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Aerospace, Volume 7, Issue 11 (November 2020) – 14 articles

Cover Story (view full-size image): The application of reduced-order modeling (ROM) techniques in the context of aerodynamic and aeroelastic nonlinear system identification has gained increasing attention in recent years. Therefore, the present study introduces the application of a recurrent neuro-fuzzy model (NFM) that is serially connected with a multilayer perceptron (MLP) neural network for the computation of transonic aileron buzz. The training of the ROM is accomplished based on a computational fluid dynamics (CFD) data set. For performance evaluation, a 2D aeroelastic model of the NACA651213 airfoil with integrated aileron is investigated at different buzz conditions. A comparison of the ROM and CFD results yields a precise prediction capability. View this paper
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Article
On the Design of Aeroelastically Scaled Models of High Aspect-Ratio Wings
Aerospace 2020, 7(11), 166; https://doi.org/10.3390/aerospace7110166 - 18 Nov 2020
Cited by 2 | Viewed by 1991
Abstract
Recently, innovative aircraft designs were proposed to improve aerodynamic performance. Examples include high aspect ratio wings to reduce the aerodynamic induced drag to achieve lower fuel consumption. Such solution when combined with a lightweight structure may lead to aeroelastic instabilities such as flutter [...] Read more.
Recently, innovative aircraft designs were proposed to improve aerodynamic performance. Examples include high aspect ratio wings to reduce the aerodynamic induced drag to achieve lower fuel consumption. Such solution when combined with a lightweight structure may lead to aeroelastic instabilities such as flutter at lower air speeds compared to more conventional wing designs. Therefore, in order to ensure safe flight operation, it is important to study the aeroelastic behavior of the wing throughout the flight envelope. This can be achieved by either experimental or computational work. Experimental wind tunnel and scaled flight test models need to exhibit similar aeroelastic behavior to the full scale air vehicle. In this paper, three different aeroelastic scaling strategies are formulated and applied to a flexible high aspect-ratio wing. These scaling strategies are first evaluated in terms of their ability to generate reduced models with the intended representations of the aerodynamic, structural and inertial characteristics. Next, they are assessed in terms of their potential in representing the unsteady non-linear aeroelastic behavior in three different flight conditions. The scaled models engineered by exactly scaling down the internal structure suitably represent the intended aeroelastic behavior and allow the performance assessment for the entire flight envelope. However, since both the flight and wind tunnel models are constrained by physical and budgetary limitations, custom built structural models are more likely to be selected. However, the latter ones are less promising to study the entire flight envelope. Full article
(This article belongs to the Special Issue Aeroelasticity, Volume II)
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Article
Evaluation of Strategies to Reduce the Cost Impacts of Flight Delays on Total Network Costs
Aerospace 2020, 7(11), 165; https://doi.org/10.3390/aerospace7110165 - 18 Nov 2020
Cited by 6 | Viewed by 1632
Abstract
Competitive price pressure and economic cost pressure constantly force airlines to improve their optimization strategies. Besides predictable operational costs, delay costs are a significant cost driver for airlines. Especially reactionary delay costs can endanger the profitability of such a company. These time-dependent costs [...] Read more.
Competitive price pressure and economic cost pressure constantly force airlines to improve their optimization strategies. Besides predictable operational costs, delay costs are a significant cost driver for airlines. Especially reactionary delay costs can endanger the profitability of such a company. These time-dependent costs depend on the number of sensitive transfer passengers. This cost component is represented by the number of missed flights and the connectivity of onward flights, i.e., the offer of alternative flight connections. The airline has several options to compensate for reactionary delays, for example, by increasing cruising speeds, shortening turnaround times, rebookings and cancellations. The effects of these options on the cost balance of airline total operating costs have been examined in detail, considering a flight-specific number of transfer passengers. The results have been applied to a 24-h rotation schedule of a large German hub airport. We found, that the fast turnaround and increasing cruise speed are the most effective strategies to compensate for passenger-specific delay costs. The results could be used in a multi-criteria trajectory optimization to find a balance between environmentally-driven and cost-index-driven detours and speed adjustments. Full article
(This article belongs to the Collection Air Transportation—Operations and Management)
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Article
Static Aeroelasticity Using High Fidelity Aerodynamics in a Staggered Coupled and ROM Scheme
Aerospace 2020, 7(11), 164; https://doi.org/10.3390/aerospace7110164 - 17 Nov 2020
Cited by 1 | Viewed by 1668
Abstract
Current technology in evaluating the aeroelastic behavior of aerospace structures is based on the staggered coupling between structural and low fidelity linearized aerodynamic solvers, which has inherent limitations, although tried and trusted outside the transonic region. These limitations arise from the assumptions in [...] Read more.
Current technology in evaluating the aeroelastic behavior of aerospace structures is based on the staggered coupling between structural and low fidelity linearized aerodynamic solvers, which has inherent limitations, although tried and trusted outside the transonic region. These limitations arise from the assumptions in the formulation of linearized aerodynamics and the lower fidelity in the description of the flowfield surrounding the structure. The validity of low fidelity aerodynamics also degrades fast with the deviation from a typical aerodynamic shape due to the inclusion of various control devices, gaps, or discontinuities. As innovative wings tend to become more flexible and also include a variety of morphing devices, it is expected that using low fidelity linearized aerodynamics in aeroelastic analysis will tend to induce higher levels of uncertainty in the results. An obvious solution to these issues is to use high fidelity aerodynamics. However, using high fidelity aerodynamics incurs a very high computational cost. Various formulations of reduced order models have shown promising results in reducing the computational cost. In the present work, the static aeroelastic behavior of three characteristic aeroelastic problems is obtained using both a full three-dimensional staggered coupled scheme and a time domain Volterra series based reduced order model (ROM). The reduced order model’s ability to remain valid for a wide range of dynamic pressures around a specific Mach number (and Reynolds number regime if viscous flow is considered) and the capability to modify structural parameters such as damping ratios and natural frequencies are highlighted. Full article
(This article belongs to the Special Issue Aeroelasticity, Volume II)
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Article
A Test Platform to Assess the Impact of Miniaturized Propulsion Systems
Aerospace 2020, 7(11), 163; https://doi.org/10.3390/aerospace7110163 - 16 Nov 2020
Cited by 1 | Viewed by 998
Abstract
Miniaturized propulsion systems can enable many future CubeSats missions. The advancement of the Technology Readiness Level of this technology passes through the integration in a CubeSat platform and the assessment of the impact and the interactions of the propulsion systems on the actual [...] Read more.
Miniaturized propulsion systems can enable many future CubeSats missions. The advancement of the Technology Readiness Level of this technology passes through the integration in a CubeSat platform and the assessment of the impact and the interactions of the propulsion systems on the actual CubeSat technology and vice versa. The request of power, the thermal environmental, and the electromagnetic emissions generated inside the platform require careful analyses. This paper presents the upgraded design and the validation of a CubeSat test platform (CTP) that can interface a wide range of new miniaturized propulsion systems and gather unprecedented information for these analyses, which can be fused with the commonly used ground support equipment. The CTP features are reported, and the main achievements of the tests are shown, demonstrating the effective capabilities of the platform and how it allows for the investigation of the mutual interactions at system level between propulsion systems and the CubeSat technology. Full article
(This article belongs to the Special Issue Verification Approaches for Nano- and Micro-Satellites II)
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Article
Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz
Aerospace 2020, 7(11), 162; https://doi.org/10.3390/aerospace7110162 - 13 Nov 2020
Cited by 1 | Viewed by 1022
Abstract
In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified [...] Read more.
In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified ROM is obtained by performing forced-motion unsteady Reynolds-averaged Navier Stokes (URANS) simulations. Further, a Monte Carlo-based training procedure is applied in order to estimate statistical errors. In order to demonstrate the method’s fidelity, a two-dimensional aeroelastic model based on the NACA651213 airfoil is investigated at different flow conditions, while the aileron deflection and the hinge moment are considered in particular. The aileron is integrated in the wing section without a gap and is modeled as rigid. The dynamic equations of the rigid aileron rotation are coupled with the URANS-based flow model. For ROM training purposes, the aileron is excited via a forced motion and the respective aerodynamic and aeroelastic response is computed using a computational fluid dynamics (CFD) solver. A comparison with the high-fidelity reference CFD solutions shows that the essential characteristics of the nonlinear buzz phenomenon are captured by the selected ROM method. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology)
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Article
Multifidelity Sensitivity Study of Subsonic Wing Flutter for Hybrid Approaches in Aircraft Multidisciplinary Design and Optimisation
Aerospace 2020, 7(11), 161; https://doi.org/10.3390/aerospace7110161 - 12 Nov 2020
Cited by 4 | Viewed by 1250
Abstract
A comparative sensitivity study for the flutter instability of aircraft wings in subsonic flow is presented, using analytical models and numerical tools with different multidisciplinary approaches. The analyses build on previous elegant works and encompass parametric variations of aero-structural properties, quantifying their effect [...] Read more.
A comparative sensitivity study for the flutter instability of aircraft wings in subsonic flow is presented, using analytical models and numerical tools with different multidisciplinary approaches. The analyses build on previous elegant works and encompass parametric variations of aero-structural properties, quantifying their effect on the aeroelastic stability boundary. Differences in the multifidelity results are critically assessed from both theoretical and computational perspectives, in view of possible practical applications within airplane preliminary design and optimisation. A robust hybrid strategy is then recommended, wherein the flutter boundary is obtained using a higher-fidelity approach while the flutter sensitivity is computed adopting a lower-fidelity approach. Full article
(This article belongs to the Special Issue Aircraft Design (SI-2/2020))
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Article
Influence of Satellite Motion Control System Parameters on Performance of Space Debris Capturing
Aerospace 2020, 7(11), 160; https://doi.org/10.3390/aerospace7110160 - 06 Nov 2020
Cited by 2 | Viewed by 1221
Abstract
Relative motion control problem for capturing the tumbling space debris object is considered. Onboard thrusters and reaction wheels are used as actuators. The nonlinear coupled relative translational and rotational equations of motion are derived. The SDRE-based control algorithm is applied to the problem. [...] Read more.
Relative motion control problem for capturing the tumbling space debris object is considered. Onboard thrusters and reaction wheels are used as actuators. The nonlinear coupled relative translational and rotational equations of motion are derived. The SDRE-based control algorithm is applied to the problem. It is taken into account that the thrust vector has misalignment with satellite center of mass, and reaction wheels saturation affects the ability of the satellite to perform the docking maneuver to space debris. The acceptable range of a set of control system parameters for successful rendezvous and docking is studied using numerical simulations taking into account thruster discreteness, actuators constrains, and attitude motion of the tumbling space debris. Full article
(This article belongs to the Special Issue Small Satellite Formation Flying Motion Control and Attitude Dynamics)
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Article
Utilization of FPGA for Onboard Inference of Landmark Localization in CNN-Based Spacecraft Pose Estimation
Aerospace 2020, 7(11), 159; https://doi.org/10.3390/aerospace7110159 - 05 Nov 2020
Cited by 11 | Viewed by 2123
Abstract
In the recent past, research on the utilization of deep learning algorithms for space applications has been widespread. One of the areas where such algorithms are gaining attention is in spacecraft pose estimation, which is a fundamental requirement in many spacecraft rendezvous and [...] Read more.
In the recent past, research on the utilization of deep learning algorithms for space applications has been widespread. One of the areas where such algorithms are gaining attention is in spacecraft pose estimation, which is a fundamental requirement in many spacecraft rendezvous and navigation operations. Nevertheless, the application of such algorithms in space operations faces unique challenges compared to application in terrestrial operations. In the latter, they are facilitated by powerful computers, servers, and shared resources, such as cloud services. However, these resources are limited in space environment and spacecrafts. Hence, to take advantage of these algorithms, an on-board inferencing that is power- and cost-effective is required. This paper investigates the use of a hybrid Field Programmable Gate Array (FPGA) and Systems-on-Chip (SoC) device for efficient onboard inferencing of the Convolutional Neural Network (CNN) part of such pose estimation methods. In this study, Xilinx’s Zynq UltraScale+ MPSoC device is used and proposed as an effective onboard-inferencing solution. The performance of the onboard and computer inferencing is compared, and the effectiveness of the hybrid FPGA-CPU architecture is verified. The FPGA-based inference has comparable accuracy to the PC-based inference with an average RMS error difference of less than 0.55. Two CNN models that are based on encoder-decoder architecture have been investigated in this study and three approaches demonstrated for landmarks localization. Full article
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Article
Method to Characterize Potential UAS Encounters Using Open Source Data
Aerospace 2020, 7(11), 158; https://doi.org/10.3390/aerospace7110158 - 04 Nov 2020
Cited by 1 | Viewed by 1172
Abstract
As unmanned aerial systems (UASs) increasingly integrate into the US national airspace system, there is an increasing need to characterize how commercial and recreational UASs may encounter each other. To inform the development and evaluation of safety critical technologies, we demonstrate a methodology [...] Read more.
As unmanned aerial systems (UASs) increasingly integrate into the US national airspace system, there is an increasing need to characterize how commercial and recreational UASs may encounter each other. To inform the development and evaluation of safety critical technologies, we demonstrate a methodology to analytically calculate all potential relative geometries between different UAS operations performing inspection missions. This method is based on a previously demonstrated technique that leverages open source geospatial information to generate representative unmanned aircraft trajectories. Using open source data and parallel processing techniques, we performed trillions of calculations to estimate the relative horizontal distance between geospatial points across sixteen locations. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
A Novel Holistic Index for the Optimization of Composite Components and Manufacturing Processes with Regard to Quality, Life Cycle Costs and Environmental Performance
Aerospace 2020, 7(11), 157; https://doi.org/10.3390/aerospace7110157 - 30 Oct 2020
Cited by 5 | Viewed by 1322
Abstract
In the present work, a novel holistic component and process optimization index is introduced. The Index is aimed to provide a decision support tool for the optimization of aircraft composite components and manufacturing processes as well as for the selection of the appropriate [...] Read more.
In the present work, a novel holistic component and process optimization index is introduced. The Index is aimed to provide a decision support tool for the optimization of aircraft composite components and manufacturing processes as well as for the selection of the appropriate manufacturing technique of a component when various techniques are considered as manufacturing options. The criteria involved in the index are quality, cost and environmental footprint functions which are considered to be interdependent. In the present concept quality is quantified through measurable technological features which are required for the component under consideration. Cost has been estimated by implementing the Activity Based Concept (ABC) using an in house developed tool. Environmental footprint is assessed by exploiting the ReCiPe method using the ‘open LCA’ software. The weight factor of each of the above criteria in the Index is calculated by using the Multi Criteria Decision (MCD) method Analytic Hierarchy Process (AHP). The Index developed has been applied to support the selection of the appropriate production technique for a typical aeronautical composite part. The alternative manufacturing options considered have been the Automated Fiber Placement (AFP) as well as the classical Autoclave manufacturing technique. By considering quality as the prevailing factor for meeting a decision the index confirms the advantage of the Autoclave process. Yet, by considering the environmental footprint and/or cost to be of equal or higher significance to quality, the implementation of the index demonstrates the clear advantage of AFP process. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology)
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Article
Climate-Optimized Trajectories and Robust Mitigation Potential: Flying ATM4E
Aerospace 2020, 7(11), 156; https://doi.org/10.3390/aerospace7110156 - 30 Oct 2020
Cited by 12 | Viewed by 2214
Abstract
Aviation can reduce its climate impact by controlling its CO2-emission and non-CO2 effects, e.g., aviation-induced contrail-cirrus and ozone caused by nitrogen oxide emissions. One option is the implementation of operational measures that aim to avoid those atmospheric regions that are [...] Read more.
Aviation can reduce its climate impact by controlling its CO2-emission and non-CO2 effects, e.g., aviation-induced contrail-cirrus and ozone caused by nitrogen oxide emissions. One option is the implementation of operational measures that aim to avoid those atmospheric regions that are in particular sensitive to non-CO2 aviation effects, e.g., where persistent contrails form. The quantitative estimates of mitigation potentials of such climate-optimized aircraft trajectories are required, when working towards sustainable aviation. The results are presented from a comprehensive modelling approach when aiming to identify such climate-optimized aircraft trajectories. The overall concept relies on a multi-dimensional environmental change function concept, which is capable of providing climate impact information to air traffic management (ATM). Estimates on overall climate impact reduction from a one-day case study are presented that rely on the best estimate for climate impact information. Specific weather situation that day, containing regions with high contrail impact, results in a potential reduction of total climate impact, by more than 40%, when considering CO2 and non-CO2 effects, associated with an increase of fuel by about 0.5%. The climate impact reduction per individual alternative trajectory shows a strong variation and, hence, also the mitigation potential for an analyzed city pair, depending on atmospheric characteristics along the flight corridor as well as flight altitude. The robustness of proposed climate-optimized trajectories is assessed by using a range of different climate metrics. A more sustainable ATM needs to integrate comprehensive environmental impacts and associated forecast uncertainties into route optimization in order to identify robust eco-efficient trajectories. Full article
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Article
A Simulation-Based Performance Analysis Tool for Aircraft Design Workflows
Aerospace 2020, 7(11), 155; https://doi.org/10.3390/aerospace7110155 - 30 Oct 2020
Cited by 7 | Viewed by 2067
Abstract
A simulation-based approach for take-off and landing performance assessments is presented in this work. In the context of aircraft design loops, it provides a detailed and flexible formulation that can be integrated into a wider simulation methodology for a complete commercial aviation mission. [...] Read more.
A simulation-based approach for take-off and landing performance assessments is presented in this work. In the context of aircraft design loops, it provides a detailed and flexible formulation that can be integrated into a wider simulation methodology for a complete commercial aviation mission. As a matter of fact, conceptual and preliminary aircraft design activities require iterative calculations to quickly make performance predictions on a set of possible airplane configurations. The goal is to search for a design that best fits all top level aircraft requirements among the results of a great number of multi-disciplinary analyses, as fast as possible, and with a certain grade of accuracy. Usually, such a task is carried out using statistical or semi-empirical approaches which can give pretty accurate results in no time. However, those prediction methods may be inappropriate when dealing with innovative aircraft configurations or whenever a higher level of accuracy is necessary. Simulation-based design has become crucial to make the overall process affordable and effective in cases where higher fidelity analyses are required. A common example when flight simulations can be effectively used to support a design loop is given by aircraft mission analyses and performance predictions. These usually include take-off, climb, en route, loiter, approach, and landing simulations. This article introduces the mathematical models of aircraft take-off and landing and gives the details of how they are implemented in the software library JPAD. These features are not present in most of the currently available pieces of preliminary aircraft design software and allow one to perform high fidelity, simulation-based take-off and landing analyses within design iterations. Although much more detailed than classical semi-empirical approaches, the presented methodologies require very limited computational effort. An application of the proposed formulations is introduced in the second part of the article. The example considers the Airbus A220-300 as a reference aircraft model and includes complete take-off and landing performance studies, as well as the simulation of both take-off and landing certification noise trajectories. Full article
(This article belongs to the Special Issue Flight Simulation)
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Article
A Performance-Based Airspace Model for Unmanned Aircraft Systems Traffic Management
Aerospace 2020, 7(11), 154; https://doi.org/10.3390/aerospace7110154 - 28 Oct 2020
Cited by 9 | Viewed by 1813
Abstract
Recent evolutions of the Unmanned Aircraft Systems (UAS) Traffic Management (UTM) concept are driving the introduction of new airspace structures and classifications, which must be suitable for low-altitude airspace and provide the required level of safety and flexibility, particularly in dense urban and [...] Read more.
Recent evolutions of the Unmanned Aircraft Systems (UAS) Traffic Management (UTM) concept are driving the introduction of new airspace structures and classifications, which must be suitable for low-altitude airspace and provide the required level of safety and flexibility, particularly in dense urban and suburban areas. Therefore, airspace classifications and structures need to evolve based on appropriate performance metrics, while new models and tools are needed to address UTM operational requirements, with an increasing focus on the coexistence of manned and unmanned Urban Air Mobility (UAM) vehicles and associated Communication, Navigation and Surveillance (CNS) infrastructure. This paper presents a novel airspace model for UTM adopting Performance-Based Operation (PBO) criteria, and specifically addressing urban airspace requirements. In particular, a novel airspace discretisation methodology is introduced, which allows dynamic management of airspace resources based on navigation and surveillance performance. Additionally, an airspace sectorisation methodology is developed balancing the trade-off between communication overhead and computational complexity of trajectory planning and re-planning. Two simulation case studies are conducted: over the skyline and below the skyline in Melbourne central business district, utilising Global Navigation Satellite Systems (GNSS) and Automatic Dependent Surveillance-Broadcast (ADS-B). The results confirm that the proposed airspace sectorisation methodology promotes operational safety and efficiency and enhances the UTM operators’ situational awareness under dense traffic conditions introducing a new effective 3D airspace visualisation scheme, which is suitable both for mission planning and pre-tactical UTM operations. Additionally, the proposed performance-based methodology can accommodate the diversity of infrastructure and vehicle performance requirements currently envisaged in the UTM context. This facilitates the adoption of this methodology for low-level airspace integration of UAS (which may differ significantly in terms of their avionics CNS capabilities) and set foundations for future work on tactical online UTM operations. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology)
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Article
Polyatomic Ion-Induced Electron Emission (IIEE) in Electrospray Thrusters
Aerospace 2020, 7(11), 153; https://doi.org/10.3390/aerospace7110153 - 24 Oct 2020
Cited by 10 | Viewed by 2034
Abstract
To better characterize the lifetime and performance of electrospray thrusters, electron emission due to electrode impingement by the propellant cation 1-ethyl-3-methylimidazolium (EMI+) has been evaluated with semi-empirical modeling techniques. Results demonstrate that electron emission due to grid impingement by EMI+ [...] Read more.
To better characterize the lifetime and performance of electrospray thrusters, electron emission due to electrode impingement by the propellant cation 1-ethyl-3-methylimidazolium (EMI+) has been evaluated with semi-empirical modeling techniques. Results demonstrate that electron emission due to grid impingement by EMI+ cations becomes significant once EMI+ attains a threshold velocity of ∼9×105 cm s1. The mean secondary electron yield, γ¯, exhibits strong linearity with respect to EMI+ velocity for typical electrospray operating regimes, and we present a simple linear fit equation corresponding to thruster potentials greater than 1 kV. The model chosen for our analysis was shown to be the most appropriate for molecular ion bombardments and is a useful tool in estimating IIEE yields in electrospray devices for molecular ion masses less than ∼1000 u and velocities greater than ∼106 cm s1. Droplet-induced electron emission (DIEE) in electrospray thrusters was considered by treating a droplet as a macro-ion, with low charge-to-mass ratio, impacting a solid surface. This approach appears to oversimplify back-spray phenomena, meaning a more complex analysis is required. While semi-empirical models of IIEE, and the decades of solid state theory they are based upon, represent an invaluable advance in understanding secondary electron emission in electrospray devices, further progress would be gained by investigating the complex surfaces the electrodes acquire over their lifetimes and considering other possible emission processes. Full article
(This article belongs to the Special Issue Electric Propulsion)
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