Engineering

Abstract: Tether-net systems represent a leading technology for the Active Debris Removal (ADR) of non-cooperative space objects; however, a fundamental operational gap persists between the discipline of Space Situational Awareness (SSA) and the mechanics of net-based capture. No existing framework propagates the observational uncertainties inherent to SSA data through net deployment dynamics to yield operationally actionable capture probability estimates. This paper addresses that gap by proposing an end-to-end SSA-to-ADR uncertainty propagation pipeline that treats tether-net debris capture as a probabilistic decision problem under observational uncertainty. Characterization of the full debris-state covariance from TLE-derived orbital uncertainties and photometric light-curve spin-state estimates; linear covariance propagation and Monte Carlo sampling through a lumped-parameter tether-net deployment dynamics model to the ejection epoch; and construction of a capture probability surface over the ejection parameter space that quantifies expected capture success as a function of observable data quality. The methodology is developed and exercised using Telkom-3, a defunct Indonesian satellite with concurrent photometric observations from Zimmerwald Observatory. The role of ground-based geographically distributed SSA networks in reducing state uncertainty and improving capture reliability is explicitly quantified. In the present implementation, the framework’s rotational-phase coupling is exercised in its conservative, uniform-phase limiting case; the architecture is designed to accommodate the spin-period-dependent phase concentration suggested by the photometric dataset as a direct extension. The proposed framework establishes a principled, transferable, and traceable methodology for probabilistic ADR mission planning conditioned on actual observational campaign quality.

Abstract: Public aircraft-engine certification data provide a reproducible basis for emissions modeling when proprietary combustor geometry, engine-cycle data, and detailed operating histories are unavailable. This study develops a physically constrained framework based on the International Civil Aviation Organization (ICAO) Aircraft Engine Emissions Databank for modeling gaseous emissions from civil aircraft gas-turbine engines over the landing-and-take-off (LTO) cycle. The analysis uses variables available directly from the ICAO Aircraft Engine Emissions Databank, together with derived LTO quantities, to construct combustor-aware reduced-order correlations for LTO-averaged emission indices of nitrogen oxides (NO_x), carbon monoxide (CO), and hydrocarbons (HC), denoted by EINO_xLTO, EICO_LTO, and EIHC_LTO, respectively. High-bypass-ratio (HBPR) turbofan engines are grouped by representative combustor technology, including conventional/single-annular combustor (Conventional/SAC), double-annular combustor (DAC), twin-annular premixing swirler (TAPS), Rolls–Royce TALON lean-burn combustor, low-emissions combustor (LEC), and Unknown categories. For each pollutant and combustor group, two-predictor quadratic response surfaces and power-law correlations are fitted using public engine-level predictors such as overall pressure ratio, bypass ratio, rated thrust, and total LTO fuel consumption. The results show that combustor-aware grouping substantially improves interpretability and that no single global predictor pair represents all pollutants or combustor technologies. For EINO_xLTO, overall pressure ratio appears in most selected predictor pairs, consistent with the pressure- and temperature-sensitive nature of NO_x formation. For EICO_LTO, robust group-specific correlations are obtained for several combustor classes, whereas EIHC_LTO is more sensitive to zero and near-zero values, making percentage-based errors and log-space power-law fits less reliable. The quadratic models generally provide stronger within-dataset descriptive fits, while the power-law models provide compact non-negative scaling relations when their errors are acceptable.The proposed framework is suitable for emissions-trend analysis, preliminary comparative assessment, and interpretation of public certification data, but it should not be used as a substitute for certification testing, detailed combustor simulation, or off-design mission-level prediction without additional validation.

Abstract: Inverse airfoil design, recovering a geometry that produces a prescribed surface pressureor edge-velocity distribution, is recast here as a single determined nonlinear root-find ratherthan an objective-function search. Parameterising the surface with Class-Shape-Transformation(CST) coefficients that enter the geometry linearly makes the geometric sensitivity of the surfaceexact, constant and design-independent. It also makes geometric design constraints, among themleading-edge radius, trailing-edge thickness and inscribed area, linear algebraic rows rather thannonlinear predicates. Appending the CST coefficients as unknowns to a coupled viscous/inviscidNewton solver (mfoil) therefore converts constrained shape optimisation into constrained root-finding: one square system, no outer loop, no surrogate. The architecture is validated with afalsifiable self-consistency test in which a known CST coefficient vector is recovered from itsown self-generated target to ∥A−A∗∥_∞= 2.75 ×10⁻¹¹ in six Newton iterations. The recoveredgeometry reproduces the reference section’s fully released (natural-transition) aerodynamiccoefficients to ∆c_l = 3.4 ×10⁻¹². An ablation matrix identifies the primary uniqueness guard forthe resulting square system: sensitivity-optimal (QR-pivoted) selection of target stations, notinitial-guess quality, separates recovery of the true design from clean convergence to a spuriousbut residual-zeroing root. Measured against a competently-tuned nested Levenberg–Marquardtbaseline under two independent fair-paired controls, the monolithic architecture requires 3.1–8.1×fewer counted flow solves and 3.4–3.5×less wall-clock time. This is a real but modest reduction,not the two-to-three-orders-of-magnitude headline hypothesised a priori, and it comes withdeterminism, an exact analytic Jacobian for the constraint rows, and per-iteration failure-modediagnostics for which the nested baseline has no analogue. Generalisation is then evaluatedon two pre-registered panels. A 20-section NACA panel recovers all 18 generable sections to∥A−A∗∥_∞ ≤1.51 ×10⁻¹⁰; a 117-section panel drawn from the UIUC coordinate databaserecovers every one of its 83 converged sections to better than 10⁻⁴, while missing the pre-registered composite criterion on iteration count rather than on accuracy. Both panel outcomesare reported alongside the exclusions they rest on and the geometric bias those exclusions carry.The architecture is finally placed on a comparison table against MISES’s own modal inverse mode,the nearest prior CST-based inverse method, and the current generative and learned-surrogateinverse-design literature, on formulation class, cost, determinism and constraint-handling groundsrather than a single flow-solve number, since the methods are not commensurable on that axisalone.

Abstract: Today’s conventional lithium-ion battery technology used for UAVs are constrained by modest specific energy values, restricting flight endurance to roughly 10–40 minutes for small-platform configurations. Therefore, the of hydrogen fuel cell technology for unmanned aerial vehicles (UAVs) has attracted growing interest from the both military and civilian aviation sectors. In contrast, Proton Exchange Membrane Fuel Cells (PEMFCs), when integrated with Type V hydrogen gaseous tanks, offer high energy densities and electrochemical conversion efficiencies, making them the most promising alternative propulsion energy source for extended-endurance missions. This new technology refers to lightweight materials such as carbon fiber reinforced polymer composite and structural adhesives utilized for assembling, which have already remarkable application in the aerospace industry. This review systematically examines the fundamentals of PEMFC technology, hydrogen storage systems, hybrid power system architectures, energy management strategies, safety requirements, representative field demonstrations, economic and environmental assessments, and the principal technical barriers and open research questions. Advanced thermal management, emerging electrode and membrane materials, and artificial intelligence-assisted energy management algorithms are identified as the defining factors that will determine whether hydrogen-powered UAV technology achieves commercial and operational maturity.

Abstract: This study investigates the spacecraft kinematics within the extreme gravitational environment of the Galactic Center, focusing on orbital dynamics near the supermassive black hole Sagittarius A* (Sgr A*). Because classical Newtonian mechanics fails in this strong-field regime, a high-fidelity numerical propagator based on the Schwarzschild metric was developed. By integrating with an explicit, adaptive-step Runge-Kutta method of order 8(5, 3) based on the Dormand-Prince coefficients (DOP853) the exact formulation of the forced geodesics, the relativistic dynamics are resolved using the proper time. The analysis explores transfer trajectories targeting both the highly eccentric stars S62 and S4714, and the wider orbits of S22 and S91. Results demonstrate that a classical open-loop Lambert guidance generates a macroscopic spatial divergence, quantified as a “Relativistic Miss Distance” exceeding 1.4 · 10⁷ kilometers. The research mathematically isolates the kinematic phenomena caused by spacetime curvature: the attractive cubic term in the effective potential, the V-shaped excursion of osculating orbital elements at pericenter, the step-wise Schwarzschild precession, and severe chronometric delay due to gravitational time dilation. The study concludes that rigorous, purely relativistic modeling is an absolute requirement to accurately describe kinematic evolution in the Milky Way's core.

Abstract: Shot peen forming and creep age forming are the principal industrial routes for generating contour in metallic aircraft wing covers. Although the mechanics of both are well documented, neither has been examined with the patent record as the unit of analysis. This study assembles comparative corpora of 157 patent families spanning 1951 to 2026, by classification-anchored retrieval and systematic citation-network tracing, coding every family by claim type and determining its jurisdictional breadth and grant outcome. The two processes exhibit measurably different bottlenecks. Creep age forming devotes 40% of its corpus to tooling against 15% for shot peen forming, whereas shot peen forming devotes 24% to control and compensation against 8% for creep age forming. The binding constraint has been geometry transfer for the former and process control for the latter, so the two routes require different de-risking strategies. Three further results follow. The foundational era of shot peen forming is tri-national rather than exclusively American. Apparent Chinese dominance of the recent record survives neither normalisation against background filing nor a breadth measure, 96% of Chinese families being filed at a single office. Citation tracing rather than classification search is required to observe such a landscape.

Abstract: Ice accumulation on aerodynamic surfaces remains a major safety and efficiency challenge for aircraft. Conventional electrothermal deicing systems are reliable but often require more electrical power than is available on small, medium-sized, and unmanned aircraft, whereas electro-impulsive deicers introduce structural fatigue and mechanical complexity. Recently developed Ice Cavitation Deicing (ICD) demonstrated highly efficient ice removal by explosively vaporizing a thin interfacial water layer. However, the original high-temperature ICD (HTICD) operates at heating rates above 106 K/s and cavitation temperatures near 300 °C, producing foil temperatures exceeding 400 °C and requiring high-voltage film capacitors. This study develops and experimentally validates Low-Temperature and Medium-Temperature Ice Cavitation Deicing (LTICD and MTICD), extending the concept of impulse cavitation deicing into the previously unexplored intermediate heating-rate regime. Analytical modeling based on energy conservation, transient heat diffusion, water thermodynamics, and thermal-stress analysis was combined with finite-element simulations and extensive experimental testing. Stainless steel 17-7PH, titanium Grade 5, titanium Grade 1, Invar, and other foil materials were evaluated over heating rates ranging from approximately 104 to 107 K/s using capacitor banks from 0.1 to 35 mF. The experimental results demonstrate that both LTICD and MTICD effectively remove thick and thin ice while operating at cavitation temperatures of approximately 120–200 °C, substantially below those of HTICD. The lower operating temperatures and heating rates reduce thermal stress, operating voltage, and current, enable the use of practical low-voltage electrolytic capacitors, and expand the range of suitable foil and substrate materials. These results demonstrate that the cavitation-deicing mechanism can be implemented at substantially lower temperatures and with a more practical electrical architecture than HTICD, making LTICD and MTICD promising candidates for future aircraft ice-protection systems.

Abstract: Aircraft electrification requires high performance thermal management systems able to cool-down power-plants with increasing power densities in electric aircraft motors. The demanding mission profiles and the request for compact electric components, in fact, induce high temperatures in power-plant system that must be cooled by proper thermal management systems, to assure systems efficiency and reliability. This paper investigates and compares two promising approaches for the cooling of megawatt order electric motor for aviation applications: nanofluid based liquid cooling and radial tube systems. Nanofluids are an innovative approach to system cooling leveraging on the physic properties of the coolant; radial tubes, conversely, represent a structural solution aimed at improving the heat removal. In particular, nanofluids are composed by colloidal suspensions of nanoparticles in a base fluid, enabling enhanced thermal conductivity and convective heat transfer coefficients compared to conventional coolants. Radial tubes improve heat removal through optimized conduction paths and increased surface to volume ratios without altering the working fluid. Through numerical analysis carried out by using state of the art Computational Fluid Dynamic (CFD) tools, results highlight the main advantages of the two systems: nanofluids provide a significant average heat transfer enhancement on the tooth, while the radial tubes involve a strong increase in the global heat exchange despite a larger oil flow rate.

Abstract: The increasing demand for SmallSats requires launch systems providing responsive, independent, and mission-specific access to orbit. This study presents the conceptual design and feasibility assessment of a Nuri-derived SmallSat-dedicated launch vehicle for delivering a 500 kg-class payload to a 500 km sun-synchronous orbit. Unlike previous planning-level studies focused on development strategies, this study quantitatively derives a vehicle configuration through staging design by incorporating geopolitical constraints on launches from the Naro Space Center, Nuri technological heritage, and emerging upper-stage engine and lightweight structural manufacturing technologies. The required velocity increment was distributed between stages, and the preliminary configuration was established through vehicle sizing. The design was evaluated using an ASTOS-based multidisciplinary design optimization framework integrating trajectory optimization, aerodynamic analysis, flight-load evaluation, and load-bearing structural mass estimation. The optimized trajectory satisfied the target-orbit and range-safety constraints and yielded a payload capability of 530 kg. The estimated dry masses of the first and second stages were 4,051 kg and 648 kg, corresponding to structural indices of 8.7% and 12.1%, respectively. These results support preliminary feasibility under the adopted modeling assumptions at the conceptual stage rather than providing detailed design verification of subsystems, while further validation is required to address structural and subsystem mass uncertainties.

Abstract: Radiometric interferometry is a powerful technique for angular spacecraft navigation, traditionally implemented through ground-based Very Long Baseline Interferometry (VLBI) and Delta Differential One-Way Ranging. A previously proposed concept, Radiometric Interferometry Navigation using GEO Satellites (RINGS), replaces terrestrial VLBI stations with geostationary satellites in order to create a space-based interferometric baseline for deep-space navigation. The present paper extends the initial RINGS concept by developing a time-position error analysis and by evaluating the impact of practical clock and GEO orbit-determination uncertainties on the reconstructed angle of arrival. The analysis focuses on two main practical error sources: residual relative clock misalignment between the GEO satellites and uncertainty in the GEO station positions that define the interferometric baseline. First, analytical models are developed to map clock timing error and GEO baseline uncertainty into angular error. The clock analysis shows that timing-induced path error is divided by the long GEO-GEO baseline, providing a baseline-leverage advantage relative to terrestrial VLBI. The paper then evaluates GNSS-based synchronization, passive-hydrogen-maser-class clock stability, two-way inter-satellite synchronization and ranging, relativistic and moving-endpoint timing corrections, and GEO orbit-determination uncertainty. A Monte Carlo simulation framework is then used to propagate clock and position perturbations through a dual-frequency RINGS angle-of-arrival estimator. The results show that picosecond to tens-of-picoseconds residual timing errors contribute only small stochastic angular scatter when considered alone. After PHM-class timing and two-way inter-satellite synchronization, a 10ps residual timing level contributes approximately 0.04nrad for a 120^∘ three-GEO baseline, while a conservative 100ps residual contributes approximately 0.4nrad. GEO position uncertainty is found to be the dominant error driver once meter-level orbit-determination errors are assumed. Under sub-meter GEO baseline knowledge and picosecond-level inter-satellite synchronization, the simulations support nanoradian-level angular performance. The results strengthen the feasibility case for GEO-based VLBI as a complementary deep-space navigation observable. The main practical requirements identified are accurate relative GEO-GEO baseline knowledge, high-stability onboard timing, two-way inter-satellite synchronization and ranging, deterministic timing-correction modeling, and robust phase-ambiguity resolution.

Abstract: This paper presents a 3D-printed wind-tunnel model of the Active Aeroelastic Aircraft Testbed developed to support experimental flutter studies. Laboratory and wind-tunnel ground vibration tests were performed using accelerometers, high-density fiber optic strain sensing, and a motion capture system to characterize the as-built structure, recover mode shapes, and reconstruct wing deformation during testing. The measurements identified an approximately 7-Hz in-plane mode that was also found to be flutter-critical by the subsequent shaker-based analysis. Updating the finite element model to represent the actual wind-tunnel mounting compliance shifted this mode to the measured frequency and reduced the frequency errors of the first five wind-tunnel-mounted modes to about 1% or less. The characterized model and wind-tunnel response data were then used in complementary flutter-prediction workflows. Multi-output autoregressive analyses of acceleration and strain data predicted nominal flutter onset between 39.7 and 40.1 m/s, while the Parametric Flutter Margin workflow used an embedded wingtip shaker to estimate flutter at 39.5 m/s and 7.3 Hz. Supporting experimental data are publicly available. The study integrates model updating, distributed sensing, deformation reconstruction, and complementary flutter-boundary identification methods into a unified experimental workflow for flexible 3D-printed aircraft structures.

Abstract: Non-cooperative sensing using signals of opportunity traditionally requires an explicit reference signal for target detection and localization. This paper introduces a referencefree sensing framework in which target geometry is inferred directly from the received waveform rather than by comparison with an acquired or reconstructed illuminator signal. The proposed framework is implemented using the Ranging, Detection, Imaging, Communications, Approach, and Landing (RaDICAL) architecture, which combines a hybrid Dish–Sparse Uniform Circular Array (SUCA) receiver with Starlink downlink transmissions as spaceborne illuminators of opportunity. Deterministic Multifrequency Dither (DMD) applied across the SUCA elements transforms spatial diversity into unique composite waveform signatures. A unified electromagnetic and signal-processing model is developed that combines spherical-wave propagation, parabolic focusing, deterministic multifrequency modulation, and QRbased waveform-domain hypothesis testing for direct target localization. Numerical simulations together with link-budget analysis demonstrate the feasibility of the proposed approach. Single-dwell detection of 0 dBsm targets is achieved at physical signal-to-noise ratios near 0 dB, while near-unity detection probability is obtained above 10 dB SNR under controlled false-alarm conditions. The results demonstrate that commercial Starlink LEO communication satellites can serve as practical illuminators of opportunity for reference-free non-cooperative sensing without requiring acquisition or reconstruction of the transmitted illuminator waveform.

Abstract: Deep space and cislunar missions, including those associated with Artemis II mission, expose spacecraft structures to sustained thermal gradients and radiation environments that differ significantly from low Earth orbit conditions. Addressing these challenges requires material and design strategies capable of managing heat transfer while maintaining structural efficiency under strict mass constraints. Digital Twin methodologies, functionally graded materials (FGMs), and additive manufacturing (AM) have each been explored in the aerospace domain; however, their integrated application at the material–structure design level remains relatively underdeveloped. This work examines the combined potential of these approaches through a consolidated review perspective and introduces a physics-based framework for evaluating graded structures under representative deep space conditions. In this design-stage interpretation, the Digital Twin is treated as a high-fidelity virtual prototype rather than a sensor-coupled operational system, enabling systematic pre-fabrication exploration of material grading strategies. The framework incorporates a one-dimensional steady-state heat conduction model with spatially varying thermal conductivity, coupled with a simplified radiation attenuation formulation based on the Beer–Lambert relation. Material grading is described using a power-law distribution, allowing systematic assessment of how thermal resistance can be redistributed across the structure. Parametric analysis shows that increasing the grading exponent significantly alters internal temperature profiles and can reduce heat flux by up to approximately 69% compared to a homogeneous configuration, without modifying boundary conditions. Within the simplified modelling assumptions, radiation attenuation is primarily governed by material thickness; however, in realistic deep space environments, attenuation is expected to depend on material composition, indicating potential coupling between thermal and shielding performance. Overall, the study provides a structured and physically interpretable pathway for extending Digital Twin–based evaluation to material-level design, offering a computationally efficient approach for the early-stage assessment and optimization of functionally graded structures for deep space applications.

Abstract: Clements, Kriezis, and Humphreys [1] (CKH) recently detected, characterized, and attributed powerful transient wide-area GNSS interference over Europe—identifying Cosmos 2546 (NORAD 45608) as the source of the February 2026 event captured in raw IQ—using a Bayesian generalized-likelihood-ratio framework over an elevation-vetted candidate set. We apply a framework with disjoint foundational commitments—possibilistic, open-world, falsification-first, and non-normalizing (the Theory of Epis- temic Abductive Geometry, TEAG [2], and the Epistemic Support-Point Filter, ESPF [3–5])—and it converges on the same attribution and the same prior-sensitivity profile: recomputed in CKH’s own calibrated metric, our admissible set reproduces their ∼500 km ephemeris-inflation result and collapses to Cosmos 2546 alone under elevation masking. We argue this convergence is itself substantive—robustness under method variation, since the two frameworks do not share failure modes—and we are precise about its kind: it is convergence of two inference calculi on shared evidence (the same two-station TDOA residuals; the two are the ℓ1 and ℓ∞ ends of one Hölder family of the same admissibility energies, Cosmos’s residual scatter here, 1.19 m, matching CKH’s 1.2 m), not independent triangu-lation from disjoint data. The agreement is not automatic: the commitment point—the whitened minimax medoid, the hypothesis most shielded from the falsification boundary—is fixed, but it re-turns the source only when the surprisal geometry carries the per-hypothesis ephemeris-tolerancechannel; score compatibility by measurement scatter alone and the most-shielded hypothesis is instead a low-scatter, high-bias fragment. The method thus has a falsifiable failure mode (in the surprisal geometry, not the commitment rule) it must pass rather than a tautology. We then add two independent evidential channels CKH did not analyze. First, an absolute-power bound (EIRP of order 10⁶ W) that is strongly inconsistent with incidental leakage and points to a directed, operated emitter. Second, a code-level identification: the 1558.5 MHz/255.8 μs waveform is the GPS C/A G1 maximal-length sequence (x¹⁰ + x³ + 1) at 4 Mcps, matching no GPS PRN—favoring ranging/sensing or denial-by-in-band-power and disfavoring matched-code spoofing. We intend this as constructive corroboration and extension, not correction.

Abstract: Hybrid composite lattice structures have emerged as a promising approach for improving the impact resistance of lightweight aerospace components. This study investigates the influence of density-gradient direction in metallic Body-Centred Cubic (BCC) lattice reinforcement on the bird-strike response of a composite UAV leading-edge (L.E) structure. Three lattice architectures uniform, backward graded, and forward graded were parametrically generated using Rhino/Grasshopper and integrated within a carbon-fibre-reinforced polyamide L.E. The hybrid structures were analysed using Abaqus/Explicit with a validated Smooth Particle Hydrodynamics (SPH) bird model (1 kg, 95 m/s). All configurations maintained nearly identical structural mass, enabling the influence of lattice density distribution on structural response to be isolated. The backward graded configuration promoted progressive plastic collapse, resulting in the highest lattice energy absorption but also increased deformation and load transfer to the spar. In contrast, the forward graded configuration suppressed progressive collapse, confined deformation near the impact interface, and significantly reduced stress transmission to critical structural components. Peak displacement and spar energy transfer were reduced by approximately 95% and 90%, respectively, compared with the backward graded configuration. The results demonstrate that density-gradient tailoring of metallic lattice reinforcement enhances the structural performance of hybrid composite-lattice L.E structures by improving load sharing, deformation control, and impact resistance without increasing structural mass.

Abstract: This paper presents a robust attitude-tracking control architecture for rigid spacecraft subject to model mismatches and external disturbances. Quaternions are utilized for attitude representation to prevent the gimbal lock associated with Euler angles. While conventional nonlinear dynamic inversion (NDI) relies on Newtonian mechanics and input-output linearization — which inadvertently generates internal zero dynamics and encounters severe control derivative discontinuities at the \( q_0 =0 \) singularity — this study proposes a novel NDI framework derived strictly from Udwadia’s Lagrangian formulation. This approach realizes an exact input-state linearization directly on the 6-degree-of-freedom active holonomic constraint manifold, completely eliminating internal zero dynamics and mathematical singularities. To ensure robustness against physical uncertainties, the singularity-free NDI is augmented with a nonlinear disturbance observer (DOBC) and an outer-loop linear-quadratic (LQ) tracking controller. A rigorous composite Lyapunov stability analysis is conducted for the complete closed-loop architecture. The analysis formally guarantees that both the isolated disturbance estimation error and the fully interconnected dual-loop NDI-DOBC system are Uniformly Ultimately Bounded (UUB), even in the presence of realistic, time-varying disturbances with non-vanishing derivatives (\( \dot{\textbf{d}}\neq \textbf{0} \)). Comprehensive numerical simulations, parameterized by a physical spherical air-bearing testbed subject to state-dependent gravitational imbalance torques, validate the architecture's exceptional tracking precision, smooth transient response, and robust disturbance rejection.

Abstract: Small multirotor UAVs frequently operate in crosswind conditions, yet the aerodynamic interaction between windward and leeward propeller pairs remains incompletely understood. This study investigates the performance of a quadcopter propeller system under lateral crosswind using steadystate RANS simulations with the Transition SST turbulence model, validated against wind tunnel measurements (thrust and torque deviations within 5.4%). A parametric matrix of five rotational speeds (8,000 − 12,000 RPM) and six freestream velocities (0 − 10 m/s) is systematically examined. While thrust and power coefficients of all propellers increase monotonically with freestream velocity, the figure of merit (FM) of leeward propellers exhibits a previously unreported non-monotonic response: it decreases from hover, reaches a minimum near 6 m/s, and partially recovers at higher velocities. Windward propellers show no such degradation. Our velocity contour and streamline analyses reveal that this behaviour originates from windward wake ingestion into the leeward inflow region, which peaks at intermediate freestream velocities and is progressively alleviated as the stronger crosswind convects the wake downstream. The non-monotonic FM response is therefore a direct consequence of the competition between wake-induced inflow degradation and freestreamdriven aerodynamic augmentation. Our findings provide a systematic aerodynamic dataset essential for crosswind attitude control and propulsion system design in multirotor UAVs.

Abstract: The response of premixed flames to external forcing is important for understanding flame dynamics and combustion instability. In this study, the velocity-field response of a laminar premixed propane–air flame under external forcing was investigated using particle image velocimetry, numerical simulation, and dynamic mode decomposition. The flame was studied under an unforced condition and several forced conditions at 20Hz and 80Hz, with an equivalence ratio of [0.95] and a Reynolds number of [800]. The results show that external forcing alters both the flame shape and the veloci-ty-field structure, and that the response is strongly frequency-dependent. The axial velocity component exhibits clear downstream convective propagation of the imposed disturbance, whereas the radial velocity response is mainly concentrated near the flame front and is associated with flame deformation and thermal expansion. Dynamic mode decomposition shows that the dominant coherent structures become weaker and decay more rapidly as the forcing frequency increases. The numerical results agree reasonably well with the experimental measurements for the unforced flame and pro-vide additional information on the downstream development of the forced flow. These results provide useful insight into forced flame-flow interaction in laminar premixed flames.

Abstract: This work presents the first complete system for automated six degrees of freedom (6DOF) satellite pose estimation from spatially resolved, ground-based, adaptive optics (AO)-corrected imagery, addressing a key challenge in Space Domain Awareness (SDA). The approach eliminates the need for human labeling by directly regressing satellite orientation and position from blurry, noisy, and deeply-shadowed imagery. A multi-stage deep neural network pipeline localizes the satellite, predicts pose, and optionally applies temporal smoothing. Networks are trained exclusively on fully synthetic imagery generated from a CAD model, yet generalize effectively to real data, bridging the Sim2Real domain gap. On 137 real, human-labeled test images of Seasat, the model achieved a mean rotation error of 5 degrees and a mean image-plane translation error of 21 cm. Qualitative evaluation of additional real Seasat imagery rated 178 of 199 predicted poses as “ground truth equivalent” or “high confidence match,” with zero catastrophic failures. The system was extended to seven degrees of freedom (7DOF) for satellites with articulating components and demonstrated on real Hubble Space Telescope (HST) imagery, achieving 5.9 degrees rotation error, 48 cm translation error, and 6 symmetry-adjusted solar array error on a 249-frame pass with temporal filtering. Across 586 real test images from Seasat and HST (captured over multiple decades under diverse conditions) the system consistently performed well. On a high-fidelity wave optics (HFWO) synthetic test set of Seasat, the model achieved 8.4 degrees mean rotation error, 34 cm image-plane translation error, and 1.4% range error at r0=6 cm and 1,031 km range. It outperformed human labeling in both accuracy (48% lower rotation error) and speed (800× faster at 7.1 Hz inference), while requiring < 40 hours on a single A100 GPU to train. The approach was also demonstrated for ARGOS, a smaller satellite with highly symmetric geometry. A GIQE-based image quality metric was introduced to forecast pose accuracy. General-purpose models like GPT-4o and Depth Anything V2 failed across most SDA tasks, but rapid gains in vision-language models warrant continued monitoring. These results establish a new operational baseline for practical, real-time satellite pose estimation from AO SDA imagery.

Abstract: Experimental studies of the “Turbine Last Stage – Exit Diffuser” system were carried out on the ET4 test bench of the Turbine Engineering Laboratory of the St. Petersburg Polytechnic University. The diffuser model design allowed for the effect of anti-surge bypass of compressor air into the diffuser on its aerodynamic characteristics to be taken into account. The flow structure in the flow section of the model compartment was studied by traversing 3D flow in control sections using five-channel pneumometric probes. Based on the measurement results, an analysis of the integral characteristics and the three-dimensional flow structure in the exhaust manifold was performed. The studies were conducted in the range from 110% of the nominal load to the idle mode of the last stage. Numerical modeling was performed using ANSYS CFX 2023 R1. RANS equations were closed using the SST turbulence model. Comparison of experimental results and numerical modeling showed good agreement in the integral characteristics within a range of up to 50% of the nominal load. At extreme partial load conditions, significant flow pulsations were observed in the annular section of the diffuser, requiring more detailed transient measurements. Based on the study’s results, requirements were formulated for modifying the experimental setup and measurement system to enable pressure pulsation studies under varying load conditions down to the gas turbine’s idle mode.