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Abstract: Abstract Cork P50 thermal protection material was characterized under the Earth atmospheric entry conditions in the framework of the in-flight experiment QARMAN. A total of 25 P50 samples were exposed to air plasma ranging the chamber static pressure values of 1500, 4100, 6180, and 20,000 Pa and heat fluxes between 280 and 3250 kW/m \(^2\) . The sample radius was also varied between 11 and 25 mm radius to investigate the effects of the stagnation line velocity gradient. The experimental results on heat flux, pressure, surface and in-depth temperatures, surface emissivity, swelling and recession rates, and computed boundary layer profiles as well as the mass blowing rates are presented. A material characterization data suite is also provided including thermogravimetric analysis, specific heat, and thermal conductivity. Overall, a wide range of experimental data of Cork P50 material in Earth atmospheric entry conditions is made available to modelers and engineers for improved material response models and heat shield design consolidation. PubDate: 2021-10-23
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Abstract: Abstract Friction stir welding (FSW) was used to join cast Ti–6Al–4V hemisphere and cylinder parts to produce a spacecraft propellant tank with reduced costs and lead time compared to conventional manufacturing. As a potential source for failure, the weld was inspected for residual stresses using three different methods: non-destructive neutron and X-ray diffraction as well as destructive hole drilling. The results showed lower residual stresses in the friction stir weld compared to results from conventional welding techniques such as electron beam welding or tungsten inert gas welding. In the hoop direction, a typical M-shaped residual stress profile centered around the weld was observed for both neutron and X-ray diffraction. According to the acquired data, the peak residual stresses (tensile) were measured in the heat-affected zone, up to a maximum of ~ 200 MPa. The results from the three different techniques generally compared well with each other, considering the rather significant differences between the methods. PubDate: 2021-10-20
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Abstract: Abstract In this study, we demonstrate how metal-oxide thin-film conformal coatings grown by atomic layer deposition (ALD) can be exploited as an effective approach to mitigate tin whisker growth on printed circuit boards. First, we study the effect of different ALD coatings and process parameters on Sn–Cu-electroplated test coupons, by combining optical imaging and scanning electron microscopy and evaluating whisker distribution on the surface. On these samples, we found that one important parameter in mitigating whisker growth is the time interval between electroplating and the ALD coating process (pre-coat time), which should be kept of the order of few days (2, based on our results). Atomic layer-deposited coatings were also found to be effective toward whisker formation in different storage conditions. Furthermore, we show that ALD coating is also effective in limiting the need for outgassing of electronic assemblies (PCBAs), which is an additional stringent requirement for applications in space industry. Our experimental results thus demonstrated that atomic layer deposition is a suitable technique for aerospace applications, both in terms of degassing and whisker mitigation. PubDate: 2021-10-18
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Abstract: Abstract An innovative concept of building compliant mechanisms by additive manufacturing (AM) developed at CSEM is presented. Bringing together CSEM’s experience in the design and development of high-performance flexural elements and mechanisms for more than 30 years has opened the doors to new opportunities. The complete development of compliant structures for AM enables CSEM to develop innovative concepts to drastically reduce the need of machining after AM. Support structures under flexure blades are integrated to the flexures with no need for removal, which makes the overall process becomes more streamlined. Thanks to this concept, CSEM has developed new architectures of compliant mechanisms based on additive manufacturing (COMAM) for the European Space Agency (ESA). These demonstrators will be used as use-case for future high-precision and harsh environment applications such as cryogenic and space. The complete development workflow, starting with the design, topology optimization, manufacturing, post-processes, validation, up to performance and environmental testing will be presented. PubDate: 2021-10-18
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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: 2021-10-08
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Abstract: Abstract CFRP lattice structures, without the skin, offer several benefits with respect to conventional sandwich or monolithic concepts in satellite applications such as mass reduction, accessibility to the interior side and superior thermo-elastic stability. Automated manufacturing process, based on placement or winding, offers opportunities to lower the overall cost of serial products. Despite the apparent simplicity of the process, there is a large variety of manufacturing solutions proposed by industry. This evidences the interest but also an inherent practical difficulty to define a single, definitive process, that is at the same time cheap and suitable for different scales of interest, as well as accounting for flat, single, or even double-curvature shapes. CIRA has developed a specific manufacturing process for grid-stiffened structures based on a combination of rubber tooling, Dry Parallel Robotic Winding (patented) and Resin Liquid Infusion. A variation of this process has been successfully applied to VEGA-C Interstage 2/3. This paper presents the extension of this approach for two applications—promoted by the “CFRP Grid Tubular Structures” ESA ITT project in the framework of Artes 5.1—highly interesting for the space market: an instrument boom segment (a part of a satellite large deployable antenna), and a satellite central tube. Both demonstrators address rather strict requirements and challenging design and manufacturing issues, ranging from a large diameter Central Tube, with stiffness and buckling constraints and thick ribs, to a slender boom segment with stiffness and thermal stability requirements and thin ribs. The two demonstrators have been successfully designed, produced and tested, confirming the efficiency and flexibility of the approach and providing new benchmarks for the space community. PubDate: 2021-10-07
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Abstract: Abstract A common practice in the field of differential lift and drag controlled satellite formation flight is to analytically design maneuver trajectories using linearized relative motion models and the constant density assumption. However, the state-of-the-art algorithms inevitably fail if the initial condition of the final control phase exceeds an orbit and spacecraft-dependent range, the so-called feasibility range. This article presents enhanced maneuver algorithms for the third (and final) control phase which ensure the overall maneuver success independent of the initial conditions. Thereby, all maneuvers which have previously been categorized as infeasible due to algorithm limitations are rendered feasible. An individual algorithm is presented for both possible control options of the final phase, namely differential lift or drag. In addition, a methodology to precisely determine the feasibility range without the need of computational expensive Monte Carlo simulations is presented. This allows fast and precise assessments of possible influences of boundary conditions, such as the orbital inclination or the maneuver altitude, on the feasibility range. PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00362-8
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Abstract: Abstract In aerospace industry, saving mass on spacecrafts always remain in large demand to save launch costs or increase the available payload mass. A case study is carried out designing a first concept of an additive manufactured flywheel of a reaction wheel, as it is one of the heaviest parts of wheel systems. As an objective the mass is minimized, while obtaining an angular momentum suitable according to mission requirements and maintaining recent performances. As references the SeaSAT mission and a commercial reaction wheel are used. The work includes a preliminary dimension of the flywheels design space by MATLAB calculations, where in total 15 shapes are analyzed and compared. The most promising design space is afterwards analyzed via the finite-element tool ANSYS and is defined as the reference flywheel. The reference flywheel is used for topology optimizations (ANSYS Topology Optimization), where different boundary conditions are considered. The final designed flywheel obtains 16% higher energy density than the reference flywheel and withstands the mission loads. It can be concluded that it was possible to design a flywheel obtaining less mass while keeping the expected performance. PubDate: 2021-10-01 DOI: 10.1007/s12567-020-00343-3
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Abstract: Abstract This paper is devoted to the development of a light-weight deployable mesh reflector antenna for mini satellites with synthetic aperture radar (SAR) payload. The analyses of the electromagnetic and mechanical properties of the multi-beam deployable reflector antenna are performed for the space-borne dual-band (X- and S-bands) synthetic aperture radar (SAR) system based on digital beam forming (DBF). The reflector antenna is of offset type with a diameter of 3.35 m and weight of 7.8 kg. The DBF-SAR system is designed for mini satellites of total mass < 150 kg. PubDate: 2021-10-01 DOI: 10.1007/s12567-020-00346-0
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Abstract: Abstract Launch loads are critical forces to the payload. Many structures are not designed to survive these loads, thus, additional systems which absorb them are required. These launch lock mechanisms are available in different varieties. For a future magnetic bearing reaction wheel, two different principles of launch lock mechanism concepts were developed and tested. The first one is based on a spring mechanism, while the second uses electromagnetism to move the locking pins. A first testing with prototypes of both was conducted to evaluate the functionality. Subsequently improvements regarding reducing the mass and construction volume were incorporated in the design. In the course of this, additive manufacturing with PLA filament has been used to study possible applications for these mechanisms. The spring concept resulted to be more reliable than the electromagnetic one, but requires a damping mechanism. A usage of additive manufactured PLA components is a promising possibility for the production. PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00353-9
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Abstract: Abstract In the last decades, green deorbiting technologies have begun to be investigated and have raised a great interest in the space community. Among the others, electrodynamic tethers appear to be a promising option. By interacting with the surrounding ionosphere, electrodynamic tethers generate a drag Lorentz force to decrease the orbit altitude of the satellite, causing its re-entry in the atmosphere without using propellant. In this work, the requirements that drive the design of the deployment mechanism proposed for the H2020 Project E.T.PACK—Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit—are presented and discussed. Additionally, this work presents the synthesis of the reference profiles used by the motor of the deployer to make the tethered system reach the desired final conditions. The result is a strategy for deploying electrodynamic tape-shaped tethers used for deorbiting satellites at the end of their operational life. PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00349-5
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Abstract: Abstract Autonomous formation flight enables new satellite missions for novel applications. The cost and limits of propulsion systems can be overcome if environmental resources are being benefitted of. Currently, atmospheric drag is used in low Earth orbit to this end. Solar radiation pressure, which is of similar order of magnitude as aerodynamic ram pressure, is, however, always neglected. We introduce this force and show that it can be exploited. We demonstrate through simulations that a formation geometry is established quicker if the solar radiation pressure is modeled. PubDate: 2021-10-01 DOI: 10.1007/s12567-020-00344-2
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Abstract: Abstract Under the umbrella of the Clean Space Initiative, ESA has promoted activities in the area of Active Debris Removal (ADR). One of the main challenges driving the complexity of the rendezvous and capture of debris is its tumbling motion. It is highly desirable that kinetic energy dissipation devices damp the angular rates of debris in advance. Unfortunately, Eddy currents in conductive structures only provide a very slow detumbling. A potentially faster solution proposed by ESA (patent pending Ref EP19182205) consists in short-circuiting the satellite Magnetic Torquers already on board LEO satellites. The tumbling motion of the satellite within the Earth magnetic field results in the induction of currents in the Magnetic Torquers coils, dissipating energy by Joule heating. With a spin rate around 1 rpm, the Gravity Gradient torques create a slow precession of the satellite angular momentum around the orbit normal while the magnetic torques generated by a potential satellite residual dipole command a perpendicular precession around the North Pole. In parallel, the short-circuited Magnetic Torquers create damping and tilting magnetic torques. The spin axis re-orientation and the reduction of the angular rates are analytically predicted. A reduced set of driving parameters (debris inertias, altitude, spin axis orientation, and Magnetic Torquers characteristics) are identified that estimate the detumbling durations. ESA aims to further study and implement this concept with industry during the procurement phase of the new Copernicus Expansion Sentinels kicked off in autumn 2020, with first launches in 2025. The increased definition of the six satellites will permit to consider the positive contribution of Eddy currents in the metallic structures as well as the detrimental impact of the Solar Radiation pressure on tumbling Solar Arrays. PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00354-8
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Abstract: Abstract The study of asteroids interior is crucial to the understanding of their accretion in the early Solar System. Furthermore, space-borne sounding radar is the most mature technique to image asteroid’s internal structure. The low-frequency radar is a bistatic radar measuring the radar wave propagation between a Lander and an Orbiter through the asteroid. Time accuracy and frequency stability are fundamental for the success of such an instrument. Furthermore, accuracy in the propagation delay measurement is a way to increase science return. This work studies the impact the drift of the clocks located on the two platforms has on the accuracy of the time measurement while taking into account the on-board processing. We present the time analysis of such a radar by developing a behavior model of the system for a long time scale which is implemented in a software simulator. A clock test bench is then developed to provide simulator inputs from true oven controlled crystal oscillators clocks under selection for the mission. The simulator coupled to the test bench allows us to better quantify the impact of the time errors on the measurement, to support clock selection and to improve science return. PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00367-3
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Abstract: Abstract A novel approach to the three-axis attitude control of a magnetically actuated spacecraft is proposed, based on hybrid systems theory. Due to the actuators type, the system model is instantaneously underactuated and time-varying, so that low pointing errors and robustness are difficult to achieve at the same time. In this work, a uniting control design is developed, which combines a local H-inf regulator, with guaranteed performance, and a global nonlinear controller for ensuring global stability and robustness. Hybrid control theory is employed to develop a mixed continuous-discrete controller able to switch between different feedbacks. Controllers’ domains are designed according to appropriate input–output functions and to the magnitude of disturbances affecting the system. As a result, global attitude stability is ensured, while achieving local optimality and robustness against bounded disturbances, both matched and unmatched by the control action, and measurement noise. Analytical results are verified by means of realistic numerical simulations: the state errors comply with the computed bounds and stability is guaranteed for conservative assumptions on the magnitude of the unmatched disturbances. PubDate: 2021-10-01 DOI: 10.1007/s12567-020-00340-6
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Abstract: Abstract The ADEO subsystem is a scalable drag augmentation device that uses the residual Earth atmosphere present in Low Earth Orbit (LEO) to passively de-orbit of satellites between 1 and 2000 kg. For the de-orbit maneuvre, a large surface is deployed which multiplies the drag effective surface of the satellite significantly. Thereby the drag force is increased as well causing accelerated decay in orbit altitude. Advantageous about a drag augmentation device is that it does not require any active steering and can be designed for passive attitude stabilization thereby making it applicable for non-operational, tumbling spacecrafts as well. The ADEO subsystem consists of four deployable booms that span four sail segments in a planar shaped configuration. While the sails are made of an aluminum-coated polyimide foil, its coating thickness was chosen such that it provides sufficient protection from the LEO space environment. The current activity commenced in August 2018 is going to provide a fully qualified Protoflight Model (PFM) for a follow-up “In Orbit Demonstration” (IOD) in 2021/2022 (ADEO is selected as payload on the European Commission IOD/IOV satellite programme). In May 2020, the team passed the Manufacturing Readiness Review (MRR). An extensive Breadboarding- and Engineering Model campaign including life tests had already been carried out in 2019. The first ADEO-L PFM consists of a 5 m x 5 m dragsail deployed under control of own onboard electronics. Optionally, ADEO-L systems can be equipped with a so-called “watchdog routine” inside the electronics which is able to recognize the point in time when the satellite has come to the end of its life circle. With the help of an on-board battery the sail will be deployed automatically after a certain time in orbit. Operating like this, ADEO-L can be truly called “100% passive”, a “CleanGreen Space Mission”. First commercial candidate missions to be targeted after the successful EC-IOD mission were already identified by Airbus DS (DE) and QinetiQ (BE). PubDate: 2021-10-01 DOI: 10.1007/s12567-021-00355-7
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Abstract: Abstract This paper reports on the design, construction, and operation of a 1 kg C3F8 bubble chamber intended for applications such as space missions for measurement and monitoring of galactic cosmic rays. The event signal analysis aims towards a full discrimination from known particles (neutrons and alphas). With the use of a hydrophone, a 95% efficiency signal detection was achieved. Test calibrations indicate an overlap of the two power distributions and 74% of well-discriminated events. Pressure signal differences also conjecture on the nature of the event signals. This work shows the performance of a bubble chamber that allows high-pressure (16 bar) operations. The increase in operational recompression leads to a reduction of the detector's dead time by a factor of six. PubDate: 2021-09-22 DOI: 10.1007/s12567-021-00389-x
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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: 2021-09-22 DOI: 10.1007/s12567-021-00390-4
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Abstract: Abstract ESA’s Next Generation Gravity Mission (NGGM) is a candidate Mission of Opportunity for ESA-NASA cooperation in the frame of the MAss change and Geosciences International Constellation (MAGIC) . The mission aims at enabling long-term monitoring of the temporal variations of Earth’s gravity field at relatively high temporal (down to 3 days) and increased spatial resolutions (up to 100 km) at longer time. Such variations carry information about mass change induced by the water cycle and the related mass exchange among atmosphere, oceans, cryosphere, and land, and will complete our picture of global and climate change with otherwise partial or unavailable data. Over the last 15 years, numerous system and technology activities have been initiated by the Earth Observation Programmes (EOP) Directorate of the European Space Agency with the aim of advancing the maturity of the NGGM system and the key subsystems: particular attention was devoted to the design of the fine attitude control system, enabled by proportional thruster like variable specific impulse electrostatic thrusters based on Field Emission Electric Propulsion (FEEP), in which a liquid propellant is electrostatically extracted and accelerated to high exhaust velocity. The core element of this propulsion technology is a passively-fed, porous tungsten crown emitter, consisting of 28 sharp needles. This emitter technology has been developed and qualified over more than a decade at FOTEC and the Austrian Institute of Technology under ten ESA/EOP contracts since 2005 targeting the NGGM needs and it has recently been adapted for use as the main propulsion system in commercial nano- and small-satellites. This paper summarizes the development efforts of the last decade and provides an assessment of the performance of this thruster technology, after extensive simulation and testing campaigns. PubDate: 2021-09-16 DOI: 10.1007/s12567-021-00386-0
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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 DOI: 10.1007/s12567-021-00379-z
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