Flight Experiment Research Articles

True self-reinforced composites enabled by tuning of molecular structure for lightweight structural materials in future mobility

The development of vehicle bodies based on lightweight structural composites is urgently required to upgrade electric cars and to commercialize urban air mobility. Self-reinforced composites (SRCs) are attracting attention due to their advantages in terms of price, lightness, disposal and recycling compared to carbon fiber-reinforced polymers (CFRPs). In this study, a new concept for 100% polypropylene (PP) SRC was proposed to simultaneously improve the adhesive, tensile and impact properties of SRCs without undermining the advantages of SRCs. For this implementation, a facile engineering strategy using quad screw extrusion (QSE) capable of generating high shear stress was employed to modify the melting temperature and impregnation properties of the PP matrix via controlling polymer chain structure. As the screw rotation speed of QSE increased, low molecular weight polymer chains with uniform chain lengths were prepared, which led to a decrease in the melting temperature of the PP matrix and an increase in the flowability and impregnation property of the matrix. Using this strategy, the adhesive strength, tensile strength and impact resistance of the optimized SRC improved by 333%, 228%, and 2700%, respectively. Racing drone flight experiments with the SRC and CFRP frames illustrated the advantages of the SRC frame such as the increase of the flight time due to low density of the SRC, the excellent impact resistant characteristics (which improves user safety), and the superior electrical insulation properties suitable for frequency transmission and reception. Therefore, the proposed SRC can be an ideal choice as a lightweight structural material for future mobility.

Databases of the evolution of the microbiome and its drug susceptibility in astronauts and hermetic facility operators

When planning lunar bases and during long-term interplanetary (autonomous) flights, the issue of accumulation of pathogenic microbiota in conditions of closed inhabited objects is relevant. This question can be answered on the basis of a long observation period. When conducting microbiological examinations on the International Space Station, it was shown that one of the main features of the human-microorganisms ecological system in the environment of manned spacecraft is the periodic accumulation of the pathogenicity potential of microorganisms. These results were confirmed in isolation ground experiments and in the analysis of the SALYUT-6, 7 and MIR, International Space Station missions. Our work presents databases of microbiota and its antibiotic resistance of cosmonauts and hermetic facility operators at various stages of space flight, or isolation experiments. The databases are designed to assess the evolution of the population of microorganisms and their antibiotic resistance in various parts of the body of cosmonauts and operators of hermetic objects before, during and after a space flight and isolation experiments. Information about the microbiome of astronauts has been streamlined and entered into the database since 1970. The databases contain information about the microbiota in chronological order and its antibiotic resistance in cosmonauts and pressurized facility operators. Samples of various parts of the body were analyzed: forehead, chest, neck, ear, arm, armpit, groin, intestines, plaque, oral cavity, pharynx, tongue, nose, cheeks. Experimental samples of microbiota obtained from the International Space Station are stored at a deep freeze of -76 °С, are examined using a standard bacteriological method, molecular biology research methods and immunochemical methods. The information obtained makes it possible to assess the normal and dysbiotic state of the cosmonauts' microbiota. The databases are constantly updated. Thanks to the adapted database format, it is possible to use neural network and BIG DATA methods for analysis.

Three-Dimensional Bearing-Only Target Following via Observability-Enhanced Helical Guidance

This paper studies the problem of air-to-air target following of micro aerial vehicles (MAVs) motivated by the application of defense against malicious MAVs. When the bearing of the target MAV has been measured by the onboard visual sensor of the pursuer MAV, the problem becomes three-dimensional (3-D) bearing-only target following, which has been rarely studied in the literature and faces some unique challenges. To solve this problem, we propose the following novel results. First, to estimate the motion of the target MAV from 3-D bearing measurements, we propose a new pseudo-linear Kalman filter, which has a concise expression and superior stability compared to the classic ones such as the extended Kalman filter and modified polar coordinate filter. Second, we propose a novel approach to analyze the observability of state estimation when only bearing information is available. While the existing approaches are applicable to 2-D and single-step time-horizon cases, ours can handle more general 3-D and multiple-step time-horizon cases. Third, based on the theoretical conclusion of our observability analysis, we design a new 3-D helical guidance law that can better exploit the additional degree of freedom in 3D. The guidance law is adapted to the quadcopter's dynamics and a low-level flight controller is designed based on geometric control. Numerical simulation results verify the superior performance of the proposed algorithms compared to the state-of-the-art ones. Flight experiments on real quadrotor platforms further show the effectiveness and robustness of the proposed algorithms in practice.

Experimental studies suggest differences in the distribution of thorax elasticity between insects with synchronous and asynchronous musculature.

Insects have developed diverse flight actuation mechanisms, including synchronous and asynchronous musculature. Indirect actuation, used by insects with both synchronous and asynchronous musculature, transforms thorax exoskeletal deformation into wing rotation. Though thorax deformation is often attributed exclusively to muscle tension, the inertial and aerodynamic forces generated by the flapping wings may also contribute. In this study, a tethered flight experiment was used to simultaneously measure thorax deformation and the inertial/aerodynamic forces acting on the thorax generated by the flapping wing. Compared to insects with synchronous musculature, insects with asynchronous muscle deformed their thorax 60% less relative to their thorax diameter and their wings generated 2.8 times greater forces relative to their body weight. In a second experiment, dorsalventral thorax stiffness was measured across species. Accounting for weight and size, the asynchronous thorax was on average 3.8 times stiffer than the synchronous thorax in the dorsalventral direction. Differences in thorax stiffness and forces acting at the wing hinge led us to hypothesize about differing roles of series and parallel elasticity in the thoraxes of insects with synchronous and asynchronous musculature. Specifically, wing hinge elasticity may contribute more to wing motion in insects with asynchronous musculature than in those with synchronous musculature.

Full Attitude Control of a Quadrotor Using Fast Nonsingular Terminal Sliding Mode With Angular Velocity Planning

In this article, a fast nonsingular terminal sliding mode combined with angular velocity planning (FNTSM-AVP) controller is developed to achieve high-speed, accurate, and robust attitude tracking performance for a quadrotor. The proposed controller employs a sliding surface function with a continuous arctangent function, which can effectively eliminate chattering behavior on the quadrotor while retaining the speed and accuracy of attitude tracking. Unlike conventional methods, the proposed controller preferentially recovers the roll and pitch angles at desired attitude by planning the shortest arrival path, which is effective to improve the tracking performance. Finally, the finite time convergence and zero tracking error properties of the closed-loop control system under the proposed FNTSM-AVP are analyzed and proved. The aggressive flight experiments demonstrate the advantage of faster convergence and fewer chattering behavior of the proposed method compared to the existing FNTSM controller.

An InSAR Interference Fringe-Matching Algorithm Based on Mountain Branch Points

Interferometric synthetic aperture radar (InSAR) is an integrated navigation technique that can be used for aircraft positioning and attitude retrieval, regardless of weather conditions. The key aspect of the entire system is interference fringe matching, which has not been extensively researched in existing literature. To address this gap, this paper proposes a terrain-feature-based interference fringe-matching algorithm. The proposed algorithm first extracts mountain line features from the interference fringes and identifies mountain branch points as key points for feature matching. A threshold is set to eliminate false detections of mountain branch points caused by phase mutation. Matching is then carried out by combining the mountain line features and curvature design feature descriptors of the area around a branch point. The proposed algorithm is verified using interference fringe data obtained from an actual flight experiment in Inner Mongolia, China, compared to a reference interference fringe dataset with errors. The results show that, under the condition of position error, the proposed algorithm yields 72 matching inliers with a precision of 0.103, a recall of 0.128, and an F1-Score of 0.144. Compared to traditional algorithms, our proposed algorithm significantly improves the problem of mismatch and opens up new possibilities for downstream interference fringe matching navigation technology. Furthermore, the proposed algorithm provides a new approach for remote sensing image matching using terrain features.

Multilayer nanoparticle-polymer metamaterial for radiative cooling of the stratospheric airship

This paper presents a promising solution to superheat of stratospheric airship with radiative cooling envelope, which has no change in pneumatic profile, structural weight, and power consumption. In this study, a multilayer nanoparticle-polymer metamaterial (MNPM) is hierarchically designed to provide reflectivity across visible wavelength and emissivity in atmospheric window. In this paper, the specimens and ball models are firstly fabricated, the cooling performances of which are tested for ground experiments. The temperatures of MNPM and silica/Ag specimens are 6.7 °C and 10.8 °C at noon in Tianjin. The inner gas and surface temperatures of MNPM scale ball are 11.7 °C and 14.6 °C, lower than silica/Ag by 4.5 °C and 4.6 °C, respectively. Subsequently, the flight experiments verify the cooling performance of MNPM, the maximum temperature of which is lower than the control group by 15.4 °C in stratosphere. Finally, the FLUENT simulations illustrate the cooling performance of stratospheric balloon and airship equipped with solar panel. The MNPM has a better cooling capacity for the internal helium and top surface throughout the day and a weak warming capacity for the bottom surface at night. Considering solar panels, the MNPM reduces the helium temperature by 8.1 °C, and the day-night superheat of the helium temperature is only 19.8 °C.

Combined wave emission system based on dual resonance method for airborne transient electromagnetic detection

To improve the detection efficiency of airborne transient electromagnetic method (ATEM) and reduce the times of flight experiments, a dual resonance-based combined wave emission circuit is proposed in this paper, which realizes the combined emission of half-sine wave and triangular wave through the selection of different resonant branches. Based on the operating principle of the proposed emission circuit, the model of second-order resistor-inductor-capacitor equivalent circuit is established. Then, the generation process of the combined wave is analyzed, and the segmentation control method is proposed. Finally, the feasibility and effectiveness of the proposed combined wave emission system are verified by simulation model building and prototype testing, and the results show that the emission current has good quality and high stability. Compared with the traditional emission of single wave current, the combined wave current has the advantages of large magnetic moment of half-sine wave and rich high-frequency components of triangular narrow pulse, which can effectively expand the detection range and improve the measurement efficiency of ATEM.

“Let's see what happens!”—His words were and still are guiding me

The first paper I read when I started studying bats as a student was Jim's paper. At the time, I never dreamed that a few years later we would be able to conduct bat experiments together in Japan and the United States. Although it was my first and last study abroad experience, and it was only for a month, the experience of working with Jim every day guided my confidence and career path as a researcher. I will never forget the excitement when we conducted a flight experiment using a telemetry microphone together and found that the big brown bats were fluctuating the pulse frequency up and down in a cluttered environment. This experience sparked my interest in the jamming avoidance behavior of bats, which has become a very important research topic for me. I have been very fortunate to have had the opportunity to see up close the ideas that come from his vast experience and knowledge and to witness the respectful attitude he has toward bats and nature as a pure researcher. Jim is a great researcher whom I genuinely admire and who taught me to enjoy bats, nature, and research indeed.

Modeling and Control of Quadcopter Based on Sliding Mode Robust Control in the Wind Field

Due to the low flying height, quadrotors are easily affected by external wind disturbances. In this paper, the dynamic model of the quadrotor flying in the wind field is established according to the Newton-Euler equation. The model introduces a weight function due to the phenomenon that different rotors are affected differently by the wind field due to their different positions relative to the wind field, and a sliding mode robust controller based on inner and outer loops is designed. The verification of the control system is carried out by means of simulation in a Gazebo and actual flight experiments in the wind field. The dynamic of the system and the controller performance under the wind field are also tested. The results show that the designed controller has the performance of stable flight in the wind field environment.

Moving Target Landing of a Quadrotor Using Robust Optimal Guaranteed Cost Control

Dear Editor, This letter proposes a robust control strategy for the autonomous landing of a quadrotor on a moving target. Specifically, a force command that consists of a cascade dynamics estimator and an optimal guaranteed cost control law is exploited for the position-loop tracking. Then, an orientation constraint torque command is employed for the attitude-loop tracking such that the quadrotor refrains from flipping during the landing operation. Stability analysis indicates that the overall closed-loop system is asymptotically stable. Finally, flight experiments validate and access the theoretical results.

Flight demonstration of a miniature atomic scalar magnetometer based on a microfabricated rubidium vapor cell.

We have developed an atomic magnetometer based on the rubidium isotope 87Rb and a microfabricated silicon/glass vapor cell for the purpose of qualifying the instrument for space flight during a ride-along opportunity on a sounding rocket. The instrument consists of two scalar magnetic field sensors mounted at 45° angle to avoid measurement dead zones, and the electronics consist of a low-voltage power supply, an analog interface, and a digital controller. The instrument was launched into the Earth's northern cusp from Andøya, Norway on December 8, 2018 on the low-flying rocket of the dual-rocket Twin Rockets to Investigate Cusp Electrodynamics 2 mission. The magnetometer was operated without interruption during the science phase of the mission, and the acquired data were compared favorably with those from the science magnetometer and the model of the International Geophysical Reference Field to within an approximate fixed offset of about 550 nT. Residuals with respect to these data sources are plausibly attributed to offsets resulting from rocket contamination fields and electronic phase shifts. These offsets can be readily mitigated and/or calibrated for a future flight experiment so that the demonstration of this absolute-measuring magnetometer was entirely successful from the perspective of increasing the technological readiness for space flight.

Design and Control of a Hand-Launched Fixed-Wing Unmanned Aerial Vehicle

In order to address the flexible requirements on load, flight speed, and maneuverability in actual flight conditions, a hand-launched fixed-wing unmanned aerial vehicle (UAV) is designed with high performance in portability, lightweight, and maneuverability. On this basis, a novel system-decomposition-based robust control method is proposed to achieve a satisfactory control performance for this designed UAV under internal/external uncertainties. First, considering the feature that the coupling terms are usually small in most flight conditions and may be regarded as disturbance, the complex flight system is decomposed into a group of simple subsystems with disturbance, namely, roll–yaw subsystem, pitch–altitude subsystem, and airspeed subsystem. Since the complexity of each subsystem is much smaller than the original system, this will reduce the difficulty of the controller design and complexity of the controller. Besides, to improve the tracking performance and robustness to disturbances, an extended state observer based robust control method is proposed for each subsystem. The stability and robustness of the proposed control method are effectively demonstrated by the theoretical analysis and the actual flight experiments on the designed UAV.

Development of a YOLO-KCF Coupling Algorithm for Miniature Fixed-Wing UAVs in Target Detection and Tracking

Target detection and tracking represent key challenges facing miniature fixed-wing unmanned aerial vehicles (UAVs), particularly at high cruising speeds. Therefore, this paper proposes a vision-based target detection and tracking algorithm that systematically couples two mainstream methods, namely, you only look once (YOLO) and kernel correlation filter (KCF) algorithms. This combination enables small fixed-wing UAVs to achieve reliable target detection and rapid target tracking. A customized vision-guidance module is constructed to implement this algorithm, and a dual-thread execution mechanism is developed to ensure that the computational resources are used effectively. A miniature fixed-wing UAV experimental platform is also constructed and evaluated. Flight experiments are performed, and the results demonstrate that the developed algorithm can achieve satisfactory detection and tracking accuracy for stationary and moving ground targets in complex environments.

Disturbance observer-based adaptive neural guidance and control of an aircraft using composite learning

An adaptive neural guidance and control system is proposed in this paper for a generic fixed-wing aerial robot. Unlike most of the existing low-level control systems, which utilize a non-adaptive guidance loop, in this work both the guidance and control loops are trained using an efficient adaptive neural algorithm. A feedforward neural network is employed in each loop to identify uncertain dynamics, while an adaptive disturbance observer allows to compensate for both the external disturbances and estimation error of the neural network. This would lead to a resilient flight control system, and thus, the asymptotic stability of both the guidance and control loops can be theoretically ensured for a generic aerial robot subject to different types of nonparametric internal and external disturbances. Besides, to enhance the learning efficiency, a composite learning method is adopted in which the neural network and the disturbance observer are trained using a composite error function consisting of the tracking error and the estimation error of an introduced adaptive state observer. To the best of the authors’ knowledge, this is the first completely adaptive integrated guidance and control system with guaranteed stability under parametric and nonparametric internal and external disturbances. The introduced control system is then applied to a simulation model of an electric aircraft that has been validated on the basis of real data and flight experiments. The obtained results indicate that the proposed approach could be considered a reliable guidance and control system for a generic fixed-wing aerial vehicle in the presence of actuator faults, unmodeled dynamics, external disturbances, and measurement noises.

Microphones as Airspeed Sensors for Unmanned Aerial Vehicles

This paper puts forward a novel design for an airspeed instrument aimed at small fixed-wing tail-sitter unmanned aerial vehicles. The working principle is to relate the power spectra of the wall-pressure fluctuations beneath the turbulent boundary layer present over the vehicle's body in flight to its airspeed. The instrument consists of two microphones; one flush-mounted on the vehicle's nose cone, which captures the pseudo-sound caused by the turbulent boundary layer, and a micro-controller that processes the signals and computes the airspeed. A feed-forward single-layer neural network is used to predict the airspeed based on the power spectra of the microphones' signals. The neural network is trained using data obtained from wind tunnel and flight experiments. Several neural networks were trained and validated using only flight data, with the best one achieving a mean approximation error of 0.043 m/s and having a standard deviation of 1.039 m/s. The angle of attack has a significant impact on the measurement, but if the angle of attack is known, the airspeed could still be successfully predicted for a wide range of angles of attack.

Key Technologies and Evaluation of a MiniSAR Experimental System for Unmanned Underwater Vehicle Detection

Synthetic aperture radar (SAR) imaging has important application potential in sea environments research, such as submarine detection. It has become one of the most significant research topics in the current SAR imaging field. In order to promote the development and application of SAR imaging technology, a MiniSAR experiment system is designed and developed, which provides a platform for related technology investigation and verification. A flight experiment is then conducted to detect the movement of an unmanned underwater vehicle (UUV) through the wake, which can be captured by SAR. This paper introduces the basic structure and the performance of the experimental system. The key technologies for Doppler frequency estimation and motion compensation, the implementation of the flight experiment, and the image data processing results are given. The imaging performances are evaluated, and the imaging capabilities of the system are verified. The system provides a good experimental verification platform to construct the follow-up SAR imaging dataset of UUV wake and investigate related digital signal processing algorithms.

Space‐ and Post‐Flight Characterizations of Perovskite and Organic Solar Cells

Perovskite and organic solar cells are promising for space applications for enabling higher specific powers or alternative deployment systems. However, terrestrial tests can only mimic space conditions to a certain extent. Herein, a detailed analysis of irradiation‐dependent photovoltaic parameters of perovskite and organic solar cells exposed to space conditions during a suborbital flight is presented. In orbital altitudes, perovskite and organic solar cells reach power‐conversion efficiencies of more than 13% and 6%, respectively. Based on postflight grazing‐incidence small‐angle and wide‐angle X‐ray scattering, the active layer morphology and crystalline structure of the returned space solar cells are studied and compared to those of reference solar cells that stayed in an inert atmosphere. Minor changes in the active layer morphology are induced by the sole transport, without causing significant performance loss. For the space solar cells, morphological changes are attributed to the flight experiment that includes rocket launch, spaceflight, and reentry, as well as short‐terrestrial environment exposure before and after launch. In contrast, no significant changes to the crystalline phase are observed. The notable performance during flight and high active layer stability, especially of perovskite solar cells, are promising results for further steps toward an orbital demonstration.

Multifunctional carbon/epoxy composites with power transmission capabilities

This study evaluates the power transmission of multifunctional composites with embedded conductors. The electrical conductors were constructed by braiding copper strands with Para-aramid fibers into a tape configuration, then placing these tapes within carbon/epoxy prepregs to create a multifunctional structure. Experiments were performed on these multifunctional composites under tensile loading conditions. During experimentation, the conductive tapes were incorporated within an electrical bridge to record their resistance change as a function of mechanical strain. The Digital Image Correlation (DIC) technique was used to obtain in-plane displacements and strains as a function of time. In addition, low-speed flight condition experiments with an airfoil shape composite system were carried out in a wind tunnel to study the temperature performance of these structures while under high currents. Computational models were then created to expand the experimental efforts and evaluate the system’s multiscale performance. Experimental results show that the mechanical load on the conductive tape is mainly carried by the Para-aramid yarns, leading to a relatively consistent electrical performance and airflow over the wind foil providing efficient power transmission. Lastly, the computational models showed consistency in the electrical/mechanical results and established a framework for analyzing multi-functional structures (MFS).

High-Fidelity Dynamics Modelling for the Design of a High-Altitude Supersonic Sounding Rocket

The accurate modelling and simulation of vehicle dynamics is a fundamental prerequisite for the design and experimental flight testing of aerospace vehicles. In the case of high-altitude supersonic sounding rockets, it is critically important to produce realistic trajectory predictions in a representative range of operational and environmental conditions as well as to produce reliable probability distributions of terminal locations. This article proposes a methodology to develop high-fidelity flight dynamics models that accurately capture aeroelastic, turbulence, atmospheric and other effects relevant to sounding rockets. The significance of establishing a high-fidelity model and of addressing such a problem in the context of developing a digital twin are discussed upfront, together with the key tools utilised in the analysis. In addition to state-of-the-art computational methods to determine the aerodynamic forces, moments and mass changes in various flight regimes (including parachute release), a detailed methodology for incorporating the dynamic aeroelastic response of the rocket is presented. The validity of the proposed method is demonstrated through a simulation case study, which utilises data from an existing rocket prototype. Results corroborate the correct implementation of the proposed algorithms and provide foundations for future research on virtual sensing and digital twin for autonomous navigation and guidance.