Aerospace doi: 10.3390/aerospace13070656

Authors: Mohamad El Hajj Ali Barada Bayram Celik

The overset grid adaptive method offers an efficient approach for the computational modeling of steady or transient three-dimensional compressible flow problems. When implementing this approach on parallel distributed memory computing systems, its scaling, load balancing, and partitioning must be addressed. In this study, we present a parallel, three-dimensional, finite volume compressible Navier–Stokes solver with block-based adaptive mesh refinement capability. The overset grid system consists of an Octree forest governed adaptive Cartesian off-body grid and a pre-partitioned body-conforming grid. To create, manage, and efficiently handle the load balancing and partitioning of the off-body grid, the developed solver utilizes the open source library of p4est. The communication between the partitions of the p4est governed off-body grid and the body-conforming grid is established by using an efficient spatial query algorithm. The parallel performance of the developed solver is evaluated by solving two benchmark problems: steady supersonic flow over a semi-infinite blunt-nose cylinder and the transient interaction of an incident planar shock with a sphere in quiescent air. The results show that the solver accurately captures and tracks the resultant flow shock structures while exhibiting good scalable parallel performance.

Aerospace doi: 10.3390/aerospace13070655

Authors: Zhichao Yu Zhanpeng Gao Wenjun Yi

In the information-supported penetration scenario, the predicted encounter point and encounter time can provide the future spatial threat position and the time margin for avoidance maneuver, respectively, which are important prior information for dangerous-area judgment, avoidance triggering, and penetration decision making. However, the data-driven prediction method based on absolute coordinates is likely to depend on the fixed training airspace, resulting in insufficient cross-space generalization ability. Meanwhile, the unconstrained prediction space will lead to an excessively large sample size and an unbalanced sample distribution. Aiming at the above problems, this paper proposes a physics-constrained relative-state prediction framework for the rapid prediction of the encounter point and encounter time. Firstly, the relative-state input centered on the maneuvering vehicle is adopted to reduce the dependence of the model on the fixed global coordinate system. Secondly, a concentric double-layer spherical-shell detectable threat domain is constructed to limit the approximately unbounded prediction space to a finite region that satisfies the sensor detection condition and the maneuvering constraint of the maneuvering vehicle. Furthermore, a physical geometric stratified sampling strategy based on relative distance, azimuth angle, and pitch angle is designed, and a sample-weight correction mechanism is combined to improve the balance of sample coverage under different distance layers and incoming directions. Finally, a ResNet-MLP joint regression model is constructed and trained using offline numerical simulation samples, which is used as an online rapid predictor. The simulation results show that, on the stratified training subset, the mean absolute error of the proposed model for encounter time is 0.1775 s, and the three-dimensional Euclidean error of the encounter point is 129.89 m. The tests with spatial position variation and bounded measurement noise further verify the generalization ability and robustness of the model. The proposed method can provide rapid spatial threat information and time-margin information for dynamic penetration decision making and reduce the computational requirement of repeated online numerical propagation.

Aerospace doi: 10.3390/aerospace13070654

Authors: Dohyeon Park Youngho Eun Sang-Young Park

University CubeSat programs are often conducted under severe constraints in budget, personnel, schedule, and knowledge continuity, while still requiring sufficient verification to support mission success. This paper presents the verification, testing, on-orbit operation, and anomaly analysis of COSMIC, a 3U university CubeSat developed by Yonsei University in less than eleven months from project kickoff to launch. COSMIC adopted a protoflight model approach, prioritized commercial off-the-shelf components with flight heritage and prior laboratory experience, and concentrated limited resources on subsystem, FlatSat, system-level, environmental, communication, and scenario-based testing. The test program is reviewed against the subsequent on-orbit results to identify which verification activities contributed to anomaly prevention, fault isolation, and recovery. The results show that system-level integration testing, thermal vacuum cycle testing, and scenario testing were particularly effective in revealing interface, software, and deployment-related issues before launch and in supporting early orbit recovery. However, the mission also exposed limitations in recovery-logic verification, long-duration software testing, communication robustness, and independent reset paths. Based on these findings, practical recommendations are derived for resource-constrained university CubeSat teams seeking to tailor verification activities without simply reducing test rigor.

Aerospace doi: 10.3390/aerospace13070652

Authors: Xijun Liu Zelin Chen Zhaoyang Li Dongcheng Luo

Dense low-altitude multi-UAV operations require conflict detection methods that can rapidly identify potential conflicts while preserving detection reliability under realistic motion constraints. This paper proposes an Adaptive Cylindrical-Pruning Decision Tree Method (AC-DTPM) for short-term conflict detection in dense low-altitude UAV traffic. A realistic UAV motion model is first constructed by considering speed limits, acceleration constraints, climb/descent limits, response delay, positioning error, and wind disturbance. Based on this model, a double-layer cylindrical protection zone is established, including a core conflict zone and an outer warning zone. The proposed AC-DTPM improves the basic Decision Tree Pruning Method through two mechanisms: adaptive time segmentation, which adjusts trajectory-segment length according to UAV speed and local traffic density, and cylindrical warning-zone lower-bound pruning, which eliminates impossible conflict candidates by separately evaluating horizontal and vertical distance lower bounds during tree search. Simulation experiments were conducted for 100–800 UAVs under locally dense and crossing-route scenarios. At 800 UAVs, AC-DTPM reduced the number of evaluated candidate pairs from 601.0 with the basic DTPM to 178.8, corresponding to a 70.3% reduction and a candidate compression ratio of <!-- MathType@Translator@5@5@MathML2 (no namespace).tdl@MathML 2.0 (no namespace)@ -->

Aerospace doi: 10.3390/aerospace13070651

Authors: Bo-Lun Zhang Jun Xia

To push the specific impulse and power output of the thrust-controlled solid rocket motor (TCSRM) even higher, the solid-propellant flame temperature is driven to 3000–3600 K. That level of thermal assault subjects the pintle to extreme heat flux and aggressive erosion, a combination that directly undercuts motor reliability. An effective cooling strategy for the pintle is therefore mandatory. Here, a film-cooling scheme is deployed for thermal protection of the pintle, and a comprehensive study on the transient aero-thermal characteristics of pintle film cooling is carried out to demonstrate how it outperforms the uncooled baseline in extending pintle survival and to reveal the effects of the blowing ratio and pintle moving speed on the performance. The results indicate that the film cooling contributes to improving the pintle cooling performance. As pintle velocity increases, the absolute velocity component of the coolant jet parallel to the mainstream velocity decreases. This causes the relative angle between the coolant jet and mainstream to increase, leading to a stronger interaction between the coolant jet and mainstream. Accordingly, except under low-blowing-ratio conditions, the time-averaged film-cooling effectiveness declines as the pintle velocity increases. Moreover, there is an optimum blowing ratio to achieve the highest time-averaged film-cooling effectiveness.

Aerospace doi: 10.3390/aerospace13070650

Authors: Yating Gao Dong Xue

This study focuses on the longitudinal dynamic stability of swifts in cruising forward flight, which is critical for their high maneuverability but remains insufficiently investigated. Understanding longitudinal dynamic stability is the essential prerequisite for revealing the physical mechanism underlying their maneuverability: it is the dynamic stability characteristics that determine how the flight state responds to disturbances and control inputs, thereby laying a foundation for subsequent flight control during agile maneuvers. Conventional studies mostly adopt steady or quasi-steady assumptions, which cannot accurately reflect the influence of periodic body vibration. This study combines CFD numerical simulation and dynamic modeling to systematically analyze the unsteady dynamic stability of swifts. A bio-inspired dynamic model is established using the BE3357B airfoil with a 5° sweep angle, and the flapping-wing motion is decomposed into three degrees of freedom: sweeping, pitching, and flapping. Numerical reliability is assessed through grid independence and time-step independence verification. Aerodynamic force and moment trimming are performed on fixed-DOF and free-DOF models, where the latter considers coupled heaving–pitching motion and adjusted trim parameters. Stability analysis is conducted using three aerodynamic derivative methods: fixed velocity, forced oscillation, and Floquet. By solving small perturbation equations, eigenvalues and eigenmodes are obtained. All three methods identify two stable modes: a short-period mode with damping coefficient 0.1236–0.1870 and oscillation period 0.1121 s–0.1380 s, and a long-period mode with damping coefficient 0.2456–0.6203 and damping half-life 3.5803 s–4.8890 s, verifying stability under periodic vibration and unsteady aerodynamic coupling. Flow field results show clear distinct dynamic pressure and drag fluctuation characteristics between the downstroke and the upstroke. The unsteady stability framework provides a theoretical reference for analyzing the longitudinal stability of biomimetic flapping-wing aircraft and offers useful insight for future bird-inspired flight dynamics studies.

Aerospace doi: 10.3390/aerospace13070649

Authors: Ainur Zhetpisbayeva Samal Kaliyeva Berik Zhumazhanov Almira Mukhamejanova Ainur Satpayeva Aliya Kargulova

Wildfires are significant ecological and environmental disasters, impacting forests, ecosystems, climate stability and human life. The visible-spectrum imagery-based traditional wildfire monitoring system can fail to perform well in the presence of smoke, haze and low lighting. A number of machine learning and deep learning techniques have been proposed, but most of the studies do not provide an integrated Short-Wave Infrared (SWIR) optical-electronic payload framework along with an intelligent optimization technique. The objective of this research is to design an intelligent SWIR-based optical-electronic payload architecture for accurate detection and remote sensing of wildfire and Earth applications via deep learning and optimization techniques. The proposed framework is based on Sentinel-2 SWIR satellite data layers with wildfire and non-wildfire samples. To enhance the quality of the images and the representation of their spectral domain, the following preprocessing operations are carried out: resizing, image normalization, SWIR band extraction, and data augmentation. The following spectral feature extraction techniques are then used: burn area analysis, vegetation stress analysis, and thermal anomaly detection. The framework also incorporates SWIR optical payload design, electronic subsystem development and SWIR InGaAs sensor modeling. Finally, a Hybrid Convolutional Neural Network (CNN)–Residual Network 50 (ResNet50) model optimized by Grey Wolf Optimization (GWO) is used for wildfire classification and hyperparameter tuning. The proposed framework achieved an accuracy of 91.03%, precision of 91.27%, recall of 91.03%, and F1-score of 91.01%. The wildfire detection capability, classification robustness, and convergence performance were enhanced through the integration of SWIR spectral analysis, hybrid deep learning and GWO. The proposed framework offers an effective and trustworthy solution for intelligent wildfire monitoring and Earth remote sensing applications with enhanced spectral sensing and classification performance.

Aerospace doi: 10.3390/aerospace13070648

Authors: Deqiu He Ping Ruan Youjin Xie Wei Hao Wei Song Kai Cui Yiming Dong Zhize Du Meilin Xie

Lunar in situ resource utilization requires solar concentrating systems that can be launched in a compact configuration and deployed reliably on the lunar surface. This paper presents a multi-link coupled deployable support mechanism for a reflector-Fresnel concentrating system. The mechanism adopts a shape-memory-alloy rigid release for the stowed state and passive spring hinges for autonomous deployment, aiming to reduce drive complexity while maintaining a high deployment ratio. To avoid interference caused by coupled link motion, a motion-envelope model is established for joint trajectory planning. The deployment process is then analyzed through vector-based kinematic modeling, D’Alembert force analysis, and Lagrange dynamic equations. The analytical predictions are corroborated through high-fidelity multibody dynamic simulations: the predicted driving torque of Link 3 is 0–0.68 N⋅m, close to the simulated range of 0–0.70 N⋅m, with a relative peak-value error of 2.8%; the maximum angular acceleration is 0.08 rad/s2. Finite-element modal analysis gives a first locked-state natural frequency of 54.969 Hz. NSGA-II optimization further reduces the maximum driving torque by 10.9%, reduces torque fluctuation by 9.7%, and increases the maximum deployment ratio from 5.6 to 7.2. The results provide a quantified design and simulation basis for passive deployable concentrating mechanisms intended for lunar surface concentrating systems.

Aerospace doi: 10.3390/aerospace13070647

Authors: Napat Harnpornchai Tatcha Sudtasan

Space economy involves all activities and resource allocations that generate additional economic and societal benefits through space exploitation. The development of space infrastructure enables a wider range of economic activities. Regarding economic sustainability and national security, the possession of the launch site within national territory is of utmost importance. This paper presents a methodology for selecting launch sites based on linguistic term evaluation using a Discrete Single-Valued Neutrosophic Number (DSVNN) representation. The existence of support makes the DSVNN interpretable, which is not possible in the case of Single-Valued Neutrosophic Number (SVNN) with only specific values of truth, indeterminacy, and falsity degrees. An ensemble of five widely well-known MCDM methods, namely TOPSIS, CODAS, COPRAS, EDAS, and MOORA, are used in the decision-making process. The whole procedure is then applied to the launch site selection in Thailand. All MCDM methods result in the same top priority location, U-Tapao Rayong–Pattaya International Airport, Chonburi. The weight sensitivity analysis and the method cross-validation are applied to test the robustness of the result.

Aerospace doi: 10.3390/aerospace13070646

Authors: Nicholas P. Kakavitsas Andrew Willis Dipankar Maity Artur Wolek

This work develops a tool to efficiently estimate the diffractive loads on a quadrotor uncrewed aerial vehicle (UAV) immediately following a nearby explosion. Existing models in the literature that predict the time history of wind velocity and the overpressure at a single distance from the blast are extended to model a moving blast wave that passes over the vehicle. The time-varying diffractive loads (i.e., due to the blast-induced pressure differential) are first modeled for a single sphere in a blast wave and then for a quadrotor approximated as a series of spheres connected by rods—one sphere for each of the four motors and one sphere for the central body. The overpressure and wind velocity models are compared with computational fluid dynamics (CFD) data. To illustrate the computational approach, a representative quadrotor model is perturbed by a blast from an initial hover flight condition in simulation. The rigid body dynamics are simulated over a short duration (ninety milliseconds) to determine the UAV’s state immediately after the explosion has concluded. The vehicle state history is predicted under the assumption of diffractive loads with a quadratic drag model and constant hover thrust.

Aerospace doi: 10.3390/aerospace13070645

Authors: Ou Li Xue Zhong Yaze Liu Peixing Li Hexi Baoyin

Solar radiation can induce circumferential temperature gradients and thermoelastic bending moments in lightweight spacecraft appendages. For spinning spacecraft, this thermal excitation is periodically modulated by spin motion and may amplify flexible response when the modulation frequency approaches a structural frequency. This study investigates the spin-modulated thermoelastic response of a spacecraft with a circular thin-walled flexible appendage under attitude-dependent solar radiation. A reduced-order rigid-flexible-thermal model is formulated by coupling rigid-body attitude motion, assumed-mode appendage deformation, first-harmonic circumferential temperature perturbations, and the resulting generalised thermoelastic bending moment. Long-time simulations, spin-period response sampling, degraded-model comparisons and modal energy/work diagnostics are used to identify the dominant response mechanism. The results show that the post-transient flexible response is governed mainly by spin rate, while the initial solar-incidence angle modifies the local response classification in the sampled high-spin region. Representative high-spin loss-of-admissibility cases lie near the first bending-frequency region, where the retained structural energy and positive thermoelastic work input are concentrated mainly in the first bending mode. Removing deformation-dependent solar-incidence feedback does not eliminate these cases, whereas suppressing thermoelastic bending does. Thus, spin-modulated thermoelastic bending is the essential pathway by which attitude-dependent solar radiation amplifies appendage response.

Aerospace doi: 10.3390/aerospace13070644

Authors: Chen Zhao Yuhao Wu Jun Guan

This study proposes an NSL-GWO-hpRPM framework for constrained glide trajectory optimization of guided projectiles. The method combines an improved Grey Wolf Optimizer with the hp-adaptive Radau pseudospectral method to reduce the dependence of hpRPM on initial guesses and improve global search performance. In the improved GWO, Sobol low-discrepancy sequence initialization is used to enhance population diversity, a nonlinear convergence strategy is introduced to balance exploration and exploitation, and Levy flight is adopted to improve the ability to escape local optima. The optimized solution obtained by NSL-GWO is then used as the initial guess for hpRPM to achieve high-precision local refinement. Simulation results show that the proposed NSL-GWO-hpRPM achieves a feasible range of 71,211.514 m, improving the range by 4.53% over hpRPM and 1.48% over GWO-hpRPM. Statistical results from 35 independent runs further demonstrate that the proposed method obtains the best mean range, Friedman mean rank, and significant Wilcoxon test results with p<0.001. The optimized trajectory reaches a maximum range of approximately 71.2 km with an optimal launch angle of 62.4∘ while satisfying all flight constraints, indicating that the proposed framework is effective for complex constrained glide trajectory optimization.

Aerospace doi: 10.3390/aerospace13070643

Authors: Liang Jin Yi Yang Kaimin Liu Fengrong Zhao Jun Lv Xiaowei Gao Huayu Liu

A novel strong-form meshless method based on Lagrange interpolation is proposed for vibro-acoustic coupling analysis. The governing equations of acoustic and structural domains, together with the coupling interface conditions, are discretized directly in differential form without relying on predefined meshes, thereby improving geometric flexibility. The computational domain is partitioned into local subdomains, within which Lagrange interpolation is employed to construct approximation functions from nodal distributions. In this manner, the proposed framework combines the flexibility of meshless formulations with a zonal parameterization strategy similar to that used in isogeometric analysis. Moreover, spatial derivatives and system matrices are directly evaluated and assembled at nodal points, avoiding numerical integration and simplifying the implementation procedure. Owing to the Kronecker delta property of Lagrange polynomials, boundary conditions can be imposed accurately and conveniently. For transient analysis, the Newmark-β scheme is adopted to integrate both first- and second-order temporal terms, ensuring stable and accurate time integration. Finally, numerical examples, including comparisons with commercial software, demonstrate the accuracy and effectiveness of the proposed method for complex vibro-acoustic problems.

Aerospace doi: 10.3390/aerospace13070642

Authors: Xu Ma Fuping Yu Di Shen

Air refueling extends aircraft range and endurance, but its operational value hinges on where the refueling airspace is placed and how tanker missions are sequenced. This paper addresses the joint optimization of refueling airspace planning and tanker scheduling, in which each receiver selects a refueling point from a continuous feasible interval along a fixed route. The upper level determines refueling point locations (continuous variables), while the lower level schedules multiple heterogeneous tankers (discrete combinatorial variables); the two levels are tightly coupled through spatiotemporal constraints and fuel propagation. We propose a bottleneck-driven decoupled update (BDDU) strategy built on the Whale Optimization Algorithm (WOA). BDDU extracts bottleneck states from lower-level scheduling feedback and applies per-dimension step-size control to damp the coupling amplification effect inherent in bi-level optimization. Across three scenarios of varying coupling intensities and scales, BDDU-WOA raises the feasibility rate from 50% (WOA baseline) to 90% (+40 percentage points; p<0.05, Fisher’s exact test). The gain stems from a bottleneck-aware, dimension-wise step-size control mechanism with an adaptive, parameter-free classification threshold and only two tunable parameters, adding roughly 10% computational overhead. The method is intended for pre-mission planning of large-scale air refueling operations.

Aerospace doi: 10.3390/aerospace13070641

Authors: Ayesha R. E. Wise Sharmila Sumsurooah Serhiy Bozhko Seang Yeoh

Sustainable aviation is an ever-growing field, with feasibility, safety, and longevity being key areas of concern. Future electric aircraft will rely on multiple energy sources. Batteries can provide a fast response to changes in power demands, and fuel cells offer high energy density for prolonged operation. This work has developed an energy management strategy (EMS) aimed to minimise the overall energy consumption from these sources. The EMS is further designed to respect the operational limits of each component. It investigates three EM approaches to account for the hydrogen consumption restriction, namely the unconstrained method, the fixed-limit method, and a novel depletion-aware method. The unconstrained method assumes there is an unlimited amount of hydrogen, meaning it uses 14.81% more hydrogen than is available, whereas the fixed-limit approach applies the maximum amount of hydrogen available within the fuel tank. However, when there is no hydrogen available, the fuel cell shuts down immediately. This work introduces a novel depletion-aware approach which is conscious of reaching the hydrogen supply minimum limit and, hence, allows for greater use of the battery energy during this period. This allows for better coordination between the battery and fuel cell. The three EMSs are simulated and verified in MATLAB/SIMULINK. The simulation results are then validated using software-in-the-loop in dSPACE. The work demonstrates that the depletion-aware approach has distinct benefits compared to the other two methods as it constrains the fuel consumption and allows a smoother transition between energy storage devices and provides a scalable energy management strategy applicable to a range of all-electric and hybrid-electric aircraft.

Aerospace doi: 10.3390/aerospace13070640

Authors: Fuli Zhang Na Liang

Space robots must be designed with a large operating radius and lightweight components (flexible joints and flexible links). The integration of flexible components inevitably affects the control accuracy of the robot. When modeling the link deformation of the space robot, the idealized description method has the problem of incomplete accuracy in link deformation due to the coupling effects of the non-fixed base, flexible joints, and changes in control parameters. To address this challenge and improve the accuracy of robot modeling, this study proposes a dynamic coupling analysis method for the link deformation of space robots based on time-domain response. The double finite difference method is adopted to calculate the time-domain response of link deformation. On this basis, using the local linear operator method, the modal information of the deformed links is extracted. This method systematically quantifies the individual and interactive effects of the robot’s base motion, joint flexibility, and control parameters on link deformation. This work not only lays a theoretical foundation for the accurate dynamic modeling of space robots but also provides practical insights for optimizing their structural design. Ultimately, it contributes to the development of more reliable and high-performance space robot systems.

Aerospace doi: 10.3390/aerospace13070639

Authors: Albertus Stephanus Louw Marco Rotondi Landon Kamps Toru Shimada

Hybrid rocket motors are an attractive option for the upper-stages of low-cost small launchers, but are susceptible to variability in performance both in time and between firings. Moreover, key contributors to hybrid motors’ performance such as oxidizer-to-fuel ratio (O/F) are difficult to estimate, and by extension, to control. Four approaches were evaluated for the estimation and control of O/F under system uncertainty, including through on-line estimation by an Unscented Kalman Filter (UKF). A Monte Carlo analysis was conducted of a simulated hybrid kick motor, where key sources of system uncertainty such as the characteristic velocity efficiency (ηc*), fuel regression coefficients, and oxidizer flow characteristics were allowed to be variable. Feedback control of O/F informed by the UKF obtained 6.8% smaller control error than the best alternative approach. Yet the Monte Carlo analysis showed that among uncertainty sources considered, ηc* was the primary driver of performance variability, while O/F regulation had a small influence. This was because the total and specific impulses were relatively insensitive to O/F for the considered motor configuration and ranges of O/F observed during the simulated burns—highlighting the importance of system uncertainty quantification when formulating performance-regulating interventions. Further, the proposed UKF observer provided data-informed estimates of combustion efficiency and propellant residuals in time, which are valuable for the planning and execution of accurate orbital insertions in a kick motor susceptible to performance uncertainty. The developed uncertainty quantification and control modeling framework can be used also during the design and assessment of other control interventions under system uncertainty.

Aerospace doi: 10.3390/aerospace13070638

Authors: Yekun Liu Xiaoyu Zhang

This study focuses on the situation where multiple vehicles simultaneously intercept a maneuvering target with desired line-of-sight (LOS) angles and impact time in a three-dimensional environment. A predefined-time cooperative guidance law is proposed, which adapts to the switching communication topologies among the vehicles. To accomplish the task of adjusting the impact time by leveraging the multi-agent consensus principle, a novel adaptive predefined-time consensus protocol is designed in the LOS direction, which allows multiple vehicles to intercept the target at the desired impact time, while ensuring that the impact times of all vehicles converge within a predefined time. In the LOS normal direction, based on the error transformation function, a novel predefined-time non-singular fast terminal sliding mode guidance law is proposed to guarantee the convergence of the LOS angular rate within the predefined time, achieving the simultaneous interception of the target by multiple vehicles at different terminal angles and eliminating singularities. At the same time, the tracking error satisfies the prescribed performance constraint. In particular, for scenarios where the target acceleration is unknown, a predefined-time external state observer is employed to estimate disturbances and compensate within the guidance law. The simulation results validate the effectiveness and robustness of the proposed method.

Aerospace doi: 10.3390/aerospace13070637

Authors: Victor Petri Milo Wolfgang Armbruster Michael Börner Justin S. Hardi

Rotating detonation engines combine compact geometry with the potential for higher specific impulse compared to deflagration-based propulsion, enabled by pressure-gain combustion. However, their increased thermal loads present a major challenge. In the current literature, thermal characterisation of rotating detonation hardware relies either on experimental reconstructions or on high-fidelity simulations. A predictive and coolant-coupled low-order heat transfer model for rotating detonation rocket engines is not yet available in the open literature. This paper introduces such a reduced-order predictive tool for rotating detonation combustors, capable of estimating both cycle-averaged wall heat flux and coolant thermal behaviour. Implemented in Python, the tool supports any propellant available in NASA’s Chemical Equilibrium with Applications and CoolProp, handles single-phase thermodynamic regimes, and spans geometric and operating ranges from laboratory-scale test rigs to engine-relevant conditions. With computation times below one second, it enables rapid trade studies, model-based screening, and sensitivity analyses. Benchmarking was performed against experimental test cases covering H2/O2, CH4/O2 and C2H4/O2 mixtures, as well as multiple injector geometries and chamber configurations. The approach complements existing high-fidelity tools by offering a low-order alternative grounded in transparent assumptions and benchmarked against multiple datasets.

Aerospace doi: 10.3390/aerospace13070636

Authors: Xiangzhi Zhou Siqin Li Qianjin Xia Shanmei Li

Urban multi-UAV navigation in dense building environments requires not only collision-free geometric paths but also executable flight processes under motion constraints and inter-UAV safety requirements. A static path that is feasible in a geometric map may still fail during closed-loop execution because of velocity limits, acceleration constraints, local path-association errors, and coupled multi-UAV interactions. Meanwhile, end-to-end reinforcement learning often suffers from unstable training, weak geometric interpretability, poor early-stage safety, and high sample complexity. To address these issues, this paper proposes a hierarchical planning-and-learning framework that connects static reference path generation, executable reference tracking, successful demonstration distillation, and conflict-aware residual reinforcement learning. First, three-dimensional reference paths are generated offline in an OpenStreetMap-based urban scene represented by cuboid buildings. Second, a damped reference-tracking mechanism transforms these static paths into closed-loop executable reference processes through local path association, monotonic progress updating, path recapture, look-ahead guidance, and bounded action construction. Third, successful pure-reference executions are distilled for behavior-cloning initialization. Finally, a bounded residual TD3 module is introduced as a local conflict-correction mechanism around the verified executable reference baseline. Experiments in an urban scene containing 754 buildings show that simplified tracking strategies fail to execute the static paths reliably, whereas the proposed full-damped reference-tracking controller achieves a 91.67% all-success rate and eliminates building collision episodes in the tracking-ablation test. Speed-sensitivity experiments at 10, 15, and 20 m/s show the same 91.67% all-success rate, indicating that the conclusion is not dependent on a single speed setting. In constructed conflict-stress tests, the conflict-aware residual TD3 module increases the all-success rate from 33.33% to 80.09%, reduces inter-UAV collision episodes from 66.67% to 11.57%, and improves the hard-safety satisfaction rate from 33.33% to 87.04%. These results show that the main contribution of the proposed framework lies in converting static geometric paths into executable reference trajectories and further enabling bounded residual correction under inter-UAV conflict conditions.

Aerospace doi: 10.3390/aerospace13070635

Authors: Shengli Xu Kechen Xiang Hongyang Xu Yonghua Fan Haoyu Cheng

This paper proposes a three-dimensional prescribed-time hierarchical cooperative guidance law (3-D PTHCGL) for rapid and reliable head-on encirclement in cooperative interception of high-speed targets under incomplete directed communication topology, target maneuvers, and limited terminal engagement time. The proposed method consists of a distributed estimator layer (DEL) and a local controller layer (LCL), addressing three key issues in head-on encirclement formation: information acquisition, rapid convergence, and geometric configuration. In the DEL, a distributed prescribed-time estimator (DPTE) is developed to enable followers without direct communication with the leader to estimate the leader’s states from neighborhood information within a prescribed time. In the LCL, a prescribed-time extended state observer (PTESO) and a three-dimensional prescribed-time cooperative guidance law (3-D PTCGL) are designed to estimate target-maneuver-induced disturbances and unknown states, and to guarantee prescribed-time convergence of estimation and cooperative tracking errors. Furthermore, virtual line-of-sight (LOS) angles are introduced based on a three-dimensional head-on interception kinematic model to characterize the head-on encirclement configuration, and range-to-go together with radial relative velocity are adopted instead of time-to-go to reduce sensitivity to time-estimation errors. Simulation results demonstrate the effectiveness and robustness of the proposed method in achieving prescribed-time head-on encirclement and simultaneous attack without a speed advantage.

Aerospace doi: 10.3390/aerospace13070634

Authors: Wenkai Sun Jinsheng Guo Xianren Kong

In this paper, the stochastic responses of multi-degree-of-freedom (MDOF) linear/nonlinear systems with rational-order fractional derivatives excited by colored noise are investigated. A closed-form expression for the PSDs of MDOF linear systems with fractional derivatives under exponential colored noise is derived by combining the eigenvector expansion method (EEM) and the pole-residue representation of the transfer function. The equivalent linearization method (ELM) is developed to determine the stochastic responses of fractional-order nonlinear systems. This is achieved by replacing the original system with an equivalent fractional-order linear system whose parameters are determined by minimizing the mean-square difference. The EEM is incorporated into the linearization framework to solve the linear fractional-order equations during the iterative process for the equivalent coefficients. Two widely adopted linearization criteria, the energy-based criterion and the equation-based criterion, are examined in detail. Numerical examples, including two linear systems and three nonlinear fractional-order systems with various types of nonlinearity under colored noise, are presented to verify the accuracy and applicability of the proposed method. Compared with Monte Carlo (MC) simulations, both criteria provide satisfactory accuracy. In addition, the results from the energy-based linearization criterion are more accurate than those from the equation-based criterion for single-degree-of-freedom (SDOF) systems, whereas for MDOF systems, the equation-based criterion yields slightly more accurate results than the energy-based criterion. The effects of nonlinear intensity and the order of the fractional derivative on the response statistics are also investigated.

Aerospace doi: 10.3390/aerospace13070633

Authors: Yilin Li Rui Zhu Xiaochen Hang Qiang Chen Qingguo Fei

The frequency-domain flutter analysis method requires a linear model as input; however, when a telescopic actuator is applied to morphing aircraft, traditional frequency-domain flutter analysis methods face challenges in addressing issues involving contact nonlinearity. To enable classical frequency-domain methods to handle this type of nonlinearity, this paper presents an equivalent linearization modeling method for morphing aircraft wing structures. The proposed modeling method uses rod elements as the equivalent linearization elements and avoids the need to handle node correspondence issues. The model is parameterized by the rod element’s elastic modulus, contact surface distance, and element length coefficient. Upon completion of the equivalent modeling, flutter analysis can be performed by the PK method. The proposed modeling method increases modeling efficiency while maintaining the accuracy of the model. A simulation study of a typical hypersonic telescopic wing structure is conducted. The effects of angle of attack and altitude on flutter characteristics are analyzed. The proposed modeling method effectively captures both the static and dynamic characteristics of the original structure. The flutter Mach number decreases with increasing extension length, and it increases with altitude and angle of attack. The flutter frequency decreases with increasing extension length, angle of attack, and altitude.

Aerospace doi: 10.3390/aerospace13070632

Authors: Guang Rong Jingyuan Yang Jinbao Chen Jian Wang Jianyuan Wang

Lightweight flapping-wing robots are affected by structural flexibility, wind disturbances, and static friction in basal passive joints during perching and attitude-holding tasks. These coupled effects can make conventional PID and sliding mode control (SMC) produce error amplification, torque fluctuation, flexible-response excitation, and attitude-boundary violation. This study establishes an ADAMS–Simulink co-simulation platform for a rigid–flexible coupled flapping-wing robot and proposes a diffeomorphism-based attitude-constrained controller. The inverse hyperbolic tangent mapping transforms bounded physical errors into unbounded virtual errors, allowing smooth small-error regulation and stronger constraint enforcement near safety boundaries. Wind-free tracking, compound wind rejection, pulse wind scanning, mapping-parameter sensitivity, and a CBF-QP safety-filtered baseline are evaluated. In manuscript parameter-synchronized ADAMS 2024 reruns under a 2 m/s steady wind with a 1 m/s pulse, PID and SMC show runaway angular excursions of 1602.56° and 381,330.03°, whereas the proposed method remains bounded at 23.58° with an RMSE of 2.943° and no boundary violation. The CBF-QP baseline still violates the boundary at 1394°. The results show improved tracking accuracy, boundary protection, measured-channel flexible-excitation attenuation, and stable disturbance recovery.

Aerospace doi: 10.3390/aerospace13070631

Authors: Meng Cao Ce Zhang Hexiang Wang Dawei Liu Jie Chen Yang Tao

The unsteady buzz characteristics of a dorsal supersonic bump inlet for a flying-wing configuration are investigated using wind-tunnel tests and three-dimensional unsteady numerical simulations. This study focuses on off-design operation at a freestream Mach number of 1.8, with particular attention to the effects of angle of attack and downstream throttling on shock motion, pressure oscillation, and inlet stability. Wind-tunnel measurements show that the onset and development of buzz are highly sensitive to angle of attack. At high angles of attack, pressure oscillations first appear near the inlet compression surface and subsequently develop into large-amplitude fluctuations at the aerodynamic interface plane. The dominant experimental buzz frequency is approximately 60–70 Hz, and the numerical prediction of 71 Hz agrees well with the measured dominant frequency of 66 Hz. The simulations further reveal a strongly three-dimensional buzz cycle in which asymmetric separation over the bump, spanwise accumulation and discharge of low-energy flow, and alternating inlet blockage and recovery govern the large-amplitude shock excursion. The oscillatory flow field is dominated by shock–system expulsion and ingestion on the spanwise side with stronger back-pressure tolerance, accompanied by the formation of strong and weak shear layers during different stages of the cycle. These results provide insight into the buzz mechanism of dorsal bump inlets and support the assessment of starting performance and stable operating limits for supersonic inlets integrated with flying-wing configurations.

Aerospace doi: 10.3390/aerospace13070630

Authors: Hong Xie Zhibiao Cai Bo Yang Chunrong Wang

Non-periodic leading-edge wear near the impeller tip is investigated with respect to the aerodynamic performance, steady flow organization, and near-stall unsteady evolution of a centrifugal compressor. A full-annulus three-dimensional impeller–vaned-diffuser model is established for a baseline configuration (O-M) and a non-periodically worn configuration (W-M). The two configurations are compared in terms of performance characteristics, near-tip pressure coefficient, static pressure, entropy, relative Mach number, three-dimensional vortical structures, and pressure fluctuation signals. The W-M generally produces a lower total pressure ratio than the O-M, with a maximum reduction of approximately 0.7%. Nevertheless, the isentropic efficiency is slightly improved over the main operating range, with a peak increase of about 0.6%, and the near-stall flow rate shifts toward a lower value. Pressure coefficient distributions at 95% span show that leading-edge wear weakens both the pressure-side pressure peak and the suction-side suction peak of the worn blades, redistributing the near-tip loading from a highly leading-edge-concentrated form to a broader chordwise distribution. The steady flow fields indicate that wear does not eliminate local low-pressure or high-entropy regions; rather, it reorganizes their circumferential arrangement, converting originally synchronized low-pressure zones, high-entropy bands, and high-speed shear layers into a non-uniform pattern with alternating strong and weak passages. Near-stall unsteady results further reveal that pressure cells, high-entropy zones, and large-scale vortical structures in the O-M exhibit clear cross-passage propagation, whereas the corresponding disturbances in the W-M remain predominantly localized, dispersed, and asynchronous. These results demonstrate that, for the wear location and blade-to-blade distribution considered here, non-periodic leading-edge wear affects stability primarily by weakening the circumferentially coherent amplification of disturbances, rather than by simply reducing all local loss sources.

Aerospace doi: 10.3390/aerospace13070629

Authors: Kai Tang Haojie Zhang Xiao Sun Xuqiang Lang

Spacecraft electrostatic discharge (ESD) can generate transient electric-field disturbances, pulse currents, and electromagnetic coupling that threaten onboard electronics and mission reliability. Localizing discharge sources in confined spacecraft spaces remains difficult because conventional time-difference-of-arrival, radio-frequency, acoustic, and optical methods often require strict synchronization, large arrays, suitable propagation media, line-of-sight conditions, or explicit propagation models. This study develops a spacecraft-oriented, ground-validated electrostatic-induction sensor-array framework for three-dimensional localization of transient discharge events. Different from conventional received-signal-strength-based Apollonius localization, the proposed approach uses relative transient electrostatic-induction response features, including root-mean-square value, envelope energy, and integrated energy, and calibrates their feature ratios into distance-ratio constraints using a Power + offset mapping. These calibrated constraints are interpreted as Apollonius-sphere constraints, and the source coordinate is estimated by nonlinear residual minimization without relying on high-precision arrival-time picking. The method is evaluated on a controlled one-cubic-meter confined-space laboratory platform with known sensor geometry. Ten independent test positions show centimeter-level localization accuracy in the present calibration domain. The envelope-energy representation performs best, with a mean three-dimensional error of 7.01 cm, a median error of 6.94 cm, and a maximum error of 10.05 cm. These results demonstrate the feasibility of the sensing–calibration–inversion chain as a preliminary ground-based proof of concept. The reported accuracy should not be interpreted as direct on-orbit performance because the present experiment does not include vacuum, plasma, thermal gradients, spacecraft materials, metallic enclosures, or electronics integrated for spacecraft onboard operation; further environment-specific calibration and validation are required before practical spacecraft deployment.

Aerospace doi: 10.3390/aerospace13070628

Authors: Rion Sobukawa Takuji Ebinuma

Lunar navigation systems are being developed to support sustained surface operations, but their early deployment phase may involve limited satellite visibility and degraded accuracy in orbit and clock determination compared with terrestrial global navigation satellite systems (GNSS). Relative positioning with a lunar-surface reference station can mitigate common error sources through differenced measurements. In conventional GNSS, this mitigation often relies on the assumption that the line-of-sight (LOS) vectors from the reference and user receivers to the same satellite are nearly identical. Because lunar navigation satellite ranges can be considerably shorter than GNSS ranges, this approximation may be insufficient for kilometer-level surface baselines. This paper analytically quantifies three error mechanisms resulting from non-identical LOS geometries: the deterministic bias of the identical-LOS-vector approximation, the residual projection of broadcast ephemeris errors into single-differenced measurements, and the satellite-position-evaluation-time error caused by receiver clock initialization. For each mechanism, a simple closed-form bound is derived as a function of the baseline length and satellite range and is verified against time-series evaluations for representative lunar orbits. For a 10 km baseline in a low lunar orbit, the approximation alone can bias positioning by several tens of meters, whereas single differencing suppresses broadcast ephemeris errors to the meter level, and the clock-initialization effect can reach the meter level or larger. These results indicate that in lunar-surface relative positioning, the single-differenced range should be evaluated from the exact receiver-dependent geometry rather than from a common LOS vector. Additionally, the derived bounds provide a practical basis for budgeting broadcast ephemeris and receiver clock synchronization requirements.

Aerospace doi: 10.3390/aerospace13070627

Authors: Zhen Huang Chao Wang Yuan Gao Hengliang Zhang Zhan Li Pat Wheeler

Switching harmonics generated by power electronic converters have become a critical power quality issue in more-electric aircraft (MEA) dual-generator power systems, and accurate harmonic prediction is essential for effective harmonic cancellation. However, conventional analytical models often suffer from limited prediction accuracy, while data-driven methods are constrained by the scarcity of labeled data under certain operating conditions. This paper presents a method for harmonic prediction and cancellation in the dual-generator power systems of more-electric aircraft. To address the accumulation of switching harmonics on the DC bus, a comparative study is conducted among simplified analytical models, feedforward neural networks, and transfer learning-based models. A harmonic modeling framework and phase shift optimization strategy are established for harmonic cancellation. To overcome data limitations on the high-pressure shaft, transfer learning is employed to transfer knowledge learned from the low-pressure side to the high-pressure side. Results show that data-driven methods outperform traditional models, while transfer learning-based models further improve prediction accuracy and generalization under limited data conditions.

Aerospace doi: 10.3390/aerospace13070626

Authors: Yuanli Cai Junchao Zhao

A graph attention network-enhanced multi-agent proximal policy optimization (GAT-MAPPO) framework is proposed for cooperative guidance in adversarial engagement scenarios. A dynamic heterogeneous interaction graph is formulated over interceptors and targets at every decision epoch. Through a multi-head graph attention encoder, relational features capturing both inter-interceptor cooperation and target threat dynamics are adaptively aggregated. These graph-enriched observations are processed by a Centralized-Training, Decentralized-Execution (CTDE) MAPPO architecture, guided by a hierarchical reward function that mandates miss distance minimization, simultaneity of arrival consensus, multi-directional encirclement, and smooth control effort. Furthermore, the integration of a three-stage curriculum learning strategy allows for robust cooperative policy derivation across transitions from rectilinear to highly adaptive evasion patterns, eliminating the need for explicit rule engineering. Extensive Monte Carlo simulations confirm GAT-MAPPO’s superior performance: achieving >95% interception success rate in 4-vs.-4 scenarios and reducing mean simultaneity error by 41.4% compared to the MAPPO baseline. Comprehensive ablation and sensitivity studies validate the critical roles played by graph attention encoding, reward hierarchy design, and progressive curriculum staging.

Aerospace doi: 10.3390/aerospace13070625

Authors: Shenglun Zhang Chuanping Tang Hamza Blala Youchen Wang Zhuo Zhou Meng Zhang

Electric ducted fans (EDFs) have emerged as promising propulsion systems due to their compact design, high thrust density, and enhanced operational safety. Accurate prediction of aerodynamic thrust is essential for EDF design and performance evaluation; however, existing numerical studies have not yet provided a systematic comparison of the thrust-prediction capability of different k−ω-based turbulence models in micro-EDF applications. In this study, a dedicated thrust-measurement platform was developed for a 120 mm EDF, and experimental thrust data were obtained under three representative hover operating conditions. Based on these measurements, six turbulence models, including SST, SKω, BSL, GEKO, EARSM, and SST-γ(alg.), were evaluated using three-dimensional CFD simulations. The numerical model was assessed through thrust validation, centerline velocity comparison, power-consistency analysis, grid independence verification, and qualitative flow-field interpretation. A two-factor full-factorial analysis was further conducted to quantify the effects of rotational speed and turbulence model on prediction accuracy and computational cost. The results show that the turbulence model has a stronger influence on the normalized thrust-prediction error than the rotational speed factor over the investigated operating range. The SST-γ(alg.) model achieves the highest thrust-prediction accuracy, with an average relative deviation of 0.47%, but requires the highest computational cost. In comparison, the SST model provides a favorable balance between accuracy and efficiency, with an average relative deviation of 1.79% and an average computation time of 184.33 min, approximately 33% lower than that of the SST-γ(alg.) model. The centerline velocity and power-consistency results further support the comparative model assessment. Overall, this study provides an experimentally validated comparative reference for turbulence model selection in simulations of similar 120 mm EDF under hover conditions. Considering both prediction accuracy and computational efficiency, the SST model can serve as a practical turbulence model choice for engineering parameter optimization of similar micro-EDF configurations.

Aerospace doi: 10.3390/aerospace13070624

Authors: Dou Zhang Xiangxin Guo Rongjia Zhang Shengbo Zhang Bao Zhao Huanhuan Wu Qifeng Li Zhecheng Li Long Ye Ting Zhang Xiaohan Liu

A compact encoder-based focusing mechanism is proposed to compensate for axial focal-plane displacement in a space optical camera. The mechanism converts the rotation of a stepper motor into linear motion of the CCD focal plane assembly through a worm gear pair, a gear pair, and a cylindrical cam pair, while an encoder provides position feedback for closed-loop control. A displacement-count transmission model was developed and verified through MTF simulation, positioning tests, autofocusing experiments, finite element analysis, and vibration tests. The mechanism achieved a single-step control resolution of 1.38 μm and an encoder-based displacement measurement accuracy of 0.486 μm. The positioning test showed a maximum absolute error of 7 μm within a ±2 mm travel range, satisfying the ±7.5 μm requirement. Optical simulation indicated that axial defocus broadened the PSF and reduced the MTF near the 50 lp/mm Nyquist frequency. Autofocusing experiments using a resolution target showed that the normalized stripe contrast recovered to its maximum near the best-focus position, supporting the practical image-quality recovery trend predicted by the MTF simulation. The measured first natural frequency was 174.64 Hz, and the random vibration amplification ratios were below 3 in all tested directions. The results demonstrate that the proposed mechanism can provide accurate and mechanically robust compensation of focal-plane displacement.

Aerospace doi: 10.3390/aerospace13070623

Authors: Christopher Warsch Arturo Carboné Philipp Maas Florian Winter Meriem Fikry Arne Seitz Mirko Hornung

Novel aircraft propulsion concepts based on electrochemical conversion technologies, such as solid oxide fuel cells (SOFCs), are being investigated to enable climate-neutral air transport. It is crucial to identify SOFC architectures that are relevant and capable of fulfilling the specific requirements for aerospace applications, i.e., optimization for mass and volume. For a mature design and performance synthesis of propulsion system concepts, including highly integrated SOFCs, more sophisticated component models are necessary for a clean and unified integration of SOFC technology. The models should include both electrochemical performance and sizing, as well as system integration, already at the early stages of system design and analysis. This work presents a MATLAB-based 0D approach within the Bauhaus Luftfahrt Aircraft Propulsion System Simulation (APSS) framework to model the steady-state operational characteristics of an SOFC stack and determine its preliminary size. The results serve as a basis to assess integration aspects and challenges for various SOFC architectures, such as planar or microtubular arrangements. For simulated fuel cell stacks, validation studies are performed to ensure realistic dimensioning, as well as selected analyses showing the sensitivity of the model and resulting stack size to relevant operating parameters, such as temperature or required power. The studies presented within this work are an important step towards enabling the design and subsequent evaluation of overall fuel cell-driven propulsion system concepts.

Aerospace doi: 10.3390/aerospace13070622

Authors: Jaeheon Cheong Youngho Eun Sang-Young Park

CubeSats operating under nadir-pointing or mission-priority attitude conditions often experience unfavorable solar incidence on their solar panels, limiting available onboard power. This study proposes a thermally driven passive sun-pointing mechanism for CubeSat solar panels and evaluates its prototype-level feasibility. The mechanism uses a photothermal panel, heat pipe, heat cartridge, shape memory alloy (SMA) spring, and universal joint to convert external thermal input into panel tilting motion without direct electrical actuation. A prototype was evaluated through SMA spring actuation tests, single-module pointing experiments, four-direction pointing tests, orbital thermal analysis, and expected annual energy-generation analysis. The experiments showed thermally induced contraction and recovery tendency of the two-way SMA spring and demonstrated that selective thermal input can generate directional tilting and return motion in a four-direction prototype. Orbital thermal analysis indicated that heat can be transferred to the actuation region while maintaining directional thermal separation. The energy-generation analysis suggested that limited-angle pointing can improve annual energy generation compared with a fixed flat panel. These results support the prototype-level feasibility of the proposed mechanism, although further multi-axis measurement, long-term cycling, and thermal-vacuum validation are required.

Aerospace doi: 10.3390/aerospace13070621

Authors: Nadir Yilmaz Hakan Ayhan Dağıstanlı Alpaslan Atmanli Michael Arowolo

The use of liquid hydrogen (LH2) in rocket propulsion systems is among the most critical technologies enabling highly efficient space exploration. Fuel-oxidizer combinations directly impact mission performance, safety, and sustainability. In the literature, determining which oxidizer to use to obtain an efficient combination in experimental studies is a valuable area of research. However, evaluating different alternatives according to various criteria in experimental studies is expensive, time-consuming, and quite dangerous. This study aims to provide decision-makers with analytical support through a novel multi-criteria decision-making methodology. In this context, the simple weight calculation (SIWEC) method is integrated to determine the weights of the criteria, and the mulTi-noRmalization mUlti-distance aSsessmenT (TRUST) method is integrated to evaluate the oxidizers. The results show that the most important criterion is combustion, followed by environmental sustainability, applicability, cost, and operational safety. The foremost oxidizer, according to the analyses, parametric sensitivity analysis scenarios, and comparative analyses, is overwhelmingly LH2-liquid oxygen (LOX). In all analyses, fluorine (F2) ranked second, followed by the FLOX mixture in third place, and ozone (O3) in last place. In addition, sensitivity analyses based on α and β parameter variations and comparative analyses were conducted to evaluate the robustness and stability of the proposed decision-making framework.

Aerospace doi: 10.3390/aerospace13070620

Authors: Guannan Chen Yue Teng Yangyang Zhang Zhenxing Gao

High-value aviation rotable parts require accurate demand forecasting because each failure simultaneously creates a replacement demand, a repair workload, and a potential aircraft on-ground (AOG) risk. This study develops a continuous-time Markov chain (CTMC) queuing framework for forecasting demand and optimizing target stock levels under realistic maintenance, repair, and overhaul (MRO) capacity constraints. Historical service-engineering records from B737 mechanical engine control (MEC) units are first benchmarked and filtered to retain inherent random failures during the useful-life phase. A Kolmogorov-Smirnov goodness-of-fit test is then used to verify the exponential time-between-failure assumption required by the Markov model. Based on this validated failure-pattern classification, the study derives steady-state probability models for both an ideal M/M/∞ repair system and a finite-capacity M/M/c repair system. The main contribution is not the isolated use of Weibull or exponential reliability models, Markov chains, or inventory optimization, which are established methods, but their auditable integration into an airline rotable-parts workflow that links failure-pattern screening, finite repair capacity, service-level constraints, and engineering validation. The empirical results show that repair bottlenecks shift probability mass toward higher numbers of failed units, create a fat-tailed backlog distribution, and double the required target stock from 6 to 12 MEC units under a 95% service-level requirement. Sensitivity experiments further show that repair turnaround time, fleet size, and MRO channel capacity jointly determine the inventory-capacity cost trade-off. The proposed framework provides an interpretable decision tool for airlines to align spare-part procurement with actual repair-system performance.

Aerospace doi: 10.3390/aerospace13070619

Authors: Leonardo Mazzini

We revise the Soft Landing Problem deriving the Optimal Guidance Policy and the Value Function of the minimum time problem in its Controllable Set. Using this Guidance Policy the lander can be guided not only along the nominal trajectory or in its neighborhood but in all conditions that can have a possible successful landing, thus providing a safer approach to changes in planning, failures or other unknown conditions. In addition to the classic solutions of this problem we have fully described a new class of broken extremals which occur when the lander is falling with an high vertical speed and can be used in case of failures or unplanned conditions.

Aerospace doi: 10.3390/aerospace13070617

Authors: Yihang Wen Hao Chen Xinfeng Sun Wenjing Li Yongxin Chen Hai Geng Jing Li

As a hundred-kilowatt-class advanced electric propulsion technology, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) holds immense potential for deep space exploration. During the ion cyclotron resonance heating (ICRH) process of VASIMR, the resonance of high-mass, low-charge-state ions demands exceptionally strong background magnetic fields; its reliance on strong magnetic fields imposes stringent thermal control requirements on superconducting magnets, significantly driving up the volume and mass penalties of the system. To address this challenge, this study explores a low-magnetic-field VASIMR architecture utilizing a light gas, Neon (Ne), as the propellant. We systematically investigate the thrust performance and the evolution of ion energy under the multivariable coupling of pre-ionization power, ICRH power, and the magnetic field topology within the resonance zone. The results demonstrate the technical and engineering feasibility of the low-magnetic-field and light-propellant propulsion scheme. Specifically, the thrust gains corresponding to the pre-ionization and ICRH power are approximately 2.2 mN/100 W and 10.3 mN/500 W, respectively. Furthermore, optimizing the magnetic field topology significantly enhances the ion energy absorption efficiency in the resonance zone, yielding a thrust improvement of 25.3 mN. This study achieves a significant reduction in the background magnetic field strength compared to conventional VASIMR, elucidating the multi-regime control mechanisms of the low-field VASIMR. These findings lay a robust theoretical and experimental basis for future lightweight designs and performance leaps.

Aerospace doi: 10.3390/aerospace13070618

Authors: Wenyu Xu Xiaoyuan Yang Nanhao Liang

Low Earth orbit (LEO) satellites are increasingly required to process and securely stream video data for remote sensing, surveillance, and onboard perception applications. However, the strict constraints of onboard computing capability, power budget, and thermal dissipation make conventional encryption schemes difficult to apply to real-time video streaming tasks. To address this challenge, this paper proposes a low-complexity real-time video encryption algorithm for resource-constrained LEO satellites. The proposed method integrates selective encryption with a lightweight permutation–diffusion mechanism to reduce computational overhead while maintaining effective protection of continuous video streams. To enhance security, a chaotic pseudo-random sequence generator is employed to improve encryption randomness, and a dynamic key scheduling strategy is introduced to increase temporal key variability and strengthen resistance to statistical and differential attacks across successive frames. The algorithm is further designed for efficient deployment on embedded onboard platforms with limited hardware resources. Experimental results show that the proposed method achieves favorable performance in encryption speed, computational complexity, information entropy, adjacent pixel correlation, and differential attack resistance. Compared with conventional full-encryption methods, the proposed algorithm offers a more balanced trade-off between security and real-time efficiency, demonstrating its potential for secure video streaming in resource-constrained LEO satellite systems.

Aerospace doi: 10.3390/aerospace13070616

Authors: Reuben-Wayne Stewart Jack Dooher Moble Benedict

This paper discusses the development of a fully nonlinear flight dynamics model of a hover-capable Air-Launched Uncrewed Aerial System (ALUAS) in order to (1) understand the dynamics, controllability, and airloads during complicated maneuvers and (2) gain insights from simulation to inform the design and operation of future ALUASs. Prior studies conducted wind tunnel tests on full-scale models to measure the airloads on the propeller, isolated fuselage, and full aircraft. The flight dynamics model, once corrected with the test data, was used to simulate maneuvers including hover-to-cruise transition, cruise-to-hover transition, ground launch, air launch from a moving helicopter, and air launch with asymmetric wing unfolding. These simulations demonstrate the capability of the vehicle to perform complicated maneuvers to meet various mission objectives in challenging environments.

Aerospace doi: 10.3390/aerospace13070615

Authors: Shan Ma Wenxin Guo Ganchao Zhao Xiaolin Sun Yang Yu

Aviation accidents during the final approach phase of transport aircraft account for nearly half of all accidents in the flight stage, with unstable approaches being a notable contributing factor. In related accident analysis research, traditional single-parameter threshold monitoring methods have shown difficulty in capturing the complex coupling relationship between kinetic energy and potential energy. This weakness results in insufficient adaptability under variable meteorological disturbances and poor risk identification. To address this limitation, this study establishes an evaluation framework based on the concepts of “energy altitude” and “balance energy, shifting the analytical focus of aircraft state variations to energy evolution. A hybrid dynamic safety boundary function is further constructed by integrating flight mechanics principles with civil aviation regulatory constraints. This boundary integrates a height attenuation mechanism, enhancing adaptability to environmental disturbances. The study adopts QAR flight data of Boeing aircraft collected at an international airport from 2015 to 2020 as the database for machine learning modeling, and selects two additional independent flight datasets under calm-air and wind-shear conditions respectively for model verification. The research results indicate that this framework provides a robust theoretical foundation for the early identification of unstable approaches and provides actionable insights for optimizing energy control strategies, thus improving flight safety under complex operational conditions. Nevertheless, the verification only relies on two groups of typical flight cases under limited meteorological conditions, which restricts the generalizability of the research conclusions. Follow-up work will expand multi-type and multi-meteorological flight samples to carry out quantitative performance evaluation and further optimize the model’s practicality under diverse operational environments.

Aerospace doi: 10.3390/aerospace13070614

Authors: Abdulrahman S. Almutairi Hamad H. Almutairi Abdulrahman H. Alenezi Hamad M. Alhajeri

Turbofan engine performance is critically sensitive to operating conditions, yet comprehensive frameworks that simultaneously assess exergo-economic, exergo-environmental, and lifecycle cost performance across realistic flight envelopes remain limited, particularly for Gulf-region climates. In this study, we present a comprehensive analysis of the exergo-economic, exergo-environmental, and lifecycle costings of five different configurations of two-spool and triple-spool turbofan engines. The analysis was carried out for a wide range of four operating conditions, namely ambient temperature, flight altitude, Mach number, and % relative humidity, with emphasis on the climate conditions likely to be found in the Gulf region. The computational models developed were validated against published data to confirm their reliability. It was found that fuel consumption was the most significant contributor to total lifecycle ownership cost, between 60 and 75% of hourly operating cost over a 20-year service period. Ambient temperature, Mach number, and Cruise altitude represented the most significant drivers of long-term economic performance, with % relative humidity having little effect. Exergo-economic analysis showed that the major cost mechanisms changed dramatically with operating conditions. Exergy destruction and component inefficiencies determined the costs at Takeoff, with capital investment being the dominant factor when cruising. Increase in both or either ambient temperature and altitude was shown to reduce cost rates but simultaneously reduced thermo-economic efficiency via higher specific exergy costs. However, increase in Mach number enhances both exergy output and cost-effectiveness, confirming that specific exergy cost is a more reliable indicator of true system performance than cost rate alone. The two-spool configurations show superior specific CO2 emissions, with Case 3 recording the lowest emissions at Takeoff and Case 2 at Cruise. For exergy-based environmental indicators, Case 3 performs best at both Takeoff and Cruise, achieving the lowest environmental destruction coefficient and index, as well as the highest environmental benign index among all five configurations. These findings provide actionable guidance for engine selection, operational optimization, and sustainable propulsion system design.

Aerospace doi: 10.3390/aerospace13070613

Authors: Jun Wei Wei Gao Bei Lu Qifu Li

The distributed electric propulsion (DEP) system offers significant potential for enhancing aerodynamic efficiency, reducing emissions, and enabling innovative aerodynamic configurations. However, the strong coupling between propeller slipstream effects and wing structural dynamics presents new challenges for aeroelastic analysis. To address this issue, this paper proposes an aeroelastic modeling approach tailored for DEP systems that systematically accounts for the effects induced by propeller slipstreams. Specifically, the induced velocity generated by the propeller slipstreams is computed using a slipstream tube model and incorporated into the unsteady aerodynamic modeling via the unsteady vortex lattice method. Under appropriate assumptions, a state-space formulation of the unsteady aerodynamic forces is derived, while the wing structural dynamics are represented using the finite element method. After establishing the subsystem models, a complete aeroelastic model of the DEP system is assembled based on the input–output relationships among the subsystems. Nonlinear simulations are conducted using this integrated model. The results demonstrate the potential of distributed propellers for suppressing wing vibrations and alleviating structural loads.

Aerospace doi: 10.3390/aerospace13070612

Authors: Chunguang Zhang Feng Sun Ye Li Haining Zhao Fangchao Xu Junyue Tang Shengyuan Jiang Chuan Zhao Ran Zhou

To accurately characterize the effects of polydisperse particle sizes, multimineral composition, and angular morphology on the packing structure of lunar regolith, a two-dimensional sequential packing method based on random convex octagons is proposed. The method establishes a particle parameter system using data from Chang’e-5 samples and generates polygonal particle models with controllable angular features through radial perturbation. On this basis, a sequential packing algorithm based on available arc analysis is developed. Non-overlapping particle insertion is achieved via geometric envelope constraints, and progressive filling is realized through effective arc sampling. Meanwhile, a packing control coefficient is introduced to enable continuous regulation of packing density. Results show that the proposed method can generate highly dense particle assemblies, with a maximum packing density of 0.8757 and an average coordination number of approximately 3.18, capturing the structural characteristics of “high compactness–low coordination number” in polydisperse angular particle systems. The algorithm exhibits a computational complexity of O(N1.628), demonstrating high efficiency. Furthermore, contact area and contact strength are quantitatively characterized through contact contour extraction and an equivalent bow-shaped model. Radial distribution function and contact statistics indicate that the generated structures possess good randomness and physical consistency. The proposed method provides a high-fidelity mesoscopic structure generation approach for discrete element modeling (DEM) of lunar regolith and establishes a reliable foundation for analyzing the mechanical behavior of granular systems.

Aerospace doi: 10.3390/aerospace13070611

Authors: Zewei Zhang Haiyan Fang Weimin Bao Xiaoping Li

High-quality X-ray pulsar observation profiles are vital for investigating both their physical properties and navigation applications. Conventional profile extraction relies on epoch folding, whose performance is constrained by observation duration and bin size, often leading to poor-quality profiles or even failure under extremely low-photon conditions. This paper proposes a novel method that directly extracts high-quality profile frequency spectra merely by statistical analysis of photon sequences followed by the reconstruction of time domain waveforms. Monte Carlo simulations and real observational data demonstrate that the proposed method exhibits higher correlation coefficients and signal-to-noise ratios than those obtained using traditional epoch folding, and also outperforms the Fourier-series-based frequency cutoff method. Moreover, comparable profile quality can be achieved using an order of magnitude fewer photons than required by epoch folding. The lower the photon count, the more significant the improvement, making the method especially suitable for small-area detectors and resource-constrained observation scenarios.

Aerospace doi: 10.3390/aerospace13070610

Authors: Aowei Shen Jiao Wang Yuan Tian Gan Yu Xiaowei Shao Dexin Zhang

Using low-Earth orbit (LEO) mobile communication constellations to transmit remote sensing satellite data represents an emerging paradigm for overcoming the bottleneck in downloading massive amounts of Earth observation data. However, dense concurrent access across multiple satellites triggers intense resource competition, severe visible-window fragmentation, and strict resource-exclusivity constraints. To address the complex scheduling challenges caused by high laser link establishment overhead and the high-dynamic motion between remote sensing satellites and LEO communication nodes, this paper proposes an Adaptive Multi-Objective Reconstruction Evolutionary Algorithm (AMOREA). The algorithm incorporates a hybrid initialization strategy to improve the quality of the initial solution set and designs a mission-level topology reconstruction mechanism that uses four complementary decomposition operators and a multi-strategy reconstruction pool to achieve effective resource aggregation. Furthermore, an adaptive weight feedback mechanism is introduced to dynamically adjust search priorities and balance global exploration with local exploitation. Simulation results show that, under the simulation settings of this study, AMOREA reaches a 100.0% completion rate for urgent high-priority tasks and an overall average task completion rate of 89.2%. In terms of multi-objective optimization performance, AMOREA obtains the highest mean hypervolume (HV) value among the compared algorithms, improving the mean HV by approximately 19.1% over NSGA-II, 17.6% over MOEA/D, and 67.6% over the Greedy baseline. These results indicate that AMOREA can generate higher-quality Pareto solution sets and improve the efficiency of high-dynamic inter-satellite transmission scheduling under the tested simulation settings.

Aerospace doi: 10.3390/aerospace13070609

Authors: Longbin Liu Mengyang Fan Shifeng Zhang Xiaolu Hu

The new type of multi-airbag hybrid airship is a novel lighter-than-air platform, but its flexible structures pose challenges for accurate modal parameter identification under complex fluid-structure interaction. Traditional methods often fail to capture the dynamic characteristics of such compliant systems. In this paper, a stochastic subspace identification method is proposed to estimate the modal parameters of the three capsule hybrid airship. The method constructs the Hankel matrix using only output response data and extracts the system matrix by singular value decomposition so as to identify the natural frequency and damping coefficient. Moreover, the numerical model of the airship (aspect ratio 2.22) is built, and the simulated response data (first five modes) are used to validate the approach. The results show that the identified frequencies and damping ratios match the theoretical values with a maximum error of 6.35%, demonstrating good accuracy and robustness. The proposed technique can provide a reliable tool for online modal identification of flexible airships, supporting structural health monitoring and vibration control.

Aerospace doi: 10.3390/aerospace13070608

Authors: Zhao Sun Peng Cao Guangshan Chen

This study presents an unsteady numerical investigation of multi-port lateral jet interaction phenomena on a hypersonic vehicle configuration. An unsteady RANS approach with Menter’s SST k-ω model is implemented to investigate the transient interference mechanisms among single-, triple-, and quintuple-port arrangements, focusing on jet initiation and termination transients. Upstream jets establish bow shocks and a separation zone that progressively degrade the effective pressure ratio for downstream ports. This aerodynamic shielding manifests as nonlinear escalation in coupling intensity, with the quintuple-port configuration exhibiting complex multi-level shock systems distinct from simple superposition of single-port effects. Flow field development completes within approximately 0.5 ms, yet jet-induced vortical structures exhibit pronounced temporal hysteresis during the decay phase, with the high-pressure zone dissipating progressively from upstream to downstream regions. Under steady-state conditions, the quintuple-port arrangement attains a normal force amplification coefficient of 1.044 alongside a pitching moment amplification coefficient of 4.387, illustrating substantial moment augmentation potential inherent to multi-port interference effects. These findings furnish theoretical foundations for Reaction Control System (RCS) port layout optimization and control strategy development in hypersonic flight vehicles.

Aerospace doi: 10.3390/aerospace13070607

Authors: Ruth Huang Regina S. K. Lee Marianna Veltri Vithurshan Suthakar Angel Porras-Hermoso

As the number of objects in orbit increases every year, the number of objects re-entering Earth’s atmosphere grows as well. Re-entry path prediction is tricky, as atmospheric modeling lacks accuracy and requires constant monitoring of the object during re-entry. Ground-based sensors face limitations due to the field of view and weather. This paper explores the novel idea of using star trackers in very low Earth orbit to image Resident Space Objects (RSOs) that are on re-entry path and provides a comparison of different star trackers to determine the most effective parameters. A simulation with 1000 Resident Space Objects on re-entry path was performed and detectability analysis was run using AURICAM, SAGITTA, PCO, IDS, and FAI sensors placed in orbit between 200 and 600 km in altitude. The results show that all star trackers at any altitude were capable of detecting at least three RSOs on re-entry path and making at least 47 detections during the simulation period. In particular, instruments with larger aperture diameters such as SAGITTA and FAI and quantum efficiency performed better, making up to 134 detections and detecting up to 10 unique RSOs. They also detected a higher average signal-to-noise ratio. Detectability of RSOs is higher when the sensor is placed closer to the objects, with the most effective performance recorded at 300–400 km altitude. Future work should include practical testing of this technique.

Aerospace doi: 10.3390/aerospace13070606

Authors: Hanzhen Li Yu Hu Lai Zhang Hongbo Sun Xuchao Zhang Sha He

Cycloidal propellers are known for their omnidirectional vectored thrust, enabling smooth transitions between hovering and forward flight, making them ideal for unmanned aerial vehicles (UAVs) and electric vertical take-off and landing (eVTOL) aircraft. However, cycloidal propellers tend to have lower hovering efficiency than screw propellers at the unmanned aerial vehicle (UAV) scale. Adding end plates to the blade tips can improve hovering efficiency by suppressing blade tip vortices. But the impact of these end plates have not been thoroughly studied. This paper aims to seek the designs with enhanced hovering efficiency and develop design guidelines for cycloidal propellers with end plates. Comprehensive force measurement experiments are performed on designs with and without end plates, and designs with rotating and static end plates. Complementary high-fidelity numerical analysis is performed to gain deeper insights into the complex 3D flow structures and the role of end plates in suppressing induced power losses. Our study reveals that end plates can effectively suppress the efficiency degradation typically associated with low aspect ratio blades. We demonstrate that even with a blade aspect ratio of 1.5, a cycloidal propeller equipped with end plates can achieve high hovering efficiency, thereby establishing a new design guideline for lightweight, high-performance propulsion systems. The designs with stationary end plates are superior to those with rotating end plates because rotation introduces additional torque caused by the friction force. Designs featuring thick end plates (t¯e=0.056) outperform those with thin end plates (t¯e=0.004), as the rounded edges can eliminate end plate vortices. A comprehensive parametric study is conducted, evaluating blade chord-to-radius ratios from 0.26 to 0.65, aspect ratios from 0.5 to 3.0, pitching amplitudes from 10° to 50°, as well as end plate configurations (stationary vs. rotating, and thin vs. thick). From this parameter space, the best design was identified as featuring stationary thick end plates (t¯e=0.056), a chord-to-radius ratio of 0.65, and a large pitching amplitude of 40 degrees. It achieves a hovering efficiency of 0.72 with a blade aspect ratio of 3, which is comparable to that of sub-scale rotors with similar Reynolds number. In contrast, for the cases without end plates, the highest hovering efficiency is lower than 0.6.

Aerospace doi: 10.3390/aerospace13070605

Authors: Lisong Hao Yunfeng Liang Taibo Li Hongwei Liu

To address the strong constraints, multiple objectives, and high dynamism of space telemetry, tracking, and command (TT&C) resource scheduling in flight-type launch scenarios, this study proposes a dynamic scheduling approach that integrates priority rules with adaptive multi-task evolution. First, a mixed-integer programming model is developed to capture fixed and mobile equipment, diverse mission requirements, and spatiotemporal coupling constraints, with the optimization objectives of minimizing the total mobile distance, the total number of deployed devices, and the number of mobile devices deployed. Second, a priority-based dynamic rescheduling mechanism is designed to support rolling insertion of emergency tasks and, when necessary, adjust conflicting tasks according to priority rules. Third, an improved NSGA-II algorithm is introduced, incorporating adaptive population adjustment, early stopping, and decoding caching to enhance multi-task search efficiency and convergence stability. Finally, a simulation experiment is constructed based on a typical commercial launch scenario, targeting three types of static task scenarios of different scales; the proposed Adaptive-NSGA-II consistently yields feasible schedules, while reducing the solution time by 70.4%, 62.7%, and 61.0%, respectively, compared with standard NSGA-II. In the dynamic emergency task insertion scenarios, the proposed priority-rule-based rolling rescheduling strategy successfully completes insertion in all three cases, achieves zero additional mobile distance in low-conflict scenarios, and remains significantly superior to the fixed-time direct insertion strategy even under high-conflict conditions. The experimental results demonstrate the effectiveness, robustness, and engineering applicability of the proposed method for TT&C resource scheduling in flight-type launch operations.

Aerospace doi: 10.3390/aerospace13070604

Authors: Edoardo Maria Leonardi Fabio Curti Lorenzo Federici Mauro Pontani

On-Orbit Servicing (OOS) represents a viable strategy toward a sustainable and extended exploitation of the Low-Earth-Orbit (LEO) environment. The design of OOS missions requires optimizing both the scheduling of visited objects and the transfer trajectory between each pair of orbits, resulting in the great complexity of the global mission planning problem. This research considers a servicing spacecraft equipped with a high-thrust propulsion system, required to perform multiple orbit transfers to visit several Resident Space Objects (RSOs) in a given time frame with minimum fuel consumption. The proposed method leverages a two-stage approach: (i) first, the optimal transfers are computed for all pairs of orbits and discretized dates, and the associated overall velocity changes are stored in a cost matrix; (ii) then, the problem of visiting all RSOs is cast as a search problem, and the solution space is explored through an A∗ algorithm. The transfer strategy exploits intermediate drift orbits to increase the differential precession due to the J2 harmonic of the Earth’s gravitational potential. Moreover, the A∗ procedure leverages a heuristic function based on a modified version of the Held–Karp algorithm, which is proven to be admissible and consistent, meaning that the optimal solution is always reached. The proposed strategy is integrated within a flexible architecture, where operational constraints on phasing and servicing activities can be enforced as well. Finally, the methodology at hand is successfully applied to a case study from the literature involving three successive missions, in charge of visiting 5 RSOs each. Different discretization grids are considered, and the results are compared in terms of overall velocity change and computational time.

Aerospace doi: 10.3390/aerospace13070603

Authors: Maria S. Palacios Julian D. Calonge Sandra Villamizar Daniel Gomez Antonio Bobet

The lunar South Pole has emerged as a strategic target for future space exploration due to its potential to host valuable resources and its favorable illumination conditions. However, the absence of a significant atmosphere leaves surface infrastructure directly exposed to meteoroid impacts, creating a critical challenge for long-term operations and mission sustainability. This study presents a probabilistic assessment of meteoroid impact hazard at the lunar South Polar region using version 3.0 of NASA’s Meteoroid Engineering Model (MEM 3.0). The proposed methodology integrates site-specific meteoroid flux estimation with probabilistic recurrence analysis to characterize meteoroid mass distributions, relative velocities, directional exposure conditions, and impact frequencies on the lunar surface. The results indicate that the meteoroid flux exhibits a well-defined peak near 25.5 km·s−1, with maximum values approaching 0.053 impacts·m−2 per year in the ram direction, confirming a pronounced directional anisotropy in the impact environment. Small particles dominate the cumulative impact frequency within the validated MEM 3.0 mass range (<101 g), whereas probabilistic extrapolation of the mass–frequency relationship suggests that extreme-mass impactors (~106 g) occur far less frequently but generate substantially greater kinetic energies. Power law scaling relationships between impact frequency, particle mass, and return period are further used to define representative impact scenarios for engineering design and hazard assessment. The proposed methodology provides a physically consistent and scalable framework for evaluating meteoroid hazard conditions in localized lunar environments and supports the development of resilient infrastructure for future long-duration exploration missions at the lunar South Polar region.

Aerospace doi: 10.3390/aerospace13070602

Authors: Valerio Parisi Roberto Capuzzo Dolcetta Fabrizio Frezza Luca Lunati

We present a preliminary feasibility assessment of a magnetic shield designed to protect a space probe from cosmic radiation via magnetic deflection using neodymium permanent magnets. This work is grounded in theoretical considerations whose preliminary indications are intended to serve as the basis for future Monte Carlo simulations and laboratory validation. The novelty of our approach lies in the use of a magnetic shield; its competitiveness with conventional passive absorbing shielding is not investigated here but warrants dedicated future work. The primary objective is to protect a spacecraft from the flux of charged particles emitted by the Sun. To this end, we combine theoretical modeling and numerical simulations, followed by the construction of a prototype for laboratory testing and, potentially, for future experimental validation at the CubeSat scale.

Aerospace doi: 10.3390/aerospace13070601

Authors: Bochang Yu Feng Gao Wen Wu Heng Chai Qun Yao Guidao Lin Qi Chen Yanbin Liu

Owing to the stringent spatio-temporal coupling and kinematic constraints, the task allocation problem for heterogeneous unmanned aerial vehicle (UAV) swarms is generally regarded as an NP-hard problem. To address this, this paper proposes the Sequentially Extended Consensus-Based Bundle Algorithm (SECBBA), a deadlock-free distributed scheduling framework. First, a multi-task allocation model is established by incorporating constraints associated with payload resources, task scheduling, and threat zone. Subsequently, the conventional Consensus-Based Bundle Algorithm (CBBA) is extended through the integration of a deadlock detection and resolution mechanism based on directed graph Depth-First Search (DFS), thereby guaranteeing conflict-free task allocation. Furthermore, a sequential hierarchical strategy is introduced to transform global temporal dependencies into tractable soft time-window constraints. Finally, to ensure physical feasibility, Dubins curves are tightly coupled with the allocation process, enabling nonholonomic path planning for fixed-wing UAVs. Simulation results demonstrate that SECBBA reduces global task costs by 13.3%, 22.7%, and 39.4% compared to the Consensus-Based Bundle Algorithm with Temporal Consistency Constraints (CBBA-TCC), Improved Genetic Algorithm (IGA) and Q-Learning baselines, respectively. It consistently maintains performance advantage of 9.8%, 23.2% and 19.0% under variable weights with high computational efficiency, significantly enhancing swarm timeliness in complex, coupled multi-task scenarios.

Aerospace doi: 10.3390/aerospace13070600

Authors: Tong Wei Jiale Huang Xingyu Zhu Fengqi Ni Xinyue Zhou Mengdie Liu Enmi Yong

Trajectory planning for morphing gliding reentry vehicles is a nonconvex optimization problem driven by nonlinearity, parameter uncertainty, and multiple constraints. No-fly zones (NFZs) are a critical constraint because their rapid movement and expansion hinder the real-time generation of optimal flight trajectories and wing morphing strategies. Therefore, this study proposes an innovative online trajectory optimization method based on sequential convex optimization integrated with a deep neural network (DNN). The proposed method first uses the Radau pseudospectral method to discretize continuous dynamics and convert the non-convex trajectory planning problem into a relaxed convex subproblem. The subproblem is reformulated as an augmented Lagrangian function through linearization and is iteratively solved using the interior-point method. Finally, the DNN learns the mapping between flight states and optimal control variables (angle of attack rate, bank angle rate, and wing sweep angle rate) to rapidly generate control variables. Different from the time-consuming offline optimization method, the proposed model only requires 0.4 ms to predict three groups of control variables, with the predicted control errors remaining below 2.25%. This method efficiently provides high-precision and stable reentry trajectories and morphing strategies for gliding reentry vehicles. Thus, the proposed method achieves synchronous flight path and wing deformation optimization and demonstrates strong robustness under time-varying mission conditions.

Aerospace doi: 10.3390/aerospace13070599

Authors: Guang Yang Yongfeng Jin Wei Wang Longlong Shi Hongwei He Mingyuan Liu Anran Ju Xiaowu Fu

To address the challenges posed by the complex flow fields of civil aircraft thrust reversers and the difficulty of quantitatively decoupling multiple interference factors in wind tunnel tests, this paper employs numerical simulation methods to conduct an in-depth investigation into the aerodynamic characteristics and environmental interference effects of a scaled thrust reverser test configuration. The results indicate that the Fan Pressure Ratio (FPR) is the primary factor governing deceleration efficiency, while an increase in the freestream Mach number exerts a significant streamwise constraining effect on the reverse jets. Under sideslip conditions, the asymmetric interference moment induced by lateral dynamic pressure superimposes positively with the inherent stability of the configuration, thereby enhancing the directional recovery capability during crosswind rollout. Analysis of wind tunnel interference reveals that the boundary layer on the static floor induces a “ground cushion effect,” leading to an overestimation of lift; meanwhile, the support structure interference results in an overall increase in aerodynamic loads. This study elucidates the physical essence of thrust reverser flow fields within confined spaces, providing critical theoretical support for the design of test schemes and the correction of experimental data.

Aerospace doi: 10.3390/aerospace13070598

Authors: Yifu Cao Zengshan Yin Shihang Wang Ruohao Zhang Kai Ye Chongbin Guo

High-precision onboard orbit propagation, often unavailable due to high demands of onboard resources, is crucial for autonomous optical link pointing and acquisition in large-scale low Earth orbit satellite constellations. For such large-scale constellations, an advantageous feature for efficient and accurate orbit propagation is the correlation or similarity in the orbit perturbations experienced by multiple satellites. Yet, this correlation has not been fully utilized in existing orbit propagation methods. In this work, we propose a cross-referential orbit propagation framework that leverages multiple historical reference arcs from other satellites within the same constellation to improve prediction accuracy and reliability. The framework achieves error reduction comparable to that of ensemble learning by aggregating the predictions from a single lightweight model under varying reference inputs, thereby preserving a simple and compact model architecture. To ensure the generalizability of this compact model, we further introduce a network architecture termed the Compressive Decoder for Orbit Propagation (CDOP). The CDOP predicts low-dimensional representations of the propagated orbits, from which the full time series are subsequently decoded. By incorporating modules from pre-trained compressive autoencoders, the CDOP mitigates overfitting while maintaining a low inference cost. The proposed method is validated on simulated Walker constellations with different geometries. The results demonstrate an average 24 h position error of approximately 200 m, with an inference cost 30 times lower than that of a reduced-dynamic numerical propagator. The framework is computationally lightweight, generalizes well across different initial conditions, and is well suited for onboard deployment in autonomous optical link acquisition.

Aerospace doi: 10.3390/aerospace13070597

Authors: Hong Zhao Zhanpeng Gao Wenjun Yi

This paper proposes a barrier-modulated probabilistic super-twisting guidance (BMPSTG) for robust three-dimensional maneuvering target interception under measurement uncertainty and packet loss. A stochastic barrier-adaptive mechanism inspired by tunneling dynamics is introduced to reshape the sliding variable evolution, enabling accelerated convergence and reduced chattering compared with conventional super-twisting schemes. To enhance disturbance reconstruction accuracy, a composite observer integrating a finite-time disturbance observer (FTDO) and a high-order extended state observer (HESO) is developed. The FTDO ensures fast transient estimation, while the HESO improves steady-state precision and robustness to noise. Simulation results demonstrate that the proposed FTDO–HESO structure outperforms both standalone FTDO and conventional FTDO–ESO configurations in terms of estimation accuracy and guidance performance. A probability-coupled gain adaptation strategy further adjusts control gains according to engagement states, improving robustness under aggressive target maneuvers. Monte Carlo simulations verify that the proposed method achieves high interception accuracy with stable convergence and reduced control effort in complex engagement scenarios.

Aerospace doi: 10.3390/aerospace13070596

Authors: Utku Yurtsever Melin Şahin Altan Kayran

A new aeroservoelastic modeling and analysis methodology is presented for an aircraft with multiple control surface freeplay nonlinearities using the fictitious mass approach. The model incorporates freeplay in the right and left ailerons and the elevator, and is developed by combining linear aeroelastic models in an external simulation environment. State-space, time-domain simulations are performed to investigate both single and multiple freeplay configurations and their effects on limit cycle oscillation (LCO) characteristics, while a flight control algorithm maintains overall stability of the aircraft. The results show that, for elevator dynamics, LCO boundary decreases when combined aileron–elevator freeplay is present compared to the case with elevator freeplay alone. In contrast, for the same combined configuration, the aileron LCO onset occurs at a lower speed, while the flutter boundary shifts to a higher velocity relative to the aileron-only freeplay case. These findings demonstrate the strong coupling between longitudinal and lateral dynamics in the presence of multiple freeplay nonlinearities. The results further suggest that multiple freeplay can alter the dominant instability mode and delay the onset of sustained oscillations.

Aerospace doi: 10.3390/aerospace13070595

Authors: Jianfeng Wang Hang Zhao Botao Tang Yi Qi Yuan Yao Zhiping Song

Accurate thrust control is vital for efficient gas turbine engine operation, yet direct in-flight thrust measurement is unavailable. Most engines rely on speed control schedules, which suffer from unplanned dead zones and poor throttle-to-thrust linearity—compromising pilot handling and fuel economy. We propose a robust thrust control schedule to improve the thrust-to-throttle relationship. It integrates two intermediate/idle thrust estimators, a degradation estimator, and a reference thrust estimator. The first intermediate/idle thrust estimator provides baseline estimates of intermediate and idle thrust. The degradation estimator compensates thrust deviations caused by engine degradation. The second intermediate/idle thrust estimator updates its estimates online using compensated estimates to track degradation. The reference thrust estimator then uses outputs from the second estimator and linearly interpolates the current power lever angle to determine reference thrust. The proposed schedule is evaluated under the considered degradation conditions. CLM-based simulations evaluate its effectiveness during the early-stage degradation period, while the micro-turbojet ground experiment demonstrates the proof-of-concept implementation of the outer thrust-loop structure.

Aerospace doi: 10.3390/aerospace13070594

Authors: Pengfei Zhang Lianguo Wang Enshi Li Jianing Rao Jianzhe Zhang Miao Ma Wenjie Zhao

With the development of space-based cloud computing and on-orbit intelligent processing, higher requirements have been imposed on standardized network interconnection for spaceborne platforms. However, constrained by size, power consumption, thermal design, and structural layout, some spaceborne platforms lack physical Ethernet interfaces and therefore cannot directly support standard Internet Protocol version 6 (IPv6) communications. In addition, harsh spaceborne operating conditions, including thermal-vacuum stress and potential radiation-induced disturbances, increase the risk of link anomalies, state inconsistency, and service interruption. To address these issues, this paper proposes a reliability-enhanced IPv6 access and transmission method for spaceborne platforms without physical Ethernet interfaces. On the processor side, a network TAP interface is established to reconstruct the semantics of a standard Layer-2 network device. Combined with a cooperative central processing unit–field-programmable gate array (CPU–FPGA) link-carrying mechanism, the proposed method enables transparent IPv6 access without modifying the native Linux protocol stack. To satisfy both standard spacecraft onboard network services and high-throughput engineering data transmission, a dual-channel architecture is designed, in which the service network channel is separated from the engineering data channel. In addition, a hierarchical reliability-oriented mechanism is constructed, consisting of hardware-level fault-tolerance design, reliable link interaction, status monitoring, and redundancy takeover. Experimental validation is conducted on a CPU-FPGA prototype platform under a thermal-vacuum environment and representative abnormal operating scenarios. The results show that the proposed method can stably support IPv6 address configuration, neighbor discovery, and end-to-end communication. Under zero-packet-loss conditions, the service network channel achieves an average stable throughput of 173.8 Mb/s, while the engineering data channel achieves a stable throughput of approximately 3.4 Gb/s. The system also demonstrates good service continuity during long-duration operation and under typical abnormal scenarios. The proposed method provides a verifiable system-level solution for realizing standardized IPv6 network access and reliability-enhanced data transmission on interface-constrained spaceborne platforms.

Aerospace doi: 10.3390/aerospace13070591

Authors: Yijun Xie Jiaxian Sun Chunyan Hu Haoran Pan Chenchen Wang Junqiang Zhu

Aero-engine safety and prognostics and health management (PHM) rely on robust vibration-based fault diagnosis. However, many deep learning studies on rotating machinery are evaluated under random train–test splits that mix hardware instances and may obscure the domain shift faced in deployment. This paper presents a protocol-driven end-to-end baseline for multi-sensor aero-engine-relevant vibration diagnosis on the HIT inter-shaft bearing benchmark. Six synchronous vibration channels are segmented into fixed-length windows, standardized using source-domain statistics, and classified by a compact 1D CNN backbone with and without squeeze-and-excitation (SE) channel attention. A deeper ResNet1D baseline is further introduced to examine whether increasing backbone capacity improves cross-bearing generalization under the same source-only training protocol. We compare random segment-level splits with bearing-level cross-splits that hold out entire bearings as unseen target domains, and we report deployment-oriented indicators including balanced accuracy, false-alarm rate (FAR), and miss rate over five random seeds. Under random splits, the compact CNN baseline reaches near-ceiling test accuracy, confirming that the benchmark is readily separable under in-domain interpolation. In contrast, cross-bearing evaluation reveals severe degradation: in the representative split, the baseline CNN accuracy collapses to approximately 15% with near-zero normal-class recall, while ResNet1D improves fault sensitivity but still retains a high FAR above 88%. Additional cross-bearing permutations further show that this degradation is not attributable to a single unfavorable source–target split. These findings indicate that, under the tested source-only backbones and protocols, distribution mismatch is a dominant bottleneck for deployment-ready cross-bearing diagnosis. The results establish a reproducible baseline for protocol-driven evaluation in aero-engine PHM and motivate future work on domain adaptation, domain generalization, calibration, and sequential decision logic.

Aerospace doi: 10.3390/aerospace13070593

Authors: Jie Song Dongdong Zhang Peng Cui Lin Wang Yanhui Tang Xiangyi Liu

This study presents a novel one-dimensional solution method to demonstrate the effects of fuel composition and channel roughness on phase-change heat transfer in spiral regenerative cooling systems. The calculated models are grounded in an experimental correlation of liquefied natural gas (LNG) flow boiling, and their accuracy is validated through ignition experiments conducted on a 1 kg/s-class thrust chamber. The experimental data shows that the physical characteristics of LNG contribute to an extended reach within the two-phase region, resulting in a calculated pressure drop that exceeds that of pure liquid methane. Variations in surface roughness influence the pressure drop by altering the frictional coefficient. Specifically, an increase in surface roughness from 2 µm to 8 µm results in a 47.8% rise in pressure drop. The proposed model demonstrates high accuracy, with deviations in the coolant temperature rise and the pressure drop being less than 9.0% and 7.6%, respectively, when compared to experimental data. The findings serve as an engineering guide for designing and optimizing heat transfer in LOX/LNG rocket engine cooling systems.

Aerospace doi: 10.3390/aerospace13070592

Authors: Jianguo Sheng Liang Chang Zhang Zhang

The automatic recognition of cargo pick-and-place actions in spacecraft cabins is important for improving the intelligence level of in-orbit cargo management. This study proposes an integrated visual recognition framework based on improved YOLOv11n, DeepSORT tracking, and SVM-based trajectory classification. To address the challenges of densely stacked cargo, local occlusion, and complex cabin backgrounds, WeightConv and the convolution and attention fusion module (CAFM) are introduced into the YOLOv11n detector to enhance cargo feature representation. Based on the detection results, DeepSORT is used to associate cargo targets across video frames and extract continuous motion trajectories. The trajectory descriptors are then classified by an SVM into three typical operation states: “pick,” “place,” and “not picked.” On the self-constructed cabin dataset, the improved detector obtains a precision of 97.3%. The tracking module obtains an MOTA of 97.1% and an IDF1 of 95.1%, while the trajectory-based SVM achieves an overall classification accuracy of 92.0%. Experimental results demonstrate that the proposed framework provides reliable visual evidence for automating the recording of typical cargo pick-and-place operations in spacecraft cabins, offering viable technical support for enhancing in-orbit cargo management efficiency.

Aerospace doi: 10.3390/aerospace13070589

Authors: Miah Md Ashraful Alam Md. Mamun Takayuki Kuri Md. Kawsarul Islam Md. Mesbah Uddin Saadi

Atmosphere-breathing Hall thrusters (ABHTs) have emerged as a promising propulsion technology for very low Earth orbit (VLEO) satellites because they can utilize residual atmospheric particles as propellant, reducing the need for onboard propellant storage. In this paper, the feasibility of an ABHT system was investigated through a combined experimental and numerical approach. Experimental tests using the THT-VI Hall thruster demonstrated stable operation with air propellant and achieved specific impulses up to 2847 s under high-voltage conditions, indicating the potential for atmospheric drag compensation. To evaluate the intake performance, Direct Simulation Monte Carlo (DSMC) simulations were conducted at an altitude of 180 km to examine the effects of intake geometry, including the duct aspect ratio and intake-to-thruster area ratio. The results showed that the intake system can generate discharge chamber pressures of approximately 10−3–10−1 Pa, which is sufficient for Hall thruster operation, but the maximum collected mass flow rate (0.298 mg/s) remained below the required 1.5 mg/s. Several modified intake configurations improved particle transport and reduced aerodynamic drag with the best design increasing mass flow rate by approximately 7.5 times compared with the baseline configuration. These findings indicate that the primary limitation of ABHT systems is the intake mass transport capability rather than the thruster performance itself. A further optimization of intake geometry and spacecraft integration is required to enable sustained VLEO operation.

Aerospace doi: 10.3390/aerospace13070590

Authors: Xiang Zhou Jiawei Sun Jiannan Zhao Feng Shuang

The Vortex Ring State (VRS) is a critical aerodynamic hazard for rotorcraft, characterized by highly unsteady fluid–structure interactions and severe low-frequency vibrations. While data-driven deep learning models have shown promise in aviation state monitoring, their inherent “black-box” nature fundamentally contradicts the stringent interpretability requirements of airworthiness certification. To address this, we propose an “AI for Science” paradigm, investigating whether advanced Vision Transformers (ViT) can autonomously discover underlying aerodynamic mechanisms without human physical priors. First, to ensure absolute data fidelity, flight test datasets of a coaxial unmanned aerial vehicle were rigorously labeled using cross-validation from high-fidelity Computational Fluid Dynamics (CFD) simulations and wind tunnel tests. One-dimensional vibration signals were then transformed into two-dimensional Continuous Wavelet Transform (CWT) spectrograms. By employing Target-Layer Gradient Adaptation (Grad-CAM) techniques, we conducted a systematic comparison between traditional Convolutional Neural Networks (ResNet50) and ViT. The results demonstrate that while CNNs suffer from diffuse attention caused by high-frequency noise, the frozen-backbone ViT model achieves a physically interpretable accuracy of 93.24%, while autonomously locking its global attention onto a perfectly horizontal feature band centered at 41.7 Hz. Crucially, this autonomously discovered feature precisely aligns with the theoretically derived once-per-revolution (1P) fundamental frequency of the rotor’s flap-lag coupling response under VRS aerodynamic turbulence. This research provides direct visual evidence bridging black-box AI decisions with classical fluid mechanics, proposing a “Mechanism-Guided Verification” framework that offers a trustworthy pathway for the future certification of AI in safety-critical aerospace systems.

Aerospace doi: 10.3390/aerospace13070588

Authors: Shengpeng Zhang Shuanglong Rong Hao Li Shuo Huang Cheng-Wei Fei Baiyang Zheng

Reliability prediction of aerospace dormant components requires fusing natural-storage observations at the operating temperature with accelerated-storage testing data at elevated temperatures. Existing scalar-weight fusion methods apply a global weight that cannot reflect the time-varying trustworthiness of the accelerated branch as Arrhenius extrapolation distance grows. Physics-based fusion propagates accelerated-test scatter through least squares but leaves the dominant error source—the degradation-model form itself—unaccounted for, and no method in either class verifies the coverage of its intervals. This paper proposes an empirically calibrated multi-fidelity fusion that selects a mechanism-specific natural-branch degradation model by the corrected Akaike information criterion and augments the accelerated-branch variance with an additive model-form term fitted from natural-storage residuals. This term turns the fusion weight into a continuous, time-varying diagnostic that detects Arrhenius misspecification from training data alone and falls back safely to the natural-only estimate. Prediction intervals are calibrated by split-conformal prediction on a disjoint simulated population, giving finite-sample, distribution-free coverage, and the remaining-storage-life interval follows from the band’s first-passage time. On a 1000-run varying-truth simulation, the calibrated band attains 95.5% trajectory coverage at the narrowest band width among six methods; on the torsion-bar case, the fusion reaches a held-out RMSE of 0.045 N·m and a remaining-life interval of 10.4–12.6 years. The model-form variance ratio provides a single-number regime diagnostic across all cases.

Aerospace doi: 10.3390/aerospace13070587

Authors: Xiaohui Li Hongliang Xiong Zhan Huang Hongwei Wang Shaojie Ren

The shock wave/boundary layer interaction (SWBLI) is a common flow phenomenon in high-speed aircraft flow fields. It is important to control the separation caused by SWBLI. This paper investigates the influence of spanwise periodic-motion micro-vortex generators (MVGs) on SWBLI. A combination of particle image velocimetry (PIV), high-frequency Schlieren and fluorescent oil-film visualization was employed to analyze the interaction region of a flat plate compression ramp model. The incoming flow Mach number was 6, and the MVGs oscillation frequencies were 10 Hz, 30 Hz and 50 Hz, respectively. The results reveal that neither the presence nor the spanwise oscillation in the MVGs fundamentally altered the separation–reattachment flow structure. Nonetheless, both factors contributed to an increase in boundary layer thickness and an expansion of the absolute size of the separation region. The trailing vortices generated by the MVGs exerted a stabilizing influence on near-wall turbulent structures, resulting in a reduction in surface friction drag. However, the drag reduction effect diminished as the oscillation frequency increased, corresponding to a weakening of the trailing vortex strength. Additionally, the MVGs and their spanwise oscillation modulated the low-frequency energy distribution of the flow, amplifying the low-frequency oscillation peak associated with the separation shock and raising the time-averaged oscillation position.

Aerospace doi: 10.3390/aerospace13070586

Authors: Concetta Palumbo Gianluca Diodati Gaetano Perillo Domenico Cristillo Antonio Sodano Stefania Atalarico Francesco Santonicola Mariacristina Nardone Antonio Negro Antonio Chiariello

This paper presents the optimization-oriented structural design of aircraft empennages developed within the HERFUSE project, funded by the Clean Aviation Joint Undertaking. The study focuses on the horizontal and vertical tailplane of a hybrid-electric regional aircraft, considering the structural challenges introduced by distributed propulsion and novel integration requirements. The distributed propulsion layout influences the tail load envelope through powered-on maneuver/gust and asymmetric-thrust conditions, which contribute to the laminate redistribution in regions subjected to high bending–torsional demand. Starting from a conceptual structural configuration, the empennage is refined through a multi-objective optimization process. The structure is discretized into multiple regions, each characterized by independent laminate definitions selected from a predefined set of stacking sequences. The optimization aims to minimize the overall structural mass while ensuring adequate structural integrity under the project complete set of load cases. Structural performance is evaluated using a failure criterion suitable for composite materials, allowing the identification of critical regions and the redistribution of material accordingly. The results highlight the effectiveness of the adopted optimization strategy in improving structural efficiency, providing a refined configuration with a final mass of 433 kg, corresponding to an approximately 27.23% reduction with respect to the reference configuration coming from project specifications, while maintaining controlled failure index levels. The proposed approach demonstrates its suitability for supporting early-stage design decisions in next-generation hybrid-electric aircraft.

Aerospace doi: 10.3390/aerospace13070585

Authors: Vincent Onoja Keerthan Ganeshan Daniel Cuppoletti

This paper presents internal flow measurements in two shape-transitioning nozzle ducts using planar Particle Image Velocimetry (PIV). Nozzle 1 is a converging nozzle transitioning from a square cross-section to a rectangular exit with an equivalent diameter (De) of 2.2 in, an exit aspect ratio of 6.68, and a length-to-diameter ratio (L/De) of 7.8. Nozzle 2 also converges globally but incorporates a diverging sidewall that introduces localized adverse pressure gradients. Both nozzles are tested at an exit Mach number of 0.2, corresponding to ReDe≈2.50×105. Wall-normal velocity profiles reveal boundary layer thinning under favorable pressure gradients followed by thickening in regions of streamwise curvature and local adverse pressure gradients. In nozzle 2, the adverse streamwise pressure gradient along the diverging wall produces thicker boundary layers than in nozzle 1, while a cross-stream pressure imbalance shifts the velocity peak toward the diverging wall. Complementary steady RANS simulations using the k–ω SST turbulence model yield wall-normal velocity profile agreement within 2% mean absolute error for both nozzles in the upstream and mid-duct regions, with errors increasing toward the exit. Discharge coefficients from CFD and experiment agree within approximately 1%, with nozzle 1 exhibiting greater integrated losses than nozzle 2 despite thinner boundary layers at the measured plane, indicating a three-dimensional loss distribution. Independent pitot probe measurements at the nozzle exit confirm the PIV trends over the CFD predictions in the near-exit region.

Aerospace doi: 10.3390/aerospace13070584

Authors: Tamila Zhakenova Marat Nurguzhin Aruzhan Toleubay Nurlybek Spandiyar Arman Komekbayev Oraz Kumarkhan

Accurate ballistic trajectory prediction for upper stages on low Earth orbit is challenged by non-stationary atmospheric density driven by solar activity: as density varies, fixed noise covariance matrices in standard Kalman filters become mismatched with actual process statistics, causing degraded estimation accuracy. Non-stationary atmospheric density disrupts fixed-covariance Kalman filters in low Earth orbit, degrading trajectory prediction for upper stages. This paper characterises the quantitative position/velocity accuracy trade-off and performance boundaries of the Sage–Husa Adaptive EKF (AEKF), identifying an empirical sensor-noise approximate crossover region near σ* ≈ 100 m where the AEKF improves velocity accuracy by 38.9% at the cost of a 59% increase in position RMSE.

Aerospace doi: 10.3390/aerospace13070583

Authors: Di Zhao Zhe Yue Wensong Zhang Jianping Yuan Weihua Ma Haofei Ban Sen Li Weiwei Lei

Accurate attitude measurement of non-cooperative space targets is essential for on-orbit servicing, active debris removal, and autonomous rendezvous missions. To address the challenges associated with unknown geometry, rapid tumbling motion, and the limited observability of single-view systems, this study proposes a cooperative multi-view measurement framework for three-dimensional reconstruction and attitude estimation. Multiple spacecraft are deployed to form a stable observation configuration, and multi-view image sequences are acquired to strengthen geometric constraints. A learning-based multi-view stereo reconstruction module is used to estimate depth information and reconstruct point clouds, which are further processed through iterative closest point (ICP) registration to derive inter-frame attitude variations. An extended Kalman filter (EKF) is then introduced to improve temporal consistency and suppress measurement noise. Validation is conducted in a numerical simulation using a simplified Fengyun-1 (FY-1) satellite model under a three-spacecraft cooperative fly-around scenario. The simulation results demonstrate that the proposed method achieves high-precision attitude estimation, with attitude errors below 0.3° and positional errors within 0.05m. Comparative experiments show that the method maintains stable measurement performance under varying observation distances and viewing configurations. The proposed framework provides a reliable and robust measurement solution for dynamic attitude determination of free-tumbling space targets.

Aerospace doi: 10.3390/aerospace13070582

Authors: Kenta Endo Manami Kanamaru Keita Tanaka

Agile attitude control of nanosatellites is increasingly required for high-resolution imaging, yet actuators that provide agility on larger spacecraft do not scale down well: reaction wheels are torque-limited and slew slowly, while miniaturized control moment gyroscopes (CMGs) deliver high torque but their stored wheel momentum produces a gyroscopic coupling torque that degrades fine pointing—an inherent agility–precision trade-off on low-inertia 3U platforms. This paper presents a two-step variable-speed CMG (VSCMG) strategy that preemptively decelerates the wheel momentum once the attitude error falls below a threshold, attenuating the gyroscopic torque before fine pointing and thus decoupling slewing from precision pointing. It is validated on an experimentally grounded model: a fabricated 1U-class four-CMG pyramid (90×90×105 mm, 584 g), gimbal dynamics identified experimentally (93.2% fit) and regulated by an integral-type optimal servo, and bench-measured wheel dynamics. At 560 km under aerodynamic and gravity-gradient disturbances, the strategy completes a 90° slew in 25.3 s at a mean slew rate of 3.55°/s with 0.42° accuracy—4.5× faster than a reaction-wheel system and 12× more accurate than single-mode CMG operation—with a Lyapunov-based stability guarantee. The spacecraft-level closed-loop performance is established in closed-loop simulation, while the component-level ground experiments verify only that the assumed wheel-speed and gimbal-rate envelopes are achievable on the prototype; the present work is thus a simulation study supported by experimentally identified actuator models, not a system-level experimental demonstration. These results show that momentum-managed VSCMG control substantially relieves the agility–precision trade-off within a 1U envelope under the single-axis 90° slew studied here, extending CMG-class agility to small form-factor satellites previously confined to reaction wheels.

Aerospace doi: 10.3390/aerospace13070581

Authors: Zongliang Li Tianyou Yu Danhuai Guo Fenglin Ding Yizhuo Liu Xunchun Li

Recurring spacecraft anomalies may reflect anomaly-prone system states shaped jointly by spacecraft geometry, recent anomaly history, and space weather forcing, rather than isolated responses to single external drivers. Distinguishing these contributions is important for interpretable anomaly monitoring in geostationary orbit. This study develops a satellite-stratified case–control framework for GOES-16/17 Extreme Ultraviolet and X-ray Irradiance Sensors (EXIS) Space Wire (SpW) anomaly records. Orbital–illumination descriptors, same-satellite event history variables, and space weather variables from the NASA OMNI database are integrated within chronological train–test validation, supported by null-baseline comparison, stratified bootstrap confidence intervals, exclusion window sensitivity analysis, feature group ablation, cross-satellite testing, and calibration diagnostics. Orbital–illumination variables provide weak but reproducible discrimination, event history descriptors capture temporal clustering, and space weather variables add complementary held-out information. The full Space Environment-Integrated Model (SEIM) reached a test area under the receiver operating characteristic curve (AUC) of 0.7540, while a compact train-only L1-selected clean Top-15 model achieved comparable held-out discrimination with a test AUC of 0.7588 after excluding direct near-neighbor history variables. Bootstrap comparisons indicate that this small difference is not statistically significant. Calibration diagnostics further confirm that fitted scores should be interpreted as discriminative anomaly-state indicators under the case–control design rather than as calibrated operational anomaly probabilities.

Aerospace doi: 10.3390/aerospace13070580

Authors: Yumeng Wei Xiao Sun Yu Shi Xiaying Meng Qinglin Niu

Flow-field parameters of bow shocks in high-altitude rarefied flow are fundamental for seeker radiation noise evaluation and thermal-protection design. The conventional direct simulation Monte Carlo (DSMC) method is computationally expensive, making it difficult to achieve real-time prediction and massive sample generation of flow-field parameters. This paper presented a surrogate model adopting a convolutional neural network (CNN) to rapidly predict bow-shock reactive flow-field parameters. A blunt body with a nose radius of 0.1–1.0 m was investigated. The Latin hypercube sampling methodwas used to construct a sample space spanning altitudes of 80–150 km and Mach numbers of 15–35. DSMC-calculated data was segmented into training and test sets at a ratio of 4:1 and verified by the bow-shock ultraviolet experiments. An encoder–decoder CNN with a parallel decoder strategy was established to develop a bow-shock reactive flow surrogate model (CNN-BS) and conduct error evaluation. The results show that the mean absolute percentage errors for temperature, velocity, pressure, and nitric oxide number density are below 8%, with coefficients of determination close to 1. The average prediction time is 0.5 s, enabling online data generation. The CNN-BS model provides efficient support for radiation-noise evaluation and thermal-protection design of hypersonic blunt bodies.

Aerospace doi: 10.3390/aerospace13070579

Authors: Alexander Kiess Joachim Siegel Andreas Strohmayer

The CONCERTO project intends to enable innovation, while maintaining the safety performance of current configurations, by drafting suggestions for new means of compliance within the scope of the three Clean Aviation branches. This paper is drafted within the high-voltage distribution branch of the CONCERTO consortium. It provides an overview of existing considerations about the certifiability of (hybrid-)electric aircraft configurations and presents a structured and methodical approach that has been established while conducting CS-23 regulatory gap analysis for the CS-25-derived CS-23 CONCERTO HVD architecture. A limiting factor when incorporating existing insights into a new regulatory gap analysis is that most studies are based on a specific configuration, limiting their applicability. One key feature of the presented methodical approach is the property-based similarity approach that overcomes this limitation by enabling systematic incorporation of existing project-specific findings into the analysis to be conducted, taking into account the specific properties of different system design and sizing. The structured comparison, based on relevant technological properties, enhances the applicability of the identified critical areas and regulatory gaps of available gap analyses by enabling a systematic transfer of gap findings to other HVD system designs, even with different properties.

Aerospace doi: 10.3390/aerospace13070578

Authors: Pengfei Xiao Guofang Mu Chunping Zhou Chong Deng Yuheng Liu Guiping Zhu Yi Huang

Magnetorheological fluids (MRFs) exhibit field-dependent mechanical properties that are governed by the evolution of their internal particle structures. In this work, a particle-dynamics-based numerical method is used to investigate the microstructure formation and shear response of monodisperse and bidisperse MRFs at volume fractions of 22% and 33% under the same magnetic field and carrier-fluid viscosity. A mechanical model based on interparticle interactions is employed to describe particle motion and magnetic-field-induced chain assembly. To quantify the structural evolution during deformation, the average coordination number is introduced as a microstructural descriptor. The results show that bidisperse MRFs exhibit distinct chain formation mechanisms from monodisperse systems, particularly with decreasing particle size ratio and increasing concentration. Under steady shear, both systems display a fluctuating increase in stress, accompanied by structural rupture, migration and reorganization. However, concentration markedly affects the dominant evolution mode, while the incorporation of small particles in bidisperse systems weakens chain integrity, leading to stronger stress fluctuations and generally lower peak stress. These results provide insight into the coupling between microstructure evolution and mechanical response in MRFs.

Aerospace doi: 10.3390/aerospace13070577

Authors: Lantian Li Jianhan Liang

Robust flame stabilization in low-Mach, low-enthalpy supersonic combustors is a core bottleneck for turbine-based combined cycle (TBCC) mode transition. Existing studies mainly focus on single-injector configurations, while the injection angle modulation mechanism for multi-injector cavity flameholders remains unclear under TBCC-relevant conditions. This work experimentally investigated the effects of 30°, 45°, and 90° injection angles on cold-flow mixing, reacting flow topology, and flame stabilization in a Mach 1.6, 660 K dual-injector cavity combustor. Results showed that the overall cold-flow jet penetration capacity in the fully developed far field increased with injection angle following the order of 90° > 45° > 30°. Combustion heat release universally enhanced jet penetration, with a maximum 25% augmentation observed at 30° injection, which attenuated with steepening injection angle. Moreover, flame stability exhibited a non-monotonic trend in the tested dual-injector configuration.

Aerospace doi: 10.3390/aerospace13070576

Authors: Chenkai Hu Xipeng Wang Xikang Cheng Mengde Zhou Wei Wu Yuhang Ren Wei Liu

In wind tunnel testing, an active vibration suppression system based on piezoelectric actuators is an effective means to ensure stable operation. However, in a cryogenic wind tunnel testing environment, the performance of piezoelectric actuators degrades significantly when they are exposed to cold temperatures and subjected to uneven cooling. This is particularly problematic during real-time changes in the attack angle of a test model. To ensure the reliable operation of wind tunnel tests, an active–passive hybrid thermal control method is proposed in this paper. First, the insulation and heating structure was designed based on the thermal analysis results. Then, combining simulation and measured data, the temperature field was reconstructed in real time using a recurrent neural network algorithm. Next, considering the non-uniform heat dissipation of the system, a thermal allocation module was designed based on digital–physical integration to actively control the overall and localized heat. Finally, a heat preservation performance test platform was established to conduct cooling experiments in a small-scale cryogenic wind tunnel. The results indicated that the proposed thermal control method reduced the average cooling rate of the system by 97% and improved the overall temperature uniformity by approximately 94.23%.

Aerospace doi: 10.3390/aerospace13070575

Authors: Ryan J. Thibaudeau Stephen A. Whitmore

Graphite nozzles remain the dominant choice for small hybrid and solid rocket motors operating on laboratory and university budgets, owing to their low cost, ease of machining, and rapid turnaround during iterative design campaigns. These same programs, however, must contend with the fact that graphite erodes through coupled thermochemical and mechanical mechanisms when exposed to the oxidizing species generated by high-energy propellant combustion, and the resulting throat-area growth fundamentally alters the time histories of chamber pressure, thrust, and delivered specific impulse. This paper presents a nozzle-erosion reconstruction model that extracts the time-resolved throat area from coupled thrust and chamber-pressure measurements using the thrust coefficient relationship, scales the reconstructed area history against pre- and post-test throat measurements, identifies the onset and rate of erosion, and accounts for variable sensor lag between the thrust-stand and pressure-transducer signal chains. The model is exercised on two complementary sets of laboratory-scale GOX/ABS hybrid hot-fire data that together span roughly two orders of magnitude in total throat-area change and peak chamber pressures from 0.5 to 3.4 MPa: a controlled three-operating-point campaign conducted in support of the NASA Plume-Surface Interaction (PSI) program, and a set of higher-pressure firings from the laboratory development series in which the technique was matured. Reconstructed erosion-onset times, erosion rates, and total throat-diameter change are reported for each firing, the reconstruction accuracy is characterized as a function of erosion magnitude. A correlation of graphite erosion with chamber pressure is examined across the combined envelope. The results demonstrate the robustness of the reconstruction technique and provide a reusable framework for post-test reconstruction of transient nozzle geometry in rocket-engine ground testing.

Aerospace doi: 10.3390/aerospace13070574

Authors: Qing Liang Yingzhi Ouyang Hui Li

Accurate and consistent self-localization is essential for multi-UAV aerial missions in complex dynamic environments. However, communication constraints and heterogeneous sensor reliability variations often lead to cumulative localization errors and degraded robustness in conventional fusion frameworks. To address these challenges, this paper proposes a distributed cooperative localization framework integrating deep temporal feature learning, heterogeneous multi-sensor fusion, and consistency-aware distributed state estimation. First, an LSTM-based staged fusion strategy is designed to integrate VIO, GPS, and UWB measurements for accurate single-UAV localization. Second, a Squeeze-and-Excitation LSTM Self-Attention (SE-LSTM-SA) network is developed to adaptively recalibrate heterogeneous sensor channels and enhance temporal feature extraction under dynamic sensing conditions. Finally, a consistency-aware distributed fusion mechanism based on the Labeled Multi-Bernoulli (LMB) framework is introduced to improve inter-UAV state consistency through iterative local-neighbor information exchange. Experiments conducted on the XTDrone platform demonstrate that the proposed framework achieves superior localization accuracy compared with traditional EKF and conventional LSTM-based methods. Specifically, the proposed method achieves lower RMSE, MAE, and Maximum Prediction Error (MaxPE), while significantly improving global consistency performance. Experimental results demonstrate that the proposed framework provides accurate and consistent localization performance for multi-UAV systems in complex dynamic environments.

Aerospace doi: 10.3390/aerospace13070573

Authors: Mohammed Aleemuddin Md Amzad Hossain Adittya Barua

Human innovation has continually expanded the boundaries of knowledge, from mastering atomic science to reaching the Moon and now into the era of Industry 4.0, where artificial intelligence, the Internet, and advanced additive manufacturing turn imagination into reality. Among these achievements, hypersonic vehicles represent a pinnacle of technological advancement. Modern vehicles reach speeds exceeding Mach 27 (approximately 9300 m/s), where the air at the leading edges transforms into a chemically reactive, thermally ionized plasma. At such velocities, stagnation temperatures climb to 9000–12,000 K (8726.85–11,726.85 °C), creating one of the most extreme environments encountered by any human-made system—conditions under which conventional materials cannot survive without advanced cooling strategies. To address this challenge, researchers worldwide have developed and experimentally validated a range of thermal protection and leading-edge cooling techniques. This review presents the historical evolution of hypersonic vehicles, highlights recent advancements, examines the key challenges posed by sustained hypersonic flight, and surveys state-of-the-art cooling strategies. The discussion emphasizes methods that combine passive, active, adaptive, and hybrid approaches to protect vehicle integrity under extreme thermal loads, providing insight into the current and future capabilities of hypersonic thermal management.

Aerospace doi: 10.3390/aerospace13070572

Authors: Gulnaz Yermoldina Aliya Yskak Nurlan Suimenbayev Elmira Yermoldina

The article presents a comprehensive methodology for optimizing ground impact zones of spent rocket stages based on the integration of geoinformation analysis, remote sensing of Earth, ballistic modeling, and ecosystem sustainability assessment. An information and analytical system (IAS) has been developed and tested, providing automated selection of environmentally sustainable landing points within acceptable dispersion zones. The methodology includes the use of the NDVI, digital terrain models, soil quality assessments, fire hazard assessments, and environmental damage calculations. For the first time, a system for classifying operational-territorial units according to their level of resilience to man-made impacts has been formed. The results suggest the potential for the reduction of the dangerous impact zone under modeled conditions. The system architecture is designed to be scalable and applicable to other spaceports located in continental regions. The presented methodology contributes to the development of an environmentally oriented approach to aerospace infrastructure management.

Aerospace doi: 10.3390/aerospace13070571

Authors: Zhuoyue Peng Qiang Shen

This paper proposes an integrated attitude control framework for flexible spacecraft subject to external disturbances, rigid–flexible dynamic coupling, and actuator faults. The control framework combines the Twin Delayed Deep Deterministic Policy Gradient (TD3) reinforcement learning algorithm with an adaptive fault-tolerant (AFT) compensator. First, a rigid–flexible coupling dynamic model is formulated using Modified Rodrigues Parameters. Second, an observer-based TD3 attitude controller is designed, where a hierarchical reward function incorporating the observer-estimated flexible modal displacement η^ is constructed to train the agent for simultaneous attitude convergence and vibration suppression. Third, a composite fault-tolerant control structure is developed by integrating the trained TD3 policy with an adaptive sliding mode compensator that handles both partial loss-of-effectiveness faults and time-varying additive faults. The proposed framework is evaluated under a progressive five-scenario uncertainty evaluation framework encompassing measurement noise, parameter mismatch, external disturbances, and actuator faults. Simulation results demonstrate that (i) the η^-augmented reward enables substantial improvements in vibration suppression over the baseline reward, achieving a better balance between pointing accuracy and vibration attenuation; (ii) under the most demanding fault scenario, the AFT compensator proves essential for precise convergence, and the composite TD3+AFT architecture achieves the best overall performance among the four compared control schemes.

Aerospace doi: 10.3390/aerospace13070570

Authors: Dixing Wang Tianhe Xu Bei He Shuai Wang

Distant Retrograde Orbits (DROs) and Near-Rectilinear Halo Orbits (NRHOs), as categories of Lagrange orbits, have been selected for the construction of future deep-space navigation constellations in the Earth-Moon space due to their unique orbital trajectories and dynamical characteristics. To obtain high-precision orbit and clock solutions, the orbit determination (OD) and time synchronization (TS) performance of DRO and NRHO based on Beidou Navigation Satellite System (BDS) L-band and Ka-band signals were analyzed. Considering the constraints of onboard resources and cost, it may be infeasible to establish Ka-band links with all BDS satellites. Therefore, multiple experiments with different link configuration schemes were designed. The results show that an orbit determination accuracy of about 500 m and the time synchronization accuracy of 50 ns can be achieved using only L-band observations. In contrast, much higher accuracy can be obtained with full Ka-band links, with orbit and clock accuracy reaching 80 m and 7 ns, respectively. Moreover, higher orbit and clock accuracies can be obtained with more Ka-band links based on L-band observations. Furthermore, with the addition of the DRO-NRHO links, the orbit determination and time synchronization performance of each scheme was further improved by 15%. And the orbit determination accuracy can be better than 65 m, while the time synchronization accuracy can be better than 5 ns. Although the analysis is based on BDS signals, the proposed framework is general in nature and can be extended to other GNSS-based or future space navigation systems, providing a reference for the design of high-precision cislunar navigation and timing architectures.

Aerospace doi: 10.3390/aerospace13070569

Authors: Jiangting Yu Minghua Hu Bing Jiang Lei Yang Zheng Zhao

The efficiency of airport resource allocation is improved through the establishment of a scientific multi-granularity configuration scheme for flight slot coordination parameters. In this study, a collaborative configuration method for hourly and 15 min coordination parameters is proposed, with Beijing Capital International Airport serving as a case study. Short-term traffic clusters are frequently omitted by traditional hourly parameters, thereby leading to sudden delay surges. First, local delays were extracted from March 2024 Automatic Dependent Surveillance-Broadcast (ADS-B) trajectory data. Subsequently, a delay prediction model was constructed through the integration of a non-stationary queuing model and a gradient boosting regression tree. Second, simulated timetables were generated via a Monte Carlo method under various parameter combinations. With a constant daily flight volume utilized as the experimental baseline, a mapping relationship was established between parameter combinations and expected local delays. Finally, feasible delay regions were delineated and interpretable configuration rules were extracted via a decision tree to maximize schedule flexibility. It was indicated by the results that at an hourly parameter of 70 flights, the target delay is maintained below 8 min by tightening the 15 min parameter to 19 flights. The findings suggest that average load is controlled by hourly parameters, while traffic clustering in high-load scenarios is effectively suppressed by 15 min parameters. A quantitative reference is provided by this method for the configuration of multi-granularity time parameters at hub airports.

Aerospace doi: 10.3390/aerospace13070567

Authors: Miguel Gabriel Cebrián Gómez Konstantinos Banitsas

Helicopter operations are often underrepresented in environmental assessments due to their relatively low number of movements and the use of aggregated indicators that do not capture their localised impacts. At the same time, rotorcraft activity typically occurs at low altitude within urban environments, where noise and emissions are directly perceptible and spatially concentrated. This creates a need for assessment approaches based on observed operations and capable of providing spatially resolved results. Automatic Dependent Surveillance-Broadcast (ADS-B) data provide high-resolution observations of aircraft trajectories and are increasingly used to analyse real-world aviation activity. However, existing approaches to ADS-B data processing have largely been developed for fixed-wing operations and do not address the specific challenges of rotorcraft activity, including low-altitude signal loss, positional artefacts, and incomplete trajectories. As a result, ADS-B data for helicopters are generally not suitable for direct use in applications requiring physically consistent and operationally defined inputs. This study proposes a methodology to condition ADS-B helicopter trajectories into a physically consistent and operationally characterised dataset suitable for downstream analysis. The approach integrates trajectory correction, reconstruction of incomplete operations, and the derivation of flight modes and associated parameters. The resulting dataset provides a complete, operation-level description of helicopter activity derived from observed data. The methodology is demonstrated through its application to helicopter operations in the Zurich area and its integration with established environmental modelling approaches, including a rotorcraft-specific noise model (NORAH2) and a flight-mode-based emissions estimation method (Rindlisbacher and Chabbey). The results produce spatially resolved maps and tabulated outputs describing environmental impacts over a defined period, enabling the identification of localised hotspots. The contribution of this work lies in providing a reproducible and integrated framework that bridges the gap between raw ADS-B rotorcraft observations and application-ready datasets for spatially explicit environmental assessment.

Aerospace doi: 10.3390/aerospace13070568

Authors: Xin Wang Mingxu Lu Yi Liu Jide Qian

Efficient detection of aircraft surface defects (ASD) is a cornerstone of aviation safety. However, ASD detection is challenged by microscopic defect scales, extremely low contrast, and severe background interference. This paper proposes the Multi-Scale Discriminative Edge Enhancement Network (DEE-Net) based on an improved YOLO11. First, to mitigate feature dissipation of tiny defects, a lossless reassembly mechanism using space-to-depth convolution (SPD-Conv) is introduced, safeguarding sub-pixel topological information through space-to-depth conversion. Second, an adaptive selective edge-enhancement (ASE) module, integrating a dual-domain selection mechanism (DSM), is designed to suppress non-target redundant information on the fuselage skin. Finally, a Wise-CIoU loss function with a non-monotonic focusing mechanism is introduced to enhance localization stability under stringent IoU thresholds. Experimental results demonstrate that DEE-Net outperforms the baseline, improving mAP50 by 7.15% and mAP50-95 by 2.43%. To provide a more reliable evaluation, a 5-fold cross-validation experiment is further conducted on the original non-augmented images, and the results are reported as mean ± standard deviation. The cross-validation results provide a more conservative estimate and indicate that the proposed method achieves competitive performance across different data partitions.

Aerospace doi: 10.3390/aerospace13070566

Authors: Radimir Y. Yanev Ingo Staack

Advances in electric flight technologies have enabled distributed electric propulsion, opening a large design space for electric vertical take-off and landing (eVTOL) aircraft with diverse configurations and mission profiles. To support rapid exploration of these trade-offs, a computationally efficient sizing and performance evaluation tool has been developed. This study focuses on the verification of the key methods within the framework. The propeller sizing and performance model is verified against conventional helicopter rotors and representative eVTOL designs, while the battery discharge model is assessed using experimental data. In addition, the overall aircraft sizing is evaluated for two configurations of NASA’s Urban Air Mobility reference vehicles and compared with results obtained using NASA’s state-of-the-art rotorcraft design tool NDARC. The results show good agreement across all levels of verification. Average deviations are within 8% for propeller performance, below 5% for battery discharge, and within 4% for maximum take-off and empty mass. Mission performance and energy consumption are predicted within approximately 10%, demonstrating the suitability of the methodology for early-stage eVTOL design.

Aerospace doi: 10.3390/aerospace13070565

Authors: Shuxia Tian Shunqiang Wang Zhenmao Chen Peng Zhang Hong-En Chen Xuan Gao Shuai Liu

Two reconstruction methods for constraint and load parameters of aero-engine pipelines based on intelligent optimization algorithms are proposed in this paper. First, a simplified finite element model (FEM) of the aero-engine pipeline structure is established, and its reliability is validated by comparing simulation data with experimental data. Second, a reconstruction algorithm for spring constraint parameters and pipeline load parameters based on the improved particle swarm optimization (IPSO) algorithm is developed on the MATLAB data analysis and ANSYS simulation platforms, which completes the reconstruction calculation of parameters such as spring constraint stiffness and applied harmonic excitation. For harmonic excitation parameter reconstruction, the maximum error of this algorithm reaches 24.9%, revealing its significant inapplicability to load parameter reconstruction. To solve this problem, a load reconstruction method based on the conjugate gradient method (CGM) is further proposed to achieve accurate reconstruction of pipeline load parameters, which mitigates the large reconstruction error of the IPSO algorithm under working conditions with multiple loads. Under 5% noise interference, the maximum error of the CGM is merely 5.16%. Finally, experimental verification of harmonic excitation amplitude reconstruction is performed using the CGM with lower reconstruction errors. Experimental results indicate that the maximum error is 14.24% for harmonic excitation amplitude reconstruction, which verifies the high applicability of the conjugate gradient algorithm to load reconstruction of aero-engine pipelines.

Aerospace doi: 10.3390/aerospace13060564

Authors: Kangkang Li Haodong Sun Chao Cheng Zhongjing Ren Jianping Yuan Mengbi Wang

This paper addresses bearing-only three-dimensional target localization using three cooperative UAVs under observation inconsistency and degraded geometry. A weighted point-to-line least-squares localization model is established to fuse multiple line-of-sight (LOS) observations derived from image measurements, camera calibration, and UAV poses. To handle unreliable measurements without ground truth, a reliability assessment mechanism is developed by combining geometric stability indicators with observation consistency metrics, enabling weak geometry and abnormal observations to be identified online. Based on this assessment, an adaptive optimization framework is introduced to perform residual-driven adaptive weighting and configuration optimization, thereby suppressing unreliable LOS measurements and improving the conditioning of cooperative geometry. Simulation results under four representative scenarios show that the proposed method consistently improves localization accuracy and robustness. The mean localization error is reduced from 0.545 m to 0.260 m under abnormal observations, from 0.355 m to 0.081 m under degraded geometry, and from 0.711 m to 0.280 m when both effects occur simultaneously. Statistical evaluations including RMSE, standard deviation, maximum error, confidence intervals, and box-plot analysis further demonstrate that the proposed framework effectively reduces error dispersion and improves robustness.

Aerospace doi: 10.3390/aerospace13060563

Authors: Khaing Phyo Zaw Sergey Vladislavovich Baranovski

Lightweight composite aircraft wing design increasingly depends on combining multidisciplinary design optimization (MDO), aeroelastic tailoring, and stacking sequence optimization. However, an overview of these interconnected fields is lacking. This study applies a PRISMA-ScR-based scoping review of 54 selected articles to map current approaches, identify emerging trends, and highlight remaining gaps. Key findings indicate six MDO architectures—with hybrid methods being increasingly preferred—and demonstrate that aeroelastic tailoring (e.g., ply angle manipulation) enhances performance while reducing weight. Manufacturing constraints (ply continuity, blending, symmetry) are addressed in a subset of the reviewed literature, with opportunities for broader integration. Critical future priorities include integrating manufacturing process models into MDO and incorporating durability considerations (fatigue, impact). This work synthesizes current approaches, identifies emerging trends, and provides a roadmap for the development of next-generation lightweight, high-performance composite wings.

Aerospace doi: 10.3390/aerospace13060562

Authors: Kunze Du Tianrun Wang Ji Chen Bin Liu Meilian Liu Haisheng Li Nan Li

High-fidelity computational fluid dynamics (CFD) remains computationally expensive for steady aerodynamic prediction under multi-condition and variable-geometry configurations, which limits rapid design iteration. To address this issue, this study proposes a data-driven surrogate framework for aircraft surface flow-field prediction on irregular meshes. The framework combines a geometry-unification strategy for variable rudder-deflection configurations with KM-GAT, a hybrid neural architecture that integrates graph attention and KAN-based nonlinear feature transformation. Geometry unification maps the surface flow fields associated with different rudder-deflection states onto a common zero-deflection reference template, thereby establishing consistent mesh correspondence and fixed prediction locations across samples while retaining the rudder angle as an operating-condition variable. The KM-GAT model further combines topology-aware message passing with localized nonlinear refinement, while the Huber loss is adopted to improve training robustness for CFD-derived data. Experiments on the F-22 research model show that the proposed framework achieves lower prediction errors and more concentrated error distributions than baseline MLP and GNN-based models. Qualitative comparisons further indicate that KM-GAT better preserves localized high-gradient structures, including pressure transitions and vortex-dominated regions. These results suggest that the proposed framework provides an effective surrogate modeling strategy for variable-geometry aerodynamic flow field prediction.

Aerospace doi: 10.3390/aerospace13060561

Authors: Lixin Li Jia Wang Lizhang Zhang Chengwei Fei Jiaqiang Li Bing Wang

The fatigue life of additively manufactured GH4169 components is strongly affected by internal defects, stress concentration, and life scatter, making reliable structural assessment difficult. In this study, a probability-based fatigue life prediction framework was developed by extending the conventional surface weakest link concept to a volume-defect weakest link formulation. Fatigue tests of smooth specimens with different build orientations were first conducted to establish baseline probabilistic fatigue relationships, and both log-normal and two-parameter Weibull distributions were considered. The proposed framework was then applied to a feature specimen representing the critical region of an aero-engine exhaust frame by combining the baseline fatigue statistics with element-wise maximum principal stress and volume information extracted from finite element analysis. The results show that the log-normal distribution provided a more stable statistical description of the smooth-specimen fatigue data than the Weibull distribution. For the feature specimens tested at 11,200 N, the measured fatigue lives ranged from 25,585 to 61,989 cycles. Compared with the conventional local stress method, the weakest link framework gave a more reasonable description of the structural fatigue life distribution, and the log-normal weakest link model showed the best overall agreement with the experimental results.

Aerospace doi: 10.3390/aerospace13060560

Authors: Hao Jiang Weili Zeng Hainuo Zhou Yannan Lu Yuheng Chen Wenbin Wei

Runway systems serve as the critical interface between airports and terminal airspace, and their efficient operation is essential for balancing air traffic demand and airport capacity. With the continuous growth of air traffic, intelligent runway demand and capacity management has become increasingly important for mitigating congestion and delays. This paper presents a comprehensive review of runway capacity–demand management from both supply-side and demand-side perspectives. On the supply side, runway configuration selection is reviewed, including runway configuration capacity envelopes, influencing factors, and existing optimization methodologies, such as prescriptive models, descriptive models, and reinforcement learning approaches. On the demand side, flight runway sequencing for arrivals, departures, and integrated arrival–departure operations is systematically analyzed. Problem analogies, operational characteristics, optimization objectives, and solution algorithms are discussed in detail. A critical comparison of existing methodologies is conducted from the perspectives of solution quality, real-time capability, human interpretability, technology readiness, trust requirements, and human–AI collaboration. Finally, future research directions are identified, including integrated runway management, multi-airport coordination, uncertainty-aware optimization, human–AI decision support, AI-enabled runway management, and integrated manned–unmanned operations. The review provides a reference for researchers, airport operators, air navigation service providers, and decision-support system developers seeking to improve runway operational efficiency and safety.

Aerospace doi: 10.3390/aerospace13060559

Authors: Donghee Lee Donggeun Lee Sungwoo Park Jungpyo Lee Heejang Moon

This study presents the preliminary development of a clustered hybrid propulsion module, and its experimental validation from static motor characterization to dynamic 1-D vertical drop tests to assess the feasibility of a hybrid propulsion system for soft-landing applications. The research progresses from preliminary design of core components (such as fuel, oxidizer supply system, engine configuration), to the performance verification of the clustering module. First, the trade-off between high regression rates and mechanical integrity was evaluated for paraffin-based fuels. However, high-density polyethylene (HDPE) was utilized as the baseline to ensure predictable combustion behavior. Second, cold flow tests of the designed multi-port manifold demonstrated a highly uniform oxidizer distribution, validating the geometric design with a maximum spatial pressure deviation of 2.44% across the four engines. Third, static fire tests confirmed robust dynamic control capabilities, successfully throttling the average chamber pressure from 100% (7.00 bar) down to 43% (3.01 bar) and back to 100% (7.01 bar) with a transient response time of approximately 0.6 s. Finally, the 1-D vertical drop test validated the operational readiness of the system; the open-loop thrust modulation successfully counteracted the module’s dynamic weight, achieving a terminal descent velocity of 1.46 m/s, which strictly satisfies planetary soft-landing safety criteria. These results demonstrate the feasibility and performance of clustered hybrid propulsion systems for planetary exploration, extending to surface launch technology for sample return missions from the Moon and Mars, and precision booster recovery for small launch vehicles.

Aerospace doi: 10.3390/aerospace13060558

Authors: Mario Román Rodríguez Cristian Builes Cárdenas Elena Rodríguez Senín Adrián López González

Graphene is a novel material that can bring several advantages in the composite materials manufacturing field, such as improved electrical and thermal properties, and high performance. In particular, functionalizing current composite materials can bring advantages in the aerospace field in thermal management for electric aircraft engines. This paper studies the addition of graphene particles into carbon fiber composites manufactured by the Resin Transfer Molding Process (RTM). Thermal and mechanical properties are evaluated and compared with a conventional composite laminate. Major improvements were achieved on the thermal behavior of the composite material while maintaining general properties, but in particular, the addition of graphene had a negative impact on transverse tensile and mode II fracture toughness due to agglomerates present in the fiber–resin interface.

Aerospace doi: 10.3390/aerospace13060557

Authors: Jose Bernardo Padaca Leif Oliver Coronado Ulysses Ante Hannah Ramos Roider Pugal Arvin Oliver Ng Renzo Wee Marc Caesar Talampas Prince William Lim

This study investigates the application of advanced metal additive manufacturing (AM) and topology optimization for the development of a structurally efficient and lightweight 3U nanosatellite frame. Payload weight is a critical factor in space mission costs; therefore, a stock 3U CubeSat design was subjected to structural optimization using specialized Generative Design Software. The optimized model was fabricated using Powder Bed Fusion—Direct Metal Laser Sintering (PBF-DMLS) on an EOS M290 metal printer with AlSi10Mg aluminum alloy. While AlSi10Mg differs in ultimate tensile strength from traditional wrought aerospace alloys, it was selected to evaluate the baseline feasibility of this application. To evaluate manufacturability and preliminary performance, Finite Element Analysis (FEA), including structural and modal response analyses, was conducted. While the optimized design successfully achieved a 53% mass reduction (from 333 g to 155 g) and met the 30 Hz minimum fundamental frequency requirement, static analysis indicated a maximum simulated stress of 287 MPa. Because this exceeds the material’s nominal yield strength of 220 MPa, localized plastic deformation is predicted in the bare-frame configuration under maximum launch loads. This necessitates further design iterations and full-assembly simulations, incorporating the load-sharing effects of integrated panels prior to physical qualification. Post-processing successfully met JAXA dimensional and surface roughness requirements. Ultimately, this study serves as a foundational manufacturability baseline, demonstrating the applicability of PBF-DMLS for nanosatellites.

Aerospace doi: 10.3390/aerospace13060556

Authors: Xin Wang Yiran Tao Guanqiao Huang Zhongyu Wang Feimeng Diao Feng Gu

The performance of the aircraft anti-skid braking system is critical to the ground operational safety of an aircraft. Conventional Pressure Bias Modulation (PBM) can suffer from deep skidding under low runway friction coefficients or low aircraft speeds. To address these issues, a composite control strategy based on Gaussian Quantum Particle Swarm Optimization (GQPSO) is proposed. This strategy employs the GQPSO algorithm for offline Proportional–Integral–Derivative (PID) parameter optimization, followed by real-time adaptive scheduling through a lookup table to accommodate varying speed domains and runway conditions. Simultaneously, by integrating the main-wheel dynamics model and friction characteristics, a runway identification function based on a Back Propagation Neural Network (BPNN) is designed to provide runway status information. The stability of the controller is verified via phase-plane analysis and Monte Carlo simulation. Subsequently, comparative Hardware-in-the-Loop (HIL) tests are conducted among PBM, PSO-PID, and the proposed GQPSO-PID controller under various runway conditions. The experimental results demonstrate that this composite controller can adapt to different speed domains and runway conditions, stably track the target slip ratio, effectively suppress skidding, and significantly improve braking efficiency, as well as exhibiting excellent robustness and control performance.