Actual Flight Environment Research Articles

APPA-3D: an autonomous 3D path planning algorithm for UAVs in unknown complex environments

Due to their high flexibility, low cost, and ease of handling, Unmanned Aerial Vehicles (UAVs) are often used to perform difficult tasks in complex environments. Stable and reliable path planning capability is the fundamental demand for UAVs to accomplish their flight tasks. Most researches on UAV path planning are carried out under the premise of known environmental information, and it is difficult to safely reach the target position in the face of unknown environment. Thus, an autonomous collision-free path planning algorithm for UAVs in unknown complex environments (APPA-3D) is proposed. An anti-collision control strategy is designed using the UAV collision safety envelope, which relies on the UAV's environmental awareness capability to continuously interact with external environmental information. A dynamic reward function of reinforcement learning combined with the actual flight environment is designed and an optimized reinforcement learning action exploration strategy based on the action selection probability is proposed. Then, an improved RL algorithm is used to simulate the UAV flight process in unknown environment, and the algorithm is trained by interacting with the environment, which finally realizes autonomous collision-free path planning for UAVs. The comparative experimental results in the same environment show that APPA-3D can effectively guide the UAV to plan a safe and collision-free path from the starting point to the target point in an unknown complex 3D environment.

Unmeasurable flexible dynamics monitoring and tracking controller design for guidance and control system of hypersonic flight vehicle

The guidance and control system (GCS) is an important and indispensable component of hypersonic flight vehicle (HFV), and it can be viewed as a special cyber–physical system (CPS). However, the monitoring of the HFV dynamics is difficult since the inertial navigation equipment can only provides the information of acceleration and angular rate. In this case, the flexible states of HFV are difficult to be measured. This paper proposes a sliding mode observer (SMO) based GCS design method for HFV. With considering the measurement difficulties, the flexible states of HFV are assumed to be unmeasurable. Then a SMO is designed to estimated them. Combined with the actual flight environment of HFV, the measuring devices are assumed to be suffering from disturbance, then the SMO should not only guarantee the estimation error stable, but also reduce the influence of external disturbances. What is worse, the input of HFV is suffering from input delay, which brings more difficulties to the controller design. By state transformation,input delay model of HFV is transformed into a delay free model,then a SMO based robust controller is proposed for HFV based on the stable inversion controller design strategy. By the proposed SMO based controller, the GCS can be constructed for HFV. Numeral simulation are carried on HFV, and simulation results show shat, the designed SMO can realize the monitoring of flexible states of HFV and the designed GCS can get a good tracking performance.

Analysis of electromagnetic scattering from hypersonic vehicle coated with non-uniform plasma sheath based on FVTD method

The finite volume time domain (FVTD) method is proposed to accurately calculate the electromagnetic (EM) scattering of hypersonic vehicles coated with non-uniform plasma sheath. The plasma sheath in the actual flight environment is accurately established by solving the Navier–Stokes equations and combining appropriate thermochemical models. The radar cross section (RCS) of metal and uniform medium coated metal targets calculated by FVTD are in good agreement with those simulated by the software FEKO (MoM) and the Mie series. The calculated RCS of the vehicle under the reentry condition is consistent with the flight test data, too. The calculated electron number density distribution is consistent with the flight experiment results. The body fitted structure EM grid is adopted. The EM grid independence of the target coated with plasma sheath is studied. Then, the scattering and plasma EM parameters of the vehicle during the actual reentry are studied. The reentry altitude is from 78 to 55 km, and the reentry velocity is from 6406 to 6350 m/s. With the reentry altitude decreasing, the plasma angular frequency and collision frequency increased gradually. The scattering of different incident conditions and different wall catalytic conditions is analyzed in depth. This paper provides a valuable reference for vehicles' detection, recognition, and stealth during reentry flights.

Evaluation of Mechanical/Electromagnetic Preformation of Single-Sided Active Frequency Selective Surface for Stealth Radomes

In this study, a pattern for an active frequency selective surface (AFSS) applicable to stealth radomes was designed and manufactured. Subsequently, its effectiveness was verified via measurements of its electromagnetic performance, and its mechanical performance was numerically evaluated in an actual flight environment. An AFSS equipped with a PIN diode was designed to have a transmission frequency in the X-band using only one side of a surface. To evaluate the mechanical performance when the designed AFSS was applied to a stealth radome, flow analysis was performed on the basis of the shape of the F-35 combat aircraft. Moreover, structural analysis of the stealth radome was performed using the pressure distribution at the maximum velocity of the F-35, as determined via the flow analysis. On the basis of the structural analysis results, the mechanical performance of the designed stealth radome was evaluated via analysis of the stress distribution of the AFSS diode. Through this study, an AFSS pattern applicable to stealth radomes was proposed, and its mechanical/electromagnetic performance was evaluated to verify the feasibility of stealth radomes incorporated with AFSSs.

Dynamic responses of the flexible beam in a three-axis centrifugal environment

The loads acting on rapid maneuver aircrafts are characterized by high accelerations, high jerks and multiple directions in the space. The flight simulation tests for aircraft loads are usually carried out on a three-axis centrifuge. Due to the difference between flight and centrifugal environments, the loads in the simulation tests are not completely consistent with those in the actual flight environment. To verify that the dynamic responses of aircrafts in the three-axis centrifuge can be used to predict the responses in the flight environment, a beam installed in the three-axis centrifuge is considered. The velocity and acceleration models of the beam are established by the motion synthesis method. The rigid-flexible coupling dynamic equations of the beam are derived using the Kane’s method. Under different flight accelerations, the dynamic responses of beam in the three-axis centrifugal environment are simulated, which agree well with the responses in the flight environment. Besides, the influence of accelerations and jerks on the responses is analyzed. The results of this paper demonstrate that the present dynamic model can be used effectively to predict the experimental results in flight environments.

On-board spectral calibration algorithm for an airborne hyperspectral imager and elimination of the effect of the atmospheric underlying surface.

As an image-spectrum merging technology, the hyperspectral sensor has become an important part in remote sensing. The spectral calibration results of the hyperspectral sensor measured in the laboratory should be refined when applied to the on-board imaging spectrometer due to variations between the laboratory and actual flight environments. The larger the spectrum offset of the spectral response function (SRF), the worse the retrieval accuracy of the reflective characteristics of the targets. Therefore, an on-board spectral calibration algorithm based on standard diffuse boards with a gradient of reflectivity is proposed in this paper. By constructing the differential function of radiation transfer coefficients, the center wavelength offsets of SRF can be solved. In addition, a back-propagation neural network has been established to eliminate the effect of the atmospheric underlying surface and improve theaccuracy of on-board spectral calibration. The three-sigma confidence interval of the on-board spectral precision is $ \pm 0.23\,\,{\rm nm}$±0.23nm (uncertainty $ \lt {0.05}$<0.05 spectral pixels). The algorithm can be applied to a general hyperspectral sensor.

Reinforcement Learning for Satellite Communications: From LEO to Deep Space Operations

The National Aeronautics and Space Administration (NASA) is in the midst of defining and developing the future space and ground architecture for the coming decades to return science and exploration discovery data back to investigators on Earth. Optimizing the data return from these missions requires planning, design, standards, and operations coordinated from formulation and development throughout the mission. The use of automation enhanced by cognition and machine learning are potential methods for optimizing data return, reducing costs of operations, and helping manage the complexity of the automated systems. In this article, we discuss the potential role of machine learning in the linkto- link aspect of the communication systems. An experiment using NASA's Space Communication and Navigation Testbed onboard the International Space Station and the ground station located at NASA John H. Glenn Research Center demonstrates for the first time the benefits and challenges of applying machine learning to space links in the actual flight environment. The experiment used machine learning decisions to configure a space link from the ISS-based testbed to the ground station to achieve multiple objectives related to data throughput, bandwidth, and power. Aspects of the specific neural-network-based reinforcement learning algorithm formation and on-orbit testing are discussed.

Accurate Measurement Calculation Method for Interferometric Radar Altimeter-Based Terrain Referenced Navigation.

In order to improve the performance of Terrain Referenced Navigation (TRN), an Interferometric Radar Altimeter (IRA) has been developed as a more accurate altimeter. The IRA outputs not only the relative distance (slant range, R) but also the cross-track angle (look angle, θ) of the closest point on the zero Doppler line by using the principle of interferometry and two or more antennas. To perform TRN using the IRA, the 3D relative position of the closest point should be calculated. There is a formula to calculate the relative position of the closest point using the Euler angles. However, in an actual flight environment in which the influence of wind exists, the angle of attack, the side slip angle and “the effective look angle” should be used rather than the Euler angles. In this paper, a new formula for calculating the relative position of the closest point is proposed and mathematically derived. The proposed formula was verified with real data from actual flight. The flight test results show that the positions of the closest points calculated using the conventional method and the proposed method are different because of the wind effect. The TRN simulation results indicate that the proposed formula calculates the closest points more accurately than the conventional formula.

Numerical Simulation of Tail Flow Field of Four - Nozzle Solid Rocket Engine

A solid rocket motor with four nozzles is taken as the research object. According to its actual flight environment and the simulation boundary conditions are given. Then, the integrated simulation of nozzle-flow field in exhaust plume of solid rocket motor is carried out by means of FLUENT. The velocity of flow field in exhaust plume, temperature, and pressure are obtained. The simulation results are in good agreement with the actual flow conditions and the existence of Mach disk is proved.

Equivalence relationship between a three-axis centrifugal test load and flight load

For aircraft flying with high accelerations and high acceleration change rates in three-dimensional space, load simulation tests are usually carried out in a three-axis centrifuge with three degrees of freedom. A triaxial centrifugal test that simulates the actual flight environment must reflect the real effect of the flight load on the structure. An acceleration analysis model of a three-axis centrifuge in body coordinates is established to meet this requirement. The spatial distribution of the acceleration and the effects of kinematic parameters on acceleration are analyzed. Using the acceleration analysis model, the displacement equivalence and strain energy equivalence relations of a beam in a centrifugal environment and actual flight environment are studied. Moreover, equivalence relationships meeting requirements are proposed and validated for a specific example. The distribution of the acceleration and the equivalence relations of the two environments are the basis for the ground simulation of flight loads.

소형 쿼드로터 플랫폼 개발 및 실외 자율 군집비행 실험

This paper describes the development of a mini quadrotor platform and its experimental results on outdoor autonomous swarming flights. The platform is very light (less than 0.1 kg), so it is not subject to the aircraft registration requirements for Unmanned Aircraft Systems (UAS). Despite this light weight, it integrates various sensors to perform autonomous flights in outdoor environments. To verify the feasibility of the developed platform, we performed autonomous swarming flights using 10 developed platforms, and the experimental results show that the mini quadrotor platform performs autonomous swarming flight with good precision and can be applied to actual outdoor flight environments.

소형 쿼드로터 플랫폼 개발 및 실외 자율 군집비행 실험

This paper describes the development of a mini quadrotor platform and its experimental results on outdoor autonomous swarming flights. The platform is very light (less than 0.1 kg), so it is not subject to the aircraft registration requirements for Unmanned Aircraft Systems (UAS). Despite this light weight, it integrates various sensors to perform autonomous flights in outdoor environments. To verify the feasibility of the developed platform, we performed autonomous swarming flights using 10 developed platforms, and the experimental results show that the mini quadrotor platform performs autonomous swarming flight with good precision and can be applied to actual outdoor flight environments.

Active disturbance rejection control (ADRC)-based autonomous homing control of powered parafoils

Powered parafoils are a kind of flexible winged vehicle. In order to realize safe and accurate homing of powered parafoils, a multiphase homing trajectory planning scheme is proposed according to their flight characteristics, and a new particle swarm optimization algorithm based on chaos searching (CPSO) is applied as a tool to optimize the designed homing path. Because it is hard to get the satisfied mechanism model, and moreover, there exist lots of disturbances in actual flight environments, traditional control methods cannot ensure the tracking accuracy. Therefore, ADRC controllers are applied to solve such problems. For ADRC, uncertain items of the model and external disturbances are estimated by extended state observer and compensated by real-time dynamic feedback. Simulation results show that the multiphase homing trajectory can fulfill the requirements of fixed-point and upwind landing. The designed ADRC controllers can efficiently overcome the internal and external disturbances and track the desired path rapidly and steadily. Compared with proportion integration differentiation (PID) controllers, ADRC controllers possess better robustness and anti-disturbance ability.

Research on Flight Control of Quad-rotor Based on Backstepping and Adaptive Control Technology

According to the uncertainty problem in the process of quad-rotor aircraft flight, As close to the actual flight environment, The nonlinear dynamic model of quad-rotor aircraft is established,On the basis of the backstepping, Analyzed the presence of interference control quantity expression and adaptive law.This paper puts forward a technique of backstepping and adaptive control technology,Through Matlab simulation and flight test of the designed adaptive inverse footwork the effectiveness of the proposed controller is verified, The simulation results show that the system has good robustness.

Spectral Calibration of Hyperspectral Data Observed From a Hyperspectrometer Loaded on an Unmanned Aerial Vehicle Platform

Hyperspectral imaging has been widely applied in remote sensing scientific fields. For this study, hyperspectral imaging data covering the spectral region from 400 to 1000 nm were collected from an unmanned aerial vehicle visible/near-infrared imaging hyperspectrometer (UAV-VNIRIS). Theoretically, the spectral calibration parameters of the UAV-VNIRIS measured in the laboratory should be refined when applied to the hyperspectral data obtained from the UAV platform due to variations between the laboratory and actual flight environments. Therefore, accurate spectral calibration of the UAV-VNIRIS is essential to further applications of the hyperspectral data. Shifts in both the spectral center wavelength position and the full-width at half-maximum (FWHM) were retrieved using two different methods (Methods I and II) based on spectrum matching of atmospheric absorption features at oxygen bands near 760 nm and water vapor bands near 820 and 940 nm. Comparison of the spectral calibration results of these two methods over the calibration targets showed that the derived center wavelength and FWHM shifts are similar. For the UAV-VNIRIS observed data used here, the shifts in center wavelength derived from both Methods I and II over the three absorption bands are less than 0.13 nm, and less than 0.22 nm in terms of FWHM. The findings of this paper revealed: 1) the UAV-VNIRIS payload on the UAV platform performed well in terms of spectral calibration; and 2) the applied methods are effective for on-orbit spectral calibration of the hyper spectrometer.

Design and Implementation of UAV 3D Visual Simulation Training System

UAV visual simulation training system is a vital part of the UAV simulation training system. It is made up of simulation models for UAV and airborne platform mathematical, UAV visual and ground-station control system. It prevents a realistic virtual environment for UAV operator by simulating UAV flight control law and the actual flight environments. In order to train operational level, test weapons and validate tactical thinking economically and efficiently. This paper prevented the function, architecture, hardware deployment, running conditions and realization of real simulation module.

Real time crack detection using mountable comparative vacuum monitoring sensors

Current maintenance operations and integrity checks on a wide array of structures require personnel entry into normally-inaccessible or hazardous areas to perform necessary nondestructive inspections. To gain access for these inspections, structure must be disassembled and removed or personnel must be transported to remote locations. The use of in-situ sensors, coupled with remote interrogation, can be employed to overcome a myriad of inspection impediments stemming from accessibility limitations, complex geometries, the location and depth of hidden damage, and the isolated location of the structure. Furthermore, prevention of unexpected flaw growth and structural failure could be improved if on-board health monitoring systems were used to more regularly assess structural integrity. A research program has been completed to develop and validate Comparative Vacuum Monitoring (CVM) Sensors for surface crack detection. Statistical methods using one-sided tolerance intervals were employed to derive Probability of Detection (POD) levels for a wide array of application scenarios. Multi-year field tests were also conducted to study the deployment and long-term operation of CVM sensors on aircraft. This paper presents the quantitative crack detection capabilities of the CVM sensor, its performance in actual flight environments, and the prospects for structural health monitoring applications on aircraft and other civil structures.

Spatial Audio as a Navigation Aid and Attitude Indicator

Most current display systems in general aviation (GA) environments employ, at best, relatively simple audio displays that do not fully exploit a pilot's auditory processing capabilities. Spatial audio displays, however, take advantage of the spatial processing capabilities of the auditory system and have the ability to provide, in an intuitive manner, comprehensive information about the status of an aircraft to the pilot. This paper describes a study conducted in order to assess the utility of spatial audio as (1) a navigation aid, and (2) an attitude indicator in an actual flight environment. Performance was measured in tasks requiring pilots to fly in the direction of a spatial audio “navigation beacon” and use an auditory artificial horizon display to detect changes in attitude and maintain straight and level flight when no visual cues were available. The results indicate that spatial audio displays can effectively be used by pilots for both navigation and attitude monitoring, and thus may be a valuable tool in supporting pilot situation awareness and improving overall safety in GA environments.

Particulate impact damage predictions

Rain and solid particle impact damage may produce significant levels of optical degradation in forward-looking IR-transmitting windows on aerospace vehicles. While a significant level of effort is devoted to characterizing the relative erosion resistance of one material compared with another, considerably less effort is devoted to establishing how the particulate impact damage affects a window or dome for in-flight environments. Short of actual flight tests this determination requires an understanding of the relation between laboratory-scale erosion testing and the in-flight conditions to which the window may be subjected. The actual flight environment is complicated by the probability that it may consist of a combination of rain and solid particles. Therefore it is necessary to establish the effects of prior particle impact damage in the sequence of exposures to the range of particulate environments that may be encountered. Particulate erosion is frequently not the damage mode that has to be considered, but catastrophic failure of the window is often a possible outcome of the particulate impacts depending on the configuration of the window and the material from which it is made. In the latter case detailed structural analyses of the damaged window are required to determine if it will survive. The factors influencing the mechanical behavior of IR-transmitting windows in realistic flight environments are outlined. The results from recent particulate impact tests representative of the flight environment are described.

Physiological assessment of pilot workload in simulated and actual flight environments : Lindholm, E., and Sisson, N.Behaviour Research Methods, Instruments and Computers, 1985, 17.2, 191–194

Physiological assessment of pilot workload in simulated and actual flight environments : Lindholm, E., and Sisson, N.Behaviour Research Methods, Instruments and Computers, 1985, 17.2, 191–194