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Aerospace, Volume 9, Issue 8 (August 2022) – 74 articles

Cover Story (view full-size image): The increasing congestion of Earth’s orbits brings with it a need for accurate orbit predictions required for collision avoidance and de-orbiting measures. Improved estimates of the drag force and solar radiation pressure acting on orbital objects are needed, for which knowledge of relevant parameters such as rotation state, shape, and surface material composition of the targets is crucial. Multispectral measurements encode this information, allowing for signal inversion techniques to be exploited to characterize spacecraft. To identify suited methods for parameter estimation from space debris, we have developed a simulation environment for spectral light curves. The simulator is validated through a series of multispectral field measurements. Using the simulation, we demonstrate how a target’s attributes can be extracted from light curve signals. View this paper
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Article
Application of Adaptive Weighted Strong Tracking Unscented Kalman Filter in Non-Cooperative Maneuvering Target Tracking
Aerospace 2022, 9(8), 468; https://doi.org/10.3390/aerospace9080468 - 22 Aug 2022
Viewed by 540
Abstract
An adaptive weighted strong tracking unscented Kalman filter is proposed in this paper for long-range relative navigation alongside non-cooperative maneuvering targets. First, an equation for obtaining the relative motion of two bodies is derived, it can be well adapted for a problem that [...] Read more.
An adaptive weighted strong tracking unscented Kalman filter is proposed in this paper for long-range relative navigation alongside non-cooperative maneuvering targets. First, an equation for obtaining the relative motion of two bodies is derived, it can be well adapted for a problem that has medium or long-distance. Secondly, a variance statistics function is introduced in the method to calculate residual weight in real time. The residual weight can be used to adjust the contribution of different measurement information to the fading factor. In this way, the sensitivity of the system to small pulse maneuvers is improved. Finally, the mean and covariance of the posterior state are calculated by the unscented transformation. A replacement equation for the fading factor is derived to improve the first-order approximation accuracy for a strong tracking system. Impulsive maneuvers with three different magnitudes are employed in a series of tests. Results from different methods showed that the proposed method could effectively detect pulse maneuvers with low latency. The proposed method is also numerically stable. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Study of the Impact of Traffic Flows on the ATC Actions
Aerospace 2022, 9(8), 467; https://doi.org/10.3390/aerospace9080467 - 22 Aug 2022
Viewed by 348
Abstract
It has always been a topic of great interest in air transport management to be able to estimate controller workload. So far, research has not had the opportunity to make use of real data on the controller’s actions. We have enough data to [...] Read more.
It has always been a topic of great interest in air transport management to be able to estimate controller workload. So far, research has not had the opportunity to make use of real data on the controller’s actions. We have enough data to be able to use machine learning methods. The aim of this work is to predict the controller’s actions to know his workload. Several machine learning models were tested to try different combinations of features and the selected algorithms and two models were finally chosen. The predictions provided by the models are good enough to be used when a first approximation of the workload in a sector is to be obtained. Finally, explainability techniques were employed to discover the patterns found by the AI in the machine learning models. Thanks to these techniques, we can build a profile of the critical flights that increase the workload the most. Full article
(This article belongs to the Special Issue Advances in Air Traffic and Airspace Control and Management)
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Article
Existence and Control of Special Orbits around Asteroid 4 Vesta
Aerospace 2022, 9(8), 466; https://doi.org/10.3390/aerospace9080466 - 21 Aug 2022
Viewed by 371
Abstract
This paper focuses on the existence and control of particular types of orbits around asteroid 4 Vesta, including Sun-synchronous orbits, orbits at the critical inclination, repeating ground-track orbits, and stationary orbits. J2, J3, and J4 terms are considered [...] Read more.
This paper focuses on the existence and control of particular types of orbits around asteroid 4 Vesta, including Sun-synchronous orbits, orbits at the critical inclination, repeating ground-track orbits, and stationary orbits. J2, J3, and J4 terms are considered in the gravity model of Vesta. First, the inclination perturbation caused by solar gravitation is studied, and preset and multiple inclination bias methods are proposed to dampen the local time drift at the ascending node. Compared with Vesta, the control periods of the Sun-synchronous orbits of 21 Lutetia and 433 Eros are much longer. Second, Vesta’s orbits with a critical inclination depend on the semi-major axis and eccentricity. If the eccentricity is not greater than 0.2, inclination decreases slowly and monotonically concerning the semi-major axis. If the eccentricity is not smaller than 0.4, inclination increases rapidly and monotonically. Third, Sun-synchronous repeating ground-track circular orbits of Vesta, which do not exist for Lutetia and Eros, are investigated. Finally, the perturbations of stationary orbits caused by solar gravitation and solar radiation pressure are analyzed. Full article
(This article belongs to the Special Issue Dynamics and Control Problems on Asteroid Explorations)
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Article
Optimizable Image Segmentation Method with Superpixels and Feature Migration for Aerospace Structures
Aerospace 2022, 9(8), 465; https://doi.org/10.3390/aerospace9080465 - 21 Aug 2022
Viewed by 460
Abstract
The lack of high-quality, highly specialized labeled images, and the expensive annotation cost are always critical issues in the image segmentation field. However, most of the present methods, such as deep learning, generally require plenty of train cost and high-quality datasets. Therefore, an [...] Read more.
The lack of high-quality, highly specialized labeled images, and the expensive annotation cost are always critical issues in the image segmentation field. However, most of the present methods, such as deep learning, generally require plenty of train cost and high-quality datasets. Therefore, an optimizable image segmentation method (OISM) based on the simple linear iterative cluster (SLIC), feature migration model, and random forest (RF) classifier, is proposed for solving the small sample image segmentation problem. In the approach, the SLIC is used for extracting the image boundary by clustering, the Unet feature migration model is used to obtain multidimensional superpixels features, and the RF classifier is used for predicting and updating the image segmentation results. It is demonstrated that the proposed OISM has acceptable accuracy, and it retains better target boundary than improved Unet model. Furthermore, the OISM shows the potential for dealing with the fatigue image identification of turbine blades, which can also be a promising method for the effective image segmentation to reveal the microscopic damages and crack propagations of high-performance structures for aeroengine components. Full article
(This article belongs to the Special Issue State Monitoring and Health Management of Complex Equipment)
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Article
Short-Term Trajectory Prediction Based on Hyperparametric Optimisation and a Dual Attention Mechanism
Aerospace 2022, 9(8), 464; https://doi.org/10.3390/aerospace9080464 - 20 Aug 2022
Viewed by 462
Abstract
Highly accurate trajectory prediction models can achieve route optimisation and save airspace resources, which is a crucial technology and research focus for the new generation of intelligent air traffic control. Aiming at the problems of inadequate extraction of trajectory features and difficulty in [...] Read more.
Highly accurate trajectory prediction models can achieve route optimisation and save airspace resources, which is a crucial technology and research focus for the new generation of intelligent air traffic control. Aiming at the problems of inadequate extraction of trajectory features and difficulty in overcoming the short-term memory of time series in existing trajectory prediction, a trajectory prediction model based on a convolutional neural network-bidirectional long short-term memory (CNN-BiLSTM) network combined with dual attention and genetic algorithm (GA) optimisation is proposed. First, to autonomously mine the data association between input features and trajectory features as well as highlight the influence of important features, an attention mechanism was added to a conventional CNN architecture to develop a feature attention module. An attention mechanism was introduced at the output of the BiLSTM network to form a temporal attention module to enhance the influence of important historical information, and GA was used to optimise the hyperparameters of the model to achieve the best performance. Finally, a multifaceted comparison with other typical time-series prediction models based on real flight data verifies that the prediction model based on hyperparameter optimisation and a dual attention mechanism has significant advantages in terms of prediction accuracy and applicability. Full article
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Article
Analysis and Control for the Mode Transition of Tandem-Wing Aircraft with Variable Sweep
Aerospace 2022, 9(8), 463; https://doi.org/10.3390/aerospace9080463 - 20 Aug 2022
Viewed by 427
Abstract
Morphing aircraft can alter their aerodynamic configuration to obtain multitask adaptability and improve flight performance. In this paper, we apply the variable sweep concept on a tandem-wing micro aerial vehicle (MAV) for multitask adaptability, the two canards of which can undergo backward sweep [...] Read more.
Morphing aircraft can alter their aerodynamic configuration to obtain multitask adaptability and improve flight performance. In this paper, we apply the variable sweep concept on a tandem-wing micro aerial vehicle (MAV) for multitask adaptability, the two canards of which can undergo backward sweep and the two wings can undergo forward sweep. The variable sweep morphing mode can not only weaken the additional inertia forces and moments caused by morphing, but can also maintain the longitudinal dynamic balance without elevator changes, which generates trim drag. What is more, it was demonstrated that sweep morphing can exert a great effect on the aerodynamic characteristics during the transition process, which are functionalized with the sweep inputs. The effect of addition forces and moments during the transition process was analyzed by dynamic response, and the longitudinal stability of the MAV were evaluated based on a linear parameter varying (LPV) model. Due to the dramatic effects of sweep morphing on the longitudinal stability, a gain scheduled transition controller based on a convex hull algorithm is proposed to guarantee the transition stability and improve the robustness, and a linear quadratic regulator (LQR) is used to guarantee the stability of the boundary point with the consideration of input saturation. Finally, the superior performance of the proposed controller was demonstrated by a theoretical simulation based on a nonlinear model. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
Predicting the Remaining Useful Life of Landing Gear with Prognostics and Health Management (PHM)
Aerospace 2022, 9(8), 462; https://doi.org/10.3390/aerospace9080462 - 20 Aug 2022
Viewed by 652
Abstract
Landing gear is an essential part of an aircraft. However, the components of landing gear are susceptible to degradation over the life of their operation, which can result in the shimmy effect occurring during take-off and landing. In order to reduce unplanned flight [...] Read more.
Landing gear is an essential part of an aircraft. However, the components of landing gear are susceptible to degradation over the life of their operation, which can result in the shimmy effect occurring during take-off and landing. In order to reduce unplanned flight disruptions and increase the availability of aircraft, the predictive maintenance (PdM) technique is investigated in this study. This paper presents a case study on the implementation of a health assessment and prediction workflow for remaining useful life (RUL) based on the prognostics and health management (PHM) framework of currently in-service aircraft, which could significantly benefit fleet operators and aircraft maintenance. Machine learning is utilized to develop a health indicator (HI) for landing gear using a data-driven approach, whereas a time-series analysis (TSA) is used to predict its degradation. The degradation models are evaluated using large volumes of real sensor data from in-service aircraft. Finally, the challenges of implementing a built-in PHM system for next-generation aircraft are outlined. Full article
(This article belongs to the Special Issue Recent Advances in Computational Mechanics)
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Article
A Thermo-Mechanical Properties Evaluation of Multi-Directional Carbon/Carbon Composite Materials in Aerospace Applications
Aerospace 2022, 9(8), 461; https://doi.org/10.3390/aerospace9080461 - 20 Aug 2022
Viewed by 330
Abstract
Carbon/carbon (C/C) composite materials are widely used in aerospace structures operating in high temperature environments based on their high performance thermal and mechanical properties. The C/C composite material has a yarn architecture in which fiber bundles in different directions cross each other, and [...] Read more.
Carbon/carbon (C/C) composite materials are widely used in aerospace structures operating in high temperature environments based on their high performance thermal and mechanical properties. The C/C composite material has a yarn architecture in which fiber bundles in different directions cross each other, and it is also divided into architecture types, such as 3-D orthogonal, 4-D in-plane, and 4-D diagonal, according to the arrangement of the fiber bundles. The thermo-mechanical performance of the carbon/carbon composite material may vary depending on the yarn architecture, and the material properties are also tailored according to constituent materials, such as fiber and matrix, and manufacturing parameters, such as yarn size, yarn spacing, and fiber volume fraction. In this paper, three types of geometric models are defined for repeating unit cells (RUCs), according to the yarn architecture of the C/C composite material, and the effective stiffness was predicted by applying the iso-strain assumption and stress averaging technique. In addition, the thermo-mechanical characteristics according to the yarn architecture and fiber volume fraction of RUC were compared and evaluated. Full article
(This article belongs to the Topic Composites in Aerospace and Mechanical Engineering)
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Article
Neural Network Based Model Predictive Control for a Quadrotor UAV
Aerospace 2022, 9(8), 460; https://doi.org/10.3390/aerospace9080460 - 20 Aug 2022
Cited by 1 | Viewed by 486
Abstract
A dynamic model that considers both linear and complex nonlinear effects extensively benefits the model-based controller development. However, predicting a detailed aerodynamic model with good accuracy for unmanned aerial vehicles (UAVs) is challenging due to their irregular shape and low Reynolds number behavior. [...] Read more.
A dynamic model that considers both linear and complex nonlinear effects extensively benefits the model-based controller development. However, predicting a detailed aerodynamic model with good accuracy for unmanned aerial vehicles (UAVs) is challenging due to their irregular shape and low Reynolds number behavior. This work proposes an approach to model the full translational dynamics of a quadrotor UAV by a feedforward neural network, which is adopted as the prediction model in a model predictive controller (MPC) for precise position control. The raw flight data are collected by tracking various pre-designed trajectories with PX4 autopilot. The neural network model is trained to predict the linear accelerations from the flight log. The neural network-based model predictive controller is then implemented with the automatic control and dynamic optimization toolkit (ACADO) to achieve real-time online optimization. Software in the loop (SITL) simulation and indoor flight experiments are conducted to verify the controller performance. The results indicate that the proposed controller leads to a 40% reduction in the average trajectory tracking error compared to the traditional PID controller. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
Nonlinear Dynamic Modeling of Joints between Solar Panels on Spacecraft
Aerospace 2022, 9(8), 459; https://doi.org/10.3390/aerospace9080459 - 20 Aug 2022
Viewed by 327
Abstract
Multiple linear and nonlinear dynamic parameters of the joints at the root of solar panels and between solar panels on spacecraft, both of which have complex nonlinear dynamic properties, were identified by using the force state mapping method for modeling complex nonlinear joints [...] Read more.
Multiple linear and nonlinear dynamic parameters of the joints at the root of solar panels and between solar panels on spacecraft, both of which have complex nonlinear dynamic properties, were identified by using the force state mapping method for modeling complex nonlinear joints in deployable mechanisms of spacecraft, and the differential equations representing the nonlinear dynamic model of the joints were derived. On the basis of the actual force characteristics of the joints, test systems were developed to investigate the vibration response of the complex nonlinear joints in spacecraft so as to acquire test data necessary for the identification. The relation between the moment and bending angle of the panel root and inter-panel joints on spacecraft was obtained through vibration tests under various frequencies and excitation forces. The validity and effectiveness of the dynamic model have been verified by vibration tests of the joints under pulsed excitation. The parameters identified in this paper reflect the nonlinear stiffness, friction and damping characteristics of the joints. The dynamic model established based on these parameters can describe multiple linear and nonlinear dynamic properties of the joints and can be further applied in modeling and control of the entire spacecraft system. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Linear Pseudospectral Method with Chebyshev Collocation for Optimal Control Problems with Unspecified Terminal Time
Aerospace 2022, 9(8), 458; https://doi.org/10.3390/aerospace9080458 - 20 Aug 2022
Viewed by 352
Abstract
In this paper, a linear Chebyshev pseudospectral method (LCPM) is proposed to solve the nonlinear optimal control problems (OCPs) with hard terminal constraints and unspecified final time, which uses Chebyshev collocation scheme and quasi-linearization. First, Taylor expansion around the nonlinear differential equations of [...] Read more.
In this paper, a linear Chebyshev pseudospectral method (LCPM) is proposed to solve the nonlinear optimal control problems (OCPs) with hard terminal constraints and unspecified final time, which uses Chebyshev collocation scheme and quasi-linearization. First, Taylor expansion around the nonlinear differential equations of the system is used to obtain a set of linear perturbation equations. Second, the first-order necessary conditions for OCPs with these linear equations and unspecified terminal time are derived, which provide the successive correction formulas of control and terminal time. Traditionally, these formulas are linear time varying and cannot be solved in an analytical manner. Third, Lagrange interpolation, whose supporting points are orthogonal Chebyshev–Gauss–Lobatto (CGL), is employed to discretize the resulting problem. Therefore, a series of analytical correction formulas are successfully derived in approximating polynomial space. It should be noted that Chebyshev approximation is close to the best polynomial approximation, and CGL points can be solved in closed form. Finally, LCPM is applied to the air-to-ground missile guidance problem. The simulation results show that it has high computational efficiency and convergence rate. A comparison with the other typical OCP solvers is provided to verify the optimality of the proposed algorithm. In addition, the results of Monte Carlo simulations are presented, which show that the proposed algorithm has strong robustness and stability. Therefore, the proposed method has potential to be onboard application. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Integrated Power and Propulsion System Optimization for a Planetary-Hopping Robot
Aerospace 2022, 9(8), 457; https://doi.org/10.3390/aerospace9080457 - 19 Aug 2022
Viewed by 334
Abstract
Missions targeting the extreme and rugged environments on the moon and Mars have rich potential for a high science return, although several risks exist in performing these exploration missions. The current generation of robots is unable to access these high-priority targets. We propose [...] Read more.
Missions targeting the extreme and rugged environments on the moon and Mars have rich potential for a high science return, although several risks exist in performing these exploration missions. The current generation of robots is unable to access these high-priority targets. We propose using teams of small hopping and rolling robots called SphereX that are several kilograms in mass and can be carried by a large rover or lander and tactically deployed for exploring these extreme environments. Considering that the importance of minimizing the mass and volume of these robot platforms translates into significant mission-cost savings, we focus on the optimization of an integrated power and propulsion system for SphereX. Hydrogen is used as fuel for its high energy, and it is stored in the form of lithium hydride and oxygen in the form of lithium perchlorate. The system design undergoes optimization using Genetic Algorithms integrated with gradient-based search techniques to find optimal solutions for a mission. Our power and propulsion system, as we show in this paper, is enabling, because the robots can travel long distances to perform science exploration by accessing targets not possible with conventional systems. Our work includes finding the optimal mass and volume of SphereX, such that it can meet end-to-end mission requirements. Full article
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Article
A Global ArUco-Based Lidar Navigation System for UAV Navigation in GNSS-Denied Environments
Aerospace 2022, 9(8), 456; https://doi.org/10.3390/aerospace9080456 - 19 Aug 2022
Viewed by 328
Abstract
With the continuous expansion of the application field of UAV intelligent systems to GNSS-denied environments, the existing navigation system can hardly meet low cost, high precision, and high robustness in such conditions. Most navigation systems used in GNSS-denied environments give up the connection [...] Read more.
With the continuous expansion of the application field of UAV intelligent systems to GNSS-denied environments, the existing navigation system can hardly meet low cost, high precision, and high robustness in such conditions. Most navigation systems used in GNSS-denied environments give up the connection between the map frame and the actual world frame, making them impossible to apply in practice. Therefore, this paper proposes a Lidar navigation system based on global ArUco, which is widely used in large-scale known GNSS-denied scenarios for UAVs. The system jointly optimizes the Lidar, inertial measurement unit, and global ArUco information by factor graph and outputs the pose in the real-world frame. The system includes a method to update the global ArUco confidence with sampling, improving accuracy while using the pose solved from the global ArUco. The system uses the global ArUco to maintain navigation when Lidar is degraded. The system also has a loop closure determination part based on ArUco, which reduces the consumption of computing resources. The navigation system has been tested in the dry coal shed of a thermal power plant using a UAV platform. Experiments demonstrate that the system can achieve global, accurate, and robust pose estimation in large-scale, complex GNSS-denied environments. Full article
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Article
A Hybrid Game Strategy for the Pursuit of Out-of-Control Spacecraft under Incomplete-Information
Aerospace 2022, 9(8), 455; https://doi.org/10.3390/aerospace9080455 - 18 Aug 2022
Viewed by 349
Abstract
This paper investigates the pursuit problem of out-of-control spacecraft under incomplete-information, and provides new ideas for the disposal of dangerous spacecraft with obstacle avoidance capability. Throughout the pursuit process, the maneuver strategy of the out-of-control spacecraft is unknown, and its possibly unconventional and [...] Read more.
This paper investigates the pursuit problem of out-of-control spacecraft under incomplete-information, and provides new ideas for the disposal of dangerous spacecraft with obstacle avoidance capability. Throughout the pursuit process, the maneuver strategy of the out-of-control spacecraft is unknown, and its possibly unconventional and irregular maneuvers may endanger the safe operation of any other spacecraft on orbit. Based on the differential game theory, complete information game strategy pairs are derived. Then, considering that the control information of the target is unavailable to the pursuer, the target’s maneuver is regarded as the disturbance item. The incomplete information game strategy is derived from the unilateral optimal cost function. Furthermore, the disturbance estimator is designed to identify the missing information of the target. The optimal hybrid game strategy is proposed as an approach to compensate the target maneuver strategy. Simulation study has been conducted and the results have validated that the missing information can be effectively estimated using the estimator. The designed hybrid game strategy can achieve rapid approach, while saving fuel consumption for on-orbit service. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Orbital Stability and Invariant Manifolds on Distant Retrograde Orbits around Ganymede and Nearby Higher-Period Orbits
Aerospace 2022, 9(8), 454; https://doi.org/10.3390/aerospace9080454 - 18 Aug 2022
Viewed by 306
Abstract
In the past few years, distant retrograde orbits (DROs) have become increasingly popular due to their conspicuous stability. Nevertheless, it is this characteristic that results in the challenge to the design of transfer orbits into/out of DROs. This paper investigates the DROs around [...] Read more.
In the past few years, distant retrograde orbits (DROs) have become increasingly popular due to their conspicuous stability. Nevertheless, it is this characteristic that results in the challenge to the design of transfer orbits into/out of DROs. This paper investigates the DROs around Ganymede in order to utilize their dynamical characteristics for Jupiter system exploration. In particular, the DRO family is calculated by numerical integration and numerical continuation, higher-period orbits near the DROs are detected using bifurcation theory, and characteristics including orbital stability and invariant manifolds of these orbits are investigated through stability indices and manifold theory. The stability of DROs and the higher-period orbits are first investigated in the circular restricted three-body problem and are then verified in a third-body gravitation perturbation model. The results show that the strong stability of DROs makes it possible to observe the Galilean moons for long periods and that the higher-period orbits that bifurcate from the DROs offer additional insight into the motion of probes approaching/departing from the vicinities of the DROs. Further investigation of the invariant manifolds around higher-period orbits reveals the feasibility of utilizing the DRO family and the nearby unstable structures for multi-target exploration and low-energy transfer between the Galilean moons. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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Article
Evaluation of Homogenization in Metroplex Operations Based on Multi-Dimensional Indicators
Aerospace 2022, 9(8), 453; https://doi.org/10.3390/aerospace9080453 - 18 Aug 2022
Viewed by 328
Abstract
The development of a Multiple Airport Region (MAR) could lead to fierce competition. To evaluate the level of homogenization between airports in a MAR, a homogenization evaluation method based on multi-dimensional indicators was developed. A multi-dimensional indicator system is proposed that takes into [...] Read more.
The development of a Multiple Airport Region (MAR) could lead to fierce competition. To evaluate the level of homogenization between airports in a MAR, a homogenization evaluation method based on multi-dimensional indicators was developed. A multi-dimensional indicator system is proposed that takes into account infrastructure, integrated support, operational efficiency and airline networks. Then the Critic method and the Delphi method are used to assign hierarchical weights for each dimension of the indicators. The multi-layer homogenization matrix of the airport pairs within the MAR is derived. For airport pairs with high comprehensive homogenization, suggestions are provided according to analysis of the indicators. This study paper selected three typical MARs internationally to demonstrate the advantage of the proposed approach. The airport pairs with high a homogenous coefficient (greater than 0.5) were selected to analyze the reasons causing high homogeneity. Results show that the multi-dimensional indicators and hierarchical fusion captured the characteristics of the homogenization of MAR. Most airport pairs in New York MAR and in London MAR had strong differentiation of route network layout, airport pairs in Greater Bay MAR had ambiguous division of labor and low homogenization of route network, except CAN and SZX airports. Suggestions are discussed separately to mitigate the homogeneity of the airports in the MAS, thus, to improve the operation performance of the MARs. Full article
(This article belongs to the Collection Air Transportation—Operations and Management)
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Article
Experimental Study into Optimal Configuration and Operation of Two-Four Rotor Coaxial Systems for eVTOL Vehicles
Aerospace 2022, 9(8), 452; https://doi.org/10.3390/aerospace9080452 - 17 Aug 2022
Viewed by 384
Abstract
Coaxial rotors are utilized in multirotor aerial vehicles for the added thrust compared to independent rotors while keeping similar area footprints; however, performance losses should be considered. This experimental study analyzes the effects of varying motor duty cycle and propeller pitch values in [...] Read more.
Coaxial rotors are utilized in multirotor aerial vehicles for the added thrust compared to independent rotors while keeping similar area footprints; however, performance losses should be considered. This experimental study analyzes the effects of varying motor duty cycle and propeller pitch values in motor-propeller systems with two to four coaxial rotors. The results demonstrate that in a two-rotor coaxial system, to lessen the adverse effects of a front rotor’s backwash and operate at the maximum performance, only the back motor should be operated initially up to 75% duty cycle before using the front motor up to its 75% duty cycle. Additional thrust requirements should be generated from the back rotor and then from the front rotor up to their maximum duty cycles. In two, three, and four-rotor coaxial setups, total thrust output generated is 1.6, 2.1, and 2.5 times the thrust output at system thrust performance of 86%, 76%, and 66%, respectively, of that of an isolated rotor. In a four-rotor coaxial setup, the maximum system performance is achieved when the propeller pitch values gradually increase from the first to the last rotor. The gradual increments in propeller pitch values also result in more uniform thrust sharing among rotors. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology III)
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Article
Application and Performance Evaluation of Resource Pool Architecture in Satellite Edge Computing
Aerospace 2022, 9(8), 451; https://doi.org/10.3390/aerospace9080451 - 17 Aug 2022
Viewed by 341
Abstract
Satellites will play a vital role in the future of the global Internet of Things (IoT); however, the resource shortage is the biggest limiting factor in the regional task of massiveequipment in the IoT for satellite service. Compared with the traditional isolated mode [...] Read more.
Satellites will play a vital role in the future of the global Internet of Things (IoT); however, the resource shortage is the biggest limiting factor in the regional task of massiveequipment in the IoT for satellite service. Compared with the traditional isolated mode of satellite resources, the current research aims to realize resource sharing through satellite cooperation in satellite edge computing, to solve the problems of limited resources and low service quality of a single satellite. We propose a satellite resource pool architecture-oriented regional task in satellite edge computing. Different from fixed servers in ground systems, the satellite orbital motion brings challenges to the construction of the satellite resource pool. After the capacity planning of the satellite resource pool for regional tasks is given, an algorithm based on search matching is proposed to solve the dynamic satellite selection problem. A ground semi-physical simulation system is built to perform experiments and evaluate the performance of three modes of satellite resource sharing: isolated mode, cooperative mode, and pooled mode. The results show that the pooled mode, compared with the isolated mode, improves the task success rate by 19.52%, and at the same time increases network resources and energy consumption in the same scenario. Compared with the cooperation mode, the performance of task success rate and resource utilization rate is close to that of the pooled mode, but it has more advantages in response time and load balancing of satellite resources. This shows that in the IoT, the resource pool is of great benefit as it improves the task response time and improves the load balance of satellite resources without degrading the performance, which makes sense in task-demanding scenarios. Full article
(This article belongs to the Special Issue Distributed Space Systems: Applications, Deployment and Control)
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Article
Natural Language Processing of Aviation Safety Reports to Identify Inefficient Operational Patterns
Aerospace 2022, 9(8), 450; https://doi.org/10.3390/aerospace9080450 - 17 Aug 2022
Viewed by 335
Abstract
With the growth in commercial aviation traffic and the need for improved environmental performance, strategies to lower emissions that can be implemented in the near term are necessary. Since novel technology takes time to enter the market, operational improvements that employ existing aircraft [...] Read more.
With the growth in commercial aviation traffic and the need for improved environmental performance, strategies to lower emissions that can be implemented in the near term are necessary. Since novel technology takes time to enter the market, operational improvements that employ existing aircraft and require no new infrastructure are fit for this goal. While quantified data collected throughout aviation, such as arrival/departure statistics and flight data, have been well-utilized, text data collected through safety reports have not been leveraged to their full extent. In this paper, a methodology is presented that can use aviation text data to identify high-level causes of flight delays and cancellations, using delays as a metric of operational inefficiency. The dataset is extracted from the Aviation Safety Reporting System (ASRS), which includes voluntary safety incident reports in text narrative and metadata formats. The methodology uses natural language processing tools, K Means clustering, and dimensionality reduction by t-Distributed Stochastic Neighbor Embedding (t-SNE) to categorize and visualize narratives. The method identified 7 major clusters and a total of 23 sub-clusters. A comparison between the subclusters’ topics and the causes of flight delays revealed by the quantified data shows that the ASRS database provides a unique safety perspective to delay cause identification, as illustrated by the method’s identification of maintenance as the main cause of delays, rather than weather. Full article
(This article belongs to the Special Issue Advances in Air Traffic and Airspace Control and Management)
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Article
Assessing the Performance of Hypersonic Inlets by Applying a Heat Source with the Throttling Effect
Aerospace 2022, 9(8), 449; https://doi.org/10.3390/aerospace9080449 - 16 Aug 2022
Viewed by 385
Abstract
Utilization of a heat source to regulate the shock wave–boundary layer interaction (SWBLI) of hypersonic inlets during throttling was computationally investigated. A plug was installed at the intake isolator’s exit, which caused throttling. The location of the heat source was established by analysing [...] Read more.
Utilization of a heat source to regulate the shock wave–boundary layer interaction (SWBLI) of hypersonic inlets during throttling was computationally investigated. A plug was installed at the intake isolator’s exit, which caused throttling. The location of the heat source was established by analysing the interaction of the shockwave from the compression ramp and the contact spot of the shockwave with that of the inlet cowl. Shockwave interaction inside the isolator was investigated using steady and transient cases. The present computational work was validated using previous experimental work. The flow distortion (FD) and total pressure recovery (TPR) of the inflows were also studied. We found that varying the size and power of the heat source influenced the shockwaves that originated around it and affected the SWBLI within the isolator. This influenced most of the performance measures. As a result, the TPR increased and the FD decreased when the heat source was applied. Thus, the use of a heat source for flow control was found to influence the performance of hypersonic intakes. Full article
(This article belongs to the Collection Hypersonics: Emerging Research)
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Article
Structural Responses of a Conceptual Microsatellite Structure Incorporating Perforation Patterns to Dynamic Launch Loads
Aerospace 2022, 9(8), 448; https://doi.org/10.3390/aerospace9080448 - 16 Aug 2022
Viewed by 308
Abstract
Satellite systems undergo several operational phases during their service life, including the assembly phase, ground transportation phase, the launch phase, and the in-orbit operation phase. Among these phases, the one that imposes the highest level of loadings on the satellite is the launch [...] Read more.
Satellite systems undergo several operational phases during their service life, including the assembly phase, ground transportation phase, the launch phase, and the in-orbit operation phase. Among these phases, the one that imposes the highest level of loadings on the satellite is the launch phase. This phase involves a number of highly dynamic loads, all being imposed upon the satellite simultaneously. Investigation of the responses of the structural subsystem of a satellite to these loadings, namely its maximum deformations and maximum von Mises stresses, is critical if a reasonably high level of confidence is to be achieved. This confidence is in terms of ensuring that no material yielding develops in the structure as a result of the imposed launch loadings. In an earlier work, the structural subsystem of a conceptual microsatellite was designed, employing aluminum 6061 alloy as its material. It was then modified through introducing sets of parametrically defined geometric patterns as perforation patterns to remove material, towards reducing the structure’s total mass, as an alternative to employing composite materials. That effort led to a mass reduction percentage of 23.15%. The current work’s research effort focused on computing the responses of the perforated structure to three of the dynamic launch loads that are imposed upon satellites while being launched, namely quasi-static, random, and shock loads. These responses were then compared to those of the baseline, unperforated, version of the same structure. The values of these loads were taken from the relevant sources, with the values being nominal, and represented the loads that any satellite must qualify for before it can be accepted by the provider for inclusion in a launcher. After imposing these load values upon the structural design it was found that the structural responses indicated that the structure would successfully survive these loads without developing stresses that would lead to material yielding failure. This was deduced from computing the yield margins of safety for each loading case, and all margin values were positive, indicating that the structure, at its current development stage, did have sufficient capacity to withstand these loads without material yielding. This reinforced the conclusion of the earlier work, namely that the perforation concept did have sufficient merit to be further developed towards being implemented in future satellite designs. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Martian Combustion-Powered Fixed-Wing UAVs: An Introductory Investigation and Analysis
Aerospace 2022, 9(8), 447; https://doi.org/10.3390/aerospace9080447 - 16 Aug 2022
Viewed by 341
Abstract
The Martian topography needs to be investigated in greater detail for human habitations, and this can be accomplished faster using unmanned aerial vehicles (UAVs). In this regard, the RQ-11B Raven appears suitable for remote sensing and topography-mapping applications on Mars, due to its [...] Read more.
The Martian topography needs to be investigated in greater detail for human habitations, and this can be accomplished faster using unmanned aerial vehicles (UAVs). In this regard, the RQ-11B Raven appears suitable for remote sensing and topography-mapping applications on Mars, due to its popularity in surveillance and reconnaissance applications on Earth. As a result, this study investigates the flight of this UAV in the Martian atmosphere with the assumptions that it employs an NACA S7012 airfoil and its electric propulsion technology is replaced with a four-stroke oxy-methane fueled Saito FG-11 internal combustion engine (ICE). This ICE is estimated to supply 367.8 W resulting in an engine speed of 6891 revolutions per minute. Based on this speed, the UAV must fly at least 72 m/s (Re = 18,100) at a 5° angle of attack to support flight under calm conditions. To achieve this speed will be difficult; thus, a weather balloon or German V1-style launch system should be employed to launch the UAV successfully. Furthermore, the UAV must operate below 165 m/s (Re = 41,450) to prevent transonic conditions. Finally, the vehicle’s fuel and oxidizer tanks can be refueled using an in situ methane and oxygen production system, enabling its sustainable use on Mars. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Design and Analysis of a Compression and Separation Device for Multi-Satellite Deployment
Aerospace 2022, 9(8), 446; https://doi.org/10.3390/aerospace9080446 - 14 Aug 2022
Viewed by 419
Abstract
The launch method of one arrow with multiple satellites can greatly shorten the time for constellation networking and improve the deployment efficiency. A new compression and separation device with a four-bar perimeter arrangement is proposed for multi-satellite compaction and in-orbit release. A compression [...] Read more.
The launch method of one arrow with multiple satellites can greatly shorten the time for constellation networking and improve the deployment efficiency. A new compression and separation device with a four-bar perimeter arrangement is proposed for multi-satellite compaction and in-orbit release. A compression device with gap elimination is designed to implement the reliable compaction of stacked flat satellites. An electromagnetic separation device is proposed to achieve the fast, low-interference release of multi-satellites. The dynamic model with flexible guide bars is established. The separation characteristics of multiple satellites are analyzed by the kinematic simulation. The prototype is developed, and the related experiment is implemented. The results show that the four-guide-bar-edge arrangement scheme with a gap elimination device achieves reliable locking and fast separation under a vibration environment. The dynamic separation characteristics of satellites are investigated by the air floatation experiments. The results show that a stable separation speed and low disturbance angular velocity are achieved under 10% spring error. Full article
(This article belongs to the Special Issue Emerging Space Missions and Technologies)
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Article
Rocket Lab Mission to Venus
Aerospace 2022, 9(8), 445; https://doi.org/10.3390/aerospace9080445 - 13 Aug 2022
Cited by 3 | Viewed by 2131
Abstract
Regular, low-cost Decadal-class science missions to planetary destinations will be enabled by high-ΔV small spacecraft, such as the high-energy Photon, and small launch vehicles, such as Electron, to support expanding opportunities for scientists and to increase the rate of science return. The Rocket [...] Read more.
Regular, low-cost Decadal-class science missions to planetary destinations will be enabled by high-ΔV small spacecraft, such as the high-energy Photon, and small launch vehicles, such as Electron, to support expanding opportunities for scientists and to increase the rate of science return. The Rocket Lab mission to Venus is a small direct entry probe planned for baseline launch in May 2023 with accommodation for a single ~1 kg instrument. A backup launch window is available in January 2025. The probe mission will spend about 5 min in the Venus cloud layers at 48–60 km altitude above the surface and collect in situ measurements. We have chosen a low-mass, low-cost autofluorescing nephelometer to search for organic molecules in the cloud particles and constrain the particle composition. Full article
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Article
Attitude Stabilization of a Satellite Having Only Electromagnetic Actuation Using Oscillating Controls
Aerospace 2022, 9(8), 444; https://doi.org/10.3390/aerospace9080444 - 13 Aug 2022
Viewed by 374
Abstract
We consider the problem of attitude stabilization for a low Earth orbit satellite having only electromagnetic actuation. Such a satellite is not fully actuated, as the control torque is the cross-product of magnetic moment due to magnetorquers and the geomagnetic field. The aim [...] Read more.
We consider the problem of attitude stabilization for a low Earth orbit satellite having only electromagnetic actuation. Such a satellite is not fully actuated, as the control torque is the cross-product of magnetic moment due to magnetorquers and the geomagnetic field. The aim of this work is to study whether oscillating controls can be designed such that a satellite actuated via magnetorquers alone can achieve full three-axis control irrespective of the position of the satellite. To this end, we propose considering oscillating feedback controls which generate the motion of the closed-loop system in the direction of appropriate Lie brackets. Simulation studies show that the proposed control scheme is able to stabilize the considered system. Full article
(This article belongs to the Special Issue Spacecraft Attitude Control Using Magnetic Actuators)
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Article
System Identification of an Aerial Delivery System with a Ram-Air Parachute Using a NARX Network
Aerospace 2022, 9(8), 443; https://doi.org/10.3390/aerospace9080443 - 12 Aug 2022
Viewed by 365
Abstract
Neural networks are one of the methods used in system identification problems. In this study, a NARX network with a serial-parallel structure was used to identify an unknown aerial delivery system with a ram-air parachute. The dataset was created using the software-in-the-loop method [...] Read more.
Neural networks are one of the methods used in system identification problems. In this study, a NARX network with a serial-parallel structure was used to identify an unknown aerial delivery system with a ram-air parachute. The dataset was created using the software-in-the-loop method (Software in the loop). Gazebo was used as the simulator and PX4 was used as the autopilot software. The performance of the NARX network differed according to parameters used, such as the selected training algorithm, input and output delays, the hidden layer, and the number of neurons. Within the scope of this study, each parameter was examined independently. Models were trained using MATLAB 2020a. The results demonstrated that the model with one hidden layer and five neurons, which was trained using the Bayesian regularization algorithm, was sufficient for this problem. Full article
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Article
A Novel Data-Driven-Based Component Map Generation Method for Transient Aero-Engine Performance Adaptation
Aerospace 2022, 9(8), 442; https://doi.org/10.3390/aerospace9080442 - 12 Aug 2022
Viewed by 372
Abstract
Accurate component maps, which can significantly affect the efficiency, reliability and availability of aero-engines, play a critical role in aero-engine performance simulation. Unfortunately, the information of component maps is insufficient, leading to substantial limitations in practical application, wherein compressors are of particular interest. [...] Read more.
Accurate component maps, which can significantly affect the efficiency, reliability and availability of aero-engines, play a critical role in aero-engine performance simulation. Unfortunately, the information of component maps is insufficient, leading to substantial limitations in practical application, wherein compressors are of particular interest. Here, a data-driven-based compressor map generation approach for transient aero-engine performance adaptation is investigated. A multi-layer perceptron neural network is utilized in simulating the compressor map instead of conventional interpolation schemes, and an adaptive variable learning rate backpropagation (ADVLBP) algorithm is employed to accelerate the convergence and improve the stability in the training process. Aside from that, two different adaptation strategies designed for steady state and transient conditions are implemented to adaptively retrain the compressor network according to measurement deviations until the accuracy requirements are satisfied. The proposed method is integrated into a turbofan component-level model, and simulations reveal that the ADVLBP algorithm has the capability of more rapid convergence compared with conventional training algorithms. In addition, the maximum absolute measurement deviation decreased from 6.35% to 0.44% after steady state adaptation, and excellent agreement between the predictions and benchmark data was obtained after transient adaptation. The results demonstrate the effectiveness and superiority of the proposed component map generation method. Full article
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Article
Experimental Study on the Effect of Rubbing Mode on Radial Crack Initiation in Labyrinth Seal Fins of Shrouded Turbine Blade
Aerospace 2022, 9(8), 441; https://doi.org/10.3390/aerospace9080441 - 12 Aug 2022
Viewed by 397
Abstract
The labyrinth-honeycomb seals have been widely used in aero-engine. However, radial cracks appear on labyrinth seal fins of shrouded turbine blade in use. To clarify the rubbing mode of radial crack initiation, a high-speed rubbing test bench was designed. The effects of five [...] Read more.
The labyrinth-honeycomb seals have been widely used in aero-engine. However, radial cracks appear on labyrinth seal fins of shrouded turbine blade in use. To clarify the rubbing mode of radial crack initiation, a high-speed rubbing test bench was designed. The effects of five rubbing modes on crack initiation were studied. Through the test, it is found that cracks would be formed at the junction of the fin tip and side of the labyrinth seal fins under all five modes. When two successive rubbing modes are different, the temperature of the last rubbing can be lower than that of it alone rubbing, and simultaneous radial and axial rubbing can inhibit each other. Radial rubbing mainly affects the initiation of cracks on fin tip, while axial rubbing mainly affects the initiation of cracks on the side. Moreover, the rubbing temperature is mainly affected by radial force. Full article
(This article belongs to the Section Aeronautics)
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Article
Numerical Analysis on the Aerodynamic Characteristics of an X-wing Flapping Vehicle with Various Tails
Aerospace 2022, 9(8), 440; https://doi.org/10.3390/aerospace9080440 - 11 Aug 2022
Viewed by 379
Abstract
X-shaped flapping wings have excellent maneuverability and flight capabilities under low-Reynolds-number conditions. An appropriate tail can extend the range of a vehicle and improve its stability. This study takes two typical configurations, the inverted T-tail and the inverted V-tail, as the research object. [...] Read more.
X-shaped flapping wings have excellent maneuverability and flight capabilities under low-Reynolds-number conditions. An appropriate tail can extend the range of a vehicle and improve its stability. This study takes two typical configurations, the inverted T-tail and the inverted V-tail, as the research object. Considering the wings’ flexible deformation in the flapping process, the computational fluid dynamics method was used to calculate the vehicles’ aerodynamic characteristics, taking into account the aerodynamic interaction effect of the wings and tail. The results show that the wake of flapping wings can significantly reduce the forward flight performance of the tails. The maximum L/D ratio of the two tails decreased by about 38%, and the static stability was also dramatically reduced in the forward flight. The inverted V-tail has better performance in fast forward flight, while the inverted T-tail had better control characteristics at low speeds. The relationship between the tail layouts and aerodynamic performance is also discussed. When the inverted V-tail is in the optimal position, the longitudinal control moment can be doubled in the hovering state. This research provides a reference for the design and arrangement of flapping wings with tails, which is beneficial to the performance improvement of vehicles. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology III)
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Article
Simulation and Analysis of Fluid–Solid–Thermal Unidirectional Coupling of Near-Space Airship
Aerospace 2022, 9(8), 439; https://doi.org/10.3390/aerospace9080439 - 11 Aug 2022
Viewed by 383
Abstract
Based on the biaxial experiment data of the membrane material under hot and cold conditions, the mechanical properties calculation model of envelope material was established with consideration of the effects of varying stress ratios, stress magnitudes and temperatures on the mechanical properties of [...] Read more.
Based on the biaxial experiment data of the membrane material under hot and cold conditions, the mechanical properties calculation model of envelope material was established with consideration of the effects of varying stress ratios, stress magnitudes and temperatures on the mechanical properties of near-space airship material. Using the heat source model, Computational Fluid Dynamics (CFD) simulation, User-Defined Function (UDF), structural finite element analysis software and the user subroutine of an airship to define the behaviour of fabric material, the fluid–structure–thermal coupling model of airship envelopes was established. In addition, a near-space airship was selected as the research subject to calculate the diurnal temperature differences during the summer solstice and analyse the diurnal temperature distribution of the envelope. Under controlled environmental conditions, the deformation law of the near-space airship under the influence of fluid–structure–thermal coupling was calculated and summarised. The present fluid–solid–thermal coupling model takes into account the anisotropy of materials, temperature, stress magnitude, stress ratio and other influencing factors, which can more accurately reflect and predict the stress–strain distribution and the deformation law of near-space airships. Full article
(This article belongs to the Special Issue Aircraft Thermal Management)
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