Tomás Belenguer

As origami-inspired solutions become more mature in spacecraft structures and applications, new alternatives are arising for traditional designs, allowing for creative and innovative answers to common problems. In this work, we look into space telescopes, one of the most feasible applications for new tubular solutions, using origami structures to propose the design of a self-retractable baffle. An element needed for mitigating both in-field and out-of-field stray light and helping to improve the image quality of the optical system. This baffle is rethought as a tubular, origami-inspired structure, built over a Kresling origami pattern. This choice can be traced back to the properties such structure has to offer: bi-stability, packaging ratio and controllability. Thus, it is becoming a promising alternative to standard baffles and helping to reduce key factors in spacecraft design, such as weight and complexity of the optomechanical mechanism. To demonstrate its effectiveness in an optical system, the professional software ASAP (Advanced System Analysis Program) is utilised to assess the optical performance of the new baffle design. As a result, we verify the applicability of these patterns and, therefore, the whole structure from an optical point of view, confirming the interest of its application as a telescope baffle. This solution also allows moving and modifying the inclination, shape or size of the baffle, selecting the amount of screening and light incidence into the telescope in a controlled manner depending on the orbit and attitude of interest.

The core of spectrometers for deep space exploration in the far- infrared spectral range is a diffraction grating optimized for a defined range of wavelengths. This contribution presents an in-depth analysis of the fabrication, morphological characterization, and spectral efficiency verification of this type of gratings operating in the THz range. Two different manufacturing techniques were used: The first one was laser ablation and micro-structuring with a 5-axis femtosecond laser system, and the second one was a traditional micro-machining technique using milling tools. The gratings have a blazed geometry with saw-tooth profiles that enhances the efficiency of the diffracted order of interest, $m=1$ , at the TM polarization mode, and within a spectral range between 70 and 114 $\mu$ m. The morphological features of the fabricated gratings were measured by confocal microscopy and analyzed using topographic parameters. The measured averaged profiles were used to compute the diffraction efficiency of the fabricated gratings and to compare the actual manufactured profiles against the experimental results. Our measurement setup fixes the wavelength of the illuminating source to six values between 60 and 120 $\mu$ m (2.5 and 4.7 THz). At each of these spectral lines, we have scanned the angle of incidence between 20 $^\circ$ and 75 $^\circ$ . This angular range includes the nominal value of the angle of incidence, $\theta _\mathrm{inc}=57^\circ$ . The experimental values of efficiency can be easily compared with those resulting from computation, where the efficiency is calculated for each one of the available wavelengths as a function of the angle of incidence. This approach has allowed us to validate the design and conclude that gratings fabricated using femtosecond laser ablation perform better than those obtained through micromachining processes. In any case, both manufacturing techniques generate gratings above the validation threshold for diffraction efficiency, $\eta > 0.65$ .

The ITER equatorial visible and infrared Wide Angle Viewing System (WAVS) will play a major role in the protection of plasma facing components by providing surface temperature measurements of these components. It will also image the plasma emission in the visible range. The WAVS is composed of 15 lines of sight located in four Equatorial Ports (EPs) 3, 9, 12, and 17. Its development is being carried out by the Consortium constituted by CEA, CIEMAT, INTA, and Bertin Technologies, within grant contracts financed by F4E. In the EP12, the in-vessel and ex-vessel components of the WAVS are at their final design phase. This article presents an overview of the opto-mechanical design of the WAVS in the EP12 presented at the final design review.

Far infrared spectrometers have a prominent role to play in future space missions devoted to unveiling the obscure universe. Diffraction gratings are the heart of these instruments that, when operating in the range of a few THz, shall cover a wide spectral range providing the highest resolution and efficiency, generally for only a single polarization, within the specified spectral range. This contribution describes the optimization of the diffraction efficiency of the first diffractive order for a blazed metallic grating working at a large angle of incidence. Since the grating period is of the same order of magnitude as the wavelength, it is necessary to approach the design by solving Maxwell's equations rigorously using computational electromagnetism. We have applied the Rigorous Coupled-Wave Analysis and the Finite Element Methods to simulate the performance of the grating. This analysis provides relevant hints for the selection of the period, and the blaze and slant angles of the grating. A metallic blazed grating has been fabricated on aluminum and its topography has been characterized to determine the discrepancies with respect to the nominal values. The fabricated profile has been simulated to obtain the expected results in efficiency in comparison with the ideal case. This analysis provides guidance for improved manufacturing processes and experimental verification.

A composite optical bench made up of Carbon Fiber Reinforced Polymer (CFRP) skin and aluminum honeycomb has been developed for the Tunable Magnetograph instrument (TuMag) for the SUNRISE III mission within the NASA Long Duration Balloon Program. This optical bench has been designed to meet lightweight and low sensitivity to thermal gradient requirements, resulting in a low Coefficient of Thermal Expansion (CTE). In addition to the flight model, a breadboard model identical to the flight one has been manufactured, including embedded fiber Bragg temperature and strain sensors. The aim of this is to explore if the use of distributed fiber Bragg gratings (FBGs) can provide valuable information for strain and temperature mapping of an optical instrument on board a space mission during its operation as well as its on-ground testing. Furthermore, surface-mounted strain FBG sensors and thermocouples have been installed in the optical bench for intercomparison purposes. This paper presents the results obtained from a thermal vacuum test consisting of three thermal cycles with stabilization steps at 100 °C, 60 °C, 20 °C and −20 °C. Experimental results provide information about how FBG embedded temperature sensors can provide a proper and quick response to the temperature changes of the optical bench and that embedded FBG strain sensors are able to measure micro-deformation induced in a close-to-zero CTE optical bench.

The composition of the Martian atmosphere and its dust content is a key factor for understanding the climate of the Red Planet, which is of vital importance to enable future human exploration. The use of atmospheric LIDARs to characterize densities and sizes of aerosol with a height profile, is commonly used on Earth. However, Earth LIDARs are heavy and very power-demanding, which make them not easily on-boardable for planetary exploration. We propose the development of a compact LIDAR aimed at providing the most precise characterization of the suspended dust and clouds of the atmosphere of Mars to-date, while maintaining very reduced power, mass and volume envelops to facilitate its accommodation in a wide variety of landed assets. Rationale and heritage In the past years, INTA has developed four miniature radiometers for different missions: MetSIS for MetNet Lander [1], DREAMS-SIS for Schiaparelli [2], SIS’20 for Kazachok [3] and RDS for Perseverance [4].  All of them, at different levels depending on their complexity, allow the estimation of the atmospheric optical depth with high time resolution, detection of clouds and estimation of the dust concentration vertical profile. A natural step forward to complement our capabilities, especially for the dust profile and characterization of clouds, is a LIDAR. There is only one LIDAR that has already operated on Mars, on board the Phoenix mission. With a 2-wavelengths configuration at 532 and 1064 nm but without depolarization, it operated in the North Pole of Mars for 90 sols [5]. The laser pulses had a power of 30-40 kW and duration of 10 ns. Total mass was 6 kg and the power consumption 30W. A '2B+1d' LIDAR configuration is proposed here to obtain the Particle Backscatter Coefficient (PBC) at two wavelengths (2B), and the depolarization ratio at one of them (1d). They both are used to obtain three LIDAR parameters relevant for dust and cloud characterization: the particle linear depolarization ratio (PLDR), the lidar ratio (LR), and the colour ratio (CR). The intended range is set around 20 km, depending on the scenario, and depolarization measurement capability shall be incorporated. Key technologies for miniaturization The target mass and power envelop are <4 kg and <15W, respectively. The instrument should be capable of operating at atmospheric temperatures below -100°C to minimize the requirements for its accommodation. Achieving those goals will be a technological challenge, and it will be necessary to use technologies not employed before in this scenario. Several key aspects are identified: Pulsed semiconductor laser diodes are proposed for the transmitter, instead of usual (and bulkier) diode-pumped, Q-switched solid-state lasers. This reduces the emitted energy and in turn requires higher repetition rates to improve the Signal-to-Noise ratio. Silicon Photomultipliers, also known as Multi Pixel Photon Counters, will be used as detectors. They allow lower biasing voltages than other high-gain technologies, while they show some trade-offs such as their so-called "cross talk" noise. Its performance under the applicable thermal and radiation environments must be addressed. The use of new synthesis methods to obtain very low thermal expansion coefficient (CTE) materials (crystalline β- eucryptite) to reduce the thermal requirements related to structure and alignment. To reduce the size of the optics and to mitigate the complexity of the collimation of a semiconductor laser (with large spots and emission apertures), 'free form' optics will be considered in the optical design. From the signal processing point of view, the aim is to design a receiver that autonomously adapts the measurement mode (analogue or pulse counting) and parameters (e.g., variable time intervals for pulse-counting) in real time, providing the best signal quality vs. vertical resolution compromise for each altitude. Feasibility To preliminarily assess the feasibility of this LIDAR to reach a scientifically meaningful range, we have performed several simulations of the expected signal and signal-to-noise ratio using extinction and backscattering profiles representative of different dust conditions on Mars, together with technical data extracted from the datasheets of real pre-selected parts and opto-mechanical parameters values that we consider feasible for a compact instrument as the intended one. Emitted pulses have a power of 600W and a duration of 150ns. We have simulated three different background illumination scenarios: night, twilight, and midmorning, as this is critical from the point of view of the “offset” signal it generates (that must be filtered out) and the noise associated with it. We employed worst-case (high) diffuse radiance values on Mars. Extinction and backscattering coefficients have been extracted from Phoenix LIDAR measurements [6], and background illumination values from RDS measurements in Perseverance. The conclusion is that, with adequate signal processing, we should be capable of reaching 4 km during the day, 6-7 at twilight and 15 at night, for the worst-case scenario. 20 km are feasible in better scenarios. On-going activity and next steps A breadboard prototype of the system is being built at INTA for only one channel (one wavelength; no polarization) based on pre-selected pulsed laser diode and silicon photomultiplier, with standard off-the-shelf optical parts and filters. Preliminary laboratory and outdoor measurements will be done to validate the simulations and confirm the feasibility of reaching a meaningful range with the strict miniaturization constraints. Low-temperature characterization of the emitters and detectors, as well as Displacement Damage tests to assess their robustness to the radiation environment will be done by the end of the year. The electronic design has a large heritage from previous Martian sensors as the ones mentioned above, all of them designed to operate down to...

This work presents an experimental study on the effects of gamma radiation on Long Period Fiber Gratings (LPFGs) in a low-dose test campaign to evaluate their eventual degradation. The study was carried out with standard single-mode fibers where the grating was inscribed using the Electric-Arc Discharge (EAD) technique. Before the gamma campaign, a detailed optical characterization was performed with repeatability tests to verify the accuracy of the setup and the associated error sources. The gamma-induced changes up to a dose of 200 krad and the recovery after radiation were monitored with the Dip Wavelength Shift (DWS). The results show that the gamma sensitivity for a total dose of 200 krad is 11 pm/krad and a total DWS of 2.3 nm has been observed with no linear dependence. Post-radiation study shows that recovery from radiation-induced wavelength shift is nearly complete in about 4000 h. Experimental results show that the changes suffered under gamma irradiation of these LPFGs are temporary making them a good choice as sensors in space applications.

This work presents an optical non-contact technique to evaluate the fatigue damage state of CFRP structures measuring the irregularity factor of the surface. This factor includes information about surface topology and can be measured easily on field, by techniques such as optical perfilometers. The surface irregularity factor has been correlated with stiffness degradation, which is a well-accepted parameter for the evaluation of the fatigue damage state of composite materials. Constant amplitude fatigue loads (CAL) and realistic variable amplitude loads (VAL), representative of real in- flight conditions, have been applied to “dog bone” shaped tensile specimens. It has been shown that the measurement of the surface irregularity parameters can be applied to evaluate the damage state of a structure, and that it is independent of the type of fatigue load that has caused the damage. As a result, this measurement technique is applicable for a wide range of inspections of composite material structures, from pressurized tanks with constant amplitude loads, to variable amplitude loaded aeronautical structures such as wings and empennages, up to automotive and other industrial applications.

We present an optical sensing methodology to estimate the fatigue damage state of structures made of carbon fiber reinforced polymer (CFRP), by measuring variations on the surface roughness. Variable amplitude loads (VAL), which represent realistic loads during aeronautical missions of fighter aircraft (FALSTAFF) have been applied to coupons until failure. Stiffness degradation and surface roughness variations have been measured during the life of the coupons obtaining a Pearson correlation of 0.75 between both variables. The data were compared with a previous study for Constant Amplitude Load (CAL) obtaining similar results. Conclusions suggest that the surface roughness measured in strategic zones is a useful technique for structural health monitoring of CFRP structures, and that it is independent of the type of load applied. Surface roughness can be measured in the field by optical techniques such as speckle, confocal perfilometers and interferometry, among others.