ABSTRACT Smart optical solar reflectors (OSRs) with temperature‐adaptive radiative emission around room temperature are highly desirable for passive thermal management in spacecraft. This work demonstrates a smart and flexible metasurface‐based OSR, or meta‐OSR, consisting of an optimized W:VO 2 ‐based metasurface and a low emissivity solar reflector. The fabricated smart meta‐OSR overcomes long‐standing challenges by combining a solar absorption ( α ) of 0.22, high‐temperature emissivity ( ε hot ) of 0.8, infrared emissivity contrast (Δ ε ) of 0.33 and a transition temperature ( T MIT ) of 30°C. In addition, through the use of nanoimprint lithography and a low‐temperature W:VO 2 process, the smart meta‐OSR is demonstrated over an area of 10 × 10 cm 2 on space‐grade polyimide, achieving significant weight reduction and easy integration on satellite surfaces. The fabricated devices successfully passed various space qualification tests, including thermal cycling, proton and electron radiation, adhesion, bending and humidity resistance, showing negligible performance degradation. The smart meta‐OSRs in this work are production‐ready and hold promise as next‐generation thermal control solution for ultralight spacecraft and small satellites.

In the frame of an ASI co-founded research project (CUP F89J20000970005) an advanced radiator with an innovative biomimetic surface was developed for new-generation satellites and pressurized modules. The project involved Thales Alenia Space in Italy, University of Roma Tre, CNR and C.R.E.O. and ran for 36 months starting in 2021. The research aimed to design and test a novel radiator with embedded a fully passive power saving feature. Main goal was to reach a radiator turn-down ratio lower than 1:4, to tune thermal rejection depending on satellite/module needs. The biomimetic surface enables passive thermal control features by covering the radiator at low temperature (closure at 0°C, exposing a low thermal emitting surface, ε≈0.1) and discovering it at high temperature (opening at 20°C, exposing a white coating, with low solar absorbance α≈0.1, and high thermal emittance ε≈0.8) in a purely passive way. In this way the power budget is reduced and the on-board computer is simplified, especially saving energy during long transient phases. Once on orbit the radiator maximizes heat rejection when fully exposed. Following the definition of requirements, technological specimens, bio-mimetic surface samples and, finally, a full-scale radiator demonstrator were developed and tested. Samples representative of bio-mimetic surface key technologies were optimized, manufactured to a full scale model and subjected to environmental tests, including exposure to protons, electrons radiation and atomic oxygen, to verify their compatibility with space conditions. A full-scale demonstrator was finally built to validate the system. During thermal vacuum testing, the bio-mimetic surface successfully demonstrated petals-like opening and closing based on radiator panel temperature. Thermalization was achieved using a heating fluid (ethylene glycol-water mixture) circulated through 4 mm internal diameter radiator piping. This project demonstrates the feasibility of an efficient radiator for space applications, with significant potential for future thermal control systems.

Optical Solar Reflectors (OSRs) constitute the physical interface between radiator panels and outer space and allow for radiative cooling of the spacecraft. The performance of an OSR is defined mainly by two Thermo-Optical (T.O.) parameters: solar absorptance ? (the lower the better) and IR emittance ? (the higher the better). The market of OSRs is dominated by OSR quartz tiles, and by flexible Second Surface Mirrors (SSMs). Quartz OSRs exhibit excellent T.O. properties and durability, but are expensive and tend to break during assembly, integration and testing. Conversely, SSMs are easy to handle and apply, but age rapidly in space, due to the effects of UV radiation, charged particles and atomic oxygen on the polymeric support of SSM tape. First-Flex is a brand-new OSR technology that aims at combining the performance and durability of quartz OSRs with the flexibility and easy handling of SSMs, at fair costs. First-Flex consists of a fully inorganic coating sputter-deposited onto the first surface of polyimide film. The coating provides the required T.O. properties, while the film remains protected from the environment and serves only as mechanical support for the coating. First-Flex stems from a study for the Bepi Colombo mission, that led to the development and qualification of an extremely durable white coating named "Interferential CERMET" (IC), now flying around Mercury on the High Gain Antenna feed of the MPO. Subsequently, in the frame of the ESA ARTES AT and C&G programs, the IC coating was transferred from rigid metal substrates to polyimide tape, to be used as a flexible OSR. This paper reports on the final stages of development and industrialization of the technology and includes, in particular, the results of qualification tests for the application of Fiirst-Flex in various environments, including GEO.

In the frame of projects funded by the European Commission and the ESA, we developed a new type of Optical Solar Reflector (OSR) that combines the flexibility and easy handling of Second Surface Mirrors with the temperature-variable emittance necessary to ensure both effective radiative cooling in the hot phase and reduced heat losses in the cold phase. The new smart OSR consists of a metamaterial coating deposited on Kapton film. The coating is made of two functional blocks, namely a variable emitter topped by a dielectric solar reflector. The variable emitter is a Metamaterial Perfect Absorber designed for strong and broadband plasmonic resonance absorption in the thermal IR. It consists of a metal back-reflector, a dielectric spacer, and an array of doped VO 2 thermochromic micro-antennas that are switched-off when the temperature drops below the metal-to-insulator transition point. The solar reflector is a wideband dielectric filter made of materials that are transparent across the entire spectrum from the VIS to the thermal IR. All the layers of the two blocks are deposited by standard vacuum techniques, while the array is patterned by Nanoimprint Lithography, a technique that is often performed at the wafer level but allows for up-scaling via roll-to-roll or roll-to-plate production setups. The paper reports on the characterization and testing of samples of size up to 100 mm x 100 mm, at the Beginning of Life and after thermal, humidity, irradiation and handling tests.

Abstract Smart radiative cooling devices based on thermochromic materials such as vanadium dioxide (VO2) are of practical interest for temperature regulation and artificial homeostasis, i.e., maintaining stable equilibrium conditions for survival, both in terrestrial and space applications. In traditional solar reflector configurations, solar absorption in the VO2 layer is a performance limiting factor due to the multiple reflections of sunlight in the stack. Here, we demonstrate a visually transparent, smart radiator panel with reduced solar absorption. An Al-doped ZnO transparent conducting oxide layer acts as a frequency selective infrared back-reflector with high transmission of solar radiation. In this study we make use of high-quality VO2 thin films deposited using atomic layer deposition and optimized annealing process. Patterning of the VO2 layer into a metasurface results in a further reduction of the solar absorption parameter α to around 0.3, while exhibiting a thermal emissivity contrast Δε of 0.26 by exploiting plasmonic enhancement effects. The VO2 metasurface provides a visual spectrum transmission of up to 62%, which is of interest for a range of applications requiring visual transparency. The transparent smart metasurface thermal emitter offers a new approach for thermal management in both space and terrestrial radiative cooling scenarios.

Optical Solar Reflectors (OSRs) play a crucial role in thermal management of spacecraft as the outer-surface to the space environment. To achieve the thermal control, an ideal OSR should be able to reflect all the UV/Vis/NIR spectrum radiation to avoid heating up by the son and also emit blackbody radiation in infrared (IR) spectrum for thermal dissipation. Conventionally, OSRs are made of aluminium plated quartz tiles and therefore have serious issues for their heavy weight and fragile format, significantly adding the launch and assembly cost, respectively. Recently, we have proposed a meta-OSR solution based on thin film technology using Al-doped ZnO (AZO) [1] and the meta-OSRs can be fabricated on flexible substrates, making them light in weight and easy for surface mounting. In addition, we have also proposed a smart meta-OSR solution based on VO 2 , which has a tunable emissivity depending on the operational temperature [2] . In this work, we report a novel meta-OSR with a planar AZO metasurface unlike island-like metasurfaces formed by etch. The planar metasurface is fabricated through our patented plasma patterning technique [3] [4] , which can locally modulate carrier density in AZO.

Metasurface devices are conventionally fabricated by physically patterning the functional film. We demonstrated a novel fabrication technique to selectively modulate Al-doped ZnO carrier concentration of planar film and form a planar optical metasurface.

Optical solar reflectors (OSRs) play a crucial role in the spacecraft thermal management. We present novel OSRs based on planar or non-planar metal oxide metasurface. Fabricated meta-OSRs are shown to give superior emittance performance.

In the frame of a project aimed at developing a new type of optical solar reflectors we present the scientific and technological issues addressed during irradiations of nano-hybrid coatings on polyimide films by using 20 keV electron beam from a modified use of Scanning Electron Microscope (SEM) and with ultraviolet (UV) dose equal to 300 space-equivalent Sun hours. Details of a new approach to use SEM for low energy electron irradiations and of a new UV irradiation setup are given.

Optical solar reflector smart radiators are able to control the temperature of spacecraft. This work demonstrates a novel smart optical solar reflector using a patterned thermo-chromic VO2 plasmonic meta-surface design. The VO2 meta-surface combines the temperature induced phase transition of VO2 with plasmonic resonances resulting in a significant enhancement of the infrared absorption. The enhanced absorption obtained at a reduced VO2 coverage results in superior emittance tunability As and lower solar absorptance a compared to a corresponding thin-film reflector. An emittance tunability of 0.48 is obtained for the meta-reflector design, representing a 30% improvement compared to the unstructured film. Meta-surface based smart optical solar reflectors offer a new route toward energy-efficient and cost-effective passive thermal control systems of spacecraft and other surfaces.

In the frame of the Bepi Colombo program, we had introduced a new type of thin film multi-layer coating named ‘Interferential CERMET’, characterized by low solar absorptance αS, high IR emissivity εIR, good electrostatic dissipation properties, and extreme durability against high temperature, UV rays and charged particles. The coating, in particular, had shown negligible degradation of αS (<2%) after 26,000 ESH at 350°C. The study had eventually led to the qualification of the Interferential CERMET as a specialty white coating for components of the HGMA antenna feed and for other rigid components made in Titanium (deployable thermal covers and hold-down & release mechanisms). This paper reports the results of a subsequent study funded by the ESA ARTES 5.1 program, in which Interferential CERMETs have been adapted and optimized for deposition on flexible foils. Foils have a typical grade of 2-3 MIL, and are made of a variety of materials, from polymers like polyimide and PEEK, to metals like Aluminum and Titanium, to Carbon Fibre Reinforced Polymers. Prototypes have been manufactured both in small and in high volume coaters, and tested at TRL 5. Test results make the new technology extremely promising for a radically new class of Optical Solar Reflectors that combine the performance and durability of traditional quartz OSRs with the flexibility and ease of use of flexible SSMs. Direct application of the coating onto the outer Aluminum or CFRP skin of radiator panels constitutes an alternative and possibly even more appealing use of the same technology. INTRODUCTION AND STUDY OBJECTIVES Optical Solar Reflectors (OSRs) are passive components that play a crucial role in the thermal design of any spacecraft, whatever its orbit altitude and operational scenario. As they constitute the physical interface between radiator panels and the outer space, OSRs are required to reject solar radiation and to dissipate radiatively the heat produced by on board instrumentation. At a good extent, the performance of an OSR is defined by the two thermo-optical parameters solar absorptance αS and IR emissivity εIR. αS should ideally approach 0, and is generally required < 0.15 at the Begin of Life (BoL). εIR should ideally approach 1, and is generally required > 0.80 BoL. αS and εIR must endure the harsh space environment, and remain ideally unaltered across the lifetime of the satellite. αS, in particular, is generally required to remain under 0.2 until the End of Life (EoL). Besides low αS and high εIR, OSRs must also feature static dissipative characteristics, with sheet resistance Rs ≤10 4 Ω/ being a typical requirement. Traditional OSRs are Second Surface Mirrors (SSMs): they consist of a transparent yet IR absorbing substrate having a metal layer (Silver or Aluminium) on the second surface, and a Transparent and Conductive Oxide (TCO) layer on the first, space-facing surface. The substrate ensures high εIR, while the metal backreflector guarantees low αS. The TCO layer, if properly grounded, enables dissipation of electrostatic charges. In high performance SSMs the substrate is quartz. Quartz OSRs are small, brittle tiles of typical size 40 x 40 mm and thickness 100-200 μm. They have excellent thermooptical properties that remain unaltered after many years in space. However, they are expensive and easy to break during Assembly, Integration, and Testing (AIT). In flexible SSMs, quartz is replaced by a foil of Poly Tetra Fluor Ethylene (PTFE) of thickness ~ 125 μm. Flexible SSMs are low cost and easy to handle and to apply with very high fill factor both on planar and on curved radiator panels. However, they are considered unfit for prolonged missions in space, as they age rather rapidly , mostly but not exclusively due to the direct exposure of PTFE to UV rays, which causes the foil to become brittle and opaque. In the frame of the ESA ARTES 5.1 project ‘ FLEX’, we have proposed and developed a totally new type of flexible OSR, from now on referred to as FF OSR, consisting of an Interferential CERMET coating deposited on the first surface of a polymer flexible metal foil (Fig. 1). The Interferential CERMET is a fully inorganic and extremely durable multi-layer coating produced by magnetron sputtering, that provides all the desired T.O. and electrical properties, and protects the flexible foil interaction with the space environment. The foil, therefore, acts only as mechanical support and carrier As in the case of flexible SSMs, FF integrated with a conductive Pressure Sensitive Adhesive (PSA) on the second surface, application, and with perforated interconnects, to electrical contact the two foil surfaces and to grounding Fig. 1. FF-OSR cross section The study had three main objectives: 1) To verify the compatibility of the Interferential CERMET with flexible foils of different nature (metals, polymers and composites) optical, electrical and mechanical properties to meet the requirements of a flexible OSR application 2) To reproduce the coating by high rate reactive sputtering in a large-area coater, and demonstrate the industrial sustainability of the technology 3) To validate the technology at TRL 5, optical, electrical, mechanical and endurance tests on coated foils, and through application tests on radiator mock ups.

Recently metal oxides have been introduced as promising materials for infrared and active plasmonics. By designing nanoantennas and metamaterials using transparent conducting oxides (TCOs), we can achieve strong light-matter interactions in the infrared while maintaining high transparency in the visible range. These properties have been used to design new types of infrared active surfaces for optical sensing and metamaterials [1, 2]. Compared to noble-metals, the TCOs offer a strongly reduced negative permittivity which allows for much more compact resonant nanostructures and hence a higher density of elements per square wavelength. Up to 80 resonant elements per square wavelength were realized using ITO split-ring resonators.

Advanced IR emitters and sensors are under development for high detection probability, low false alarm rate, and identification capability of toxic gases. One of the most reliable techniques to identify the gas species is absorption spectroscopy, especially in the medium infrared spectral range, where most of existing toxic compounds exhibit their strongest rotovibrational absorption bands. Following the results obtained from simulations and analysis of expected absorption spectra, a compact nondispersive infrared multispectral system has been designed and developed for security applications. It utilizes a few square millimeters thermal source, a novel design multipass cell, and a smart architecture microbolometric sensor array coupled to a linear variable spectral filter to perform toxic gases detection and identification. This is done by means of differential absorption spectroscopic measurements in the spectral range of the midinfrared. Experimental tests for sensitivity and selectivity have been done with various chemical agents (CAs) gases and a multiplicity of vapour organic compounds (VOCs). Detection capability down to ppm has been demonstrated.

We report on a significant photocurrent generation from a planar device obtained by coating a bare n doped silicon substrate with a random network of multiwall carbon nanotubes (MWCNTs). This MWCNT/n-Si hybrid device exhibits an incident photon to current efficiency reaching up to 34% at 670 nm. We also show that MWCNTs covering a quartz substrate still exhibit photocurrent, though well below than that of the MWCNTs coating the silicon substrate. These results suggest that MWCNTs are able to generate photocurrent and that the silicon substrate plays a fundamental role in our planar device. The former effect is particularly interesting because MWCNTs are generally known to mimic the electronic properties of graphite, which does not present any photocurrent generation. On the basis of theoretical calculations revealing a weak metallic character for MWCNTs, we suggest that both metallic and semiconducting nanotubes are able to generate e-h pairs upon illumination. This can be ascribed to the presence of van Hove singularities in the density of states of each single wall carbon nanotube constituting the MWCNT and to the low density of electrons at the Fermi level. Finally, we suggest that though both MWCNTs and Si substrate are involved in the photocurrent generation process, MWCNT film mainly acts as a semitransparent electrode in our silicon-based device.

The success rate of clinical drug development is significantly lower in oncology than in other therapeutic areas. Predicting the activity of new compounds in humans from preclinical data could substantially reduce the number of failures. A novel approach for predicting the expected active doses in humans from the first animal studies is presented here. The method relies upon a PK/PD model of tumour growth inhibition in xenografts, which provides parameters describing the potency of the tested compounds. Anticancer drugs, currently used in the clinic, were evaluated in xenograft models and their potency parameters were estimated. A good correlation was obtained between these parameters and the exposures sustained at the therapeutically relevant dosing regimens. Based on the corresponding regression equation and the potency parameters estimated in the first preclinical studies, the therapeutically active concentrations of new compounds can be estimated. An early knowledge of level of exposure or doses to be reached in humans will improve the risk evaluation and decision making processes in anticancer drug development.

The electronic structure of thin blend films composed of copper phthalocyanine (CuPc) and fullerene (C60) have been studied by x ray, soft-x-ray photoemission spectroscopy, and by theoretical simulations. Samples with different C60∕CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. A strong shift of the highest occupied molecular orbital (HOMO) of CuPc towards the Fermi level and of the HOMO C60 states towards higher binding energy was observed. The comparison between valence band structures and core level line shape indicates that the central part of the CuPc molecule is lightly modified by the presence of the C60 molecule. The theoretical analysis, performed using density functional theory, confirms this small interaction between the two molecules, with a small charge density localized between the two molecules and a structural modification of the CuPc molecule.

The preclinical development of antitumor drugs would greatly benefit from the availability of models capable of predicting tumor growth as a function of the drug administration schedule. For being of practical use such models should be simple enough to be identifiable from standard experiments conducted on animals. In the present paper, a simple mathematical model of tumor dynamics is derived from a set of minimal assumptions formulated at cellular level. In the model there are two classes of tumor cells: proliferating and non-proliferating. Assuming independence between the cells, the mean tumor mass obeys two differential equations: an ordinary and a partial differential one. It is shown that, due to the large number of cells in measured tumor masses, the variance of the mass tumor is negligible compared to its expected value so that the stochastic model can be replaced by a deterministic one. For suitable choice of the model parameters, the proposed minimal model yields the so-called TGI (tumor growth inhibition) model. This is a lumped parameter model, based on only five parameters, that in the last few years has been successfully used to fit and predict the effect of several antitumor drugs