Front Matter for Volume 11180

The presentation slides for “Optics in ESA’s Earth Observation Program” are available at http://doi.org/10.1117/12.2535921, under the Supplemental Content tab.

The presentation slides for “Optics in Japan’s Space Missions – Mainly for Earth Observation” are available at http://doi.org/10.1117/12.2535922, under the Supplemental Content tab.

Sentinel-5/UVNS instrument is an Earth atmospheric monitoring spectrometer developed within the Copernicus program. The mission objective is to monitor the chemical composition of the Earth’s atmosphere on a daily basis. Airbus Defense and Space GmbH acts as the prime contractor for the instrument under a European Space Agency contract.

The current paper will focus on four themes. First it will provide a brief historical and technical overview of the Sentinel-5/UVNS instrument. Second, the key design drivers will be described. Third, the key optical technologies carried on board the instrument will be elaborated. Finally, the paper concludes with a short look at the current state of the instrument’s development cycle.

Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space as prime contractor under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate applications. This paper gives an overview of the Sentinel-4 system architecture, its design & development status.

The Infrared Atmospheric Sounding Interferometer New Generation (IASI-NG) is a key payload element of the second generation of European meteorological polar-orbit satellites (METOP-SG) dedicated to operational meteorology, oceanography, atmospheric chemistry, and climate monitoring.

It will continue and improve the IASI mission in the next decades (2020-2040) in the field of operational meteorology, climate monitoring, and characterization of atmospheric composition related to climate, atmospheric chemistry and environment. The performance objective is mainly a spectral resolution and a radiometric error divided by two compared with the IASI first generation ones.

The measurement technique is based on wide field Fourier Transform Spectrometer (operating in the 3.5 - 15.5 μm spectral range) based on an innovative Mertz compensated interferometer to manage the so-called self-apodisation effect and the associated spectral resolution degradation.

We present here the design of the instrument, the development status of the main units, critical technologies and subsystems and the first test results performed on engineering models.

The Environmental Mapping and Analysis Program (EnMAP) is a German spaceborne science mission that aims at characterizing the Earth’s environment on a global scale. The single payload of the satellite is the hyperspectral imager (HSI). It is capable of measuring the solar radiance reflected from the Earth’s surface as a continuous spectrum in the spectral range of 420nm to 2450nm, with a spectral sampling of 6.5nm (VNIR) and 10nm (SWIR). The EnMAP on ground swath of 30km is sampled with 30m.

The instrument features a telescope with a 18cm aperture. A double-slit splits the field of view into the two separate fields for VNIR and SWIR. Two spectrometers disperse the light using large, curved prisms and collect the light in an Offner configuration onto the VNIR and the SWIR detector. In addition, the instrument features calibration capabilities using a deployable, full aperture solar diffuser in front of the telescope and on-board calibration sources that can be fed into the spectrometers. The instruments demanding requirements on thermal stability are covered by an active thermal control of the whole instrument using loop-heat pipes.

In this proceeding, we give a short overview on the design, application and current integration status of the mission, which is currently in Phase D. The focus is on the important steps recently accomplished or currently ongoing, specific on the:

• completion of the telescope setup

• assembly of the spectrometers with the optical components of both spectrometer paths already in place, aligned and successfully characterized

• setup and characterization of the on-board calibration source OBCA

• integration of the calibration chain including the above mentioned OBCA into the spectrometer

• implementation of the first of the two front end devices, the VNIR camera and the SWIR camera

• assembly of the platform

The present situation suggests an EnMAP launch by the end of 2020.

Thales Alenia Space has been involved in the design and the development of space observation instruments for over 40 years. This paper will explain why active optics is needed for next generation of instruments for Earth observation. We will also describe what kind of solution is preferred and why. We will give an overview of the development status on the associated technologies. Indeed, the future missions will have to deal with better performance, better optical quality while from manufacturing point of view, the total mass, the development schedule and the final cost have to be reduced. These constraints induce a new generation of solutions based on large entrance optics associated to high lightweight ratio which naturally provide solutions sensitive to gravity deformation. In these conditions, the enhancement of the final performance can only be guaranteed by using active optics in flight. A deformable mirror is therefore foreseen to be implemented in future large telescopes in order to correct manufacturing residues, ground/flight evolution including gravity. Moreover, low mass and low cost require more compact designs which entail solutions more sensitive to misalignment. An active positioning mechanism is then also needed in order to correct the telescope alignment during operation conditions. Thales Alenia Space has been selected by CNES to develop and qualify active optics building blocks and then to test and demonstrate the improvement that new active technologies can bring in a full size instrument representative of the next generation of observation instruments. An overview of the current development status and the achievable performances is given.

The multi-billion dollar Earth observation applications market continues to demand better spatial and temporal resolution; simply put, this means bigger apertures and more satellites. This paper describes a novel deployable telescope that addresses the market needs for a <1m GSD imager in a small launch volume. This system will allow many identical satellites to be launched into a constellation from a single launch vehicle, providing a low-cost solution to rapid-revisit high resolution imaging requirements. Alternatively, two or three satellites could be launched in a dedicated small satellite launch vehicle, where previously only one would have fit.

Surrey Satellite Technology Ltd. (SSTL) has already demonstrated low-cost 1m GSD imagery from the Carbonite-2 platform, but the deployable telescope solution presented here provides the opportunity to build on this capability by significantly improving revisit time, without the typical increase in cost.

SSTL is developing, alongside the Surrey Space Centre (SSC) and the Dynamic Optics and Photonics Group at the University of Oxford, a telescopic deployable structure and a fine alignment system to align the Cassegrain-type telescope in-orbit. The three-concentric barrel deployable structure and mechanisms are discussed including the associated requirements and trade-off study that led to this design.

The dynamic nature of this system exacerbates traditional optical challenges such as alignment and stray light control; solutions to these are proposed, the optical design rationale is explained and predicted imaging performance shown. The novel autonomous fine alignment system, both algorithms and mechanisms, is presented. The last section deals with the spacecraft level implications and accommodation. Then finally the constellation level system design is shown with regards to the launch vehicle options and orbit configuration for coverage optimization; both global and target-specific.

Deployable optics can bring major cost reductions to the field of Earth Observation. One of the key challenges in the development of a deployable optical system, however, is making sure that it can meet its performance targets following its deployment. In this paper, a novel active correction system for a deployable telescope is described. The correction system co-aligns and phases the primary mirror segments and subsequently corrects remaining aberrations using a deformable mirror. A novel phasing sensor called PistonCam can bring telescope segments into phase while the telescope is staring at extended scenes. By only sampling segment boundaries, PistonCam is able to isolate piston and tip/tilt errors which allows the errors to be corrected more effectively. After phasing process has been completed, a moving scene sharpness optimization technique is used to correct the remaining aberrations with a deformable mirror, The technique does not require a constant scene, unlike existing sharpness optimization techniques. As such, the telescope does not need to track a ground scene during the correction process. The technique can also be used for continuous correction of telescope deformations. The active optics system offers robust aberration correction, is computationally inexpensive and requires limited additional optical hardware.

The urgent need for the precise, real-time position metrology between the optical components in a modern space camera is becoming more critical with the increased resolution, aperture, focal length, and light-weighted structure. Gravity offload, composite material humidity desorption, temperature cyclical variation with the illumination, and micro-vibration on platform would introduce unpredictable affect to decrease the imaging quality. The solution of the optical system disorders would mainly rely on the ground-based stimulation and on that basis, active optics compensation, which could not be accurate. This influence expands within the opto-mechanical structure complexity. This paper represents an implement solution for position and attitude metrology used for on-orbit real-time measurement. To deal with the contradiction of system accuracy and simplicity, we simplified the system to a measurement model equivalent to 6 degree of freedom Stewart Platform structure. The works on this paper tightly coupled to the accuracy requirement of a long focal length optical system. After carefully compare the systematic requirement and balance the implementation costs, we applied the common-path, multi-channel heterodyne interferometers to accomplish the large-scaled coarse measurement for the step disturbance and small-range fine measurement to sense the ambient vibration. The metrology accuracy analysis and error evaluation indicated an effectiveness of this metrology system, which met the requirement of our given optical system. It was indicated in this paper that the metrology method could be generalized in other optical systems and similar long focal length optical systems in the future.

Within the European Space Agency (ESA) activity “Gravitational Wave Observatory Metrology Laser” we designed a laser head to fulfill the LISA laser requirements using a non-NPRO seed laser technology: an external cavity diode laser (ECDL) with resonant optical feedback from an external cavity as master oscillator for further linewidth narrowing. Furthermore, our design features a single-stage fiber amplifier with an amplification factor of about 20 dB. This paper covers the requirements on the laser source for LISA, the design and first results of performance characterization of the laser head breadboard.

The Laser Interferometer Space Antenna (LISA), with its extreme distance measurement requirements (pm over arm lengths of 2.5 million km), imposes many stringent requirements on the laser systems used for the distance metrological measurements. In particular, frequency and power stability, sideband phase noise, and frequency reproducibility, the need of manufacturing multiple laser systems and extremely challenging lifetime (extended mission duration of 12.5 years) which demand a streamlined laser design and a particular attention to reliability and procurement strategy, all pose a significant challenge. The main requirements will be presented and analysed. Some preliminary strategies as it pertains to procurement and lot screening shall also be approached.

The current configuration and break-down of the future on-board laser systems shall be provided detailing in particular the critical interfaces.

Existing space heritage hardware (such as the LISA Pathfinder Master Oscillator) and new specialized developments are under study in both Europe and the US. European industry is developing custom Power Amplifiers to reach the end-of-life requirement of 2W (in Continuous Wave operation). In parallel alterative possible sources for a back-up Master Oscillator are also being investigated, based on off the shelf components and proprietary technologies. An overview of the development strategy shall be presented as well as some details on the specific hardware.

NASA Goddard Space Flight Center is developing a master oscillator power amplifier (MOPA) laser transmitter for the ESA-led Laser Interferometer Space Antenna (LISA) mission. Taking advantage of our space laser experience and the emerging telecom laser technology, we are developing a full laser system for the LISA mission. Our research effort has included both master oscillator (MO) and power amplifier (PA) developments, and their environmental testing and reliability for space flight. Our current baseline for the MO is a low-mass, compact micro non-planar ring oscillator (m- NPRO) laser. The amplifier uses a robust mechanical design based on fiber components. We have performed laser system noise tests by amplitude- and frequency-stabilizing the PA output. We will describe our progress and plans to demonstrate a TRL 6 laser system, which is an essential step toward qualifying lasers for space applications, by 2021.

In this work the first diode-pumped Alexandrite ring laser in Q-switched single-longitudinal mode (SLM) operation is presented. A carefully designed and complex ring resonator with several functional components is combined with an innovative pumping scheme with high-power red laser diodes.

The spectral and energetic suitability of a first laser was demonstrated in hundreds of operating hours and, with a novel mobile lidar system, by the first measurements in the atmosphere by means of a diode-pumped Alexandrite laser, yielding data from the stratosphere to the mesosphere.

An improved laser yields a pulse energy of 1.7 mJ at a repetition rate of 500 Hz with an excellent beam quality of M² < 1.1. By seeding the resonator with a narrow-band diode laser, SLM operation with a linewidth below 4 MHz is achieved. The electro-optical efficiency of 2 % is the highest archived for all Alexandrite lasers in SLM operation and reasonable for space-operation.

The performance analysis as well as benchmarking with the space-qualified mounting technology point out the TRL and the remaining effort of development of the technology.

ESA's Telecommunications and Integrated Applications Directorate (TIA) runs a dedicated programmatic framework to Optical Communication Technologies, called ARTES ScyLight (SeCure and Laser communication Technology, pronounced "skylight").

ScyLight supports the development and deployment of innovative optical technologies for satellite communication as well as assisting industry to develop new market opportunities for optical communication technologies.

The ScyLight programme focuses the efforts of European and Canadian industry on optical communication technologies in the following areas:

•Optical Communication Technology at System Level

•Optical Communication Terminal Technology

•Intra-Satellite Photonics/Optical Payloads

•Quantum Cryptography Technologies in Space and initial services demonstration

The paper will give an overview of the programme status and an outlook on its evolution.

The paper will inform about the status of a new proposed ESA project on optical communications called “High thRoughput Optical Network” (HydRON), which aims to demonstrate European and Canadian capabilities in all fields of optical communications and with the seamless integration into terrestrial network structures, via a dedicated mission.

The Laser-Enhanced Mission Communications Navigation and Operational Services (LEMNOS) office at Goddard Space Flight Center (GSFC) manages two NASA optical communication related projects, the Orion EM-2 Optical Communications Terminal (O2O) and the Integrated Laser Communications Relay Demonstration (LCRD) Low-Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) projects. The main goal of LEMNOS is the advancement and implementation of optical communications systems and technologies for NASA missions. The O2O mission is sponsored by NASA’s Human Exploration and Operations (HEO) Mission Directorate. The O2O project will provide optical communications capability to the Orion series of spacecraft, starting with the demonstration of operational utility on EM-2. It will be the first time a human exploration mission will rely on optical communications for its high-bandwidth link. ILLUMA-T is sponsored by the Space Communications and Navigation (SCaN) Program Office. It is destined for the International Space Station (ISS) as an external payload attached to the Japanese Experiment Module - Exposed Facility (JEM-EF). The ILLUMA-T project is developing an optical communications user terminal to demonstrate high bandwidth data transfer between LEO and the ground through the geosynchronous LCRD relay. ILLUMA-T will be the first demonstration of a LEO user of the LCRD system, pointing and tracking from a moving spacecraft at LEO to GEO satellite and vice versa, end-to-end operational utility of optical communications, and 51 Mbps forward link to ISS from ground. Both projects are collaborations between GSFC, Massachusetts Institute of Technology – Lincoln Laboratory (MIT-LL), and a number of contractors.

Optical satellite downlinks have gained increasing attention throughout the last years. Especially for the application of optical satellite downlinks, DLR's Institute of Communications and Navigation is developing a number of payloads for various satellites. Within the OSIRIS program, DLR develops experimental optical terminals and systems which are optimized for small satellites.

This presentation will give an update on DLR's existing payloads (i.e. on the satellites Flying Laptop and BIROS, which have been launched in 2017 and 2016, respectively). First results will be presented. Furthermore, an outlook to planned missions will be given. This includes OSIRIS4Cubesat, which is planned for launch in Q4/2018, and OSIRISv3, which will be installed at the Airbus DS Bartolomeo platform aboard the ISS in 2019.

In this presentation, we discuss the first demonstration of a lasercom downlink from a LEO 1.5U 2.3 kg CubeSat to our optical ground station at The Aerospace Corporation in El Segundo, CA. Two vehicles, AC7-B&C, built under NASA’s Optical Communications and Sensors Demonstration (OCSD) program and described in previous presentations, were launched in November 2017 and placed in a 450-km circular orbit. Following on-orbit checkouts and preliminary pointing calibration utilizing on-board star trackers, we have demonstrated (at the time of this manuscript submission) communications links up to 100 Mbps with bit error rates near 10-6 without any forward error correction. Further optimization of the vehicle pointing and detection electronics and operating the transmitter at its full power capacity should enable performance improvements and potential for higher data rates.

Optical communications will complement radio frequency (RF) communications in the coming decades to enhance throughput, power efficiency and link security of satellite communication links. To enable optical communications technology for intersatellite links and (bi-directional) ground to satellite links, TNO develops a suite of technologies in collaboration with industry, which comprises of terminals with different aperture sizes, coarse pointing assemblies and fast steering mirrors. This paper presents the current state of the development of TNO technology for optical space communications. It mainly focuses on the development of an optical head with an entrance aperture of 70 mm, an optical bench for CubeSats and coarse pointing assemblies (CPAs). By continuing these steps, world wide web based on satellite communications will come closer.

We have developed a 6 dm³-sized optical instrument to characterize the microphysical properties of fine particulate matter or aerosol in the Earth atmosphere from low Earth orbit. Our instrument can provide detailed and worldwide knowledge of aerosol amount, type and properties. This is important for climate and ecosystem science and human health [1, 2]. Therefore, NASA, ESA and the European Commission study the application of aerosol instruments for planned or future missions. We distinguish molecular Rayleigh scattering from aerosol Mie-type scattering by analyzing multi-angle observations of radiance and the polarization state of sun light that is scattered in the Earth atmosphere [3]. We measure across the visible wavelength spectrum and in five distinct viewing angles between -50° and +50°. Such analysis has been traditionally done by rotating polarizers and band-filters in front of an Earth observing wide-angle imager. In contrast, we adopt a means to map the linear polarization state on the spectrum using passive optical components [4]. Thereby we can characterize the full linear polarization state for a scene instantaneously. This improves the polarimetric accuracy, which is critical for aerosol characterization, enabling us to distinguish for example anthropogenic from natural aerosol types. Moreover, the absence of moving parts simplifies the instrument, and makes it more robust and reliable. We have demonstrated this method in an airborne instrument called SPEX airborne [5, 6] in the recent ACEPOL campaign together with a suite of state-of-the art and innovative active and passive aerosol sensors on the NASA ER-2 high-altitude research platform [7]. An earlier report on the SPEX development roadmap was given in [8]. In this contribution we introduce SPEXone, a compact space instrument that has a new telescope that projects the five viewing angles onto a single polarization modulation unit and the subsequent reflective spectrometer. The novel telescope allows the observation of five scenes with one spectrometer, hence the name. We describe the optical layout of the telescope, polarization modulation optics, and spectrometer and discuss the manufacturability and tolerances involved. We will also discuss the modelled instrument performance and show preliminary results from optical breadboards of the telescope and polarization modulation optics. With SPEXone we present a strong and new tool for climate research and air quality monitoring. It can be used to study the effect of atmospheric aerosol on the heating/cooling of the Earth and on air quality. Also, SPEXone can improve the accuracy of satellite measurements of greenhouse gas concentrations and ocean color that rely on molecular absorption of reflected sunlight by providing detailed knowledge of the aerosol properties, required to accurately trace the light path in presence of scattering.
SPEXone is developed in a partnership between SRON Netherlands Institute for Space Research and Airbus Defence and Space Netherlands with support from the Netherlands Organisation for Applied Scientific Research (TNO) as a Dutch contribution to the NASA PACE observatory launching in 2022.

Responding to plans of the European Commission for extending the observation capabilities of the Copernicus programme, the European Space Agency (ESA) has initiated Phase A industrial (technical feasibility) studies for several new space-borne Earth Observation missions. High priority is given to a constellation of LEO satellites in Sunsynchronous orbit with the purpose of observing anthropogenic carbon dioxide (CO₂) emissions [European Commission, 2017]. The observing system shall acquire images of CO₂ concentration in terms of dry air column-averaged mole fractions (XCO₂), providing complete global land coverage at high spatial resolution (4 km²) within five days. The demanding requirements call for a payload comprising a combination of multiple instruments, which perform simultaneous measurements. The XCO2 is inferred from reflectance measurements in the Near-Infrared (NIR) and Short-Wave Infrared spectral regions (SWIR). This requires at least three spatially co-registered push-broom imaging spectrometers, measuring spectral radiance and solar irradiance in the NIR (747-773 nm), SWIR-1 (1595-1675 nm) and SWIR-2 (1990-2095 nm) at moderate spectral resolving power (R~5000-7000). In addition, the observations for CO₂ concentration will be complemented by Differential Optical Absorption Spectroscopy (DOAS) measurements of nitrogen dioxide (NO₂) over the same area. The NO₂ measurements in the visible region (400-500 nm) are expected to serve as a tracer for plumes of high CO₂ concentration resulting from high temperature combustion, which will facilitate plume identification and mapping. The third component of the payload is a multiple-angle polarimeter (MAP), performing high-precision measurements of aerosol (and cloud) properties. Its measurements of polarized radiance under various observation angles are expected to reduce XCO₂ bias error and significantly increase the yield of useful retrievals from the NIR and SWIR spectra. The complex observation architecture, involving multiple instruments and platforms, call for optimized observational requirements, driven by the primary goal of detecting and quantifying point-sources of greenhouse gas emissions. In particular, high single-sounding precision is essential for identifying plumes of elevated CO₂ concentration from instantaneous image acquisitions without regional and temporal averaging. This translates into stringent requirements for Signal-to-noise ratio (SNR), as well as spatial co-registration and spectral stability, which drive the instrument design. The presentation will introduce the different elements of the candidate Copernicus mission, in view of the ambitious mission goals. The payload components and observation requirements are addressed with special emphasis on the derivation of the SNR and spectral resolution requirements, which determine the instrument sizing.

High accuracy multi-angle polarimetry is of crucial importance for remote sensing of aerosol and cloud properties with accuracies demanded by climate and air quality studies. In this contribution, we provide an detailed description of the multi-angle spectro-polarimetric instrument “SPEX airborne” that was developed to operate from NASA’s high altitude research aircraft ER-2. SPEX airborne delivers measurements of radiance and linear polarization at nine fixed viewports with angles equally distributed over at total angular range of 112°, at visual wavelength in the range 400-760nm. Each viewport acts as a pushbroom spectrometer with a swath of 6°. SPEX airborne participated in the recent the ACEPOL campaign in October-November 2017 when it flew together with NASA’s Research Scanning Polarimeter (RSP), the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), and the Airborne Hyper-Angular Rainbow Polarimeter (AirHARP). We compare polarimetric and radiometric measurements from SPEX airborne with those collected by RSP at four visible wavelength bands. Simultaneous measurements were made while flying over widely different scenes, under different illumination and meteorological conditions. This provided a large dynamic range in radiometric and polarimetric values. We find that the Degree of Linear Polarization (DoLP) measured by both instruments agrees well with a RMS differences of ~0.005 as the best result for 555nm. For radiance measurements excellent agreement is obtained with a RMS difference of ~4%. The in-flight comparison results provide verification of SPEX airborne’s capability to deliver high-quality data.

The DLR Earth Sensing Imaging Spectrometer (DESIS) is a space-based hyperspectral instrument developed by Deutsches Zentrum für Luft- und Raumfahrt (DLR). The optical system of the spectrometer was fabricated and prealigned by the Fraunhofer-Institut für Angewandte Optik und Feinmechanik (IOF).

The paper describes the manufacturing, integration, and testing of this optical system. It was realized as an all reflective system using metal-based mirrors and a modular, so-called snap-together approach, which allows to simplify the integration of optical systems considerably. Measured r.m.s. wavefront errors of the complete system are in the range of 63 nm to 120 nm, which is compliant with the instrument’s requirements.

The introduction of freefrom optical surfaces in a space instrument offers the possibility to improve its performance, its volume and weight or a combination of both. This is shown to be valid for either imaging systems or spectroscopic systems. At Safran Reosc we master freeform robotic polishing technology since more than 25 years and we will show how we continue to improve it in term of quality, productivity and adequacy to ceramic materials like Silicon Carbide. Surprisingly, the conservative space industry evolved slowly from spherical to rotationnally symmetric aspherical and off-axis optics during the last decades. This is no more valid today and we are proud to contribute to MicroCarb and IASI NG, two recent innovative projects taking benefit of such freeform optics designs enabling more cost-effective advanced missions. These projects will be briefly presented with their status of progess of work at the company. We will also take this opportunity to present our work on the extreme off-axis optics used within the MERLIN lidar project, produced with the same freeform technology.

The purpose of this work is to develop a low-cost space telescope for Earth remote sensing that could be housed in a 12U CubeSat with a GSD of 25 meters at LWIR. It will be used the Three Mirror Anastigmatic concept and Commercial Off- The-Shelf components whenever it is possible.

The telescope main mission is the oil spill detection, mainly in ocean environment. Beyond the obvious functionality of this main mission, the oil spill detection can be very useful to detect crashed aircrafts in the ocean.

As secondary missions, this telescope can be used to map deforestation, finding lost ships in the ocean and help the drug smuggling by finding camouflaged man-made objects.

The Project current stage consists in preliminaries optical and mechanical projects in which the mirrors follow ITAR regulation.

The telescope will operate in LWIR frequencies and will extract polarization information from the target.

The preliminary optical project indicates that the telescope optical performance has Modulation Transfer Function greater than 45% at Nyquist frequency, native GSD of 25 meters and that the telescope is diffraction limited (wavefront error of 0.012 wavelengths and Strehl ratio of 99.38%).

The preliminary mechanical project indicates that the maximum deflection caused by gravity induces to a despicable error (smaller than one over one hundred and forty) when compared to the mean wavelength of operation.

The preliminary radiometric analyses indicates that the telescope has a NETD of 0.90 K.

A 1-m aperture optical telescope is planned for a future Japanese solar mission. The telescope is designed to provide high spatial resolution data of solar lower atmosphere from the photosphere to the uppermost chromosphere with enhanced spectroscopic and spectro-polarimetric capabilities covering a wide wavelength region from UV to near IR where many useful spectral lines and continua exist for physical diagnosis of the solar magnetized atmosphere. We designed an allreflective telescope to fulfill the scientific and engineering requirements. From a thermal view point, a Gregorian telescope is the most suitable. To avoid chromatic aberration, a tri-aspheric-mirror collimator coupling to the Gregorian was designed to give a diffraction-limited performance over the FOV by allowing a field curvature. The field curvature can be compensated by an off-axis Ritchey Chretien reimaging optics at an entrance of focal plane instrument, which has an opposite sign in the field curvature to the Gregorian. We also briefly studied structural design of all-reflective 1-m aperture solar optical telescope for the space solar mission.

The large-caliber light-weight reflector assembly is the core optical component of the large-size space camera. It needs to be highly light-weight to meet the constraint of emission weight. At the same time, the on-orbit reflector assembly needs to have extremely high force and thermal stability, be able to withstand the changes in the in-orbit temperature environment and the resulting stress changes and maintain the profile quality. This paper introduces the development of 1.3m caliber space mirror module. The reflector adopts the uniform thickness back arc design and the positioning support adopts the six-bar Bipod support technology. The simulation analysis verifies that the reflector component has good force and heat stability. The optical axis vertical test is carried out on the surface of the reflector assembly which has been processed and adjusted. The test results are consistent with the mechanical analysis results of the reflector assembly under the condition of gravity field, which meets the technical requirements of the spatial reflector.

We report on a compact optical frequency standard (OFS) based on a Telecom laser diode operating at ~ 1542 nm, frequency stabilized to a narrow iodine transition located in the green range of the visible domain (~514 nm), after a highly efficient frequency tripling process. We use two cascaded waveguide Lithium Niobate nonlinear crystals for the third harmonic generation process (THG), resulting in a harmonic power of 300 mW in the green range (@3ω) using 800 mW of infrared power (@ω ). This result corresponds to an optical conversion efficiency Pω/Pω 36 % which is -to our knowledge- the best result ever reported for a third harmonic process in continuous wave regime (CW). This process uses only 20 W of total consumption power, which can be drastically reduced, knowing that less than 10% of that green power level is needed for the iodine Doppler free spectroscopy, and consequently for the frequency stabilization purpose. We have already demonstrated a frequency stability of 2.9 x10^-14 τ^-1/2 conferred to a laser diode operating at ~ 1542 nm, using the a1 hyperfine component of the R34 [44-0] located at ~ 514 nm. This corresponds to an amplitude spectral density of the residual frequency fluctuations < 10 Hz/√Hz.

We plan to extend this approach to set up a new OFS by using a narrow linewidth fiber-laser emitting at ~1597 nm, which will be used for the phase-locking of a 1064 nm laser. Thus, this OFS, compact and mainly fibered, will perform the same role as that of a rigid optical cavity, widely used to stabilize 1064 nm lasers, involved in various terrestrial applications or space missions. The compact design of the whole setup will make it easily transportable to different sites and could be readily used as an ultra-stable frequency reference.

Many of the high accuracy Earth science survey missions are planned to use laser-based remote sensing instruments. The 2-μm laser wavelength is of particular interest due to the presence of many CO₂ and H₂0 absorption lines in its vicinity¹. Transmitter architectures are typically composed of an optically pumped, frequency-stable, solid-state seed laser and a high-power optical amplifier.^{2, 3} Taking advantage of the reliability and relative simplicity of semiconductor lasers, this architecture can substantially improve by replacing the solid-state light source with semiconductor lasers of comparable performance. This approach will greatly improve the system reliability, and will simplify instrument integration and space qualification. There are currently very limited semiconductor lasers operating in the 2-μm range with performance satisfactory enough for use as an injection seed in a laser absorption spectrometer. Optimally, seed lasers producing greater than 50 mW of continuous-wave (CW), with frequency jitter of less than 1 MHz are desired to reliably resolve the CO₂ absorption lines near 2-μm. In this paper, we report the demonstration of high-power, single-longitudinal-mode laterally coupled distributed feedback (LC-DFB) lasers at 2.05 μm wavelength. We measured more than 80 mW of CW power at -10 ºC for devices with a 4-μm-wide ridge and 2-mm-long cavity.

We have developed the frequency-stabilized lasers for gravitational wave detector DECIGO, whose short-term and long-term frequency stability is required to be df/f=10^-15 level with the high output power of 10 W. The short- and long-term frequency stability is realized by using frequency reference of an iodine absorption signal at 515 nm. We made two Breadboard models to evaluate the frequency stability of the laser. The short-term frequency stability is improved to 30 Hz/√Hz at 1 Hz by suppressing the intensity noise of the laser at modulation frequency of 200 kHz, and long-term frequency stability also improved by suppressing residual amplitude modulation (RAM). For increasing the output power with keeping its frequency stability, a 2-stage cascade fiber amplifier has been developed. In the current presentation, we report the status of our frequency stabilized lasers and the schematic of its higher power unit.

The emergence of quantum technologies, including cold atom based accelerometers, offers an opportunity to improve the performances of space geodesy missions. In this context, CNES initiated an assessment study called GRICE (GRadiométrie à Interféromètres quantiques Corrélés pour l’Espace) in order to evaluate the impact of cold atom technologies to space geodesy and to the end users of the geodetic data. In this paper, we present a specific mission scenario for gravity field mapping based on a twin satellite concept. The mission uses a constellation of two satellites each equipped with a cold atom accelerometer. A laser link measures the distance between the two satellites and couples these two instruments in order to produce a correlated differential acceleration measurement. The main parameters, determining the performances of the payload, have been investigated. In addition, a preliminary study of mass, consumption and volume has been conducted to ensure the onboard feasibility of these instruments. A general study of the satellite architecture, including all the subsystems, has also been realized and is presented here.

The Public-Private-Partnership between ESA and Airbus Defense and Space (Germany) has created the European Data Relay System (EDRS), which is operational since 2016.

The joint teams are running the Phase B of the globalisation of the European Data Relay System (EDRS) with an addition to the programme called EDRS Global (former GlobeNet).

EDRS Global is planning to increase the capacity of EDRS by adding a geostationary data relay payload, called EDRSD, over the Asia-Pacific region – in cooperation with Airbus DS partner JSAT (Japan). The heart of the system will be multiple laser terminals, based on TESATs upgraded design, featuring also a dual wavelength capability (1064 nm and 1550 nm) to serve more customers at the same time. The 1550 nm capabilities will be implemented in a cooperation between Airbus and TESAT (Germany), and NEC (Japan).

The evolution of the service will also aim for security sensitive user missions, including RPAS missions. The Laser Communication Technology on-board EDRS-D will be the starting point for the world’s first global laser based network in space, providing Global Secure Quasi-Real- Time-Services at Gigabit per second speed back to Europe by connecting its EDRS GEO nodes (EDRS-A/-C and EDRS-D) over 80,000 km distance by the means of optical communication.

The paper will provide details of the project and information about the latest status.

The CubeSat Laser Infrared CrosslinK mission is a joint Massachusetts Institute of Technology (MIT), University of Florida (UF), and NASA Ames Research Center effort to develop laser communications (lasercom) transceivers. The terminals demonstrate full-duplex intersatellite communications and ranging capability using commercial components to enable future large constellations or swarms of nanosatellites as coordinated distributed sensor systems.

CLICK will demonstrate a crosslink between two CubeSats that each host a < 2U lasercom payload. Range control is achieved using differential drag in Low Earth Orbit (LEO), with attitude controlled using a three-axis reaction wheel assembly and attitude sensors, including star trackers.

The lasercom terminals are direct-detect and rate scalable, designed to achieve a 20 Mbps crosslink at ranges from 25 km to 580 km and operate full-duplex at 1537 nm and 1563 nm with 200 mW of transmit power and a 14.6 arcscecond (0.07 milliradian) full width half max (FWHM) beamwidth. The terminals also use a 976 nm, 500 mW, 0.75 degree FWHM beacon and a quadcell for initial acquisition, and a low-rate radio crosslink for exchanging orbit information.

The payload transmitter is a master oscillator power amplifier (MOPA) with fiber Bragg grating for pulse shaping and MEMS fast steering mirror (FSM) for fine pointing, modeled after the MIT Nanosatellite Optical Downlink Experiment. The transceiver leverages UF’s Miniature Optical Communications Transmitter (MOCT) including a chip-scale atomic clock (CSAC). The receiver implements both a time to digital converter (TDC) as well as pulse recovery and matched filtering for precision ranging.

Satellite constellations are used for navigation purposes since long. Connecting the satellites in a constellation by intersatellite links (ISLs) offers a full range of new possibilities. Ranging and time synchronization information can be exchanged between the satellites to improve the in orbit SC positioning knowledge. Besides ranging and time synchronization, ISLs can be used for service channel purposes or to distribute SW updates for the spacecrafts in a short period of time. ISLs improve the navigation constellations autonomy properties being less vulnerable to ground station unavailabilities.

For ISLs, radio frequency (RF) and optical technologies have been investigated. Due to the shorter wavelength, a better ranging resolution can be achieved with optical than with RF ISL solutions. Optical ISLs (OISLs) offer a very attractive solution for intersatellite links in terms of size, weight and power while providing multi gigabit per second data rate capabilities. In addition, optical communication links offer high operational security and immunity to interference sources while benefitting from a non-regulated optical frequency spectrum. For those reasons, optical intersatellite links for navigation constellations have been investigated in several studies supported by DLR and ESA. TESAT with partners have investigated the benefit of OISLs for navigation systems and on the Galileo OISL Terminal design.

In this paper, the results of these studies will be presented. Various OISL connection schemes in a navigation constellation are compared. The key design parameters of a Laser Communication Terminal for navigation systems will be given. Furthermore, the results of a lab demonstration showing the parallel distribution of ranging and communication data will be summarized. The focus of the investigation is on the Galileo navigation constellation.

Satellite-to-satellite laser communication technology underpins high-speed l0-Gbps optical links for the new generation of satellite constellations that will serve as global telecommunications networks. LEO satellite-to-satellite links may extend over distances of >5000 km, necessitating an optical-power budget of ~70 dB to compensate for diffraction-limited opticalbeam divergence. This can be achieved by boosting the transmitted laser diode signal to around 1 W, and by amplifying the received signal by 40 dB. Such performances are attained by terrestrial fiber amplifiers, operating in the telecom 1550- nm wavelength window, which are produced in volume of thousands and are (in relative terms) of low cost. Based on MPBC’s large volume production experience of fiber amplifiers and its heritage of space system design and manufacturing, a new product line of Laser Communication Terminals (LCTs) for space is presented. It is designed to be lower cost, exploiting commercial off-the-shelf (COTS) components whenever possible. Most of these fiber-optic components are extensively employed in large terrestrial telecom equipment and are already qualified to telecommunications standards. However, additional tests are required to ensure reliable long-term operation in a space environment. We have subjected the components, both active and passive, to gamma- and proton-radiation tests including total ionization doses of up to 100 kRad, Temperature vacuum cycling over extended temperature range have been performed and are still ongoing. Finally, considering manufacturing costs, we are packaging both the transmission optical booster unit and receiver optical amplification unit in the same housing, in order to co-locate both the transmit and receive functions of the link. These units are compact and stackable and save on the enclosure weight.

Modern space-born spectrometer applications more and more rely on highest-precision slit devices defining the spectrometer entrance aperture. Reason for this is the increasing demand for broadband and high-resolving spectrometer or imaging spectrometer applications. High-NA optics necessitate very thin (microns) and accurate slit structures, whose manufacturing is demanding or impossible with common technology. In addition, they must withstand harsh environmental loads like shock, vibration and thermal cycling.

The hyperspectral imager of the Environmental Mapping and Analysis Program (EnMAP) satellite mission comprises two spectrometers whose entrance slits are realized by an all-silicon, highly integrated double slit device. It is manufactured by use of micro-machining and lithographic processes, reaching sub-micron geometric precision. Each slit aperture is 24 μm x 24 mm large, corresponding to an aspect ratio of 1:1000. In some critical respects – such as planarity or coalignment – the technology excells established manufacturing technologies like metal electroforming, milling and others.

In addition to slit aperture definition, the double slit device achieves field separation for the two imaging spectrometers. One of the two transmitted light beams is deflected by a flat mirror. The minute silicon mirror is completely integrated into the device. The EnMAP slit assembly has undergone an intensive qualification test program. Included were vibrational, shock and thermal load tests as well as a more specific sun intrusion test. The results of these tests are briefly presented and discussed.

Tropomi, successfully launched in October 2017, and Sentinel-5, with launch due in 2021, are two pushbroom spectrometers measuring Earth’s radiance from a Low Earth Orbit (LEO) at a high spectral resolution. Both instruments have strongly overlapping spectral channels (UV-VIS, NIR, SWIR-3). While the Tropomi spectrometers are designed with standard slits, all Sentinel-5 channels make use of complex slit assemblies called “slit homogenizers” that aim at mitigating the slit heterogeneous illumination that results from the along track spatial non-uniformity of the observed scenes, and is known to distort the instrument spectral response function (ISRF). The similarity between the two missions will allow, in a few years from now, to evaluate the performance gain resulting from these devices. If their expected success is confirmed, slit homogenizers may become standard components of future space missions. This paper aims at providing a comprehensive, yet as simple and accessible as possible, overview of the slit homogenizer performance. The Sentinel-5 slit homogenizers, based on two parallel mirrors will be discussed, and a new and promising family of slit homogenizer designs will be presented for the first time. The new designs offer several advantages in terms of performance and manufacturability.

The launch of ESA EUCLID mission is foreseen in 36020. The goal of the mission is to understand the nature of the dark energy and to map the geometry of the dark matter. The EUCLID telescope will be equipped with two instruments working in the visible range (VIS) and in the IR range (NISP) to investigate the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) will operate in the near-IR spectral range (0.9-2μm) with two observing modes: the photometric mode for the acquisition of images with broadband filters, and the spectroscopic mode for the acquisition of slitless dispersed images on the detectors. NISP is then using four low resolution grisms to acquire spectroscopic image in different orientations to better distinguish the spectra observed and to cover two spectral ranges: 1250-1850nm range, and 920-1300nm range. Since 2010, Laboratoire d’Astrophysique de Marseille is working on the development and the test of the NISP grisms, that are complex optical components. The grism combines four main optical functions: a grism function done by the grating on the prism hypotenuse, a spectral filter done by a multilayer filter deposited on the first face of the prism, a focus function done by the curved filter face of the prism and a spectral wavefront correction done by the grating which grooves paths are nor parallel, neither straight. The NISP instrument is now entering in the integration phase of the proto flight model of the instrument. Therefore, the NISP grism flight models have been manufactured and delivered to the grism wheel assembly for integration by end of 2017. In this paper, we present the optical performance and characteristics of the four EUCLID NISP grisms flight models that have been developed and manufactured by four different industrial partners then integrated and tested by LAM. We focus on the performance obtained on the optical performance of the component; wavefront error of the components, the spectral transmission and groove profiles. The test results analysis show that the grisms flight models for NISP are well within specifications with an efficiency better than 70% on the spectral bandpass and a wavefront error on surfaces better than 30nm RMS. The results on the component show a good control of the manufacturing and integration process despite the difficulties at the beginning of the project to manufacture these components.

Here, we report on the approach of realizing an all-fused-silica PGP disperser (prism + grating + prism) by low temperature direct bonding. A surface relief grating with period 660nm and overall depth of approximately 2000nm is sandwiched between two equal prisms. Direct bonding of glass relies on the formation of covalent bonds between hydrophilic silicon-oxide surfaces. Compared to other joining technologies, like adhesive bonding or optical contacting, the established connection is stiff, shows no outgassing, is highly resistant against chemical and radiative degradation and the established optical interface is intrinsically impedance-matched. In summary, two prototypes were realized, optically characterized and successfully underwent environmental testing. The overall diffraction efficiency of the PGP is larger than 90%.

Advanced Manufacturing (AM) has the potential to improve existing technologies and applications in terms of performance, light-weighting and costs. In the context of the SME4ALM initiative, launched by DLR and ESA, the company Kampf Telescope Optics GmbH (KTO) in cooperation with the Fraunhofer Institute for Material and Beam Technology (IWS) have assessed the feasibility of AM to build a high-performance optical mirror for space applications.

For the assessment of the AM potentials, a mirror design concept for cryogenic instruments for observations in the IR and NIR range was baselined. In a second step, Nickel-Phosphorus (NiP) was selected as optical coating. The combination of coating and mirror material is a primary design driver for optical performance. Both materials must have a very similar CTE as well as be compliant to modern optical manufacturing (diamond turning, polishing). As a promising candidate for NiP coating the AlSi40 was selected for the mirror structure.

The potential advantages of AM for optical mirrors in terms of mechanical performance, cost, and manufacturing time were exploited. The achievement of those objectives was / will be demonstrated by:

1. verifying AM material properties and manufacturability of AM mirrors by material sample tests and subcomponent tests

2. designing AM mirror demonstrator by structural, thermal, and optical performance analysis

3. applying and elaborating AM specific design methods (topology optimization, sandwich structures with internal microstructures, monolithic design, etc.)

4. manufacturing, assembling, and testing AM mirror demonstrator to verify manufacturability and optical performance

5. comparing optical and mechanical performance of the AM mirror demonstrator to a conventional mirror by numerical analysis to exploit potential advantages of AM

We present a method for the manufacturing of thin shells of glass, which appears promising for the production of lightweight mirrors for future space telescopes. The method exploits the synergy of different mature technologies, while it takes advantage of the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via hot slumping technology. The replication concept can be strongly beneficial for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporary stiffened by a removable holder. In this paper, we report on the latest results achieved on a 130 mm glass shell case study.

Demanding new environmental requirements for earth observation, and for astrophysics, may impose ultrastability requirements on telescope mirrors. Dimensional stability of the mirror material under environmental boundary conditions is as important to the success of a mission, if not more so, than considerations of strength and stiffness. Among these characteristics is the response of the mirror material to variable thermal stimulus. It is found that not only the mirror material’s coefficient of thermal expansion (CTE) is important, but also the homogeneity of the material characteristics. Furthermore the match of thermal characteristics between the mirror material and those of metering structure contributes to maintaining a manageable error budget for operations under various view factors to sun and earth.

Modern optical telescopes for Earth observation and remote sensing operations often rely on off-axis mirror designs with aspheric or free-shaped surfaces in order to generate an unobscured image while at the same time covering a large field of view and maintaining an excellent system quality. Continuous improvements in manufacturing and test methods allow for the fabrication of freeform surfaces with low tolerances on figure and roughness. We describe the development, fabrication, and testing of an anamorphic imaging four mirror freeform telescope that operates diffraction limited at visible wavelengths. Based on fabrication and test techniques developed, figure errors of each optical freeform surface were reduced to < 12 nm rms. Roughness values < 0,5 nm rms have been realized based on the applied polishing processes. The optomechanical design of the telescope aims at a minimum of integration effort, reducing the relevant degrees of freedom during mirror alignment from 24 to 3 only and thus allowing for a total system integration within one single day. The telescope concept ensures a reproducible integration and therefore allows for a multi-stage integration after different manufacturing steps in order to correlate surface errors of different spatial frequency with observed wave aberrations on system level. The final experimentally obtained wave aberration is in excellent agreement to the optical design.

Lifetime data is presented for ruggedized commercial NPRO lasers used in the Tropospheric Emission Spectrometer (TES) Instrument on NASA’s Aura Earth-orbiting spacecraft, including 20 years of data from two life test units on the ground, 12 years of on-orbit data from TES Laser A, and 2 years of on-orbit data from TES Laser B. The TES lasers are diode-pumped Non-Planar Ring Oscillator (NPRO) lasers using Nd:YAG crystals. Since accelerated life testing was not possible on the complete laser, early prototype lasers that had gone through thermal cycling and vibration testing were placed on non-accelerated life tests with the hope of gathering at least a couple of years of data before launch. Long-term lifetime data for hybrid laser systems in space applications is not abundant, and out of necessity, accelerated reliability testing is usually done over a relatively short time with a large number of devices. The data presented in this paper is unique as it tracks the optical power output over time of a total of four lasers on the order of decades rather than months or years. Two of the lasers have each been on life test for over 20 years on the ground and are still operating, and the other two lasers have been on-orbit for 14 years. TES Laser A was still operating when the TES Instrument was decommissioned in January 2018. Therefore, the data presented covers over 450,000 non-accelerated device-hours, with 23% of those hours being in space.

The MetOp-SG satellite program is an EUMETSAT/-ESA cooperation with the objective to obtain long-term collection of remotely sensed data of uniform quality for meteorology and climate monitoring state analysis and forecast. A series of three satellite pairs (MetOp-SG-A1, -A2 and –A3) are to be launched, ensuring continuity of data to beyond 2045.

The Infrared Atmospheric Sounder Interferometer Next Generation (IASI-NG), being developed by CNES, is one of the instruments on the MetOp-SG-A’s. The IASI-NG is a Fourier Transform Infrared Spectrometer scanning the atmosphere to provide data for atmospheric gas characterisation.

Kongsberg Defence and Aerospace (KDA) has developed the LAser Source Electronics (LASE) for the IASI-NG instrument. The LASE provides a wavelength-stabilized optical source to be injected into the IASI-NG with a wavelength stability within ± 0.00015 nm throughout the instrument lifetime. The wavelength is locked and controlled using a feedback-loop containing a gas cell filled with ¹³C₂H₂. The LASE shall in addition perform the conversion of the optical signal from the interferometer into analogue electrical signal which can be further processed. The lifetime includes 15.75 years of storage and 7.75 years in space.

The challenge of meeting the required Polarisation Extinction Ratio (PER) for a fiber optical system, as the one in LASE, is discussed.

The flight model of the laser system for the Mars Organic Molecule Analyzer (MOMA) instrument within the ExoMars 2020 mission for Martian planetary surface exploration has been developed, assembled, tested, and finally integrated to the NASA Goddard Space Flight Center (GSFC) mass spectrometer. The nanosecond laser system consists of a longitudinally pumped, passively Q-switched Nd:YAG based laser oscillator with a two-stage frequency doubling to 266 nm. The laser design was implemented in robust and lightweight models of the laser head (LH) with the pump unit in a separate electronics box.

In parallel to the laser head integration and testing, materials and optics qualification and acceptance tests have been performed, e.g. to determine the optical damage threshold or the susceptibility to laser induced contamination processes.

Before delivery to the NASA GSFC for integration to the mass spectrometer (MS) flight model (FM), the laser system has been qualified in an environmental test campaign including vibration, shock and thermal-vacuum testing. After delivery to GSFC and integration to the FM MS, the system has been successfully re-tested on the instrument level.

Over the last decade, frequency comb spectroscopy have led to significant developments in view of the identification of varied species and of the understanding of the structure of matter.
Highly efficient amplification of frequency comb femtosecond oscillators in the high pulse energies regime should allow future applications using this approach to Lidar-type measurements.
We report on the millijoule level design of femtosecond amplifiers near 2 μm wavelength having a great optical efficiency and compactness in order to be carrier in satellites. In addition to space applications, laser systems at 2 μm become more and more popular because they offer elegant solutions to generate ultra-broad band super-continuum in the mid-infrared and for material processing.
Our study helps to compare the optical performance of Tm:YAG, Tm:YAP and Tm:YLF crystals as active media, for designing ultrashort pulse regenerative amplifiers with a high gain and wall-plug efficiencies up to 10%. We will present our approach to ensure the conservation of the initial phase shift between the envelope and the carrier of pulses during amplification.
We primarily discuss an innovative model which proposes a gradual path towards the optimization of any regenerative amplifier using crystalline thulium-based, end-pumped doped rods. This also involves the analysis of sizing criteria based on the assumption of rod-based active media, including the doping content, the length of the rod and the beam size inside.

After more than 3 years of operational experiences with the Transportable Adaptive Optical Ground Station (T-AOGS) it is not any more the question whether optical communication through atmosphere is possible for Geo to ground applications. It is important to understand the performance of optical communication under different atmospheric-conditions and which the key parameters are to improve simplicity, robustness and availability of optical bi-directional satellite to ground links (SGL). We report within this paper on the characterization of the atmospheric channel for ground to GEO optical communication without adaptive optics correction in the uplink. Besides the telemetry data of the space segment and the T-AOGS, also a special measurement campaign was carried out using the 1m telescope of the ESA-OGS in parallel. An outlook for further analysis and activities is given.

In the development of laser communication networks, atmospheric turbulence remains an obstacle in the efficiency optimisation of bidirectional optical links. Post-compensation of the downlink signal through adaptive optics (AO) has been verified as a method of increasing the efficiency of satellite-to-ground optical links, however, similar efficiencies have yet to be achieved in the opposite direction (uplink) largely due to the shower curtain effect and the consequent impossibility of conducting post-compensation over the smaller receiver aperture at the satellite terminal. Pre-compensation is anticipated to be a promising method of increasing the efficiency in uplink communications for Earth-to- GEO optical feederlinks, by pre-distorting the uplink wavefront prior to propagation through the atmosphere using measurements of the downlink. Here, we present the recent modifications to our current experimental setup and initial results of a pre-compensation experiment conducted over a 1 km horizontal path. The experiment aimed to investigate pre-compensation under a point-ahead-angle for the special case of a focussed uplink beam. Two optical terminals were developed, a “ground terminal breadboard” (GTB) consisting of a commercially available 30 cm reflective telescope in combination with an AO-box [3] capable of simultaneous post-and pre-compensation and a “satellite terminal breadboard” (STB) with separate transmission and receiving apertures for measurement of the uplink beam under a point-ahead-angle (PAA). We present a first look at and discussion of the experimental results which show that AO pre-compensation increased the measured intensity of the uplink beam over the receiving aperture of the STB for a PAA of up to 0.27 mrad.

Free space optical communications systems have to deal with several impairments originating from the interaction of optical signals with the local environment and the atmosphere. These impairments include cloud blockage, aerosols scattering, molecules absorption and turbulence. In this paper, we focus on the impact of molecular absorption bands on the choice of uplink/downlink data wavelength division multiplexing grids (WDM) as well as uplink Pointing/Acquisition and Tracking (PAT) beacon wavelength.

In this paper, a methodology for the generation of cloud free line of site time series for low earth orbit optical satellite communication systems is presented. The proposed methodology is based on the synthesis of 3D cloud fields employing Integrated Liquid Water Content (ILWC) statistics. The methodology captures the temporal and spatial variability of cloud coverage and takes into account the varying elevation angle of the LEO optical link with each optical ground station (OGS) and the altitude of each OGS for the estimation of the CFLOS probability. The ILWC statistical parameters required for the CFLOS time series are taken from ERA Interim data base, European Centre for Medium- Range Weather Forecasts (ECMWF). Finally CFLOS numerical results are reported and some significant conclusions are drawn.

The presentation slides for “Innovative Optics in ESA’s Space Science Program” are available at http://doi.org/10.1117/12.2535972, under the Supplemental Content tab.

The presentation slides for “Innovative Optics in ESA’s Space Science Program” are available at http://doi.org/10.1117/12.2535973, under the Supplemental Content tab.

We report on the design and fabrication of a reflection grating for hyperspectral applications operating in the range from 340 nm to 1040 nm wavelength. The blazed grating is based on an effective medium approach, where the desired functionality is realized using a binary surface relief structure. For each period, a gradient in size of the local grating features mimics an interface which adds a linear phase profile to the illuminating beam – thus introducing diffraction. The surface relief structure is composed of 2D structures - pillars with diameters from 200 nm to 350 nm to voids with diameters from 300nm to 120 nm. Overall, an entire number of ~50 such features are arranged to establish an overall unit cell of the grating over a length of 30 μm. By purposeful design of size, shape and arrangement of the sub-wavelength features such gratings offer novel opportunities in tailoring the spectral response, i.e. particular broadband efficiency or the enhancement of the efficiency in specific sub-domains of the spectrum. We will present measured performance results of a grating covering a circular area of 80mm in diameter manufactured on a 4inch-wafer. Finally, we will give an outlook on how such structures can be applied to curved surfaces and even ultra-broadband operation.

Dispersive elements are in general the key components of spectrometers and define mainly their performance. Prisms and filters are typically used for lower resolution applications, e.g. color measurement for industrial applications. Many high performance spectrometer applications are using gratings as dispersive elements instead. Different spectrometer layouts require various grating approaches in order to maintain the optical imaging performance. A frequent aim is a progressively optimization of the optical performance in balance to the mechanical parameters like weight, volume or robustness against variations of environmental conditions of a spectrometer module as well. Thus, the optical designer has to draw on additional design degrees of freedom. This in turn results often in more and more complex grating types featuring curved substrates and/or variable and bended grating lines. Especially the trend toward hyperspectral imaging applications demands appropriate options for enhanced field correction. The main ZEISS technology chain for grating manufacturing includes holography and reactive ion etching is a flexible base for these special types of gratings. A close entanglement between holography and accurate test procedures for the optical functionality of the holographic grating is a pre-condition for the ability to meet the often challenging specifications. Therefore, beside the brief description of the manufacturing technology in this text we show a set of newly developed measuring procedures supporting the holographic surface patterning approach.

In this article the immersed gratings for the ESA Copernicus Sentinel-5 mission are presented. The manufacturing approach is shown and the optical performance of the SWIR-3 immersed gratings as well as the results of the environmental tests are discussed. The immersed gratings show an average efficiency of 60% and a wavefront error of 200 nm rms. The total integrated scatter over the complete stray-light hemisphere excluding ghosts from internal reflections is found to be 0.2% using a conservative estimate. A method for the derivation of the wavefront error from separate surface measurements is presented and the results are compared to measurements with an experimental Shack- Hartmann setup. The immersed gratings are produced by bonding a prism to a wafer with a grating. Environmental tests and testing at operational temperatures show the suitability of this approach for complex space optical components. The article concludes with possible improvements in the optical performance of future immersed gratings.

NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission advances the understanding of planetary habitability and climate change by investigating how Mars lost its early atmosphere and abundant liquid water. We will present here the UV ruled master diffraction grating design, development and performances provided for the MAVEN mission. We will firstly focus introduce HORIBA Scientific capabilities and heritage for low groove density ruled blazed grating development. Then, we will introduce the grating design with the blazed profile and efficiency optimization and finally the performances characterization we obtained on the flight model gratings.

ATHENA (Advanced Telescope for High-ENergy Astrophysics) is the next high-energy astrophysical mission of the European Space Agency currently planned to be launched in the early 2030s, as part of its Cosmic Vision program, on the scientific topic of “Hot and Energetic Universe”. The optics technology is based on the Silicon Pore Optics (SPO). About 678 SPO mirror modules will have to be integrated and co-aligned onto the optical bench of the Mirror Assembly Module (MAM) of ATHENA. This activity will have to be completed in about two years. Media Lario leads an industrial and scientific team that has developed the process to align and integrate the SPO Mirror module with an accuracy better than 1 arcsec. The process is based on position of the centroid of the point spread function produced by each mirror module when illuminated by a collimated planewave at 218 nm taken at 12 m focal length. Experimental tests, using two SPO mirror modules, and correlation with X-ray measurement at the PANTER test facility in Münich have demonstrated that this process meets the accuracy requirement. It was also demonstrated, that a mirror module can be removed again from the MAM, and re-installed, without compromising the adjacent mirror modules. This technique allows arbitrary integration sequence and integration of two Mirror Modules per day. Moreover, it enables monitoring the telescope point spread function during the whole integration phase.

The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm). It is composed of three channels, each one containing a telescope.

Two of these channels are high resolution imagers (HRI) at respectively 17.1 nm (HRI-EUV) and 121.6 nm (HRI-Ly∝), each one composed of two off-axis aspherical mirrors. The third channel is a full sun imager (FSI) composed of one single off-axis aspherical mirror and working at 17.1 nm and 30.4 nm alternatively. This paper presents the optical alignment of each telescope.

The alignment process involved a set of Optical Ground Support Equipment (OGSE) such as theodolites, laser tracker, visible-light interferometer as well as a 3D Coordinates Measuring Machine (CMM).

The mirrors orientation have been measured with respect to reference alignment cubes using theodolites. Their positions with respect to reference pins on the instrument optical bench have been measured using the 3D CMM. The mirrors orientations and positions have been adjusted by shimming of the mirrors mount during the alignment process.

After this mechanical alignment, the quality of the wavefront has been checked by interferometric measurements, in an iterative process with the orientation and position adjustment to achieve the required image quality.

Euclid is a part of the European Space Agency Cosmic Vision Medium Class program. This mission’s goal is to investigate the nature of dark energy, dark matter and gravity by observing the geometry of the Universe and the formation of structures over cosmological timescales.

Euclid Payload Module (PLM) includes a large three mirrors anastigmatic Korsch telescope feeding a visible imager (VIS) and a near-infrared spectrometer and photometer (NISP). The hardware of all of them will be mainly made of Boostec® SiC material.

The SiC telescope has been designed by Airbus Defence and Space team in Toulouse (France).
The PLM is divided in two cavities which are separated and hold by a very large SiC baseplate; the front one includes the primary and secondary mirrors and the associated support structure while the back one consists of the telescope folding mirrors, the tertiary mirror, the two instruments (VIS and NISP) and other optical devices. The focal length is 24.5 m and the useful pupil diameter is 1.2 m. A passive thermal concept has been developed, thus requiring minimum heating power and providing best thermal stability. The telescope will operate at ≈130 K.
In addition to its high thermal conductivity, the Boostec® SiC has been chosen for its mechanical properties and its ability to greatly reduce mass. The full SiC telescope architecture gives high optical stability.
The present paper describes the very large full-SiC telescope and the manufacturing process of its SiC parts, in particular the mirrors, the lightweight baseplate and the spider.

JAXA has developed the Advanced Optical Satellite (ALOS-3) as a successor to the optical mission of the Advanced Land Observing Satellite (ALOS) "Daichi" (2006 - 2011) since FY 2016. The wide-swath and high-resolution optical imager (WISH) is the main instrument of ALOS-3 and equipped with a panchromatic (Pa) band and 6 multispectral (MS) bands. For the optics of WISH, a large off-axis four mirror anastigmat type has been selected to achieve both highresolution (0.8 m Pa, 3.2 m MS) and wide-swath (70 km). The proto-flight model (PFM) of all mirrors has already in the precision polishing process, and highly accurate measurements of large off-axis aspherical surfaces (primary and tertiary mirror) are carried out both in a contact and a non-contact method. The verification concerning the high precision assembly of the large off-axis optical system was also carried out using the structural model which is manufactured with the same design for the PFM. Manufacture and test of the PFM of WISH would be conducted over the next one year and the PFM would be delivered to the ALOS-3 satellite system within FY 2019. ALOS-3 is scheduled to be launch from Tanegashima Space Center in FY 2020.

ESA deployed the first Doppler Wind lidar in space within its Earth Explorer Mission Aeolus. The objective of Aeolus is to provide tropospheric and lower stratospheric wind profiles globally for the improvement of weather forecasts on short and medium term. Spin-off products are profiles of atmospheric backscatter and extinctions coefficients and lidar ratio. The observations will also be used as input to air quality models and to verify climate model parameterization and predictability. After the successful launch in late August this year an intensive commissioning phase is taking place in the first three month of the mission, including the first switch on of the instrument ALADIN and its calibration in flight. First preliminary results will be presented during the talk.

The ATmospheric LIDar (Light Detection and Ranging), ATLID, is part of the payload of the Earth Cloud and Aerosol Explorer (EarthCARE) mission, the sixth Earth Explorer Mission of the European Space Agency (ESA) Living Planet Program. After the successful major step of optical and electrical integration, ATLID has started its performance and functional testing in Toulouse Airbus Defence and Space. The emission part of the instrument has been operated with both TxA (Laser transmitter units) delivered from Leonardo team: as major achievement the main performance of both flight lasers have been tested and confirmed with more than 40mJ UV emission @51Hz with operation via instrument control ACDM flight unit (ATLID control and data management). Tests are parallelized with on one side the EFM test (Electrical Flight Model), and on the other side the OFM tests (Optical flight model). The EFM tests aim at validating the functional and electrical architecture via functional testing on each nominal and redundant path with all the flight electronic units and laser sources. The OFM tests aims validating the receiver alignment from telescope input till fiber detectors, the field of view of the three detection channels and their radiometric performance. OFM vibration tests have been performed and have validated design stability against mechanical loads. End of OFM and EFM tests is planned at summer 2018 and will give go ahead for instrument assembly in its final ATLID PFM configuration with laser cooling system integration. After Ambient performance testing, the environmental test campaign immediately start with EMC, mechanical and thermal vacuum testing.

As compared to near InfraRed passive instruments, lidars reduce the biases on the measurement of concentrations in the presence of diffusion by aerosols, but until recent days they were limited to one active wavelength at a time.

CNES and ONERA conceived a novel type of lidar based on short frequency combs that provides the spectrum of a complete absorption line of the target molecule. The technique of Dual Comb Spectroscopy is adapted to short (up to 13 teeth) combs, as a compromise between spectral richness and Signal to Noise Ratio. The advantages of DCS remain: reduction of the impact of scene evolutions and spectral mis-calibration. The latter will make the high power laser emitters easier. Above all, the acquisition of a complete absorption line opens the path to the retrieval of two or more independent elements in the vertical profile of molecule concentration.

We describe the technique of comb generation, the layout of the emitter section and the detection principles. Then we introduce the Short Comb Atmospheric Lidar Experiment (SCALE) project led by CNES in the frame of a new advance “phase 0” study. We expose the preliminary performances of this space lidar that could fit on a microsatellite platform in the case of CO₂ sounding at 1.57 or 2 μm.

Results of CNES-ONERA four-year R&T activities are also presented that validate in the laboratory and in open space the short comb lidar.

Finally first results of retrieval simulations are exposed.

The LIDAR Echo Emulator (LEE) emulates the returned signals from a Lidar system. As the return signal of a Lidar system depends on the target, this implies the capability of shaping the lasers returns. In brief, long echo corresponds to a natural or diffusive object (canopy, clouds) and short echoes to a hard object like roofs, ground, etc. Such signals are necessary to be simulated to study and validate new detectors and detection systems without developing/procuring entire Lidar system. LEE consists of pulse shaping electronics to drive independently the lasers for each echo and internal detection system to monitor the pulses. The short echoes can be in the range from 5 ns to hundreds of ns and the long echoes from 1 μs up to hundreds of μs. The repetition rates of the developed emulator are from 100 Hz to 10 kHz with limitation that the longest pulse does not exceed 10% of the duty cycle. The power difference between both echoes can be set and is as high as 60 dB. The dynamics of the echoes is better than 50 dB within the 8 ns in the rising/falling edge of the pulse (echo). The output power can be tuned by means of variable attenuators giving a range of the incoming echoes from -35 dBm to -100 dBm. The LEE can also emulate multiple returns with aforementioned dynamics.

In the absence of technically mature quantum repeaters, losses in optical fibers limit the distance for ground-bound quantum key distribution (QKD). One way to overcome these losses is via optical links to satellites, which has most prominently been demonstrated in course of the Chinese-Austrian QUESS mission. Though its findings were impressive, such a large-scale project requires massive financial and time resources. We propose a 34x10x10cm³ nanosatellite orders of magnitude cheaper which is able to perform QKD in a trusted-node scenario, using only commercially available components.

We have performed a detailed analysis of such a CubeSat mission (“Q³Sat”), finding that cost and complexity can be reduced by sending the photons from ground to satellite, i.e. using an uplink. Calculations have been done for a prepare-and- send protocol (BB84 with decoy pulses) using polarization as information carrier. We have created a preliminary design of a 3U CubeSat including a detailed size, weight and power budget and a CAD to account for the assembly of the components. Deploying a 10 cm long mirror telescope covering the small surface of the satellite leaves enough space for a polarization analysis module and housekeeping, communication and computing electronics.
For one such CubeSat, we estimate the quantum secure key to be acquired between two ground stations during one year to be about 13 Mbit. A Bell test between ground and satellite would also be feasible. The uplink design allows to keep the more sensitive, computation-intensive and expensive devices on ground. The experiment proposed by us therefore poses a comparably low-threshold quantum space mission. For a two-year lifetime of the satellite, the price per kilobit would amount to about 20 Euro. In large constellations, Q³Sats could be used to establish a global quantum network, which would further lower the cost. Summarizing, our detailed design and feasibility study can be readily used as a template for global-scale quantum communication.

Quantum key distribution (QKD) can in principle offer unconditional security by making use of the fundamental laws of quantum mechanics. In practice, this is typically achieved by preparing individual photons in quantum superposition states and sending them to a remote receiver. To date, most commercially available QKD systems rely on the transmission of the photons via optical fibers, which, due to channel loss and detector noise, limits the distance over which QKD is feasible to a few hundred kilometers. Alternatively, satellite-based QKD facilitates low photon loss and negligible signal disturbance and offers a viable solution for establishing a global scale quantum network. Recently, a quantum science mission of the Chinese Academy of Sciences (CAS) in collaboration with the Austrian Academy of Sciences (AAS) and the University of Vienna aimed at a satellite-based intercontinental quantum-key relay. Using the Chinese Quantum Science Satellite “Micius” as a trusted relay, a quantum network consisting of three optical ground stations located in China (Xinglong, Nanshan) and Austria (Graz-Lustbühel) has been demonstrated successfully. Here we report on the development of a quantum receiving module, installed at the Satellite Laser Ranging Station in Graz (Austria) capable of implementing the so-called decoy-state QKD protocol in a downlink scenario from the LEO satellite “Micius”. Furthermore, we will present the experimental results obtained during several downlinks from the Chinese satellite focusing on the performance of the Austrian receiving station.

We present a ground-to-space quantum key distribution (QKD) mission concept and the accompanying feasibility study for the development of the low earth orbit CubeSat payload. The quantum information is carried by single photons with the binary codes represented by polarization states of the photons. Distribution of entangled photons between the ground and the satellite can be used to certify the quantum nature of the link: a guarantee that no eavesdropping can take place. The versatile space segment is compatible with a multiple of QKD protocols, as well as quantum physics experiments.

This paper explores the secrecy performance of the recently proposed intensity modulation/direct detection (IM/DD) terrestrial free-space quantum key distribution (QKD) system, by using a Gaussian-beam propagation model and considering the combined effects of atmospheric turbulence and legitimate transceivers’ misalignment. Secrecy performance metrics including quantum bit error rate (QBER) and ergodic secret-key rate are newly derived in closedform expressions, taking into account all combined effects of turbulence- and misalignment-induced fading channels, the eavesdropper’s location relative to the legitimate receiver, and receiver noises. To satisfy security constraints, the system designs based on the intensity modulation depth and beam waist of the Gaussian beam at the transmitter, and dualthreshold (D-T) selection at the receiver, are comprehensively discussed under turbulence and misalignment conditions as well as different eavesdropper’s locations. Monte-Carlo (M-C) simulations are also implemented to verify the analytical results. Remarkably, this paper also offers the first framework in the literature to evaluate the secrecy performance of free-space optical (FSO) systems considering the eavesdropper’s location under the effect of misalignment between legitimate transceivers.

ABSTRACT The worldwide growing interest in small payloads and platforms require the use of solutions that are compact, cost effective and simple to align and test. In particular, the possibility to use constellations of small satellites require the payloads to be easily built in a relatively large number compared to typical space missions where only the flight model and possibly few flight spares need to be procured. This clearly drives the payload architecture towards solutions that can be easily manufactured, and in large quantities.
The recent progress of manufacturing techniques favours this rapid change. For instance, for some applications the possibility to use a spectrometer with a magnification different from one is a key factor to enable instrument designs that are compact, cost effective and with high performance. This can be for instance achieved by using freeform or aspheric mirrors and freeform or spherical gratings. Other compact designs use instead linearly variable filters as dispersive devices, pointing to a different set of applications and performance.
The progress on small satellites and payloads, especially in the vision of large constellations, also benefits from the rapid development of imaging processing and deep learning machines, for instance equipping the payloads with powerful onboard data processor for real time generation of Level 2 data to face the challenge of handling the huge amount of data that is produced on-board.
By combining all these developments, it is possible to produce a portfolio of innovative multi/hyperspectral payloads covering a broad range of applications, spanning from high spatial resolution to large swath width, from minisatellite to cubesat format. Exploiting the flexibility and interoperability of these payloads, the users will be provided with turnkey solutions and real time response to their specific needs.
The European Space Agency is leading several R&D activities in the field of compact multispectral and hyperspectral payloads, fit for small platforms. These activities encompass technology development of novel optical designs, materials and processes, including also engineering of detectors, EEE components and dedicated data processing to achieve innovative and cost-effective solutions.
The paper provides an overview of the technology developments, the status of the instruments manufactured so far and those in operation, their performance and their expected applications. An example of an imaging spectrometer design that is extremely compact, realized with only two spherical optical elements and with a magnification different from one (1:3) is also addressed.

HyperScout-1 is the first smart hyperspectral imager for nanosatellites. It has been launched on the 2^nd of February 2018 at 8:51 CET, from the Jiuquan Satellite Launch Center in China. The launch vehicle Long March 2D lifted off on schedule and the satellite was separated from the launch vehicle minutes later. Approximately after 6 hours the first contact was established.

HyperScout-1 is based on a long line of development led by cosine measurement systems. The project to develop, build and launch the first HyperScout-1 was funded by ESA, with support from the Dutch, Belgian and Norwegian national space organizations: Netherlands Space Office, BELSPO and Norsk Romsenter. cosine, as the prime contractor, enlisted the help of consortium partners S&T, TU Delft, VDL and VITO.

The aim of the demonstration mission is to assess the quality of the data that will be acquired and the consequent suitability for the intended applications. Furthermore, the basic functionalities of the instrument as well as the onboard processing in real time will be demonstrated. The demonstration is divided in three operational blocks, during which HyperScout® will be operated to acquire data from invariant sites for vicarious calibration, from application sites to qualify HyperScout® for all the applications it has been conceived for, and to perform software experiments to demonstrate the novel approach to overcome the bandwidth limitation on small platforms.

Nanocarb is a snapshot imaging interferometer concept dedicated to the measurement of CO2. Thanks to its very compact design, it is a good candidate for small satellites, which would pave the way to a constellation of satellites to monitor emission of anthropogenic greenhouse gases from space. Nanocarb is based on a multiaperture design, with a stepcase interferometric plate to measure partial interferograms. It is developed in the framework of the Scarbo project, an European project involving several partners, the aim of which being to design and analyse the performances of the Nanocarb concept, complemented by collocated compact aerosol sensor and CO2 reference instruments. The overall measurement concept will be experimentally validated through a dedicated airborne campaign featuring instrument prototypes.

We present a novel optical design tool that makes use of an evolutionary global optimization algorithm. The algorithm has several characteristics that make it well-suited for freeform optics design. With the design tool it is no longer necessary to make the distinction between paraxial degrees of freedom and degrees of freedom related to freeform surface description. The design process, which typically involves a multi-stage scheme consisting of finding an optimal paraxial starting layout, optimization, gradually including freeform degrees of freedom to yield an optimal nominal design, and finally a step in which the as-built design is optimized, is shortened because optimal paraxial starting point and optimal freeform shapes are combined to a single optimization step. Optionally, as-built performance can be included in this step as well. The design tool is applied to the design of a compact spectrometer.

Silicon Pore Optics (SPO) has been established as a new type of x-ray optics that enables future x-ray observatories such as Athena. SPO is being developed at cosine with the European Space Agency (ESA) and academic and industrial partners. The optics modules are lightweight, yet stiff, high-resolution x-ray optics, that shall allow missions to reach an unprecedentedly large effective area of several square meters, operating in the 0.2 to 12 keV band with an angular resolution better than 5 arc seconds. In this paper we are going to discuss the latest generation production facilities and we are going to present results of the production of mirror modules for a focal length of 12 m, including x-ray test results.

Currently for the European Space Agency (ESA) ATHENA [1,2] mission Silicon Pore Optic (SPO) [3-8] Mirror Modules (MM) with a focal length of f = 12 m, are being developed and tested. The SPO MMs are also the baseline optic for the NASA medium explorer high-resolution spectroscopy mission Arcus [9-10] with f = 12 m that is currently undergoing a phase A study. SPOs are currently being tested at both the PTB laboratory of the BESSY synchrotron facility in Berlin using an X-ray pencil beam and the PANTER X-ray test facility in Neuried of the Max-Planck-Institut für extraterrestrische Physik, Garching using a long vacuum beamline (distance source to optic ~120 m). The different types of measurements performed at PANTER to characterise the ATHENA and Arcus optics will be discussed. This will be done on the level of an X-ray optical unit (XOU) composed of both a primary and secondary High Performance Optic (HPO) stack, a mirror module (MM) composed of two XOUs, small (<4 MMs) and large (< 25 MM) petals, and the complete integrated optic Athena (700-1000 MMs) and Arcus (4 petals each with 38 MMs). The main set of tests that are currently done at PANTER make full use the possibility to fully-illuminate single XOUs, MMs, and petals to determine their optical characteristics such as the half energy width of the point spread function as well as the effective area and the vignetting function at different energies. To ensure that the measurements, that are required to demonstrate the performance of ATHENA, are possible, a description of recent and upcoming upgrades to the PANTER X-ray test facility will be given. Finally, a status update on the progress on designing the new facility to be used to test and calibrate the complete ATHENA mirror will be presented.

The ATHENA X-ray observatory is a large-class ESA approved mission, with launch scheduled in 2028. The technology of Silicon Pore Optics (SPO) was selected since 2004 as the baseline for making the X-ray Mirror Assembly. Up to 700 mirror modules to obtain a nested Wolter like optics. The maximum diameter of the shells will be 2.5 m while the focal length is 12 m. The requirements for on-axis angular resolution and effective area at 1 keV are 5 arcsec HEW and 1.4 m², while the field of view will be 40 arcmin in diameter (50 % vignetting). While in this moment there an on-going effort aiming at demonstrating the feasibility of a so large optics with so stringent scientific requirements, an important aspect to be considered regards the scientific calibrations of the X-ray optics. In this respect, the Point Spread Function and effective area have to be correctly measured and calibrated on-ground at different energies across the entire field of view, with a low vignetting. The approach considered so far foresees the use of a long (several hundreds of meters) facility to allow a full illumination with low divergence of the entire optics module (or at least of large sections of it). The implementation of similar configurations in a completely new facility to be realized in Europe (friendly called "super Panter") or the retrofitting existing facilities like the XRCF at NASA/MSFC are being considered. In both cases the costs and the programmatic risks related to the implementation of these huge facilities, with their special jigs for the alignment of the ATHENA optics, represent important aspects to be considered. Moreover, the horizontal position of the optics to be used in full illumination facilities would determine gravitational deformations, not easy to be removed with actuators or by modeling. In this talk we will discuss a completely different concept, based on the mount of the optics in vertical position and the use of a raster scan of the ATHENA optics with a small (a few cm² wide) highly collimated (1 arcsec or so) white beam X-ray. This system will allow us to operate a much compact system. The use of a vertical configuration will imply smaller gravitational deformations, that can be controlled with actuators able to compensate them. A proper camera system with a sufficient energy resolution will be able to grant a correct measurement of both PSF and effective area of the Mirror Assembly within the calibration requirements and in a reasonable integration time. Moreover, it may allow us also to perform end-to-end tests using the two flight focal plane instruments of ATHENA. The cost and risks for the implementation would be much lower than for the full illumination systems. The conceptual configuration and preliminary expected performance of the facility will be discussed.

ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM) have to be tested and accepted prior to integration in the full ATHENA Mirror Assembly (MA). X-ray tests of the MMs are currently performed at the PTB laboratory of the BESSY synchrotron facility in pencil beam configuration, but they require a PSF reconstruction. Full illumination X-ray tests could be performed using a broad, low-divergent X-ray beam like the one in use at PANTER (MPE, Neuried, Germany), but the large volume to be evacuated makes it impossible to perform the functional tests at the MMs production rate (3 MM/day).
To overcome these limitations, we started in 2012 to design a facility aimed at generating a broad (170 x 60 mm²), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m²), to characterize the ATHENA MM. BEaTriX (the Beam Expander Testing X-ray facility) makes use of an X-ray microfocus source, a paraboloidal mirror, a crystal monochromation system, and an asymmetrically-cut diffracting crystal for the beam expansion. These optical components, in addition to a modular low-vacuum level (10^-3 mbar), enable to match the ATHENA SPO acceptance requirements.
The realization of this facility at INAF-OAB in Merate (Italy) is now on going. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. In this paper we report the advancement status of the facility.

The global and regional quantification of methane fluxes and identification of its sources and sinks has been highlighted as one of the goals of the NASA 2017 Earth Science Decadal Survey. Detecting methane from space and airborne platforms with an active (laser) remote sensing instrument presents several unique technology and measurement challenges. The instrument must have a single frequency, narrow-linewidth light source, and photon-sensitive detector at the right spectral region to make continuous measurements from orbit, day and night, all seasons and at all latitudes. It must have a high signal to noise ratio and must be relatively immune to biases from aerosol/cloud scattering, spectroscopic and meteorological data uncertainties, and instrument systematic errors.
At Goddard Space Flight Center (GSFC), in collaboration with industry, we have developed an airborne instrument to measure methane. Our instrument is a nadir-viewing lidar that uses Integrated Path Differential Absorption (IPDA), to measure methane near 1.65 μm. We sample the absorption line using multiple wavelengths from a narrow linewidth laser source and a sensitive photodetector. This measurement approach provides maximum information content about the CH4 column, and minimizes biases in the XCH4 retrieval.
In this paper, we will review our progress to date and discuss the technology challenges, options and tradeoffs to measure methane from space and airborne platforms.

The Methane Remote Sensing LIDAR Mission (MERLIN) is a joint French-German cooperation on the development, launch and operation of a climate monitoring satellite, executed by the French Space Agency CNES and the German DLR Space Administration. It is focused on global measurements of the spatial and temporal gradients of atmospheric Methane (CH4) with a precision and accuracy sufficient to constrain Methane fluxes significantly better than with the current observation network.

Merlin is a LIDAR Instrument using the IPDA principle. This instrument principle relies on the different absorption of the laser signal by atmospheric Methane at two laser wavelengths – on-line and off-line – both around 1.645 μm, reflected by the Earth surface or by cloud tops. The attenuation is strong at the on-line wavelength; the off-line “reference” wavelength is selected to be only marginally affected by Methane absorption. Being an active instrument with its own light source, the MERLIN LIDAR Instrument does not have to rely on sun illumination of the observed areas and can therefore continuously operate over the orbit.

Airbus DS GmbH was selected by the German DLR Space Administration as the industrial Prime Contractor for the Mission Phase C/D, to build the MERLIN Payload, which is the first realization of such an instrument for space in Europe.

This presentation will concentrate on the Architecture and the Design of the MERLIN Payload developed during the ongoing Mission Phase C. Further details of the instrument development status will be shown by an overview of the current hardware and design status of the major subsystems.

First atmospheric measurements with a diode pumped alexandrite ring laser in a ground-based general-purpose Doppler lidar demonstrates high-resolution spectral measurements with minimum hardware requirements. Two decades of Doppler measurements by flash lamped pumped alexandrite ring laser within the worldwide only existing mobile Doppler resonance lidar have shown the capability of such scanning lidar to measure any spectrum from the troposphere to the thermosphere without a frequency reference at the wavelength of desire. An improved second-generation system with a size of 1 m³, including a 50 cm telescope, is currently under development for ground-based automatic observations at harsh environments, such as Antarctica. Minimizing the size, complexity, maintenance time and improving the optical setup pave the way of this technology for future space missions. As an example for a possible future space mission, we discuss a mesospheric potassium resonance Doppler lidar by extrapolating the signal from ground-based measurements.

The optical design for the MERLIN instrument was driven by a concept which ensures reliable, high performance operation of the bi-static DIAL, consisting of separate transmitter (TX) and receiver paths (RX). The MERLIN satellite is a secondary passenger payload on the launcher. As such, the satellite places many constraints on the instrument, pertaining to the power, mass and volume allowable. The available resources force the MERLIN instrument to have passive thermal control while necessitating a very compact design due to the demanding envelope constraints. This creates a large operational temperature range with thermal gradients on the structure, requiring an extremely robust optical design in a compact envelope. Typically, a compact envelope requirement drives an optical design towards tight tolerances, which is in contradiction with a large operational temperature range.

The robust optical design, for the RX- and TX-paths, employs several passive measures and an active pointing control for RX and TX co-alignment. These actions are necessary to ensure good instrument performance, despite the demanding environmental requirements. Presented here will be selected load case examples for the entire design and analysis chain, from the instrument performance model towards optical, structural and thermal design.

The paper deals with an analysis of very High Throughput Satellite (VHTS) systems employing optical feeder links. To do so, a fixed set of user requirements is selected that allows for different optical feeder link options to be compared and evaluated on a common basis. The main system aspects are discussed and a rough assessment of the payload resources in terms of mass, power and dissipated power required for each is provided. This exercise reveals important trade-offs and new research avenues for the optical communications community.

Adaptive-Optics (AO) pre-compensation of atmospheric turbulence effects is one of the most promising technologies for achieving very high throughput optical GEO feeder links. However, its great performance has been proven mostly through numerical simulations until now, and experimental work on the subject is still at a very preliminary stage [1]. The FEEDELIO experiment (FEEDELIO for FEEDEr Link adaptive Optics), contracted to ONERA by ESA and described in this paper, goes one step further towards an experimental validation of this concept.

This paper describes the experimental implementation of an AO pre-compensated link on a 13 km slant path in Tenerife, Canary Islands. This experiment is designed to be representative of a GEO feeder link, and aims at demonstrating a significant increase of the mean received power and decrease of the power fluctuations thanks to AO. It will also allow to study the impact of the point-ahead angle on overall performance of the AO system.

The FEEDELIO experiment is planned for spring 2019.

For the next generation of very high throughput communication satellites, TNO and DLR envision optical free-space communication between ground stations and geostationary telecommunication satellites to replace the traditional RF links. To mitigate atmospheric turbulence, an Adaptive Optics (AO) system will be used to apply uplink pre-correction. OFELIA, an ground terminal breadboard was developed to demonstrate the pre-correction principle over an realistic link. Currently, integration tests have been performed to verify the AO performance. Also a laser link experiment over 10 km distance has already been established, in a scenario relevant to ground-to-satellite links. The paper shows that AO is clearly beneficial for the downlink performance. In addition the first preliminary experimental results of the pre-correction show it is also beneficial for the uplink.

This paper investigates the effectiveness of pre-compensating the beam wander effect (tip-tilt distortion) experienced by an uplink optical signal, from a ground station to a satellite, based on the tip-tilt information of the downlink signal (from the satellite to the ground). A test campaign was carried out in May 2018 at the Optical Ground Station (OGS) of the European Space Agency (ESA), to perform measurements of double stars featuring angular separations representative of the point-ahead angle of GEO/LEO satellites. The purpose of gathering these measurements is to investigate the relationship between double stars angular separation and their differential tip-tilt distortion. This analysis evaluates the influence of the point-ahead angle of the satellite, on the tip-tilt correlation between the uplink and the downlink signals. This paper describes the algorithm used to determine the tip-tilt error due to anisoplanatism, and presents the preliminary results that were extracted from the measurements. Then, it is shown how to estimate the jitter of the telescope from the common motion of two independent stars as seen in the focal plane of the telescope. Finally, the paper provides a methodology to determine the maximum transmitter aperture diameter of a ground-based laser communication terminal, in case tip-tilt pre-compensation is applied to the uplink signal based on the received satellite signal.

The presentation slides for “Small Optics for Earth Science: Roundtable” are available at http://doi.org/10.1117/12.2536006, under the Supplemental Content tab.

Silicon particle reinforced aluminum containing 42 wt.% silicon (Al-42Si) offers higher specific stiffness, higher resistance to thermal gradients, and an athermal behavior combined with electroless nickel, in comparison to state-of-the-art aluminum alloys (e.g. Al6061). Nevertheless, typical surface modifications (e.g. black anodization) lead to a nonsufficient optical stray light suppression due to the high amount of silicon particles on the surface. Therefore, a coating technique is required that fulfils the optical and the mechanical (e.g. adhesive strength) specifications for stray light reduction on Al-42Si. Different components like housings and barrels made of Al-42Si were coated with amorphous NiP and with Fractal Black^™ by Acktar Ltd. The optical performance is analyzed by angle-resolved light scattering (ARS) at two different wavelengths (532 nm and 1064 nm). Fractal Black^™ offers a total scattering level of lower than 2 % at 532 nm and 1064 nm. Fractal Black^™ has been proven as a suitable coating for components made of Al-42Si.

PROBA-3 is a mission devoted to the in-orbit demonstration (IOD) of precise formation flying (F²) techniques and technologies for future ESA missions. The mission includes two spacecraft. One of them will act as an external occulter for scientific observations of the solar corona from the other spacecraft, which will hold the ASPIICS coronagraph instrument, under CSL responsibility.

The ASPIICS instrument on PROBA-3 looks at the solar corona through a refractive telescope, able to select 3 different spectral bands: Fe XIV line @ 530.4nm, He I D3 line @587.7nm, and the white-light spectral band [540;570nm]. The external occulter being located at ~ 150 meters from the instrument entrance, will allow ASPIICS to observe the corona really close to the solar limb, probably closer than any internally or externally occulted coronagraph ever observed.

This paper will present the straylight model and analyses carried out by CSL. A first specificity of the analysis is that the scene on the useful Field of View (FOV) is the solar corona which has a brightness dynamic range as high as 10³ between the close corona, close to 1 solar radius (Rsun), and the “distant” corona around 3RSun. The specifications are very stringent for this type of instrument. A consensus was found and will be presented regarding the expected straylight within the FOV. It will also be shown that to achieve realistic estimations it is required to take into account the exact location of the created straylight as well as the entrance field.

The second specificity that had to be analyzed is that the diffraction from the solar disk by the external occulter enters the instrument un-obstructed until the internal occulter, and with a brightness 100 times higher than the close corona (~1RSun) brightness. The simulation of this diffraction as well as its propagation inside the ASPIICS telescope creating additional straylight, had to be carefully established in order to give realistic results of its impact on the performances while being actually possible to compute.

The Solar Orbiter/Metis visible and UV solar coronagraph redefines the concept of external occultation in solar coronagraphy. Classical externally occulted coronagraphs are characterized by an occulter in front of the telescope entrance aperture. Solar Orbiter will approach the Sun down to 0.28 AU: in order to reduce the thermal load, the Metis design switches the positions of the entrance aperture and the external occulter thus achieving what is called the inverted external occultation. The inverted external occulter (IEO) consists of a circular aperture on the Solar Orbiter thermal shield that acts as coronagraph entrance pupil. A spherical mirror, located 800 mm behind the IEO, back rejects the disklight through the IEO itself. To pursue the goal of maximizing the reduction of the stray light level on the focal plane, an optimization of the IEO shape was implemented.

The stray light calibration was performed in a clean environment in front of the OPSys solar disk divergence simulator (at ALTEC, in Torino, Italy), which is able to emulate different heliocentric distances. Ground calibrations were a unique opportunity to map the Metis stray light level thanks to a pure solar disk simulator without the solar corona. The stray light calibration was limited to the visible light case, being the most stringent. This work is focused on the description of the laboratory facility that was used to perform the stray light calibration and on the calibration results.

Ingenio/SEOSAT is a high-spatial-resolution optical mission developed under the Spanish Earth Observation National Program for Satellites (PNOTS), and managed technically in the framework of an ESA contract. It features as Primary Payload (PP) a high-resolution optical payload with one 2.5 meter resolution panchromatic channel and four 10 meter resolution visible/near infrared spectral channels. It is based on a twin Korsch telescope concept, each telescope covering half of the instrument’s swath width. In this communication is presented a detailed account of the work performed to accurately characterize and correct by post-processing an image ghost present in the multi-spectral channels of the primary payload. The work reported here includes the description and analysis of the results of three test campaigns, performed at Thales Alenia Space. Tests carried out include radiometric tests at focal plane level, generic stray-light tests and a novel test to characterize specifically the parameters of the studied cross-talk image ghost. Field-dependent point spread functions for the studied image ghost have been generated by optical analysis, and have been adjusted with the results of the performed tests. From these, image filters have been devised to reproduce, and remove by subtraction, the image ghost. Quantitative image ghost correction results on an actual test image are shown.

Flash Imaging LiDARs (Light Detection and Ranging) are active systems that resolves depth in a scene by time-of-flight measurements and are being seen as a competitive technological alternative that presents great advantages in the space scenario. The system records full 3D-images with a single laser pulse, thus eliminating the need for a scanning device.

A first step to improve the overall quality of the measurements is the calibration of the camera. There is a vast literature and well-stablished techniques concerning radiometric calibration (2D information). However, for time-of-flight (3D information) the subject remains open to improvement and dependent upon the specific characteristics of the detector. In this article we propose a calibration scheme for CEA-LETI’s LiDAR that combines both intensity, range accuracy and range precision calibration and presents the first enhanced results based on data acquired under laboratory conditions.

This project is a partnership between ESA and CEA-LETI aiming the design of a LiDAR system based on a custom MCTAPD FPA (Avalanche PhotoDiode Focal Plane Array) detector developed by CEA-LETI and the formulation of a set of imaging processing algorithms. The target is to demonstrate the potential of such detector technology and to evaluate the performances of the full system chain in the frame of the targeted application. In the future, a validation campaign on a real terrain, at ESA’s campsite, will be performed to demonstrate the system in a close-to-real configuration.

Light detection and ranging (LIDAR) systems have become an important technology in a variety of industrial and scientific applications. In spectroscopy, LIDAR systems can improve the sensitivity by orders of magnitude but require the laser source to have a sufficient small linewidth and stability. For terrestrial applications, such systems have been developed over the last decade and are commercially available. In space, this technology does not have a comparable maturity level and is still far from being a standard technology. In this paper, we present the design and first measurement results of a spaceborne absolute frequency reference based on the absorption feature at 1645.55 nm of methane gas. The frequency reference unit is used in the instrument of the French-German Methane Remote Sensing LIDAR Mission, MERLIN. It provides the stabilized seed lasers for the high power laser sources at the required wavelengths and measures the absolute frequency of the outgoing laser pulses by means of a wavemeter.

Based on ChemCam/SuperCam heritage, a laser with improved performances is built on a table top set-up. The optical configuration is implemented into new lasers proposed for next generation of LIBS – Raman instruments.

We are developing an Integrated Path Differential Absorption (IPDA) LIDAR based on dual comb spectroscopy and recently achieved measurements of 𝐶𝑂₂and 𝐻₂𝑂 concentrations over 280 meters in the atmosphere. High repetition rate (100 MHz) femtosecond fiber laser frequency combs with spectral bandwidth over 100 nm around 1550 nm are used.

The presentation slides for “Optical Technologies in Future CNES Missions” are available at http://doi.org/10.1117/12.2536015, under the Supplemental Content tab.

The presentation slides for “Optics in Russia’s Space Science Program” are available at http://doi.org/10.1117/12.2536016, under the Supplemental Content tab.

Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space as prime contractor under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate applications. Stray light, which is unwanted light captured by the detectors, is one of the major contributors to such important instrument performance metrics as absolute and relative spectral and spatial radiometric accuracies. Amongst the different sources of stray light, Out-of-Band stray light can not be corrected. It is thus important to ensure its impact is limited. The main scope of this paper is to describe the stray light simulations performed in the frame of the Sentinel-4 project: the models, analysis approach and the results. Also, the technical challenges faced in building the models and performing the analysis and the solutions found to solve them are presented.

Jena-Optronik GmbH is developing the Sentinel-5 NIR spectrometer optics operating in the spectral range from 685 nm to 773 nm. It is purely based on refractive optics and makes use of a grating as dispersive element and a prism for aberration correction. One of the design drivers for the optics design is straylight as small absorption effects in the atmosphere need to be detected. To minimize false light on the detector the straylight characteristics have been analyzed and optimized together with Hembach Photonik GmbH. Special attention needs to be paid to the dispersive nature of the optics as compared to a pure imaging system. Sources of ghosts and scattered light such as surface roughness, particle contamination and scattering at mechanical surfaces are quantified. Main contributors to straylight are identified and strategies for straylight reduction are discussed. Among others this comprises effective means to suppress out-of-band light.

MicroCarb is a space program which uses a passive Short Wave InfraRed (SWIR) spectrometer instrument. MicroCarb will provide measurements of the atmospheric concentration of the carbon dioxide at global level with a precision sufficient in order to permit to the scientific community to improve the model of the carbon cycle by understanding the mechanisms governing the exchanges of CO2 between the sources and the sinks.

The MicroCarb Instrument is currently under development at Airbus Defense & Space (ADS). Among the spectral requirements that it must meet, some concern the Instrumental Spectral Response Function (ISRF), which is a key quantity of spectrometers, needed for spectral instrument calibration and atmospheric inversion calculations.

During the development of the Instrument, ADS proposed a method based on several Fourier Transforms to compute the ISRF, based on the one developed by R. Berlich for the FLORIS Instrument ^[1], in order to have an accurate model of its spectral performances.

In this paper, we will explain the simulation method, which allows to take into account diffraction at the system entrance pupil, the spectrometer slit and the dispersion grating, and also the theoretical optical quality of the Instrument. We will describe the preliminary experiments ADS performed to validate this approach. We will then present the work done at ADS and CNES for validating and cross-checking the results of our computations, that required the use of advanced light propagation modules of CODE V.

Once validated, this tool allows to accurately compute the theoretical performances of a given working point, such as the Full-Width at Half Maximum (FWHM) of the ISRF, the resolution of the spectrometer and the likeness of the ISRF to a gaussian function. It is also a powerful tool to quickly compute many ISRFs and thus carry out trade-offs on several parameters of the instrument.

Finally, by including this static computation into a loop and by varying the radiance inside the slit, it is possible to obtain dynamic ISRFs of complex scenes on the ground, and thus have a complete and validated model of the spectral performances of the MicroCarb instrument.

BepiColombo, a cornerstone mission of European Space Agency (ESA) in cooperation with the Japan Aerospace Exploration Agency (JAXA), will explore Mercury the planet closest to the Sun. This first European mission toward Mercury will be launched in October 2018 from the Guiana Space Centre, on a journey lasting up to six and a half years. The data that will be brought back from the two orbiters will tell us about Mercury’s surface, the atmospheric composition, and the magnetospheric dynamics; it will also contribute to understanding the history and formation of terrestrial planets. Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS) is a double spectrometer that will be flown on the Mercury Planetary Orbiter (MPO) one of the two BepiColombo orbiters. This French-led instrument was developed with the purpose of detecting emission lines from Mercury’s exosphere to reveal its composition and distribution, in the wide UV range 55 nm - 315 nm and by recording full spectra. In this paper, we present the instrument design by focusing on the optical subsystems and giving a technical feedback of the major challenges we had to face. We also introduce the calibration philosophy and the main performance results of the instrument.

The ESA S mission CHEOPS relies on a photometer for the precise measurement of the radius of exoplanet. This information is essential to better constrain the nature and structure of exoplanets. The CHEOPS payload is a small defocused telescope of 32-cm aperture that went through its characterization campaign in the first quarter of 2018. We report here on the techniques developed for the calibration campaign and the results of the obtained. In particular we have measured high-precision color-dependent flat fields, measured the characteristics of the detection chain, gain, full-well capacity, read-out noise, measured the instrument distortion and explored the PSF behavior across the field. The end-toend photometric stability of the instrument has also been measured and we will be reporting on the results and the difficulties that have come up while attempting this very difficult measurement, for which sophisticated design and methods were developed.

The Euclid payload features two instruments that are observing the sky simultaneously. The visual light high spatial resolution imager (VIS) and the Near Infrared Spectrometer and Photometer (NISP). A Korsch type telescope with 1,2m diameter feeds both instruments via a dichroic beamsplitter. The NISP instrument reduces the incoming f/#20 beam of the telescope to an f/# 10 beam. The instruments optical system, the NISP Optical Assembly (NI-OA) contains 4 lenses, one single lens in front of a Grism and Filter wheel which is called collimator lens assembly (CoLA), and a lens triplet between these Grism and Filter wheel and the instruments focal plane, which is called camera lens assembly (CaLA). The focal plane consists of 16 Hawaii 2RG detectors.

The required alignment accuracy of the lens triplet and of the singlet relative to the triplet is very demanding and needs to be achieved and verified at the operational temperature of 134K. As an introduction the design, the integration and alignment concept are briefly summarized, as well as the measurement concept to verify the cold alignment within the cryostat. Alignment results for the integration of CaLA EQM and FM at room temperature are presented, the alignment stability after vibrational loads and thermal vacuum cycling is high, only minor changes of a few μm and arcsecs can be detected. The accuracy of the measured cryogenic alignment is demonstrated to be just a few μm and arcsec off the ideal predicted opto-mechanical alignment.

The extremely low surface brightness sensitivity required to observe the ultra-low-surface brightness universe lead us to propose MESSIER, a space mission designed to drift-scan the entire sky in 6 filters covering the 200-1000 nm range and reaching unprecedented surface brightness levels of 34 and 37 mag arcsec² in the optical and UV, respectively. Here, we present the ground-based MESSIER pathfinder aimed at testing several breakthrough technologies involved (e.g. curved detectors) and carrying out observations. We present here a detailed analysis of the optical quality achievable through photon Monte Carlo simulations of the system, including atmospheric effects.

The development of small space-based platforms for nulling interferometric observations could be the pathfinder of a new era in exoplanetology. While planetary transit and radial velocity are the most productive ways to detect exoplanets, such techniques are indirect detections. For deeper characterization of exoplanets, direct detection techniques should be developed. By injecting direct light coming from exoplanets into spectrometers, we could study their chemical composition, search for biosignatures, and possibly infer the presence of life.

The low number of photons to be gathered from the planets, high contrast with the star and small angular resolution are the major difficulties for a direct detection. However, nulling interferometry seems to be a solution to tackle these challenges. By combining the light of two or more telescopes, we would considerably increase the angular resolution, and thus could potentially lead to the detection of Earth-size rocky exoplanets around Solar-type stars. Moreover, with a π- phase shift between the two interferometer arms, the starlight is reduced which allows the detection of much fainter objects around the star. In this paper it will be presented the development of a new mission based on nulling interferometry and dedicated to the Alpha Centauri system. As our nearest stellar system, it is a prime target to investigate for the research of new worlds. Monte-Carlo simulations about potential exoplanet yield of such an interferometer will be described, for different assumptions such as the detection wavelength and telescope size. Single-mode fibers and integrated optics will also be investigated for this mission. This could lead to low-cost type missions with a high potential of scientific return.

The emergence of curved sensors technologies opens a new way to design compact high-performance optical systems. Recent progress on the French activity on curved sensors are presented in terms of optical performance and experimental results. The existing prototypes are demonstrated at TRL4, for VIS and SWIR domains. We present the roadmap jointly developed by CEA and CNRS to reach a higher TRL either on the performance of the devices or on the mass production processes. We present the results obtained on two demonstrators

3D PLUS has developped in the framework of R&D activities an advanced CMOS camera for Space applications. The Centre National d’Etudes Spatiales (CNES), also called French space agency, is leading the developement of this camera, see Figure 1. This instrument has been integrated using the 3D PLUS technology [1] in order to be as compact as possible. Particular attention has been paid to ensure a good radiation tolerance to cover a wide range of scientific applications such as planetology, but also platform or launcher monitoring and star trackers

The microchannel plate (MCP) has been used for decades as a photon, electron and atoms detector in most of the space instruments dedicated for X-rays, energetic neutral atoms, and charged particle imaging. The deep-space missions, as nearfuture ESA Jupiter Icy moon Explorer (JUICE) mission, expect very low temperature conditions on the destination orbit. Since instruments are usually calibrated on the ground under the “room” temperature, it is very important to know the variation of the detectors properties with temperature. The resistance and the gain of the MCP detectors, dedicated for the JENI (PEP package) instrument onboard of JUICE, were measured as a function of temperature at INTRASPEC TECHNOLOGIES, Toulouse, France for the temperature range -50 to +50°C and at the CALIPSO-3 facility of the Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France for the temperature range -25 to +25°C using samples from PHOTONIS France and PHOTONIS USA. It is also important to know how the resistance of the MCP detector behaves with temperature either to properly size the high-voltage source or, conversely, to choose a technology according to the size of the MCP detector and the maximum current that the high-voltage source can supply. Since the environment of Jupiter is very severe, the instruments will operate in the presence of high-energy particles that will induce background noise on the MCP detectors due to the shielding of the instruments against radiation. Therefore, the background noise in the Jovian environment represents a crucial issue for the MCP detectors whose gain can be degraded prematurely if too much charge is extracted from them due to the induced particles. Ours measurements show that the resistance of the MCP detector increases when the temperature decreases and is influenced by its self-heating, whereas the gain behavior depends on the technology of the MCPs. This is an important result which can be used to optimize the gain performance and the lifetime of the MCP detector. These experimental tests were funded by the French Space Agency CNES.

In this paper the focus is on the implementation of Photonis MCP-PMTs with single photon counting capability for LIDAR applications. In particular we are presenting our MCP-PMTs based on HI-QE photocathodes optimized for different spectral ranges (UV, Blue, Green with typical QE<30%) and for fixed laser wavelength of 355 nm and 532 nm [1]. In addition to the high QE, those photocathodes demonstrate low dark rates, typically below 50 Hz/cm₂, property that is important for low-rate signal detection. The collection efficiency of the MCP is also improved to reach almost 100%, allowing to increase the detective QE by a factor of 1.5 compared to conventional MCP-PMTs [2]. The timing performance for MCP-PMTs operated at low and high rate photon fluxes are also studied. Non-linearity effects for high rate of illumination are analyzed and MCP-PMTs with extended linearity are presented. All these improved detection properties can be combined with the possibility of fast triggering and extended life time technology making these devices unique for future atmospheric and altimetry LIDAR missions.

Optical communications systems using pulsed optical modulations and photon-counting receivers have been demonstrated to be capable of very high photon efficiencies. The basic trade is to achieve high photon efficiency by using more bandwidth along with higher ratios of peak-to-average transmitted power. We investigate here the efficiency a photon-counting receiver could achieve in the lower bandwidth regime. It is well known that the best efficiencies at high bandwidths are achieved using two-level pulsed signaling. We will show that it is possible to achieve medium efficiencies at somewhat reduced bandwidth if the pulses are allowed to have more than one level. Equivalently, we show that at fixed slot rates, it is possible to more than double the data rates achievable by a photon-counted, pulsed optical system, although at somewhat decreased photon efficiency.

A high-power, double-pass (DP), and double-clad (DC) Erbium (Er)-Ytterbium (Yb) doped optical fiber amplifier (EYDFA) was fabricated and experimentally evaluated. Because optical amplifiers for space missions must achieve higher electrical-to-optical conversion efficiency in consideration of power consumption and heat generation, we focused on a DP optical fiber amplifier that can be expected to achieve high optical-to-optical conversion efficiency. Free-space optics and integrated design were adopted for a DP module and a Faraday mirror (FM) module, so as to ensure low transmission loss (high efficiency). The DP module including a tap mirror, isolators, and a polarizing beam splitter measured 70×50×22.5 mm in size, with transmission loss of 0.65 dB (from input port to pump combiner port) and 0.52 dB (from pump combiner port to output port). In contrast, the FM module was 40×37×18.5 mm in size, with round-trip transmission loss of 0.66 dB. The fabricated DP-DC-EYDFA achieved output power of around 7 W in the wavelength range from 1540 to 1560 nm and optical-to-optical conversion efficiency exceeding 32%. To the authors’ knowledge, this is the highest output power ever recorded by a DP-DC-EYDFA. The measured polarization extinction ratio (PER) of the fabricated DP-DC-EYDFA was 23.6 dB without using PM EYDF. And in comparison with a single-pass DC EYDFA using the same EYDF, we obtained results showing that the conversion efficiency of the DP-EYDFA was at least 4.2% higher than that of the SP-EYDFA.

Several operators plan to launch mega-constellations of several hundred or even thousands of satellites over the next years to provide global, high-speed and secure backbone communications. Most of these constellations will use a hybrid approach, with radio links for communications with the ground and free-space optical communications for inter-satellite links. First demonstration satellites were successfully launched in 2018.

Since 2009 Mynaric has successfully demonstrated high-speed laser communications in air-to-air, air-to-ground and ground-to-ground applications. Data rates up to 10 Gbps were achieved and altitudes up to 20 km were reached. First airborne terminals and ground stations for airborne and space applications were delivered to commercial customers. Building on the heritage from operations in the harsh environment of the stratosphere, Mynaric started two years ago with the development of a low-earth orbit (LEO) optical terminal for inter-satellite links.

The LEO terminal will provide a data rate of 10 Gbps full duplex over distances of up to 4500 km and a compact design with simple mechanical and thermal interfaces to the satellite bus. The Critical Design Review (CDR) shall be held in autumn 2018 and completion of the qualification is planned for 2019. A demonstration mission in LEO using two satellites is planned in 2019/2020.

Breadboard testing is in progress for several key components such as the coarse pointing assembly (elevation and azimuth axes), the fine pointing assembly and the communication subsystem. Radiation tests were successfully performed to verify the EEE parts approach using COTS and automotive components. RFI/RFP processes are being done to select key subcontractors/suppliers and to gather costing information for the recurring, high-volume serial production of the terminals.

The paper presents the design overview of the terminal and reports on the current development status. The CDR status and results of the breadboard tests are presented and an outlook towards the first demonstration in space is given.

MPB is developing space qualified 10 W End Of Life (EOL) optical amplifiers for longer range applications. Their design employs Polarization Maintaining (PM) Erbium and Erbium-Ytterbium Double Clad Fiber (EDF, EYDF) singlemode fibers. Absorption losses of the EDF and EYDF due to radiation in space are the major challenge to overcome. The gamma radiation tests show that the PM fibers have a greater sensitivity than standard fibers. However, in many applications, PM amplifiers show greater performances which is important for the power consumption.

Furthermore, MPB’s design minimizes Stimulated Brillouin Scattering in the fibers, a major obstacle to be overcome at this power level, even for on ground applications. Moreover, the compatibility with space environment (vacuum, temperature cycling, and radiation) of the high-power optical and electronic components (isolators, laser-diode pumps, current drivers) has to be demonstrated.

The proposed optical designs compensate for radiation-induced losses, without resorting to the use of expensive radiation qualified fibers- a unique method of power recuperation through the photo-bleaching of the active fiber.

ARIEL (the Atmospheric Remote-sensing Infrared Exoplanet Large-survey) has been selected by ESA as the next medium-class science mission (M4), expected to be launched in 2028. The mission will be devoted to observing spectroscopically in the infrared a large population of warm and hot transiting exoplanets (temperatures from ~500 K to ~3000 K) in our nearby Galactic neighborhood, opening a new discovery space in the field of extrasolar planets and enabling the understanding of the physics and chemistry of these far away worlds. ARIEL was selected for implementation by ESA in March 2018 from three candidate missions that underwent parallel phase A studies. This paper gives an overview of the design at the end of phase A and discusses plans for its evolution during phase B1, in the run-up to mission adoption.

ARIEL is based on a 1 m class telescope feeding two instruments: a moderate resolution spectrometer covering the wavelengths from 1.95 to 7.8 microns; and a three-channel photometer (which also acts as a fine guidance sensor) with bands between 0.5 and 1.2 microns combined with a low resolution spectrometer covering 1.25 to 1.9 microns. During its 3.5 years of operation from an L2 orbit, ARIEL will continuously observe exoplanets transiting their host star.

This paper presents an overall view of the integrated design of the payload proposed for this mission. The design tightly integrates the various payload elements in order to allow the exacting photometric stability targets to be met, while providing simultaneous spectral and photometric data from the visible to the mid-infrared. We identify and discuss the key requirements and technical challenges for the payload and describe the trade-offs that were assessed during phase A, culminating in the baseline design for phase B1. We show how the design will be taken forward to produce a fully integrated and calibrated payload for ARIEL that can be built within the mission and programmatic constraints and will meet the challenging scientific performance required for transit spectroscopy.

In July 2020, NASA will launch the Mars2020 mission. This mission, very similar to the Mars Science Laboratory and its rover Curiosity, consists in landing an instrumented rover on the Martian surface in order to characterize the geology and history of a new landing site on Mars, investigate Mars habitability, seek potential biosignatures, cache samples for an eventual return to Earth, and demonstrate in-situ production of oxygen needed for human exploration.
The rover will carry several different instruments to perform field analyses in biology, climatology, mineralogy, geology and geochemistry. Among this payload, the SuperCam instrument, an improved new generation of the ChemCam instrument on Curiosity, has been developed for remote microscale characterization of the mineralogy and elemental chemistry of the Mars surface, along with the search for extant organic materials. In addition to the elemental characterization offered by Laser-Induced Breakdown Spectroscopy (LIBS), a new remote Raman spectroscopy analysis and an infrared spectrometer have been added for a complete mineralogical and chemical characterization of the samples. A context color imaging capability is also implemented to place the analyzed samples in their geological context.

SuperCam consists of three units. The “Body Unit” built by the LANL (Los Alamos National Laboratories) in the US, the “Mast Unit” built by a French consortium of 5 laboratories (IRAP as leader, LESIA, LATMOS, IAS, and LAB) funded by the French Space Agency (CNES), and a “Calibration Target Unit“ under the responsibility of the University of Valladolid in Spain.

A very compact IRS (Infrared Spectrometer) is part of the SuperCam-MU payload. The IRS concept is based on the spectral selection by an Acousto-Optic Tunable Filter (AOTF) in the 1.3-2.6 μm range with a spectral resolution better than 30 wavenumbers. The AOTF is driven by radio frequencies injected in a transducer mounted directly on a birefringent crystal. This coupling creates acoustic waves in the crystal that behave like a Bragg grating. The incident light is then diffracted in two orders (e-ray and o-ray) at the same wavelength following a so-called tuning relation law (relation between diffracted wavelength and injected radio frequency). Each diffracted order is focused on a photodiode. A complete spectrum is obtained after the scan of all individual wavelengths.

The IRS is built by LESIA and LATMOS, two French laboratories located in Paris area.
After intensive performance and qualification tests as well as a calibration on a flight-representative model, the team has built the flight model. The qualification results and the performances of the instrument are presented.

The Raman Laser Spectrometer (RLS) is one of the Pasteur Payload instruments within the ESA’s ExoMars mission. The RLS instrument scientific goal consists of perform in-situ Raman spectroscopy over different organic and mineral powder samples of the Mars subsoil. It consists of three main units: SPU (Spectrometer Unit), iOH (Internal Optical Head), ICEU (Instrument Control and Excitation Unit) which are interconnected by an optical and electrical harnesses (OH and EH).

The SPU is one of the most critical units of the RLS instrument. The Engineering Qualification Model (EQM) unit has been already delivered after a proper qualified campaign in a very demanding environment with very restrictive design constraints, including Planetary Protection requirements. Also, a complete set of functional tests had been carried out under representative environment, simulating not only Mars rover´s laboratory conditions (thermal range and pressure), but also the cruise phase. Previously, an exhaustive qualification campaign was developed with two different purposes: to mitigate the risks associated to new optical elements included in the design and without space heritage; and to obtain a detailed comprehension of their behaviour under Mars conditions for facing the Flight Model (FM) optical design with guarantee of success.

EQM results were successful in terms of Engineering, and a SWaP-optimized system had been reached. The acquired knowledge of that model has been used to implement little improvements into SPU FM for acceptance. For operations, a big amelioration has been the reduction of the image ROI on the Charge-Coupled Device (CCD) after the improving of the alignment of the inclination degree of the image plane on CCD under the tightly integration constrains, letting to download the minimum necessary data bytes. These improvements achieved by a proper analysis of the image on the SPU CCD will allow to evaluate far better the Raman spectrum effects.

SPU FM Mechanical, Thermal-Vacuum campaign has been already finished in order to accept for flight the current unit which will be already completed and “flight qualified” at RLS system level before the congress. If everything continues on this way, the desired Technology Readiness level, TRL 8 maturity level, will be reported during the following text.

The discoveries of main belt comets (MBC) in early twentieth century have attracted great interests of the planetary society, as the water ice and other volatile rich MBCs are located in the main belt and thus may have played a fundamental role in supplying waters to the early Earth. Therefore, MBCs are very interesting and important candidate objects for near future deep space exploration missions. We first summarize the scientific objectives of visible and infrared spectrometers for a flyby mission. Then we propose the major technical specifications for the spectrometers, based on the optical and thermal properties of one of the major targets, 133P/Elst-Pizarro. Our proposed spectral coverage is from 0.4 to 50 μm, which is realized by two spectrometers covering 0.4-5 μm and 5-50 μm, respectively. Visible and infrared imaging spectrometer (VIIS) is a grating spectrometer covering 0.4 to 5 μm with a spectral resolution of 5 nm in the VIS/NIR band and 10 nm in the SWIR/MWIR band. The spatial resolution of the VIIS is 0.5 m at an observational distance of 5 km. The signal to noise ratio of the spectrometer is better than 100 using cryogenic optics technology. Thermal emission spectrometer (TES) is a time modulated Fourier transform spectrometer which covers5-50 μmby one single interferometer. The spectral resolution of TES is 8 cm^-1. The spatial resolution of TES is 10 m at an observational distance of 5 km.

Accurate prediction of the arrival of solar wind phenomena, in particular coronal mass ejections (CMEs), is becoming more important given our ever-increasing reliance on technology. SCOPE is a coronagraph specifically optimised for operational space weather prediction, designed to provide early evidence of Earth-bound CMEs. In this paper, we present results from phase A/B1 of the instrument’s development, which included conceptual design and a program of breadboard testing.

We describe the conceptual design of the instrument. In particular, we explain the design and analysis of the straylight rejection baffles and occulter needed to block the image of the solar disc, in order to render the much fainter corona visible. We discuss the development of in-house analysis code to predict the straylight diffraction effects that limit the instrument’s performance, and present results, which we compare against commercially available analysis tools and the results from breadboard testing. In particular, we discuss some of the challenges of predicting straylight effects in this type of instrument and the methods we have developed for overcoming them.

We present the test results from an optical breadboard, designed to verify the end-to-end straylight rejection of the instrument. The design and development of both the breadboard and the test facility is presented. We discuss some of the challenges of measuring very low levels of straylight and how these drive the breadboard and test facility design. We discuss the test and analysis procedures developed to ensure a representative, complete characterisation of the instrument’s straylight response.

Metis is the solar coronagraph of the ESA mission Solar Orbiter. For the first time, Metis will acquire simultaneous images of the solar corona in linearly polarized, broadband visible light (580-640 nm) and in the narrow-band HI Ly-α line (121.6 nm). The visible light path includes a polarimeter, designed to observe and analyse the K-corona linearly polarized by Thomson scattering. The polarimeter comprises a liquid crystal Polarization Modulation Package (PMP) together with a quarter-wave retarder and a linear polarizer. The Metis PMP consists of two Anti-Parallel Nematic Liquid Crystal Variable Retarders (LCVRs) with their fast axis parallel with respect to each other and a pre-tilted angle of the molecules in opposite direction. This configuration results in an instrumental wide field of view (±7°). The LCVRs provide an electro-optical modulation of the input polarized light by applying an electric field to the liquid crystal molecules inside the cells. A given optical retardance can be induced in the LCVRs by selecting a suitable voltage value. This paper reports the polarimetric characterization of the Visible-light channel for the Metis/Solar Orbiter coronagraph. The retardance-to-voltage calibration of the electro-optical polarimeter was characterized over the entire field of view of the coronagraph yielding a complete “polarimetric flat-field” of the Metis Visible-light channel.

Teledyne is one of the world’s leaders in the provision of infrared sensors for Earth science, planetary science, and astronomy. This paper presents Teledyne’s focal plane array technologies that provide high performance for space missions, with sections on substrate-removed HgCdTe (that provides simultaneous visible / IR detection) and fully depleted HgCdTe (that enables detectors to be operated at significantly increased temperatures). We give examples of the image sensors provided for Euclid, WFIRST, AVIRIS-NG, ECOSTRESS, and NEOCam.

SOFRADIR is one of the main companies involved in the development and manufacturing of infrared detectors for space applications leading to many space studies and programs from visible up to VLWIR spectral ranges. Numerous programs are currently running for different kinds of missions: meteorology (MTG), Copernicus with the Sentinel detectors series, Metop-SG system (3MI, Sentinel-5 and Metimage), Mars exploration (Exomars), moon exploration (Chandrayaan mission with Indian space agency)…

Apart from these programs, the development of scientific missions is increasing. In particular, for the last 5 years, Sofradir and CEA-LETI have worked on specific detectors in SWIR bands to address these needs. The ALFA detector development in progress is the result of these developments. It is expected to propose the first generation of this detector in 2019 for upcoming scientific mission and / or ground universe exploration.

In this paper, an overview of space activity at Sofradir with the main space programs and developments will be described, followed by a description of very large detector developments made for science.

AIM has developed IR modules including the FPAs for a wide range of applications. For SWIR applications FPAs based on liquid phase epitaxy (LPE) are available. These devices having different array sizes and are usable in a wide range of hyperspectral imaging applications. Silicon readout circuits provide various integration and readout modes including specific functions for spectral imaging applications.

An important advantage of MCT based detectors is the tunable band gap. The spectral sensitivity of MCT detectors can be engineered to cover the extended SWIR spectral region up to 2.5μm without compromising in performance.

AIM developed and released the technology option to extend the spectral sensitivity of its SWIR modules also into the VIS. This has been successfully demonstrated for different FPA designs. A short overview is given in tis paper.

AIM has qualified this VIS technology option based on a 1024x256 FPA capable for extended hyperspectral applications. Within this paper the test approach and the results will be presented.

Improvements as well as new functionalities can be implemented in IR sensors by depositing a stack of thin film layers on top their surface. For this purpose, Safran Reosc has developed and qualified various processes, from conventional deposition methods to planar structuration approaches. In this article, the usefulness of thin film AR coatings are addressed and the latest results obtained on projects like Sentinel-5 and Microcarb IR focal planes are presented and discussed. We also address our progress in pixelization of the coating by structuration of these optical layers. Eventually, the most recent developments of sub-lambda photonic filtering structures are discussed.

The next generation of telecom satellite makes the industry facing a technological rupture to reach high data throughput up to 1 terabit/s, while making communications links reconfigurable during all mission phases. That is why the introduction of optical communication technologies like laser links or photonic payloads in telecom satellites is foreseen to revolutionize the space telecom market. Hence the groundbreaking photonic payload will enable reaching the increasing demand of debit and flexibility thanks to miniaturization. In such photonic payload, the proposed optical switch will provide both the added value of optical fiber and new flexibility, redundancy and adaptability functions. Sodern, a recognized space equipment provider is presently spatializing the DirectLight® 1,55 μm Optical Switching Technology from HUBER+SUHNER Polatis Ltd (UK), the worldwide leader in optical switch technology for ground telecommunications and datacenter networks.
This paper focuses on the development activities of Sodern and Polatis on their Space Optical Switch development both for GEO 1 terabit/s high reliability and for low cost LEO constellations. An overview of the technology evaluations and design studies as well as of breadboard performance and environmental testing will be presented. Finally Sodern will explain the product development roadmap including the upcoming EQM.

We present the development and qualification testing of G&H multi-channel fiber amplifier unit developed for satellite to ground free space laser communications. The qualification results show robust functional and structural performance following stress at all 3 possible excitation axes with high level sine vibration, random vibration and mechanical shock as well as thermal cycling between survival and operating temperatures in vacuum condition.

This article reports the development of 200-mW 1.55-μm DFB laser module with RIN below -162 dB/Hz which are well suited for microwave photonics or free space optical communication applications. Specific design has allowed reaching high power (>300 mW), low noise and high spectral purity laser chip. The chip has been packaged in Butterfly module optimized for reducing the module power consumption. DFB laser module system validations have been done on three laboratory test-beds representative of target applications, namely high-frequency optical LO distribution, photonic RF frequency conversion, and free space optical communication links.