The detection of molecular traces in the environment is a technical problem that is critical in pollutant control procedures at all stages of spacecraft assembly, in space flight, as well as in other technological processes such as food production, medical diagnostics, environmental control, warfare. However, in the aerospace industry, it is necessary to detect molecular traces of contaminants with extreme sensitivity, as even concentrations as low as part-per-billion (ppb) can be critical during long missions. The high sensitivity of the Volatile Organic Compounds (VOCs) detection within the air can be a challenge because of the poor affinity of VOC’s to the metal surface of the sensor substrate. In this work, we present a surface‐enhanced Raman scattering (SERS) spectroscopy technique as a highly sensitive and selective molecular sensor for gas trace detection not sensitive to molecules adsorbtion on sensing element. The developed hybrid SERS platform for molecular trace detection is supported by the hybrid nanoplasmonic porous silicon membrane in conjunction with micropump to achieve the trace level detection of VOCs in the environment. The combination of silicon membrane, made by electrochemical etching of the microchannels in the silicon chip, with chemical deposition of the silver nanoparticles inside the channels, produce a porous Ag nanoparticles membrane with a high density of plasmonic nanostructures (“hot spots”). The micropump integrated with the SERS sensor, pump the air with VOC’s molecules through the plasmonic membrane “hot spots” to increase the probability of interaction of VOC’s molecules with SERS substrate and to increase the enhancement factor. The sensor chip structure was designed, gas flow in the sensor was simulated, and the sensor was fabricated using 3D printing. The limit of detection of hydrazine with concentration level 10–12 M from solution and the vapor phase 0.1 ppm was demonstrated. The anisole vapors with concentration 0.5 ppb spectra in the air were recorded. Our results demonstrate that plasmonic membrane can be used as a high enhancement factor SERS sensor for many pollutants molecules detection with the nanomolar sensitivity and can be applied in the design of sensors for space applications, environment control, biomedical diagnostic.

Structural Health Monitoring (SHM) is a promising approach to overcome the unpredictable failure behaviour of composite materials and further foster their use in aerospace industry with increased confidence. SHM may require a complex system, including sensors, wiring and cabling, data acquisition devices and software, data storage equipment, power equipment and algorithms for signal processing, involving a multidisciplinary team for its adequate development considering the operational environment and requirements of a certain application. This review paper focuses on the most promising type of sensors, laboratory made and commercially available, for SHM of aerospace composites. Sensing principles, characteristics, embedding procedures, sensor/ host materials interactions and acquired sensor data/ material behaviour are discussed. The use of sensors for in-situ process monitoring, specifically for curing and mould filling monitoring in liquid composite moulding processes are discussed. General considerations for the development of SHM systems for the aerospace environment are also briefly mentioned.

Out of autoclave (OoA) processing techniques, such as liquid composite moulding techniques (LCM) and, particularly, the vacuum-assisted resin infusion (VARI) technique, are being used, with increasing success, in replacement of prepreg/autoclave technologies to produce structural aircraft/aerospace polymer composite parts, due to its better cost effectiveness and competitiveness. This work aims to embed Fibre Bragg grating (FBG) sensors to monitor the VARI manufacturing of carbon fibre reinforced polymer (CFRP) composites and evaluate the associated phenomena: ambient curing and post curing reactions and resulting residual strains. The curing kinetics of the epoxy resin system alone was initially studied through isothermal differential scanning calorimetry (DSC) tests and applying the isoconversional Friedman method, and further studied by strain monitoring during ambient curing and post curing resorting to FBG sensors. The FBG sensors in the CFRP laminates were able to detect a subtle increase of strain as infusion of the CFRP started and to measure decreasing strain as resin filled in the dry fabric layers. Subtle strain decrease revealed forming crosslink bonds. Compressive strains measured by the FBG sensors during post curing show that further crosslink takes place. A comparison of resultant residual strains was made between specimens with embedded FBG sensors on small-diameter optical fibres (SDOF) and on large-diameter optical fibres (LDOF).

Solid-state energy conversion through thermoelectric effects remains the technology of choice for space applications for which, their low energy conversion efficiency is largely outweighed by the reliability and technical requirements of the mission. Radioisotope thermoelectric generators (RTGs) enable the direct conversion of the heat released by nuclear fuel into the electrical power required to energize the scientific instruments. The optimization of the conversion efficiency is intimately connected to the performances of the thermoelectric materials integrated which are governed by the transport properties of these materials. Recent advances in the design of highly efficient thermoelectric materials raise interesting prospects to further enhance the performances of RTGs for future exploratory missions in the Solar system. Here, we briefly review the knowledge acquired over the last years on several families of thermoelectric materials, the performances of which are close or even higher than those conventionally used in RTGs to date. Issues that remain to be solved are further discussed.

Wide temperature range, high UV/VUV intensities, and long duration of the BepiColombo mission impose stringent requirements on the materials of the spacecraft. One of the challenges is to keep critical parts of the spacecraft within acceptable temperature limits in the harsh conditions close to the Sun and Mercury. To this purpose, the High Gain Antenna (HGA) reflector and edges of the solar arrays are coated with the low solar absorptance, high emissivity NV14 white ceramic coating. However, UV/VUV radiation induces deposition of contaminants on the coating, potentially leading to significant increases of the solar absorptance values. Therefore, a prediction of the contamination effects on the solar absorptance of the coating during the entire mission is one of the crucial tasks. Several short environmental tests were initially performed aiming to investigate the contamination deposition on NV14 coating under UV/VUV radiation. However, the complexity of contamination deposition processes and the unknown influence of the large acceleration factors applied in these tests did not allow the development of a reliable model to predict the evolution of the solar absorptance during the mission lifetime. Therefore, it was decided to perform a long duration test (LDT), with a close to 1:10 test to mission duration ratio. Dedicated in-situ measurements techniques were developed to reduce actual test duration and avoid sample exposure to air.

Multilayer thin film systems on flexible polymer substrates are used as flexible optical solar reflectors or thermal insulation of satellites and spacecraft. During one year of operation, a satellite in low earth orbit typically encounters 6000 thermal cycles of +/- 100 degrees C. Due to the different coefficients of thermal expansion between the individual layers and the substrate it is important to investigate the thermo-mechanical stability of the multilayers as a function of the cyclic heat load. Scanning electron microscopy and focused ion beam cross-sectioning revealed that Inconel-Ag bilayers on fluorinated ethylene propylene (FEP) substrate severely degrade during thermal cycling of +/- 150 degrees C in a gaseous N-2 atmosphere. After only 100 cycles through thickness cracks and subsurface voids in the Ag layer form as a result of equi-biaxial thermal stresses caused by the large difference in thermal expansion between film and substrate. Transmission Kikuchi Diffraction (TKD) before and after thermal cycling also revealed grain growth and twin widening in the Ag layer. Cracking and void formation are detrimental to application relevant material properties including corrosion protection (Inconel) and reflectivity (Ag). Reflectance measurements revealed that the amount of reflected energy as well as the reflection mode (specular vs. diffuse) significantly change during the first 100 cycles. Saturation of reflection characteristics was observed after 25 cycles, which correlates to a turning point in the evolution of Ag voids. Results of this study indicate that special focus should be directed towards thermal stress control (Delta alpha) and tailoring of the metal-polymer interface to improve resistance of versatile metal-polymer systems against thermal cycling.

The thermo-oxidative degradation of a multiply-alkylated cyclopentane (MAC) lubricant for space applications is investigated. Accelerated aging tests at temperature levels between 60 °C and 150 °C are performed and the aging behavior is investigated in detail with spectroscopic, mass spectrometric and chromatographic techniques as well as tribological testing on a ball-on-disk setup. The degree of oxidative aging of the MAC lubricant is monitored with the carbonyl index (CI), which is shown to be well-suited to monitor the degree of degradation of the lubricant. Gas chromatography/mass spectrometry (GC/MS) analysis is applied to identify 9-nonadecanone as the main volatile degradation product in all aged samples, suggesting a similar decomposition pathway at all tested temperatures. Size exclusion chromatography (SEC) is further applied to confirm the formation of higher molecular weight degradation products upon aging, affecting the viscosity of the lubricant. In the subsequent ball-on-disk tests, a good correlation of the performance loss with the FTIR measurements is seen and CI values of approx. 0.64 are regarded as threshold for the complete loss of performance at the selected test conditions. The determined CI values in dependence of the aging duration are further used to perform a time–temperature superposition (TTS) to acquire a master curve for accelerated aging. In the resulting Arrhenius plot, non-linear behavior is observed, highlighting the importance of a precise control of accelerated aging parameters for reliable lifetime estimations.

Because the binary chalcogenide SnTe is an interesting Pb-free alternative to the state-of-the-art thermoelectric material PbTe, significant efforts were devoted to the optimization of its thermoelectric properties over the last few years. Here, we show that saturation-annealing treatments performed at 823, 873 or 973 K under Sn-rich conditions provide a successful strategy to prepare polycrystalline samples with a controlled concentration of Sn vacancies. Both scanning transmission electron microscopy and Mössbauer spectroscopy demonstrate the absence of Sn-rich areas at the grain boundaries in the saturation-annealed samples. Transport property measurements, performed over a wide range of temperatures (5-800 K), show that this technique enables achieving thermoelectric performances at 800 K similar to those obtained using Sn self-compensation. The three saturation annealing temperatures result in comparable transport properties across the entire temperature range due to similar hole concentrations ranging between 1.0 and 1.5 × 1020 cm-3 at 300 K. As equally observed in samples prepared by other synthetic routes, the temperature dependence of the Hall mobility evidences that charge transport is strongly affected by point-defect scattering caused by the random distribution of Sn vacancies.

We report a detailed investigation of the low-temperature transport properties (5-300 K) on polycrystalline samples of Sn1+xTe (x = 0 and 0.03) prepared by melt quenching in water and slow cooling. These two different synthetic routes result in variations in the hole concentration over more than one order of magnitude, allowing for a systematic investigation of the influence of Sn vacancies on the transport properties. The results evidence a strong correlation between the details of the synthetic process and the concentration of Sn vacancies. Transmission electron microscopy and Mossbauer spectroscopy show that the excess Sn, which helps to lower the hole concentration, segregates at grain boundaries. Interestingly, Hall-effect measurements reveal that charge transport is dominated near 300 K by alloy scattering regardless of the hole concentration. In addition to dictating the electronic properties, the concentration of Sn vacancies has also a significant impact on the thermal transport, with the magnitude of the low-temperature Umklapp peak observed in the lattice thermal conductivity near 30 K scaling with the concentration of Sn vacancies that act as efficient point-defect scatterers.

BepiColombo is a mission planned by the European Space Agency (ESA) to reach Mercury, the least explored planet in our Solar System. The mission has been launched on October 20, 2018, and will face long-term exposure to temperatures up to 400 degrees C, thermal cycling between extreme temperature values, and high levels of radiation (UV, protons). A new thermal "Nanovation" coating (V14) was developed by CeraNovis in cooperation with ESA to deal with the harsh conditions. The coating comprises a sintered mixture of oxides/nitrides using a silicate binder, deposited on a grade-5 or grade-2 titanium substrate. It is organic-free after sintering and distinguished by its low solar absorptance of 0.2 with IR emittance of 0.87-0.89, as well as very good thermoshock resistance and excellent adhesion on titanium grade 2 and 5, combined with a low layer thickness of 20-35 mu m. In the presence of contaminants, though, V14 is inclined of trapping the mostly organic contaminants. Upon UV-irradiation in vacuum black carbon clusters are formed from these contaminants, resulting in a higher solar absorptance value. Eventually this might lead to a higher surface temperature of the coated satellite parts. To decompose the contaminants, a cleaning procedure involving gaseous ozone has been developed, which effectively cleans contaminated surfaces involving only volatile gaseous materials and decomposition products. To minimize contamination, a sealing with a very thin vitreous layer can be applied as well. Results of tests conducted by ESA are presented. The coating's structural integrity was followed using powder X-ray diffractometry. Impact of sealing of the a priori porous coating with additional agents, batch variability, environmental testing, and in situ thermal cycling are assessed, employing also other techniques, such as scanning electron microscopy/energy dispersive X-ray spectroscopy, atomic force microscopy, and optical microscopy.

Aerogels are promising materials for thermal insulation applications for Mars exploration mission. To assess the use of hydrophobic silica based aerogels for the specificity of the Mars environment, the samples were exposed to a laboratory simulation of the Mars environment, resorting to gamma radiation exposure and thermal cycling tests. To validate their use and study the effect of the simulated Mars environment on their thermal, mechanical and chemical properties, the aerogel materials were characterized before and after that environmental testing, to evaluate and identify eventual changes. Outgassing tests were also conducted. We found minor changes on the aerogels properties, showing that the materials can keep their thermal insulation performance after thermal cycling tests and that the storage modulus during dynamic mechanical analysis in compression mode was improved.

The influence of irradiation on mechanical properties of polymer foils used in spacecraft applications has widely been studied via macroscopic tensile samples. An increase in the local resolution of this investigation can be achieved by reducing the sample’s dimensions. A femtosecond laser enables a fast fabrication of micro-samples with dimensions from tens of μ m to the mm range, with ideally no influence on the material. Tensile experiments using such micro-tensile samples were conducted on FEP, Upilex-S and PET foils. The influence of the laser processing on the polymer foils was evaluated. Additionally an investigation of degradation due to electron irradiation was performed. Furthermore an outlook to extend this technique to depth-resolved measurements by preparing samples from locally thinned foils is presented. The study demonstrates the feasibility of femtosecond laser processing for rapid fabrication of micro-samples, enabling insights into the effect of electron irradiation on local mechanical properties of polymers.

3D printing will revolutionize the manufacturing industry. Significant advances in computer aided design, additive manufacturing and materials science have opened up the possibilities of self-assembly systems, self-healing and material property alterations. Printing layer by layer allows complex geometries to be built, previously difficult under conventional manufacturing routes. This paper is a review of the current materials available for 3D printing that enable the emergence of 4D printing, a ‘smart material’ that responds in a programmed way to an external stimuli. The outlook is towards potential space applications, in all areas including deployable structures, antennas and medical supplies.

The aim of our work was to investigate the degradation mechanisms involved, using detailed surface analysis techniques such as X-ray photoelectron spectroscopy (XPS) and Secondary-ion mass spectrometry (TOF-SIMS) depth profiling. Contamination witness samples exposed together with the main DVT test item hardware, and the surface chemistry of the samples was analysed in detail. Results from different exposures are presented, with varying UV dose and temperature, and possible degradation mechanisms discussed. The environmental conditions during the testing were also monitored in detail in order to determine possible correlation of results from surface analysis with the observed degradation. This included detailed characterisation of the in-situ contamination environment using quartz crystal microbalances (tQCM) and contamination witness plates. Considerable effort was also made to accurately measure the UV and VUV intensity on the samples and the methodology used is summarised.

The surface preparation and curing regimes belong to the key steps for success in the case of adhesive bonding and are currently under investigation in ESA/ESTEC in collaboration with Rescoll. A general overview of the adhesive bonding for space applications and its criticalities in this context is summarised in this work, focusing in particular on the importance of surface treatment, accelerated exposure conditions and impact of the curing regime on adhesive joint performance. Experimental part consisted of series of mechanical tests on standard lap shear samples which were performed before and after exposure to humidity. This paper also summarises results from tests performed so far on “difficult” substrates such as FeNi36 alloy and standard aluminium AL 2024 T351 substrate. Further work will continue to support the MPTB initiative to assess the impacts of formulation changes anticipated by key adhesive manufacturers (optimisation of manufacturing process, obsolescence and changes driven by REACH restrictions). Preliminary results from the “formulation change” assessment for selected adhesives are also part of this work.

Understanding the thermal stability of metal‐polymer interfaces is essential for the reliability of innovative high‐tech devices, including flexible electronics or satellite insulation. In this study, the interfacial stability of aluminum‐polyimide (Al‐PI) is investigated as a function of thermal cycling (±150°C) and thermal annealing treatments (150°C‐300°C) with X‐ray photoelectron spectroscopy measurements performed after peeling and cross‐sectional transmission electron microscopy analysis. Small mutations in the interface chemistry and structure were detected and identified after annealing at 225°C for 140 hours, including the thickness increase of an amorphous interlayer between Al and PI of about 2 nm and a change in the failure mechanism during the peeling. Being able to trace subcritical mutations before they become fatal is essential to predict the reliability and lifetime of metal‐polymer composites.

An overview of coatings and thin films for spacecraft applications is provided, focusing on coatings for thermal control and optical applications. An outline of the requirements imposed by the harsh conditions in space is given. Space applications of coatings are listed and their qualification is described, including testing in the ESA laboratories at ESTEC. Coatings degradation in space and environmental testing, including degradation due to vacuum, thermal cycling, radiation, atomic oxygen, space debris, and outgassing effects, is covered in detail. Recent advances in the field and perspectives for future development are also reviewed based on the published literature.

PEEK polymers are investigated as replacement materials for metallic liners in composite overwrapped pressure vessels (COPVs) for fuel tank applications in space. A novel, integrally heated, rotational moulding tool has been developed to produce PEEK polymer liners, samples of which have then been overwrapped using CF/PEEK in a laser assisted tape-placement (LATP) process to produce demonstrator samples of a polymer lined COPV. Helium permeability testing has shown that the designs are capable of resisting leakage to acceptable levels for fuel storage, while X-ray CT scanning and cryogenic cycling have shown that the current design is capable of resisting crack growth over multiple cycles. Nano-indentation testing has shown that the LATP process has created a region of reduced modulus in the PEEK polymer at the surface of the liner where the CF/PEEK has been tape-laid. This laser-affected zone of reduced polymer modulus in the composite interface region has enabled an enhanced resistance to crack growth formations from thermal residual stresses in comparison to hot plate moulded test samples.

Many different environmental factors can have an effect on optical coating durability for space applications. This includes in-orbit effects such as vacuum exposure, UV radiation, particle radiation, atomic oxygen, thermal cycling, contamination and orbital debris, as well as ground based effects such as cleaning, contamination and humidity [1].

This study demonstrates two-stage cracking of an Inconel‑silver film system on a flexible Teflon substrate under uniaxial tension. In situ fragmentation experiments revealed that primary fracture of the brittle 30nm Inconel overcoat induced brittle, secondary fracture of the normally ductile 150nm silver base layer. Good correlation exists between the ratios of primary and secondary saturation crack spacing and individual layer thicknesses. Two-stage cracking was confirmed by cross-sectional analysis and explained by different steady state energy release rates of the individual layers. The results further illustrate how brittle layers are detrimental to the mechanical behaviour of polymer-supported thin film multilayer structures.