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Abstract: A correction to this paper has been published: https://doi.org/10.1007/s12567-021-00379-z PubDate: 2021-07-16
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Abstract: 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. PubDate: 2021-07-16
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Abstract: Jupiter Icy Moons Explorer (JUICE) is a large (L-class) mission led by the European Space Agency (ESA). It will explore Jupiter and its system. The spacecraft’s external materials will endure a wide range of temperatures and the harsh Jovian environment. Scientific measurements require that any gradient of electrical potential along the external surfaces of the spacecraft should be kept under few Volts. This constitutes a challenge concerning materials selection. In this frame, charging behaviour of white thermal control coatings named PCBE, Z-93C55, and AZ-2000-IECW was investigated in our dedicated facility. Surface potential decay method, direct current (DC) resistance, and on-surface DC resistance measurements were used. Included in this investigation, aged multi-layer insulation (MLI) outmost layers of germanium/1.6 mil 160 XC Black Kapton/vapour-deposited aluminium (VDA) and of StaMet/1.6 mil 160 XC Black Kapton/VDA were also characterized. For the solar wings external surfaces, rear side’s Black Kapton skin configurations were measured after electron radiation and solar cells cover glass indium tin oxide (ITO) coating were measured during atomic oxygen exposure. Testing temperatures range from − 210 to 20 °C. PubDate: 2021-07-07
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Abstract: For safe operation of active space crafts, the space debris population needs to be continuously scanned, to avoid collisions of active satellites with space debris. Especially the low Earth orbit (LEO) shows higher risks of collisions due to the highest density of orbital debris. Laser ranging stations can deliver highly accurate distance measurements of debris objects allowing precise orbit determination and more effective collision avoidance. However, a laser ranging station needs accurate a priori orbit information to track an orbital object. To detect and track unknown orbital objects in LEO, here, a passive optical staring system is developed for autonomous 24/7 operation. The system is weather-sealed and does not require any service to perform observations. To detect objects, a wide-angle imaging system with 10° field of view equipped with an astronomical CCD camera was designed and set up to continuously observe the sky for LEO objects. The system can monitor and process several passing objects simultaneously without limitations. It automatically starts an observation, processes the images and saves the 2D angular measurements of each object as equatorial coordinates in the TDM standard. This allows subsequent initial orbit determination and handover to a laser tracking system. During campaigns at twilight the system detected up to 36 objects per hour, with high detection efficiencies of LEO objects larger than 1 m3. It is shown that objects as small as 0.1 m3 can be detected and that the estimated precision of the measurements is about 0.05° or 7 × the pixel scale. PubDate: 2021-07-05
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Abstract: The role of N2 in the upper atmosphere on the atomic oxygen (AO)-induced erosion of polyimide in low Earth orbit (LEO) and sub-LEO is investigated through ground-based experiments and flight data. The experiment is performed by adding an Ar beam at the same collision energy as an undecomposed O2 component in the AO beam formed by laser detonation to simulate the physical effect of simultaneous N2 collision in sub-LEO. The Ar beam is added by the dual-pulsed supersonic valve-equipped laser-detonation system developed at Kobe University. The experimental results indicate that the erosion of polyimide in the laser-detonation system is promoted by the presence of O2 and Ar in the beam, corresponding to N2 in the sub-LEO. On-ground experimental results are compared with in-orbit AO measurements. Previous space shuttle, international space station-based exposure experiments, as well as the world’s first real-time sub-LEO material erosion data aboard a super low altitude test satellite (SLATS) orbiting at an altitude of 216.8 km are presented. The SLATS data suggests the presence of an acceleration effect by N2 collision on AO-induced polyimide erosion, as predicted by ground-based experiments. PubDate: 2021-07-01
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Abstract: 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. PubDate: 2021-07-01
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Abstract: 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. PubDate: 2021-07-01
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Abstract: The purpose of this research was to investigate the suitability of the Fused Filament Fabrication (FFF) process for low pressure/vacuum environment. This included investigating the ability of an FFF printer to function in a vacuum and evaluation of the dimensional accuracy and mechanical properties of the manufactured components. For this purpose, a commercially available FFF printer using polycarbonate as raw material was placed in a vacuum environment of 10 mbar. Test components were then fabricated in vacuum with a control group fabricated in a normal atmosphere (1 bar). Test components were evaluated for dimensional and mass accuracy, quality and presence of defects. Flexural, tensile and compressive testing was carried out according to ASTM D790, D638 and D695 respectively. Dimensional analysis of components showed equivalent small deviation for both environments. Components fabricated in the vacuum environment had 5.4% higher tensile yield strength and 59% higher extension at break compared to components printed in a normal atmosphere indicating an increased strength and ductility. Components tested in compression had approximately 11.2% higher compressive strength when printed in a vacuum environment. No differences were observed during the flexural test. In space, due to the vacuum environment, polymers and organic material are susceptible to release molecules via an outgassing process. Assessment of the molecular organic contamination generate during the printing process in vacuum is low and seems to mostly originated from the components of the printer. The results provided demonstrated the possibility to use the FFF process in a vacuum environment to fabricate dimensionally accurate, high-quality polycarbonate components with a variety of geometries without loss of mechanical performance. This work provides a proof of concept that FFF can be used to develop out-of-earth manufacturing technologies (in orbit/in space/on planet) allowing part production for new maintenance and repair strategy or to potentially manufacture entire structure more efficiently overpassing launch constrain by using only raw material brought from earth. PubDate: 2021-07-01
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Abstract: The Bepi Colombo spacecraft was successfully launched on 20th October 2018 and is now on its way to Mercury. The materials and coatings on the Mercury Planetary Orbiter (MPO) and Mercury Transfer Module (MTM) solar arrays will need to withstand a prolonged extreme environment of high-intensity UV radiation at high-temperature (HIHT). The solar arrays must be gradually off-pointed at close sun distances in order to avoid over-heating, up to an angle of over 70° at 0.3 AU for the MPO. This means that some of the materials and coatings, as well as the solar cells, will always be operating reasonably close to their temperature limits. Extensive on-ground testing was performed to qualify the solar arrays for the BepiColombo mission environment and during this testing some materials and coatings were pushed beyond acceptable performance limits. In this paper we give an overview of selected test programmes related to the solar array materials, and we present results of experimental investigations which provide some scientific insight into the likely causes of the materials degradation observed, and the lessons learnt in the cases where over-testing had occurred. This included testing on bare and bonded optical solar reflectors, solar cell cover glass and adhesive, and the solar array edge shields. PubDate: 2021-07-01
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Abstract: Copolymers and blends of polyhedral oligomeric silsesquioxane (POSS) and polyimides have been shown to resist atomic-oxygen (AO) attack, making them promising candidates as space-durable materials in the harsh oxidizing environment of low Earth orbit (LEO). CORIN® is a commercially available and colorless POSS–polyimide which has the desirable but uncommon property among polyimides that it may be dissolved in a solvent and applied at room temperature, thus making it possible to have a widely applicable clear coating for protection from AO in LEO. The physical properties of CORIN® have been largely characterized, but its AO resistance has received limited study. We have thus used a hyperthermal AO beam to expose CORIN® and other POSS-containing polyimides, 7.3 wt% and 9.1 wt% Si7O9 trisilanolphenyl POSS blended with poly(pyromellitic dianhydride-co-4,4′-oxydianiline), to characterize their resistance to AO attack. CORIN® was found to have a particularly low erosion yield that is ≲1% that of the ubiquitous satellite material, Kapton, which agrees favorably with a result from an experiment on the International Space Station. The other POSS-containing polymers exhibited somewhat higher erosion yields of 1.4 and 2.2% that of Kapton, respectively. Surface characterization of CORIN® showed that it remained relatively smooth during AO exposure and implied that a passivating silicon oxide was formed. The comparison of the AO effects on CORIN® and the other POSS–polyimides suggests that the net effect of AO on such POSS–polyimides depends on the density of Si atoms as well as the reactivity of the organic component of the polymer. This work adds to our confidence in the use of POSS-containing polymers in LEO and, especially, in very LEO, where the necessity of protecting satellite materials and components from AO attack is critical. PubDate: 2021-07-01
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Abstract: As part of a large program conducted between years 2010 and 2018, a number of ion beam surface treatments and proprietary coatings formed on advanced space polymers by direct ion beam deposition were developed at Integrity Testing Laboratory (ITL) Inc, in Canada. This technology allowed producing surfaces with controlled surface resistivity in a wide range of charge dissipation values, with negligibly low additional RF losses and other important functional properties, that allowed using such treated materials and products in modern space antennae, solar arrays and other external applications on spacecrafts in GEO environment. This paper will present an overview of results achieved throughout the years on enhancement of radiation stability of space polymers that were ion beam treated and coated with special multifunctional thin coatings by direct ion beam deposition. The treated/coated subjects have been ground-based tested in a range of radiation conditions, simulating the GEO radiation environment, conducted in three world-recognized GEO simulation facilities. PubDate: 2021-07-01
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Abstract: 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). PubDate: 2021-07-01
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Abstract: Liquid lubricants and greases used in space applications are generally susceptible to degradation or aging. Depending on the specific material combination and storage conditions, aging effects are also relevant for long-term storage (LTS). An overview on both physical and chemical aging processes for liquid lubricants and greases is given and processes which are seen as relevant for LTS and may impact the long-term performance of these materials are identified. Individual degradation processes as well as causes and potential risks are discussed, providing complementary data for two liquid perfluoropolyether (PFPE) lubricants (Fomblin Z25 and Brayco 815Z) and a PFPE grease (MAPLUB PF 100-b), focussing on thermo-oxidative and catalytic degradation. For these lubricants, monitoring of degradation effects is done indirectly by their mass loss at different temperatures and in the presence of a catalyst over a total duration of 1000 h. An increased mass loss during accelerated thermo-oxidative aging at temperatures above 200 °C is observed, with overlapping effects of thickener degradation for the investigated grease. Noticeable catalytic degradation effects are further seen for accelerated thermo-oxidative aging in the presence of Al2O3 above 200 °C. PubDate: 2021-07-01
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Abstract: We expect satellites at altitude below 300 km, very low Earth orbit (VLEO), making observations of the Earth at optical wavelength with increasingly higher resolution. The density of atomic oxygen (AO) at VLEO is significantly higher than that at LEO; severe degradation of spacecraft materials (polymers) due to the high-flux AO is a serious concern. To clarify VLEO environmental effects on spacecraft materials, we designed the Material Degradation Monitor (MDM) and MDM2 missions. The MDM is a material exposure experiment onboard the Super Low-Altitude Test Satellite (SLATS). It aims to understand reactions and degradation of polymeric materials depending on AO fluence in VLEO. In the MDM, samples of spacecraft material were exposed at altitude of 160–560 km; their degradation behaviors were observed optically by a CCD camera for 1.8 years. The MDM2 is a material exposure experiment onboard the International Space Station (ISS) and aims to correctly understand surface reactions and degradation of the same samples used in the MDM at a given AO fluence. In the MDM2, the samples were exposed at altitude of 400 km for 1 year and then returned to Earth for analysis. Based on the results from both missions, we will help in the molecular design of more-durable materials, and establish design standards for future VLEO satellites. This study aims to quantitatively understand the surface reactions and degradation of the 11 types of thermal control materials exposed on the ISS in the MDM2. Five types of multilayer insulation (MLI) films (three types of Si-containing AO protective materials (a silsesquioxane-(SQ-) containing coated polyimide film, two types of polysiloxane-block polyimide (BSF-30) films), an ITO-coated polyimide film, and a Beta Cloth), and flexible optical solar reflectors (flexible OSRs) were found to have a high durability against erosion by AO. This was determined by measuring their loss of mass and thermo-optical properties. The Ag/Inconel layer’s discoloration and peeling were observed for three types of FEP/Ag films as determined by the Ag layer’s oxidation by AO. Also, X-ray photoelectron spectroscopy (XPS) showed that reactions of the Si-containing materials, the SQ-coated polyimide film and the BSF-30 film, form a layer of silica that protects against AO. Even though the concentration of Si in the SQ-coating is the same or greater than in the BSF-30 film, the amount of the SQ-coating that reacted was larger than that of the BSF-30 film under the same AO fluence. Moreover, the effective ability of the UV-shielding coating, composed of ITO and CeO2 coated onto one of the BSF-30 films, was demonstrated by UV–Vis spectrometry. Its sufficient AO protection was confirmed by mass measurements, XPS analyses, and FE-SEM observations. PubDate: 2021-06-28
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Abstract: As space traffic increases, Space Situational Awareness (SSA) is becoming fundamental for safe spaceflight operations. Cost-driven missions based on small satellite platforms would benefit from the availability of alternative tools providing preliminary SSA from publicly available information, such as two-line elements. In this work, we propose an orbit prediction and uncertainty evaluation method based on the well-established TLE differencing technique aided by a machine learning corrector. By designing a Recurrent Neural Network with carefully chosen input parameters, the TLE prediction accuracy is significantly improved, when tested against precise orbital data of real satellites. The prediction error is reduced, on average, by 45% across a prediction window of 16 days which may include manoeuvres. We further show that in combination with a statistical test for equality between error distributions, the differencing technique applied to the corrected TLE allows a reliable variance estimate in most situations. Limitation of the work is the training of a dedicated neural network corrector for each specific space object, which will be deposed as part of our ongoing efforts. PubDate: 2021-06-15 DOI: 10.1007/s12567-021-00375-3
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Abstract: This paper introduces an algorithm to perform optimal reorientation of a spacecraft during a high speed flyby mission that maximizes the time a certain target is kept within the field of view of scientific instruments. The method directly handles the nonlinear dynamics of the spacecraft, sun exclusion constraint, torque and momentum limits on the reaction wheels as well as potential faults in these actuators. A sequential convex programming approach was used to reformulate non-convex pointing objectives and other constraints in terms of a series of novel convex cardinality minimization problems. These subproblems were then efficiently solved even on limited hardware resources using convex programming solvers implementing second-order conic constraints. The proposed method was applied to a scenario that involved maximizing the science time for the upcoming Comet Interceptor flyby mission developed by the European Space Agency. Extensive simulation results demonstrate the capability of the approach to generate viable trajectories even in the presence of reaction wheel failures or prior dust particle impacts. PubDate: 2021-06-14 DOI: 10.1007/s12567-021-00368-2
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Abstract: Within a Belgian-German GSTP project, an experimental setup was designed, manufactured and tested to provide data on the behaviour of a shear-driven liquid film. The tests were performed on a flat plate in a rectangular duct using ethanol as film coolant at DLR’s vitiated hot air facility M11. In addition to standard measurement equipment comprising thermocouples and pressure sensors, nonintrusive measurement techniques were applied to acquire additional data of the film. The Von-Karman-Institute for Fluid Dynamics provided in-situ film temperature measurement using a dedicated laser-induced fluorescence setup. DLR performed background-oriented Schlieren measurements to record information on the film thickness. The experimental data was used by ArianeGroup and Numeca International to validate different software tools to describe the heat flux to the film and its dry-out. While ArianeGroup used its film cooling model implemented in the Rocflam3 code, Numeca performed VOF simulations using its updated Fine™/Open flow solver. PubDate: 2021-06-14 DOI: 10.1007/s12567-021-00373-5
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Abstract: In the last decade, self-healing materials have become extremely appealing for the field of space applications, due to their technological evolution and the consequent possibility of designing space systems and structures able to repair autonomously after damage arising from impacts with micrometeoroids and orbital debris, from accidental contact with sharp objects, from structural fatigue or simply due to material aging. The integration of these novel materials in the design of spacecraft structures would result in increased reliability and safety leading to longer operational life and missions. Such concepts will bring a decisive boost enabling new mission scenario for the establishment of new orbital stations, settlement on the Moon and human exploration of Mars. The proposed review aims at presenting the newest and most promising self-healing materials and associated technologies for space application, along with the issues related to their current technological limitations in combination with the effect of the space environment. An introductory part about the outlooks and challenges of space exploration and the self-healing concept is followed by a brief description of the space environment and its possible effects on the performance of materials. Self-healing materials are then analysed in detail, moving from the general intrinsic and extrinsic categories down to the specific mechanisms. PubDate: 2021-04-21 DOI: 10.1007/s12567-021-00365-5
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