International Journal of Aerospace Engineering The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Space Object Detection in Video Satellite Images Using Motion Information Tue, 17 Oct 2017 07:27:20 +0000 Compared to ground-based observation, space-based observation is an effective approach to catalog and monitor increasing space objects. In this paper, space object detection in a video satellite image with star image background is studied. A new detection algorithm using motion information is proposed, which includes not only the known satellite attitude motion information but also the unknown object motion information. The effect of satellite attitude motion on an image is analyzed quantitatively, which can be decomposed into translation and rotation. Considering the continuity of object motion and brightness change, variable thresholding based on local image properties and detection of the previous frame is used to segment a single-frame image. Then, the algorithm uses the correlation of object motion in multiframe and satellite attitude motion information to detect the object. Experimental results with a video image from the Tiantuo-2 satellite show that this algorithm provides a good way for space object detection. Xueyang Zhang, Junhua Xiang, and Yulin Zhang Copyright © 2017 Xueyang Zhang et al. All rights reserved. Three-Dimensional CST Parameterization Method Applied in Aircraft Aeroelastic Analysis Wed, 04 Oct 2017 08:08:07 +0000 Class/shape transformation (CST) method has advantages of adjustable design variables and powerful parametric geometric shape design ability and has been widely used in aerodynamic design and optimization processes. Three-dimensional CST is an extension for complex aircraft and can generate diverse three-dimensional aircraft and the corresponding mesh automatically and quickly. This paper proposes a parametric structural modeling method based on gridding feature extraction from the aerodynamic mesh generated by the three-dimensional CST method. This novel method can create parametric structural model for fuselage and wing and keep the coordination between the aerodynamic mesh and the structural mesh. Based on the generated aerodynamic model and structural model, an automatic process for aeroelastic modeling and solving is presented with the panel method for aerodynamic solver and NASTRAN for structural solver. A reusable launch vehicle (RLV) is used to illustrate the process for aeroelastic modeling and solving. The result shows that this method can generate aeroelastic model for diverse complex three-dimensional aircraft automatically and reduce the difficulty of aeroelastic analysis dramatically. It provides an effective approach to make use of the aeroelastic analysis at the conceptual design phase for modern aircraft. Hua Su, Chunlin Gong, and Liangxian Gu Copyright © 2017 Hua Su et al. All rights reserved. Designing a Control System for an Airplane Wing Flutter Employing Gas Actuators Sun, 01 Oct 2017 10:30:24 +0000 The wing flutter is a dynamic instability of a flight vehicle associated with the interaction of aerodynamic, elastic, and inertial forces (aeroelastics phenomena). In this study, just the primary control is investigated. Also, in order to control the two-dimensional wing flutter, the force jet and pulse width pulse frequency (PWPF) are suggested. The PWPF modulator has the advantage of almost linear operation, low jet gas consumption, flexibility in addressing various needs, and good accuracy in presence of oscillations. This scheme makes use of quasi-steady dynamic premises and incompressible flow, as well as the thin airfoil theory. It should be noted that, to justify the application of the aerodynamic theory, we have speculated that the thruster jet ejected through a nozzle with a diameter smaller than several millimeters has a supersonic regime (with Mach number of the order of ). Consequently, the interference of the thruster jet in the boundary layer, flow, and circulation around the airfoil which are characterized by low speed would be negligible. The operation of the jet as a thruster is handled by the PWPF modulator, and the process output is fed back to the system via a PD controller. In order to control the wing flutter oscillation, the location of installing the actuator on the airfoil is investigated. A. R. Ansari and A. R. B. Novinzadeh Copyright © 2017 A. R. Ansari and A. R. B. Novinzadeh. All rights reserved. Concise Neural Nonaffine Control of Air-Breathing Hypersonic Vehicles Subject to Parametric Uncertainties Sun, 01 Oct 2017 00:00:00 +0000 In this paper, a novel simplified neural control strategy is proposed for the longitudinal dynamics of an air-breathing hypersonic vehicle (AHV) directly using nonaffine models instead of affine ones. For the velocity dynamics, an adaptive neural controller is devised based on a minimal-learning parameter (MLP) technique for the sake of decreasing computational loads. The altitude dynamics is rewritten as a pure feedback nonaffine formulation, for which a novel concise neural control approach is achieved without backstepping. The special contributions are that the control architecture is concise and the computational cost is low. Moreover, the exploited controller possesses good practicability since there is no need for affine models. The semiglobally uniformly ultimate boundedness of all the closed-loop system signals is guaranteed via Lyapunov stability theory. Finally, simulation results are presented to validate the effectiveness of the investigated control methodology in the presence of parametric uncertainties. Xiangwei Bu, Qiong Wang, Yan Zhao, and Guangjun He Copyright © 2017 Xiangwei Bu et al. All rights reserved. Mars Atmospheric Entry Integrated Navigation with Partial Intermittent Measurements Sun, 24 Sep 2017 00:00:00 +0000 Signal degradation suffered by the vehicle is a combination brownout and blackout during Mars atmospheric entry. The communications brownout means that signal fades and blackout means that the signal is lost completely. The communications brownout and blackout periods are analyzed and predicted with an altitude and velocity profiles. In the brownout period, the range measurements between the vehicle and the orbiters are modeled as intermittent measurements with the radio signal arrival probabilities, which are distributed as a Rayleigh distribution of the electron number density around the entry vehicle. A new integrated navigation strategy during the Mars atmospheric entry phase is proposed to consider the probabilities of the radio measurements in the communications brownout and blackout periods under the IMU/beacon scenario based on the information filter with intermittent measurements. Numerical navigation simulations are designed to show the performance of the proposed navigation strategy under the integrated navigation scenario. Tai-shan Lou, Yan Wang, Guo-qiang Ding, and Liang-yu Zhao Copyright © 2017 Tai-shan Lou et al. All rights reserved. Deformation Measuring Methods Based on Inertial Sensors for Airborne Distributed POS Sun, 10 Sep 2017 00:00:00 +0000 This paper is focused on deformation measuring methods based on inertial sensors, which are used to achieve high accuracy motion parameters and the spatial distribution optimization of multiple slave systems in the airborne distributed Position and Orientation System or other purposes. In practical application, the installation difficulty, cost, and accuracy of measuring equipment are the key factors that need to be considered synthetically. Motivated by these, deformation measuring methods based on gyros and accelerometers are proposed, respectively, and compared with the traditional method based on the inertial measurement unit (IMU). The mathematical models of these proposed methods are built, and the detailed derivations of them are given. Based on the Kalman filtering estimation, simulation and semiphysical simulation based on vehicle experiment show that the method based on gyros can obtain a similar estimation accuracy to the method based on IMU, and the method based on accelerometers has an advantage in -axis deformation estimation. Xiaolin Gong, Haojie Liu, and Xing-Gang Yan Copyright © 2017 Xiaolin Gong et al. All rights reserved. A Novel Highly Accurate Finite-Element Family Tue, 05 Sep 2017 07:18:24 +0000 A novel th order finite element for interior acoustics and structural dynamics is presented, with arbitrarily large. The element is based upon a three-dimensional extension of the Coons patch technique, which combines high-order Lagrange and Hermite interpolation schemes. Numerical applications are presented, which include the evaluation of the natural frequencies and modes of vibration of (1) air inside a cavity (interior acoustics) and (2) finite-thickness beams and plates (structural dynamics). The numerical results presented are assessed through a comparison with analytical and numerical results. They show that the proposed methodology is highly accurate. The main advantages however are (1) its flexibility in obtaining different level of accuracy (-convergence) simply by increasing the number of nodes, as one would do for -convergence, (2) the applicability to arbitrarily complex configurations, and (3) the ability to treat beam- and shell-like structures as three-dimensional small-thickness elements. Giovanni Bernardini, Fabio Cetta, and Luigi Morino Copyright © 2017 Giovanni Bernardini et al. All rights reserved. Nonlinear Material Behavior Analysis under High Compression Pressure in Dynamic Conditions Tue, 29 Aug 2017 06:47:32 +0000 Gun chamber pressure is an important parameter in proofing of ammunition to ensure safety and reliability. It can be measured using copper crushers or piezoelectric sensor. Pressure calculations in copper crusher method are based on linear plastic deformation of copper after firing. However, crusher pressure deformation at high pressures deviates from the corresponding values measured by piezoelectric pressure transducers due to strain rate dependence of copper. The nonlinear deformation rate of copper at high pressure measurements causes actual readings from copper crusher gauge to deviate from true pressure values. Comparative analysis of gun chamber pressure was conducted for 7.62 × 51 mm ammunition using Electronic Pressure, Velocity, and Action Time (EPVAT) system with piezoelectric pressure transducers and conventional crusher gauge. Ammunitions of two different brands were used to measure chamber pressure, namely, NATO standard ammunition and non-NATO standard ammunition. The deformation of copper crushers has also been simulated to compare its deformation with real time firing. The results indicate erratic behavior for chamber pressure by copper crusher as per standard deviation and relative spread and thus prove piezo sensor as more reliable and consistent mode of peak pressure measurement. The results from simulation, cost benefit analysis, and accuracy clearly provide piezo sensors with an edge over conventional, inaccurate, and costly method of copper crusher for ballistic measurements due to its nonlinear behavior. Muhammad Zubair Zahid, Shahid Ikramullah Butt, Tauqeer Iqbal, Syed Zohaib Ejaz, and Zhang Faping Copyright © 2017 Muhammad Zubair Zahid et al. All rights reserved. Pose and Shape Reconstruction of a Noncooperative Spacecraft Using Camera and Range Measurements Mon, 28 Aug 2017 00:00:00 +0000 Recent interest in on-orbit proximity operations has pushed towards the development of autonomous GNC strategies. In this sense, optical navigation enables a wide variety of possibilities as it can provide information not only about the kinematic state but also about the shape of the observed object. Various mission architectures have been either tested in space or studied on Earth. The present study deals with on-orbit relative pose and shape estimation with the use of a monocular camera and a distance sensor. The goal is to develop a filter which estimates an observed satellite’s relative position, velocity, attitude, and angular velocity, along with its shape, with the measurements obtained by a camera and a distance sensor mounted on board a chaser which is on a relative trajectory around the target. The filter’s efficiency is proved with a simulation on a virtual target object. The results of the simulation, even though relevant to a simplified scenario, show that the estimation process is successful and can be considered a promising strategy for a correct and safe docking maneuver. Renato Volpe, Marco Sabatini, and Giovanni B. Palmerini Copyright © 2017 Renato Volpe et al. All rights reserved. Experimental Study of the Swirling Oxidizer Flow in HTPB/N2O Hybrid Rocket Motor Sun, 27 Aug 2017 08:18:06 +0000 Effects of swirling oxidizer flow on the performance of a HTPB/N2O Hybrid rocket motor were studied. A hybrid propulsion laboratory has been developed, to characterize internal ballistics characteristics of swirl flow hybrid motors and to define the operating parameters, like fuel regression rate, specific impulse, and characteristics velocity and combustion efficiency. Primitive variables, like pressure, thrust, temperature, and the oxidizer mass flow rate, were logged. A modular motor with 70 mm outer diameter and variable chamber length is designed for experimental analysis. The injector module has four tangential injectors and one axial injector. Liquid nitrous oxide (N2O) as an oxidizer is injected at the head of combustion chamber into the motor. The feed system uses pressurized air as the pressurant. Two sets of tests have been performed. Some tests with axial and tangential oxidizer injection and a test with axial oxidizer injection were done. The test results show that the fuel grain regression rate has been improved by applying tangential oxidizer injection at the head of the motor. Besides, it was seen that combustion efficiency of motors with the swirl flow was about 10 percent more than motors with axial flow. Mohammad Mahdi Heydari and Nooredin Ghadiri Massoom Copyright © 2017 Mohammad Mahdi Heydari and Nooredin Ghadiri Massoom. All rights reserved. Characterization of the Aerodynamic Ground Effect and Its Influence in Multirotor Control Thu, 17 Aug 2017 06:50:30 +0000 This paper analyzes the ground effect in multirotors, that is, the change in the thrust generated by the rotors when flying close to the ground due to the interaction of the rotor airflow with the ground surface. This effect is well known in single-rotor helicopters but has been assumed erroneously to be similar for multirotors in many cases in the literature. In this paper, the ground effect for multirotors is characterized with experimental tests in several cases and the partial ground effect, a situation in which one or some of the rotors of the multirotor (but not all) are under the ground effect, is also characterized. The influence of the different cases of ground effect in multirotor control is then studied with several control approaches in simulation and validated with experiments in a test bench and with outdoor flights. Pedro Sanchez-Cuevas, Guillermo Heredia, and Anibal Ollero Copyright © 2017 Pedro Sanchez-Cuevas et al. All rights reserved. Experimental Validation of Fly-Wheel Passive Launch and On-Orbit Vibration Isolation System by Using a Superelastic SMA Mesh Washer Isolator Thu, 17 Aug 2017 00:00:00 +0000 On-board appendages with mechanical moving parts for satellites produce undesirable micro-jitters during their on-orbit operation. These micro-jitters may seriously affect the image quality from high-resolution observation satellites. A new application form of a passive vibration isolation system was proposed and investigated using a pseudoelastic SMA mesh washer. This system guarantees vibration isolation performance in a launch environment while effectively isolating the micro-disturbances from the on-orbit operation of jitter source. The main feature of the isolator proposed in this study is the use of a ring-type mesh washer as the main axis to support the micro-jitter source. This feature contrasts with conventional applications of the mesh washers where vibration damping is effective only in the thickness direction of the mesh washer. In this study, the basic characteristics of the SMA mesh washer isolator in each axis were measured in static tests. The effectiveness of the design for the new application form of the SMA mesh washer proposed in this study was demonstrated through both launch environment vibration test at qualification level and micro-jitter measurement test which corresponds to on-orbit condition. Seong-Cheol Kwon, Mun-Shin Jo, and Hyun-Ung Oh Copyright © 2017 Seong-Cheol Kwon et al. All rights reserved. Two-Phase Optimal Guidance Law considering Impact Angle Constraint with Bearings-Only Measurements Tue, 15 Aug 2017 00:00:00 +0000 The implementation of advanced guidance laws with bearings-only measurements requires estimation of the range information. To improve estimation accuracy and satisfy the impact angle constraint, this paper proposes a two-phase optimal guidance law consisting of an observing phase and an attacking phase. In the observing phase, the determinant of Fisher information matrix is maximized to achieve the optimal observability and a suboptimal solution expressed by leading angle is derived analytically. Then, a terminal sliding-mode guidance law is designed to track the desired leading angle. In the followed attacking phase, an optimal guidance law is integrated with a switching term to satisfy both the impact angle constraint and the field-of-view constraint. Finally, comparison studies of the proposed guidance law and a traditional optimal guidance law are conducted on stationary targets and maneuvering targets cases. Simulation results demonstrate that the proposed guidance law is able to improve the range observability and achieve better terminal performances including impact angle accuracy and miss distance. Tianning Wang, Shengjing Tang, Jie Guo, and Haoqiang Zhang Copyright © 2017 Tianning Wang et al. All rights reserved. An Approach to Mathematical Modeling and Estimation of Probe-Drogue Docking Success Probability for UAV Autonomous Aerial Refueling Tue, 08 Aug 2017 10:06:12 +0000 One of the keys to the success of aerial refueling for probe-drogue aerial refueling system (PDARS) is the successful docking between the probe and drogue. The study of probe-drogue docking success probability offers an important support to achieving successful docking. During the docking phase of PDARS, based on prior information and reasonable assumptions for the movements of the drogue under atmospheric disturbance, the probe-drogue docking success probability is converted to the probability of the drogue center located in a specific area. A model of the probe-drogue docking success probability is established with and without actuation error, respectively. The curves of the probe-drogue docking success probability with the standard deviation of the drogue central position, the maximum distance from the drogue center position to the equilibrium position, the actuation error, and the standard deviation of the actuation error are obtained through simulations. The study has referential value for the docking maneuver decision of aerial refueling for PDARS. Xufeng Wang, Jianmin Li, Xingwei Kong, Xinmin Dong, and Bo Zhang Copyright © 2017 Xufeng Wang et al. All rights reserved. Anti-Unwinding Attitude Control with Fixed-Time Convergence for a Flexible Spacecraft Mon, 07 Aug 2017 00:00:00 +0000 This paper investigates the fixed-time attitude tracking control problem for flexible spacecraft with unknown bounded disturbances. First, with the knowledge of norm upper bounds of external disturbances and the coupling effect of flexible modes, a novel robust fixed-time controller is designed to deal with this problem. Second, the controller is further enhanced by an adaptive law to avoid the knowledge of norm upper bounds of external disturbances and coupling effect of flexible modes. This control law guarantees the convergence of attitude tracking errors in fixed time where the settling time is bounded by a constant independent of initial conditions. Moreover, the proposed controllers can prevent the unwinding phenomenon. Simulation results are presented to demonstrate the performance of the proposed control scheme. Chutiphon Pukdeboon and Anuchit Jitpattanakul Copyright © 2017 Chutiphon Pukdeboon and Anuchit Jitpattanakul. All rights reserved. Robust Control of Aeronautical Electrical Generators for Energy Management Applications Sun, 06 Aug 2017 07:40:02 +0000 A new strategy for the control of aeronautical electrical generators via sliding manifold selection is proposed, with an associated innovative intelligent energy management strategy used for efficient power transfer between two sources providing energy to aeronautical loads, having different functionalities and priorities. Electric generators used for aeronautical application involve several machines, including a main generator and an exciter. Standard regulators (PI or PID-like) are normally used for the rectification of the generator voltage to be used to supply a high-voltage DC bus. The regulation is obtained by acting on a DC/DC converter that imposes the field voltage of the exciter. In this paper, the field voltage is fed to the generator windings by using a second-order sliding mode controller, resulting into a stable, robust (against disturbances) action and a fast convergence to the desired reference. By using this strategy, an energy management strategy is proposed that dynamically changes the voltage set point, in order to intelligently transfer power between two voltage busses. Detailed simulation results are provided in order to show the effectiveness of the proposed energy management strategy in different scenarios. Giacomo Canciello, Alberto Cavallo, and Beniamino Guida Copyright © 2017 Giacomo Canciello et al. All rights reserved. Optimal Trajectory Determination and Mission Design for Asteroid/Deep-Space Exploration via Multibody Gravity Assist Maneuvers Thu, 03 Aug 2017 00:00:00 +0000 This paper discusses the creation of a genetic algorithm to locate and optimize interplanetary trajectories using gravity assist maneuvers to improve fuel efficiency of the mission. The algorithm is implemented on two cases: (i) a Centaur-class target close to the ecliptic plane and (ii) a Centaur-class target with a high inclination to the ecliptic plane. Cases for multiple numbers of flybys (up to three) are discussed and compared. It is shown that, for the targets considered here, a single flyby of Jupiter is the most efficient trajectory to either target with the conditions and limitations discussed in this paper. In this paper, we also iterate on possible reasons for certain results seen in the analysis and show how these previously observed behaviors could be present in any trajectory found. The parameters and methods used in the algorithm are explained and justified over multiple real-life interplanetary missions to provide deeper insights into the development choices. Sean Fritz and Kamran Turkoglu Copyright © 2017 Sean Fritz and Kamran Turkoglu. All rights reserved. The Coupled Orbit-Attitude Dynamics and Control of Electric Sail in Displaced Solar Orbits Mon, 31 Jul 2017 11:51:45 +0000 Displaced solar orbits for spacecraft propelled by electric sails are investigated. Since the propulsive thrust is induced by the sail attitude, the orbital and attitude dynamics of electric-sail-based spacecraft are coupled and required to be investigated together. However, the coupled dynamics and control of electric sails have not been discussed in most published literatures. In this paper, the equilibrium point of the coupled dynamical system in displaced orbit is obtained, and its stability is analyzed through a linearization. The results of stability analysis show that only some of the orbits are marginally stable. For unstable displaced orbits, linear quadratic regulator is employed to control the coupled attitude-orbit system. Numerical simulations show that the proposed strategy can control the coupled system and a small torque can stabilize both the attitude and orbit. In order to generate the control force and torque, the voltage distribution problem is studied in an optimal framework. The numerical results show that the control force and torque of electric sail can be realized by adjusting the voltage distribution of charged tethers. Mingying Huo, He Liao, Yanfang Liu, and Naiming Qi Copyright © 2017 Mingying Huo et al. All rights reserved. Improvement of Carrier Phase Tracking Based on a Joint Vector Architecture Sun, 30 Jul 2017 06:15:46 +0000 Carrier phase measurements are essential to high precision positioning. Usually, the carrier phase measurements are generated from the phase lock loop in a conventional Global Navigation Satellite System (GNSS) receiver. However there is a dilemma problem to the design of the loop parameters in a conventional tracking loop. To address this problem and improve the carrier phase tracking sensitivity, a carrier phase tracking method based on a joint vector architecture is proposed. The joint vector architecture contains a common loop based on extended Kalman filter to track the common dynamics of the different channels and the individual loops for each channel to track the satellite specific dynamics. The transfer function model of the proposed architecture is derived. The proposed method and the conventional scalar carrier phase tracking are tested with a high quality simulator. The test results indicate that carrier phase measurements of satellites start to show cycle slips using the proposed method when carrier noise ratio is equal to and below 15 dB-Hz instead of 21 dB-Hz with using the conventional phase tracking loop. Since the joint vector based tracking loops jointly process the signals of all available satellites, the potential interchannel influence between different satellites is also investigated. Shaohua Chen and Yang Gao Copyright © 2017 Shaohua Chen and Yang Gao. All rights reserved. Development of Dual Power Multirotor System Sun, 30 Jul 2017 00:00:00 +0000 Vertical take-off and landing (VTOL) aircraft has good flight characteristics and system performance without runway. The multirotor system has been tried to expand into larger size for longer endurance or higher payload. But the motor power to endurance ratio has been limited. Due to the specific energy of gasoline being much higher than battery, introducing gasoline engine into multirotor system can be considered. This paper proposes a dual power multirotor system to combine a quadrotor using gasoline engines to provide major lift in shorter arm with another quadrotor using brushless DC motors to offer most controllable force with longer arm. System design, fabrication, and verification of the proposed dual power multirotor system development are presented. Preliminary flights have achieved 16 kg payload for long endurance flight. This is useful for various applications with advanced improvements. Chin E. Lin and Thanakorn Supsukbaworn Copyright © 2017 Chin E. Lin and Thanakorn Supsukbaworn. All rights reserved. Tendon-Sheath Mechanisms in Flexible Membrane Wing Mini-UAVs: Control and Performance Mon, 24 Jul 2017 00:00:00 +0000 Flexible membrane wings (FMWs) are known for two inherent advantages, that is, adaptability to gusty airflow as the wings can flex according to the gust load to reduce the effective angle of attack and the ability to be folded for compact storage purposes. However, the maneuverability of UAV with FMWs is rather limited as it is impossible to install conventional ailerons. The maneuver relies only on the rudders. Some applications utilize torque rods to warp the wings, but this approach makes the FMW become unfoldable. In this research, we proposed the application of a tendon-sheath mechanism to manipulate the wing shape of UAV. Tendon-sheath mechanism is relatively flexible; thus, it can also be folded together with the wings. However, its severe nonlinearity in its dynamics makes the wing warping difficult to control. To compensate for the nonlinearity, a dedicated adaptive controller is designed and implemented. The proposed approach is validated experimentally in a wind tunnel facility with imitated gusty condition and subsequently tested in a real flight condition. The results demonstrate a stable and robust wing warping actuation, while the adaptive washout capability is also validated. Accurate wing warping is achieved and the UAV is easily controlled in a real flight test. Tegoeh Tjahjowidodo and Shian Lee Copyright © 2017 Tegoeh Tjahjowidodo and Shian Lee. All rights reserved. Variable-Time-Domain Online Neighboring Optimal Trajectory Modification for Hypersonic Interceptors Wed, 12 Jul 2017 07:35:22 +0000 The predicted impact point (PIP) of hypersonic interception changes continually; therefore the midcourse guidance law must have the ability of online trajectory optimization. In this paper, an online trajectory generation algorithm is designed based on neighboring optimal control (NOC) theory and improved indirect Radau pseudospectral method (IRPM). A trajectory optimization model is designed according to the features of operations in near space. Two-point boundary value problems (TPBVPs) are obtained based on NOC theory. The second-order linear form of transversality conditions is deduced backward to express the modifications of terminal states, costates, and flight time in terms of current state errors and terminal constraints modifications. By treating the current states and the optimal costates modifications as initial constraints and perturbations, the feedback control variables are obtained based on improved IRPM and nominal trajectory information. The simulation results show that when the changes of terminal constraints are not relatively large, this method can generate a modified trajectory effectively with high precision of terminal modifications. The design concept can provide a reference for the design of the online trajectory generation system of hypersonic vehicles. Ningbo Li, Humin Lei, Jin Zhou, Lei Shao, and Bin Wang Copyright © 2017 Ningbo Li et al. All rights reserved. Mission Overview and Initial Observation Results of the X-Ray Pulsar Navigation-I Satellite Thu, 06 Jul 2017 08:49:53 +0000 The newly launched X-ray pulsar navigation-I (XPNAV-1) is an experimental satellite of China that is designed for X-ray pulsar observation. This paper presents the initial observation results and aims to recover the Crab pulsar’s pulse profile to verify the X-ray instrument’s capability of observing pulsars in space. With the grazing-incidence focusing type instrument working at the soft X-ray band (0.5–10 keV), up to 162 segments of observations of the Crab pulsar are fulfilled, and more than 5 million X-ray events are recorded. Arrival times of photons are corrected to the solar system barycentre, and the 33 ms pulse period is sought out for Crab. Epoch folding of all the corrected photon times generates the refined pulse profile of Crab. The characteristic two-peak profile proves that the Crab pulsar has been clearly seen, so that the conclusion is made that XPNAV-1’s goal of being capable of observing pulsars is achieved. Xinyuan Zhang, Ping Shuai, Liangwei Huang, Shaolong Chen, and Lihong Xu Copyright © 2017 Xinyuan Zhang et al. All rights reserved. Numerical Simulations of the Flame of a Single Coaxial Injector Tue, 27 Jun 2017 00:00:00 +0000 The processes of mixing and combustion in the jet of a shear-coaxial injector are investigated. Two test cases (nonreacting and reacting) are simulated using the commercial computational fluid dynamics code ANSYS CFX. The first test case is an experiment on the mixing in a nonreacting coaxial jet carried out with the use of planar laser induced fluorescence (PLIF). The second test case is an experiment on the visualization of hydrogen-oxygen flame using PLIF of OH in a single injector combustion chamber at pressure of 53 bar. In the first test case, the two-dimensional axisymmetric simulations are performed using the shear-stress turbulence (SST) model. Due to the dominant flow unsteadiness in the second test case, the turbulence is modeled using transient SAS (Scale-Adaptive Simulation) model. The combustion is modeled using the burning velocity model (BVM) while both two- and three-dimensional simulations are carried out. The numerical model agrees with the experimental data very well in the first test case and adequately in the second test case. Victor P. Zhukov and Markus Feil Copyright © 2017 Victor P. Zhukov and Markus Feil. All rights reserved. Autonomous Orbit Determination for Lagrangian Navigation Satellite Based on Neural Network Based State Observer Wed, 21 Jun 2017 00:00:00 +0000 In order to improve the accuracy of the dynamical model used in the orbit determination of the Lagrangian navigation satellites, the nonlinear perturbations acting on Lagrangian navigation satellites are estimated by a neural network. A neural network based state observer is applied to autonomously determine the orbits of Lagrangian navigation satellites using only satellite-to-satellite range. This autonomous orbit determination method does not require linearizing the dynamical mode. There is no need to calculate the transition matrix. It is proved that three satellite-to-satellite ranges are needed using this method; therefore, the navigation constellation should include four Lagrangian navigation satellites at least. Four satellites orbiting on the collinear libration orbits are chosen to construct a constellation which is used to demonstrate the utility of this method. Simulation results illustrate that the stable error of autonomous orbit determination is about 10 m. The perturbation can be estimated by the neural network. Youtao Gao, Tanran Zhao, Bingyu Jin, Junkang Chen, and Bo Xu Copyright © 2017 Youtao Gao et al. All rights reserved. Performance and Vibration Analyses of Lift-Offset Helicopters Thu, 15 Jun 2017 08:18:26 +0000 A validation study on the performance and vibration analyses of the XH-59A compound helicopter is conducted to establish techniques for the comprehensive analysis of lift-offset compound helicopters. This study considers the XH-59A lift-offset compound helicopter using a rigid coaxial rotor system as a verification model. CAMRAD II (Comprehensive Analytical Method of Rotorcraft Aerodynamics and Dynamics II), a comprehensive analysis code, is used as a tool for the performance, vibration, and loads analyses. A general free wake model, which is a more sophisticated wake model than other wake models, is used to obtain good results for the comprehensive analysis. Performance analyses of the XH-59A helicopter with and without auxiliary propulsion are conducted in various flight conditions. In addition, vibration analyses of the XH-59A compound helicopter configuration are conducted in the forward flight condition. The present comprehensive analysis results are in good agreement with the flight test and previous analyses. Therefore, techniques for the comprehensive analysis of lift-offset compound helicopters are appropriately established. Furthermore, the rotor lifts are calculated for the XH-59A lift-offset compound helicopter in the forward flight condition to investigate the airloads characteristics of the ABC™ (Advancing Blade Concept) rotor. Jeong-In Go, Do-Hyung Kim, and Jae-Sang Park Copyright © 2017 Jeong-In Go et al. All rights reserved. Numerical and Experimental Investigation of Wrinkling Pattern for Aerospace Laminated Membrane Structures Tue, 06 Jun 2017 06:10:08 +0000 Al-polymer laminated membranes are widely used in large aerospace structures. When the laminated membranes are pressurized, wrinkles emerge, which have an important effect on the performance of the structures during operation. This paper describes the numerical simulation and experimental investigation of wrinkles in laminated membranes. The nonlinear postbuckling analysis method, based on laminated thin-shell elements, was used to simulate the onset, growth, and final configuration of wrinkles when laminated membranes are subjected to external loads. The simulations are conducted with the ANSYS finite element package. Changing regularities of number, wavelength, and range for the wrinkles during the onset and growth processes are investigated. The wrinkles of laminated membranes with different design parameters such as material selection, ply number, ply angle, and ply mode are predicted. Devices that can be used to clamp and load laminated membranes in several load cases were designed and developed. A 3D photogrammetry system was constructed to characterize wrinkling patterns of laminated membranes subjected to shear displacement loads. By comparing the results of numerical analysis and experimental results, the accuracy of the numerical analysis method was verified. This study work is expected to inform wrinkling simulation and shape control of aerospace laminated membrane structures. Yihong Hong, Wenjuan Yao, and Yan Xu Copyright © 2017 Yihong Hong et al. All rights reserved. Drilling Load Model of an Inchworm Boring Robot for Lunar Subsurface Exploration Thu, 01 Jun 2017 08:05:58 +0000 In the past decade, the wireline robot has received increasing attention due to the advantages of light weight, low cost, and flexibility compared to the traditional drilling instruments in space missions. For the lunar subsurface in situ exploration mission, we proposed a type of wireline robot named IBR (Inchworm Boring Robot) drawing inspiration from the inchworm. Two auger tools are utilized to remove chips for IBR, which directly interacted with the lunar regolith in the drilling process. Therefore, for obtaining the tools drilling characteristics, the chips removal principle of IBR is analyzed and its drilling load model is further established based on the soil mechanical theory in this paper. And then the proposed theoretical drilling load model is experimentally validated. In addition, according to the theoretical drilling load model, this paper discusses the effect of the drilling parameters on the tools drilling moments and power consumption. These results imply a possible energy-efficient control strategy for IBR. Weiwei Zhang, Shengyuan Jiang, Dewei Tang, Huazhi Chen, and Jieneng Liang Copyright © 2017 Weiwei Zhang et al. All rights reserved. Satellite Constellation Orbit Design Optimization with Combined Genetic Algorithm and Semianalytical Approach Wed, 31 May 2017 09:37:56 +0000 This paper focuses on maximizing the percent coverage and minimizing the revisit time for a small satellite constellation with limited coverage. A target area represented by a polygon defined by grid points is chosen instead of using a target point only. The constellation consists of nonsymmetric and circular Low Earth Orbit (LEO) satellites. A global optimization method, Genetic Algorithm (GA), is chosen due to its ability to locate a global optimum solution for nonlinear multiobjective problems. From six orbital elements, five elements (semimajor axis, inclination, argument of perigee, longitude of ascending node, and mean anomaly) are varied as optimization design variables. A multiobjective optimization study is conducted in this study with percent coverage and revisit time as the two main parameters to analyze the performance of the constellation. Some efforts are made to improve the objective function and to minimize the computational load. A semianalytical approach is implemented to speed up the guessing of initial orbital elements. To determine the best parametric operator combinations, the fitness value and the computational time from each study cases are compared. Tania Savitri, Youngjoo Kim, Sujang Jo, and Hyochoong Bang Copyright © 2017 Tania Savitri et al. All rights reserved. Experimental Design Validation of Tilting Calibration Mechanism by Using Shape Memory Alloy Spring Actuator Tue, 30 May 2017 00:00:00 +0000 A tilting calibration mechanism is periodically deployed to view the reference temperature target during on-board calibration of a spaceborne imaging sensor and stowed after calibration. In the present work, we have proposed a new design strategy using a shape memory alloy (SMA) spring as an actuator that provides a fail-safe function to prevent the blocking of the main optical path when the mechanical driving part of the mechanism is stopped at a certain position during on-board calibration. Although a launch locking device was not considered in the design, this approach makes it possible to impose mechanical constraints on the driving part of the mechanism in severe launch vibration environments. The effectiveness of the proposed design was experimentally validated by a deploying and stowing function test and launch vibration environment tests such as a sine burst test, a random vibration test, and a pyroshock simulating impulse shock test. The test results demonstrated that the mechanism fulfills all the required functions for on-board calibration. The use of an SMA spring actuator was proved effective for implementing the dual function of a fail-safe in an emergency phase and a mechanical constraint on the driving part of the mechanism in severe launch vibration environment. Hyun-Ung Oh, Myeong-Jae Lee, and Taegyu Kim Copyright © 2017 Hyun-Ung Oh et al. All rights reserved.