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During the New Space era small countries are becoming important players in the space business. While space activities are rapidly increasing globally, it is important to make operations in a sustainable and safe way in order to preserve satellite services for future generations. Unfortunately, the sustainability aspect has been largely overlooked in the existing surveys on space technologies. As a result, in this survey paper, we discuss the multi-layer networking approaches in the 6G era specifically from the sustainability perspective. Moreover, our comprehensive survey includes aspects of some interesting industrial, proprietary, and standardization views. We review the most important regulations and international guidelines and revisit a three-dimensional architecture vision to support the sustainability target for a variety of application areas. We then classify and discuss space safety paradigms that are important sustainability enablers of future satellite communications. These include space traffic management, debris detection, environmental impacts, spectrum sharing, and cyber security aspects. The paper also discusses advances towards a planned European connectivity constellation that could become a third flagship infrastructure along with the Galileo and Copernicus systems. Finally, we define potential research directions into the 2030s.

The trust-region-based sequential convex programming (TSCP) method is designed to solve the nonlinear trajectory planning problem using successive linearization and trust region. The TSCP method has a good real-time performance suitable for onboard aerospace applications. However, the main challenge in practical applications is its poor convergence. In this article, we reveal an oscillation phenomenon, which is an important factor affecting the convergence. The main contribution of this article is threefold: 1) the oscillation phenomenon is proved to be an inherent property of the TSCP method for the nonlinear trajectory planning problem; 2) the oscillation condition that determines whether oscillation occurs is obtained; and 3) the oscillation-condition-based remedy to address the oscillation is presented. The effectiveness and robustness of the proposed remedy have been verified via a complex reentry trajectory planning problem. [ABSTRACT FROM AUTHOR]

For the problem of intercepting a maneuvering target with a desired terminal impact angle, we propose a guidance law in this article based on a nonlinear relative virtual guidance model in which the origin is attached to the target. In this way, the original maneuvering target is transformed to a stationary one. We introduce the idea of polynomial guidance in the range domain into the relative virtual guidance model, then the acceleration command is obtained considering the terminal line-of-sight angle constraint and the terminal virtual look angle constraint. After linearization, the proposed law turns to a similar structure with the trajectory shaping guidance law, which is the optimal guidance law in the linear system. Finally, the performance of the proposed guidance law is demonstrated through numerous nonlinear simulations. [ABSTRACT FROM AUTHOR]

Controllability analysis is significant for guidance law optimization and control system synthesis during atmospheric landing of hypersonic flight vehicles. This article concerns the problem of quantifying the controllability and developing a novel controllability measure, i.e., the degree of controllability (DOC), for linear (or linearized) time-varying systems, and conducts the hierarchically quantitative controllability analysis in high-dynamic guidance for autonomous vehicle landing. In particular, a novel DOC criterion is derived via analyzing the characteristics of singular values and the condition number of the controllability Gramian. The proposed DOC criterion can offer a deep insight into the controllability of both the system and each state subspace, and thus, it possesses a clear physical meaning in practice. Furthermore, a certain normalization and modification method is designed to make the criterion more applicable in aerospace engineering. To validate the derived criterion, the scenario of 3-DOF Mars entry guidance is simulated based on a reference-trajectory tracking scheme with active disturbance rejection control algorithm. According to the simulation results, the optimality of different reference trajectories can be evaluated and compared via the DOC criterion. Therefore, the DOC criterion can function as an indicator to analyze the influence of trajectory parameters on the landing process from the perspective of controllability analysis. [ABSTRACT FROM AUTHOR]

In-plane bending traveling wave ultrasonic motors (USM), which are compact in structure and flexible in design, have been widely applied in biological engineering, optical engineering, and aerospace engineering. However, the high driving voltage and complicated driving circuit of this kind of USM restrict their further miniaturization and electromechanical integration in these applications and bring some potential safety hazards. To solve this problem, a low-voltage-driving traveling wave USM incorporating cofired multilayer piezoelectric ceramics was proposed in this work. Four cofired piezoelectric ceramics were strategically designed to excite two orthogonal third-order in-plane bending modes with the same frequency of the USM. The principles of traveling wave synthesis and low-voltage-driving of the USM were deduced, and the stator dynamic design and transient dynamic simulation were carried out by finite-element method. The microproperties of cofired piezoelectric multilayer ceramics, the vibration characteristics of the stator, and the mechanical output performance of the USM were tested by experiments. The results indicated that the motor can work as low as 5 $\text{V}_{\text {p-p}}$. A long stroke with a maximum forward and reverse rotational speeds of 187.7 and 176.6 r/min were obtained, respectively, and a maximum stalling torque of 4.8 mN $\cdot$ m at 47.3 kHz under 15 $\text{V}_{\text {p-p}}$ was achieved. The results showed that the proposed USM is small, low in driving voltage, and high in torque output, which has promising applications in aerospace, biomedicine, and other fields that require a lightweight and integration of driving devices. [ABSTRACT FROM AUTHOR]

A path modification method using the Bézier curve is proposed to enhance pedestrian dead reckoning (PDR) information. The proposed method utilizes the encounter information between multiagents. The PDR information of an individual agent contains errors due to integration drift of the inertial sensors, and the encounter locations of multiple agents may not match. Therefore, path modification of each agent using the encounter information is required. In this study, the trajectory of a pedestrian is represented with a geometric curve, and the shape of the curve is optimized for path modification. The benefit of the proposed method lies in the ability to fuse various types of information into the algorithm to improve the performance. The optimized curve always satisfies the encounter condition, and various types of information can be considered in the optimization process. In this study, PDR information, anchor information, relative information, and heuristic information are used. The performance of the proposed method is demonstrated by simulation using indoor navigation experimental data. [ABSTRACT FROM AUTHOR]

Radio occultation (RO) is a powerful tool for remotely sensing the atmosphere, producing globally distributed soundings with both high vertical resolution and high temperature retrieval accuracy, especially in the stratosphere. The spatial distribution of the soundings typically prevents the use of these measurements for studying atmospheric effects with small horizontal or temporal scales. However, careful arrangement of a dedicated RO constellation can yield sounding clusters useful for the tomographic reconstruction of internal gravity waves with horizontal wavelengths in the tens of kilometers. This article presents occultation cluster quality metrics predictive of internal gravity wave tomographic reconstruction error and uses these metrics to compare the performance of two alternative RO constellation geometries: mutual orbit groups (MOG) and a spread in right ascension of the ascending node (RAAN). MOG constellations have better overall performance and yield more consistent cluster quality across all sampled latitudes, while RAAN-spread constellations have improved equatorial quality and a trend toward reduced quality at the edges of the latitude range. Additionally, analysis of clusters by latitude, ray azimuth, and quality is performed in order to examine the trends in the outlier best- and worst-performing clusters for each constellation type.

This article presents a novel high temperature heat flux (HTHF) sensor based on micromachined thermocouple (MTC) to meet the needs of transient high heat flux detection in ultrahigh temperature environments, such as fire research, high-power pulsed lasers testing, and aerospace engineering. The targeted design, fabrication, and package of an MTC-based HTHF sensor with excellent heat dissipation capacity are proposed, and relevant experiments were conducted in two aspects. First, powerful laser tube-based tests at ambient temperature show that such a sensor can detect a heat flux high to 10.8 MW/m2 with an extremely fast response; its response time, in this case, is 1.9 ms. And then, turbine engine test pipe based tests at high temperature reveal that the sensor with water cooling could survive at 1200 °C for at least 100 s. Compared to conventional heat flux sensors, it is more sensitive to transient heat flux changes and has a faster response speed. Such satisfactory performance makes the sensor extremely competitive in ultrahigh heat flux detection in extremely harsh environments. [ABSTRACT FROM AUTHOR]

Scale diversity, small target, and power limitation have made remote sensing imagery a challenging field in object detection on satellites. Aiming at the aspects of scale diversity and small target, this paper provides a novel feature pyramid network with Adaptive Residual Spatial Bi-Fusion (ARSF) as a solution. ARSF nets introduce a robust fusion of multi-scale semantic information and fine spatial details. A spatial feature fusion module designed in networks with ARSF adapts to object size variation by learning the most crucial feature maps. Comparing to the original feature pyramid network, a shorter critical path for information transmission is formed in our method. Experiments show that a validation instance of YOLOv3-ARSF can achieve a state-of-the-art performance of 85.8 mAP on the NWPU-VHR10 dataset. YOLOv3-ARSF only 3MB larger than YOLOv3 but far exceeds YOLOv3 by 2.3% mAP, which shows our ARSF is efficient. As for the last challenge, two lightweight versions, ARSF(lite) and ARSF(lite+) are also validated for future research of online object detection on satellites in aerospace engineering. Visualizations and details are provided for a more comprehensive understanding.

The development of vision-based navigation algorithms using a camera is becoming more important. The vision-based navigation can be categorized into two types. The first is to use sequential camera images as relative navigation. The second is to estimate the absolute navigation solution using a camera image and database. In absolute navigation, the difference between the database and the camera image is a major obstacle to image registration. One of the factors that make a lot of difference is the shadow effect. This shadow increases the inconsistency between the two images and eventually degrades the localization accuracy. This means that shadows have a significant impact when measuring the similarity of the two templates. To mitigate this effect, we inherited and developed the Monte Carlo Localization (MCL) algorithm based on a new similarity cost function, which is a key contribution to this article. We have established the importance of information with information reallocation logic that considers shadow areas. The proposed algorithm allocates the importance of the information considering a portion of the shaded area in the camera image. First of all, we analyzed the effects of shadows on the camera. To compare the performance of the algorithm, we used not only the shadow restoration algorithm but also various template-based matching algorithms. The proposed algorithm is validated through various simulations and real flight experiments as well.

Recent years have shown a noticeable rise in the number of incidents with drones, related to both civilian and military installations. While drone neutralization techniques have become increasingly effective, detection most often relies on professional equipment, which is too expensive to be used for all critical nodes and applications. Therefore, there is a need for drone detection systems that could work on low performance hardware. Its critical component consists of an object detection system. In this article, we introduce a new object detection dataset, built entirely to train computer vision based object detection machine learning algorithms for a task of binary object detection to enable automated, industrial camera based detection of multiple drone objects using camera feed. The dataset expands existing multiclass image classification and object detection datasets (ImageNet, MS-COCO, PASCAL VOC, anti-UAV) with a diversified dataset of drone images. In order to maximize the effectiveness of the model, real world footage was utilized, transformed into images and hand-labelled to create a custom set of 56821 images and 55539 bounding boxes. Additionally, semi-automated labelling was proposed, tested and proved to be very useful for object detection applications. The dataset was divided into train and test subsets for further processing and used to generate 603 easily deployable Haar Cascades as well as 819 high performing Deep Neural Networks based models. They were used to test different object detection methods to determine the long term feasibility of a large scale drone detection system utilizing machine learning algorithms. The study has shown that Haar Cascade can be used as the Minimum Viable Product model for mediocre performance but fails to scale up effectively for a larger dataset compared to the Deep Neural Network model.

Space debris represents a threat to space missions and operational satellites. Failing to control its growth might lead to the inability to use near-Earth space. However, this issue is still largely unknown to most people. In this paper, we present an educational experience in virtual reality created to raise awareness about the problem of space debris. The application exploits the entity-component-system (ECS) programming pattern to manage around 20000 orbiting objects with a high frame rate to convey a fluid experience. We preliminarily validated our application, in terms of usability as well as quality of user experience, during several events involving both a broad audience (e.g., citizens of all ages, from teenagers to elders) and an experienced audience (e.g., engineering students enrolled in the aerospace degree). The results of the evaluation were extremely positive, showing once again that virtual reality can be an effective means to engage people in captivating and interactive activities, making them experience what can only be imagined - the thousands pieces of space debris surrounding our planet.

Agile satellites with advanced attitude maneuvering capability are the new generation of earth observation satellites (EOSs). The continuous improvement in satellite technology and decrease in launch cost have boosted the development of agile EOSs (AEOSs). To efficiently employ the increasing orbiting AEOSs, the AEOS scheduling problem (AEOSSP) aiming to maximize the entire observation profit while satisfying all complex operational constraints, has received much attention over the past 20 years. The objectives of this article are, thus, to summarize current research on AEOSSP, identify main accomplishments and highlight potential future research directions. To this end, general definitions of AEOSSP with operational constraints are described initially, followed by its three typical variations including different definitions of observation profit, multiobjective function and autonomous model. A detailed literature review from 1997–2019 is then presented in line with four different solution methods, i.e., exact method, heuristic, metaheuristic, and machine learning. Finally, we discuss a number of topics worth pursuing in the future. [ABSTRACT FROM AUTHOR]

This article aims at proposing a multistage linear Gauss pseudospectral method (MS-LGPM) for solving the piecewise continuous nonlinear optimal control problem (OCP) with interior-point constraints and terminal constraints. First, the first-order necessary conditions for the multistage nonlinear OCP are derived, and a typical multipoint boundary value problem is obtained. Second, the original problem can be solved iteratively by integral prediction and quasi-linearization. Then Lagrange interpolation polynomials are used to approximate the state, control, and costate variables, to transfer those differential equations into a set of linear algebraic equations. Therefore, the control update coming closer to the optimal solution can be derived in an analytical manner. Additionally, those linear algebraic equations are formulated in regular banded matrix forms to make the code as concise as possible. Finally, the proposed method is applied to the midcourse guidance design for a dual-pulse missile to evaluate its performance. Simulation results show that the proposed method performs well in providing the optimal control with high accuracy and computational efficiency. Furthermore, a comparison with other typical guidance method and Monte Carlo simulations are also provided. Results demonstrate, even with some random uncertainties, the proposed method still has strong robustness and superior performance. [ABSTRACT FROM AUTHOR]

The present study proposes a sensor selection method based on the proximal splitting algorithm and the A-optimal design of experiment using the alternating direction method of multipliers (ADMM) algorithm. The performance of the proposed method was evaluated with a random sensor problem and compared with previously proposed methods, such as the greedy and convex relaxation methods. The performance of the proposed method is better than the existing greedy and convex relaxation methods in terms of the A-optimality criterion. Although, the proposed method requires a longer computational time than the greedy method, it is quite shorter than that of convex relaxation method in large-scale problems. Then the proposed method was applied to the data-driven sparse-sensor-selection problem. The dataset adopted was the National Oceanic and Atmospheric Administration optimum interpolation sea surface temperature dataset. At a number of sensors larger than that of the latent variables, the proposed method showed similar and better performance compared with previously proposed methods in terms of the A-optimality criterion and reconstruction error. [ABSTRACT FROM AUTHOR]

Understanding the physical properties and scattering mechanisms contributes to synthetic aperture radar (SAR) image interpretation. For single-polarized SAR data, however, it is difficult to extract the physical scattering mechanisms due to lack of polarimetric information. Time–frequency analysis (TFA) on complex-valued SAR image provides extra information in frequency perspective beyond the “image” domain. Based on TFA theory, we propose to generate the subband scattering pattern for every object in complex-valued SAR image as the physical property representation, which reveals backscattering variations along slant-range and azimuth directions. In order to discover the inherent patterns and generate a scattering classification map from single-polarized SAR image, an unsupervised hierarchical deep embedding clustering (HDEC) algorithm based on TFA (HDEC-TFA) is proposed to learn the embedded features and cluster centers simultaneously and hierarchically. The polarimetric analysis result for quad-pol SAR images is applied as reference data of physical scattering mechanisms. In order to compare the scattering classification map obtained from single-polarized SAR data with the physical scattering mechanism result from full-polarized SAR, and to explore the relationship and similarity between them in a quantitative way, an information theory based evaluation method is proposed. We take Gaofen-3 quad-polarized SAR data for experiments, and the results and discussions demonstrate that the proposed method is able to learn valuable scattering properties from single-polarization complex-valued SAR data, and to extract some specific targets as well as polarimetric analysis. At last, we give a promising prospect to future applications. [ABSTRACT FROM AUTHOR]

The pilot-operated proportional directional valve is a crucial component in the airplane landing gear retraction system. The time delay of the proportional valve directly affects the retraction behavior even the flight safety and needs to be analyzed. Therefore, the modeling and analysis of a typical pilot-operated proportional directional valve are presented in this paper. Substantially, the nonlinear valve system is composed of four subsystems: mechanical, electronic, electromagnetic, and fluid dynamic subsystems. The subsystems are modeled based on a lumped parameter approach. The coupling among the subsystems is analyzed. The nonlinearity is implemented using a specific set of equations in the model. Especially, the nonlinearity observed in practical application is considered in modeling the effect of the electronic anti-unloading power drive circuit on the pulse-width modulation signal. The analytical results of the model show good agreement with the experimental ones. The investigation shows that the delay of the valve results from multiple subsystems' dynamic performances which act sequentially on the main spool. The effect of the electronic part and the structural part is analyzed, and the proportion of each part is given based on the simulation results. The analysis shows that the model can provide a direct suggestion in choosing the valve part to optimize and the optimization effect limit.

A method is proposed to improve system reliability in terms of self-detection and isolation of discrete faults. The application of this method on the design of built-in tests for maintenance is presented using the case of aircraft environmental control system maintenance testing. Built-in testing during aircraft on-ground maintenance allows for wider system input variability due to the absence of operational constraints and requirements. This provides an opportunity to optimally design tests that improve the fault detection and isolation capabilities for operators and maintenance crews. A general mathematical framework for built-in test design is shown using a model-based active fault detection and isolation technique. The motivation for this paper is first illustrated through a case study showing the inability to detect and isolate faults at different conditions, demonstrating how system states contribute to these issues. The success of the proposed framework is demonstrated by designing built-in tests that are capable of fully detecting and isolating a multiplicity of faults common to aircraft environmental control systems. We conclude by presenting the value of the proposed method of detecting and isolating faults, as a solution to a constrained optimization problem with the admissible system inputs as manipulated variables.

The study of direct push sampling characteristics forms the theoretical basis for deep sampling tool design. In this paper, a ground test of the direct push sampling was carried out to analyze three influencing factors: tube diameter; friction coefficient; and soil plug length. Using the discrete element method software, EDEM, a lunar subsurface direct push sampling model was established. We propose a vortex structure of the particle displacement field in the sampling tube and establish a connection between the three influencing factors and the structure disturbance of the soil plug. The EDEM simulation revealed the microscopic mechanism of penetration sampling disturbance. The results show that the soil plug in the compressive state had a small disturbance and a high degree of sequence retention and that the internal stress was changed compared to that in the in-situ state. The structure disturbance of the soil plug in the stick-slip state was large, while the parts of the soil plug that are away from the center line of the tube were in disorder. In the center line of the tube, the in-situ sequence state was gradually restored with the increase in tube diameter or decrease in soil plug length. Increasing the friction coefficient would change the soil plug from the compression state to the stick-slip or adhesion state. In case of the stick-slip state or adhesion, reducing the diameter of the tube or increasing the length of the soil plug would change the soil plug from the stick-slip state or adhesion state to the compression state.

This paper deals with a new modeling method and a powerful planning approach for deep space probes. The key technique is based on the concept of extended state model. Furthermore, extended state model planning (ESMP) algorithm is designed to be fully compliant with the model, and flaw selection strategies are proposed to avoid redundant work. Finally, we discuss the time complexity of ESMP, and computational results comparing ESMP with the algorithm in Europa are presented. [ABSTRACT FROM AUTHOR]

This article describes the design and fabrication of an active four-port microwave switching network embedded into a multilayer aerospace composite structure. The multifunctional design is based on three broadband Integrated Device Technology (IDT) F2972 single-pole-double-throw (SP2T) RF switches and also includes a control and power supply circuit. The composite structure has been developed using a preimpregnated structural glass (S-Glass) material (Hexcel HexPly 914E). The conductive tracks of the switch and its ground plane have been fabricated using a nonwoven carbon–nickel–copper (CNC) veil material and a semiflexible conducting silver ink. This article contains an analysis of the electrical properties of both materials at microwave frequencies. The equivalent electrical conductivities of materials were determined using a curve fitting method that was then used to verify the computational modeling of the switching network. The RF switching network was developed based on a hybrid manufacturing approach. The RF transmission lines and a component of the control circuitry were transferred onto uncured pre-preg material using a laser to ablate select regions of the CNC veil material. Postcuring, flexible silver ink was additively printed onto the surface to create the remaining control circuits. The RF performance of the design has been evaluated, and it indicates that the overall performance was consistent with the measured S-parameters of the same circuit fabricated on Rogers 5880 substrate. [ABSTRACT FROM AUTHOR]

NorSat-1 was launched on July 14, 2017 as a satellite carrying, among other instruments, the multineedle Langmuir probe (m-NLP), an instrument which, on NorSat-1, is capable of measuring the ionospheric plasma electron density with the high sampling frequency of 1000 Hz. The m-NLP instrument operates by analyzing the current–voltage diagram resulting from the measurements from each individual probe. In principle, the m-NLP operation methodology should be insensitive to spacecraft charging. However, this is not always the case. In this paper, we present an overview of the instrument response to passes into and out of eclipse. When the satellite exits eclipse, we observe a collapse in the collected probe currents. This acute drop is unaccounted for by the theoretical operation of the instrument. We present a statistical analysis of the phenomenon based on several months of NorSat-1 data, and we suggest a plausible reason for the observed drop in the current, namely, spacecraft charging, by solar cell arrays upon eclipse exit. We briefly discuss how satellite orientation and plasma wake affect the current drop. With this paper, we address Langmuir probe current susceptibility to spacecraft potential. [ABSTRACT FROM AUTHOR]

This paper presents an overview of technology related to on-board microgrids for the more electric aircraft. All aircraft use an isolated system, where security of supply and power density represents the main requirements. Different distribution systems (ac and dc) and voltage levels coexist, and power converters have the central role in connecting them with high reliability and high power density. Ensuring the safety of supply with a limited redundancy is one of the targets of the system design since it allows increasing the power density. This main challenge is often tackled with proper load management and advanced control strategies, as highlighted in this paper. [ABSTRACT FROM AUTHOR]

Background: With communication skills deemed increasingly important for engineering graduates, we wanted to understand how writing is currently included in engineering classes, what challenges are caused by including writing in such classes, and what resources would be most useful to help engineering instructors more easily include writing in engineering classes. Literature review: Writing is a necessary skill for engineering graduates and has received increased attention in engineering classes. However, despite many instructors’ beliefs that writing is an important skill for engineers, it is not typically taught in a systematic and comprehensive way across the engineering curriculum. Research questions: 1. What perceptions of writing, and specifically writing in engineering, do engineering instructors hold? 2. To what extent do engineering instructors report incorporation of writing activities and assignments in their classes? 3. What barriers do engineering instructors perceive as inhibiting the inclusion of more writing in engineering courses? 4. What resources do engineering instructors desire to expand and improve the inclusion of writing in engineering courses? Research methods: A survey was completed by engineering instructional staff (n = 190 respondents, 10.7% response rate) from seven institutions as well as by some members of the Big10+ Engineering Deans Mailing List. Instructors were asked about their general perceptions about writing in engineering and were also asked to consider the most recent engineering course that they taught and reflect on how they included (or did not include) writing in their course. Findings and conclusions: As expected, we found that most engineering instructional staff agree that writing skills are very important in engineering. Yet, we found that constraints on time and resources kept instructors from including more writing in their courses. This paper concludes with a discussion of our efforts to develop resources, such as rubrics, graded writing examples, and strategies for developing writing prompts, to help instructors include more writing in their engineering courses. [ABSTRACT FROM AUTHOR]

This paper presents an impact angle control guidance law that confines the missile look angle during homing in order to not exceed a seeker's field-of-view limit. A sliding surface variable whose regulation guarantees the interception of a stationary target at the desired impact angle is designed, and the guidance law is derived to make the surface variable go to the sliding mode. Using a magnitude-limited sigmoid function in the surface variable, the proposed law prohibits the look angle from exceeding the specified limit during the entire homing. This capability to confine the missile look angle is valuable when a seeker's field-of-view is restricted, since imposing the terminal impact angle constraint demands the missile to fly a curved trajectory. Furthermore, the proposed law can be implemented under bearings-only measurements because the command does not involve any information of the relative range and line-of-sight rate. Numerical simulations are conducted to demonstrate the validity of the proposed law. The result shows that the proposed guidance law accomplishes the impact angle constraint without violating the prescribed look angle limit although it only uses the information of bearing angles. [ABSTRACT FROM AUTHOR]

Reliability of power inverters is of dominant importance in various applications, including industrial, military, aerospace, and commercial applications. Therefore, developing fault tolerant (FT) power inverters is extremely needed from the viewpoints of system availability and avoiding harmful consequences. Tolerating various types of faults, preserving full output ratings after the fault, and being cost-effective represent the main challenges for most of existing FT solutions. In this paper, a new FT single-phase five-level inverter topology is proposed. The proposed topology can effectively tolerate both of single or multiple switches faults whether they are of open- or short-circuit fault types. Moreover, the proposed topology does not deteriorate system efficiency in postfault operation compared to the previously developed FT solutions. Evaluation of the effectiveness and robustness of the proposed topology is verified in both of simulation and experimental environments. Different case studies are investigated in order to cover various types and locations of switches’ faults. Moreover, comprehensive comparisons are provided to validate the superiority of the proposed topology over the previously addressed techniques. [ABSTRACT FROM AUTHOR]

Manipulation of deformable linear objects (DLOs) has potential applications in the fields of aerospace and automotive assembly. In this paper, we introduce a problem formulation for attaching a set of interlinked DLOs to a support structure using a set of clamping points. The formulation describes the manipulation planning problem in terms of known clamp poses; predetermined ideal clamping locations on the cables, called “reference points;” and a set of finite gripping points on the DLOs. We also present a prototype algorithm that generates a solution in terms of primitive manipulation actions. The algorithm guarantees that no interlink constraints are violated at any stage of manipulation. We incorporate gravity in the computation of a DLO shape and propose a property linking geometrically similar cable shapes across the space of cable length and stiffness. This property allows for the computation of solutions for unit length and scaling of these solutions to appropriate length, potentially resulting in faster shape computation. Note to Practitioners—This paper was motivated by the problem of automated robotic installation of electrical wiring into an aircraft fuselage. This process typically involves the alignment of a set of long cables along the side of the fuselage with temporary fasteners, followed by final clamping. The cables are connected to each other through electrical interlinks at certain intervals, and cannot be treated as independent entities during installation. Previous approaches have addressed the problem of motion planning for only a single DLO; these methods would fail to model interlinked DLOs. Here, we present a mathematical formulation for modeling the installation process as a manipulation planning problem. This approach would generate a plan to complete the installation process using a finite set of primitive actions. We demonstrate the use of this algorithm to produce plans for installation of cables into an aircraft fuselage, using specifications for an actual aircraft in production. [ABSTRACT FROM AUTHOR]

In this letter, we propose to integrate a microstrip antenna with commercial solar cells for CubeSat applications where there is a small surface area available for a combination of antennas and solar cells. By placing the radiator for an aperture-coupled patch antenna under the solar cells, it is shown that a directional antenna system can be incorporated into a CubeSat without significant impact to the performance of the antenna. Considering stringent size restrictions involved in CubeSat designs, the proposed solution provides significant overall system size reduction and design flexibility. The solar cell integrated antenna is designed for operation in the 2.2–2.3 GHz space-to-Earth downlink band. Circular polarization is achieved by feeding two 90° rotated patches with a 90° phase offset signal. The results show very promising performance. [ABSTRACT FROM AUTHOR]

This paper presents the drift error analysis of the integrated resistive sensor interfaces and its improvement using the drift-cancellation techniques. This paper focuses on the highly digital time-domain bang-bang phase-locked loop-based architectures that—when ideal—are intrinsically resilient to the drift generated by environmental and circuit degradation effects. Nevertheless, for applications aiming at nearly zero drift, nonideal effects resulting from mismatch and nonlinearity are still creating a residual drift error of the order of 0.5% of the full scale. The feedback mechanisms of the architecture are studied under nonideal circuit conditions using system-level analysis and simulations. The residual drift error is canceled using the system-level time-based compatible techniques applied in an online fashion, without external references and with low power and area overhead due to their highly digital implementation. The system-level simulation results show that the drift error due to mismatch is attenuated within ±0.05% of the full scale, corresponding to a $10\times $ improvement with respect to the previous publications. [ABSTRACT FROM AUTHOR]

An adaptive mesh refinement method for solving optimal control problems is described. The method employs orthogonal collocation at Legendre-Gauss–Radau points. Accuracy in the method is achieved by adjusting the number of mesh intervals, the polynomial degree within each mesh interval, and, when possible, reducing the mesh size. The decision to increase the degree of the polynomial within a mesh interval or to create new mesh intervals is based on the decay rate of the coefficients of a Legendre polynomial approximation of the state as a function of the index of the Legendre polynomial expansion. The polynomial degree in a mesh interval is increased if the Legendre polynomial coefficient decay rate exceeds a user-specified threshold. Otherwise, the mesh interval is divided into subintervals. The method developed in this brief is then demonstrated on two examples, one of which is a practical problem in aircraft performance optimization. It is found that the approach developed in this brief is more efficient, is simpler to implement, and requires the specification of fewer user-defined parameters when compared with recently developed adaptive mesh refinement methods for optimal control. [ABSTRACT FROM AUTHOR]

In this paper, we argue that current state-of-the-art methods of aircraft localization such as multilateration are insufficient, in particular for modern crowdsourced air traffic networks with random, unplanned deployment geometry. We propose an alternative, a grid-based localization approach using the k-nearest neighbor (k -NN) algorithm, to deal with the identified shortcomings. Our proposal does not require any changes to the existing air traffic protocols and transmitters, and is easily implemented using only low-cost, commercial-off-the-shelf hardware. Using an algebraic multilateration algorithm for comparison, we evaluate our approach using real-world flight data collected with our collaborative sensor network OpenSky. We quantify its effectiveness in terms of aircraft location accuracy, surveillance coverage, and the verification of false position data. Our results show that the grid-based k-NN approach can increase the effective air traffic surveillance coverage compared to multilateration by a factor of up to 2.5. As it does not suffer from dilution of precision to the same extent, it is more robust in noisy environments and performs better in pre-existing, unplanned receiver deployments. We further find that the mean aircraft location accuracy can be increased by up to 41% in comparison with multilateration while also being able to pinpoint the origin of potential spoofing attacks conducted from the ground. [ABSTRACT FROM AUTHOR]

The problem of spacecraft attitude tracking with limited communication to actuators is addressed in this paper. A hysteresis quantizer is employed to quantize the signal of control torque. The hysteresis quantizer requires low communication rate and avoids control chattering. An indirect (nonregressor-based) robust adaptive control scheme is proposed to deal with the effects of quantization error and external disturbances. The proposed control scheme together with the quantizer ensures global boundedness of all the signals in the closed-loop system and enables the attitude tracking error to converge toward a residual. [ABSTRACT FROM AUTHOR]

In this paper, a permanent magnet alternator which presently relies on magnetic slot wedges is redesigned to give lower iron loss. The new segmented stator design is used as the basis for a validated loss study—comparing bonded lamination stacks with those held together with a punched notch. Segmentation is shown to improve the production process, reduce losses, and remove the need for wedges, while not significantly altering the acoustic performance. In the first series of prototypes, however, where notching is used to secure lamination packs, the process is shown to have adversely affected material properties of the nickel iron laminations and overall measured losses increased. In the second prototype, with thinner laminations and glued stacks, iron loss predictions and measurement agree and are less than the present slot wedge design. [ABSTRACT FROM AUTHOR]

With the development of computing technologies, computer-based simulation methods have gained increasing attention in reliability analysis of engineering systems, among which subset simulation (SS) provides a robust yet efficient tool for exploring system rare failure events and evaluating system reliability. However, the component limit state functions (LSFs) of a system can be formulated in different forms (e.g., linear, exponential, and scaled), depending on mathematical modeling of the engineering systems concerned. This affects the system LSF and the performance of SS, and may lead to inconsistent system reliability analysis results. This study systematically explores effects of the functional form of component LSFs on the performance of SS in system reliability analysis and accounts for such effects from the perspective of sampling procedures. It is found that the efficient generation of conditional samples during SS, which is pivotal to the success of SS, is affected by the functional form of component LSFs in the system concerned. The performance of SS can be sensitive to the functional form of component LSFs. Normalizing component LSFs eliminate the effects of scaled LSFs on the performance of SS, but it does not improve the robustness (insensitivity) of SS in system reliability analysis involving exponential LSFs that are nonlinear. Understanding the effects of component LSFs on the performance of SS, a generalized SS (GSS) algorithm is proposed for system reliability analysis, which is robust to different functional forms of component LSFs provided that the functional transformation of component LSFs does not change their monotonicity and failure domains. Numerical examples and a real engineering example showed that the proposed algorithm is more robust to the functional form of component LSFs in system reliability analysis than standard SS. [ABSTRACT FROM PUBLISHER]

In this paper, a system-of-systems (SoS) framework is proposed for bottom-up assessment of complex engineering projects. Two principles of SoS analysis (i.e., base-level abstraction and multilevel aggregation) are used to develop the proposed framework. At the base level, complex engineering projects are abstracted as various entities (i.e., human agents, resources, and information) whose attributes and interactions influence the dynamic behaviors of project systems. The performance of project systems at higher levels (i.e., activity level, process level, and project level) is then determined by aggregating entities at the levels below. Through the use of the proposed SoS framework, new dimensions of analysis for better understanding of the performance of engineering projects were explored. One application example of the proposed framework was demonstrated in a case study of a complex construction project. The findings highlight the capability of the proposed framework in providing a novel approach for bottom-up assessment of performance in engineering projects. [ABSTRACT FROM PUBLISHER]