandwidths of 65 Hz for the tip-tilt and 25 Hz for higher order aberrations are obtained. The system has been tested in the visible range for the WHT with a 9 x 9 subpupil configuration, low star magnitude, wind speeds up to 10 m/s and Fried parameter down to 18 cm, and a resolution below the EIFU’s fiber section has been obtained.
We develop an algorithm to retrieve mesospheric Na profiles from the ESO-IAC LGS experiment at Teide
Observatory (OT). We are using a bistatic configuration for Na LGS profiling between the ESO Wendelstein
LGS Unit (WLGSU) and the IAC80 telescope with a baseline of 126 m. We describe the geometry of the problem
and discuss the errors. The inputs are the observer pointing coordinates and the azimuth of the launcher, avoiding
the refraction effect on the beam. Accuracy in the coordinates is a must and the images should be astrometrized.
With an accuracy of 1" in the launcher azimuth, the absolute Na heights can be obtained with a resolution
better than 200 m (ZD=40°). We also propose a double observer telescope, 90° shifted, to avoid the effect of a
divergent solution when launching in the azimuth subtended between observer and launcher.
The paper describes the operations of ESA’s Optical Ground Station (OGS) during the Lunar Laser Communications
Demonstration (LLCD) experiment, performed in October and November 2013 with NASA’s Lunar Atmospheric and
Dust Environmental Explorer (LADEE) spacecraft. First the transmitter and receiver designs at the OGS telescope are
described, which are geometrically separated to prevent cross-talk. Problems encountered and the lesson learned will be
explained. As it turned the chosen arrangement was not sufficiently stable in terms of alignment and the paper will
describe the solution found. A new industrial contract has been placed for improvement of the design of two solutions
will be presented, which will both be tested in a follow-up laser communication campaign, scheduled for end March
2014.
EDIFISE is a technology demonstrator instrument developed at the Institute of Astrophysics of the Canary Islands
(IAC), intended to explore the feasibility of combining Adaptive Optics with attenuated optical fibers in order to obtain
high spatial resolution spectra at the surroundings of a star, as an alternative to coronagraphy. A simplified version with
only tip tilt correction has been tested at the OGS telescope in Observatorio del Teide (Canary islands, Spain) and a
complete version is intended to be tested at the OGS and at the WHT telescope in Observatorio del Roque de los
Muchachos, (Canary Islands, Spain).
This paper describes the FPGA-based real time control of the High Order unit, responsible of the computation of the
actuation values of a 97-actuactor deformable mirror (11x11) with the information provided by a configurable wavefront
sensor of up to 16x16 subpupils at 500 Hz (128x128 pixels). The reconfigurable logic hardware will allow both zonal
and modal control approaches, will full access to select which mode loops should be closed and with a number of
utilities for influence matrix and open loop response measurements. The system has been designed in a modular way to
allow for easy upgrade to faster frame rates (1500 Hz) and bigger wavefront sensors (240x240 pixels), accepting also
several interfaces from the WFS and towards the mirror driver.
The FPGA-based (Field Programmable Gate Array) real time controller provides bias and flat-fielding corrections,
subpupil slopes to modal matrix computation for up to 97 modes, independent servo loop controllers for each mode with
user control for independent loop opening or closing, mode to actuator matrix computation and non-common path
aberration correction capability. It also provides full housekeeping control via UPD/IP for matrix reloading and full
system data logging.
We present EDiFiSE, a prototype instrument for the observation of high-contrast systems, combining an adaptive
optics (AO) system and an equalized integral field unit (EIFU). The design of the AO system takes into account
the statistical behaviour of the atmospheric turbulence structure at the Canary Islands (Spain) astronomical
observatories: Roque de los Muchachos (ORM) on the island of La Palma and Teide observatory (OT) in
Tenerife. The AO will have the capability of adapting to the prevailing turbulence conditions; in this sense,
the EDiFiSE AO unit will be an 'adaptable' adaptive optics system. The corrected beam feeds an hexagonal
integral field unit formed by 331 micro-lenslets, which focus the intensity distribution at the focal plane into 331
optical fibers. The central seven fibers of the bundle include variable attenuators for the equalization of these
fibers output intensities, matching them to the dynamical range of the detector and reducing the optical cross
talk inside the spectrograph. This technique, called equalized integral field spectroscopy (Arribas, Mediavilla &
Fuensalida 19981), permits to obtain spectral and spatial information of the equalized object and its surroundings
as well as accurate relative photometry and astrometry.
Laser Guide Stars -LGS- has been widely proposed to extend the domain of stable operation for adaptive
optics systems in large telescopes. As LGS are formed in a finite distance, bistatic schemes with two or more
additional telescopes has been noted as the most efficient configuration from the point of view of full aperture
tip-tilt correction. In these schemes it is crucial to know the height of the LGS. In this sense, an adequate
characterization of the messopheric sodium layer is needed. Based on the experience acquired in a bistatic
instrumental setup to characterize the sodium layer over the Teide Observatory (Canary Islands), we describe
the general height equations and the accuracy required.
Real-time control has been clearly identified as a separate challenging field within Adaptive Optics, where a lot of computations have to be performed at kilohertz rate to properly actuate the mirror(s) before the input wavefront information has become obsolete. When considering giant telescopes, the number of guide stars, wavefront samples and actuators rises to a level where the amount of processing is far from being manageable by today's conventional processors and even from the expectations given by Moore's law for the next years. FPGA (Field Programmable Gate Arrays) technology has been proposed to overcome this problem by using its massively parallel nature and its superb speed. A complete laboratory test bench using only one FPGA was developed by our group [1], and now this paper summarizes the early results of a real telescope adaptive optics system based in the FPGA-only approach. The system has been installed in the OGS telescope at "Observatorio del Teide", Tenerife, Spain, showing that a complete system with 64 Shack-Hartmann microlenses and 37 actuators (plus tip-tilt mirror) can be implemented with a real time control completely contained within a Xilinx Virtex-4 LX25 FPGA. The wavefront sensor has been implemented using a PULNIX gigabit ethernet camera (714 frames per second), and an ANDOR IXON camera has been used for the
evaluation of the overall correcting behavior.
Since the European Space Agency (ESA) geostationary data-relay satellite ARTEMIS started its operation in February 2003, ESA and the Instituto de Astrofisica de Canarias (IAC) have carried out routinely bidirectional optical link experiments between ARTEMIS and the Optical Ground Station (OGS), installed in the Teide Observatory of the IAC in the Canary Islands, Spain. The experiments aimed at characterizing statically and dynamically the performance of the optical downlinks and uplinks in different atmospheric turbulence conditions, together with the development and testing of appropriate theoretical models to predict the link performance. An overview of the OGS and additional facilities on top the IAC Teide Observatory is given, as well as a summary of the statistical results on propagation and communication for different experimental configurations, including different number of transmitting subapertures and divergence in the uplink. Key parameters, like scintillation and fade and surge statistics, are correlated with theoretical predictions and an analysis of the far field pattern is included. The results of the deep space uplink experiments between the OGS and ESA satellite SMART-1 are also presented. Finally ESA free space optical communication programs are summarised, including optical payloads on board different satellites.
As a support for the experimental activities related to the operation of bi-directional optical links between the European Space Agency (ESA) ARTEMIS geostationary satellite and the Optical Ground Station (OGS) in Teide Observatory (Tenerife island, Canary Islands, Spain), carried out by ESA and Instituto de Astrofisica de Canarias (IAC), calculations on the behavior of a multi-beam ground-to-satellite link have been performed. The goal is to assess the impact of refractive turbulence on the uplink (deemed to be more critical than the downlink because of beam-wander effects) and the mitigation effect on the power fluctuations in the satellite receiver achievable with such a space diversity approach, that involves several mutually time-incoherent beams in the uplink. Results from the multiple-beam uplink model and comparison with experiments are presented.
FPGA (Field Programmable Gate Array) technology has become a very powerful tool available to the electronic designer, specially after the spreading of high quality synthesis and simulation software packages at very affordable prices. They also offer high physical integration levels and high speed, and eases the implementation of parallelism to obtain superb features. Adaptive optics for the next generation telescopes (50-100 m diameter) -or improved versions for existing ones- requires a huge amount of processing power that goes beyond the practical limits of today's processor capability, and perhaps tomorrow's, so FPGAs may become a viable approach. In order to evaluate the feasibility of such a system, a laboratory adaptive optical test bench has been developed, using only FPGAs in its closed loop processing chain. A Shack-Hartmann wavefront sensor has been implemented using a 955-image per second DALSA CA-D6 camera, and a 37-channel OKO mirror has been used for wavefront correcting. Results are presented and extrapolation of the behavior for large and extremely large telescopes is discussed.
The experimental study of sodium layer is relevant to fields such as adaptive optics, in particular for laser guide star generation. We have developed an instrument to make systematic measures of the most relevant parameters of the sodium layer above canarian observatories. The measurement provides information about sodium layer: the medium altitude, the columnal abundance, the density profile and temporal evolution. These observations are important to design the new generation of adaptive optic instruments. We present the experimental set-up, the first results of the experiment and the plans to conduct a statistical study in the future.
The European Space Agency has built an optical ground station sited at the Observatorio del Teide operated by the Instituto de Astrofísica de Canarias. This station, equipped with a 1m telescope, has a multipurpose configuration for in-orbit commissioning and checkout of laser communication payloads. Since November 2001, the bidirectional link with satellite ARTEMIS has been established in more than 80 successful sessions. In this paper, we analyze the influence of turbulence parameters on the performance of communications in the bidirectional ground to space laser communication experiments. The link performance observed in the satellite-to-ground channel showed average bit error rates of 1E-6 over long durations (20 minutes), however in some occasions BER's of at least 10-9 -10-10 over durations of 5 to 30 minutes were observed. The behavior of the Bit Error Rate measurements performed in different turbulence conditions is characterized.
The European Space Agency (ESA) geostationary data-relay satellite ARTEMIS started its operation in February 2003, after reaching its final position in the geostationary orbit. Since then, ESA and the Instituto de Astrofísica de Canarias (IAC) have carried out routinely bidirectional optical link experiments between ARTEMIS and the Optical Ground Station (OGS), installed in the Teide Observatory of the IAC in the Canary Islands, Spain. The main purpose of such experimental campaigns is to characterise and model the optical links performance from the propagation and communication points of view, under different atmospheric turbulence conditions. The statistical results presented in this paper cover the uplink and downlink performance, including scintillation, fade and surge statistics, intensity distributions and spectral analysis. The effect of using different number of transmitted beams and different divergences is also considered. Additionally, the results are correlated with the atmospheric turbulence conditions, in terms of profiles of the index of refraction structure constant, isoplanatic angle, seeing and wind profiles, measured in most of the cases simultaneously with the laser communication experiments
The European Space Agency (ESA) has built an optical ground station (OGS) for commissioning and checkout of its laser communication payloads in orbit. The first such payload is the laser communication terminal (LCT) onboard ARTEMIS, ESA's latest data-relay and telecommunication satellite in geostationary orbit. ARTEMIS is now routinely relaying Earth observation data sent via a similar LCT from the low-earth orbiting satellite SPOT-4 to a ground station in Toulouse. This paper focuses on bidirectional space to ground laser communication experiments, which have been performed between the OGS and ARTEMIS. ESA's interest in laser communication is first briefly explained, then the design of the ground and space terminals is introduced, the pointing, acquisition and tracking strategies are explained and a summary of all laser links performed so far is given. Experimental uplink and downlink results are presented in terms of temporal irradiance behavior and link statistics. The uplink irradiance behavior is investigated with changing number of transmit beams. Finally, ESA's future activities and upgrades planned for the OGS are discussed.
Optical acquisition, tracking and communication tests were performed between a Japanese laser communications terminal placed within the ESAs optical ground station at Tenerife, Spain and a European optical payload onboard the ARTEMIS satellite in geostationary earth orbit at 21.5° East. The optical communications tests at Tenerife were to verify the end-to-end optical characteristics such as intensity, sensitivity, wavelength, and polarization, as well as the modulation scheme of optical signals and acquisition sequences of the terminals under fairly good atmospheric conditions. The downlink's bit error rate was on the order of 10-10 in spite of atmospheric turbulence. Atmospheric turbulence induced signal fading increased the uplink bit error rate, the best value of which was 2.5x10-5. The Japanese laser communication terminal itself autonomously established and maintained the ground-to-satellite optical link with the ESA's optical payload from the beginning to the end of a 20-minute session. The test results show that the laser communication terminal which is to be launched with the Japanese OICETS satellite is optically compatible with the optical communications payload onboard the European ARTEMIS satellite.
The experimental study of laser beam propagation in turbulence is relevant to fields such as adaptive optics and optical communications. Turbulence sensing for astronomical purposes requires a convergent laser beam adequately focused on the sodium mesospheric layer. Free Optical communications ground-to-satellite usually are based on divergent laser beams travelling partially through the atmosphere. We present several measurements of the gaussian beam radius for divergent and convergent laser beams propagated in vertical paths. The determinations were carried out at the Teide Observatory (Canary Islands) from the analysis of Rayleigh scattering. The turbulence profile was simultaneously measured with a SCIntillation Detection And Ranging (SCIDAR) instrument. This way, we analyse the influence of the different turbulence layers in the focusing problem through the empirical relation between the beam waist radius and the intensity of the turbulence. We present the experimental set-up, the first results of the experiment and the plans to conduct a statistical study in the future.
The European Space Agency (ESA) has launched the geostationary data-relay satellite ARTEMIS with one of its payloads being a laser communication terminal (LCT). The LCT is used within the semiconductor-laser intersatellite link experiment (SILEX) to receive Earth observation data transmitted from a similar LCT onboard the SPOT-4 satellite. To support SILEX, ESA has also reached an agreement with the Instituto de Astrofisica de Canarias (JAC) to build the Optical Ground Station (OGS), in the Teide Observatory ofthe IAC. ARTEMIS and the OGS are an ideal and unique test-bed to study and characterise laser beam propagation through atmospheric turbulence. Theoretical models of laser beam propagation through atmospheric turbulence have been reviewed and developed, to predict the performance of the optical links from the propagation and communication point of view. Special effort has been invested in modelling the uplink effects. Optical link experiments have been planned in detail, to gather the necessary data required to be statistically representative, to compare the results with theoretical predictions and to validate and adjust the theoretical models. This comparison will pave the way towards the implementation of deep-space laser communication links. The first results ofthese experiments, presenting the theoretical models, analysing separately downlink and uplink measurements, and comparing the data with the theoretical predictions, are presented.
It is foreseen that Extremly large telescope (ELT) will include Adaptive Optics Systems to provide diffraction-limited images in the near infrared. The preliminary atmospheric turbulence properties which affects laser guide star (LGS) generation are presented here. The results of modern model developed in optical communication through atmosphere is used to evaluate LGS size for many different atmospheric situation, with the turbulence intensity concentrate to different heights. This introduce the focusing problem and requirements above the observatory where the adaptive optics system with a reference source will be install. In other case, focus a laser in the mesosphere is impossible in a generic place. In high altitude observatories this is possible, like in canarian observatories. We took 6 experimental turbulence profile to evaluate the beam radius with altitude. A mean value of 0.2 m are found for the diameter of mesospheric volume illuminated by the laser. This is small enough to create an useful LGS for adaptive optics proposes.
In the frame of the SILEX project, the European Space Agency (ESA) has put into orbit two Laser Communication Terminals, to establish an experimental free space optical communication link between a GEO satellite (ARTEMIS) and a LEO satellite (SPOT IV), to relay earth observation data. In order to perform In Orbit Testing (IOT) of these, and other, optical communications systems, ESA and the Instituto de Astrofisica de Canarias (IAC) reached an agreement for building the Optical Ground Station (OGS), in the Teide Observatory of the IAC. With ARTEMIS placed in a circular parking orbit at about 31000 kilometres, its optical payload has been preliminary tested with the OGS. First results and analysis are presented on the space-to-ground bi-directional link, including pointing acquisition and tracking performance, Bit-Error Rate (BER) and transmitted beam divergence effects related with atmospheric models and predictions. Future plans include deeper optical bi-directional communication tests of OGS, not only with ARTEMIS but also with OSCAR-40 (downlink) and SMART-1 (up-link) satellites, in order to do a full characterisation of the performances of laser beam propagation through atmospheric turbulence and a comparison with theoretical predictions.
KEYWORDS: Satellites, Optical communications, Data communications, Acquisition tracking and pointing, Space operations, Satellite communications, Observatories, Polarization, Signal attenuation, Scintillation
ESA and the Instituto de Astrofisica de Canarias (IAC) reached an agreemenet for building the Optical Ground Station (OGS), in the IAC Teide Observatory, in order to perform In Orbit Testing (IOT) of Optical Data Relay payloads onboard communication satellites, the first being ARTEMIS. During its recent launch, ARTEMIS was put into a degraded orbit due to a malfunction on the launcher's upper stage. ESA rapidly adopted a recovery strategy aimed to take the satellite to its nominal geostationary position. After completion of the first manoeuvres, ARTEMIS was successfully positioned in a circular parking orbit, at about 31,000 kilometers, and turned into full operation. In this orbit, its optical payload has been tested with the OGS, before establishing the link with SPOT IV. New tracking algorithms were developed at OGS control system in order to correct for ARTEMIS new orbit. The OGS has established a bi-directional link to ARTEMIS, behaving, seen from ARTEMIS, as a LEO terminal. Preliminary results are presented on the space-to- ground bi-directional link, including pointing acquisition and tracking (PAT) performance, received beam characterization and BER measurements.
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