Formation Flight Research Articles

A Quadral-Fuzzy Control Approach to Flight Formation by a Fleet of Unmanned Aerial Vehicles

This paper addresses the control of a fleet of unmanned aerial systems (UAVs), termed as drones, for flight formation problems. Getting drones to fly in formation is a relevant problem to be solved when cooperative cargo transportation is desired. A general approach for this problem considers the coordination of a fleet of UAVs, by fusing all information coming from several individual sensors posed on each UAVs. However, this approach induces a high cost as every UAV should have its advanced perception system. As an alternative, this paper proposes the use of a single perception system by a fleet composed of several elementary drones (workers) with primitive low-cost sensors and a leader drone carrying a 3D perception source. We propose a Quadral-Fuzzy approach to ensure that all drones fly in formation and will not collide with each other or with environment obstacles. We also develop a new way to compute potential fields based on possibility fuzzy (fuzziness) measure with the focus of avoiding collisions between the drones. The proposed approach encompasses four high-coupled intelligent controllers that respectively control the leader and worker drones’ motion and implement obstacle and collision avoidance procedures. Simulation results using a fleet of four aerial drones are presented, showing the potential for solving usual problems to flights in formation, such as dodging obstacles, avoiding collisions between the drones, among others.

The methods of relative navigation of satellites formation flight

The methods of relative navigation of satellites formation flight

The methods of relative navigation of satellites formation flight

This paper is devoted that relative navigation of satellites which fly within a formation. The concept and the methods of swarm satellites technology and architecture are explained. The difference between the constellation and the formation architecture of satellites are focused. Analyses of relative motion between satellites are simulated by mathematical model which used Hill-Clohessy-Wiltshire (HCW) equations and Keplerian orbital equations. The results of the analysis show that all axes shift by formation. The control algorithms requirements of follower satellite are decided according to the drift of the all axes. Extended Kalman filters are used for optimisation, estimation and control stability of nonlinear orbital relative motion of satellites. At last, comparison of relative navigation models are focused.

Multi UAV Cluster Control Method Based on Virtual Core in Improved Artificial Potential Field

In this paper, a method of multi UAV cluster control based on improved artificial potential field (APF) is proposed. The k-means method is used to integrate and optimize the attractive force between UAVs, and the concept of virtual core is introduced to realize the cluster control and adaptive formation flight of multiple UAVs. The attractive disturbance component of the target point is introduced and the backtracking-filling method is proposed to solve the local minimum problem in the APF. The repulsion force in the APF can realize obstacle avoidance and collision avoidance, and the virtual core can control the UAV cluster to fly to the target point under the attractive force of potential field, so as to realize the track planning and multi aircraft cooperative task. In the process of cluster flight when the UAV fails, merges or dispatches, the method can realize cluster reconfiguration and the cluster control effect and task execution success rate can be improved. The simulation experiments in virtual APF and urban environment APF show the effectiveness of this method.

A globally fixed-time solution of distributed formation control for multiple hypersonic gliding vehicles

This paper investigates the distributed formation control problem for multiple hypersonic gliding vehicles (HGVs) under direct communication topology. Based on a formation flight framework of multiple HGVs, a globally fixed-time formation control scheme is proposed by using the fixed-time stability and the hierarchical control theory. Firstly, a fixed-time consensus law is addressed in the three-dimensional formation flight dynamics to generate the virtual control inputs. In order to design appropriate actual control inputs to track the virtual control commands rapidly and accurately, a composite fixed-time feedback control law is then put forward, where a new fixed-time tracking differentiator is designed to obtain the information on the time derivatives of virtual control inputs. Following, the problem of “explosion of complexity” can be resolved effectively. Finally, the globally fixed-time convergence is achieved in spite of the initial conditions of HGV's states, where the upper bound of the settling time can be estimated in advance by only using the control parameters and the direct communication topology. The desired formation configuration can be established within a prescribed convergence time. Extensive numerical simulations are performed to demonstrate the effectiveness and superiority of the proposed formation control strategy.

Feature-Based Stereo Vision Relative Positioning Strategy for Formation Control of Unmanned Aerial Vehicles

As inspired by birds flying in flocks, their vision is one of the most critical components to enable them to respond to their neighbor’s motion. In this paper, a novel approach in developing a Vision System as the primary sensor for relative positioning in flight formation of a Leader-Follower scenario is introduced. To use the system in real-time and on-board of the unmanned aerial vehicles (UAVs) with up to 1.5 kilograms of payload capacity, few computing platforms are reviewed and evaluated. The study shows that the NVIDIA Jetson TX1 is the most suited platform for this project. In addition, several different techniques and approaches for developing the algorithm is discussed as well. As per system requirements and conducted study, the algorithm that is developed for this Vision System is based on Tracking and On-Line Machine Learning approach. Flight test has been performed to check the accuracy and reliability of the system, and the results indicate the minimum accuracy of 83% of the vision system against ground truth data.

UAVs-based antenna arrays using time modulation

This paper applies time modulation to deal with the design of antenna arrays for UAVs formation flight using a rectangular micro-strip as antenna element in the frequency of 2.4 GHz. The motivation for this paper is to exploit the properties and advantages of time-modulated arrays in an interesting application: UAVs formation flight. This design considers the optimization of the position of the drones (or antenna elements) and the time switched sequences of the elements in a linear geometry. The design process to find the optimal positions of the drones for flight formation and the switch-on interval of each element is carried out by means of the methods of Particle Swarm Optimization and Invasive Weed Optimization. The main contribution to the field of this paper is a performance evaluation of the design problem for UAVs-based linear antenna arrays considering time modulation in terms of side lobe level (SLL) and sideband levels (SBLs). Simulation results are provided in terms of SLL, SBLs, switching time and positions of the drones. These simulation results illustrate that the time modulation could provide a SLL improvement with respect to previous results in literature.

Decentralized finite-time adaptive fault-tolerant synchronization tracking control for multiple UAVs with prescribed performance

This paper is concerned with the decentralized finite-time fault-tolerant attitude synchronization tracking control problem for multiple unmanned aerial vehicles (multi-UAVs) with prescribed performance. Failure to counteract actuator faults in the formation flight of multi-UAVs in a limited time may lead to catastrophic consequences. By integrating the prescribed performance functions into the synchronization tracking errors, a new set of errors is defined. Based on the transformed errors, a finite-time attitude synchronization tracking control scheme is developed by using neural networks and finite-time differentiator techniques. The neural networks are utilized to identify the unknown nonlinear terms induced by uncertainties and actuator faults. To reduce the computational burden caused by estimating the weight vectors, the norms of weight vectors are used for the estimation, such that the number of adaptive parameters is significantly reduced and independent from the number of neurons. The finite-time differentiators are utilized to estimate the intermediate control signals and their derivatives. Moreover, auxiliary dynamic signals with explicit consideration of differentiator estimation errors are introduced into the control scheme to guarantee the finite-time convergences of the synchronized tracking errors. Furthermore, it is shown that by using the Lyapunov method, all UAVs can track their individual attitude references, while the synchronized tracking errors among UAVs are all bounded in finite time and confined within the prescribed performance bounds. Finally, comparative simulation studies on multi-UAVs are conducted to verify the effectiveness of the proposed scheme.

Distributed Radar Sounder: A Novel Concept for Subsurface Investigations Using Sensors in Formation Flight

Spaceborne radar sounders are nadir-looking sensors operating in the high frequency (HF) or very high frequency (VHF) bands with subsurface sensing capabilities. Due to technological limitations, this type of sensors often deploys omnidirectional antennas. This results in undesired artifacts such as off-nadir clutter which could hinder data interpretation. Very recent technological advancements open up the possibility of synthesizing very large antenna apertures in HF/VHF band by using small satellites array deployed in suitable orbital formation flying. Accordingly, in this study, we propose a novel concept of distributed radar sounder system. The proposed concept is complemented with a mathematical model for performance prediction which takes into account the uncertainty on the position of the sensors. Moreover, we discuss possible orbital solutions for the problem of the deployment of the distributed radar sounder system. The results show that a distributed radar sounder operating in small satellites formation flying is particularly appealing as it can: 1) substantially reduce the impact of surface clutter; 2) increase the across-track resolution; 3) increase the signal-to-noise ratio (SNR) (or, alternatively, decrease the overall required transmitted power with respect to a traditional single configuration radar sounder design); and 4) provide large flexibility in the data processing of the signals acquired by the different sensors.

Satellite Formation Flight Simulation Using Multi-Constellation GNSS and Applications to Ionospheric Remote Sensing

The Virginia Tech Formation Flying Testbed (VTFFTB) is a global navigation satellite system (GNSS)-based hardware-in-the-loop (HIL) simulation testbed for spacecraft formation flying with ionospheric remote sensing applications. Past applications considered only the Global Positioning System (GPS) constellation. The rapid GNSS modernization offers more signals from other constellations, including the growing European system—Galileo. This study presents an upgrade of VTFFTB with the incorporation of Galileo and the associated enhanced capabilities. By simulating an ionospheric plasma bubble scenario with a pair of LEO satellites flying in formation, the GPS-based simulations are compared to multi-constellation GNSS simulations including the Galileo constellation. A comparison between multi-constellation (GPS and Galileo) and single-constellation (GPS) shows the absolute mean and standard deviation of vertical electron density measurement errors for a specific Equatorial Spread F (ESF) scenario are decreased by 32.83% and 46.12% with the additional Galileo constellation using the 13 July 2018 almanac. Another comparison based on a simulation using the 8 March 2019 almanac shows the mean and standard deviation of vertical electron density measurement errors were decreased further to 43.34% and 49.92% by combining both GPS and Galileo data. A sensitivity study shows that the Galileo electron density measurements are correlated with the vertical separation of the formation configuration. Lower C/N 0 level increases the measurement errors and scattering level of vertical electron density retrieval. Relative state estimation errors are decreased, as well by utilizing GPS L1 plus Galileo E1 carrier phase instead of GPS L1 only. Overall, superior performance on both remote sensing and relative navigation applications is observed by adding Galileo to the VTFFTB.

Linearized relative motion and proximity control of E-sail-based displaced orbits

This paper discusses the linearized relative motion and control of Electric Solar Wind Sails (E-sails) operating in formation flight around a heliocentric displaced orbit. An E-sail is constituted by thin and centrifugally stretched tethers, and generates a propulsion by momentum interaction with the charged particles from the solar wind. Feasible regions and linear stability of circular displaced non-Keplerian orbits generated by E-sails are investigated using the latest thrust model. The linearized relative motion of E-sails in a formation flight is developed in the chief's orbital frame, and a linear stability analysis of the relative motion is carried out with eigenvalue decomposition. Relative trajectories are classified into three categories, according to whether the relative orbit is stable, fully unstable or locally unstable, the latter corresponding to an instability in the along-track direction. Two control strategies are proposed for stabilization, the first one is an active control aiming to change the topology of the relative motion to eliminate the instability caused by positive real eigenvalues, and the other is a closed-loop feedback control to maintain stability in the along-track direction. Numerical simulations indicate a high accuracy of the linearized relative dynamical model and a good performance of the control strategies.

Adaptive Differential Evolution-Based Distributed Model Predictive Control for Multi-UAV Formation Flight

The complicated formation flight for multi-unmanned aerial vehicles is a challenge, especially when multi-mission requirements are taken into account. This paper studies the adaptive differential evolution-based distributed model predictive control approach to deal with the multi-unmanned aerial vehicle flight achieving obstacle/collision avoidance and formation keeping simultaneously in the complex environment. Specifically, the distributed model predictive controller is designed to achieve stable flight for each unmanned aerial vehicle as well as taking the state and input saturation into account, where the local optimization problem is solved by the adaptive differential evolution algorithm. Besides, the adaptive adjustment to the prediction horizon for the model predictive controller is introduced, while the asymptotic convergence of the rolling optimization is analyzed as well. Finally, simulation examples are provided to illustrate the validity of the proposed control structure.

Stellar spectrum-based relative velocimetry with spectrometer and its integrated navigation

To enhance the velocimetry’s accuracy for the Mars explorer formation flight, especially the relative one, we develop a relative velocimetry method. In this method, the spectrometers at two Mars explorers are adopted to measure the stellar spectrum shift and to get the velocity relative to the star. Unfortunately, the instantaneous stellar velocity cannot be predicted accurately, which results in a high error in this velocimetry. The difference of these two velocities, which does not include the stellar proper motion, is the relative velocity between a pair of Mars explorers at the stellar direction. However, this navigation method cannot operate independently because of unobservability. To make the navigation system observable and enhance the accuracy of both absolute and relative navigation for the Mars explorer formation flight, the relative velocimetry and the inter-satellite links assist X-ray pulsar navigation. And we propose an autonomous integrated navigation method with observability. This integrated navigation scheme makes use of the extended Kalman filter to deal with the relative velocity, the inter-satellite links and the pulse time-of-arrival. The extended Kalman filter estimates the absolute and relative navigation information for the Mars explorer formation flight. Simulation results manifest that both absolute and relative navigation error of our method are lower than that of X-ray pulsar navigation, especially the relative one.

Fully distributed guidance laws for unmanned aerial vehicles formation flight

In this paper, three fully distributed guidance laws are designed for unmanned aerial vehicles formation flight, which have the following advantages. Adaptive technology in novel guidance laws can adapt to various graphs that only need one spanning tree. Cooperative formation does not need to set the virtual structure of formation in advance, but only needs to adjust the formation parameters in the guidance law to achieve the desired time-varying formation. This paper uses a guidance law perpendicular to the line of sight to make the flight trajectory more straight; hence, enhancing its applicability in real-world scenarios. These new guidance laws also enable group formation transformation and can optimize the unmanned aerial vehicles’ formation without global information to obtain the optimum performance of the formation. The simulation results show the practicability and effectiveness of the new method.

Tracking control of multiple unmanned aerial vehicles incorporating disturbance observer and model predictive approach

This paper studies the disturbance observer-based model predictive control approach to deal with the unmanned aerial vehicle formation flight with unknown disturbances. The distributed control problem for a class of multiple unmanned aerial vehicle systems with reference trajectory tracking and disturbance rejection is formulated. Firstly, a local distributed controller is designed by using the model predictive control method to achieve stable tracking, where the local optimization problem is solved by an adaptive differential evolution algorithm. Then, a feedforward compensation controller is introduced by using a disturbance observer to estimate and compensate disturbances, and improve the ability of anti-interference. Besides, the stability of the proposed composite controller is analyzed as well. Finally, the simulation examples are provided to illustrate the validity of proposed control structure.

Detection method of wash angle caused by wingtip vortex for formation flight

The largest civil aviation aircraft in operation, Boeing 787 and A380, have very strong wingtip eddies. Wingtip eddy currents generally have many adverse effects on the aircraft in its range of influence. The influence of tip eddy current will cause different wash angles in different areas after the aircraft. The purpose of this method is to obtain the wash angle at different positions by using the calculated data. The wash angle obtained has important reference significance for the wash correction and risk assessment of aircraft flying in the tip swirl region.

Plasma propulsion for telecommunication satellites

Electric thrusters are used for in-space propulsion of spacecraft for a combination of practical and economic reasons. These devices that use electric power to accelerate the mass flow of the propellant at exhaust velocities are one or two order of magnitude faster than those achieved in conventional chemical propulsion. This feature results in significant propellant savings that allows longer mission times and heavier payloads, however, the thrusts achieved are lower for important electric power consumptions. The different electric thrusters that are currently used in Europe for both in-orbit corrections and also for orbit raising to the operational orbit from the separation stage of the launcher will be introduced. This propulsion system also serves to expel these vehicles from their orbit at the end of their useful life to control the increase of space debris in Earth orbit. Additionally, the characteristics of new low-power electric engines with thrust levels in the range 0.1-10 mN and electric power consumptions below 500 W will be discussed. These are required for flight formation, orbital corrections and end-of-life disposal in the new constellations of small satellites in low Earth orbit intended for planetary internet coverage and interactive television services.

Disturbance observer-based coordinated control for three dimensional formation of unmanned autonomous helicopter

PurposeThis paper aims to study the issue of the three-dimensional formation coordinated control for the unmanned autonomous helicopter (UAH) by using the sliding mode disturbance observer. Under the designed formation coordinated controller, the desired formation can be maintained and the closed-loop system stability is analyzed by using the Lyapunov theory.Design/methodology/approachConsidering the unknown time-varying external 10; disturbance in formation flight of UAHs, a sliding mode disturbance observer has been employed to estimate them.FindingsThis work is supported in part by the National Natural Science Foundation of China under Grant 61803207, and in part by the Fundamental Research Funds for the Central Universities under Grant LGZD201806.Originality/valueA sliding mode disturbance observer has been designed to estimate the unknown time-varying external disturbance in formation flight of UAHs. Aiming at the leading UAH maneuver in three-dimensional space during the formation flight progress, the formation coordinated controller has been proposed based on the output of the disturbance observer to maintain the formation.

Coordinated flight control of miniature fixed-wing UAV swarms: methods and experiments

In this paper, we present our recent advances in both theoretical methods and field experiments for the coordinated control of miniature fixed-wing unmanned aerial vehicle (UAV) swarms. We propose a multi-layered group-based architecture, which is modularized, mission-oriented, and can implement large-scale swarms. To accomplish the desired coordinated formation flight, we present a novel distributed coordinated-control scheme comprising a consensus-based circling rendezvous, a coordinated path-following control for the leader UAVs, and a leader-follower coordinated control for the follower UAVs. The current framework embeds a formation pattern reconfiguration technique. Moreover, we discuss two security solutions (inter-UAV collision avoidance and obstacle avoidance) in the swarm flight problem. The effectiveness of the proposed coordinated control methods was demonstrated in field experiments by deploying up to 21 fixed-wing UAVs.

Circular formation flight control for unmanned aerial vehicles with directed network and external disturbance

This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles ( UAVs ) to perform coordinated circular tracking around a set of circles on a target sphere. Different from the previous results limited in bidirectional networks and disturbance-free motions, this paper handles the circular formation flight control problem with both directed network and spatiotemporal disturbance with the knowledge of its upper bound. Distinguishing from the design of a common Lyapunov function for bidirectional cases, we separately design the control for the circular tracking subsystem and the formation keeping subsystem with the circular tracking error as input. Then the whole control system is regarded as a cascade connection of these two subsystems, which is proved to be stable by input-to-state stability ( ISS ) theory. For the purpose of encountering the external disturbance, the backstepping technology is introduced to design the control inputs of each UAV pointing to North and Down along the special sphere ( say, the circular tracking control algorithm ) with the help of the switching function. Meanwhile, the distributed linear consensus protocol integrated with anther switching anti-interference item is developed to construct the control input of each UAV pointing to east along the special sphere ( say, the formation keeping control law ) for formation keeping. The validity of the proposed control law is proved both in the rigorous theory and through numerical simulations.