A formation flying control algorithm using the Lorentz force for Low Earth Orbits to achieve a trajectory with required shape and size is proposed in the paper. The Lorentz force is produced as a result of interaction between the Earth’s magnetic field and an electrically charged spacecraft. Achievement of the required trajectories represents a challenge since the control in three-dimensional space is a scalar value of the satellite’s charge. A Lyapunov-based control algorithm is developed for elimination of the initial relative drift after the launch. It also aims at reaching a required amplitudes for close relative trajectories for in-plane and out-of-plane motion. Due to the absence of full controllability, the algorithm is incapable of correcting all the parameters of the relative trajectory such as in-plane and out-of-plane phase angles. The proposed control allows to converge to the trajectory with required shape and size, though with some oscillating errors in the vicinity of the required trajectory parameters. Numerical simulation of the relative motion is used to study performance of the control algorithm for one case of one controlled satellite and two cases of five controlled satellites forming a nested ellipses and train formations. The convergence time and final trajectory accuracy are evaluated for different control parameters and orbits using Monte Carlo approach. Full article

The ducted coaxial propeller (DCP) has great application value in eVTOL aircraft because of its high safety, compactness, and low noise. A numerical simulation method for the DCP is established using the sliding mesh technique. A DCP was designed and manufactured for the lift and power test to verify the numerical method. The characteristics of airflow separation inside the DCP were studied, and the influence of the vortex restrain ring (VRR) on the suppression of airflow separation and on lift augmentation of the duct is analyzed. Results show that, when the tip clearance ratio increases from 0.336% to 1.342%, both the total lift and aerodynamic efficiency decrease by about 11.3%. The influence is mainly reflected in the formation of the tip vortex, airflow separation in the straight, and diffusion sections of the duct. Tip vortex and airflow separation increases DCP energy dissipation and clogs the inner wall of the duct, reducing the effective inner diameter and airflow through the duct. Moreover, the role of the duct is weakened, and the wake is contracted, which increases the induced power loss. By adding a VRR to the diffusion section, the tip vortex and airflow separation can be effectively suppressed, which can increase the aerodynamic efficiency by 5.1%. Full article

On-orbit object detection has received extensive attention in the field of artificial intelligence (AI) in space research. Deep-learning-based object-detection algorithms are often computationally intensive and rely on high-performance devices to run. However, those devices usually lack space-qualified versions, and they can hardly meet the reliability requirement if directly deployed on a satellite platform, due to software errors induced by the space environment. In this paper, we evaluated the impact of space-environment-induced software errors on object-detection algorithms through large-scale fault injection tests. Aside from silent data corruption (SDC), we propose an extended criterial SDC-0.1 to better quantify the effect of the transient faults on the object-detection algorithms. Considering that a bit-flip error could cause severe detection result corruption in many cases, we propose a novel automated model hardening with reinforcement learning (AMHR) framework to solve this problem. AMHR searches for error-sensitive kernels in a convolutional neural network (CNN) through trial and error with a deep deterministic policy gradient (DDPG) agent and has fine-grained modular-level redundancy to increase the fault tolerance of the CNN-based object detectors. Compared to other selective hardening methods, AMHR achieved the lowest SDC-0.1 rates for various detectors and could tremendously improve the mean average precision (mAP) of the SSD detector by 28.8 in the presence of multiple errors. Full article

Unmanned aerial vehicles (UAVs) are becoming popular in various applications. However, there are still challenging issues to be tackled, such as effective obstacle avoidance, target identification within a crowd, and specific target tracking. This paper focuses on dynamic target following and obstacle avoidance to realize a prototype of a quadcopter drone to serve as an autonomous object follower. An adaptive target identification system is proposed to recognize the specific target in the complicated background. For obstacle avoidance during flight, we introduce an idea of space detection and use it to develop a so-called contour and spiral convolution space detection (CASCSD) algorithm to evade obstacles. Thanks to the low architecture complexity, it is appropriate for implementation on onboard flight control systems. The target prediction is integrated with fuzzified flight control to fulfill an autonomous target tracker. When this series of technical research and development is completed, this system can be used for applications such as personal security guard and criminal detection systems. Full article

Decision support tools for arrival sequencing and scheduling could assist air traffic controllers in managing the arrival aircraft in terminal areas. However, one critical issue is that the current method for dealing with the arrival sequencing and scheduling problem does not consider the dynamic traffic situation and the human working experience, which results in a deviation between the scheduled and actual landing sequences. This paper develops a data-driven method to address this issue. Firstly, the random forest model is applied to predict the estimated time of arrival (ETA). During the ETA prediction, the trajectory, operation, and airport-related factors that could increase the prediction accuracy are considered. Secondly, the landing sequence is obtained by sorting the predicted ETAs. Thirdly, two optimization methods are proposed to generate the scheduled time of arrival (STA). The former uses the predicted ETAs as inputs and then directly optimizes the landing sequence and the STA. The latter uses both the predicted ETA and the landing sequence as inputs for further optimization. Finally, these proposed methods are evaluated with three sets of historical data on arrival operations at Changsha Huanghua International Airport (ZGHA). The results show that the RF-based ETA prediction method could improve scheduling performance. Moreover, the proposed optimization methods could provide controllers with a more appropriate decision advisory. Such advisories could simultaneously reduce the operation efficiency indicators (average/maximum delay or dwell time) and the operation complexity indicators (Kendall rank correlation or position shift). Full article

This paper presents how the Inspection Development Framework’s (IDF) novel maintenance scheduling technique increased aircraft utilization and availability in a sample of the United States Air Force’s (USAF) C-5M Super Galaxy fleet. The hypothesis tested was “Can we execute segmented maintenance requirements during ground time opportunities in order to optimize flying?” We applied IDF to decompose the C-5M’s five-day Home Station Check (HSC) inspection into smaller work packages that subordinate to operational requirements and maintenance resource availability. Ten HSCs at Dover and Travis Air Force Base (AFB) were modified using IDF and measured against a control group of traditional HSCs. While statistical significance was not achieved given the small sample size, anecdotal results demonstrate improvements in maintenance downtime, sortie count, and flight hours for the experimental group across the two bases. Specifically, the pathfinder’s observed results extrapolated to all HSCs at each base projected an additional 15 flying days per year at Dover AFB and 29 sorties per year at Travis AFB. These C-5M improvements serve as a proof-of-concept for the USAF adapting commercial best practices to address declining aircraft readiness. IDF’s more agile and dynamic scheduling techniques also enable easier adoption of Condition Based Maintenance through a more integrated approach to optimally schedule maintenance requirements. Full article

The rising interest in the evolvability of electric vertical takeoff and landing (eVTOL) promises substantial potential in the field of urban air mobility (UAM). Challenges in energy storage density and geometry restriction both emphasize the propeller efficiency for endurance and takeoff weight, whereas the contra-rotating propellers (CRP) advantage is balancing high thrust and efficiency over a single propeller. The aim of this paper is twofold: (i) to present a novel rapid CRP blade shape optimization framework and (ii) to study the impact of the dual propellers revolution speed allocations on the overall CRP power efficiency. The core of the framework is the blade element momentum theory (BEMT)-based blade shape optimization considering the wake effect of the upper propeller by the rotational CFD (computational fluid dynamics) actuator-disc simulation method. The results show that for the same thrust, the optimized CRP at the equal revolution speed is superior to the original (upper-lower-identical) one by 5.9% in thrust-to-power ratio. The overall efficiency can be additionally lifted by 5.3% when the dual propellers share similar torques. By excluding the integral propeller CFD simulation and empirical parameters estimation, the framework enables the swift obtaining of an optimized CRP scheme while maintaining robustness as well. Full article

Queueing theory is currently a widely used method for optimizing activities not only in air transport but also in other sectors, in both production and the use of personnel. Using this theory, it is possible to simulate in advance various scenarios that may arise during aircraft handling, handling of passengers and their luggage, cargo, or in production lines. This article aims to point out the possibilities of modeling queueing systems in air transport using a simulation model. It applies the measured data from the airport to the created simulation model, analyzes the knowledge gained from the simulations, and then proposes improvements or elimination of problems that may arise during the process in order to dimension the most favorable number of parallel service desks. During this process, we chose to evaluate the criteria of the efficiency of service check-in desks in the passenger handling process at the international airport in Košice and Prague. The handling process at the airport in Košice for weekly flights to Warsaw and at the airport in Prague also for flights to Warsaw during one week in the summer of 2019 was analyzed in more detail. During modeling, five efficiency criteria were monitored, which were focused on the probability of passengers waiting and their time spent waiting for their handling at the check-in desk. However, in these experiments, only the time spent at the check-in desk was taken into account; the following security, passport, and other checks were not included. As part of the evaluation of the efficiency of the passenger handling process, it was concluded that the critical point in the optimization of the handling process is dimensioning the optimal number of check-in desks, which had the greatest impact on the speed and possibility of processing all requests that entered the system. Therefore, it is advisable to first choose the most suitable number of desks and then work with other parameters that are adapted to the individual requirements for optimizing the handling process at airports. Full article

Outgassing or thruster’s generated contaminants are critical for optical surfaces and optical payloads because scientific measurements and, in general, the performances can be degraded or jeopardized by uncontrolled contamination. This is a well-known issue in space technology that is demonstrated by the growing usage of quartz crystal microbalances as a solution for measuring material outgassing properties data and characterizing the on-orbit contamination environment. Operation in space requires compatibility with critical requirements, especially the mechanical and thermal environments to be faced throughout the mission. This work provides the design of a holding structure based on 3D printing technology conceived to meet the environmental characteristics of space application, and in particular, to face harsh mechanical and thermal environments. A kinematic mounting has been conceived to grant compatibility with a large temperature range, and it has been designed by finite element methods to overcome loading during the launch phases and cope with a temperature working range down to cryogenic temperatures. Qualification in such environments has been performed on a mockup by testing a prototype of the holding assembly between −110 ${}^{\circ }$C and 110 ${}^{\circ }$C and allowing verification of the mechanical resistance and stability of the electrical contacts for the embedded heater and sensor in that temperature range. Moreover, mechanical testing in a random environment characterized by an RMS acceleration level of 500 m/s² and excitation frequency from 20 to 2000 Hz was successfully performed. The testing activity allowed for validation of the proposed design and opened the road to the possible implementation of the proposed design for future flight opportunities, also onboard micro or nanosatellites. Moreover, exploiting the manufacturing technology, the proposed design can implement an easy assembling and mounting of the holding system. At the same time, 3D printing provides a cost-effective solution even for small series production for ground applications, like monitoring the contaminants in thermo-vacuum chambers or clean rooms, or depositions chambers. Full article

Space-based gravitational wave (GW) detection at low frequencies is of great scientific significance and has received extensive attention in recent years. This work designs and optimizes the low-energy transfer of the heliocentric formation of GW detectors, which starts from a geosynchronous transfer orbit and targets an Earth-like orbit. Based on the example of the Laser Interferometer Space Antenna (LISA), the transfer is first designed in two-body dynamical models and then refined in simplified high-fidelity dynamical models that only consider the major orbital perturbations evaluated here. The main contributions of this work are to present an adaptive model continuation technique and to exploit the lunar swingby technique to reduce the problem-solving difficulty and velocity increment of orbital transfer, respectively. The adaptive model continuation technique fully reveals the effect of perturbations and rapidly iterates the solutions to the simplified models. The simulation results show that the lunar swingby does reduce the energy needed to escape the Earth’s sphere of influence. It is found that the gravitation of the Earth–Moon system has a significant contribution to reducing the velocity increment. The solution of low-energy transfer in the simplified models is that the duration is 360.6615 days and the total velocity increment is 0.8468 km/s. Full article

A model-free control method is applied to the attitude and orbital operation of the post-capture combined spacecraft, which consists of a space robot and debris. The main contribution of this paper lies in the following three aspects. Firstly, the discrete dynamic linearization method of the motion equation for a post-capture combined spacecraft is proposed, and then, the standardized expression form of multiple input and multiple output system for the attitude and orbital dynamics motions of post-capture combined spacecraft are presented. Secondly, the data mapping model of the post-capture combined spacecraft is defined, and based on this, an initial value online optimization method for the data mapping model is provided, which is key for the convergence of model-free control. Finally, a test system based on the ground-based three-axis spacecraft simulator is built to simulate the attitude and orbital operation of post-capture combined spacecraft, and the experimental system is implemented to verify the validation of the model-free control method proposed in this paper. The results show that the model-free control has a good control effect on the attitude and orbit of the post-capture combined spacecraft, even if the configuration of the spacecraft is time-varying. Full article

The efficiency increase that distributed propulsion could deliver for future hybrid-electric aircraft is in line with the urgent demand for higher aerodynamic performances and a lower environmental impact. Several consolidated proprietary tools (not always available) are developed worldwide for distributed propulsion simulation. Therefore, prediction and comparisons of propeller performances, with computational fluid dynamic codes featuring different implementation of solvers, numerical schemes, and turbulence models, is of interest to a wider audience of research end-users. In this framework, the paper presents a cross-comparison study among different CFD solvers, the SU2 Multiphysics Simulation and Design Software, the CIRA proprietary flow solver UZEN, and the commercial ANSYS-FLUENT code, for the simulation of a wing section with a tractor propeller at different flow attitudes. The propeller is modelled as an actuator disk according to the general momentum theory and is accounted for in the flow solvers as a boundary condition, for the momentum and energy equations. In this study, a propeller with a fixed advance ratio $J=0.63$ is considered, while propeller performances are assumed variable along with the radius. To perform the comparisons among the solvers, an in-house procedure, which provides the input thrust and torque distributions in a unified format among the three solvers, is developed. Steady RANS simulations are performed at $R{e}_{\infty }=1.7\times {10}^6$ and $M_{\infty }=0.11$, for the flowfield of an isolated propeller. Successively, a wing section with a fixed forward-mounted propeller configuration with no nacelle, is studied at $\alpha =0^{\circ },4^{\circ },$ and $8^{\circ }$ angles of attack. The comparisons in terms of the lift coefficient show a good agreement among the three flow solvers both in power-off and power-on conditions. Simulations also evidenced the strong stability preserving property of upwind schemes, applied to propeller simulation at low-Mach number. Some discrepancies in the drag coefficient are observed and related to different levels of numerical diffusion between the three codes, which affects the downstream wake. Differences in flow properties in near disk region are observed and explained considering the different hub implementations. Full article

The laser gyroscope of Laser Inertial Navigation System (LINS) eliminates the influence of the locked zone with mechanical dither. The output information of laser gyroscopes must be filtered before use to eliminate vibration noise. Laser gyroscope filters are designed according to the instrument accuracy, calculation capacity, vibration frequency, system dynamic characteristics, and other indicators. In this paper, a pigeon-inspired optimization (PIO) method is proposed for use in filter design. The PIO method can flexibly design filters with excellent performance according to the indicator requirements. In the method, the constraints and indicators of the amplitude, phase and order of the LINS filter are firstly confirmed according to the application requirements; then, the objective function is established, and the parameters to be optimized of the PIO are set according to the order of the filter; finally, the PIO method is used to obtain filter parameters that can satisfy the constraints and achieve better performance. Referring to the idea of biological evolution mechanisms, we propose a new improved pigeon-inspired optimization method based on natural selection and Gaussian mutation (SMPIO), which can obtain more stable results and higher accuracy. In the SMPIO method, the particle swarm is firstly selected by natural selection, that is, the particles are sorted according to the fitness function, and some particles with poor fitness are replaced by those with better fitness; then, all particles are subjected to Gaussian mutation to obtain a better global optimum. SMPIO method can flexibly design filters according to the comprehensive requirements of laser gyro performance and navigation control indicators, which cannot be achieved by traditional filter design methods; the improvement based on natural selection and Gaussian mutation enables SMPIO to have faster convergence speed, and higher accuracy. Full article

While the growth of unmanned aerial vehicle (UAV) usage over the next few years is indisputable, cooperative operation strategies for UAV swarms have gained great interest in the research community. Mission capabilities increase while contingencies can be mitigated through intelligent management between the operating swarm and the available fleet. The importance of observing the system reliability and of risk assessment grows because the dysfunction of one asset within a system of systems endangers the superordinate mission goals of the operating UAV swarm. Thus, not only is trajectory planning beneficial for usage optimization, but prognostic and health management (PHM) methods, including diagnostics and prognostics, also enable situational awareness and condition-driven asset management to achieve higher mission reliability. The novelty of this work is the observation of asset states based upon a generically modeled multi-component degradation behavior and the integration of PHM methods with real-time capabilities in order to support decision making during mission execution in a highly dynamic and event-based environment. The developed simulation enables the testing and comparison of different maintenance strategies that are integrated into the simulation to show and discuss the effectiveness and benefits of real-time-capable PHM methods. Full article

With the need for more condensed airborne clusters in a shortened time, there are increased risks of parachute collision and other interactions in the air. In this paper, the flight dynamics model of the parachute system is proposed for the whole deplaning airborne process, including parachute deployment, inflation, and the steady descent stages. The trajectories and velocities of the typical parachute airborne system are simulated, and the results are validated against the experimental measurement. To understand the potential interactions between parachutes, the flight dynamics of parachute airborne clusters, are then studied based on this model. The main parameters include the airborne altitudes, deplaning velocities, and airborne mass. The results show that the flight characteristics of parachutes are determined by the competence of the inertia effect and aerodynamic drags. The flight interactions of parachute clusters are most likely to occur at the moment of deployment, where the distance between parachutes is at a minimum. This critical distance increases with deplaning velocities and is insensitive to airborne altitudes. Adjusting the airborne order or using adaptive time periods by airborne mass can also avoid the potential interactions. The results of this paper can provide support for airborne strategies and help increase the safety and efficiency of airborne systems. Full article