Aerospace

17 pages, 6868 KiB

Open AccessArticle

Development of a Throttleable 6 kN H₂O₂/Butyl Alcohol Rocket Engine

by Zbigniew Gut, Adrian Parzybut and David Perigo

Aerospace 2025, 12(7), 617; https://doi.org/10.3390/aerospace12070617 - 8 Jul 2025

The increasing demand for versatile and sustainable propulsion systems has intensified research into green propellants and advanced thrust modulation technologies. This study presents the development and testing of a throttleable rocket engine utilizing 98% hydrogen peroxide by mass as the oxidizer and butyl [...] Read more.

The increasing demand for versatile and sustainable propulsion systems has intensified research into green propellants and advanced thrust modulation technologies. This study presents the development and testing of a throttleable rocket engine utilizing 98% hydrogen peroxide by mass as the oxidizer and butyl alcohol (as isomers n-butanol) as the fuel. Combining the environmental benefits of green propellants with variable thrust capabilities, the system addresses the challenges of modern space missions. Butyl alcohol was selected for its low toxicity, safety, storability, and favorable combustion performance, making it a strong candidate for future applications. The engine was designed to deliver a nominal thrust of 6 kN with the capability to throttle down to 1.2 kN. Experiments investigated the effects of pintle injector positions, supply pressures, and combustion chamber parameters on performance. Results demonstrated stable and efficient combustion across a wide operating range, highlighting the critical role of injector design and chamber geometry in ensuring consistent thrust and combustion efficiency. This research validates the potential of hydrogen peroxide and butyl alcohol as a sustainable propellant pair, particularly for planetary landers requiring precise thrust modulation for controlled descent. It marks a significant step in advancing sustainable propulsion technologies, contributing to the future of planetary exploration and interplanetary mission capabilities. Full article

(This article belongs to the Special Issue Green Propellants for In-Space Propulsion)

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31 pages, 5571 KiB

Open AccessArticle

Resolving Non-Proportional Frequency Components in Rotating Machinery Signals Using Local Entropy Selection Scaling–Reassigning Chirplet Transform

by Dapeng Quan, Yuli Niu, Zeming Zhao, Caiting He, Xiaoze Yang, Mingyang Li, Tianyang Wang, Lili Zhang, Limei Ma, Yong Zhao and Hongtao Wu

Aerospace 2025, 12(7), 616; https://doi.org/10.3390/aerospace12070616 - 8 Jul 2025

Abstract

Under complex operating conditions, vibration signals from rotating machinery often exhibit non-stationary characteristics with non-proportional and closely spaced instantaneous frequency (IF) components. Traditional time–frequency analysis (TFA) methods struggle to accurately extract such features due to energy leakage and component mixing. In response to [...] Read more.

Under complex operating conditions, vibration signals from rotating machinery often exhibit non-stationary characteristics with non-proportional and closely spaced instantaneous frequency (IF) components. Traditional time–frequency analysis (TFA) methods struggle to accurately extract such features due to energy leakage and component mixing. In response to these issues, an enhanced time–frequency analysis approach, termed Local Entropy Selection Scaling–Reassigning Chirplet Transform (LESSRCT), has been developed to improve the representation accuracy for complex non-stationary signals. This approach constructs multi-channel time–frequency representations (TFRs) by introducing multiple scales of chirp rates (CRs) and utilizes a Rényi entropy-based criterion to adaptively select multiple optimal CRs at the same time center, enabling accurate characterization of multiple fundamental components. In addition, a frequency reassignment mechanism is incorporated to enhance energy concentration and suppress spectral diffusion. Extensive validation was conducted on a representative synthetic signal and three categories of real-world data—bat echolocation, inner race bearing faults, and wind turbine gearbox vibrations. In each case, the proposed LESSRCT method was compared against SBCT, GLCT, CWT, SET, EMCT, and STFT. On the synthetic signal, LESSRCT achieved the lowest Rényi entropy of 13.53, which was 19.5% lower than that of SET (16.87) and 35% lower than GLCT (18.36). In the bat signal analysis, LESSRCT reached an entropy of 11.53, substantially outperforming CWT (19.91) and SBCT (15.64). For bearing fault diagnosis signals, LESSRCT consistently achieved lower entropy across varying SNR levels compared to all baseline methods, demonstrating strong noise resilience and robustness. The final case on wind turbine signals demonstrated its robustness and computational efficiency, with a runtime of 1.31 s and excellent resolution. These results confirm that LESSRCT delivers robust, high-resolution TFRs with strong noise resilience and broad applicability. It holds strong potential for precise fault detection and condition monitoring in domains such as aerospace and renewable energy systems. Full article

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20 pages, 5690 KiB

Open AccessArticle

Wind Tunnel Experimental Study on the Flight Parameters of a Bio-Inspired Bat-like Flapping-Wing Robot

by Bosong Duan, Junlei Liu, Shuai Wang, Zhaoyang Chen and Bingfeng Ju

Aerospace 2025, 12(7), 615; https://doi.org/10.3390/aerospace12070615 - 8 Jul 2025

Abstract

With the in-depth study of the unique flight ability of bats in the field of bionic robots, wind-tunnel experiments have become an important means to verify the feasibility of bat-like flying robot structures. However, due to the complex structure of a bat’s flexible [...] Read more.

With the in-depth study of the unique flight ability of bats in the field of bionic robots, wind-tunnel experiments have become an important means to verify the feasibility of bat-like flying robot structures. However, due to the complex structure of a bat’s flexible wing membrane and multi-joint linkage, there is still a significant gap in the systematic experimental study of its flightability. In this study, a remote-controlled bionic prototype was designed and manufactured for the bat-like flapping-wing flying robot, and the changes in wing flight performance at different flapping frequencies (1–3.5 Hz) and angles of attack (0–15°) were tested in a low-speed (2–6 m/s) wind tunnel experiment. Six flight parameters were obtained through experiments. It was found that the flight performance of the prototype was successfully verified under a specific flapping frequency, angle of attack, and flight speed. This result not only determines the optimal flight parameter combination under the model, but also reveals the key influence of the flexible deformation of the wing membrane and the flapping frequency on the flight performance, which provides a key experimental basis for the structural optimization and control strategy design of the bat-like flapping-wing robot. Full article

(This article belongs to the Section Aeronautics)

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22 pages, 4871 KiB

Open AccessArticle

Multi-Objective Optimization Method for Multi-Module Micro–Nano Satellite Components Assignment and Layout

by Hao Zhang, Jun Zhou and Guanghui Liu

Aerospace 2025, 12(7), 614; https://doi.org/10.3390/aerospace12070614 - 8 Jul 2025

Abstract

The assembly optimization design of satellite components is a crucial element in the overall design of satellites. In this paper, a novel three-dimensional assembly optimization design problem (3D-AODP) for multi-module micro–nano satellite components is proposed according to the engineering requirements, aiming at optimizing [...] Read more.

The assembly optimization design of satellite components is a crucial element in the overall design of satellites. In this paper, a novel three-dimensional assembly optimization design problem (3D-AODP) for multi-module micro–nano satellite components is proposed according to the engineering requirements, aiming at optimizing the satellite mass characteristics, and taking into account constraints such as space interference, space occupation and special location. Multi-module micro–nano satellites are a new type of satellite configuration based on the assembly of multiple U-shaped cube units. The 3D-AODP of its components is a challenging two-layer composite optimization task involving discrete variable optimization of component allocation and continuous variable optimization of component layout, which interact with each other. To solve the problem, a hybrid assembly optimization method based on tabu search (TS) and multi-objective differential evolutionary (MODE) algorithms is proposed, in which the assignment problem of the components is converted into a domain search problem by the TS algorithm. The space interference constraints and space occupancy constraints of the components are considered, and an assignment scheme with the minimum mass difference is obtained. On this basis, a bi-objective differential evolutionary algorithm is used to develop the layout optimization problem for the components, which takes into account the spatial non-interference constraints and special location constraints of the components, and obtains the Pareto solution set of the assembly scheme under the optimal mass characteristics (moment of inertia and product of inertia). Finally, the feasibility and effectiveness of the proposed method is demonstrated by an engineering case. Full article

(This article belongs to the Section Astronautics & Space Science)

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19 pages, 3118 KiB

Open AccessArticle

A Stackelberg Game Approach to Model Reference Adaptive Control for Spacecraft Pursuit–Evasion

by Gena Gan, Ming Chu, Huayu Zhang and Shaoqi Lin

Aerospace 2025, 12(7), 613; https://doi.org/10.3390/aerospace12070613 - 7 Jul 2025

Abstract

A Stackelberg equilibrium–based Model Reference Adaptive Control (MSE) method is proposed for spacecraft Pursuit–Evasion (PE) games with incomplete information and sequential decision making under a non–zero–sum framework. First, the spacecraft PE dynamics under

J_{2}

perturbation are mapped to a dynamic Stackelberg game [...] Read more.

A Stackelberg equilibrium–based Model Reference Adaptive Control (MSE) method is proposed for spacecraft Pursuit–Evasion (PE) games with incomplete information and sequential decision making under a non–zero–sum framework. First, the spacecraft PE dynamics under

J_{2}

perturbation are mapped to a dynamic Stackelberg game model. Next, the Riccati equation solves the equilibrium problem, deriving the evader’s optimal control strategy. Finally, a model reference adaptive algorithm enables the pursuer to dynamically adjust its control gains. Simulations show that the MSE strategy outperforms Nash Equilibrium (NE) and Single–step Prediction Stackelberg Equilibrium (SSE) methods, achieving 25.46% faster convergence than SSE and 39.11% lower computational cost than NE. Full article

(This article belongs to the Section Astronautics & Space Science)

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13 pages, 2285 KiB

Open AccessArticle

STHFD: Spatial–Temporal Hypergraph-Based Model for Aero-Engine Bearing Fault Diagnosis

by Panfeng Bao, Wenjun Yi, Yue Zhu, Yufeng Shen and Boon Xian Chai

Aerospace 2025, 12(7), 612; https://doi.org/10.3390/aerospace12070612 - 7 Jul 2025

Abstract

Accurate fault diagnosis in aerospace transmission systems is essential for ensuring equipment reliability and operational safety, especially for aero-engine bearings. However, current approaches relying on Convolutional Neural Networks (CNNs) for Euclidean data and Graph Convolutional Networks (GCNs) for non-Euclidean structures struggle to simultaneously [...] Read more.

Accurate fault diagnosis in aerospace transmission systems is essential for ensuring equipment reliability and operational safety, especially for aero-engine bearings. However, current approaches relying on Convolutional Neural Networks (CNNs) for Euclidean data and Graph Convolutional Networks (GCNs) for non-Euclidean structures struggle to simultaneously capture heterogeneous data properties and complex spatio-temporal dependencies. To address these limitations, we propose a novel Spatial–Temporal Hypergraph Fault Diagnosis framework (STHFD). Unlike conventional graphs that model pairwise relations, STHFD employs hypergraphs to represent high-order spatial–temporal correlations more effectively. Specifically, it constructs distinct spatial and temporal hyperedges to capture multi-scale relationships among fault signals. A type-aware hypergraph learning strategy is then applied to encode these correlations into discriminative embeddings. Extensive experiments on aerospace fault datasets demonstrate that STHFD achieves superior classification performance compared to state-of-the-art diagnostic models, highlighting its potential for enhancing intelligent fault detection in complex aerospace systems. Full article

(This article belongs to the Special Issue Challenges and Recent Advances in Model-Based Engineering for Aerospace)

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27 pages, 20103 KiB

Open AccessArticle

Dynamics and Staged Deployment Strategy for a Spinning Tethered Satellite System

by Yue Zhang, Kai Chen, Jiawen Guo and Cheng Wei

Aerospace 2025, 12(7), 611; https://doi.org/10.3390/aerospace12070611 - 7 Jul 2025

Abstract

This paper investigates flexible multibody dynamic modeling and a staged deployment strategy for large-scale spinning tethered satellite systems, targeting deployment instability, inefficiencies, and tension-induced fracture risks. A nonlinear flexible multibody model is constructed using the absolute nodal coordinate formulation within an arbitrary Lagrangian–Eulerian [...] Read more.

This paper investigates flexible multibody dynamic modeling and a staged deployment strategy for large-scale spinning tethered satellite systems, targeting deployment instability, inefficiencies, and tension-induced fracture risks. A nonlinear flexible multibody model is constructed using the absolute nodal coordinate formulation within an arbitrary Lagrangian–Eulerian framework, enabling accurate large-deformation modeling of the tether with geometric nonlinearity. This model surpasses traditional massless/rigid rod models by integrating tether mass distribution, flexible dynamics, and satellite attitude dynamics. A two-stage deployment strategy is proposed based on tether safe tension thresholds. Stage 1 optimizes deployment velocity to eliminate libration angles, ensuring stability while maintaining deployment efficiency. Stage 2 employs dynamic angular velocity tracking and torque compensation to reduce tether tension, prioritizing deployment safety. Numerical simulations validate the model’s accuracy and the strategy’s effectiveness, showing significant tension reduction compared to the single-stage strategy and suppressing libration angle oscillations within ±0.5°. The impact of space environmental forces on deployment stability across different orientations is analyzed, highlighting the necessity of force compensation for parallel-to-ground configurations. This research integrates dynamics and control, providing a practical solution for safe and efficient deployment of the spinning tethered satellite system. Full article

(This article belongs to the Section Astronautics & Space Science)

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23 pages, 4068 KiB

Open AccessArticle

Linear Gauss Pseudospectral Method Using Neighboring Extremal for Nonlinear Optimal Control Problems

by Tianyou Zhang, Wanchun Chen and Liang Yang

Aerospace 2025, 12(7), 610; https://doi.org/10.3390/aerospace12070610 - 6 Jul 2025

Viewed by 1

Abstract

This article proposes a method to solve nonlinear optimal control problems with arbitrary performance indices and terminal constraints, which is based on the neighboring extremal method and Gauss pseudospectral collocation. Firstly, a quadratic performance index is formulated, which minimizes the second-order variation of [...] Read more.

This article proposes a method to solve nonlinear optimal control problems with arbitrary performance indices and terminal constraints, which is based on the neighboring extremal method and Gauss pseudospectral collocation. Firstly, a quadratic performance index is formulated, which minimizes the second-order variation of the nonlinear performance index and fully considers the deviations in initial states and terminal constraints. Secondly, the first-order necessary conditions are applied to derive the perturbation differential equations involving deviations in state and costate variables. Therefore, a quadratic optimal control problem is formulated, which is subject to such perturbation differential equations. Thirdly, the Gauss pseudospectral collocation is used to transform the differential and integral operators into algebraic operations. Therefore, an analytical solution of the control correction can be successfully derived in the polynomial space, which comes close to the optimal solution. This method has a fast computation speed and low computational complexity due to the discretization at orthogonal points, making it suitable for online applications. Finally, some simulations and comparisons with the optimal solution and other typical methods have been carried out to evaluate the performance of the method. Results show that it not only performs well in computational efficiency and accuracy but also has great adaptability and optimality. Moreover, Monte Carlo simulations have been conducted. The results demonstrate that it has strong robustness and excellent performance even in highly dispersed environments. Full article

(This article belongs to the Section Astronautics & Space Science)

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13 pages, 3096 KiB

Open AccessArticle

Towards Accountability: A Primer on the Space Debris Problem and an Overview of the Legal Issues Surrounding It

by William Schonberg

Aerospace 2025, 12(7), 609; https://doi.org/10.3390/aerospace12070609 - 6 Jul 2025

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Abstract

Since 1957, the near-Earth population of trackable space objects has grown in number to over 36,000. Of these 36,000+ trackable objects now in low Earth orbit, just a few thousand are working spacecraft. The rest are Earth-orbiting objects which are no longer operational [...] Read more.

Since 1957, the near-Earth population of trackable space objects has grown in number to over 36,000. Of these 36,000+ trackable objects now in low Earth orbit, just a few thousand are working spacecraft. The rest are Earth-orbiting objects which are no longer operational and are considered to be space junk. Because this junk can no longer receive maneuvering commands from its Earth-based owners, the survivability of other spacecraft traveling through or operating in Earth orbit can be jeopardized by the impacts of any number of pieces of this space junk, whose origins can usually be traced back to defunct satellites. As a result, a major design parameter for Earth-orbiting spacecraft is the possibility of such high-speed impacts and the damage they can cause. Furthermore, several private companies are now launching several thousand spacecraft into Earth orbit, many of which are satellites built for communication purposes. Other satellites have been launched to expand the reach of the World Wide Web and to provide better tools for disaster management. Two questions quickly become evident, namely, what is the beneficial purpose of these large satellite constellations, and what are some of the deleterious consequences of their proliferation? Numerous topics related to space debris will be discussed in this paper, including issues in space law that concern the growing problem of orbital debris. In the end, several areas of concern will be noted that are vital to the continuing presence of humans in near-Earth space and must be addressed as the near-Earth orbital environment becomes more congested and space traffic management becomes more difficult. Full article

(This article belongs to the Special Issue Development of Novel Orbital Debris Protection Systems)

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22 pages, 11772 KiB

Open AccessArticle

Effect of Slide Valve Gap Surface Roughness on Particle Transport Properties

by Jin Zhang, Ranheng Du, Pengpeng Dong, Kuohang Zhang, Shengrong Wang, Ying Li and Kuo Zhang

Aerospace 2025, 12(7), 608; https://doi.org/10.3390/aerospace12070608 - 5 Jul 2025

Abstract

Fuel electro-hydraulic servo valves are core components in the fuel control system of aero-engines, and their performance directly affects thrust regulation and power output precision. Due to the combustibility of the working medium in fuel systems and the lack of effective circulation filtration, [...] Read more.

Fuel electro-hydraulic servo valves are core components in the fuel control system of aero-engines, and their performance directly affects thrust regulation and power output precision. Due to the combustibility of the working medium in fuel systems and the lack of effective circulation filtration, the retention of micron-sized particles within the valve gap can lead to valve spool jamming, which is a critical reliability issue. This study, based on fractal theory and the liquid–solid two-phase flow model, proposes a parametric model for non-ideal surface valve gaps and analyzes the dynamics of particles subjected to drag, lift, and buoyant forces on rough surfaces. By numerically analyzing flow field models with different roughness levels and comparing them with an ideal smooth gap model, the migration characteristics of particles were studied. To verify the accuracy of the model, an upscaled experimental setup was built based on similarity theory, and PIV experiments were conducted for validation. Experimental results show that the particle release position and valve surface roughness significantly affect particle migration time. The weight of the release position on particle migration time is 63%, while the impact of valve surface roughness is 37%. In models with different roughness levels, the particle migration time increases more rapidly for roughness values greater than Ra0.4, while for values less than Ra0.4, the increase in migration time is slower. Furthermore, the study reveals that particle migration trajectories are independent of flow velocity, with velocity only affecting particle migration time. This research provides theoretical support for enhancing the reliability of fuel electro-hydraulic servo valves and offers a new perspective for the design of highly reliable hydraulic components. Full article

(This article belongs to the Section Aeronautics)

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28 pages, 3174 KiB

Open AccessArticle

Enhancing Fault Detection and Isolation in All-Electric Auxiliary Power Unit (APU) Gas Generator by Utilizing Starter/Generator Signal

by Haotian Mao, Khashayar Khorasani and Yingqing Guo

Aerospace 2025, 12(7), 607; https://doi.org/10.3390/aerospace12070607 - 4 Jul 2025

Abstract

This study proposes a novel paradigm for enhancing the fault detection and isolation (FDI) of gas generators in all-electric auxiliary power unit (APU) by utilizing shaft power information from the starter/generator. First, we conduct an investigation into the challenges and opportunities for FDI [...] Read more.

This study proposes a novel paradigm for enhancing the fault detection and isolation (FDI) of gas generators in all-electric auxiliary power unit (APU) by utilizing shaft power information from the starter/generator. First, we conduct an investigation into the challenges and opportunities for FDI that are brought about by APU electrification. Our analysis reveals that the electrification of APUs opens new possibilities for utilizing shaft power estimates from starters/generators to improve gas generator FDI. We then provide comprehensive theoretical and analytical evidence demonstrating why, how, and to what extent the shaft power information from the starter/generator can fundamentally enhance the estimation accuracy of system states and health parameters of the gas generator, while also identifying key factors influencing these improvements in FDI performance. The effectiveness of the proposed paradigm and its theoretical foundations are validated through extensive Monte Carlo simulation runs. The research findings provide a unique perspective in addressing three fundamental questions—why joint fault diagnosis of the starter/generator and gas generator in all-electric APUs is essential, how it can be implemented, and what factors determine its effectiveness—thereby opening up promising new avenues for FDI technologies in all-electric APU systems. Full article

(This article belongs to the Section Aeronautics)

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19 pages, 598 KiB

Open AccessArticle

Trajectory Planning and Optimisation for Following Drone to Rendezvous Leading Drone by State Estimation with Adaptive Time Horizon

by Javier Lee Hongrui and Sutthiphong Srigrarom

Aerospace 2025, 12(7), 606; https://doi.org/10.3390/aerospace12070606 - 4 Jul 2025

Abstract

With the increased proliferation of drone use for many purposes, counter drone technology has become crucial. This rapid expansion has inherently introduced significant opportunities and applications. This creates applications such as aerial surveillance, delivery services, agriculture monitoring, and, most importantly, security operations. Due [...] Read more.

With the increased proliferation of drone use for many purposes, counter drone technology has become crucial. This rapid expansion has inherently introduced significant opportunities and applications. This creates applications such as aerial surveillance, delivery services, agriculture monitoring, and, most importantly, security operations. Due to the relative simplicity of learning and operating a small-scale UAV, malicious organizations can field and use UAVs (drones) to form substantial threats. Their interception may then be hindered by evasive manoeuvres performed by the malicious UAV (mUAV). Novice operators may also unintentionally fly UAVs into restricted airspace such as civilian airports, posing a hazard to other air operations. This paper explores predictive trajectory code and methods for the neutralisation of mUAVs by following drones, using state estimation techniques such as the extended Kalman filter (EKF) and particle filter (PF). Interception strategies and optimization techniques are analysed to improve interception efficiency and robustness. The novelty introduced by this paper is the implementation of adaptive time horizon (ATH) and velocity control (VC) in the predictive process. Simulations in MATLAB were used to evaluate the effectiveness of trajectory prediction models and interception strategies against evasive manoeuvres. The tests discussed in this paper then demonstrated the following: the EKF predictive method achieved a significantly higher neutralisation rate (41%) compared to the PF method (30%) in linear trajectory scenarios, and a similar neutralisation rate of 5% in stochastic trajectory scenarios. Later, after incorporating adaptive time horizon (ATH) and 20 velocity control (VC) measures, the EKF method achieved a 98% neutralization rate, demonstrating significant improvement in performance. Full article

(This article belongs to the Special Issue Advances in UAV Technology: Dynamics, Guidance, Navigation, and Control of Transformative Aerial Vehicles)

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23 pages, 769 KiB

Open AccessArticle

Enhancing Urban Air Mobility Scheduling Through Declarative Reasoning and Stakeholder Modeling

by Jeongseok Kim and Kangjin Kim

Aerospace 2025, 12(7), 605; https://doi.org/10.3390/aerospace12070605 - 3 Jul 2025

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Abstract

The goal of this paper is to optimize mission schedules for vertical airports (vertiports in short) to satisfy the different needs of stakeholders. We model the problem as a resource-constrained project scheduling problem (RCPSP) to obtain the best resource allocation and schedule. As [...] Read more.

The goal of this paper is to optimize mission schedules for vertical airports (vertiports in short) to satisfy the different needs of stakeholders. We model the problem as a resource-constrained project scheduling problem (RCPSP) to obtain the best resource allocation and schedule. As a new approach to solving the RCPSP, we propose answer set programming (ASP). This is in contrast to the existing research using MILP as a solution to the RCPSP. Our approach can take complex scheduling restrictions and stakeholder-specific requirements. In addition, we formalize and include stakeholder needs using a knowledge representation and reasoning framework. Our experiments show that the proposed method can generate practical schedules that reflect what stakeholders actually need. In particular, we show that our approach can compute optimal schedules more efficiently and flexibly than previous approaches. We believe that this approach is suitable for the dynamic and complex environments of vertiports. Full article

(This article belongs to the Special Issue Next-Generation Airport Operations and Management)

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28 pages, 3444 KiB

Open AccessReview

A Review on Liquid Pulsed Laser Propulsion

by Sai Li, Baosheng Du, Qianqian Cui, Jifei Ye, Haichao Cui, Heyan Gao, Ying Wang, Yongzan Zheng and Jianhui Han

Aerospace 2025, 12(7), 604; https://doi.org/10.3390/aerospace12070604 - 2 Jul 2025

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Abstract

Laser propulsion is a new conceptual technology that drives spacecraft and possesses advantages such as high specific impulse, large payload ratio, and low launch cost. It has potential applications in diverse areas, such as space debris mitigation and removal, microsatellite attitude control, and [...] Read more.

Laser propulsion is a new conceptual technology that drives spacecraft and possesses advantages such as high specific impulse, large payload ratio, and low launch cost. It has potential applications in diverse areas, such as space debris mitigation and removal, microsatellite attitude control, and orbital maneuvering. Liquid pulse laser propulsion has notable advantages among the various laser propulsion systems. We review the concept and the theory of liquid laser propulsion. Then, we categorize the current state of research based on three types of propellants—non-energetic liquids, energetic liquids, and liquid metals—and provide an analysis of the propulsion characteristics arising from the laser ablation of liquids such as water, glycidyl azide polymer (GAP), hydroxylammonium nitrate (HAN), and ammonium dinitramide (ADN). We also discuss future research directions and challenges of pulsed liquid laser propulsion. Although experiments have yielded encouraging outcomes due to the distinctive properties of liquid propellants, continued investigation is essential to ensure that this technology performs reliably in actual aerospace applications. Consistent results under both spatial and ground conditions remain a key research content for fully realizing its potential. Full article

(This article belongs to the Special Issue Laser Propulsion Science and Technology (2nd Edition))

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15 pages, 1458 KiB

Open AccessArticle

Independence Requirement Analysis for Common-Mode Analysis of Aircraft System Safety Based on AADL

by Hongze Ruan, Fan Qi, Xiaohui Wei, Yadong Zhou and Zhong Lu

Aerospace 2025, 12(7), 603; https://doi.org/10.3390/aerospace12070603 - 1 Jul 2025

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Abstract

Common-mode analysis (CMA) is a qualitative analytical method used to support the evaluation of independence in the system safety assessment of civil aircraft. In traditional CMA, independence requirements are usually identified by evaluating the combination of events using the fault tree AND-gates. This [...] Read more.

Common-mode analysis (CMA) is a qualitative analytical method used to support the evaluation of independence in the system safety assessment of civil aircraft. In traditional CMA, independence requirements are usually identified by evaluating the combination of events using the fault tree AND-gates. This approach is cumbersome and highly dependent on the skills and experiences of system safety engineers. An Architecture Analysis and Design Language (AADL)-based methodology is proposed to derive independence requirements for CMA. Error propagation data in AADL is extracted to develop a fault propagation model. Subsequently, potential factors contributing to common-mode failures (CMFs) are identified using the fault propagation model. A Primary Flight Computer (PFC) of an aircraft is used as a case study to illustrate the effectiveness of our proposed method. Full article

(This article belongs to the Section Aeronautics)

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37 pages, 2546 KiB

Open AccessArticle

Advancing Aviation Safety Through Predictive Maintenance: A Machine Learning Approach for Carbon Brake Wear Severity Classification

by Patsy Jammal, Olivia Pinon Fischer, Dimitri N. Mavris and Gregory Wagner

Aerospace 2025, 12(7), 602; https://doi.org/10.3390/aerospace12070602 - 1 Jul 2025

Viewed by 3

Abstract

Braking systems are essential to aircraft safety and operational efficiency; however, the variability of carbon brake wear, driven by the intricate interplay of operational and environmental factors, presents challenges for effective maintenance planning. This effort leverages machine learning classifiers to predict wear severity [...] Read more.

Braking systems are essential to aircraft safety and operational efficiency; however, the variability of carbon brake wear, driven by the intricate interplay of operational and environmental factors, presents challenges for effective maintenance planning. This effort leverages machine learning classifiers to predict wear severity using operational data from an airline’s wide-body fleet equipped with wear pin sensors that measure the percentage of carbon pad remaining on each brake. Aircraft-specific metrics from flight data are augmented with weather and airport parameters from FlightAware^® to better capture the operational environment. Through a systematic benchmarking of multiple classifiers, combined with structured hyperparameter tuning and uncertainty quantification, LGBM and Decision Tree models emerge as top performers, achieving predictive accuracies of up to 98.92%. The inclusion of environmental variables substantially improves model performance, with relative humidity and wind direction identified as key predictors. While machine learning has been extensively applied to predictive maintenance contexts, this work advances the field of brake wear prediction by integrating a comprehensive dataset that incorporates operational, environmental, and airport-specific features. In doing so, it addresses a notable gap in the existing literature regarding the impact of contextual variables on brake wear prediction. Full article

(This article belongs to the Section Air Traffic and Transportation)

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34 pages, 10462 KiB

Open AccessArticle

Inter-Laboratory Characterisation of a Low-Power Channel-Less Hall-Effect Thruster: Performance Comparisons and Lessons Learnt

by Thomas F. Munro-O’Brien, Mohamed Ahmed, Andrea Lucca Fabris and Charles N. Ryan

Aerospace 2025, 12(7), 601; https://doi.org/10.3390/aerospace12070601 - 1 Jul 2025

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Abstract

A collaborative inter-laboratory study was conducted to characterise the performance of the novel 250 W External Discharge Plasma Thruster (XPT) with a channel-less Hall effect-type thruster designed to address lifetime limitations and lower-power efficiency challenges in conventional Hall effect thrusters. This study aimed [...] Read more.

A collaborative inter-laboratory study was conducted to characterise the performance of the novel 250 W External Discharge Plasma Thruster (XPT) with a channel-less Hall effect-type thruster designed to address lifetime limitations and lower-power efficiency challenges in conventional Hall effect thrusters. This study aimed to validate performance measurements across different facilities and thrust stands, investigating potential facility effects on thrust characterisation. Performance testing was conducted both at the University of Surrey using a torsional thrust balance and at the University of Southampton with a double inverted pendulum thrust stand, providing independent verification of the thrust and efficiency metrics. The comparison highlighted the importance of cross-facility testing with differing background pressures, calibration methods, and thrust balance types. These differences provide valuable insights, ensuring more robust and reliable low-power thruster characterisation. The XPT thruster demonstrated consistent performance across both the University of Surrey and University of Southampton facilities, with thrust levels ranging from 1.60 mN to 11.8 mN, specific impulses from 327 s to 1067 s, and anode efficiencies up to 11%. Higher anode voltages and mass fluxes at Southampton enabled extended operational envelopes, revealing performance plateaus at elevated powers, particularly for flow rates above 8 sccm. Cross-facility testing highlighted facility-dependent influences, with Southampton achieving a higher thrust and specific impulse at lower flow rates (5–6 sccm) due to increased anode currents, while discrepancies between test sites of up to 25% were observed at higher flow rates (8–10 sccm) and powers above 200 W. Characterisation identified an optimal operating range at 200 W of anode power with a mass flux below 8 sccm. This work underscores the importance of inter-laboratory validation in electric propulsion testing and provides insights into the best practices for assessing next-generation Hall effect-type thrusters. Full article

(This article belongs to the Section Astronautics & Space Science)

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24 pages, 7077 KiB

Open AccessArticle

Manufacturing Process of Stealth Unmanned Aerial Vehicle Exhaust Nozzles Based on Carbon Fiber-Reinforced Silicon Carbide Matrix Composites

by Byeong-Joo Kim, Jae Won Kim, Man Young Lee, Jong Kyoo Park, Nam Choon Cho and Cheul Woo Baek

Aerospace 2025, 12(7), 600; https://doi.org/10.3390/aerospace12070600 - 1 Jul 2025

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Abstract

This study presents the development of a manufacturing process for a double-serpentine (DS) exhaust nozzle for unmanned aerial vehicles (UAVs) based on carbon fiber-reinforced silicon carbide matrix composites (C/SiCs). The DS nozzle is designed to reduce infrared emissions from hot exhaust plumes, a [...] Read more.

This study presents the development of a manufacturing process for a double-serpentine (DS) exhaust nozzle for unmanned aerial vehicles (UAVs) based on carbon fiber-reinforced silicon carbide matrix composites (C/SiCs). The DS nozzle is designed to reduce infrared emissions from hot exhaust plumes, a critical factor in enhancing stealth performance during UAV operations. The proposed nozzle structure was fabricated using a multilayer configuration consisting of an inner C/SiC layer for thermal and oxidation resistance, a silica–phenolic insulation layer to suppress heat transfer, and an outer carbon fiber-reinforced polymer matrix composite (CFRPMC) for mechanical reinforcement. The C/SiC layer was produced by liquid silicon infiltration, preceded by pyrolysis and densification of a phenolic-based CFRPMC preform. The final nozzle was assembled through precision machining and bonding of segmented components, followed by lamination of the insulation and outer layers. Mechanical and thermal property tests confirmed the structural integrity and performance under high-temperature conditions. Additionally, oxidation and ablation tests demonstrated the excellent durability of the developed C/SiC. The results indicate that the developed process is suitable for producing large-scale, complex-shaped, high-temperature composite structures for stealth UAV applications. Full article

(This article belongs to the Section Aeronautics)

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26 pages, 6535 KiB

Open AccessArticle

Aerodynamic Optimization of Morphing Airfoil by PCA and Optimization-Guided Data Augmentation

by Ao Guo, Jing Wang, Miao Zhang and Han Wang

Aerospace 2025, 12(7), 599; https://doi.org/10.3390/aerospace12070599 - 1 Jul 2025

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Abstract

An aircraft that has been carefully optimized for a single flight condition will tend to perform poorly at other flight conditions. For aircraft such as long-haul airliners, this is not necessarily a problem, since the cruise condition so heavily dominates a typical mission. [...] Read more.

An aircraft that has been carefully optimized for a single flight condition will tend to perform poorly at other flight conditions. For aircraft such as long-haul airliners, this is not necessarily a problem, since the cruise condition so heavily dominates a typical mission. However, other aircraft, such as Unmanned Aerial Vehicles (UAVs), may be expected to perform well at a wide range of flight conditions. Morphing systems may be a solution to this problem, as they allow the aircraft to adapt its shape to produce optimum performance at each flight condition. This study proposes an aerodynamic optimization framework for morphing airfoils by integrating Principal Component Analysis (PCA) for geometric dimensionality reduction and deep learning (DL) for surrogate modeling, alongside an optimization-guided data augmentation strategy. By employing PCA, the geometric dimensionality of airfoil surfaces is reduced from 24 to 18 design variables while preserving 100% shape fidelity, thus establishing a compressed morphing parameterization space. A Multi-Island Genetic Algorithm (MIGA) efficiently explores the reduced design space, while iterative retraining of the surrogate model enhances prediction accuracy, particularly in high-performance regions. Additionally, Shapley Additive Explanation (SHAP) analysis reveals interpretable correlations between principal component modes and aerodynamic performances. Experimental results show that the optimized airfoil achieves a 54.66% increase in low-speed cruise lift-to-drag ratio and 10.90% higher climb lift compared to the baseline. Overall, the proposed framework not only enhances the adaptability of morphing airfoils across various low-speed flight conditions but also facilitates targeted surrogate refinement and efficient data acquisition in high-performance regions. Full article

(This article belongs to the Section Aeronautics)

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30 pages, 6330 KiB

Open AccessArticle

Design to Deployment: Flight Schedule-Based Analysis of Hybrid Electric Aircraft Variants in U.S. Regional Carrier Operations

by Emma Cassidy, Paul R. Mokotoff, Yilin Deng, Michael Ikeda, Kathryn Kirsch, Max Z. Li and Gokcin Cinar

Aerospace 2025, 12(7), 598; https://doi.org/10.3390/aerospace12070598 - 30 Jun 2025

Abstract

This study evaluates the feasibility and benefits of introducing battery-powered hybrid electric aircraft (HEA) into regional airline operations. Using 2019 U.S. domestic flight data, the ERJ175LR is selected as a representative aircraft, and several HEA variants are designed to match its mission profile [...] Read more.

This study evaluates the feasibility and benefits of introducing battery-powered hybrid electric aircraft (HEA) into regional airline operations. Using 2019 U.S. domestic flight data, the ERJ175LR is selected as a representative aircraft, and several HEA variants are designed to match its mission profile under different battery technologies and power management strategies. These configurations are then tested across over 800 actual daily flight sequences flown by a regional airline. The results show that well-designed HEA can achieve 3–7% fuel savings compared to conventional aircraft, with several variants able to complete all scheduled missions without disrupting turnaround times. These findings suggest that HEA can be integrated into today’s airline operations, particularly for short-haul routes, without the need for major infrastructure or scheduling changes, and highlight opportunities for future co-optimization of aircraft design and operations. Full article

(This article belongs to the Special Issue Electric Power Systems and Components for All-Electric Aircraft (2nd Edition))

25 pages, 2703 KiB

Open AccessArticle

Strategy Analysis of Seamlessly Resolving Turbulent Flow Simulations

by Stefan Heinz

Aerospace 2025, 12(7), 597; https://doi.org/10.3390/aerospace12070597 - 30 Jun 2025

Abstract

Modeling of wall-bounded turbulent flows, in particular the hybridization of the Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) methods, has faced serious questions for decades. Specifically, there is continuous research of how usually applied methods such as detached eddy simulation (DES) and [...] Read more.

Modeling of wall-bounded turbulent flows, in particular the hybridization of the Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) methods, has faced serious questions for decades. Specifically, there is continuous research of how usually applied methods such as detached eddy simulation (DES) and wall-modeled LES (WMLES) can be made more successful in regard to complex, high-Reynolds-number (

R e

) flow simulations. The simple question is how it is possible to enable reliable and cost-efficient predictions of high-

R e

wall-bounded turbulent flows in particular under conditions where data for validation are unavailable. This paper presents a strict analysis of strategies for the design of seamlessly resolving turbulent flow simulations for a wide class of turbulence models. The essential conclusions obtained are the following ones: First, by construction, usually applied methods like DES are incapable of systematically spanning the range from modeled to resolved flow simulations, which implies significant disadvantages. Second, a strict solution for this problem is given by novel continuous eddy simulation (CES) methods, which perform very well. Third, the design of a computational simplification of CES that still outperforms DES appears to be very promising. Full article

(This article belongs to the Section Aeronautics)

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19 pages, 5196 KiB

Open AccessArticle

Analysis of the Influence of Tether–Soil Interaction on the Attachment Trajectory of Small Celestial Body Detector

by Yuyan Pei, Yu Yang, Guoning Wei, Yanchen Li, Hao Tian and Yang Zhao

Aerospace 2025, 12(7), 596; https://doi.org/10.3390/aerospace12070596 - 30 Jun 2025

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Abstract

Multi-tethered spacecraft formation refers to a group of spacecraft that are connected by tethers. These spacecraft work together to perform tasks, such as encircling and capturing small celestial bodies. When the multi-tethered spacecraft formation is in the process of encircling and capturing small [...] Read more.

Multi-tethered spacecraft formation refers to a group of spacecraft that are connected by tethers. These spacecraft work together to perform tasks, such as encircling and capturing small celestial bodies. When the multi-tethered spacecraft formation is in the process of encircling and capturing small celestial bodies, there is a significant risk of the tethers colliding with the soil (or surface material) of the small celestial body. Such a collision can affect the trajectory of the small celestial body detector. To address this issue, a coupled dynamic model has been proposed. This model takes the interaction between the tethers and the soil of the small celestial body into account. The discrete element method is used to establish the asteroid soil model, and the multi-body-tethered spacecraft system is simplified into a two-spacecraft system. The detector model is established by using the dual quaternion, and the tether model is established by using the chain rod model combined with the finite element method. Finally, a multi-condition simulation test is carried out. The results show that the influence of tether–soil coupling on the trajectory of the detector is mainly as follows: the influence of tether–soil interaction on the trajectory of the detector is mainly reflected in the displacement of the detector along the axial direction of the tether. Full article

(This article belongs to the Special Issue Application of Tether Technology in Space)

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32 pages, 2155 KiB

Open AccessArticle

A Study on Information Strategy Planning (ISP) for Applying Smart Technologies to Airport Facilities in South Korea

by Sunbae Moon, Gutaek Kim, Heechang Seo, Jiwon Jun and Eunsoo Park

Aerospace 2025, 12(7), 595; https://doi.org/10.3390/aerospace12070595 - 30 Jun 2025

Abstract

This study aims to develop an information strategy plan (ISP) for the integrated management of airport facility information in South Korea by applying smart technologies such as building information modeling (BIM), digital twins, and openBIM. As the demand for intelligent lifecycle management and [...] Read more.

This study aims to develop an information strategy plan (ISP) for the integrated management of airport facility information in South Korea by applying smart technologies such as building information modeling (BIM), digital twins, and openBIM. As the demand for intelligent lifecycle management and efficient facility operations continues to grow, airport infrastructure requires standardized and interoperable systems to manage complex assets and stakeholder collaboration. This research addresses three core challenges facing Korean airports: the lack of sustainable maintenance environments, the absence of data standards and systems, and the insufficiency of user-oriented platforms. Through system analysis, benchmarking, and SWOT assessment, the study proposes a stepwise implementation roadmap consisting of development, integration, and advancement phases and designs a “To-Be” model that incorporates 37 component technologies and a standardized information framework. The proposed ISP supports data-driven airport operations, enhances collaboration, and accelerates digital transformation, ultimately contributing to the development of smart and globally competitive airports. Full article

(This article belongs to the Section Air Traffic and Transportation)

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15 pages, 2292 KiB

Open AccessArticle

Analytical Shaping of a Rocket Nose as a Stage of Preliminary Aerodynamic Modification

by Adrian Szklarski and Robert Głębocki

Aerospace 2025, 12(7), 594; https://doi.org/10.3390/aerospace12070594 - 30 Jun 2025

Abstract

The article discusses the problem of a preliminary analytical method for modifying the shape of a rocket’s nose. The purpose of this method is to determine the shape that minimizes aerodynamic drag, in the context of modifying a ballistic missile to incorporate guidance [...] Read more.

The article discusses the problem of a preliminary analytical method for modifying the shape of a rocket’s nose. The purpose of this method is to determine the shape that minimizes aerodynamic drag, in the context of modifying a ballistic missile to incorporate guidance systems. The traditional design process relies on numerical methods such as CFD (Computational Fluid Dynamics) or machine learning techniques; however, the method presented here can serve as a first iteration to support the design. Advanced simulation tools are often expensive and difficult to access for smaller companies, while open-source software can sometimes be unreliable, difficult to use, and incompatible with professional solutions. This can pose a challenge for businesses planning to collaborate in the future with large corporations that rely on advanced engineering tools. The proposed solution, as previously mentioned, provides a starting point for the entire design process. The approach has been shown to be sufficient from the design work. The entire process was validated during test range trials, during which rockets were launched, and the flight measurement results accurately reflected the aerodynamic properties of the missiles. In the next stages of the project, numerical methods including CFD simulations are planned to verify the analytical results and enable further aerodynamic modification of the design. Full article

(This article belongs to the Section Aeronautics)

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26 pages, 4613 KiB

Open AccessArticle

Adaptive Neural Network-Based Fixed-Time Trajectory Tracking Control of Space Robot with Uncertainties and Input Nonlinearities

by Haiping Ai, Lei Jiang, An Zhu and Xiaodong Fu

Aerospace 2025, 12(7), 593; https://doi.org/10.3390/aerospace12070593 - 30 Jun 2025

Viewed by 1

Abstract

In this paper, a fixed-time control strategy based on neural networks is proposed for a space robot with an input dead zone. First, a model-based control method is proposed based on the fixed-time convergence framework. Due to internal errors and external environmental disturbances, [...] Read more.

In this paper, a fixed-time control strategy based on neural networks is proposed for a space robot with an input dead zone. First, a model-based control method is proposed based on the fixed-time convergence framework. Due to internal errors and external environmental disturbances, the inertial parameters of dynamic models generally exhibit uncertainties, and model-based control methods may exhibit deviations in trajectory tracking. In order to counteract the adverse effects of uncertain inertial parameters on the system and ensure the stability of the control system, an adaptive learning control method based on neural networks is further proposed. To enhance the learning rate of neural networks and achieve the convergence of neural weights within a fixed time, a neural network update rate combined with virtual control rate is proposed. In addition, considering the issue of the joint input dead zone affecting the precision and stability of the space robot, a novel adaptive law is proposed in conjunction with system error signal feedback to mitigate adverse effects. According to the Lyapunov stability theory, the stability of the closed-loop system is proven, with the trajectory tracking error converging to a small neighborhood around zero. Finally, numerical simulation results demonstrate the effectiveness of the control algorithm. Full article

(This article belongs to the Special Issue Space Mechanisms and Robots)

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14 pages, 5698 KiB

Open AccessArticle

Airworthiness Compliance Methods for Low-Cost Wet Composite Structures in General Aviation Aircraft

by Xiuzhi Liu, Shuang Zheng and Fengtian Yang

Aerospace 2025, 12(7), 592; https://doi.org/10.3390/aerospace12070592 - 30 Jun 2025

Viewed by 1

Abstract

With the continuous development of new aircraft, the application of low-cost composite materials technology still encounters numerous challenges and issues. The development of low-cost composite technology, while ensuring the high reliability of aircraft components, has become a common concern among aerospace composites. The [...] Read more.

With the continuous development of new aircraft, the application of low-cost composite materials technology still encounters numerous challenges and issues. The development of low-cost composite technology, while ensuring the high reliability of aircraft components, has become a common concern among aerospace composites. The research presented in this paper examines the findings related to the conformity verification process of an electric aircraft in China. This is an all-composite structural general aviation aircraft certified under CCAR Part 23. This study focuses on the quality characteristics of low-cost wet vacuum bagging composites, addressing the causes and effects of high porosity in the manufacturing process. Based on the research findings, a relationship between porosity and the strength of wet vacuum bagging composites is established. Consequently, a safe and reliable method for ensuring airworthiness conformity of low-cost composites is proposed and implemented in the aircraft type’s conformity verification. Furthermore, this paper discusses the development trends of low-cost composites for general aviation, providing valuable insights for the advancement of low-cost technologies in the future. Full article

(This article belongs to the Special Issue Airworthiness, Safety and Reliability of Aircraft)

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26 pages, 6918 KiB

Open AccessArticle

Coordinated Reentry Guidance with A* and Deep Reinforcement Learning for Hypersonic Morphing Vehicles Under Multiple No-Fly Zones

by Cunyu Bao, Xingchen Li, Weile Xu, Guojian Tang and Wen Yao

Aerospace 2025, 12(7), 591; https://doi.org/10.3390/aerospace12070591 - 30 Jun 2025

Abstract

Hypersonic morphing vehicles (HMVs), renowned for their adaptive structural reconfiguration and cross-domain maneuverability, confront formidable reentry guidance challenges under multiple no-fly zones, stringent path constraints, and nonlinear dynamics exacerbated by morphing-induced aerodynamic uncertainties. To address these issues, this study proposes a hierarchical framework [...] Read more.

Hypersonic morphing vehicles (HMVs), renowned for their adaptive structural reconfiguration and cross-domain maneuverability, confront formidable reentry guidance challenges under multiple no-fly zones, stringent path constraints, and nonlinear dynamics exacerbated by morphing-induced aerodynamic uncertainties. To address these issues, this study proposes a hierarchical framework integrating an A-based energy-optimal waypoint planner, a deep deterministic policy gradient (DDPG)-driven morphing policy network, and a quasi-equilibrium glide condition (QEGC) guidance law with continuous sliding mode control. The A* algorithm generates heuristic trajectories circumventing no-fly zones, reducing the evaluation function by 6.2% compared to greedy methods, while DDPG optimizes sweep angles to minimize velocity loss and terminal errors (0.09 km position, 0.01 m/s velocity). The QEGC law ensures robust longitudinal-lateral tracking via smooth hyperbolic tangent switching. Simulations demonstrate generalization across diverse targets (terminal errors < 0.24 km) and robustness under Monte Carlo deviations (0.263 ± 0.184 km range, −12.7 ± 42.93 m/s velocity). This work bridges global trajectory planning with real-time morphing adaptation, advancing intelligent HMV control. Future research will extend this framework to ascent/dive phases and optimize its computational efficiency for onboard deployment. Full article

(This article belongs to the Section Aeronautics)

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19 pages, 5011 KiB

Open AccessArticle

Vector Field-Based Robust Quadrotor Landing on a Moving Ground Platform

by Woohyun Byun, Soobin Huh, Hyeokjae Jang, Suhyeong Yu, Sungwon Lim, Seokwon Lee and Woochul Nam

Aerospace 2025, 12(7), 590; https://doi.org/10.3390/aerospace12070590 - 29 Jun 2025

Viewed by 61

Abstract

The autonomous landing of unmanned aerial vehicles (UAVs) on moving platforms has potential applications across various domains. However, robust landing remains challenging because the detection reliability of UAVs decreases when the UAV is close to a moving platform. To address this issue, this [...] Read more.

The autonomous landing of unmanned aerial vehicles (UAVs) on moving platforms has potential applications across various domains. However, robust landing remains challenging because the detection reliability of UAVs decreases when the UAV is close to a moving platform. To address this issue, this paper proposes a novel landing strategy that ensures a high detection rate. First, a robust detectable region was established by considering the sensing range and maneuverability limitations of the UAV. Second, a vector field was designed to guide the UAV to the moving platform while remaining in a robust detectable region. Next, safe and accurate landings were achieved by considering the current velocity and vector field. The landing strategy was validated through outdoor flight experiments. A quadrotor equipped with a gimbal-mounted camera was used, and a fractal marker was attached to the moving platform for detection and tracking. When the moving platform moved at a speed of 2–4.3 m/s, the UAV successfully landed on the platform with a distance error of 0.4 m. Because of the robust detectable region and vector field, the detection was conducted with a high success rate (94.9%). Full article

(This article belongs to the Special Issue Flight Guidance and Control)

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20 pages, 4995 KiB

Open AccessArticle

Constant Strain Aging Model of HTPB Propellant Involving Thermal–Mechanical Coupled Effects

by Pengju Qin, Xiangyu Zhang, Kai Jiang and Jiming Cheng

Aerospace 2025, 12(7), 589; https://doi.org/10.3390/aerospace12070589 - 29 Jun 2025

Viewed by 69

Abstract

To investigate the aging behavior of HTPB composite solid propellant under constant strain conditions, this study analyzed the aging patterns of the propellant’s maximum elongation at four temperatures (323.15 K–343.15 K) and five strain levels (0–18%) using thermal–mechanical coupled accelerated aging tests. The [...] Read more.

To investigate the aging behavior of HTPB composite solid propellant under constant strain conditions, this study analyzed the aging patterns of the propellant’s maximum elongation at four temperatures (323.15 K–343.15 K) and five strain levels (0–18%) using thermal–mechanical coupled accelerated aging tests. The results show that the maximum elongation initially increases, then decreases under constant strain conditions. To measure the mechanical work-induced decrease in the activation motor, we created a modified Arrhenius model with a strain correction factor based on empirical observations. The acceleration coefficient of a solid motor grain at the accelerated aging temperature (323.15 K) in comparison to the long-term storage temperature (293.15 K) was found to be 20.08 through finite element analysis. This means 206.80 days at the accelerated aging temperature is equivalent to 10 years at the long-term storage temperature. Full article

(This article belongs to the Special Issue Combustion of Solid Propellants)

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39 pages, 3707 KiB

Open AccessArticle

Real-Time Gas Path Fault Diagnosis for Aeroengines Based on Enhanced State-Space Modeling and State Tracking

by Siyan Cao, Hongfu Zuo, Xincan Zhao and Chunyi Xia

Aerospace 2025, 12(7), 588; https://doi.org/10.3390/aerospace12070588 - 29 Jun 2025

Viewed by 54

Abstract

Failures in gas path components pose significant risks to aeroengine performance and safety. Traditional fault diagnosis methods often require extensive data and struggle with real-time applications. This study addresses these critical limitations in traditional studies through physics-informed modeling and adaptive estimation. A nonlinear [...] Read more.

Failures in gas path components pose significant risks to aeroengine performance and safety. Traditional fault diagnosis methods often require extensive data and struggle with real-time applications. This study addresses these critical limitations in traditional studies through physics-informed modeling and adaptive estimation. A nonlinear component-level model of the JT9D engine is developed through aero-thermodynamic governing equations, enhanced by a dual-loop iterative cycle combining Newton–Raphson steady-state resolution with integration-based dynamic convergence. An augmented state-space model that linearizes nonlinear dynamic models while incorporating gas path health characteristics as control inputs is novelly proposed, supported by similarity-criterion normalization to mitigate matrix ill-conditioning. A hybrid identification algorithm is proposed, synergizing partial derivative analysis with least squares fitting, which uniquely combines non-iterative perturbation advantages with high-precision least squares. This paper proposes a novel enhanced Kalman filter through integral compensation and three-dimensional interpolation, enabling real-time parameter updates across flight envelopes. The experimental results demonstrate a 0.714–2.953% RMSE in fault diagnosis performance, a 3.619% accuracy enhancement over traditional sliding mode observer algorithms, and 2.11 s reduction in settling time, eliminating noise accumulation. The model maintains dynamic trend consistency and steady-state accuracy with errors of 0.482–0.039%. This work shows marked improvements in temporal resolution, diagnostic accuracy, and flight envelope adaptability compared to conventional approaches. Full article

(This article belongs to the Section Aeronautics)

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