Aerospace

19 pages, 3133 KiB

Open AccessArticle

Prediction of Spectral Response for Explosion Separation Based on DeepONet

by Xiaoqi Chen, Zhanlong Qu, Yuxi Wang, Zihao Chen, Ganchao Chen, Xiao Kang and Ying Li

Aerospace 2025, 12(4), 310; https://doi.org/10.3390/aerospace12040310 (registering DOI) - 4 Apr 2025

Strong shock waves generated during the pyrotechnic separation process of aerospace vehicles can cause high-frequency damage or even structural failure to the vehicle’s structure. Existing structural designs for shock attenuation typically rely on shock response spectra methods, which require multiple finite element calculations [...] Read more.

Strong shock waves generated during the pyrotechnic separation process of aerospace vehicles can cause high-frequency damage or even structural failure to the vehicle’s structure. Existing structural designs for shock attenuation typically rely on shock response spectra methods, which require multiple finite element calculations to determine the optimal geometric parameters, leading to relatively low efficiency. In this work, we propose a spectral response prediction method for spacecraft structures using the Deep Operator Network (DeepONet). This method preserves the physical relationships between input variables, modularizes geometric and positional input data, and outputs the spectral response. We integrate this neural model to analyze the impact of spacecraft structural parameters on shock resistance performance, revealing that circumferential reinforcement has the most significant influence on shock resistance. Then, we conduct a detailed analysis of the DeepONet model, noting that models with a higher number of neurons per layer train more quickly but are prone to overfitting. Additionally, we find that focusing on specific frequency bands for spectral response prediction yields more accurate results. Full article

24 pages, 5232 KiB

Open AccessArticle

An Innovative Priority-Aware Mission Planning Framework for an Agile Earth Observation Satellite

by Guangtong Zhu, Zixuan Zheng, Chenhao Ouyang, Yufei Guo and Pengyu Sun

Aerospace 2025, 12(4), 309; https://doi.org/10.3390/aerospace12040309 (registering DOI) - 4 Apr 2025

Abstract

Earth observation satellites, particularly agile Earth observation satellites (AEOSs) with enhanced attitude maneuverability, have become increasingly crucial in emergency response and disaster monitoring operations. Efficient mission planning for densely distributed ground targets with diverse priorities poses significant challenges, especially when considering strict attitude [...] Read more.

Earth observation satellites, particularly agile Earth observation satellites (AEOSs) with enhanced attitude maneuverability, have become increasingly crucial in emergency response and disaster monitoring operations. Efficient mission planning for densely distributed ground targets with diverse priorities poses significant challenges, especially when considering strict attitude maneuver constraints and time-sensitive requirements. To address these challenges, this paper proposes a target clusters and dual-timeline optimization (TCDO) framework that integrates priority-based geographical clustering with temporal–spatial coordination mechanisms for efficient mission planning. The proposed approach effectively maintains satellite maneuver constraints while achieving significant improvements in priority-based target acquisition and computational efficiency. Experimental results demonstrate the framework’s superior performance, achieving a 94% coverage rate and a 99.5% reduction in computation time compared to traditional scheduling methods, such as linear programming and genetic algorithms. Full article

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

18 pages, 3522 KiB

Open AccessArticle

Aerodynamic Characteristics of the Opposing Jet Combined with Magnetohydrodynamic Control in Hypersonic Nonequilibrium Flows

by Wenqing Zhang, Zhijun Zhang and Weifeng Gao

Aerospace 2025, 12(4), 308; https://doi.org/10.3390/aerospace12040308 (registering DOI) - 3 Apr 2025

Viewed by 25

Abstract

To improve the thermal protection effect of an opposing jet, a novel thermal protection technology (i.e., an opposing jet combined with magnetohydrodynamic (MHD) control technology) is proposed in this study. Considering the flight conditions of an ELECTRE vehicle and the unsteady state of [...] Read more.

To improve the thermal protection effect of an opposing jet, a novel thermal protection technology (i.e., an opposing jet combined with magnetohydrodynamic (MHD) control technology) is proposed in this study. Considering the flight conditions of an ELECTRE vehicle and the unsteady state of the opposing jet, we employed the time-accurate nonequilibrium N-S equations coupled with a low-magnetic-Reynolds-number model to explore the jet characteristics, thermal protection effects, and aerodynamic drag characteristics of this novel technology. Two jet conditions (PR2.53 and PR5.07) and four magnetic field conditions (no-MHD, B₀ = 1 T, 2 T, and 4 T) were employed. The results show that the introduction of a magnetic field can guide the flow of the opposing jet by reconstructing the shock, where the reattachment shock is pushed away from the surface and the shock standoff distance (SSD) increases. Compared with the opposing jet and the MHD control technologies, this novel technology can provide a better thermal protection effect. In particular, it enables a long penetration mode (LPM) jet, which aggravates the aerodynamic heating environment around the vehicle at lower flow rates to provide effective thermal protection for the vehicle. Moreover, this novel technology can achieve effective thermal protection without increasing the aerodynamic drag at an appropriate jet mass flow rate and a magnetic field strength. For example, under the B₀ = 2 T magnetic field, the ratios of peak wall heat flux for the two technologies (the MHD control technology and the PR2.53 jet combined MHD control technology) are 0.908 and 0.820, respectively, whereas the ratios of average drags for the two technologies are 1.235 and 0.993, respectively. Full article

(This article belongs to the Special Issue Thermal Protection System Design of Space Vehicles)

22 pages, 3399 KiB

Open AccessArticle

Augmented Hohmann Transfer for Spacecraft with Continuous-Thrust Propulsion System

by Alessandro A. Quarta

Aerospace 2025, 12(4), 307; https://doi.org/10.3390/aerospace12040307 (registering DOI) - 3 Apr 2025

Viewed by 22

Abstract

Hohmann transfer is the classical approach used in astrodynamics to analyze the optimal bi-impulsive transfer, from the point of view of the total velocity change, between two circular, coplanar orbits of assigned radius. The Hohmann transfer is characterized by an elliptical trajectory tangent [...] Read more.

Hohmann transfer is the classical approach used in astrodynamics to analyze the optimal bi-impulsive transfer, from the point of view of the total velocity change, between two circular, coplanar orbits of assigned radius. The Hohmann transfer is characterized by an elliptical trajectory tangent to both circular orbits at the points where the transfer begins or ends and can be used to simply model, in a Kepler problem, a possible optimal transfer of a spacecraft equipped with a high-thrust propulsion system. Recent literature has proposed a sort of extension of the Hohmann transfer to a heliocentric mission scenario, where the total velocity change is reduced compared to the classical result by employing a photonic solar sail operating along the deep-space transfer trajectory. The study of this so-called augmented Hohmann transfer, where the spacecraft uses both two tangential impulses (one at the beginning and one at the end of the flight) provided by a high-thrust propulsion system and the propulsive acceleration (during the flight) provided by a low-thrust propulsion system, is extended in this paper by considering a more general case where the spacecraft moves around a generic primary body and uses, along the transfer, a freely orientable propulsive acceleration vector with constant and assigned magnitude. This scenario is consistent, for example, with the use of a typical electric thruster instead of the photonic solar sail considered in recent literature. In particular, the paper studies the impact of the continuous-thrust propulsion system on the transfer performance between the two circular orbits, analyzing the variation of the total velocity change as a function of the propulsive acceleration magnitude. The procedure, which uses an optimal approach to performance estimation, can be used both in a heliocentric and planetocentric mission scenario and can also be employed to analyze the performance of a spacecraft equipped with a multimode propulsion system. Full article

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

33 pages, 976 KiB

Open AccessReview

Urban Air Mobility Aircraft Operations in Urban Environments: A Review of Potential Safety Risks

by Chananya Charnsethikul, Jose M. Silva, Wim J.C. Verhagen and Raj Das

Aerospace 2025, 12(4), 306; https://doi.org/10.3390/aerospace12040306 (registering DOI) - 3 Apr 2025

Viewed by 37

Abstract

The expansion of Urban Air Mobility (UAM) has led to diverse aircraft designs, with piloted systems expected to evolve into remotely piloted and automated operations. Future advancements in Intelligent Transportation Systems (ITSs) will further improve automation capabilities, promising significant benefits to the environment [...] Read more.

The expansion of Urban Air Mobility (UAM) has led to diverse aircraft designs, with piloted systems expected to evolve into remotely piloted and automated operations. Future advancements in Intelligent Transportation Systems (ITSs) will further improve automation capabilities, promising significant benefits to the environment and overall efficiency of UAM aircraft. However, UAM aircraft face unique operational conditions that need to be accounted for when assessing safety risks, such as lower operating altitudes and hazards present in urban settings, thus leading to a potential increased risk of collisions with foreign objects, particularly birds and drones. This paper reviews historical safety data with an aim to better assess the potential risks of UAM aircraft. A survey was conducted to gather quantitative and qualitative insights from subject matter experts, reinforcing findings from existing studies. The results highlight the need for a comprehensive risk assessment framework to guide design improvements and regulatory strategies, ensuring safer UAM operations. Full article

(This article belongs to the Special Issue Next-Generation Drones for Urban Air Mobility: Advances and Innovations)

17 pages, 31599 KiB

Open AccessArticle

Study on the Influence of Rigid Wheel Surface Structure on the Trafficability of Planetary Rover on Soft Ground

by Xinju Dong, Jingfu Jin, Zhicheng Jia, Yingchun Qi, Lianbin He, Qingyu Yu and Meng Zou

Aerospace 2025, 12(4), 305; https://doi.org/10.3390/aerospace12040305 (registering DOI) - 3 Apr 2025

Viewed by 47

Abstract

In order to explore the influence of wheel surface structure on the trafficability of planetary rovers on soft ground, three kinds of wheels with different rigid wheel surface structures were selected for research. The basic performance parameters of the wheel on simulated planetary [...] Read more.

In order to explore the influence of wheel surface structure on the trafficability of planetary rovers on soft ground, three kinds of wheels with different rigid wheel surface structures were selected for research. The basic performance parameters of the wheel on simulated planetary soil are measured and tested to explore the law of the wheel’s sinkage, slip rate and traction coefficient. The results show that the wheel grouser increases the sinkage and slip rate of the wheel. The tread reduces the sinkage of the wheel, but it also reduces the traction performance of the wheel at a higher slip rate. Considering the complex working conditions of the planetary rover on the soft ground, the six-wheeled three-rocker-arm planetary rover is used to carry out passability tests in three terrains: obstacle crossing, out of sinkage and climbing. The results show that the grousers can cause disturbance and damage to the soft soil and have significant passing advantages. There may also be a slip phenomenon when crossing the obstacle, but it does not affect passing. The completely closed tread structure will cause soil accumulation between the tread and the grouser, affecting the wheel’s ability to escape sinkage. This study provides a reference for the design of a rigid wheel surface structure for planetary rovers from the perspective of passing performance. Full article

(This article belongs to the Special Issue Space Sampling and Exploration Robotics)

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23 pages, 2649 KiB

Open AccessArticle

Transonic Dynamic Stability Derivative Estimation Using Computational Fluid Dynamics: Insights from a Common Research Model

by Roberta Bottigliero, Viola Rossano and Giuliano De Stefano

Aerospace 2025, 12(4), 304; https://doi.org/10.3390/aerospace12040304 - 3 Apr 2025

Viewed by 46

Abstract

Dynamic stability derivatives are critical parameters in the design of trajectories and attitude control systems for flight vehicles, as they directly affect the divergence behavior of vibrations in an aircraft’s open-loop system when subjected to disturbances. This study focuses on the estimation of [...] Read more.

Dynamic stability derivatives are critical parameters in the design of trajectories and attitude control systems for flight vehicles, as they directly affect the divergence behavior of vibrations in an aircraft’s open-loop system when subjected to disturbances. This study focuses on the estimation of dynamic stability derivatives using a computational fluid dynamics (CFD)-based force oscillation method. A transient Reynolds-averaged Navier–Stokes solver is utilized to compute the time history of aerodynamic moments for an aircraft model oscillating about its center of gravity. The NASA Common Research Model serves as the reference geometry for this investigation, which explores the impact of pitching, rolling, and yawing oscillations on aerodynamic performance. Periodic oscillatory motions are imposed while using a dynamic mesh technique for CFD analysis. Preliminary steady-state simulations are conducted to validate the computational approach, ensuring the reliability and accuracy of the applied CFD model for transonic flow. The primary goal of this research is to confirm the efficacy of CFD in accurately predicting stability derivative values, underscoring its advantages over traditional wind tunnel experiments at high angles of attack. The study highlights the accuracy of CFD predictions and provides detailed insights into how different oscillations affect aerodynamic performance. This approach showcases the potential for significant cost and time savings in the estimation of dynamic stability derivatives. Full article

(This article belongs to the Special Issue Experimental Fluid Dynamics and Fluid-Structure Interactions)

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16 pages, 3851 KiB

Open AccessArticle

Spaceborne Detection Technology for Assessing Particle Radiation in Highly Elliptical Orbits

by Guohong Shen, Lin Quan, Shenyi Zhang, Huanxin Zhang, Donghui Hou, Chunqin Wang, Ying Sun, Bin Yuan, Changsheng Tuo, Zida Quan, Zheng Chang, Xianguo Zhang and Yueqiang Sun

Aerospace 2025, 12(4), 303; https://doi.org/10.3390/aerospace12040303 - 1 Apr 2025

Viewed by 53

Abstract

Satellites traversing highly elliptical orbits (HEOs) encounter more severe radiation effects caused by the space particle environment, which are distinct from those in a low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO). This study proposed a space environment detection [...] Read more.

Satellites traversing highly elliptical orbits (HEOs) encounter more severe radiation effects caused by the space particle environment, which are distinct from those in a low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO). This study proposed a space environment detection payload technology for assessing the particle radiation environment in HEOs. During ground tests, all technical indicators of the detection payload were calibrated and verified using reference signal sources, standard radioactive sources, and particle accelerators. The results indicate that the space environment detection payload can detect electrons and protons within the energy ranges of 30 keV to 2.0 MeV and 30 keV to 300 MeV, respectively, with an accuracy greater than 10%. The detection range of the surface potential spans from −11.571 kV to +1.414 kV, with a sensitivity greater than 50 V. Furthermore, the radiation dose detection range extends from 0 to 3.38 × 10⁶ rad (Si), with a sensitivity greater than 3 rad (Si). These indicators were also validated through an in-orbit flight. The observation of the particle radiation environment, radiation dose accumulation, and satellite surface potential variation in HEOs can cover space areas that have not been addressed before. This research helps fill the gaps in China’s space environment data and promotes the development of a space-based environment monitoring network. Full article

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

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37 pages, 740 KiB

Open AccessArticle

Optimal Pursuit Strategies in Missile Interception: Mean Field Game Approach

by Yu Bai, Di Zhou and Zhen He

Aerospace 2025, 12(4), 302; https://doi.org/10.3390/aerospace12040302 - 1 Apr 2025

Viewed by 52

Abstract

This paper investigates Mean Field Game methods to solve missile interception strategies in three-dimensional space, with a focus on analyzing the pursuit–evasion problem in many-to-many scenarios. By extending traditional missile interception models, an efficient solution is proposed to avoid dimensional explosion and communication [...] Read more.

This paper investigates Mean Field Game methods to solve missile interception strategies in three-dimensional space, with a focus on analyzing the pursuit–evasion problem in many-to-many scenarios. By extending traditional missile interception models, an efficient solution is proposed to avoid dimensional explosion and communication burdens, particularly for large-scale, multi-missile systems. The paper presents a system of stochastic differential equations with control constraints, describing the motion dynamics between the missile (pursuer) and the target (evader), and defines the associated cost function, considering proximity group distributions with other missiles and targets. Next, Hamilton–Jacobi–Bellman equations for the pursuers and evaders are derived, and the uniqueness of the distributional solution is proved. Furthermore, using the

ϵ

-Nash equilibrium framework, it is demonstrated that, under the MFG model, participants can deviate from the optimal strategy within a certain tolerance, while still minimizing the cost. Finally, the paper summarizes the derivation process of the optimal strategy and proves that, under reasonable assumptions, the system can achieve a uniquely stable equilibrium, ensuring the stability of the strategies and distributions of both the pursuers and evaders. The research provides a scalable solution to high-risk, multi-agent control problems, with significant practical applications, particularly in fields such as missile defense systems. Full article

(This article belongs to the Section Aeronautics)

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10 pages, 3124 KiB

Open AccessArticle

Surface-Tailoring and Morphology Control as Strategies for Sustainable Development in Transport Sector

by Luis Antonio Sanchez de Almeida Prado, Selim Coskun, Anne-Laure Cadène, Ramón Angel Antelo Reguengo, Jake Carter, Kyle Ito, Minok Park and Vassilia Zorba

Aerospace 2025, 12(4), 301; https://doi.org/10.3390/aerospace12040301 - 1 Apr 2025

Viewed by 77

Abstract

Surface wetting plays an important role in the corrosion protection processes of aerospace applications. Here, we demonstrate the use of ultrafast femtosecond (fs) laser processing techniques to tailor the wetting properties of aluminum (Al) substrates by creating diverse surface morphologies. Specifically, two distinct [...] Read more.

Surface wetting plays an important role in the corrosion protection processes of aerospace applications. Here, we demonstrate the use of ultrafast femtosecond (fs) laser processing techniques to tailor the wetting properties of aluminum (Al) substrates by creating diverse surface morphologies. Specifically, two distinct laser scanning methods—dot-hatching and cross-hatching—were employed to fabricate microstructures on the substrates. By varying the incident laser parameters, we confirmed that the resulting surface morphologies exhibit different wetting behaviors, spanning from hydrophilicity to hydrophobicity. Furthermore, time-resolved spreading tests validate that dynamic wetting behaviors can also be modified. This fs laser processing approach provides a straightforward, one-step fabrication method for effectively modifying the wetting properties of Al alloys. Full article

(This article belongs to the Special Issue 14th EASN International Conference on Innovation in Aviation & Space towards Sustainability Today & Tomorrow)

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12 pages, 2580 KiB

Open AccessArticle

Reliability Evaluation of Landing Gear Retraction/Extension Accuracy Based on Bayesian Theory

by Yuanbo Lv, Xianmin Chen, Yao Li, Yuxiang Tian and Feng Zhang

Aerospace 2025, 12(4), 300; https://doi.org/10.3390/aerospace12040300 - 1 Apr 2025

Viewed by 67

Abstract

The angular motion of aircraft landing gear retraction and extension must be accurate to ensure flight safety. Therefore, this study experimentally evaluated the motion accuracy of the landing gear retraction and extension processes associated with a specific aircraft to construct a reliability evaluation [...] Read more.

The angular motion of aircraft landing gear retraction and extension must be accurate to ensure flight safety. Therefore, this study experimentally evaluated the motion accuracy of the landing gear retraction and extension processes associated with a specific aircraft to construct a reliability evaluation model for the landing gear angle. Considering the limitations of data acquisition in practical applications, the Bayesian method, which combines prior knowledge with experimentally measured data to reasonably estimate the variable parameters in the evaluation model, was applied to obtain more accurate parameter distributions. The constructed Bayesian-updated iterative model was shown to effectively expand upon limited test data to provide a novel approach for accurately evaluating landing gear angle reliability. The results of this study not only enrich the theoretical basis underpinning aircraft landing gear reliability assessment but also provide a valuable reference for technical support and decision-making in related engineering practice. Full article

(This article belongs to the Section Aeronautics)

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27 pages, 6948 KiB

Open AccessArticle

A Patrol Route Design for Inclined Geosynchronous Orbit Satellites in Space Traffic Management

by Ning Chen, Zhanyue Zhang, Songjiang Feng, Wu Xue and Boya Jia

Aerospace 2025, 12(4), 299; https://doi.org/10.3390/aerospace12040299 - 31 Mar 2025

Viewed by 42

Abstract

Conducting surveys and the timely acquisition of satellite status, especially for high-value geostationary orbit (GEO) targets, is of great significance for space traffic management. This article proposes an approach for patrolling inclined geosynchronous orbit (IGSO) targets based on crossing points and spiral rings. [...] Read more.

Conducting surveys and the timely acquisition of satellite status, especially for high-value geostationary orbit (GEO) targets, is of great significance for space traffic management. This article proposes an approach for patrolling inclined geosynchronous orbit (IGSO) targets based on crossing points and spiral rings. The method involves six steps: (1) calculate the crossing position and crossing time of the IGSO targets; (2) design a spiral trajectory that satisfies the desired patrol time; (3) divide IGSO targets into regions using a dichotomy approach; (4) calculate the bidirectional longitude drift rate within each region; (5) determine the starting position of patrol for each region; and (6) determine the transfer trajectory for each region. By selecting a class of IGSO satellites as the target set, the proposed approach is analyzed and validated in detail. The results show that the patrol orbit can effectively achieve patrol all of IGSO targets, with a period of no more than 40 days and less than 13.5 kg fuel consumption. The total fuel consumption of a single patrol cycle in all regions does not exceed 91.82 kg. Full article

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

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16 pages, 2716 KiB

Open AccessArticle

The Modulatory Effect of Inhibitors on the Thermal Decomposition Performance of Graded Al@AP Composites

by Kan Xie, Jing Wang, Zhi-Yu Zhang, Bin Tian, Su-Lan Yang, Jingyu Lei and Ming-Hui Yu

Aerospace 2025, 12(4), 298; https://doi.org/10.3390/aerospace12040298 - 31 Mar 2025

Viewed by 33

Abstract

In this paper, a series of graded Al-based composites, including Al@AP, Al@AP/BM−52, and Al@AP/BPE−1735, have been prepared by spray drying technology. The thermal decomposition characteristics, kinetic parameters of the decomposition reaction, and Pyro-GC/MS products were comprehensively investigated. The results showed that two inhibitors, [...] Read more.

In this paper, a series of graded Al-based composites, including Al@AP, Al@AP/BM−52, and Al@AP/BPE−1735, have been prepared by spray drying technology. The thermal decomposition characteristics, kinetic parameters of the decomposition reaction, and Pyro-GC/MS products were comprehensively investigated. The results showed that two inhibitors, BM−52 and BPE−1735, had a significant effect on the thermal decomposition of AP. The addition of BM−52 conspicuously enhanced the thermal interaction, resulting in a more complete decomposition reaction of AP. Meanwhile, the incorporation of BPE−1735 significantly enhanced the heat releases of AP, leading to a significant enhancement in the energetic performance during the decomposition process of AP. BM−52 and BPE1735 inhibit AP decomposition as evidenced by higher activation energies for thermal decomposition and altered physical models of decomposition. Pyro-GC/MS results reveal that the fundamental pathway of Al@AP thermal decomposition remains unaltered by BM−52. However, the proportion of oxygen-containing compound products is moderately reduced. In contrast, for Al@AP/BPE−1735, in addition to the same products as those from Al@AP pyrolysis, new pyrolysis peaks emerge. It is implied that specific chemical reactions or interactions are triggered during the thermal decomposition process, thereby resulting in the formation of distinct chemical species. Full article

(This article belongs to the Special Issue Artificial Intelligence in Aerospace Propulsion)

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17 pages, 13877 KiB

Open AccessArticle

Experimental–Numerical Comparison of H₂–Air Detonations: Influence of N₂ Chemistry and Diffusion Effects

by Vigneshwaran Sankar, Karl P. Chatelain and Deanna A. Lacoste

Aerospace 2025, 12(4), 297; https://doi.org/10.3390/aerospace12040297 - 31 Mar 2025

Viewed by 23

Abstract

This study evaluates the performance of two-dimensional (2D) detonation simulations against recent experimental measurements for a stoichiometric hydrogen–air mixture at 25 kPa. The validation parameters rely on the average cell size (

λ

), the cell size variability (

2 σ / λ

[...] Read more.

This study evaluates the performance of two-dimensional (2D) detonation simulations against recent experimental measurements for a stoichiometric hydrogen–air mixture at 25 kPa. The validation parameters rely on the average cell size (

λ

), the cell size variability (

2 σ / λ

), and the dynamics of both the relative detonation speed (D/D_CJ) and the local induction zone length (

Δ_{i}

) along the cell cycle. We select Mével 2017’s and San Diego’s chemical models for 2D simulations, after evaluating 13 chemical models with Zeldovich–von Neumann–Döring (ZND) simulations. From this model selection, the effects of nitrogen chemistry and diffusion (Navier–Stokes or Euler equations) are evaluated on the validation parameters. The main findings are as follows: the simulations conducted with the Mével 2017 (with N₂ chemistry) model provide the best agreement with

λ_{mean}^{\exp}

(≈17%), while the experimental cell variability (

2 σ / λ

) is reproduced within 20% by most simulation cases. This model (Mével 2017 with N₂ chemistry) also presents good agreement with both the

Δ_{i}

and D/D_CJ dynamics, whereas San Diego’s simulations under-predict them along the cell. Interestingly, the speed decay along the cell length exhibits self-similar behavior across all cases, suggesting independence from cell size variability, unlike the

Δ_{i}

dynamics. Finally, this study demonstrates the minimal impact of the diffusion on the simulation results. Full article

(This article belongs to the Special Issue Scientific and Technological Advances in Hydrogen Combustion Aircraft)

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25 pages, 9613 KiB

Open AccessArticle

Design and Analysis of a Launcher Flight Control System Based on Incremental Nonlinear Dynamic Inversion

by Pedro Simplício, Paul Acquatella and Samir Bennani

Aerospace 2025, 12(4), 296; https://doi.org/10.3390/aerospace12040296 - 31 Mar 2025

Viewed by 58

Abstract

This paper investigates the application of Incremental Nonlinear Dynamic Inversion (INDI) for launch vehicle flight control, addressing the limited exploration of nonlinear control architectures and their potential benefits in the context of the current “New Space” era. In this context, this study aims [...] Read more.

This paper investigates the application of Incremental Nonlinear Dynamic Inversion (INDI) for launch vehicle flight control, addressing the limited exploration of nonlinear control architectures and their potential benefits in the context of the current “New Space” era. In this context, this study aims to bridge the gap between the launcher’s traditional linear control practice and nonlinear methods, focusing on INDI, which offers the potential to enhance limits of performance while reducing mission preparation (“missionisation”) efforts. INDI control commands incremental inputs by exploiting feedback acceleration estimates in a feedback-linearised plant in order to reduce model dependency, making it easier to design and resulting in a robust closed loop as compared to nonlinear dynamic inversion. The objective of this paper is therefore to demonstrate INDI’s implementation in a representative industrial launch ascent scenario, evaluate its strengths and limitations relative to industry standards, and promote its adoption within the launcher Guidance, Navigation, and Control (GNC) community. Comparative simulations with traditional scheduled PD controllers, with and without angular acceleration feedback, are highlighted together with several trade-offs. Furthermore, this paper presents a new and practical INDI stability analysis method as applied in the context of aerospace attitude control, as well as an augmentation of the design with an outer control loop for active load relief. Results indicate that while INDI exhibits increased sensitivity to sensor noise and actuator delays as compared to the linear controllers, its advantages in robustness and performance are significant. Notably, INDI’s ability to handle nonlinearities without extensive tuning and gain-scheduling surpasses the capabilities of the traditional linear control counterparts. These results highlight the potential of INDI as a more robust and efficient alternative to state-of-practice launcher control design methodologies. Full article

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

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10 pages, 1865 KiB

Open AccessArticle

Theoretical Research on the Combustion Characteristics of Ammonium Dinitramide-Based Non-Toxic Aerospace Propellant

by Jianhui Han, Ming Wen, Yanji Hong, Baosheng Du, Luyun Jiang, Haichao Cui, Gaoping Feng and Junling Song

Aerospace 2025, 12(4), 295; https://doi.org/10.3390/aerospace12040295 - 31 Mar 2025

Viewed by 41

Abstract

Propellants play a crucial role in the propulsion systems of aerospace vehicles, and their combustion characteristics are susceptible to external environmental conditions. This study systematically investigated the impact of various initial conditions on the combustion process of ADN-based propellant, including combustion products, equilibrium [...] Read more.

Propellants play a crucial role in the propulsion systems of aerospace vehicles, and their combustion characteristics are susceptible to external environmental conditions. This study systematically investigated the impact of various initial conditions on the combustion process of ADN-based propellant, including combustion products, equilibrium pressure, adiabatic temperature, and ignition delay time. The results indicate that the primary combustion products of ADN-based propellant include N₂O, N₂, CO₂, OH, and others. ADN-based propellant exhibits a distinct two-stage combustion process under low pressure and temperature conditions (P₀ = 2 atm, T₀ = 586 K). Conversely, under high pressure and temperature conditions (P₀ = 10 atm, T₀ = 2930 K), the two stages of combustion occur almost simultaneously, making them difficult to distinguish. Furthermore, as the initial temperature increases, the ignition delay time decreases significantly, and the combustion rate accelerates. When the initial temperature rises from 400 K to 2800 K at a pressure of P₀ =10 atm, the ignition delay time decreases from 3.5 ms to 0.6 μs. Interestingly, changes in initial pressure have a relatively minor impact on the ignition delay time compared to changes in temperature. Therefore, temperature has a more crucial influence on the combustion characteristics of ADN-based propellant than pressure. This study holds promise for providing new combustion optimization strategies for the aerospace industry and promoting the development of aircraft designs towards higher performance and sustainability. Full article

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

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25 pages, 3298 KiB

Open AccessArticle

Non-Linear and Quasi-Linear Models for the Large-Amplitude Static Aeroelastic Response of Very-Flexible Slender Wings in Subsonic Flow at Low Speed

by Marco Berci

Aerospace 2025, 12(4), 294; https://doi.org/10.3390/aerospace12040294 - 31 Mar 2025

Viewed by 118

Abstract

In the framework of lightweight aircraft preliminary design and optimisation, different computational approaches are formulated and assessed for the large-amplitude static aeroelastic response of very-flexible slender thin wings in subsonic incompressible flow at low speed. Starting from either a continuous or a discrete [...] Read more.

In the framework of lightweight aircraft preliminary design and optimisation, different computational approaches are formulated and assessed for the large-amplitude static aeroelastic response of very-flexible slender thin wings in subsonic incompressible flow at low speed. Starting from either a continuous or a discrete model, either numerical or semi-analytical solutions are derived and compared for several combinations of flow speed and angle of attack. Exploiting the Euler–Bernoulli beam idealisation for the wing structure and its local deformation, non-linear and quasi-linear models are presented where the elastic axis is inextensible and its global displacement is geometrically nonlinear; to this purpose, Hencky’s model is also adopted. Employing modified strip theory for the airload, reduced-order conceptual assessments and parametric evaluations are possible, and the results are shown for the Pazy wing which exhibit excellent agreement with nonlinear higher-fidelity simulations in the literature. Both closed-loop and open-loop solutions are then provided, with the latter being readily resumed from the former in the low-speed limit far away from static aeroelastic divergence. In conclusion, the novel approaches hereby explored demonstrate overall consistency while offering both theoretical insights and practical recommendations for their trust region, especially in terms of the impact and importance of the linear and nonlinear features as well as their effects. Full article

(This article belongs to the Special Issue Recent Advances in Applied Aerodynamics)

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27 pages, 5047 KiB

Open AccessArticle

Inertial Subrange Optimization in Eddy Dissipation Rate Estimation and Aircraft-Dependent Bumpiness Estimation

by Zhenxing Gao, Qilin Zhang and Kai Qi

Aerospace 2025, 12(4), 293; https://doi.org/10.3390/aerospace12040293 - 30 Mar 2025

Viewed by 41

Abstract

Atmospheric turbulence leads to aircraft bumpiness. In current vertical wind-based eddy dissipation rate (EDR) estimation algorithms based on flight data, the inertial subrange is determined empirically. In application, specific aircraft bumpiness can only be described by an EDR indicator. In this study, the [...] Read more.

Atmospheric turbulence leads to aircraft bumpiness. In current vertical wind-based eddy dissipation rate (EDR) estimation algorithms based on flight data, the inertial subrange is determined empirically. In application, specific aircraft bumpiness can only be described by an EDR indicator. In this study, the objective turbulence severity and aircraft-related bumpiness estimation were explored with an optimized inertial subrange. To obtain the inertial subrange, the minimum series length to estimate EDR was determined under different flight data sampling rate. In addition, the basic series length to estimate the inertial subrange was determined according to Blackman–Tukey spectra estimation theory. In aircraft-dependent bumpiness estimation, the unsteady vortex lattice method (UVLM) was designed to obtain an accurate aircraft acceleration response to turbulence. An in situ aircraft bumpiness estimation and bumpiness prediction method were further proposed. Simulation and experiments on real flight data testified the optimized aircraft-independent EDR estimation and aircraft-dependent bumpiness estimation successively. This study can be further applied to estimate the turbulence severity on a particular airway, while the bumpiness of specific aircraft can be predicted. Full article

(This article belongs to the Special Issue Advanced Aircraft Technology (2nd Edition))

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24 pages, 5291 KiB

Open AccessArticle

Aerodynamic Prediction and Design Optimization Using Multi-Fidelity Deep Neural Network

by Bingchen Du, Ennan Shen, Jiangpeng Wu, Tongqing Guo, Zhiliang Lu and Di Zhou

Aerospace 2025, 12(4), 292; https://doi.org/10.3390/aerospace12040292 - 30 Mar 2025

Viewed by 68

Abstract

With the rapid development of data-driven methods in recent years, deep neural networks have attracted significant attention for aerodynamic predictions and design optimizations. Among these methods, the multi-fidelity deep neural network (MFDNN), which can combine high-fidelity (HF) and low-fidelity (LF) data, has gained [...] Read more.

With the rapid development of data-driven methods in recent years, deep neural networks have attracted significant attention for aerodynamic predictions and design optimizations. Among these methods, the multi-fidelity deep neural network (MFDNN), which can combine high-fidelity (HF) and low-fidelity (LF) data, has gained popularity. This paper systematically investigates the performances of employing MFDNN models in predicting aerodynamic coefficients and in performing aerodynamic shape optimizations (ASOs), especially the impact of using various HF/LF data ratios for training models. The results of the prediction accuracy of the aerodynamic coefficients of airfoils show that the less HF data used, the more advantages can be achieved by the MFDNN models than the single-fidelity models. The well-trained MFDNN models are then employed in an ASO problem of airfoil in the subsonic regime, and it is found that a higher HF/LF data ratio does not definitely result in a better performance in the ASO. As the insufficiency in the prediction accuracy of the optimal shapes appears when employing the non-updated MFDNN models, an update strategy is developed by tightly integrating the MFDNN models with the particle swarm optimization algorithm. To further reduce the time costs for updating models, a dual-threshold update strategy is then introduced, which can half the counts of evaluating HF data. Full article

(This article belongs to the Section Aeronautics)

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29 pages, 6040 KiB

Open AccessArticle

Properties and Behavior of 3D-Printed ABS Fuel in a 10 N Hybrid Rocket: Experimental and Numerical Insights

by Sergio Cassese, Veniero Marco Capone, Riccardo Guida, Stefano Mungiguerra and Raffaele Savino

Aerospace 2025, 12(4), 291; https://doi.org/10.3390/aerospace12040291 - 30 Mar 2025

Viewed by 62

Abstract

In a global landscape where the launch of satellites into space is growing exponentially, there is an increasing demand for propulsion solutions to perform various types of maneuvers. In this context, the present study aims to investigate a 3D-printed ABS (Acrylonitrile Butadiene Styrene)-based [...] Read more.

In a global landscape where the launch of satellites into space is growing exponentially, there is an increasing demand for propulsion solutions to perform various types of maneuvers. In this context, the present study aims to investigate a 3D-printed ABS (Acrylonitrile Butadiene Styrene)-based fuel for use in a 10 N-scale hybrid rocket in order to promote cost-effective and environmentally friendly access to space. As this material is currently unknown in this field and lacks a thermodynamic database, characterization of its pyrolysis process was carried out through a mixed approach combining experimental data and numerical simulations. The experiments show excellent performance of the H₂O₂-3D-printed ABS pair; despite the lack of information on its thermodynamically relevant quantities, it was possible to accurately reconstruct the fuel consumption profile as well as its regression rate and the spatial and temporal average values using the numerical model and Arrhenius parameters derived in this work. The methodology and results obtained herein represent tools that can be useful for the design of small-scale rockets using 3D-printed ABS-based fuels as well as a starting point for the development and analysis of the complex geometries made possible through additive manufacturing. Full article

(This article belongs to the Special Issue Space Propulsion: Advances and Challenges (3rd Volume))

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18 pages, 8602 KiB

Open AccessArticle

A Preliminary Exploratory Study of the Flow and Heat Transfer Characteristics of Fuel Elements in Low-Enriched Uranium Cores

by Mingxue Shao, Songjiang Feng, Kangkang Guo, Yiheng Tong and Wei Lin

Aerospace 2025, 12(4), 290; https://doi.org/10.3390/aerospace12040290 - 30 Mar 2025

Viewed by 41

Abstract

Nuclear thermal propulsion, which uses a reactor core as the energy source of a nuclear thermal rocket, is expected to become an effective means of deep space exploration in the future. The reactor core can be damaged by a large temperature gradient. Thus, [...] Read more.

Nuclear thermal propulsion, which uses a reactor core as the energy source of a nuclear thermal rocket, is expected to become an effective means of deep space exploration in the future. The reactor core can be damaged by a large temperature gradient. Thus, investigating the structural distribution of its internal components and understanding its flow and heat transfer characteristics is highly important. In this study, a 19-hole hollow hexagonal prism fuel element is selected for simulation. A new type of fuel element is proposed by changing the diameter of the channels in the work material, and the heat transfer characteristics are compared and analyzed. Compared with a conventional fuel element under uniform inlet conditions, when the inlet conditions and the diameter of the channel in the work material are changed, the peak temperature inside the fuel element decreases, but the overall temperature distribution is more uniform. Along the flow direction, the temperature distribution boundary is located at y = 300–500 mm. From the inlet to this position, the temperature distribution on the axial cross-section is uniform. From this position to the outlet, the temperature difference along the radial cross-section is significantly reduced, and the temperature fluctuation at the periphery of the fuel element is significantly improved. The research results can provide a reference for the design of fuel elements. Full article

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

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20 pages, 12586 KiB

Open AccessArticle

Design of an Orbital Infrastructure to Guarantee Continuous Communication to the Lunar South Pole Region

by Nicolò Trabacchin and Giacomo Colombatti

Aerospace 2025, 12(4), 289; https://doi.org/10.3390/aerospace12040289 - 30 Mar 2025

Viewed by 81

Abstract

The lunar south pole has gained significant attention due to its unique scientific value and potential for supporting future human exploration. Its potential water ice reservoirs and favourable conditions for long-term habitation make it a strategic target for upcoming space missions. This has [...] Read more.

The lunar south pole has gained significant attention due to its unique scientific value and potential for supporting future human exploration. Its potential water ice reservoirs and favourable conditions for long-term habitation make it a strategic target for upcoming space missions. This has led to a continuous increase in missions towards the Moon thanks mainly to the boost provided by NASA’s Artemis programme. This study focuses on designing a satellite constellation to provide communication coverage for the lunar south pole. Among the various cislunar orbits analysed, the halo orbit families near Earth–Moon Lagrangian points L1 and L2 emerged as the most suitable ones for ensuring continuous communication while minimising the number of satellites required. These orbits, first described by Farquhar in 1966, allow spacecraft to maintain constant communication with Earth due to their unique geometric properties. The candidate orbits were initially implemented in MATLAB using the Circular Restricted Three-Body Problem (CR3BP) to analyse their main features such as stability, periodicity, and coverage time percentage. In order to develop a more detailed and realistic scenario, the obtained initial conditions were refined using a full ephemeris model, incorporating a ground station located near the Connecting Ridge Extension to evaluate communication performance depending on the minimum elevation angle of the antenna. Different multi-body constellations were propagated; however, the constellation consisting of three satellites around L2 and a single satellite around L1 turned out to be the one that best matches the coverage requirements. Full article

(This article belongs to the Special Issue Advances in Lunar Exploration)

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22 pages, 6290 KiB

Open AccessArticle

The Concept of an Early Warning System for Supporting Air Traffic Control

by Piotr Konopka and Paweł Rzucidło

Aerospace 2025, 12(4), 288; https://doi.org/10.3390/aerospace12040288 - 29 Mar 2025

Viewed by 111

Abstract

This article addresses the issue of loss of separation incidents and discusses currently implemented technological solutions designed to minimize the risk of such occurrences. An evaluation of these solutions is conducted, highlighting their key advantages and disadvantages. Additionally, a literature review of proposed [...] Read more.

This article addresses the issue of loss of separation incidents and discusses currently implemented technological solutions designed to minimize the risk of such occurrences. An evaluation of these solutions is conducted, highlighting their key advantages and disadvantages. Additionally, a literature review of proposed new solutions is presented, emphasizing the necessity of introducing a new system to address previously identified shortcomings. This work proposes an early warning system for potential airspace collisions based on an artificial neural network. Drawing from the literature analysis, five fundamental assumptions for an early conflict warning system to support air traffic control are formulated. Each assumption is justified, with some addressing the weaknesses of existing solutions. The contributions of this paper, in relation to previously analyzed works, are as follows: (1) the system does not rely on the dynamics model of a specific aircraft type, (2) the possibility of radar vectoring (vectors to final) is considered, (3) the input data are not limited to the horizontal plane and time differences, (4) the system does not require identifying the most similar historical trajectories to assess minimum separation values and potential conflicts, and (5) the system is expected to perform better in airspace where radar vectoring prevails compared to flight along standard routes. The research methodology is discussed in detail, including the operational environment of the system and the applied algorithms. A feedforward neural network was selected, featuring 32 neurons in the first hidden layer and 16 neurons in the second hidden layer. The training process was conducted using the Levenberg–Marquardt algorithm, chosen for its fast convergence. The presented analyses confirm that the developed system meets the established assumptions. Full article

(This article belongs to the Special Issue Future Airspace and Air Traffic Management Design)

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15 pages, 5021 KiB

Open AccessArticle

Off-Axial Tensile Test and Analysis for Stratospheric Airship Envelope Material

by Zhanbo Li, Yanchu Yang, Rong Cai and Lin Song

Aerospace 2025, 12(4), 287; https://doi.org/10.3390/aerospace12040287 - 28 Mar 2025

Viewed by 68

Abstract

The mechanical properties of envelope materials play a critical role in determining the service life of stratospheric airships. This paper investigates the failure analysis and strength criteria of a plain-woven stratospheric envelope material. First, a series of off-axial tensile tests were conducted, revealing [...] Read more.

The mechanical properties of envelope materials play a critical role in determining the service life of stratospheric airships. This paper investigates the failure analysis and strength criteria of a plain-woven stratospheric envelope material. First, a series of off-axial tensile tests were conducted, revealing that the material exhibits significant nonlinearity and orthotropic behavior under off-axial loading. Notably, the failure strength of the material decreases dramatically at small off-axial angles. Second, finite element simulations were performed to analyze the failure mechanisms of specimens at various off-axial angles and a potential explanation for the sharp decline in failure strength is proposed. Third, the predictions of several existing strength criteria were compared with experimental results, showing limited agreement. To address this, a new strength criterion is introduced to more accurately predict the failure strength of the envelope material across different off-axial angles. The results demonstrate that the proposed criterion offers a significant improvement in predicting the mechanical behavior of plain-woven stratospheric envelope materials Full article

(This article belongs to the Section Aeronautics)

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26 pages, 18712 KiB

Open AccessArticle

Numerical Investigation of Stage Separation Control of Tandem Hypersonic Vehicles Based on Lateral Jet

by Wenhua Guo, Jiawei Fu, Pengzhen He and Shuling Tian

Aerospace 2025, 12(4), 286; https://doi.org/10.3390/aerospace12040286 - 28 Mar 2025

Viewed by 162

Abstract

The stage separation of hypersonic vehicles is critically challenged by severe aerodynamic interference, which induces significant attitude deviations and jeopardizes subsequent flight missions. This study investigates open-loop and closed-loop attitude control methods utilizing lateral jets to stabilize the forebody during separation. Dynamic CFD-based [...] Read more.

The stage separation of hypersonic vehicles is critically challenged by severe aerodynamic interference, which induces significant attitude deviations and jeopardizes subsequent flight missions. This study investigates open-loop and closed-loop attitude control methods utilizing lateral jets to stabilize the forebody during separation. Dynamic CFD-based numerical simulations were conducted for a tandem hypersonic vehicle, analyzing trajectories and aerodynamic characteristics under free separation, open-loop, and closed-loop control. Results show that open-loop control achieves a maximum forebody pitch angle of only 0.27° at

α = 0 °

, but performance degrades drastically to 24.88° at

α = 2.5 °

, highlighting its sensitivity to freestream variations. In contrast, a cascade PID-based closed-loop control system dynamically adjusts lateral jet total pressure, reducing the maximum pitch angle to 0.006° at

α = 0 °

and maintaining it below 0.2° even at

α = 5.0 °

. The closed-loop system exhibits periodic fluctuations in jet pressure, with amplitude increasing alongside angle of attack, yet demonstrates superior robustness against aerodynamic disturbances. Flow field analysis reveals enhanced shockwave interactions and vortex dynamics under closed-loop control, effectively mitigating pitch instability. While open-loop methods are constrained to specific conditions, closed-loop control significantly broadens applicability across variable flight environments. Full article

(This article belongs to the Special Issue Sustainable Civil Supersonic and Hypersonic Aircraft: Main Challenges and Latest Developments)

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26 pages, 3411 KiB

Open AccessArticle

Examining the Accuracy of Differenced One-Way Doppler Orbit Determination Derived from Range-Only Relay Satellite Tracking

by Ashok Kumar Verma

Aerospace 2025, 12(4), 285; https://doi.org/10.3390/aerospace12040285 - 28 Mar 2025

Viewed by 363

Abstract

This paper delves into the impact of the Tracking and Data Relay Satellite (TDRS) constellation orbit accuracy on Differenced One-Way Doppler (DOWD)-based user spacecraft orbit determination, specifically when the TDRS orbit is derived solely from Telemetry, Tracking, and Command (TT&C) range-only tracking. The [...] Read more.

This paper delves into the impact of the Tracking and Data Relay Satellite (TDRS) constellation orbit accuracy on Differenced One-Way Doppler (DOWD)-based user spacecraft orbit determination, specifically when the TDRS orbit is derived solely from Telemetry, Tracking, and Command (TT&C) range-only tracking. The study revealed that retiring the Bilateration Ranging Transponder System (BRTS) without fully comprehending the TT&C bias and its uncertainty could hinder achieving the required level of orbit precision for both TDRS satellites (<75 m) and user spacecraft (<300 m). If the TT&C range bias and its associated uncertainties are not accurately calibrated in a TT&C-based TDRS orbit, it could lead to an orbit error of up to 17 km in the TDRS, yielding a DOWD-based orbit error of up to 5 km for the user spacecraft. The research identifies a linear relationship between TDRS orbit error and user spacecraft orbit error, with several factors impacting the slope of this relationship, including the number of DOWD passes obtained, the TDRS’s relative position during DOWD measurement acquisition, and dynamic errors in the user spacecraft orbit. Despite the imprecision in the orbits of the TDRS and user spacecraft, the Local Oscillator Frequency drift estimation remains accurate. Full article

(This article belongs to the Special Issue Precise Orbit Determination of the Spacecraft)

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22 pages, 2256 KiB

Open AccessArticle

Air Traffic Trends and UAV Safety: Leveraging Automatic Dependent Surveillance–Broadcast Data for Predictive Risk Mitigation

by Prasad Pothana, Paul Snyder, Sreejith Vidhyadharan, Michael Ullrich and Jack Thornby

Aerospace 2025, 12(4), 284; https://doi.org/10.3390/aerospace12040284 - 28 Mar 2025

Viewed by 166

Abstract

With the significant potential of Unmanned Aircraft Vehicles (UAVs) extending throughout various fields and industries, their proliferation raises concerns regarding potential risks within the national airspace system (NAS). To enhance the safe and efficient integration of UAVs into airport environments, this paper presents [...] Read more.

With the significant potential of Unmanned Aircraft Vehicles (UAVs) extending throughout various fields and industries, their proliferation raises concerns regarding potential risks within the national airspace system (NAS). To enhance the safe and efficient integration of UAVs into airport environments, this paper presents an analysis of temporal statistical patterns in flight traffic, the predictive modeling of future traffic trends using machine learning, and the identification of optimal time windows for UAV operations within airports. The framework was developed using historical Automatic Dependent Surveillance–Broadcast (ADS-B) data obtained from the OpenSky Network. Historical flight data from Class B, C, and D airports in California are processed, and statistical analysis is carried out to identify temporal variations in flight traffic, including daily, weekly, and seasonal trends. A recurrent neural network (RNN) model incorporating Long Short-Term Memory (LSTM) architecture is developed to forecast future flight counts based on historical patterns, achieving mean absolute error (MAE) values of 4.52, 2.13, and 0.87 for Class B, C, and D airports, respectively. The statistical analysis findings highlight distinct traffic patterns across airport classes, emphasizing the practicality of utilizing ADS-B data for UAV flight scheduling to minimize conflicts with manned aircraft. Additionally, the study explores the influence of external factors, including weather conditions and dataset limitations on prediction accuracy. By integrating machine learning with real-time ADS-B data, this research provides a framework for optimizing UAV operations, supporting airspace management and improving regulatory compliance for safe UAV integration into controlled airspace. Full article

(This article belongs to the Special Issue Research and Applications of Low-Altitude Urban Traffic System)

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28 pages, 16669 KiB

Open AccessArticle

Spin Period Evolution of Decommissioned GLONASS Satellites

by Abdul Rachman, Alessandro Vananti and Thomas Schildknecht

Aerospace 2025, 12(4), 283; https://doi.org/10.3390/aerospace12040283 - 27 Mar 2025

Viewed by 130

Abstract

Light curve analysis of defunct satellites is critical for characterizing their rotational motion. An accurate understanding of this aspect will benefit active debris removal and on-orbit servicing missions as part of the solution to the space debris issue. In this study, we explored [...] Read more.

Light curve analysis of defunct satellites is critical for characterizing their rotational motion. An accurate understanding of this aspect will benefit active debris removal and on-orbit servicing missions as part of the solution to the space debris issue. In this study, we explored the attitude behavior of inactive GLONASS satellites, specifically a repeating pattern observed in their spin period evolution. We utilized a large amount of data available in the light curve database maintained by the Astronomical Institute of the University of Bern (AIUB). The morphology of the inactive GLONASS light curves typically features four peaks in two pairs and is presumably attributed to the presence of four evenly distributed thermal control flaps or radiators on the satellite bus. The analysis of the periods extracted from the light curves shows that nearly all of the inactive GLONASS satellites are rotating and exhibit a periodic oscillating pattern in their spin period evolution with an increasing or decreasing secular trend. Through modeling and simulation, we found that the periodic pattern is likely a result of canted solar panels that provide an asymmetry in the satellite model and enable a wind wheel or fan-like mechanism to operate. The secular trend is a consequence of differing values of the specular reflection coefficients of the front and back sides of the solar panels. Assuming an empirical model describing the spin period evolution of 18 selected objects, we found significant variations in the average spin period and amplitude of the oscillations, which range from 8.11 s to 469.58 s and 1.10 s to 513.24 s, respectively. However, the average oscillation period remains relatively constant at around 1 year. Notably, the average spin period correlates well with the average amplitude. The empirical model can be used to extrapolate the spin period in the future, assuming that the oscillating pattern is preserved and roughly shows a linear trend. Full article

(This article belongs to the Special Issue Innovative Methods for Satellite and Space Debris Identification and Motion Reconstruction)

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24 pages, 5221 KiB

Open AccessArticle

Slot Allocation for a Multi-Airport System Considering Slot Execution Uncertainty

by Fengfan Liu, Minghua Hu, Qingxian Zhang and Lei Yang

Aerospace 2025, 12(4), 282; https://doi.org/10.3390/aerospace12040282 - 27 Mar 2025

Viewed by 82

Abstract

Capacity–flow balance constitutes the primary challenge in strategic slot allocation. Both air traffic flow and airport flow are significantly influenced by departure/arrival times of flights. However, due to various uncontrollable factors such as flow control, delay propagation, and weather conditions, the actual departure/arrival [...] Read more.

Capacity–flow balance constitutes the primary challenge in strategic slot allocation. Both air traffic flow and airport flow are significantly influenced by departure/arrival times of flights. However, due to various uncontrollable factors such as flow control, delay propagation, and weather conditions, the actual departure/arrival times of flights inevitably deviate from their schedules. This reflects the inherent uncertainty in flight slot execution, which directly introduces uncertainty into capacity–flow analysis. In this paper, we develop an uncertainty slot allocation model for the multi-airport system (MAS), which incorporates slot execution deviation as an uncertainty factor with fix capacity restrictions formulated as chance constraints to balance robustness and optimality. To solve the model, we employ an equivalent model transformation approach and develop a scenario generation methodology. We applied our model to the MAS of Beijing–Tianjin for slot allocation. The results show that when the violation probability

α \in [0, 0.2]

, the model achieved fully robust optimization. Even when

α

increases to 0.4, under all scenario combinations, at the selected fix, compared with the results of the deterministic model and original schedules, the number of peak flow time windows in the expected traffic statistics decreased by 84.6% and 75%, respectively, and the average maximum values of traffic in the maximum traffic statistics decreased by 31.1% and 33.5%, respectively. Furthermore, the incorporation of the chance constraint provides slot coordinators with flexible optimization solutions based on their acceptable risk levels. Full article

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

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19 pages, 10969 KiB

Open AccessArticle

Heat Shield Properties of Lightweight Ablator Series for Transfer Vehicle Systems with Different Laminated Structures Under High Enthalpy Flow Environments

by Masayuki Ohkage, Kei-ichi Okuyama, Soichiro Hori and Tsumugi Ishida

Aerospace 2025, 12(4), 281; https://doi.org/10.3390/aerospace12040281 - 27 Mar 2025

Viewed by 109

Abstract

The thermal protection system of a re-entry vehicle requires a high-heat-resistant heat shield to protect the spacecraft. Most of the ablative materials developed so far have high heat resistance but have technical issues such as long production times. In this study, we propose [...] Read more.

The thermal protection system of a re-entry vehicle requires a high-heat-resistant heat shield to protect the spacecraft. Most of the ablative materials developed so far have high heat resistance but have technical issues such as long production times. In this study, we propose a new ablative material (LATS/PEEK) consisting of PEEK and carbon felt as a material that can solve these problems. PEEK has excellent properties such as a short production time and its ability to be produced using 3D printer technology. In addition, PEEK can be molded with a variety of fusion bonding methods, so it is possible to mold the heat shield and structural components as a single structure. However, heating tests conducted in previous research have confirmed the expansion phenomenon of CF/PEEK produced by 3D printers. The expansion of the ablative material is undesirable because it changes the aerodynamic characteristics during re-entry flight. Therefore, the purpose of this research is to clarify the mechanism of the expansion phenomenon of the ablative material based on PEEK resin. Therefore, we conducted thermal gravimetric analysis (TGA) and thermomechanical analysis (TMA) and concluded that the expansion phenomenon during the heating test was caused by the pressure increase inside the ablative material due to pyrolysis gas. Based on this mechanism, we developed a new 3D LATS/PEEK with a structure that can actively release pyrolysis gas, and we conducted a heating test using an arc-heating wind tunnel. As a result, it was found that 3D LATS/PEEK had less expansion and deformation during the heating test than CF/PEEK manufactured using a 3D printer. Full article

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

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Aerospace, Volume 12, Issue 4 (April 2025) – 44 articles

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