PASTEL embarked on-board SPOT4, French LEO earth observation satellite, and OPALE mounted on-board ARTEMIS, European GEO telecommunication satellite are the key components of SILEX (Semi-conductor Inter-satellite Link Experiment) system. Launched in March 1998, PASTEL terminal was first verified via star tracking. Then, first SILEX optical communication was successfully performed in December 2001 with ARTEMIS at 31000 km. Following 12 months ARTEMIS orbit rising, SILEX commissioning phase was successfully achieved in spring 2003. Today, more than hundred successful optical communications have been achieved. On 1st of October 2003, the SILEX optical link was declared fully operational by the European and French space agencies. After a recall of SILEX architecture, design and onground verification, this paper reports on in-orbit results.
On December 5th, 2006, a laser link was for the first time established between an optical terminal on-board an aircraft flying at 9,000 m and the SILEX terminal on the Artemis geostationary satellite. This world first event was the result of the 3-year demonstration program LOLA performed by EADS Astrium for the arms procurement agency of the French Ministry of Defense (DGA) to investigate the feasibility of high data rate optical communications through the atmosphere. This first link was followed by a 6-month flight test campaign totalizing more than 50 successful communication sessions over 20 flights. The campaign allowed assessing the operational link performances (bit error rate before and after decoding, availability) in a variety of flight conditions (altitude and weather) and to correlate the model of optical propagation in the atmosphere. The test campaign was concluded by realtime data transmission offering HD video quality between the aircraft and the DGA stand at the Paris "Le Bourget" Air Show.<p> </p> In addition to the technical challenges common to instruments with sub-μrad pointing requirements (e.g. highly stable structures), optical communications set specific challenges on the optical design and on the detection chain. <li> </li>High level of isolation between emission and reception to handle the huge ratio (~109) between emitted and received laser power levels (~150 mW and 20 to 200 pW); <li> </li>Efficient straylight protection to communicate with the Sun down to 5 deg from the field of view; <li> </li>Accurate co-alignment between emission and reception directions
The LOLA program aims at characterising a 40.000 km optical link through the atmosphere between a high altitude aircraft and a geostationary platform. It opens a new area in the field of optical communications with moving platforms. A complete new optical terminal has been designed and manufactured for this program. The optical terminal architecture includes a specific pointing subsystem to acquire and stabilize the line of sight despite the induced vibrations from the aircraft and the moving pattern from the received laser signal. The optical configuration features a silicon carbide telescope and optical bench to ensure a high thermoelastic angular stability between receive and transmit beams. The communications subsystem includes fibered laser diodes developed in Europe and high performance avalanche photo detectors. Specific encoding patterns are used to maintain the performance of the link despite potential strong fading of the signal. A specific optical link model through the atmosphere has been developed and has been validated thanks to the optical link measurements performed between ARTEMIS and the Optical Ground Station located in the Canarian islands. This model will be used during the flight tests campaign that is to start this summer.
The Sentinel-2 program will provide a permanent record of comprehensive data to help inform the agricul-tural sector (utilisation, coverage), forestry industry (population, damage, forest fires), disaster control (management, early warning) and humanitarian relief programmes. Sentinel-2 will also be able to observe natural disasters such as floods, volcanic eruptions, subsidence and landslides. <p> </p>In the Sentinel-2 mission programme, Astrium in Friedrichshafen is responsible for the satellite’s system design and platform, as well as for satellite integration and testing. Astrium Toulouse will supply the Multi-Spectral imaging Instrument (MSI), and Astrium Spain will be in charge of the satellite’s structure and will produce its thermal equipment and cable harness. The industrial core team also comprises Jena Optronik (Germany), Boostec (France), Sener and GMV (Spain). Sentinel-2 is intended to image the Earth’s landmasses from its orbit for at least 7.25 years. In addition, its onboardresources will be designed so that the mission can be prolonged by an extra five years. From 2012 onwards, the 1.1-metric-ton satellite will circle the Earth in a sun-synchronous, polar orbit at an altitude of 786kilometres, fully covering the planet’s landmasses in just ten days. The multi-spectral instrument (MSI) will generate optical images in 13 spectral channels in the visible and shortwave infrared range down to a resolution of 10 metres with an image width of 290 kilometres. <p> </p>The instrument is composed of two main parts: <p> </p>• The telescope assembly , combining in one instrument both VNIR and SWIR channels, is mounted on the upper plate of the Bus <p> </p>• The Video and Compression Electronic Units mounted inside the Bus. <p> </p>This telescope is based on a Three Mirror Anastigmat optical concept. This three mirror optical combination is corrected from spherical aberration, coma and astigmatism. It provides a large field of view with very good optical quality. The telescope mirrors and structural baseplate are made of Silicon Carbide material in order to minimise thermo-elastic distortions. Isostatic mounts decouple the instrument from potential deformations of the platform upper plate. <p> </p>The optical beam is spectrally separated thanks to a dichroic filter towards two different focal planes with different detector technologies: Silicon is used for the VNIR domain whereas Mercury Cadmium Telluride is required for the SWIR spectral domain. The VNIR detector is a CMOS device. The SWIR detector is a hybridised component where the MCT photosensitive arrays are hybridised on top of a CMOS circuit. The separation of the individual spectral bands(10 spectral bands, for the VNIR detectors and 3 spectral bands for the SWIR detectors) is performed by specific strip filters mounted on top of the detectors. The telescope is thermally decoupled from the external environment and the platform thanks to a thermal enclosure. A calibration and shutter mechanism avoids direct sun incidence inside the telescope during launch, specific platform manoeuvres and safe mode. The video signals coming out of the VNIR and SWIR focal planes are digitised and compressed inside the Video and Electronic Units prior to be sent to the bus.
The MSI EM campaign has been conducted before releasing the flight model integration and test. This paper presents the MSI EM configuration and the various tests results. Experience gained through this extensive test program allowed securing the MSI PFM integration and test activities.
Proc. SPIE. 10563, International Conference on Space Optics — ICSO 2014
KEYWORDS: Staring arrays, Defense and security, Signal to noise ratio, Short wave infrared radiation, Sensors, Satellites, Multispectral imaging, Modulation transfer functions, Astronomical imaging, Polonium
The development and testing of the MSI PFM for the first Sentinel-2 satellite is now completely achieved, in particular tests and characterization of the VNIR FPA and of the whole instrument. This paper provides main results obtained for the 12 VNIR detection chains of the Sentinel-2 Multi-Spectral Instrument and highlights some of the most outstanding characteristics and performances achieved.
The Sentinel-2 multi-spectral instrument (MSI) will provide Earth imagery in the frame of the Global Monitoring for
Environment and Security (GMES) initiative which is a joint undertaking of the European Commission and the Agency.
MSI instrument, under Astrium SAS responsibility, is a push-broom spectro imager in 13 spectral channels in VNIR and
SWIR. The instrument radiometric calibration is based on in-flight calibration with sunlight through a quasi Lambertian
diffuser. The diffuser covers the full pupil and the full field of view of the instrument. The on-ground calibration of the
diffuser BRDF is mandatory to fulfil the in-flight performances.
The diffuser is a 779 x 278 mm<sup>2</sup> rectangular flat area in Zenith-A material. It is mounted on a motorised door in front of
the instrument optical system entrance. The diffuser manufacturing and calibration is under the Centre Spatial of Liege
The CSL has designed and built a completely remote controlled BRDF test bench able to handle large diffusers in their
mount. As the diffuser is calibrated directly in its mount with respect to a reference cube, the error budget is significantly
improved. The BRDF calibration is performed directly in MSI instrument spectral bands by using dedicated band-pass
filters (VNIR and SWIR up to 2200 nm). Absolute accuracy is better than 0.5% in VNIR spectral bands and 1% in SWIR
spectral bands. Performances were cross checked with other laboratories.
The first MSI diffuser for flight model was calibrated mid 2013 on CSL BRDF measurement bench. The calibration of
the diffuser consists mainly in thermal vacuum cycles, BRDF uniformity characterisation and BRDF angular
characterisation. The total amount of measurement for the first flight model diffuser corresponds to more than 17500
Performance results are discussed in comparison with requirements.
The MSI PFM campaign is built around 4 major steps : the focal planes alignment and testing, the telescope alignment
and testing, the instrument performance testing and the instrument environmental qualification.. This paper presents the
results of the first 3 steps covering major performance aspects of the Sentinel-2 Multi-Spectral Instrument.
2A and Sentinel-2B satellites currently under development will ensure systematic global acquisition of all land and
coastal waters in the visible and short-wave infrared spectral domain with a 5 day revisit time at the equator.
The Multi Spectral Instrument is a push-broom imager providing imagery in 13 spectral channels with spatial resolutions
ranging from 10 m to 60 m and a swath width of 290 Km, larger than SPOT and Landsat. The instrument features a full
field of view calibration device, a silicon carbide Three Mirror Anastigmat telescope with mirror dimensions up to 600
mm, specific filter stripe assemblies, newly developed Si-CMOS and HgCDTe detectors and a low noise wavelet
compression video electronics. The 1.4 Tbits/s raw image date rate is reduced down to 490 Mbits/s at the output of the
instrument to cope with the overall system transmission capability.
The Sentinel-2 program has entered in the CD phase in 2009. Launch of Sentinel-2A satellite is scheduled for 2013.
SILEX (Semi-Conductor Inter-satellite Link EXperiment) consists of one optical terminal on-board the French LEO observation satellite SPOT 4, and another on-board the European GEO telecommunication satellite ARTEMIS. While the first part of the SILEX verification plan had been oriented towards verification at equipment and subsystem levels, the final stages have mainly been devoted to terminal and system (terminals coupling effects) verification. During this final stage, a thermal vacuum test was conducted in a class 100- cleanliness environment with optical ground support equipment of outstanding performances. The obtained tests results, used to determine software compensations and verify optical and static pointing performances, have been entered into overall system simulation models to finalize flight performances budgets. In addition, systems tests were performed on each terminal with respective partner simulator to validate system simulation models and assess link performances and robustness and to verify communication bit error rate.