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Abstract: Abstract When operated with a Hall effect thruster, either centrally or externally mounted, the hollow cathode discharge occurs in a magnetic field environment. Therefore, it is important to assess the influence of the magnetic field on the standalone operation of a hollow cathode to better predict device behavior when coupled with a Hall effect thruster. This study focuses on the influence of an applied axial magnetic field on the main oscillatory phenomena in the plume of a Kr-fed sub-ampere hollow cathode operated with an external disk anode. A probe array consisting of two cylindrical Langmuir probes and an emissive probe is used to assess changes in plasma parameters and collected ion saturation current as the magnetic field strength is varied up to 3 mT at the cathode’s location. The electron transport along the cathode–anode space is analyzed in terms of total electron collision frequency. It is shown that a higher magnetic field strength induces larger plasma densities and lower electron temperatures. Applying a magnetic field to the discharge of a cathode operating in plume mode causes a reduction in both the ionization instability and ion acoustic turbulence (IAT) energies. This suggests a dampening of the main oscillatory phenomena in the plume of the hollow cathode. Furthermore, the total electron collision frequency and its main contributor, the anomalous collision frequency due to high-frequency IAT, decrease at higher field strengths. The results included in this communication are, to the best of the authors’ knowledge, the first characterization of the response in low- and high-frequency wave content depending on a magnetic field in low-current hollow cathodes operating in standalone mode at \(<1\) A. PubDate: 2022-11-21
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Abstract: Abstract This contribution describes the investigation of flow channels which are designed to be directly integrated into an aerospike engine by means of additive manufacturing with laser powder bed fusion (LPBF). During the experimental testing of a previous aerospike engine in 2019, it was observed that high surface roughness of such additively manufactured integrated channels caused a significant reduction in the mass flow rates of the propellants ethanol and liquid oxygen as well as the coolant due to increased pressure drop. In an extensive study within the CFDmikroSAT project, various factors influencing this surface roughness are, therefore, being investigated, which include the geometry of the channels as well as selected manufacturing parameters of the LPBF process, such as layer thickness and component orientation. To further reduce the roughness after manufacturing, suitable post-processing methods are also being investigated for internal cavities, initially analysing the abrasive flow machining process. Within the paper, the overall investigation approach is presented, such as the overview of the considered specimens, and the initial results of a various studies with selected specimens are discussed. These studies consist of the examination of surface roughness reduction, shape accuracy and flow behaviour of post-processed cooling channel specimens. Finally, a brief overview of the already manufactured aerospike demonstrator is presented. PubDate: 2022-10-27
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Abstract: Abstract Metal-filled polymers can serve as the starting material to produce complex metal structures using the cost-effective additive manufacturing process Fused Filament Fabrication (FFF). In this process, the filaments consisting of polymer binders (e.g., polylactic acid (PLA)) and micropowder of highly conductive metals (e.g., copper) are extruded through a nozzle to build up the desired geometry layer by layer. The manufacturability of a complex copper coil for use in satellite actuators with two commercially available filaments (Electrifi and Filamet Copper) using FFF was investigated and the electrical conductivity of the printed material was determined. A design of experiment with variation of extruder temperature and printing speed was used to evaluate different parameter sets. The selected parameter set was then used to produce cuboids to determine the electrical conductivity and an exemplary coil geometry. While the coil could be printed in two sizes (original and enlarged by a factor of two) with one of the investigated filaments, this was not possible with the other filament because the printed material was not dimensionally stable with the selected process parameter set. For the Electrifi filament, that is electrically conductive without post processing, the material achieved a maximum electrical conductivity of \(5.59 \cdot 10^{ - 3} {\text{\% IACS }}\left( {0.033{ }\Omega {\text{cm}}} \right)\) . This was in alignment with other published results for this filament. The other filament Filamet Copper is not conductive in the as-built state. After debinding and sintering, the material achieved a maximum electrical conductivity of \(45.84{\text{\% IACS}} \left( {3.77 \cdot 10^{ - 6} { }\Omega {\text{cm}}} \right)\) . PubDate: 2022-10-15
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Abstract: Abstract Space manipulators allow to respond to a variety of problems in future space exploitation and exploration such as on-orbit deployment, active debris removal or servicing operations. However, a difficulty to autonomously control space manipulator systems arise with large and light structures presenting flexible behavior. Flexible dynamics remain a challenging study focus as its modeling may present a first difficulty while the different coupling with the manipulator may deteriorate the control quality. This paper addresses design and control problems related to autonomous space manipulator equipped with kinetic moment exchange devices for spacecraft rotation control when dealing with system internal disturbances, model uncertainties and measurement errors. One advantage of modeling the rigid–flexible dynamics of a multi-body system is the possibility of including the non-measurable states in the system decoupling and linearization. In this work, in addition to the development of an extended state observer (ESO) that estimate the flexible dynamics, a nonlinear disturbance observer (NDO) is also introduced and included in a nonlinear dynamic inversion (NDI) framework where both modeling uncertainties and measurement errors are considered. Inter-dependencies between observers and control dynamics motivate a simultaneous computation of their gains to improve system stability and control performances. This is achieved by the resolution of linear matrix inequalities (LMI). In order to highlight the interest of the proposed scheme and validate our approach in a realistic environment, extensive tests of an on-orbit space telescope assembly use-case are performed on a high-fidelity simulator. PubDate: 2022-10-14
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Abstract: Abstract A business roadmap is a high-level strategic management tool that maps the actions to develop new industries. It serves as a guide to plan and forecast technological, market and product developments in a more operational way. Precisely, the business roadmap of this article highlights the main actions to be taken by the European Union (EU) space ecosystem with regards to Low Earth Orbit (LEO)—orbits from 450 to 2000 km—and Very Low Earth Orbit (VLEO)—orbits from 150 to 450 km. On the one hand, it is necessary to (1) develop industrial and technological space capabilities, (2) continue investing public funds in European Programs to develop new vehicle concepts of access to space, (3) improve testing, demonstration and exploration for faster the Technology Readiness Level (TRL) development, (4) promote an entrepreneurial and risk-taking culture, and (5) leverage the private investment to boost the development of advanced access to space technologies, attract talent, promote collaboration between public and private companies, and finance NewSpace Small–Medium sized Enterprises (SMEs). On the other hand, it should also strengthen its relationship with the European Space Agency (ESA) to foster its space capabilities and become a competitive player in the access to space market in the medium term (5–10 years). The implementation of these actions will help the EU to improve its international positioning, and adapt the technology to the needs and requirements of NewSpace demand, mobilizing around €40,500 million euros for the EU economy during the first 10–15 years of operations with an average Leverage Factor (LF) of 4. PubDate: 2022-10-01
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Abstract: Abstract Cold Atom technology has undergone rapid development in recent years and has been demonstrated in space in the form of cold atom scientific experiments and technology demonstrators, but has so far not been used as the fundamental sensor technology in a science mission. The European Space Agency therefore funded a 7-month project to define the CASPA-ADM mission concept, which serves to demonstrate cold-atom interferometer (CAI) accelerometer technology in space. To make the mission concept useful beyond the technology demonstration, it aims at providing observations of thermosphere mass density in the altitude region of 300–400 km, which is presently not well covered with observations by other missions. The goal for the accuracy of the thermosphere density observations is 1% of the signal, which will enable the study of gas–surface interactions as well as the observation of atmospheric waves. To reach this accuracy, the CAI accelerometer is complemented with a neutral mass spectrometer, ram wind sensor, and a star sensor. The neutral mass spectrometer data is considered valuable on its own since the last measurements of atmospheric composition and temperature in the targeted altitude range date back to 1980s. A multi-frequency GNSS receiver provides not only precise positions, but also thermosphere density observations with a lower resolution along the orbit, which can be used to validate the CAI accelerometer measurements. In this paper, we provide an overview of the mission concept and its objectives, the orbit selection, and derive first requirements for the scientific payload. PubDate: 2022-10-01
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Abstract: Abstract Very low Earth orbits (VLEOs) have been proposed as a beneficial space mission regime due to their propensity to increase instrument spatial resolution and reduce launch cost per unit mass. However, for visual instruments, these benefits come at the cost of a decreased instrument swath width. This reduction results in longer revisit periods for regions on Earth and longer time until global coverage is achieved. Conversely, light detection and ranging (lidar) as an active remote sensing technique, can benefit from larger swath widths at lower altitudes, due to the increased signal-to-noise ratio. Investigation of this relationship shows that lidar swath width is inversely proportional to altitude squared, and, as a result, the number of spacecraft required to provide a desired lidar coverage also decreases approximately in inverse proportion to altitude squared. Investigation of suitable propulsion systems shows that although propellant mass and number of thrusters required for orbit maintenance increases with decreasing altitude, the overall system mass, and hence launch cost, will, in general, tend to decrease with decreasing altitude due to the lower number of spacecraft required. For a given mission, spacecraft bus, and propulsion system, a VLEO altitude can be identified that will result in the minimum overall mission cost. PubDate: 2022-10-01
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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: 2022-10-01
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Abstract: Abstract Spacecraft charging affects the accuracy of in-situ plasma measurements in space. We investigate the impact of spacecraft charging on upper thermospheric plasma measurements captured by a 2U CubeSat called Phoenix. Using the Spacecraft Plasma Interactions Software (SPIS), we simulate dayside surface potentials of − 0.6 V, and nightside potentials of − 0.2 V. We also observe this charging mechanism in the distribution function captured by the Ion and Neutral Mass Spectrometer (INMS) on-board Phoenix. Whilst negative charging in the dense ionosphere is known, the diurnal variation in density and temperature has resulted in dayside potentials that are smaller than at night. We apply charging corrections in accordance with Liouville’s theorem and employ a least-squares fitting routine to extract the plasma density, bulk speed, and temperature. Our routine returns densities that are within an order of magnitude of the benchmarks above, but they carry errors of at least 20%. All bulk speeds are greater than the expected range of 60–120 m/s and this could be due to insufficient charging corrections. Our parameterised ion temperatures are lower than our empirical benchmark but are in-line with other in-situ measurements. Temperatures are always improved when spacecraft charging corrections are applied. We mostly attribute the shortcomings of the findings to the ram-only capture mode of the INMS. Future work will improve the fitting routine and continue to cross-check with other in-flight data. PubDate: 2022-10-01
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Abstract: Abstract The air-breathing ion engine (ABIE), a concept for atmosphere-breathing electric propulsion for atmospheric drag compensation for satellites in very low earth orbit, is expected to be realized. The ABIE employs electron cyclotron resonance (ECR) ion engine technology and consists of an intake, an ECR plasma generator, ion optics, and a neutralizer. In the present study, a plasma generator with ion optics was designed and fabricated, and its performance was evaluated. In the ABIE, rarefied air in a vacuum chamber enters a discharge chamber, and it is then ionized by an ECR discharge. Finally, the generated ions are extracted by the ion optics. By measuring the current, we investigated the location of the specific source of ions extracted from the plasma generator. It was found that ions leak from the discharge chamber through apertures for air inflow on the yokes and side shielding panels of the plasma generator. The function of the side panels around the plasma generator is not only to prevent electron inflow but also to prevent ion outflow. We modified the side surface of the plasma generator to a three-layer structure, which suppressed the ion leakage successfully. PubDate: 2022-10-01
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Abstract: Abstract Is there a business, service and technology case for flying constellations lower' This study describes work by Thales Alenia Space UK and Thales Alenia Space France and the Satellite Applications Catapult to select an attractive telecommunications application for Very Low Earth Orbit (VLEO) satellites. Through a trade process comparing 8 different applications, mobile 5G internet access was selected as a financially compelling prospect for a VLEO constellation. This work develops a conceptual design of the payload and platform for the satellites in the constellation. A constellation was selected which will provide coverage between latitudes of ± 55° (as these latitudes cover > 95% of the Earth’s population). This consists of 33 planes of 70 satellites each inclined at 55° which will cover many potential users, with extended service in northern highly populated areas. The constellation will be able to provide an average 3.8 Mbps downlink data rate per beam to a conventional mobile phone handset, with each satellite supporting 320 beams. The flexibility of the payload allows this rate to be increased if not all beams are in use. PubDate: 2022-10-01
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Abstract: Abstract A more detailed understanding of the role of N2 in very low Earth orbit (VLEO) on atomic oxygen (AO)-induced material erosion is necessary for future development of the sub-LEO region. Accordingly, a laser-detonation source capable of capturing two different beams is developed. A dual-pulsed supersonic valve (dual-PSV) system is designed to form two beams in one nozzle configuration. It is demonstrated that the dual-PSV is capable of forming two atomic beams at individual energies with various composition ratios. This system is successfully applied for a ground-based simulation of the world’s first material erosion experiment in a sub-LEO aboard Super Low Altitude Test Satellite (SLATS). PubDate: 2022-10-01
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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: 2022-10-01
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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: 2022-10-01
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Abstract: Abstract Challenging space missions include those at very low altitudes, where the atmosphere is the source of aerodynamic drag on the spacecraft, that finally defines the mission’s lifetime, unless a way to compensate for it is provided. This environment is named Very Low Earth Orbit (VLEO) and it is defined for \(h<{450}{\mathrm{km}}\) . In addition to the spacecraft’s aerodynamic design, to extend the lifetime of such missions, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP), in which the propulsion system collects the atmospheric particles to be used as propellant for an electric thruster. The system could remove the requirement of carrying propellant on-board, and could also be applied to any planetary body with atmosphere, enabling new missions at low altitude ranges for longer missions’ duration. One of the objectives of the H2020 DISCOVERER project, is the development of an intake and an electrode-less plasma thruster for an ABEP system. This article describes the characteristics of intake design and the respective final designs based on simulations, providing collection efficiencies up to \(94\%\) . Furthermore, the radio frequency (RF) Helicon-based plasma thruster (IPT) is hereby presented as well, while its performances are being evaluated, the IPT has been operated with single atmospheric species as propellant, and has highlighted very low input power requirement for operation at comparable mass flow rates \(P\sim {60}{\mathrm{w}}\) . PubDate: 2022-10-01
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Abstract: Abstract Operating satellites in Very Low Earth Orbit (VLEO) benefit the already expanding New Space industry in applications including Earth Observation and beyond. However, long-term operations at such low altitudes require propulsion systems to compensate for the large aerodynamic drag forces. When using conventional propulsion systems, the amount of storable propellant limits the maximum mission lifetime. The latter can be avoided by employing Atmosphere-Breathing Electric Propulsion (ABEP) system, which collects the residual atmospheric particles and uses them as propellant for an electric thruster. Thus, the requirement of on-board propellant storage can ideally be nullified. At the Institute of Space Systems (IRS) of the University of Stuttgart, an intake, and a RF Helicon-based Plasma Thruster (IPT) for ABEP system are developed within the Horizons 2020 funded DISCOVERER project. To assess possible future use cases, this paper proposes and analyzes several novel ABEP-based mission scenarios. Beginning with technology demonstration mission in VLEO, more complex mission scenarios are derived and discussed in detail. These include, amongst others, orbit maintenance around Mars as well as refuelling and space tug missions. The results show that the ABEP system is not only able to compensate drag for orbit maintenance but also capable of performing orbital maneuvers and collect propellant for applications such as Space Tug and Refuelling. Thus, showing a multitude of different future mission applications. PubDate: 2022-10-01
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Abstract: Abstract The eventual aim of this research work was to develop a new low-cost synthesis route to produce ultralight aluminum oxide ceramic fibers for high temperature insulation. This paper mainly focuses on the application of Al2O3 fibers as insulation materials in space vehicles. The study extended to check the fibers during the launch and in the conditions of space by a satellite test. The materials were monitored by thermo-vacuum and vibration tests before the launch. The long-term stability, the daily maximum and minimum temperature, and the temperature fluctuation were investigated in the satellite test. The data derived from satellite was collected in about 9 months. The other focus of this study was the characterization of fibers at high temperature. Al2O3 fibers were prepared by a new solution method and electrospinning technique. The developed Al2O3 fibers can be characterized by 0.035–0.037 W⋅mK−1 thermal conductivity, excellent heat resistance (up to 1600 °C), and good flexibility. PubDate: 2022-09-27
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Abstract: Abstract The space industry is growing and space data are becoming accessible to businesses that were previously unthinkable. Constellations of small satellites in Very Low Earth Orbit (VLEO) have created a gap that is allowing small and medium-sized space companies to gain momentum by developing new strategies and technologies. According to Euroconsult forecasting, the NewSpace market will grow from $12.6 billion to $42.8 billion in the next decade (2019–2028). Despite the study’s limitations and the uncertainties of the small satellite market, the results obtained in this exploratory research suggest that the Low-Cost Carriers (LCC) market, an already established market in the aviation industry, and the growing market of EO small satellite constellations in VLEO have similar behaviours. This behaviour shows that the evolution of EO smallsat constellations in VLEO is comparable with the evolution of the LCC airlines. In addition, the result also identifies a set of competitive factors that allow the researchers to observe similar strategic behaviour in both markets. PubDate: 2022-08-24 DOI: 10.1007/s12567-022-00462-z
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