This PDF file contains the front matter associated with SPIE Proceedings Volume 12777, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

SUAVE (Solar Ultraviolet Advanced Variability Experiment) is a far UV imaging solar telescope (Lyman Alpha, 121.6 nm, Herzberg continuum, 200-242 nm, etc.) of novel design for ultimate thermal stability and long lasting performances over several years instead of, often, a few weeks or months in this wavelength range. SUAVE is a 80 mm Ritchey-Chrétien off-axis telescope with "mushroom type" SiC mirrors and no entrance window for long and uncompromising observations in the UV (no coatings of mirrors, flux limited to less than 2 solar constants on filters to avoid their degradation), associated with an ultimate thermal control (no central obscuration resulting in limited thermal gradients and easier heat evacuation, focus control, stabilization). Design and performances will be detailed as well as results of thermal/optical tests performed on the SiC primary mirror and its regulated support plate also in SiC. Plans for the realization of a representative breadboard for testing of both optical and thermal properties are presented. SUAVE is the main instrument of the Solar/Climate microsatellite SoSWEET mission (Solar ultraviolet variability and Space Weather Extreme EvenTs).

Helianthus is a technological development project funded by the Italian Space Agency for a Phase A study of a space weather station with solar photonic propulsion. Helianthus will have a synchronous orbit with the Earth-Moon barycenter, positioned at about 7 millions km from Earth towards the Sun, thus much closer to the Sun with respect to historical Space Weather instrumentation, which are typically orbiting the Earth or L1. This sub-L1 halo orbit is maintained by radiation pressure on a solar sail as the propulsion mechanism: once in flight, the spacecraft will have a huge square sail, about 40 m long. The scientific payload will be hosted at the center of the sail and will comprise remote-sensing and in situ instruments. Remote sensing: an X-ray detector to detect Solar Flares and SailCor, a coronagraph with a wide field of view. In situ: a plasma analyzer and a magnetometer. For this ”Sailcraft”, a scientific payload with reduced mass and envelope is under study. The maximum allowed mass for the entire scientific payload shall not exceed 5 kg. Both the X-Ray detector and the in situ instruments have a flight heritage. This study aims at developing a laboratory prototype of a coronagraph matching the constraints of mass and envelope of the Helianthus payload. SailCor is a 20 cm long coronagraph with a field of view ranging heliocentric heights 3-30 solar radii. The external occulter is mounted on an extendable boom that will be deployed once in flight. SailCor presents an innovative solution that combines the diffraction apodization by the external occulter and the internal occulter positioning so that no Lyot stop is required. The classical design of externally occulted coronagraphs foresees the positioning of an internal occulter as a conjugated element to the external occulter with respect to the primary objective. The function of the internal occulter is to block the image of of the diffraction from the external occulter edge. Then, a secondary objective generates the coronal image on the detection system. The SailCor solution takes advantage of the focusing effect that the entrance aperture of the instrument induces on the light diffracted by the external occulter. This effect is used to calculate the position of the internal occulter with respect to the primary focal plane. With this approach, there is no need for a Lyot stop and the detection system can be placed at the first focal plane, with a significant reduction of envelope and mass. This contribution describes the design of the prototype of SailCor, used in laboratory to experimentally define the geometry of the occultation system. The activity has been carried out in the INAF OPSys facility clean environment (ISO5/6) hosted at ALTEC S.p.A. (Torino). The source is a solar divergence simulator.

After the 10th February 2020 launch (04:03 UTC), Solar Orbiter has recently begun its Nominal Mission Phase and is collecting imaging data as never seen before due to its peculiar orbit. The Metis coronagraph produces maps of the linearly polarized visible light corona in the wavelength band 580-640 nm and UV maps in the Lyman alpha H i 121.6 nm line. Metis is a coronagraph characterized by an innovative external occultation system that has a twofold function: reduce the thermal load and remove the diffraction due to the external occulter support. The positions of the entrance pupil (which is called Inverted External Occulter, IEO) and of the actual occulter are switched so that the pupil is the surface facing the solar disk and the occultation is performed by a spherical mirror, M0. M0 is positioned 800 mm behind IEO and reflects the disk light back through the IEO aperture. An Internal Occulter (IO) is conjugated to the IEO with respect to the primary mirror. IO is mounted on a motorized 2-axis stage that allows to perform in-flight fine adjustments to its position. During the on-ground calibration campaign the contribution of the stray light due to the diffraction from the IEO and scattering off the optics was measured. The measurement was carried out by using the OPSys facility in Torino (Italy), which is equipped with a clean environment and a source that simulates the solar disk divergence. A stray light measurement in flight is not trivial due to the presence of the solar corona. Nevertheless, an IO position optimization campaign has been conducted in order to reduce the stray light. A procedure was developed in order to minimize the stray light level on the instrument focal plane. This contribution reports on the procedure and on the results.

On-board the Solar Orbiter ESA/NASA mission there is Metis, a coronagraph designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels working at the ultraviolet Lyman-α (121.6 nm) and in the visible light (580-640 nm). On-ground, the Metis radiometric performance has been tested using a flat-field panel (uniform illumination); the stability of the performance can be verified in-flight through the analysis of the stars passing in the Metis Field of View. Care must be taken to ensure the quality of the calibration, both before launch and for the long period associated with the space mission lifetime. For this reason, we are carrying out long period research of stars that cross the Field of View of Metis. In this paper, we describe the vignetting function acquired: on-ground, simulated via a raytracing code and in-flight derived from on-ground measurements (performing some adjustments to account for the real Metis flight configuration). These vignetting functions are then compared with the vignetting data derived from the passage of the star Theta Ophiuchi in March and December 2021. Additional presentation content can be accessed on the supplemental content page.

AEOLUS underwent a long development led by Airbus Defence and Space both for the LIDAR instrument (ALADIN) in France, and the platform in the UK, and was successfully launched into a Sun-synchronous 320 km dawn-dusk orbit by a Vega launcher in August 2018. The ALADIN Doppler wind LIDAR is pioneering the application of such kind of instrument in space and widens the field for space based LIDAR applications. Initially the mission was designed to be a demonstrator but can be actually considered as operational as the data are used routinely with positive impact on the Numerical Weather Predictions (NWP) models after less than one year of operations in-orbit. After four years of operational lifetime, and also thanks to a strong support to in-flight operations, AIRBUS has learnt, together with ESA customer and scientist user teams, many things about ALADIN LIDAR instrument behavior and its performance monitoring in orbit. While temperature and power telemetries monitoring are quite standard in post-delivery, the follow up of the instrument optical alignment and performance is less direct and lesson learnt show it can be however very profitable in particular for the first UV LIDAR in orbit. The ALADIN architecture is recalled with its measurement principle, and its calibration mode and measurement mode, summarizing the available data for monitoring its behavior in orbit: this covers far field pattern from the atmospheric echo, or near field pattern from the atmospheric echo or internal calibration path; this allows to derive alignment stability of the transmitter and receiver part of the instrument. Also, spectral calibration curves trends allow to retrieve information’s about spectrometers stability. In addition, energy monitoring trend are presented with several means available, and linked lessons learnt are driven. As an important contributor for ALADIN performances, the telescope stability is analyzed and thermal correlation presented with representative Earth albedo maps. The telescope stability is shown as a contributor to link budget but also to spectrometers systematic error limitation due to their sensitivity to variations of divergence and line of sight (angle of incidence). As other key element, the CCD sensor "hot pixel" observation is described with the workaround solution operation at instrument allowing to remove their negative impact on measurement data. Overall conclusion is driven with lessons learnt and perspective for a follow on instrument.

In cooperation with the European Space Agency (ESA) and Airbus Defense and Space (DS), the German Aerospace Center (DLR) developed the ALADIN Airborne Demonstrator (A2D). Also operating at 355 nm wavelength, it is the prototype of the first direct-detection Doppler wind lidar instrument in space - ALADIN (Atmospheric Laser Doppler Instrument) - the single payload of ESA’s Aeolus mission. The A2D was deployed for extensive ground-based measurements and airborne campaigns in the years of mission preparation, with the goal to test operational procedures and refine the algorithms for the processing chain. Experience gained with the A2D supported the ground tests conducted with ALADIN before the launch of Aeolus in 2018. It also laid the foundation for the continuous performance monitoring of the mission, performed within the Data Innovation and Science Cluster (DISC), led by DLR. After launch, DLR executed four airborne campaigns with a focus on validating the Aeolus wind products during different phases of the mission and in diverse geographical and meteorological conditions. During these campaigns, the DLR Falcon aircraft was equipped with the A2D and a high-accuracy scanning heterodyne-detection 2-µm Doppler wind lidar (DWL), used as a reference. Complementary and synergistic results from both DWLs do not only allow for the characterization of the Aeolus and A2D wind errors, but also provide recommendations for the optimization of the Aeolus wind retrieval. Fielding the A2D as a test-bed and validation tool for the Aeolus mission has been a milestone for space lidars and vital for the success of Aeolus, as it has been providing efficient access to instrument specifics in the technological, analytical and scientific domains. The paper covers selected aspects of the airborne technology demonstration program that has supported Aeolus in becoming a successful explorer mission, able to provide high impact data for numerical weather prediction institutions around the world on an operational basis.

During ICSO 2020, the development & characterization of a compact low-resource Correlation Lidar (CWL) for the 3-D atmospheric wind measurements has been reported1 . It was demonstrated that 3-D vector winds could be measured with a ground demonstrator scanning in azimuth. In addition to 3-D winds, it was shown that backscattering & extinction coefficients could also be extracted from the atmospheric lidar profiles. An essential part of the vector wind information retrieval was the development of suitable algorithms to implement the data processing. The demonstration was implemented by means of CCA algorithms based on MATLAB Image processing routines. The present work presents the ongoing effort for the development, characterization & testing of an optimized dataprocessing Algorithm & its implementation on a Raspberry Pi board. The present work will describe the definition & evaluation of an optimized algorithm using synthetic Data. We will compare the performance and stability of both CCA & Point Cloud Optical Flow algorithms. The key issues are wind accuracy and the stability of the wind product under adverse conditions (limited SNR etc), the processing resources required for on-board implementation with a view to the development of a spaceborne instrument. The Optimized algorithm & processor has been tested with a ground CWL instrument. The wind data obtained have been verified and fit well with co-located empirical Data. The results of the processor development & field tests will be presented and discussed with a view to operation from a future Space-based implementation. The further development of the current Processor to a future Spaceborne wind sensor using a FPGA-based processor implementation for Meteorological applications will be given. Keywords: Lidar, Photon Counting, Signal Processing

The European Space Agency’s (ESA) Aeolus satellite was launched on 22 August 2018 from Centre Spatial Guyanais in Kourou, French Guyana. The Aeolus data has been extensively analysed by a number of meteorological centres and found to have a positive impact on NWP forecasts, particularly in the tropics and polar regions. These positive results, along with the successful in-orbit demonstration of the measurement concept and associated technologies utilised on Aeolus, resulted in a statement of interest from EUMETSAT in a future, operational DWL mission in the 2030 to mid-2040’s timeframe and a request to ESA to carry out the necessary pre-development activities for such a mission. This paper will describe the current status of instrument pre-development activities that are being performed in the frame of a potential Aeolus-2 mission. The main inputs for a future Doppler Wind Lidar (DWL) instrument that have been used are: lessons learned from the Aeolus development phases and the in-orbit operations and performance; initial inputs from EUMETSAT including a total mission lifetime of higher than 10-15 years utilizing 2 spacecraft (implying a lifetime of 5.5 years for each) with a launch of the first satellite in 2030, increased robustness and operability of the instrument, and an emphasis on reduction of recurrent costs; the maximum utilization of the demonstrated design heritage; and a number of recommendations for the requirements of a future DWL mission from the Aeolus Scientific Advisory Group (ASAG). These inputs have been collated and combined into a set of preliminary requirements which have been used as the basis for a dedicated Instrument Consolidation Study. An extensive review and trade-off of the above inputs by Airbus Defence & Space, ESA, and independent experts, resulted in the decision to baseline a bi-static instrument design. In addition, three instrument subsystem pre-development activities are currently running: two laser transmitter pre-developments and the pre-development of an improved detector. These developments have the aim to demonstrate that issues identified from the above are resolved and that the technology levels are sufficiently mature for the follow-on DWL mission. The status of these pre-developments will be summarise

Optical imagery from space-based telescopes is one of the most valuable tools for understanding various large and small-scale processes on planetary bodies. Whether in orbit around the Earth or another body in the solar system, it is desirable to obtain the highest resolution imagery possible of the central body. The traditional approach to achieving higher resolution imagery is to increase the size of the optical payload’s aperture. However, larger aperture payloads become prohibitively difficult to manufacture and excessively expensive to design, build, launch, and operate. Application of rotating synthetic apertures (RSA), which is a form of dilute aperture imaging system, to space telescope designs have the potential to unlock the design space of low mass and cost, high resolution space telescopes. RSAs employ a high aspect ratio rectangular aperture that is spun about its principal optical axis. A complete image is formed after a 180° rotation during which multiple frames are acquired to fully sample the imaging system’s optical transfer function. The sampling strategy, which involves the number of individual frames captured and the rate of spin about the principal optical axis, is a function of the RSA’s aperture dimensions. The purpose of this work is twofold. First, an expression for resolution in reconstructed images is derived as a function of orbital altitude, RSA aperture dimensions, and amount of spatial oversampling of the target scene. This expression is used to predict potential science data return for a given orbit, RSA design, and sampling strategy. Second, a multi-objective optimization analysis is performed between reconstructed image resolution and optical telescope assembly (OTA) cost from which a Pareto frontier is defined. This analysis informs an ensuing discussion of optimal RSA aperture dimensions for achieving optimal conditions in resolution and cost. Additionally, the effects of different RSA aperture dimensions on sampling strategies are discussed. Based on these results and discussions, a high-level design for an RSA demonstration mission is proposed. Additional presentation content can be accessed on the supplemental content page.

The latest high-performance telescopes for deep space observation employ very large primary mirrors that are made of smaller segments, like the JWST which employs monolithic beryllium hexagonal segments. A very promising development stage of these systems is to make them active and to operate on their reflective surfaces to change their shape and compensate for aberrations as well as to perform a very precise alignment. This is possible by employing a reference body that stores actuators to modify the shape of the shell, like in the SPLATT project where voice coil actuators are used. However, the lack of physical contact between the main body and shell places – along with the many advantages related to the physical decoupling of the two bodies - some concerns related to the retaining of the shell under all the possible acceleration conditions affecting the system during the mission lifetime. This paper aims to study the acceleration environment affecting the spacecraft during its lifetime and to use it as a baseline for operational requirements of a retaining system for the shells. Any solution is selected in this paper to leave complete freedom for the development of a constraining system, just some are qualitatively discussed.

A concept of optical interferometric imager was proposed by Lockheed-Martin in the early 2010s. In this concept, the aperture is paved by lenses. The optical signals collected by these lenses are combined in photonic integrated circuits, allowing the simultaneous measurement of the Fourier components of the observed object at a number of spatial frequencies. This concept allows one to consider a very significant reduction of the size of optical telescopes, e.g., for Earth observation. Indeed, the transverse dimension of a device based on this concept remains close to that of a telescope of the same resolution since the transverse size determines the spatial resolution. On the other hand, its size along the optical axis is much smaller than that of a conventional telescope. After a quick description of this concept, its intrinsic performance will be analyzed. The field of this device, its spatial resolution, the spectral constraints imposed by the interferometric measurement will be presented. Based on these preliminary considerations, the noise on the measurement will be evaluated. The measurement noise will be compared to that obtained with a focal plane imaging instrument. The geometry of combination of the signals collected by the lenses, or aperture configuration, is a key issue to minimize the size of the device and optimize the quality of the reconstructed image at a given spatial resolution. The literature proposes solutions leading to a partial frequency coverage. In this communication, solutions will be presented leading to a frequency coverage that is more suitable for applications such as Earth observation.

Curved imaging sensors bring significant size, weight and cost reduction to imaging systems while mitigating off-axis optical aberrations, as opposed to current flat sensors. Unlocking these key features has captured the interest of major players over the last two decades. SILINA has been developing a CMOS Image Sensor (CIS) curving process, which adapts to various sensor characteristics. This enables the design of image focal planes to various shapes to specifically maximize the optical performance of every single imaging system. We demonstrated the manufacturing of spherical and aspherical CIS in 2021, opening a new area of compact, fast, wide-angle and high-resolution optical system solutions. From concave to convex, spherical, aspherical, cylindrical, toroidal, or even freeform shapes can be reached. These new degrees of freedom offered to CIS can significantly simplify optical systems through a reduction of the number of elements and improve optical performance in many different ways. The field of view, the contrast, the F-number can be increased while optical aberrations and distortion can be minimized. At the end, the different costs related to manufacturing, metrology, integration, and alignment are reduced. This is of great importance for applications requiring compact payload, high resolution, high transmission factor and shorter integration time. In this paper we address the challenges caused by the adoption of curved image sensors, notably the different approaches for the adaptation of existing designs with a highlight on the optimization and tolerancing methodology. We describe our approach to enhance existing designs by including a curved focal plane, from the first analysis to the last optimization run, in order to improve key performance criteria while maintaining first order parameters. We discuss the improvement expected for space observation through a focus on a two-mirror telescope design based on the Hubble Space Telescope characteristics.

The demonstration of interoperability of the deep-space optical ground demonstration infrastructures of the two space agencies, NASA and ESA, will reinforce optical communication for the use case of fast deep-space data return. The operational experience gained by this joint demonstration will enable future mission designers to efficiently trade the option of using optical communication as data-return vehicle for upcoming deep-space missions. ESA is investigating potential mission scenarios at Mars for which this technology demonstration and validation is considered essential. In this paper ESA's ground demonstration infrastructure for optical data return from the Psyche mission is outlined. The deep-space mission to the asteroid Psyche will host a technology demonstration payload, the Deep Space Optical Communication (DSOC) system, developed by NASA. The mission’s objective is to investigate the asteroid and its unique metallic surface. In addition to its primary objective, the mission will demonstrate an optical communication link between the spacecraft and earth with a separation of up to 2.5 AU. Here we provide link budget calculations for the data up- and the data downlink. Optical communication has the potential to deliver 10- to 100 times higher data rate compared to radio frequency, at lower size, weight and power consumption.

In deep-space optical communications, one particular challenge encountered at the ground receiver side are the wavefront deformations caused by atmospheric turbulence. This gives rise to reduced signal-to-background ratios and signal fades, especially during daytime. Background rejection is therefore a fundamental requirement for optical links operating in the low-photon-count regime with a strong solar background. Both, spectral and spatial filtering subsystems are essential for this application. To this end, we have analyzed several spectral filters and wavefront sensing approaches. In laboratory experiments, a combination of a bandpass filter and a Fabry-Pérot etalon delivered the required bandwidth of 0.17 nm and transmission of 90%, while a SWIR Shack-Hartmann sensor, combined with custom-built wavefront reconstruction software, directed the adaptive optics loop. We have obtained improvements in the Strehl ratio for signal-to-background ratios down to 0.2

We show that utilizing pulse position modulation and photon number resolving detectors together with techniques such as quantum pulse gating allows to approach ultimate quantum limit on optical communication capacity in the presence of background noise in the weak output power regime. This shows that for communication over long distances by means of current existing technology it is possible to attain optimal performance, limited only by laws of quantum mechanics.

The growing interest into exploration of the Moon poses several technological challenges, one of them is surely the need to ensure that the future Moon robots andinhabited colonies will be able to rely on a solid and performing communication infrastructure both within the Lunar environment and with Earth control centers. In this view, a study with ESA (OCRSG) has been carried out by TASI, SSSA and TASCH, in order to start the design of such infrastructure. Severaloptical terminals have been sized to guarantee a downlink from the Moon to Earth at <2 Gbps, and the same performance between Moon orbiters and Moon surface users, and among orbiters themselves, including the future Lunar Gateway. The design is based on state-of-the-art technologies; we also compared the existing radio-frequency subsystem performance, demonstrating the advantages of optical technologies. The optimalmodulation scheme for each scenario has been individuated, starting from high-photon-efficiency modulation (HPE/PPM) but preferring, when possible, more “conventional” schemes, like OOK and DPSK (to exploit a better technological availability). This optimization was possible thanks to the consideration of high power optical boosters which are now available for terrestrial applications. Another part of the study focused on the definition of FoR (Field of Regard)requirements for the different use cases: this realization can be done in different ways, e.g. using a single mirror mechanism up to a fully hemispherical gimballed or periscopic telescope. The study conclusion also draws a technological roadmap, addressing the critical technologies in the gap between the state-of-the-art and the baseline design

The ALTIUS Mission (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at the development of a limb sounder based on a small satellite concept to monitor the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long-term trend monitoring. The ALTIUS instrument consists of three spectral imagers flying at an altitude of approximately 700 km Sun-Synchronous Orbit. The three hyperspectral channels are based on Acousto-Optic Tuneable Filters (AOTFs) in the Visible (440-675nm) and NIR (600-1020nm) range, and a cascade of Fabry-Pérot Interferometers (FPI) in the UV (250-355nm). The use of tuneable active spectral filters will allow the ALTIUS Instrument to perform observations with a spectral resolution ranging between 1nm and 10nm in an extremely versatile operational concept. This paper presents the key technical challenges to be controlled on the design and technologies of the ALTIUS 2D imager for limb sounding. A particular insight will be given on its optical concept including the choice of tuneable spectral filters in each channel and the key development of optical elements such as mirrors, filters and coatings, ensuring the straylight performances of the instrument. The paper also provides a deep dive into the structural and thermal design of the instrument ensuring the pointing accuracy, and the way to achieve L1 radiometric performances from L0 instrument performances through calibration needs and data processing strategies. Along the lines, the stringent cleanliness and contamination control and related envisaged strategy to ensure sustained optical performances will be also described

The FLuorescence Explorer (FLEX) is the 8th Earth Explorer mission currently being developed by ESA with the objective to measure solar induced vegetation fluorescence. This will advance our understanding of photosynthesis and the health of vegetation. Vegetation fluorescence is a very faint signal, and this brings many challenges for the instrument design, development and test, in particular for the very stringent straylight requirement. The development of the FLEX payload (FLORIS instrument) is led by Leonardo (Italy) with OHB (Germany) in its core industrial team. A major milestone has been achieved by completing the instrument Critical Design Review beginning of 2022, allowing now to move into the phase of flight hardware integration. Most of the instrument flight components and subsystems are already manufactured and ready for integration. An extensive test campaign has been already performed on an optically representative engineering model. This campaign provided very useful results in particular for the validation and optimization of the instrument alignment procedures, of cleanliness & contamination preventive measures and the assessment of the optical performances predictions, in particular straylight in flight representative conditions. In this paper an overview of the instrument design, status and development progress is provided including an outlook of the follow up project activities to get ready for FLEX mission launch in 2025. The main results of the engineering model test campaign will be provided with emphasis on the achieved optical performance results. In addition to the project status this paper highlights also some of the most important lessons learnt during the project development as reported in section 4.

A new category of SmallSat research missions, called Scouts, is introduced by ESA. Scout missions distinguish themselves from Earth Explorers by relying on the New Space paradigm, by giving industry and non-profit R&D/academia a more pro-active role. This allows a low-cost approach (≤30M€) and a rapid development cycle (3 years from KO to launch) while using disruptive sensing techniques. CubeMAP is one of the two first Scout missions selected for implementation. CubeMAP is a constellation of three identical 12U satellites, each being designed to perform limb-sounding measurements of atmosphere transmission. Each satellite carries a payload made of two kinds of instruments. The first one, the High-resolution Infra-Red Occultation Spectrometer (HIROS), is a high spectral resolution spectrometer operating in LWIR narrow spectral range (1 cm^-1) with high resolution (0.005 cm^-1). It is based on the measurement of the interferences between the observed Sun scene and an on-board Quantum Cascade Laser (QCL), whose signals propagate through a Hollow Wave Guide (HWG). This configuration limits the sensitivity to shot noise in a compact design with low volume and mass. The second one, the Hyperspectral Solar Disk Imager (HSDI), is a multi-spectral Sun Disk imager. It aims at providing accurate pointing reference to the payload as well as pressure and aerosol measurements. The overall payload allows a spectroscopic measurement of the atmosphere transmission with high vertical resolution (~ 1 km FWHM) between 6 and 50 km altitude

The TRUTHS (Traceable Radiometry Underpinning Terrestrial and Helio Studies) mission is a concept initially proposed by NPL which will enhance our understanding of the Earth’s changing radiation budget by an order of magnitude. This is a UK led mission within the ESA Earthwatch programme with prime, platform and instrument being led by Airbus UK. At the heart of the payload is the ability to calibrate the high resolution hyperspectral imager with a SI calibration traceable to national standards using the payload’s on-board calibration system (OBCS). This in turn provides accurate continuous measurements from the top of atmosphere of reflected, lunar and spectral solar radiance. This paper will concentrate on the hyperspectral instrument part of the payload. The optical design boasts low polarisation sensitivity, good MTF and Smile, and has a compact accommodation to optimise the instruments size and weight footprint within the Payload. The electro-optical back end consists of one Teledyne CHROMA-D MCT detector, with low noise and high SNR achieved through cold operation through a passive cooling system. Pixel correction, customised spectral and spatial binning and compression provided by the electronics front end produces an output dataset with a Spatial Sampling Distance (SSD) of 50m over a spectral range from 320 to 2400nm with a Spectral resolution between 0.3 and 7 nm. This paper will summarise the design status of the TRUTHS hyperspectral imager at the end of phase A/B1. The current spatial and spectral performance will be presented as well as the accommodation and thermal performance.

MERLIN (Methane remote sensing LIDAR mission) is a joint DLR/CNES mission, which will measure column densities of methane in the Earth atmosphere. The heart of the instrument is the laser transmitter subsystem, developed and built by Airbus (Ottobrunn, Germany) in cooperation with the Fraunhofer Institute for Laser Technology (Aachen, Germany), being in charge of the laser’s optomechanical assembly. The project is currently in Phase D with an expected instrument delivery date to the satellite prime in 2026 and launch in 2028. The laser system features key technologies, as already demonstrated successfully in the frame of the FULAS project, to enable reliable long term and high-stability laser performance operation under space conditions. The technologies are optimized with respect to thermal and mechanical stability and developed with special attention on LIC (laser induced contamination) issues by aiming for a fully inorganic design, avoiding any critical organic and outgassing materials. This publication provides an insight into the system design. Furthermore first results from the ongoing qualification model assembly and integration activities are presented, including evidence of the technology maturity for space, based on subassembly and component level qualifications as well as representative bread board activities. Additional presentation content can be accessed on the supplemental content page.

As part of the European Space Agency's AEOLUS mission, the global wind distribution in the atmosphere is currently being measured with a satellite based Doppler lidar. For the AEOLUS-2 mission, a more powerful laser is required which can emit single frequency pulses of 150 mJ energy at a pulse repetition rate of 50 Hz and a wavelength of 355 nm. Fraunhofer ILT is currently developing an engineering model of the laser beam source in cooperation with Airbus Defense and Space Germany. The work on the laser housing and heat removal system is performed by Airbus whereas the work on the laser opto-mechanical assembly is performed by ILT. This work is based on the results of previous projects and focuses on maximizing the use of heritage: The required optical parameters in the infrared have been validated by means of a breadboard demonstrator within the NIRLI project and the optomechanical platform suitable for AEOLUS-2 has been developed in the frame of the OPTOMECH, FULAS and MERLIN projects. For the engineering model presented in this article the proven optical design supplemented by a frequency tripling unit is transferred to the proven and to a large extent space qualified optomechanical platform with an adapted heat removal system. The design is ready, pending the detailed review.

Airbus Defense and Space GmbH, in cooperation with Fraunhofer ILT, is currently developing an engineering model (EM) of the laser transmitter for the AEOLUS-2 mission in frame of the ESA contract ALTA. . For this follow-up mission, a more powerful Laser transmitter is required, to provide single frequency laser pulses of 150 mJ energy. The design focuses on maximizing the use of the heritage from previous space-borne laser designs of the projects FULAS (ESA, EM-like Technology Demonstrator) and MERLIN (DLR/CNES, French-German Climate Mission). The FULAS laser comprises INNOSLAB based MOPA delivering IR laser pulses in the 100 mJ class at 100 Hz PRF. It has undergone a test program demonstrating outstanding thermal insensitivity and robustness and optical and mechanical stability, showing no degradation or misalignment at all after seven years. The laser transmitter of MERLIN, evolved from FULAS, comprises a scaled MOPA, combined with a subsequent Optical Parametric Oscillator (OPO) for frequency conversion. While the Laser opto-mechanical assembly (LASO) is developed by Fraunhofer ILT, Airbus Defence and Space GmbH is in charge of the system concept and the hermetically sealed Laser Housing (LASH) as well as the innovative thermal control system. This publication will provide insight in the transfer of the FULAS and MERLIN system concepts to the Doppler Wind LIDAR Transmitter. Emphasis will be on the robust thermo-mechanical design, with its thermally and mechanically decoupled optical bench and the sophisticated thermal control system based on heat pipes for effective heat removal directly from the individual heat sources of the system. This design is chosen to provide hands off operation of the Transmitter over life time.

We have improved on the characteristics of a diode-pumped, 1064-nm amplifier. The system can deliver 400 mJ @ 100 Hz with very limited wavefront distortion due to thermal effects. It follows that the amplifier can be powered on and reach full energy in a few seconds. The amplifier stable long thermal lens ensures that optical elements used downpath (potentially non-linear crystals for frequency conversion, or a telescope) are at no risk of laser damage, even during the short warm-up time. Additionally, the amplifying system can be operated at any repetition rate up to 100 Hz, and at any energy level, without having to adjust the hardware. The ease of operation, and number of shots saved on the diode lifetime can be a critical advantage in space. The amplifier pumping design enables duplication of the pump source with only 3% increase of the system mass: the doubling of the stacks does not require any additional optical component, nor any moving part. With solar radiation, the diode stacks are among the weakest link of the system, so this unique property is valuable for space applications. The laser amplifier was set-up and characterized as a laboratory breadboard, and a CAD version of a robust system was drawn and analyzed. We will review the properties of this compact amplifying system. Due to its uniform output beam distribution, it is very well suited for non-linear frequency conversion, and for long-range space applications. Additional presentation content can be accessed on the supplemental content page.

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission is the current 2nd ‘Large’ mission (L2) in the ESA Cosmic Vision programme currently. It is currently at Phase B1 but the mission concept will now enter a reformulation phase that will follow a design-to-cost approach. This paper describes the main technologies behind its reference X-ray telescope based on the modular Silicon Pore Optics (SPO) technology. The large X-ray mirror is the mission enabler being specifically developed for ATHENA, in a joint effort by industry, research institutions and ESA. All aspects of the optics are being addressed, from the mirror plates and their coatings to the mirror modules and their assembly into the ATHENA telescope, as well as the facilities required to build and test the flight optics, demonstrating performance, robustness, and programmatic compliance. An overview of the status of the design and demonstration of the telescope is given. The risks that have successfully been mitigated are made explicit and the remaining risks are identified. Additional presentation content can be accessed on the supplemental content page.

Athena is the European Space Agency’s next flagship telescope, scheduled for launch in the 2030s. Its 2.5 m diameter mirror will be segmented and comprise more than 600 individual Silicon Pore Optics (SPO) mirror modules. Arranged in concentric annuli and following a Wolter-Schwartzschild design, the mirror modules are made of several tens of grazing incidence primary-secondary mirror pairs, each mirror made of silicon, coated to increase the effective area of the system, and shaped to bring the incoming photons to a common focus 12 m away. The mission aims to deliver a half-energy width of 5" and an effective area of about 1.4 m² at 1 keV. We present the status of the optics technology, and illustrate recent X-ray results and the progress made on the environmental testing, manufacturing and assembly aspects of the optics.

Several hundreds of Silicon Pore Optics (SPO) mirror modules need to be integrated and co-aligned onto the ATHENA (Advanced Telescope for High-ENergy Astrophysics) Mirror Assembly Module (MAM). The selected integration process, developed by Media Lario, exploits a full-size optical bench to capture the focal plane image of each mirror module when illuminated by a collimated UV wavefront at 218 nm. Each mirror module, handled by a manipulator, focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope. The image is processed in real time to calculate the centroid position and overlap it to the centroid of the already integrated Mirror modules. The 600 mirror modules must be accurately aligned on the ATHENA optical bench, with tolerances of few micrometers and arcseconds. The concept has been demonstrated in a preceding competitive technology development activity. This Assembly Integration and Test (AIT) facility is a vertical optical bench with a collimated UV beam, generated by a 2.6 m Zerodur® parabolic mirror. This UV collimator mirror is already completed and ready to be delivered to Calar Alto Observatory (CAHA, Sierra de Los Filabres, Spain) for the deposition of the reflective coating. In the AIT facility, the ATHENA telescope structure is positioned horizontally on a rigid mechanical structure, called MAIS, and supported by 9 actuators to minimize the gravity effects. One by one, the mirror modules are aligned under the UV beam, ensuring that they all focus into a common point and glued to the dowel pins connecting them to the mirror structure. The building housing the AIT facility is under construction at Media Lario premises near Milan, Italy, and extends 6.5 m below and 17 m above ground. The building is dimensioned to also accommodate the vertical X-ray test facility (Vert-X). The co-location of these two facilities is strategic for the project and will permit regular checks of the mirror module alignment while the MAM is populated. A rail system connects the two facilities.

The ESA Advanced Telescope for High-ENergy Astrophysics (ATHENA) will be the largest X-ray optics ever built. The ground calibration of its mirror assembly raises significant difficulties due to its unprecedented size, mass and focal length. The VERT-X project aims at developing an innovative calibration system which will be able to accomplish this extremely challenging task. The design is based on a 2.5 cm²parallel beam produced by an X-ray source positioned in the focus of a highly performing collimator; in order to cover the whole 2.5m diameter mirror, the beam is accurately moved by a raster-scan mechanism. The same device has the capability to tilt the beam by 3 degrees, in order to test both the off-axis performance and the out-of-field stray-light contamination. By design, VERT-X will be able to measure the ATHENA mirror half energy width (HEW) with a precision of 0.1”, all over the field of view, with the source size, the collimator error and the raster scan tracking accuracy being the most important terms of the error budget. With respect to the traditional long-tubes, the VERT-X facility is much more compact. The entire system will be enclosed in a cylindrical 18m-high vacuum chamber with diameter ranging from 7m as maximum to 4m at minimum. Besides the smaller amount of involved resources, there are important benefits generated by the small scale design. First, it allows a vertical geometry which largely simplifies the mirror support and reduces to zero the PSF degradation due to the lateral gravity. Then, the location of the facility can be chosen flexibly and according to the project needs. Indeed, VERT-X will be built in continuity to the ATHENA mirror assembly integration facility, simplifying the verification and testing procedures. The VERT-X project, started in January 2018, is financed by ESA and conducted by a consortium that includes INAF, EIE, Media Lario, Apogeo Space (former GPAP), and BCV Progetti.

In this paper, we present first results in the experimental demonstration campaign of optical feeder link conducted in November 2021, by using the Laser Utilizing Communication System (LUCAS) onboard the optical data relay GEO satellite. This campaign has been worked under the collaboration for both the National Institute of Information and Communications Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA). In our experiment, we utilize the optical ground station with 1 meter telescope, which is installed in the Okinawa Electromagnetic Technology Center of NICT. This paper mainly discuss received optical power, acquisition and tracking performance, bit error rate performance of the downlink and received optical power of the uplink in an optical feeder link.

Earth Observation missions generate an increasing volume of data as their spatial resolution and swath have constantly increased over the last years. Downloading to ground such amounts of data with limited end-user latency is quite challenging. In this context, optical links offer an effective solution for such image downlink. To demonstrate the feasibility and the relevance of using direct optical links from LEO satellites to ground, to download large volume of data, Airbus DS and CNES have joined to develop LASIN. LASIN, which stands for LASer through the INstrument, is flown onboard the CO3D constellation and will provide a 10 Gbps optical link dedicated to image data downlink. This is achieved thanks to a laser system which transmits directly through the CO3D instrument. LASIN requires only few equipment to turn the instrument into a laser terminal. No pointing mechanisms are required as the beam pointing is achieved thanks to the satellite attitude control capability. LASIN also benefits from the implementation of a new family of high-efficiency LDPC codes recently adopted by the CCSDS and optimized by Airbus DS. In the frame of this demonstration, the optical ground station is developed by CNES and located at the Observatoire de la Côte d’Azur in south of France. The first optical links will take place in 2024. Beyond this demonstration, the goal is to propose a fully operational downlink capability for future EO missions. The system is designed to be compatible with low cost optical ground stations in order to offer innovative and competitive solution for image downlink for the EO export market. Additional presentation content can be accessed on the supplemental content page.

Architecture of a 10 Gbauds link between new high complexity optical ground station suitable for feeder link and a geo-stationary satellite is described. Such link is tested in laboratory environment with emulation of power fluctuations representative of the power budget between the optical ground station and the satellite. The software and hardware developed reach the expected performance and the system performance model is demonstrated to be accurate at 1 dB.

Optical free-space data downlinks from LEO satellites benefit considerably from reduced effort on the space segment, when a dedicated pointing mechanism and active tracking of a ground beacon can be avoided. Instead, the attitude of the satellite is dynamically determined from its star cameras and other sensors. Initial calibration for this technique requires recording of the spatial and temporal beam distribution on the Earth’s surface. We describe the measurement of the beam intensity on ground by the power detectors of three ground stations in parallel, exemplarily for one specific downlink. From this data we derive the instantaneous center of gravity of the beam spot, and its dynamic movement during the downlink. By comparison with the satellite’s own recorded attitude data and its error, the dynamic offset to be corrected on the satellite can be calculated, resulting in optimized pointing-control for future operational open-loop downlinks.

Stray light characterization using ultrafast time of flight imaging was demonstrated recently for the testing of refractive telescopes, using a streak tube with a femtosecond laser. It was shown that individual contributors such as ghost reflections and scattering features can be measured individually and identified, allowing unprecedented understanding of stray light properties in telescopes. This opens the door to the development of higher performing instruments, with stray light properties significantly reduced compared to the state of the art. In this paper, we will present the latest advances in the domain of stray light characterization by ultrafast time-of-flight imaging. This includes the characterization of imaging instruments, and the use of the time-of-flight measurements for reverse engineering instruments properties. In addition of using the time-of-flight approach for characterizing instruments, we will show that this method can be used to validate and improve conventional stray light measurement devices and facilities. In the case of large facilities, the typical optical path lengths is of the order of several centimeters to tens of meters. Therefore, in that case streak cameras can be replaced by a less expensive alternative, namely SPAD detectors. We will present the dedicated SPAD detector that we developed and the results obtain in the validation and improvement of the stray light facility for the FLEX Earth observation instrument. This system will be also used in the near future also for the NAC instrument in the ERO mission to Mars

Even high-end optical components exhibit small amounts of imperfections, which can easily limit the performance of optical systems with respect to imaging contrast, optical throughput, imaging ghosts, and increased light scattering. Characterizing the scattering properties of optical components is thus an important step during the development of sophisticated optical systems as well as to identify and steadily improve materials as well as manufacturing and assembling steps. This is illustrated for different optical components as well as optical systems. Furthermore, different characterization concepts are discussed, which allow overcoming typical limits for angles resolved light scattering measurements, such as scattering very close to the specular beam directions (off specular scattering angles < 0.1°) or measurements in retro-reflection, which are important for gratings used in Littrow configuration or optical mirrors for laser-based communication

In this work, we recorded the retro-reflected and back-scattered light from a system of two components i.e, a single side AR coated SiO₂ window and a mirror placed at tilt angle of 10◦ in the transmission of the window. Retro-reflection and back-scattering from components in an optical system can be detrimental for system performance such as the phase measurement errors, ghost images and laser induced damage in gravitational wave interferometry, optical communications, biomedical imaging and high power laser systems, respectively. Therefore, an accurate determination of the retro-reflected and back-scattered light in such systems is imperative for optimized system performance, particularly the systems where extreme phase sensitive measurements are of keen interest such as the gravitational wave detectors LIGO, Virgo, KAGRA, the future planned Einstein Telescope (ET) and Laser Interferometer Space Antenna (LISA). Using a balanced optical low coherence interferometer, we recorded and distinguished the contribution of light retro-reflected and back-scattered from the different optical surfaces of the two-component assembly. This work would pave the way for simultaneous characterization of the spectral properties of light retro-reflected and back-scattered by components in an optical system with the capability to accurately and effectively identify the impact of individual components as well as the global system performance.

The FLuorescence EXplorer (FLEX) European Space Agency (ESA) mission with its payload, the FLuORescence Imaging Spectrometer (FLORIS), aims at performing quantitative measurements of the solar induced chlorophyll fluorescence from space, with the purpose of improving the monitoring of the health of Earth vegetation. The retrieval of a faint signal, such as the one from chlorophyll fluorescence, requires very low Stray-Light (SL) levels. The SL reduction in FLORIS implied constraints impacting the design, by means of using low roughness optical components, the integration, through a strict contamination control, but also the data processing with the need of a very accurate correction strategy making use of numerical models well correlated with experimental data, to be acquired during the On Ground Calibration (OGC) activities. In order to assess and validate the correction strategy, an accurate SL characterization has been anticipated during the FLORIS Optical Model Refurbished (OMR) campaign. Different methods, such as out-of-field and out-of-band measurements, have been investigated in order to avoid the detector blooming affecting measurements with high input signals. By combining the results from the different approaches, it has been possible to achieve up to 9-10 decades of explored dynamic range. The model, correlated with measurements, has finally proved to be capable to correct SL with a reduction factor <10, down to a level less than 40% of the required fluorescence error (10% of a fluorescence level of about 2 mW/m²/sr/nm). Additional presentation content can be accessed on the supplemental content page.

Teledyne e2v is continuing to invest in CCD and CMOS sensors innovation for higher performance in the visible, soft X-Ray and NIR parts of the spectrum for space applications. Space missions are becoming ever more complex and Teledyne e2v, to support this growth, has developed technologies to improve the intrinsic performance of the detector, new features for low noise or data stream approach and improved interfaces to ease integration at system level. As Teledyne also covers commercial and industrial markets it is possible to take advantages of the state-of-the-art development made in those markets to enhance detector performance for space with limited risk and shorter R&D development time. This paper covers the latest innovations for CCD and CMOS technologies and in particular the large area and low noise platform (CIS300 family) and TDI charge domain CIS125. In the last section an overview on the detector electrical interface innovation is given.

ELFIS2 is the second generation of the European Low Flux Image Sensor (ELFIS), developed by Caeleste, manufactured at LFoundry and tested by Airbus on behalf of the European Space agency. As the High flux program was aborted, it was decided to continue ELFIS as a High Dynamic Range (HDR) sensor, enabling the simultaneous integration and readout of the same charge packet on a large and a small conversion capacitance. It is combined with charge domain global shutter, so that motion artefacts, typical for multi-exposure or dual photodiode architectures are completely eliminated. The ELFIS core pixel uses the Global Shutter technology pixel, developed at LFoundry, allowing charge domain Integrate-While-Read operation and on-chip CDS. In order to handle photocharge packets that exceed the full well of the core pixel, there are two low gain overflow capacitors, used alternatingly for signal integration and read-out. Whereas ELFIS1 was a fixed size device, ELFIS2 is designed for stitching. The stitch block of 512*1024 pixels can realize every n*m multiple of 1/2k by 1k pixels, as long as it fits on the wafer. The Initial prototype presented has a 2k*2k format. 4k*4k, 8k*8K, etc. can be realized with the same mask set, as well as elongated (hyperspectral) sensors up to 512*10 k pixels. As each stitch segment has its own output amplifiers, the ultimate frame rate is only determined by the number of rows to be read. Frame rate can be increased by applying row random addressing, which are especially versatile in hyperspectral applications. The initial functional tests of ELFIS2 are promising: without further optimization the noise spec of less than 5 e-rms is reached with a HDR full well of 160 ke- ; the core Global Shutter high gain full well is 10 ke- , resulting in a smooth photon shot noise limited behavior from the high gain noise floor till the low gain saturation. The full functional testing and circuit optimization is now starting and will be finished at the moment of this presentation. Also, radiation pre-qualification is planned. Due to the good SEE results obtained in another Rad-Hard by Design (RHbD) in the same technology we are also confident that the SEE will have a LET < 63 MeV/mg/cm² for both SEL and SEU.

For the last two decades, CNES optoelectronic detection department has studied and evaluated space environment effects on a large panel of CMOS image sensors (CIS), coming from a wide range of commercial foundries and device providers (cf. Table 1). Many environmental tests have been realized in order to bring insights on detection chain degradation in modern CIS for space applications (cf. Table 2). Thanks to their good electro-optical performances, high integration level, low power consumption and tolerance to the space radiation environment, CIS are more and more preferred over Charged Coupled Devices (CCD) in many future space imaging missions. Moreover, the CIS technology has drastically improved during the las decade, reaching very high performances in term of Quantum Efficiency (QE) and spectral selectivity. These improvements are obtained thanks to the introduction of various components in the pixel optical stack such as microlenses^[1], color filters^[2] and polarizing filters^[3]. However, since these parts have been developed for a commercial purpose, it is crucial to evaluate if these technologies can handle space environment for future imaging missions and very few literatures exist on that robustness. Several space imaging systems have thus been able to benefit from these technologies on which these tests have been carried out, such as the Remote Micro-Imager (RMI) in the SuperCam instrument aboard the Mars 2020 rover Perseverance^[4] . This CNES work demonstrates that these kinds of optical stacks show little variation in terms of efficiency when exposed to space environment. It also allowed studying the response of various optical systems at pixel level for various technologies such as microlenses, color filters and polarizing filters (shown respectively in Figures 1, 2 and 3). In the presentation, an overview of environmental tests results (cf. Table 2) on many CIS from different commercial technologies and several optical stacks are compared and show that they are suitable for space applications. Thanks to their robustness, they can significantly increase CIS performances without being a limiting path for them along the mission. Since the full paper containing data and more will be published later in MDPI Sensors^[5] , it is on purpose that we prefer submitting a more consistent abstract with detailed Tables showing the amount of realized tests, and CNES photos of the optical stacks we are talking about. Additional presentation content can be accessed on the supplemental content page.

3D PLUS has developed in the framework of its R&D activities two new high performance camera heads for space applications. The Centre National d’Etudes Spatiales (CNES) is leading the development of these two new cameras: a 12Mpx space camera head (3DCM800), and a 1.3 Mpx Short Waves InfraRed (SWIR) space camera head (3DCM830). Those camera heads have been integrated using 3D PLUS packaging technology and expertise in order to be as compact as possible and provide the high performances of two images sensors associated with a high performance FPGA based electronic architecture to its Space Camera Product line. Particular attention has been paid to ensure radiation and harsh environment tolerance in order to cover a wide range of application, including equipment or key events monitoring, in-flight spacecraft navigation and rendezvous applications, as well as observation and scientific applications benefiting of the high performance of the sensors (earth observation, hyper/multispectral imaging, planetology).

We show that metrology at the working wavelength is possible with a wave front sensor in the Mid-Infrared range (MWIR, 3-5µm). We demonstrate the implementation of an Interband Cascade Laser for double-pass optical qualification with a quadriwave lateral shearing interferometer. To avoid any parasitic interference fringes, which limit the phase accuracy, we modulate the diode driving current with an external analog signal. While the power stability is kept constant, the phase noise is reduced and no artefact limits the measurement accuracy.

The knowledge of the bi-directional scattering distribution function (BSDF) of an optical component is an import requirement for the design and assessment of high-performance optical instruments. However, precise BSDF measurement with high resolution close to the specular beam can be very challenging and require sophisticated instrumentation. In this paper, we present a newly developed scatterometer, the “Enhanced Resolution Light Scattering Analyzer for Curved Gratings (single detector axis)” – ELSA/CG-S which is designed specifically to measure the BSDF of curved optical components with a very high resolution not only close to the specular direction, but throughout the whole angular measurement range with an instrument signature that can compete with the top of the class of current commercially available instruments. The distinguishing feature of the instrument is the use of a high-resolution silicon sCMOS imaging detector which enables fast acquisition times and provides access to a two-dimensional section of the BSDF around the main detection plane of the instrument with an out-of-plane FoV of about ±0.6°. In the following, we will describe the general design of the instrument and explain the measures that have been taken to enable a very low stray light signature with the chosen detection scheme. After this, we will assess the instruments capabilities and present measurements of the instrument signature and BRDF measurements of plane and curved diffraction gratings with high groove densities. These measurements will also demonstrate the additional value that is provided by using an imaging detector. All measurements will be compared to results obtained with ESTEC’s commercial CASI scatterometer from The Scatter Works, that represent the current state of the art.

Cold atom based quantum sensors require robust and miniaturized optical systems for applications on mobile platforms. A micro-integrated optical system (volume ∼25 mL) for trapping and manipulation of neutral atoms is presented. This setup focuses and precisely overlaps two high power laser beams (1064 nm, up to 2W total, wR = 34 µm) launched via a single-mode, polarization maintaining optical fiber, thereby realizing a crossed beam optical dipole trap (ODT). Adhesive bonding is qualified in application relevant geometries and material systems of micro-integrated optical systems for application on mobile platforms or space. Fused silica test blocks (bond area 2 × 4 mm² ) are bonded with four different adhesives on silicon wafers. Theses samples are aged by thermal cycling (up to −55 °C to 150 °C) and/or gamma-radiation (10 000 mSv) and subsequently the bond strength is evaluated by die shear testing according to MIL-STD-883L. The influence of the environmental aging on the bond strength is presented, the failure mode and the influence of fillets discussed. In addition, the effects of plasma cleaning on the bond strength in this geometry is presented.

Joining technologies are of great importance for space-based applications. Given the very low environmental temperatures, high temperature differences, vacuum, and high acceleration loads during rocket launch, the (thermo-)mechanical requirements on the joining technologies are demanding. Plasma-activated bonding (PAB) and silicate bonding (SB) meet all these requirements. We developed PAB and SB to assemble an all-glass four-channel beam splitter. This development was initiated by a satellite mission concept, devoted to transient astronomy. Central part of this satellite mission is a novel beam splitter that divides the incoming telescope beam into four near infrared channels (λ = 800 − 1700 nm), by using a Kosters prism type design. As a final result, we built a demonstrator for the validation of the developed technological concept. Additional presentation content can be accessed on the supplemental content page.

While the next generation of satellite constellations provide improved capacity through the use of optical inter-satellite links, there is still a capacity bottleneck at the RF feeder links between satellites and ground stations, which are an order of magnitude slower in moving data. In order to move to all optical feeder links, there is a challenge to overcome the distortion associated with atmospheric turbulence. Laser Guide Star (LGS) adaptive optics systems are a key enabling technology to help solve this beam wander problem for ground to space optical systems. For guide star lasers suitable for daytime LGS operation, high power is key. To respond to this need, a 100-W continuous-wave (CW) 1178-nm narrow-band polarization-maintaining (PM) Raman fiber amplifier (RFA) has been developed and fully engineered. A linearly-polarized single-frequency 1178-nm seed laser with an output power of only a few mW is amplified up to 100 W in a two-stage RFA counter-pumped by a 200-W 1120-nm PM fiber laser. Techniques for efficient suppression of stimulated Brillouin scattering (SBS) have been optimized, resulting in the RFA SBS threshold being pushed beyond the 100-W level. The narrow linewidth of the seed laser is well preserved in the RFA, without any evidence of linewidth broadening up to 100 W. The RFA is based on true single-mode PM fibers and has excellent polarization purity and output beam quality, key factors for subsequent efficient frequency doubling to the Na absorption line at 589 nm in a resonant frequency-doubling cavity. Similar to the widely-deployed MPBC/TOPTICA SodiumStar 20/2, the new 100-W RFA system is a compact, modular, reliable and ruggedized off-the-shelf system ready for integration. Compared to solid-state alternatives, a guide star laser based on an all-fiber, highly-reliable, 100-W RFA not only provides excellent overall wall-plug efficiency due to its high pump-to-Raman optical conversion efficiency, but also maximizes the important “up time” for the optical channel at ground station facilities since it is a maintenance-free and turn-key system. To confirm the stability and reliability of this next-generation guide star RFA, the system was run 24/7 at the full 100 W for a total of 1300 hours. The test results confirmed that the 100-W RFA system is extremely robust and reliable, with a sufficient built-in 1120-nm pump power margin. Re-measurements of key RFA parameters, such as polarization purity and output beam quality, also confirmed that the RFA performance remained unchanged after the 1300-hour 100-W test. Assuming a conservative conversion efficiency of ~ 80% by a resonant frequency doubler and taking into account typical passive coupling losses into the doubler cavity of < 15%, narrow-linewidth CW guide star lasers with powers < 70 W at 589 nm can confidently be expected for future optical ground station adaptive optics systems. The RFA output power was shown to be solely limited by the SBS threshold. Since all the laser components showed sufficient higher optical power handling potential, it is expected that, with further optimization of the SBS suppression, the RFA output power can be scaled significantly beyond the current 100-W level.

We propose and analyze numerically concurrent intensity modulation/direct detection (IM/DD) optical key distribution (OKD) combined with conventional data transmission over a LEO-to-ground optical link. The idea is validated by numerical simulations which indicate that in a realistic scenario it is possible to generate simultaneously up to 200 Mbits of a secret key and downlink transmit up to 140 Gbits of data during a single nearly-zenithal pass of a LEO satellite. Such lengths of the secret key are three orders of magnitude higher in comparison to typical quantum key distribution systems, although they are generated under different security assumptions. The simplicity and robustness of IM/DD OKD protocols could make them an attractive and cost-effective option to provide security in the physical layer of space communication systems.

Optical feeder links (OFL) are expected to become part of future Very High Throughput Satellite (VHTS) systems in response to the growing demand for higher capacity and lower costs. H2020 VERTIGO (Very High Throughput Satellite Ground Optical Link) project was set to prove key optical communication technologies and to address: 1) Throughput increase with high spectral and power efficiencies. 2) Higher optical power generation and delivery. 3) Atmospheric turbulence mitigation by optical and digital processing. Transmit and receive optical communication models were developed in rack units for assessing, in laboratory and outdoor trials, their intrinsic performance, robustness against atmospheric turbulence and compatibility with other technologies. The models for 25 Gbps OOK/DPSK and RF analog modulation with optically pre-amplified direct or differential detection are reported with the achieved performance. An atmospheric channel emulator fed with time series established by simulations was used to mimic the propagation losses and fading of the optical signal coupled into the receiver. Both the downlink and uplink under weak or strong turbulence were emulated. For digital transmission experiments, the performance metrics include BER curves, detection sensitivity and power penalty. State-of-the-art sensitivities were achieved especially under 25 Gbps DPSK. For RF analog transmission, the performance metrics were constellation diagrams and Error Vector Magnitude (EVM) measured for various modulations from QPSK to 64-QAM. Are reported the results of optical transmission experiments first performed in the laboratory under static and dynamic propagation channels, then in the outdoor trial successfully carried out in July between Jungfraujoch and Zimmerwald in Switzerland.

High throughput optical satellite communication (SATCOM) systems need to rely on effective and robust technology to enable wavelength-division multiplexing (WDM) in a commercially viable way. The main challenge to implement WDM in optical feeder links deals with the multiplexing of high power channels. Currently the levels of power required for communication, tens of watts per channel, make unfeasible to multiplex several channels in a waveguiding device. A free space architecture is devised to mitigate this issue. The paper describes the architectural choices made, the optical and mechanical design for a multiplexer to be employed in a Optical Feeder Link terminal combining 13 channels, each carrying 50W of optical power. Within the TOmCAT (Terabit Optical communiCation Adaptive Terminal) project a demonstrator of the full system has been realized. The demonstrator multiplexer supports 5 channels, each carrying up to 2W of optical power, with an optical bandwidth of 25 GHz, centered on the 200 GHz ITU grid. The design and the experimental results obtained during the integration of the multiplexer demonstrator are here presented and discussed.

The Mars Sample Return mission is a multiple probe mission to collect rock samples from Mars and bring them to Earth. The Perseverance rover is currently collecting samples on Mars. Tasked with the recovery of the Mars samples in Mars orbit and their return to Earth, the Earth Return Orbiter (ERO) is the last probe of the mission. In order to capture the Orbiting Sample (OS), which contains the Mars rock samples, the ERO will first detect the OS at long distance using its Narrow Angle Camera (NAC). Because the OS will be a faint object of magnitude 12, its detection is a challenge. One part of this challenge is to minimize the straylight caused by the illumination of the camera by much brighter out of field sources, such as the Sun and also the planet Mars. We describe here the design steps taken to minimize straylight, starting with measurement, design principles for the baffle and the objective, then finally simulations and their results.

EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) is the 6th Earth Explorer mission of ESA‘s “Living Planet Earth“ Program. The EarthCARE satellite is about to start its environmental test campaign in autumn 2022. This Core Explorer mission (Core Explorer missions that focus on scientific objectives of a large scientific community) is a large and very complex Earth Explorer mission with 4 Instruments on board. It improves the representation and understanding of Earth's radiative balance for climate and numerical forecast models by advancing our understanding of the role that clouds and aerosols play in reflecting incident solar radiation back into space and trapping infrared radiation emitted from Earth's surface. To achieve this goal, EarthCare is hosting a Multi-Spectral Imager (MSI), an Atmospheric Lidar (ATLID) and a Broad-Band Radiometer (BBR) under European ESA authority and a Cloud Profiling Radar (CPR) under JAXA (Japan Aerospace Exploration Agency) authority. The EarthCare MSI Instrument consists in two camera units, the TIR (Thermal Infrared Radiometer) part with 3 channels (Band7 [8800nm], Band8 [10800nm] and Band9 [12000nm]) and an VNS (Visible, Near-infrared and Short-wave infrared) part with 4 channels (VIS [670nm], NIR [867nm], SWIR1 [1654nm] and SWIR2 [2214nm]) and by an overall weight of around 50kg (including control units, harness and thermal hardware). The Instrument performance qualification consist in a full performance verification testing on instrument level and of regular instrument performance checks (IPCs) on Satellite level after Instrument integration. This performance checks for the MSI concentrate on a simplified test approach and are regularly repeated along the entire S/C AIT campaign until launch. The test results will be compared with first reference IPC measurements from instrument Level. MSI IPC definition does focus on radiometric key performance parameters as noise and responsivity to identify optical or detection chain degradations, as well as detector dead pixels. This paper will present the MSI IPC approach for EarthCare and the first ambient results from S/C Level MSI IPCs performed so far. Furthermore this paper will show that the ambient S/C Level MSI IPC results are in line with the ambient IPC on instrument level but it will also shows good agreement with thermal vacuum results on Instrument level.

Meteosat Third Generation (MTG) is the new European mission for accurate observation of the Earth dedicated to meteorological applications. MTG Program is being realised through the well-established and successful cooperation between EUMETSAT and ESA. MTG system will ensure continuity and enhancement of operational meteorological (and climate) data from Geostationary Orbit as currently provided by the Meteosat Second Generation (MSG) system. The industrial Prime Contractor for the Space segment of MTG is Thales Alenia Space (France) with a core team consortium including OHB (Germany). This contract includes the provision of six satellites, four Imaging satellites (MTG-I) and two sounding satellites (MTG-S), which will ensure a total operational life of the MTG system in excess of 20 years. MTG-I first satellite will be launched end of 2022, starting point of the in-orbit story of MTG. MTG-I embarks the FCI (Flexible Combined Imager), optical payload developed at Thales Alenia Space in France. The FCI is an imaging radiometer which provides simultaneously to the users 16 spectral channels from Visible to Very Long Wave InfraRed (0.4µm – 13.3µm) delivering full disk services (in 10 minutes) at their nominal sampling distance (1 to 2km). Four channels are also delivered at a smaller spatial sampling distance (down to 500m). FCI also provides local area scanning possibilities with a higher repeat cycle (down to 2.5 minutes). The present paper is dedicated to the FCI end-to-end radiometric performance. After an overview of the FCI and the design specificities of its detection chains, its key radiometric performance will be presented. It will focus on FCI PFM test results, which has successfully passed the on-ground fine radiometric calibration and characterization campaign under optical vacuum in 2021. After 10 years of development at Thales Alenia Space, with a fruitful cooperation of many European sub-contractors, the results of the performance characterization and calibration of the FCI have been successfully demonstrated. This work has been achieved thanks to the major support and supervision of ESA.

The Multi-viewing, Multi-spectral, Multi-polarisation Imager (3MI) is one of the payloads that will be on board of the MetOp-SG “Satellite A”, developed to provide information on atmospheric aerosols. 3MI is a space-based, wide field-of-view polarimeter that is designed to acquire sequential images of the same ground target, which are then combined with multiple spectral views in both un-polarized and polarized channels. This article presents the On-Ground calibration results on the 3MI PFM payload. The calibration request the measurement of a set of Key Data Parameters (KDP). These are needed in an instrument model. In the frame of 3MI calibration additionally to the geometrical, spectral and radiometric KDP, polarization and Stray Light are also considered. Because of 3MI wide FOV and polarization performance, dedicated Ground System Equipment GSE have been developed. Test results of the PFM calibration campaign are discussed and lessons learnt for the next campaign are proposed.

EarthCARE is the 3rd Earth Explorer Core Mission of the European Space Agency (ESA) Living Planet Program, with the fundamental objective of improving understanding of the processes involving clouds, aerosols and radiation in the Earth’s atmosphere [2] [3] [5] [6]. EarthCARE data products will be used to improve climate and numerical weather prediction. The data products include vertical profiles of aerosols, liquid water and ice, observations of cloud distribution and vertical motion within clouds, and will allow the retrieval of profiles of atmospheric radiative heating and cooling [4]. For above mission objective, the EarthCARE satellite hosts four complex instruments, the ATLID, (ATmospheric LIDAR from Airbus Toulouse), the CPR (Cloud Profiling Radar, from JAXA/NEC), the MSI (Multi Spectral Imager from SSTL) and the BBR (Broad Band Radiometer from TAS-UK). The instrument performance verification approach is based on (a) the full performance verification testing done on instrument level, and (b) on Instrument Performance Checks (IPCs) to be repeated periodically on instrument and satellite level. IPCs are designed to confirm that the core instrument performance as verified on instrument level does not degrade after integration on the platform and throughout the overall satellite AIT campaign until launch. Five ATLID IPCs have been defined in close cooperation between Airbus instrument and satellite prime teams, considering instrument performance verification needs as well as feasibility of IPC repetition in satellite AIT. This feasibility refers mainly to satellite AIT limitations for laser hazard protection measures, cleanliness (ISO8 environment), complexity of optical setups, need for limited test durations<1 day and more difficult instrument accessibility (instrument integrated at more than 3m height on the satellite). For the ATLID Lidar instrument, the following IPCs have been defined: (1) Transmit Laser Beam Line of Sight (LoS) stability, (2) Activation of Transmit Laser beam steering mechanism, (3) Laser pulse energy knowledge stability, (4) Overall Receive chain optical response check and (5) Detection chain total noise in darkness. IPC test definition as well as test results from instrument level and satellite level IPC testing will be presented. The trend of ATLID IPC test results is found stable along all test repetitions done until today. Additional presentation content can be accessed on the supplemental content page.

Thanks to a large set of available photocathodes with first in class QE, high gain, high collection efficiency, high dynamic range while keeping low dark count rate and single photon resolution capability with excellent timing, MCP-PMTs have emerged as candidates for LIDAR receivers. We present results of Ageing tests and Radiation tests carried out with Photonis and Airbus Defence & Space on High QE, and High linearity MCP-PMT for UV LIDAR receivers. Ageing of the photocathode is usually due to electron-induced ion feedback and molecule desorption from the MCP and anode, causing degradation of the photocathode layer leading to a progressive loss of QE related to the quantity of electron charges generated along lifetime. Expected Coulomb charges generated along a typical and worst-case mission were estimated from the atmosphere profiles. Thanks to a design change of the MCP-PMT and the implementation of Long-Lifetime MCP technology, ageing of the photocathode was drastically reduced. The new design showed no Quantum Efficiency nor Collection Efficiency degradation up to 20 C. Proton radiation tests were performed to evaluate false signal generated, end-of-life impact on performance, loss of transmission depending on the photocathode glass substrate as well as cathodoluminescence and photoluminescence at the photocathode. Quantum Efficiency, Collection Efficiency, PHD shape, Gain, and Linearity were found to be unchanged for fluences of 5x1011 p+/cm² with 60 MeV protons. Only small increase of DCR for about 120 cps/cm² was recorded about 8 weeks after the radiation.

The probe of HERA mission has a semi-autonomous navigation system that will perform fly-byes to the moon of the binary asteroid, called Didymos-B. The navigation is based on information given by the cameras and by the Planetary Altimeter (PALT). PALT is a Time-of-Flight (TOF) LIDAR that emits laser pulses of 2 ns, with 100 µJ of energy, at 1535 nm. PALT has a 70 mm Cassegrain telescope with an APD. PALT can take distance measurements from 500 m to 14 km with an accuracy of 0.5m. Aside from assisting navigation, the instrument will take scientific measurements that will contribute to the characterization of the asteroid topography. In this paper we present the Critical Design Review (CDR), which includes the optical, mechanical, and thermal designs, before manufacture. Regarding the optical system, the two mirrors are made of Zerodur, the secondary mirror is supported by a tripod structure made of carbon fibres, and the lenses are radiation resistant. The mechanical design has an innovative system that comprises a stainless-steel spring blades solution, which has the aim of protecting the optics bench plate and allows the survivability of the optics during launch. The thermal design solution was achieved by isolating the sub-systems with thermal washers and by implementing an optimized isostatic bipod mount structure in the primary mirror, making possible to reduce the stress on the optical component, while keeping the performance of the instrument. Additional presentation content can be accessed on the supplemental content page.

For crisis management and monitoring, a geostationary Earth observation telescope with large segmented aperture is investigated in JAXA. The preliminary study showed the feasibility of the aperture size of 3.6 m consisted with six primary mirror segments and the fundamental optical design. In order to obtain nearly diffraction limited performance with the optical system in the orbit, the aperture synthesis and wavefront error correction have to be conducted through precise alignment procedure, and therefore the system needs to equip several actuators and sensors dedicatedly designed for the purpose. We constructed the system design through the combination of structural-thermal analysis and optical consideration, and then planned the alignment procedure after launch. Those design concept are planned to be tested in the miniature testbed of segmented optical system under construction. We show the testing equipment and procedure for segment co-phasing and wavefront correction intending in space use.

For more than half of a century, Safran Reosc has been a key player in the development of optical components and equipment for space applications. From the Meteosat first generation and the SPOT 1 optics up to the most advanced enabling technology using silicon carbide off axis mirrors that are the key components of the Near Infrared Spectrometer, one of the instrument on board the recently launched James Webb Space Telescope, Safran Reosc has delivered optics for the most advanced scientific and earth observation satellites. This paper will highlight some of the recent developments in space optics and equipment: low CTE ceramics mirrors and silicon carbide free form mirrors and the SEEING instruments suite for nano-satellite earth observation and SSA applications. Ultra stable ceramics mirrors are still widely used for space mirrors application both for earth imaging applications and climate monitoring missions. The demands for extreme light-weighting mirrors are still further pushing the limits of glass machining technology and this trend is well illustrated by the primary mirror of the receiving channel of the MERLIN telescope, one of the most critical component of this mission devoted to the monitoring of the methane concentration in the Earth atmosphere. In the field of silicon carbide mirrors, Safran Reosc has delivered to Airbus Defence the highly aspheric freeform mirrors of the MICROCARB telescope to achieve unprecedented compactness. Safran Reosc has designed and developed the SEEING imagers, a family of 16U- 30U instruments for earth observation of meter class ground resolution. The first imager, the SEEING 130 a wide field of view instrument, will be delivered later this year to the Norwegian Research Defence Establishment and will be part of the NorSat-4 satellite.

ALTIUS is the next ESA limb-sounding mission for monitoring of stratospheric ozone at high vertical resolution and of NOx molecules and aerosols. With a platform based on the PROBA-NEXT concept flying in a Sun-Synchronous orbit, the data provided by the ALTIUS Mission will support the scientific community addressing key questions related to atmospheric chemistry composition and climate changes. The ALTIUS Instrument features wavelength-tuning capabilities in the UV (250-355nm), VIS (440-675 nm) and NIR (600-1020) bands using a Fabry-Perot interferometer (FPI) stack in the UV band and an Acousto-Optic Tunable Filter technologies (AOTF) in the VIS and NIR bands. This Instrument topology allows ALTIUS to perform 2D imaging with high resolution in the vertical profile of the Earth limb. The optical layout of 2D imagers, characterized by a more extensive field of view (FOV), makes them more susceptible to stray light issues in comparison to more conventional optical designs such as grating systems. These particular design aspects in combination with the use of novel technologies (FPI’s and AOTF’s) and the irradiance distribution of the observed bright limb scenes makes the stray light prediction very interesting and complex. An accurate modelling of scatter contributors involving optical and mechanical surfaces is, therefore, required. Due to the cost-effective model philosophy applied for the ALTIUS Instrument, no hardware model is available for stray light correlation purposes prior to the Instrument Proto-flight. Hence, a study was performed to benchmark the stray light analyses results obtained with Optic Studio with the ones obtained with FRED. This paper provides a description of the optical modelling features of the ALTIUS Instrument with specific attention to the novel optical devices, AOTF and FPI stack. It also addresses the particularities and differences observed when modelling the Instrument using two different commercial optical design suites. A comparison of scattered stray light computations for the ALTIUS Instrument ran in OpticStudio and FRED is also presented highlighting reflections on modelling approach and used mathematical models, with an outlook on consistency at L1. Finally, lessons learned from this exercise are presented along with the conclusions and plans for future work. Additional presentation content can be accessed on the supplemental content page.

This paper points out the lack of existing ground infrastructure that will be needed to communicate with the upcoming lunar missions. It discusses basic considerations about site locations and the pros and cons between Radio Frequency and laser-based communications. It also points out the challenges and risks that industry needs to consider for building this infrastructure. Finally, it recommends a hybrid solution for the future.

These last years have seen a raising interest for ground to GEO satellites optical very high throughput links, i.e. GEO-feeder links, or GEO-FL. However, despite their potential, these applications have to overcome atmospheric turbulence, which requires the development of mitigation techniques, such as adaptive optics (AO). In the case of GEO-FL, AO performance is limited by the Point-Ahead Angle (PAA) induced anisoplanatism. We describe here how our feedback on our field experiments helped us to design ONERA’s AO-compensated ground station, FEELINGS, and the status of said ground station in the fall of 2022.

In this paper we speak about the double-axicon unit built for the CaNaPy instrument, the LGS-AO backbone of the ESA ALASCA TRL6 facility, to demonstrate Optical Feeder Links for Satellite Communications in 2023 using Laser Guide Star Adaptive Optics technologies. The ALASCA system will co-propagate a guidestar laser (λ = 589 nm) and an infrared laser (λ = 1075 nm), using the monostatic approach through the entire 1-m Optical Ground Station (OGS) at Teide Observatory, Canary Islands (Spain). Provisions have been made to use either the full aperture or a section of the OGS primary mirror. The OGS telescope secondary mirror would introduce 30% central vignetting losses on the uplink laser beams. In order to minimise the losses, a double-axicon module shapes the gaussian beam as an annulus, thus optimises the laser profile to match the telescope pupil and nulls the losses, achieving the most efficient coupling to the OGS telescope. We present the CaNaPy axicon module design and analysis for the 589-nm laser as well as the ALASCA axicon module design for the OFL; we describe the tests done and the gain achieved in power transmission when shaping the laser compared to propagating a conventional Gaussian beam through a telescope with a non-negligible central obstruction.

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is a potential solution to overcome the limitations of RF links. To mitigate atmospheric turbulence effects, TNO proposes Adaptive Optics (AO) to apply uplink pre-correction. As a successor of Optics Feeder Link Adaptive Optics (OFELIA) breadboard [1], [2], the Terabit Optical Communication Adaptive Terminal (TOmCAT) project phase 2 aims to demonstrate the AO pre-correction technology for a terabit Optical Ground Station (OGT) in a ground-to-ground link field test over 10 km. Within this demonstrator an upgraded version of the OFELIA breadboard is used as optical bench for the AO (pre-)correction, but moreover the demonstrator enables the (future) integration of equipment for the final OGT configuration including the Beam Multiplexer (BMUX) and communication equipment. Apart from the OGT demonstrator, the overall layout of the field test has been upgraded, including the test site and the Ground Support Equipment (GSE), with the goal to create a better understanding of the encountered link phenomena and the instant (turbulence) conditions at which it was measured. New additions to the GSE are several weather stations placed along the link path to quantify the local turbulence and to relate the measured link performance to the instant turbulence conditions. The test campaign is split in two successive field tests: First the AO Demonstrator evaluates the upgraded AO pre-correction performance with a single non-modulated link, followed by the OGT Demonstrator which will include the multiplexing of multiple uplink channels and RF end-to-end modems to prove the technical feasibility of supporting a terabit communication link. This paper covers the design of the AO demonstrator and GSE, the field test layout and the preliminary results for the AO demonstrator field test. For the downlink correction the residual Wave Front Error (WFE) is presented. The pre-correction performance is depicted in the uplink transmission loss and scintillation, all as function of the encountered turbulence conditions.

The current paper introduces the Twin ANthropogenic Greenhouse Gas Observers (TANGO) instruments and mission. The purpose of TANGO is monitoring and quantifying greenhouse gas emissions, with a focus on characterizing emission sources down to the level of individual facilities. The TANGO mission was developed for the ESA-Scout program by a consortium consisting of ISISpace, TNO, SRON and KNMI. It consists of two agile CubeSat satellites that fly in tandem, with less than 1 minute between observations of the same target, each satellite equipped with a spectrometer of the TNO Spectrolite family of instruments that observes a different part of the spectrum. TANGO-Carbon measures emission of CH₄ and CO₂ in the SWIR1 spectral band. TANGO-Nitro measures emission of NO₂ in the visible spectral range. The Nitro instrument has a multifunctional role, using the NO₂ measurements to improve the detection of (anthropogenic) CO₂ plumes, deriving historic CO₂ emission trends based on available global NO₂ observations, and quantifying the possible CO₂ contribution in mixed CH₄-CO₂ sources. Each TANGO instrument fits in an 8U volume (on a 16U platform) and are all-aluminium, reflective pushbroom spectrometers covering a 30-km swath from a 500-km altitude, with a ground sampling distance of 300 m × 300 m. In this paper we will present the mission, the shared instrument concept, as well as the design and performance of both Carbon and Nitro instruments. Additional presentation content can be accessed on the supplemental content page.

METimage is a cross-purpose, medium resolution, multi-spectral optical imaging radiometer for meteorological applications on-board the MetOp-SG satellites. The fully representative instrument engineering model has been successfully tested and delivered to MetOp-SG. On METimage level this model served for instrument mechanical, thermal and EMC verification, at MetOp-SG level it supports the entire satellite test campaign. The instrument PFM integration is under finalisation by integrating the optical subsystems into the optical head. The preparation of the environmental test campaign and of the calibration and characterization campaign is ongoing.

The Infrared Atmospheric Sounding Interferometer New Generation (IASI-NG) is a key element of the second generation of EUMETSAT European Polar System (EPS SG) dedicated to operational meteorology, oceanography, atmospheric chemistry, and climate monitoring. A series of three IASI-NG instruments will be embarked on the second generation of European Meteorological Operational satellites (METOP SG) developed by ESA. CNES (Centre National d’ Etudes Spatiales) is in charge of IASI-NG overall system including the ground processing, the Technical Expertise Center and the Instrument, which is developed by Airbus Defence and Space. It will continue and improve the IASI mission in the next decades (2020-2040). The performance objective is mainly a spectral resolution and a radiometric error divided by two compared with the IASI first generation. The measurement technique is based on wide field Fourier Transform Spectrometer (operating in the 3.5 - 15.5 µm spectral range) using an innovative Mertz compensated interferometer to manage the so-called self-apodization effect and the associated spectral resolution degradation. We present here a synthesis of the development strategy, including the EM instrument campaign in parallel of the PFM, and the main milestones achieved on PFM instrument, which should be delivered for integration on Satellite in September 2022. In parallel, FM2 subsystems are under integration and first results on focal plane and interferometer should be available in third quarter of 2022. Additional presentation content can be accessed on the supplemental content page.

The detection and quantification of greenhouse gas (GHG) emissions, in particular carbon dioxide (CO2) and methane (CH4), is presently one of the main goals of remote sensing of atmospheric gasses on a global scale, for the strong impact these molecules have on climate change. Of particular urgency is the quantification of emissions from anthropogenic sources, a high-priority task addressed by the ESA Copernicus mission CO2M, which will provide global coverage detection of CO2 and CH4. The observation of CO2M, capable of quantifying emissions from the major sources, can be complemented by other observation systems addressing the smaller, and more numerous, sources. In this domain, static interferometers can offer several advantages. This paper reports on the main results of two activities completed within the ESA Future Missions activities in the Earth Observation Program, for the development of small instruments based on static interferometer designs, for the detection of CO2. The two studies, named Carbon-HIGS and Carbon-CGI, investigated two instruments operating in the SWIR and NIR bands, with a targeted precision of 2 ppm and an accuracy of 1 ppm for CO2 atmospheric concentration, covering a relatively small swath of 50 km at a spatial sampling better than 300 m. We summarize the general detection principles, the result of the design activities, and the estimated instrument performances. Both concepts are suitable candidates to work in conjunction with the Copernicus mission offering a zoom-mode observation, for quantification of medium-sized GHG sources and improved localization and understanding of anthropogenic emissions. Additional presentation content can be accessed on the supplemental content page.

A lot of investigations are ongoing for the development of laser systems with Alexandrite as active laser medium. These laser systems fulfill the general laser requirements for spaceborne Earth observation missions such as altimetry. However, to date, the laser systems and especially the coated Alexandrite crystals do not exceed Technology Readiness Level (TRL) 4. Therefore, the Horizon 2020 project GALACTIC was initiated to develop reproducible, fully European supplier-based functionally coated Alexandrite crystals, which show at least the same optical quality and laser performance in comparison to the components from the leading suppliers on the global market (mainly US and Chinese companies) and further fulfill the qualification to be generally used in space (i.e. verification of TRL 6). We present the high optical quality and good laser performance results of our developed Alexandrite crystals tested in a cavity-dumped Q-switched laser system. Furthermore, we show on the one hand the reproducibility and on the other hand the competitiveness of our crystals by a comparison study with our GALACTIC samples and crystals from two non-European suppliers. Additional presentation content can be accessed on the supplemental content page.

We report a lighter version of SuperCam laser for LIBS only operation. We investigate through CAD simulation the potential of an unsealed passively Q-switched Nd:YAG laser. We are able to reach a less than 100 g laser within 122 x 38 x 50 mm. Table top experiments are conducted. The final version leads to a 12.6 mJ, 4 ns laser with M² = 1.2.

Spaceborne precision frequency reference is one of the essential technologies for extensive applications in metrology, astronomy, remote sensing and global navigation satellite system, and we have researched and developed a high-precision microwave generation system which is based on an optical frequency reference. In our system, a highly-stable optical frequency is generated from an iodine-stabilized laser whose frequency is down-converted to the microwave region without degradation by using an optical frequency comb. The frequency stability of the iodine-stabilized laser would reach 10−15 level. In this conference, we will mainly present the development of the optical frequency comb. Nonlinear amplifying loop mirror (NALM)-type mode-locked fiber lasers have two kinds of configurations, figure-8 and figure-9. The figure-9 laser is widely used as an oscillator for the optical frequency comb due to its excellent low phase noise, and there are few reports of the figure-8 mode-locked fiber laser-based optical frequency comb. On the other hand, the operation of the figure-8 would be very stable against external perturbations because of its all polarization-maintaining fiber configurations. Therefore, we have developed low-phase-noise figure-8 lasers for our optical frequency comb because its robustness is suitable for the spaceborne system. One of the significant points of our figure-8 laser is that two types of erbium-doped fibers with different concentrations are used as the gain media of the oscillator. The repetition rate, the center wavelength and the width of the optical spectrum of our figure-8 laser are 51 MHz, 1560 nm and 58 nm, respectively. Though any NALM type mode-locked fiber laser needs initial impulse for starting mode-locking operation, our figure-8 laser can start mode-locking automatically without special procedure, which is called self-starting. We tried the operation test repeatedly for about 1600 times whose success rate reaches 99.94%. The disturbance tests and the thermal vacuum tests have been applied to our figure-8 laser, and under the conditions of both tests, our figure-8 laser shows the stable mode-locked operation without any break of mode-locking. In the radiation exposure test, we have confirmed the stable operation of our figure-8 laser till 30 krad radiation dose, and at higher radiation doses the mode-locking operation stopped.

A radiation tolerant Erbium fiber based optical frequency comb has been developed and environmentally tested. The system remained operable after an accumulated dose of 1 kGy^∗

. The underlying femtosecond fiber oscillator and Erbium fiber amplifiers have been manufactured from speciality doped fibers. The fiber optic system has been assembled and packaged using low outgassing components in a flight representative package before it was irradiated under active operation in two stages a 500 kGy. The accelerated ageing with dose rates of 10 mGy/s in water was tested using the calibrated Cobalt 60 source of the ESA-ESTEC facilities. The comb laser remained fully functional while the oscillator lost up to 30% of output power after the full exposure to the accumulated dose of 1 kGy. The fiber amplifiers lost 5-7% of output power.

BEaTriX (Beam Expander Testing X-ray facility) is the new facility available at the INAF-Osservatorio Astronomico Brera (Merate, Italy) for the calibration of X-ray optics. Specifically designed to measure the point spread function (PSF) and the effective area (EA) of the mirror modules (MM) of the ATHENA X-ray telescope at their production rate, BEaTriX gives the unique possibility to test the optics with a source that approximate an astronomical source, i.e. with a large, parallel X-ray beam (170 × 60 mm²) that fully covers the entrance pupil of the MM. For a fast and precise testing, BEaTriX is a compact facility (9 × 18 m²) with fast vacuum pump-down (to 10^-6 mbar), and an optical setup able to create the X-ray beam with a residual divergence of about 2-3 arcsec, HEW, and with a flux of 60 photons/s/cm². The first beam line at the energy of 4.51 keV is now operative, and a second beam line, working at the energy of 1.49 keV, will be implemented in the coming future. The unique characteristics of the BEaTriX X-ray beam are obtained with an X-ray microfocus source placed in the focus of a paraboloidal mirror, a monochromation stage with 4 symmetrically cut crystals, and an expansion stage where the beam is diffracted and expanded by an asymmetrically-cut crystal. The beam, reflected by the MMs, is then imaged at 12 m distance, where a directly-illuminated CCD camera is placed. This paper presents the facility, the calibration of the beam and the latest results with the ATHENA MMs.

MINERVA is an X-ray beamline designed to contribute to the development of the ATHENA^{1, 14} mission (Advanced Telescope for High Energy Astrophysics) at the ALBA synchrotron2 (Barcelona, Spain). Originally based on the monochromatic pencil beam XPBF 2.0 at the Physikalisch-Technische Bundesanstalt (PTB at BESSY II), MINERVA will be furnished with the necessary equipment to produce and characterize the mirror modules (MM) of ATHENA by adjusting and assembling 4 SPO stacks together (manufactured by cosine measurement systems) ^4,5. The construction of MINERVA is also an opportunity to bring some innovations in order to improve the characterization time of each MM produced⁶. Full interoperability with XPBF 2.0 is secured to allow operators to work on both beamlines the same way. The MINERVA project started in March 2020 and the last past months were dedicated to the definition, design, procurement, partial assembly and installation of the different beamline components. MINERVA is funded by the European Space Agency (ESA) and the Spanish Ministry of Science and Innovation and will be completed for operation at the turn 2022/2023.

At the PANTER X-ray test facility of the Max Planck Institute for Extraterrestrial Physics the testing of optics for ESAs ATHENA Mission is ongoing, as part of work towards the mission acceptance review. The ATHENA 2.6-m diameter mirror assembly comprises an aluminium support structure that holds the 600 Silicon Pore optic Modules (SPOs) that focus the X-rays coming from the sources in the universe. At PANTER, these lightweight SPO modules are being tested individually or mounted in a petal that represents a sixth of the mirror structure. MM-0051 is the last iteration of a single mid-radius SPO to be tested at PANTER. A detailed description of the MM-0051 measurements is presented here. The characterization of three ATHENA “row 8” SPO optics produced to be inserted into the test petals shows that they will provide the necessary precision on the localization of the PSF on the detector to allow the verification of the thermal models of different mirror structure designs by the primes Airbus Defense and Space and Thales Alenia Space. Currently the opto-thermo-mechanical tests are ongoing at PANTER

LEXI is a wide-field X-ray imager using bare-glass slumped micropore optics. The LEXI optic was recently characterized at PANTER to measure both the point spread function and the effective area as a function of energy. The effective area measurements were made with a continuum source in order to characterize the effective area curve at moderate energy resolution over the 0.2-4.0 keV range. Comparison of measurements with ray-tracing suggests a number of ways modeling can be improved in the future.

Quantum Key Distribution (QKD) is the most mature quantum technology, having achieved on-ground applications and commercially available products. In this domain, satellite platforms are essential to achieve a communication range reaching the intercontinental scale, acting thus as enablers for the future global quantum internet operation. This paper will report on the main results of the TNO-Eutelsat-TAS Italy project aiming to evaluate a novel hybrid approach for improved QKD performance particularly suited for geostationary orbits (GEO); the Dutch TKI HTSM sponsors the overall activity. We will present the results of lab-based tests of a novel QKD free-space approach that simultaneously implements the BBM92 protocol in both trusted and trust-free mode, following a joint Eutelsat-TNO patent. The trust-free mode between two ground receivers is the standard BBM92 protocol that uses entangled photons and there is no need for further security assumptions on the satellite payload. In trusted mode operation, one of the two entangled photons is measured directly on board. Key material is generated between ground and satellite. Security measures will be needed in the space segment, which therefore needs to be trusted. Further, we will present a demonstration roadmap aiming at free space field test to validate loss and key rate models for a free space link up to 2.5km in one of the arms. We also present a perspective on potential future GEO-based quantum applications beyond QKD. Additional presentation content can be accessed on the supplemental content page.

In the frame of the Secure And cryptoGrAphic (SAGA) project under ESA ARTES 4.0 program, we report the design and the test of a High-Performance Entangled Photon Source (HP-EPS) dedicated to QKD satellite-based communication, by using the Conventional-band optical fiber telecom components. We developed an asynchronous time binning higher than 10 bits/sec and 5 bits/sec for respectively a 60 dB (LEO) and a 65 dB (GEO) transmission loss budgets (both downlinks combined). The compactness and simplicity of the optical design, the low electrical consumption and the low mass combined with the robustness of the all-fibered design to the space environment (mechanical vibrations, shock, and radiations) make the HP-EPS a valuable and serious candidate for the satellite-based QKD quest.

In recent years, quantum key distribution (QKD) has seen the first proof-of-concept demonstrations from space. Next on the agenda towards a full-blown global quantum internet is to address the more practical aspects, such as efficiency, flexibility, and accessibility of QKD services. One of the main challenges that remains to be solved in this regard is to enable operation in the presence of daylight noise. Here, we present a complete framework for modelling daylight QKD from an orbiting satellite. We include the effects of atmospheric turbulence and adaptive optics correction at the receivers. We consider single- and multi-mode fibre coupling as a means of spatial filtering, for which we derived simple formulas for estimating coupling efficiencies of signal as well as noise. Using our framework, we identify the most critical system parameters for daylight operation and discuss the choice of signal wavelength and detection technology. Finally, we provide simulation results for various parameter combinations in a hypothetical daylight QKD between Berlin and Munich via a satellite in a low Earth orbit. The results show a clear advantage of 800 nm signal wavelength over 1550 nm with the currently available technology. Moreover, we show the relevance of single-mode fibre coupling and the importance of detectors with low timing jitters. We anticipate our work will provide valuable insight and tools to aid the future feasibility studies of daylight QKD in dual-downlink configurations. Additional presentation content can be accessed on the supplemental content page.

Quantum key distribution (QKD) enables tap-proof exchange of cryptographic keys guaranteed by the very laws of physics. One of the last remaining roadblocks on the way towards widespread deployment of QKD is the high loss experienced during terrestrial distribution of photons, which limits the distance between the communicating parties. A viable solution to this problem is to avoid the terrestrial distribution of photons via optical fibers altogether and instead transmit them via satellite links, where the loss is dominated by diffraction instead of absorption and scattering. First dedicated satellite missions have demonstrated the feasibility of this approach, albeit with relatively low secure key rates. In order for QKD to become commercially viable, the design of future satellite missions must be focused on achieving higher key rates at lower system costs. Current satellite missions are already operating at almost optimal system parameters, which leaves little room for enhancing the key rates with currently deployed technology. Instead, fundamentally new techniques are required to drastically reduce the costs per secret bit shared between two distant parties. Entanglement-based protocols provide the highest level of security and offer several pathways for increasing the key rate by exploiting the underlying quantum correlations. In this contribution, we review the most relevant advances in entanglement-based QKD which are implementable over free-space links and thus enable distribution of secure keys from orbit. The development of satellite missions is notoriously lengthy. Possible candidates for a new generation of quantum payloads should therefore be scrutinized as early as possible in order to advance the development of quantum technologies for space applications.

TRUTHS (Traceable Radiometry Underpinning Terrestrial – and Helio- Studies) is a hyperspectral climate mission which, with the support of an on board calibration system traceable to national standards, will enhance our understanding of the Earths changing radiation budget by an order of magnitude. The payload being developed by consortium led by Airbus UK includes three major subsystems: a hyperspectral imager capable of high resolution spatial and spectral lunar and earth measurements, a cryogenic radiometer with three high precision temperature controlled cavities traceable to national standards and a transfer systemto convert this calibration into one of diffused radiance for comparability with measurements made with the hyperspectral imager. The on board calibration system also includes a solar monochromator and a range of mechanisms and distribution optics to enable the calibration sequence and the required modes of the instrument. This paper will summarise the design concept for the on board calibration chain developed during the Phase A/B1 instrument studies carried out in 2020-2022. The presentation will discuss the main engineering challenges and tradeoffs and the outlook and development plan for the Phase B2CD programme will be presented.

The PROBA-3 double-spacecraft formation flying mission of the European Space Agency (ESA) has been presented in recent papers with details about the mission profile, the operation objectives, and the implemented technologies. PROBA-3 will fly the externally occulted coronagraph ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), with the telescope on one satellite and the occulter on the other one, at 144m. The scientific objective is to realize an artificial total solar eclipse to observe the lower Sun corona. The high accuracy metrology control is the core of the mission and several sub-systems will be verified and validated to realize the coronagraphic formation. Between these, the Shadow Position Sensors (SPS), composed of eight photo-multipliers mounted around the ASPIICS entrance pupil monitoring the solar penumbra symmetry, will return the 3D positioning of the formation with the highest accuracy. The SPS on-ground calibration was completed in 2021 and one of the main aspects of the test has been the implementation of an illumination scheme to simulate the same conditions the SPS will experience in flight. This was realized using a suite of LED sources properly assembled in a testbed used to reproduce the expected observation configurations. This testbed is supported by a dedicated software able to simulate the different illumination conditions and to drive the control of the LEDs in order to feed each SPS sensor with the proper light flux. In this paper, we review the SPS metrology system, the calibration testbed setup, and we discuss the interface control software, the simulation tool, and the data acquisition procedure adopted to calibrate the LED sources. Additional presentation content can be accessed on the supplemental content page.

Within the DLR project COMPASSO, optical clock and link technologies will be evaluated in space on the Bartolomeo platform attached to the Columbus module of the ISS. The system utilizes two iodine-based frequency references, a frequency comb, an optical laser communication and ranging terminal and a GNSS disciplined microwave reference. While COMPASSO is specifically dedicated to test optical technologies relevant for future satellite navigation (i.e. Galileo), the technologies are also crucial for future missions related to Earth observation and science. The optical frequency reference is based on modulation transfer spectroscopy (MTS) of molecular iodine near a wavelength of 532 nm. An extended cavity diode laser (ECDL) at a wavelength of 1064 nm is used as light source, together with fiber-optical components for beam preparation and manipulation. The laser light is frequency-doubled and sent to a mechanically and thermally highly stable free-beam spectroscopy board which includes a 20 cm long iodine cell in four-pass configuration. The iodine reference development is lead by the DLR-Institute of Quantum Technologies and includes further DLR institutes, space industry and research institutions. Phase B of the project will be finalized soon and an Engineering Model of the iodine reference, which represents the flight models in form, fit and function, will be realized by mid 2023. The launch of the COMPASSO payload is planned for 2025. Additional presentation content can be accessed on the supplemental content page.

The Meteosat Third Generation is the new generation of European operational geostationary meteorological system. The MTG series will comprise 4 imaging (MTG-I) and 2 sounding (MTG-S) satellites. The MTG-S sounding satellites, whose development is led by OHB System (Wessling, Germany), will carry 2 instruments: an Infrared Sounder (IRS) and an Ultraviolet Visible Near-Infrared spectrometer (UVN). The aim of IRS instrument is to provide detailed vertical profiles of atmospheric temperature and water vapor at a high spatial resolution of 4km. These data will be used in the future for numerical weather prediction and nowcasting. In the framework of this project, AMOS (Liège, Belgium), as a subcontractor of OHB, is the responsible for the design, manufacturing, integration, alignment and testing of the Geometrical and Spectral Test Assembly (GESTA) for the performance tests and calibration if the IRS under operational conditions. GESTA is an Optical Ground Support Equipment (OGSE) used for optical measurements during the alignment and test phases of the Infra-Red Sounder (IRS) instruments. The GESTA is composed of three different main subassemblies: The source Assembly (SA), designed by Bertin Technologies (Aix-en-Provence, France) is composed of a heated pattern plate mounted on an XY translation stage enabling to position it across the focal plane of the collimator. A Cold Black Body, operated at 90K, ensures the necessary contrast for the geometrical measurements. An Integrated Sphere is fed with MWIR and LWIR laser outputs, which are located outside of the vacuum chamber, and hence generates a uniform monochromatic output towards the collimator and ultimately the IRS. The Gas Cell, designed by Centre Spatial de Liège (CSL – Liège, Belgium), consists of a Hot Black Body, operated at high temperature (295K, 523K), as broad-band MWIR/LWIR light source and an atmospheric gas cell, operated at 293K with the possibility to fill it with up to 4 different gases in order to check the spectral and radiometric sensitivities of the IRS. The collimator, designed by AMOS, consists in a four mirror anastigmatic telescope with focal length of 2600 mm and an entrance pupil size of 320mm, operated at ambient temperature (293K). The collimator mirrors are made out of light-weighted aluminum structure with gold coating. The mirrors are mounted on a baseplate, which is of the same material and allows low stresses and deformations due to differential thermal dilatation. In view of its qualification, GESTA underwent an extensive testing campaign including thermal control performances, alignment stability and radiometric performances under operational conditions (i.e. same conditions as the ones encountered with the IRS instrument in front of GESTA). The results of the tests allow to demonstrate the compliance of the GESTA OGSE to the requirements. Additional presentation content can be accessed on the supplemental content page.

LiDAR remote sensing of the atmosphere requires a photons detection chain with a high sensitivity and a high dynamic range associated with a good temporal resolution. To meet these requirements, a specific CMOS read out circuit (ROIC) has been studied, design and realized at CEA/Leti within the frame of the H2020 project HOLDON. This ROIC is based on a CTIA amplifier with four different current/voltage conversion gain thanks to capacitance ranging from 10 fF to 10 pf. Other functionalities like on chip sampling, auto-reset or programmable low pass filtering have been implemented to optimize the detector for different measurement chain. Based on this circuit architecture, two versions of the ROIC with different way to connect the circuit to the photodiodes have been manufactured and tested. The first one is design to be directly hybridized to a small array of photodiodes with a format imposed by the ROIC design in term of pixel pitch and array size. For the second ROIC version, the photodiode array is hybridized to an interconnection circuit used as a fan-out of electrical connections to a bonding pad. This module is then wire-bonded to the ROIC to get the final detector assembly. This configuration allows us to couple the ROIC with different APD geometry adapted to a specific application need. The performances of one of the first hybridized devices were previously presented during ICSO 2020[1]. For this review, we focus on the second version of the ROIC. The tested detector module is made of an array of 76 HgCdTe APD in parallel with a pixel pitch of 15 µm. The array forms a 150 µm diameter macro-photodiode. The device was tested at 78K within a liquid nitrogen cooled cryostat. Under photon flux, we have obtained a linear response of the device with an incoming flux varying over more than six orders of magnitude without varying the APD gain. This wild dynamic is associated with a high sensitivity with a noise standing below the unique photon. The response to a brief laser pulse gives a rise time ranging from 175 ns for the highest CTIA gain to 6 ns for the lowest CTIA gain.