On-board Computer Research Articles

Modeling irregular small bodies gravity field via extreme learning machines and Bayesian optimization

Close proximity operations around small bodies are extremely challenging due to their uncertain dynamical environment. Autonomous guidance and navigation around small bodies require fast and accurate modeling of the gravitational field for potential on-board computation. In this paper, we investigate a model-based, data-driven approach to compute and predict the gravitational acceleration around irregular small bodies. More specifically, we employ Extreme Learning Machine (ELM) theories to design, train and validate Single-Layer Feedforward Networks (SLFN) capable of learning the relationship between the spacecraft position and the gravitational acceleration. ELM-base neural networks are trained without iterative tuning therefore dramatically reducing the training time. Analysis of performance in constant density models for asteroid 25143 Itokawa and comet 67/P Churyumov-Gerasimenko show that ELM-based SLFN are able learn the desired functional relationship both globally and in selected localized areas near the surface. The latter results in a robust neural algorithm for on-board, real-time calculation of the gravity field needed for guidance and control in close-proximity operations near the asteroid surface.

RobHortic: A Field Robot to Detect Pests and Diseases in Horticultural Crops by Proximal Sensing

RobHortic is a remote-controlled field robot that has been developed for inspecting the presence of pests and diseases in horticultural crops using proximal sensing. The robot is equipped with colour, multispectral, and hyperspectral (400–1000 nm) cameras, located looking at the ground (towards the plants). To prevent the negative influence of direct sunlight, the scene was illuminated by four halogen lamps and protected from natural light using a tarp. A GNSS (Global Navigation Satellite System) was used to geolocate the images of the field. All sensors were connected to an on-board industrial computer. The software developed specifically for this application captured the signal from an encoder, which was connected to the motor, to synchronise the acquisition of the images with the advance of the robot. Upon receiving the signal, the cameras are triggered, and the captured images are stored along with the GNSS data. The robot has been developed and tested over three campaigns in carrot fields for the detection of plants infected with ‘Candidatus Liberibacter solanacearum’. The first two years were spent creating and tuning the robot and sensors, and data capture and geolocation were tested. In the third year, tests were carried out to detect asymptomatic infected plants. As a reference, plants were analysed by molecular analysis using a specific real-time Polymerase Chain Reaction (PCR), to determine the presence of the target bacterium and compare the results with the data obtained by the robot. Both laboratory and field tests were done. The highest match was obtained using Partial Least Squares-Discriminant Analysis PLS-DA, with a 66.4% detection rate for images obtained in the laboratory and 59.8% for images obtained in the field.

SISTEMAS DE DIAGNÓSTICOS DE FALLOS EN VEHÍCULOS AÉREOS NO TRIPULADOS

Unmanned aerial vehicles (UAVs) are small aircraft that fly without a pilot, either operated remotely by a human being or autonomously. Autonomous UAVs are controlled by an on-board computer (electronic card) that is programmed to perform one or more specific tasks.

Development of an Autonomous Redundant Attitude Determination System for Cubesats

This work deals with the problem of the design of an autonomous redundant system for the attitude determination of nanosatellites. The system consists of a circuit board equipped with three microcontrollers, a magnetic field sensor in three axes, and complementary commercial-of-the-shelf (COTS) components and connectors to provide data signal exchange the vehicle on-board computer. The main goal of this system, named SDATF (of the acronym in Portuguese Sistema de Determinação de Atitude com Tolerância a Falhas), is to provide autonomously the vehicle attitude from the information collected from the onboard computer (OBC) and the magnetometer. The adopted attitude determination algorithm is based on the well-known QUEST method, and the goal of this system is to get accurate attitude computations to low-orbit CubeSat satellites using COTS electronic components, and to provide highly reliable data and high availability levels using fault tolerance tools to avoid the harmful consequences of spatial radiation and its faults known as single event upsets (SEU). The article presents the general design of the fault-tolerant systems and experimental tests using bit flip injection methodology.

Solution of problem of returning to the starting point of autonomously flying UAV by visual navigation

An autonomous visual navigation algorithm is considered, designed for “home“ return of unmanned aerial vehicle (UAV) equipped with on-board video camera and on-board computer, out of GPS and GLONASS navigation signals. The proposed algorithm is similar to the well-known visual navigation algorithms such as V-SLAM (simultaneous localization and mapping) and visual odometry, however, it differs in separate implementation of mapping and localization processes. It calculates the geographical coordinates of the features on the frames taken by on-board video camera during the flight from the start point until the moment of GPS and GLONASS signals loss. After the loss of the signal the return mission is launched, which provides estimation of the position of UAV relatively the map created by previously found features. Proposed approach does not require such complex calculations as V-SLAM and does not accumulate errors over time, in contrast to visual odometry and traditional methods of inertial navigation. The algorithm was implemented and tested with use of DJI Phantom 3 Pro quadcopter.

Explicit Aerodynamic Model Characterization of a Multirotor Unmanned Aerial Vehicle in Quasi-Steady Flight

Abstract In the last years, the research on unmanned aerial systems (UASs) has shown a marked growth and the models to simulate UASs have been deeply studied. Although onboard controller algorithms have increased their complexity, most of them still rely on simplistic models. In essence, aerodynamic forces/torques are generally considered either insignificant compared to propulsion and inertial forces or acceptably modeled with constant aerodynamic coefficients estimated in a particular flight regime. However, the increase of power in the onboard computers allows to make controller algorithms more complex, and therefore, to increase the total performance of the UAS. In this regard, this work provides an explicit aerodynamic model for multirotor UAS that, unlike most of the current models, does not need iterations to be adjusted to the flight conditions at a higher computational cost. This explicit nature makes it an excellent choice for being implemented in onboard computers, thus covering a broad range of applications, from controller design to numerical analysis (e.g., the capture nonlinear phenomena like bifurcations). To obtain this accurate explicit mathematical aerodynamic model, a thorough analysis of a batch of simulations is carried out. In these simulations, the aerodynamic forces and torques are estimated using computer fluid dynamics (CFD), and the propulsive effects are taken into account via blade element momentum theory (BEMT). A study of its implementation for different regimes and platforms is also provided, as well as some potential applications of the solution, like robust control strategies or machine learning.

Throttled explicit guidance for pinpoint landing under bounded thrust acceleration

Onboard computation of a fuel-optimal trajectory is an indispensable technology for future lunar and planetary missions with pinpoint landings. This paper proposes a throttled explicit guidance (TEG) scheme under bounded constant thrust acceleration. TEG is capable of achieving fuel-optimal large diversions with good accuracy and can find optimal solutions. Thus far, the TEG algorithm is unique as it offers an explicit and simultaneous search method for the fuel-optimal thrust direction and thrust magnitude switching in predictor-corrector iterations. Fast numerical search is realized with a straightforward computation of seven final states (position, velocity, and the Hamiltonian) from seven unknowns (six adjoint variables for position and velocity and one final time). In addition, global convergence capability is enhanced by implementing the damped Newton's method. A number of simulations of large diversions show the excellent convergence of the TEG algorithm within at most 15 iterations from a cold start. The experimental results of the runtime measurement of the TEG algorithm support its real-time feasibility on a flight processor. These features of the TEG are suitable for onboard guidance of pinpoint landings.

Improving the usability of the Multi-angle Imaging SpectroRadiometer (MISR) L1B2 Georectified Radiance Product (2000–present) in land surface applications

Abstract. The Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's Terra platform has been acquiring global measurements of the spectrodirectional reflectance of the Earth since 24 February 2000 and is still operational as of this writing. The primary radiometric data product generated by this instrument is known as the Level 1B2 (L1B2) Georectified Radiance Product (GRP): it contains the 36 radiometric measurements acquired by the instrument's nine cameras, each observing the planet in four spectral bands. The product version described here is projected on a digital elevation model and is available from the NASA Langley Atmospheric Science Data Center (ASDC; http://doi.org/10.5067/Terra/MISR/MI1B2T_L1.003; Jovanovic et al., 1999). The MISR instrument is highly reliable. Nevertheless, its onboard computer occasionally becomes overwhelmed by the number of raw observations coming from the cameras' focal planes, especially when switching into or out of Local Mode acquisitions that are often requested in conjunction with field campaigns. Whenever this occurs, one or more lines of data are dropped while the computer resets and readies itself for accepting new data. Although this type of data loss is minuscule compared to the total number of measurements acquired and is marginal for atmospheric studies dealing with large areas and long periods of time, this outcome can be crippling for land surface studies that focus on the detailed analysis of particular scenes at specific times. This paper describes the problem, reports on the prevalence of missing data, proposes a practical solution to optimally estimate the values of the missing data and provides evidence of the performance of the algorithm through specific examples in southern Africa. The software to process MISR L1B2 GRP data products as described here is openly available to the community from the GitHub website (https://github.com/mmverstraete or https://doi.org/10.5281/zenodo.3519988). Two additional sets of resources are also made available on the research data repository of GFZ Data Services in conjunction with this paper. The first set (A; Verstraete et al., 2020, https://doi.org/10.5880/fidgeo.2020.012) includes five items: (A1) a compressed archive (L1B2_Out.zip) containing all intermediary, final and ancillary outputs created while generating the figures of this paper; (A2) a user manual (L1B2_Out.pdf) describing how to install, uncompress and explore those files; (A3) an additional compressed archive (L1B2_Suppl.zip) containing a similar set of results, only for eight other sites, spanning a much wider range of geographical, climatic and ecological conditions; (A4) a companion user manual (L1B2_Suppl.pdf) describing how to install, uncompress and explore those additional files; and (A5) a separate input MISR data archive (L1B2_input_68050.zip) for Path 168, Orbit 68050. This latter archive is usable with the second set (B; Verstraete and Vogt, 2020; https://doi.org/10.5880/fidgeo.2020.011), which includes (B1) a stand-alone, self-contained, executable version of the L1B2 correction codes (L1B2_Soft_Win.zip) that uses the IDL Virtual Machine technology and does not require a paid IDL license as well as (B2) a user manual (L1B2_Soft_Win.pdf) that explains how to install, uncompress and use this software.

ACOUSTIC EXPRESS METHOD FOR MEASURING ELASTIC METAL CONSTANTS OF HIGH-LOADED CONSTRUCTIONS WORKING IN EXTREME CONDITIONS. PART 1

A review of contingencies related to the failure of potentially hazardous equipment of the aviation and space-rocket complexes showed that they lead to explosions, fires, deaths and destruction of infrastructure. The causes of accidents and disasters are errors in the selection of technical solutions and materials during design, imperfection of algorithms and software for flight control systems, malfunctions in on-board computers and security systems, navigation systems, engine failure, defects in components and assemblies. Examples of accidents and disasters related to technical failures leading to a violation of the tightness of the aircraft fuselage and depressurization of spacecraft are given. It is shown that the main types of damage to the units are corrosion damage, fatigue and metal wear. The conclusion is made about the negative impact of the “human factor” regarding the adoption of erroneous decisions, failure to comply with regulatory requirements and actions in extreme situations. There is a risk of fatigue cracks and degradation of the properties of stringer metal, landing gear struts, wing tail trim, fuel tanks, engine pylon flanges, and imperfect methods, equipment, and technology for monitoring fatigue defects of critical components and mechanisms of aircraft, helicopters, and space systems. It is shown that modern achievements are poorly used in research and development of physical methods and diagnostics of elastic constants of metals working under high pressure, their changes in conditions of wide temperature drops, cosmic vacuum, vibration and other influences. It is proposed to combine efforts with scientists and experts in the field of strength, resource assessment and operational safety of aviation and space technology.

Transmission Line Wire Following System Based on Unmanned Aerial Vehicle 3D Lidar

UAV(Unmanned aerial vehicle) wire checking is an efficient and scientific solution of transmission line operations. Aiming at the existing technology, this paper put forward a kind of based on 3D laser radar and ROS (Robot Operating System) of the UAV wire follow System. In the process of power transmission line inspection of wire, the system capture the wire by 3D laser radar mounted on the UAV and calculate the space distance between UAV and the wire and angle of this distance in 3D laser radar coordinate axis, control drone aircraft by PID(Proportion Integration Differentiation) algorithm in the attitude of UAV and inspection speed by the ROS on the onboard computer system platform for real-time wire following and automatic inspection task. Field experiments show that the system can effectively improve the efficiency and safety of wire inspection, and is conducive to the automation, safety and informatization of transmission line inspection process.

Design and Development of an Autonomous Pilot Drone for Security and Rescue Assistance

The proposed project is to design an Autonomous Pilot Drone to assist the police or rescue team or an ambulance in order to rescue the casualties during accidents or in emergency situations and to monitor the area during that incident. There are many commercially available drone platforms, but all of them require manual interaction through a remote controller. This resulted in building an Autonomous Pilot Drone for Security and Rescue Assistance. In the proposed system the drone is a design using an autonomous guiding system with GPS technology. Such drones can fly and hover with programmed input from the on-board computer. Several unexpected issues made to sort out problems like slight weight imbalance, noisy sensor data, error in PID tuning and problem occurred when the battery gets voltage droplet. To fly such drone in autonomous mode, obstacle avoiding sensor is used to avoid accidents. The results are presented and discussed to demonstrate the technical feasibility of the proposed drone through Mission planning software and hardware result

Multimode guided wave extraction capabilities using embedded thin film sensors in a composite laminated beam

A novel method to extract individual wave modes from the ultrasonic multimode guided wave response sensed by embedded piezoelectric sensors is presented. Multimode response involving two fundamental modes, i.e., flexural and axial, and two higher-order wave-modes, i.e., shear and thickness contraction have been considered in the present work. The model is based on higher order beam theory which uses wave kinematics to extract individual wave modes from the multimode response. Further, a numerical finite element model is employed to validate the deformation profile of this analytical model. The embedment of thin film sensors at the same location but within different layers produce signals that exhibit a relative difference in the phase and amplitude due to kinematics. The sensor signals are then post-processed to obtain individual Lamb wave modes. Experiments are carried out to validate the procedure for extracting individual guided wave mode response. The method is independent of sampling rate and works in the presence of complicated mode converted responses. Electronic analog circuits can also be used to perform operations on sensor signals before analog-to-digital conversion, thereby eliminating digital signal processing and the requirement of onboard computers for structural health monitoring especially in aircraft. Such capability minimizes power consumption and weight since we may be able to avoid the use of a computer.

Spacecraft onboard computers control automation

This paper concerns the task of onboard spacecraft’s computers functioning analysis problem. Existing approach is analyzed. Criteria of onboard computers normative functioning and source data for analysis implementation are defined. As a result, telemetry analysis algorithm for forming decisions about onboard computer normative functioning is offered. Program based on it is developed.

LaserCube optical communication terminal for nano and micro satellites

This paper presents the design and testing of LaserCube, a miniature optical communication terminal conceived for nano and microsatellites. The system architecture has been defined for both the downlink and intersatellite link version of the system. Then, a complete engineering model of LaserCube in its intersatellite link configuration has been developed and tested. It features (1) a dual stage pointing and tracking system based on a coarse pointing mechanism patented by Stellar Project, (2) an optical head with a full–duplex telecom channel with transmission and reception on the same wavelength for two–way links, (3) a transceiver section with telecom laser source and optical receiver and (4) the terminal control unit with onboard computer, actuator drivers and data interface. Experimental validation of the system is achieved through a laboratory simulation of an intersatellite link scenario with realistic dynamic disturbance coming from the host satellite attitude jitter.

Mid-range natural orbits around the triple asteroid 2001SN263

The goal of the present paper is to search for natural trajectories that can be used to place a spacecraft to observe the triple asteroid 2001SN263. For a first set of observations mid-range distance orbits are ideal. To model this triple asteroid from a mid-range distance, it is considered that it can be modeled as a single ellipsoid body, which gives a simple mathematical model that allows on-board computation of trajectories. The mass is assumed to be equal to the sum of the masses of the three bodies and its dimensions are calculated considering the size of the orbits of Beta and Alpha. The objective is to search for orbits that can be used at the arrival time of the spacecraft in the vicinity of the triple asteroid to observe the bodies to make a better evaluation of their dimensions and dynamics before a good choice for a final orbit can be made. The two-dimensional elliptic restricted three-body problem is used as the mathematical model with the addition of the perturbations coming from the asteroid and the Sun irregular gravity fields (J2). It is also considered the disturbance caused by the solar radiation pressure, a major force near asteroids.

75 ЛЕТ ГЕОРГИЮ МИХАЙЛОВИЧУ ВАЛЯШКО – ОСНОВОПОЛОЖНИКУ НОВОГО ПОДХОДА К ИЗУЧЕНИЮ МАГНИТНОГО ПОЛЯ ОКЕАНА

G.M. Valyashko is one of the founders of the new methodology for processing and interpreting the results of marine magnetometric measurements. In the 70s, he created an automated system for collecting and processing geophysical information, which was called “Sailor”. G.M. Valyashko continuously improved the Sailor, who lived a long life on the ships of the Institute of Oceanology from the first on-board computers to modern personal computers.

A generalized multi-snapshot model for 3D homing and route following

Inspired by the learning walks of the ant Ocymyrmex robustior, the original multi-snapshot model was introduced, which—in contrast to the classical “single snapshot at the goal” model—collects multiple snapshots in the vicinity of the goal location that subsequently can be used for homing, that is, for guiding the return to the goal. In this study, we show that the multi-snapshot model can be generalized to homing in three dimensions. In addition to capturing snapshots at positions shifted in all three dimensions, we suggest to decouple the home direction from the orientation of snapshots and to associate a home vector with each snapshot. We then propose a modification of the multi-snapshot model for three-dimensional route following and evaluate its performance in an accurate reconstruction of a real environment. As an illumination-invariant alternative to grayscale images, we also examine sky-segmented images. We use spherical harmonics as efficient representation of panoramic images enabling low memory usage and fast similarity estimation of rotated images. The results show that our approach can steer an agent reliably along a route, making it also suitable for robotic applications using on-board computers with limited resources.

Online Safe Flight Envelope Protection for Icing Aircraft Based on Reachability Analysis

Icing encountered by an aircraft in flight can pose a great threat to flight safety, which is the foremost concern in aviation. Ice accretion has nonlinear and coupling properties, and therefore, a conventional envelope protection system cannot successfully deal with the condition. A safe flight envelope based on reachability analysis is proposed in this paper as a basis for designing an online envelope protection system for aircraft under icing conditions. This system uses a neural network method to identify changes in the aerodynamic coefficients and to classify the degrees of icing and uses a database-driven approach to solve the onboard safe flight envelope computation problem. The database of icing safe flight envelopes is created offline and can be retrieved in real time. The Research Civil Aircraft Model (RCAM) encountering icing conditions in the climbing phase was taken as an example to verify the feasibility of the online safe flight envelope protection system. The simulation results showed that the system can classify the degrees of icing efficiently, prevent the aircraft from deviating from the safe flight envelope, guide it back to the envelope along the fastest path, and reduce the risk of loss of control under icing conditions.

Anytime Computation and Control for Autonomous Systems

The correct and timely completion of the sensing and action loop is of utmost importance in safety critical autonomous systems. Crucial to the performance of this feedback control loop are the computation time and accuracy of the estimator which produces state estimates used by the controller. These state estimators often use computationally expensive perception algorithms like visual feature tracking. With on-board computers on autonomous robots being computationally limited, the computation time of such an estimation algorithm can at times be high enough to result in poor control performance. We develop a framework for codesign of anytime estimation and robust control algorithms, taking into account computation delays and estimation inaccuracies. This is achieved by constructing an anytime estimator from an off-the-shelf perception-based estimation algorithm and obtaining a trade-off curve for its computation time versus estimation error. This is used in the design of a robust predictive control algorithm that at run-time decides a contract, or operation mode, for the estimator in addition to controlling the dynamical system to meet its control objectives at a reduced computation energy cost. This codesign provides a mechanism through which the controller can use the tradeoff curve to reduce estimation delay at the cost of higher inaccuracy, while guaranteeing satisfaction of control objectives. Experiments on a hexrotor platform running a visual-based algorithm for state estimation show how our method results in up to a 10% improvement in control performance while simultaneously saving 5%–6% in computation energy as compared to a method that does not leverage the codesign.

Study of highly perturbed spacecraft formation dynamics via approximation

This paper explores methods for approximating and analyzing the dynamics of highly perturbed spacecraft formations with an emphasis on computationally efficient approaches. This facilitates on-board computation or rapid preliminary mission design analysis. Perturbed formation dynamics are often approximated as linear time-varying (LTV) systems, for which Floquet theory can be used to analyze the degree of system instability. Furthermore, the angular momentum of the relative orbital state can be computed with the approximate dynamics to provide additional insight. A general methodology is developed first and then applied to the problem of unstable formation dynamics in asteroid orbits. Here the dominant perturbative effects due to low-order gravitational harmonics and solar radiation pressure are modeled. Numerical simulations validate the approach and illustrate the approximation accuracy achieved.