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Abstract: Abstract Space Systems have been historically characterised by high performance, high reliability and high cost. Every new generation of space systems tends to improve performance, keep as much as possible reliability, speeding the lead time and lower the cost. Aggressive approach is nowadays followed by some of the players of the new space ecosystem where, for instance, reliability can be relaxed thanks for the in-orbit redundancy or robustness to failures by having a constellation with a high number of satellites. This push towards the technology and system limit requires to investigate new methods for the manufacturing of RF/Microwave parts. RF devices such as those based on waveguide structures, benefit from an additive manufacturing approach in terms of radio frequency (RF) performance and compactness. However each manufacturing approach comes with specific features and limitations which need to be well understood and, in some cases, even taking advantage of them. This paper provides a short review of some of the RF/Microwave parts already manufactured using this technology. The paper will focus mainly on metal 3D printing parts since this technology is, at the moment, well accepted by the space community. PubDate: 2022-05-06
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Abstract: Abstract The purpose of this research activity is to develop and assess the performance of 3D honeycombs for space applications. Different honeycomb materials have been used to manufacture 3D honeycomb including aluminum, phenolic resin reinforced with quartz-, glass- and carbon fibers and were further characterized. Glass fiber and aluminum-based 3D honeycombs were chosen to manufacture demonstrator parts (antenna reflector and Vespa structure) to show the applicability and advantage of 3D honeycombs to space components. PubDate: 2022-05-04
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Abstract: Abstract This contribution summarizes recent progress in research and development of an electron-cyclotron-resonance-based air breathing electric propulsion (ABEP) concept. We discuss various simulation sub-modules that have been developed to understand the key physics phenomena underpinning the intended ABEP concept. We also describe the first breadboard ionizer that has been constructed and experimentally characterized and we report on the status of the second breadboard ionizer that is to be constructed in the coming months. The aim of the bread board models being built is especially to maximize the power utilization efficiency in the electron cyclotron resonance ionization chamber. We show that, whenever a comparison is possible, the models are consistent with the obtained experimental data. The combination of experimental and theoretical data presented in this manuscript confirms that it is feasible to operate the proposed ionizer concept at VLEO conditions. PubDate: 2022-05-04
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Abstract: Abstract One of the aspects that semiconductor devices have to cope with in space applications is radiation induced damage. Therefore, radiation hardness studies are crucial for the space missions and a comprehensive on-ground testing of the components needs to be performed aiming at identifying the most radiation tolerant technologies. This paper reports the test results on newly designed and fabricated 8-channel silicon phototransistors arrays, their performance against various layouts designs, and process implementations, and discusses the achieved reliability after exposure to gamma rays, protons radiations, and high-temperature storage at wafer level in the framework of Optoi’s aerospace activities. This work was funded by the European Space Agency. The results also represent a complementary analysis aimed at better understanding and interpreting the outcomes of the non-packaged devices. In conclusion, the best combination of design parameters proving the most robust with respect to the others could be selected, being considered satisfactory and acceptable for the next phase of component assessment. PubDate: 2022-05-02
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Abstract: Abstract Since March 2014, all ESA satellites and launcher upper stages which will be disposed of by atmospheric re-entry at the end of their operational life must demonstrate that the risk from fragments surviving the re-entry and causing casualties on ground is less than 1 in 10,000. This casualty risk is calculated by re-entry tools simulating the uncontrolled re-entry event using a computer aided design model of the spacecraft. The uncertainties on several parameters such as the aerothermodynamics fluxes model, the structural interfaces model, the materials model, and the level of detail of the spacecraft architecture will have an impact on the re-entry event simulation and the associated casualty risk calculations. To better understand the uncertainties associated to material modelling, five materials often used on space missions were tested in Plasma Wind Tunnels, mimicking atmospheric re-entry environment. Thermo-physical properties, thermo-optical properties and mechanical properties at high temperature were also characterized. Analysis of the samples after plasma wind tunnel tests was performed. A database compiling the materials properties measured and the plasma wind tunnel test results was created. The material properties characterised and generated during the activities will serve as inputs for the re-entry simulation events at equipment and system level. PubDate: 2022-05-02
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Abstract: Abstract The possibility of efficiently exploiting Very Low Earth orbits (VLEO) poses significant technological challenges. One of the most demanding constraints is the need to counteract the drag generated by the interaction of the spacecraft with the surrounding atmosphere. Funded by the European Commission under the H2020 programme, the Air-breathing Electric THrustER (AETHER) project aims at developing the first propulsion system able to maintain a spacecraft at very-low altitudes for an extended time. The main objective of the project is to demonstrate, in a relevant environment, the critical functions of an air-breathing electric propulsion system, and its effectiveness in compensating atmospheric drag. This achievement will involve multiple research activities, among which: (i) the characterization of specific application cases through an extensive market analysis in order to define specific requirements and constraints at different design levels, (ii) fulfilment of pertinent testing conditions of flight conditions on-ground, relevant to the specific mission cases, (iii) the development of critical technologies, in particular those relevant to the collection, the ionization and the acceleration of rarefied atmospheric mixtures and (iv) the testing of the RAM-EP thruster to assess the system performance. In this paper, the main activities foreseen in the AETHER project are described, providing the detailed perspective towards an effective exploitation of the project outcomes for a possible future in-orbit demonstration. PubDate: 2022-04-29
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Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The ever-increasing number of man-made space debris creates the need for new technologies to mitigate it. Therefore, within the ESA-funded project BIOINSPACED, biologically inspired solutions for active debris removal were investigated, conceptualized and integrated to innovative and comprehensive scenarios. In the following, the collection process of existing and new biomimetic concepts as well as the evaluation of ten concepts based on a feasibility analysis will be presented. Out of the ten, the three most promising scenarios, were chosen for further investigation and further elaborated in detail specifying the biological models incorporated as well as how the scenario could be implemented in a simple demonstrator. The first scenario (A) is a gecko kit canon and describes a system that fires deorbiting kits towards the target from a safe distance. The second scenario (B) involves a robotic arm with a gecko-adhesive end-effector and a bee-inspired harpoon to achieve a preliminary and subsequent rigid connection to the target. The last scenario (C) is mimicking a Venus Flytrap and its bi-stale mechanism to capture its prey. One of these scenarios will be manufactured and built into a demonstrator to showcase biology’s potential for the development, optimization and improvement of technologies, especially within the space industry. PubDate: 2022-04-22
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Abstract: Abstract The Satellite for Orbital Aerodynamics Research (SOAR) is a 3U CubeSat mission that aims to investigate the gas–surface interactions (GSIs) of different materials in the very low Earth orbit environment (VLEO), i.e. below 450 km. Improving the understanding of these interactions is critical for the development of satellites that can operate sustainably at these lower orbital altitudes, with particular application to future Earth observation and communications missions. SOAR has been designed to perform the characterisation of the aerodynamic coefficients of four different materials at different angles of incidence with respect to the flow and at different altitudes in the VLEO altitude range. Two conventional and erosion-resistant materials (borosilicate glass and sputter-coated gold) have first been selected to support the validation of the ground-based Rarefied Orbital Aerodynamics Research (ROAR) facility. Two further, novel materials have been selected for their potential to reduce the drag experienced in orbit whilst also remaining resistant to the detrimental effects of atomic oxygen erosion in VLEO. In this paper, the uncertainty associated with the experimental method for determining the aerodynamic coefficients of satellite with different configurations of the test materials from on-orbit data is estimated for different assumed gas–surface interaction properties. The presented results indicate that for reducing surface accommodation coefficients the experimental uncertainty on the drag coefficient determination generally increases, a result of increased aerodynamic attitude perturbations. This effect is also exacerbated by the high atmospheric density at low orbital altitude (i.e. 200 km), resulting in high experimental uncertainty. Co-rotated steerable fin configurations are shown to provide generally lower experimental uncertainty than counter-rotated configurations, with the lowest uncertainties expected in the mid-VLEO altitudes ( \(\sim\) 300 km). For drag coefficient experiments, configurations with two fins oriented at 90 \(^{\circ }\) were found to allow the best differentiation between surfaces with different GSI performance. In comparison, the determination of the lift coefficient is found to be improve as the altitude is reduced from 400 to 200 km. These experiments were also found to show the best expected performance in determining the GSI properties of different materials. SOAR was deployed into an orbit of 421 km \(\times\) 415 km with 51.6 \(^{\circ }\) inclination on 14 June 2021. This orbit will naturally decay allowing access to different altitudes over the lifetime of the mission. The results presented in this paper will be used to plan the experimental schedule for this mission and to maximise the scientific output. PubDate: 2022-04-07
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Abstract: Abstract The growing number of deep space exploration missions operating simultaneously in the solar system triggers an increasing demand for large ground antennas capable of tracking distant spacecraft. Several space agencies have their own deep space tracking networks, where each antenna belonging to a ground station complex is meant to be shared among different deep space missions in flight, significantly constraining the tracking schedule. A typical ranging and Doppler radio tracking session requires long tracking passes and a single ground antenna, while angular (Delta-DOR) observations require at least two antennas but usually for much shorter tracking sessions. However, during Delta-DOR observations, the baseline between the two receiving antennas should be kept as large as possible, thus reducing the time windows in which Delta-DOR observations are actually feasible. This leaves little room for adaptation of the tracking schedules of these antennas and calls for the need for possible alternatives for the receiving stations. The antennas belonging to the very long baseline interferometry (VLBI) network worldwide meet the requirements to carry out Delta-DOR tracking sessions. Here, we present an experimental activity carried out tracking ESA’s GAIA spacecraft using a mixed deep space antenna configuration involving an ESA ESTRACK antenna at New Norcia (Australia) and a VLBI antenna at Medicina (Italy). This baseline was used to form Delta-DOR observables with the aim of demonstrating that VLBI antennas offer the capability to track deep space missions, thus increasing the number of possible baselines and observation time windows. PubDate: 2022-04-01
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Abstract: Abstract The measurement accuracy of recent and future space-based imaging spectrometers with a high spectral and spatial resolution suffer from the inhomogeneity of the radiances of the observed Earth scene. The Instrument Spectral Response Function (ISRF) is distorted due to the inhomogeneous illumination from scene heterogeneity. This gives rise to a pseudo-random error on the measured spectra. In order to assess the spectral stability of the spectrograph, stringent requirements are typically defined on the ISRF such as shape knowledge and the stability of the centroid position of the spectral sample. The high level of spectral accuracy is particularly crucial for missions quantifying small variations in the total column of well-mixed trace gases like \(\hbox {CO}_{2}\) . In the framework of the \(\hbox {CO}_{2}\) Monitoring Mission (CO2M) industrial feasibility study (Phase A/B1 study), we investigated a new slit design called 2D-Slit Homogenizer (2DSH). This new concept aims to reduce the Earth scene contrast entering the instrument. The 2DSH is based on optical fibre waveguides assembled in a bundle, which scramble the light in across-track (ACT) and along-track (ALT) direction. A single fibre core dimension in ALT defines the spectral extent of the slit and the dimension in ACT represents the spatial sample of the instrument. The full swath is given by the total size of the adjoined fibres in ACT direction. In this work, we provide experimental measurement data on the stability of representative rectangular core shaped fibre as well as a preliminary pre-development of a 2DSH fibre bundle. In our study, the slit concept has demonstrated significant performance gains in the stability of the ISRF for several extreme high-contrast Earth scenes, achieving a shape stability of \(<0.5{\%}\) and a centroid stability of \(<0.25 \ \text {pm}\) (NIR). Given this unprecedented ISRF stabilization, we conclude that the 2DSH concept efficiently desensitizes the instrument for radiometric and spectral errors with respect to the heterogeneity of the Earth scene radiance. PubDate: 2022-04-01
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Abstract: Abstract The sensitivity of hybrid RANS-LES methods like Improved Delayed Detached Eddy Simulation (IDDES) to numerical model parameter variations related to generic space launch vehicle aft-body flows is investigated. In particular, the changes resulting from the choice of the time-step size, the turbulence model, the fluid modelling, the circumferential grid resolution, the filter length definition, and the data collection period is considered. The results are also compared to experimental and numerical data taken from the available literature. The sensitivity to the time-step size and the turbulence model is minuscule with respect to the obtained mean flow field, wall pressure distributions, azimuthal modes, and wall pressure frequency spectra. However, circumferential resolution, fluid model, and filter length definition affect the solution to a higher extent. Buffeting spectra are very sensitive to the data collection period. PubDate: 2022-04-01
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Abstract: Abstract This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding flight scenario is derived using a ground-to-flight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered. PubDate: 2022-04-01
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Abstract: Abstract This paper investigates tilt decorrelations due to atmospheric anisoplanatism occuring when observing wavefronts emerging from distinct line of sight. The targeted application is ultimately the (pre-)compensation of the atmospheric turbulence experienced by a laser beam during ground-to-satellite optical links. The purpose of the study is to evaluate the effectiveness of the uplink pre-compensation, if the downlink signal (received from the satellite) is used as a reference. Because of the point-ahead angle of the satellite, one expects some decorrelation between the downlink and the uplink signals, which, in turn, impacts the efficacy of the pre-compensation. The larger the beam, the smaller its divergence and the more sensitive it is to pointing errors. In this framwork, a test campaign was carried out in May 2018 at the Optical Ground Station (OGS) of the European Space Agency (ESA), to perform measurements of double stars featuring angular separations representative of the point-ahead angle of GEO/LEO satellites. The differential Tip/Tilt distortion between the double stars is used as an estimator of the typical decorrelation between the downlink and the uplink signal, hence the present study. The algorithm used to extract the tip-tilt error due to anisoplanatism is described, and the experimental results are compared to the numerical predictions. It is then shown how to estimate the jitter of the telescope, based on the common motion of two independent stars as seen in the focal plane of the telescope. Finally, the paper provides a methodology to determine the maximum transmitter aperture of a ground-based terminal, in case a tilt pre-compensation is applied based on the satellite signal. PubDate: 2022-04-01
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Abstract: 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: 2022-04-01
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Abstract: Abstract We introduce a novel compact 4-channel beam splitter which is based on a combination of dichroic coatings and internal total reflection, similar in concept to the interference double prism invented by Kösters 90 years ago [1]. Used with a rapidly-slewing 50 cm telescope in space, this would allow to double the presently known gamma-ray bursts at high (> 5) redshift within 2 years. PubDate: 2022-04-01
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Abstract: Abstract In this paper, a generic full-system estimation software tool is introduced and applied to a data set of actual flight missions to derive a heuristic for system composition for mass and power ratios of considered sub-systems. The capability of evolutionary algorithms to analyse and effectively design spacecraft (sub-)systems is shown. After deriving top-level estimates for each spacecraft sub-system based on heuristic heritage data, a detailed component-based system analysis follows. Various degrees of freedom exist for a hardware-based sub-system design; these are to be resolved via an evolutionary algorithm to determine an optimal system configuration. A propulsion system implementation for a small satellite test case will serve as a reference example of the implemented algorithm application. The propulsion system includes thruster, power processing unit, tank, propellant and general power supply system masses and power consumptions. Relevant performance parameters such as desired thrust, effective exhaust velocity, utilised propellant, and the propulsion type are considered as degrees of freedom. An evolutionary algorithm is applied to the propulsion system scaling model to demonstrate that such evolutionary algorithms are capable of bypassing complex multidimensional design optimisation problems. An evolutionary algorithm is an algorithm that uses a heuristic to change input parameters and a defined selection criterion (e.g., mass fraction of the system) on an optimisation function to refine solutions successively. With sufficient generations and, thereby, iterations of design points, local optima are determined. Using mitigation methods and a sufficient number of seed points, a global optimal system configurations can be found. PubDate: 2022-04-01
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Abstract: Abstract The link performance of free space optical communications (FSOC) and deep space optical communications (DSOC) are investigated by considering two scenarios in space communications, for example, for the downlink and uplink between the earth ground stations and the near earth geostationary (GEO) satellites, and between the earth and spacecraft with large distance of 1 astronomical unit (AU) to the earth. Generally a distance larger than 0.01 AU or approximately 1,500,000 km from Earth is considered as deep space. In these theoretical investigations, different realistic system parameters for the optical lasers, transmitters, receivers, avalanche photodiodes (APDs), optical telescopes, atmospheric disturbances like scintillation and absorption are considered. The simulation results are compared with existing project data and valuable ESA experimental results to verify and improve the simulation models. The comparison in this paper shows that the simulation models for the link budget and the scintillation estimation are feasible for the investigations of FSOC and DSOC, and can be used to investigate improved design and implementation of DSOC projects for planned long-term and medium-term space missions. PubDate: 2022-04-01
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Abstract: Abstract Different and exciting exploration opportunities toward the Moon are opening in this decade. In particular, the major space agencies are putting a considerable effort in designing and studying a broad spectrum of missions that will bring back the humans on the Moon. During the evaluation of Lunar mission concepts, having a tool that can quickly assess the best communication and data-handling architecture given a set of satellites and a site of interest is mandatory. In this work, a novel parametric framework is presented and applied to the study of the expected connectivity of Lunar networks. The framework comprises bent-pipe, store-and-forward and store-carry-and-forward networking approaches, covering most common data management options. The methodology is designed to determine the best communication architecture given an arbitrary set of available satellites, ground stations, point of interest, and data volume. The proposed algorithm has been applied in a motivating case study of a networked mission devoted to observing lava tubes sites on the Moon surface. Results validate the approach which can identify the inflection points where different data handling techniques outperform each other. PubDate: 2022-04-01
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