Development of autonomous navigation controller for agricultural vehicles

Agricultural vehicles are adopted to undertake farming tasks by traversing along crop rows in the field.Working quality depends significantly on the driving skills of the operator.Automatic guidance has been introduced into agriculture to achieve high-accuracy path tracking during the last decades,which contributes considerably to straight-line navigation.The objective of this research was to develop an autonomous navigation controller that allowed movement autonomy for various agricultural vehicles.Three wheel-type vehicles were used as the test platform featuring automatic steering,hydrostatic transmission and speed control,which included a rice transplanter,a high-clearance sprayer and a tractor.A dual-antenna RTK-GNSS receiver was attached to the vehicles to provide spatial information on both positioning and heading by using the RTX service from Trimble.A path planning method was proposed to create a straight-line reference path by giving two points,and the target path was determined according to the vehicle initial status and working assignment.Headland turning was comprehensively taken into account by listing different turn patterns in order to realize autonomous navigation at the headland.The navigation controller hardware was fabricated for program execution,data processing and information communication with peripherals.A human-machine interface was designed for the operator to complete basic setting,path planning and navigation control by providing controls.Field experiments were conducted to evaluate the performance and versatility of the newly developed autonomous navigation controller in guiding agricultural vehicles to follow straight paths and turn at the headland.Results showed that an appropriate turn pattern was automatically executed when finishing straight-line navigation.The lateral error in straight-line tracking was no more than 6 cm,6 cm and 5 cm for the rice transplanter,the high-clearance sprayer and the tractor,respectively.And the maximum lateral RMS error was 3.10 cm,4.75 cm,2.21 cm in terms of straight-line tracking,which indicated that the newly developed autonomous navigation controller was versatile and of high robustness in guiding various agricultural vehicles.

H_∞ Robust Fault-Tolerant Controller Design for an Autonomous Underwater Vehicle’s Navigation Control System

In order to improve the security and reliability for autonomous underwater vehicle （AUV） navigation, an H∞ robust fault-tolerant controller was designed after analyzing variations in state-feedback gain Operating conditions and the design method were then analyzed so that the control problem could be expressed as a mathematical optimization problem. This permitted the use of linear matrix inequalities （LMI） to solve for the Hv controller for the system. When considering different actuator failures, these conditions were then also mathematically expressed, allowing the H∞ robust controller to solve for these events and thus be fault-tolerant. Finally, simulation results showed that the H∞ robust fault-tolerant controller could provide precise AUV navigation control with strong robustness.

UPF based autonomous navigation scheme for deep space probe

The autonomous "celestial navigation scheme" for deep space probe departing from the earth and the autonomous "optical navigation scheme" for encountering object celestial body are presented. Then, aiming at the conditions that large initial estimation errors and non-Gaussian distribution of state or measurement errors may exist in orbit determination process of the two phases, UPF (unscented particle filter) is introduced into the navigation schemes. By tackling nonlinear and non-Gaussian problems, UPF overcomes the accuracy influence brought by the traditional EKF (extended Kalman filter), UKF (unscented Kalman filter), and PF (particle filter) schemes in approximate treatment to nonlinear and non-Gaussian state model and measurement model. The numerical simulations demonstrate the feasibility and higher accuracy of the UPF navigation scheme.

GPS/VISNAV integrated relative navigation and attitude determination system for ultra-close spacecraft formation flying

For the improvement of accuracy and better fault-tolerant performance, a global position system （GPS）/vision navigation （VISNAV） integrated relative navigation and attitude determination approach is presented for ultra-close spacecraft formation flying. Onboard GPS and VISNAV system are adopted and a federal Kalman filter architecture is used for the total navigation system design. Simulation results indicate that the integrated system can provide a total improvement of relative navigation and attitude estimation performance in accuracy and fault-tolerance.

Navigation and Control of the PRISMA Formation： In-Orbit Experience

This paper presents flight results and lessons learned from the Spaceborne Autonomous Formation Flying Experiment （SAFE） conducted by the German Space Operations Center in the frame of the Swedish PRISMA technology demonstration mission. PR1SMA involves two fully autonomous formation-flying spacecraft which have been launched in June 2010 in a dawn/dusk orbit at an altitude of 750 km. SAFE represents one of the first demonstrations in low Earth orbit of an advanced guidance, navigation and control system for dual-spacecraft formations. Innovative techniques based on carrier-phase differential GPS （Global Positioning System）, relative eccentricity/inclination vectors and impulsive maneuvering are validated and tuned in orbit to achieve centimeter accurate real-time relative navigation, reliable formation keeping at the meter level and flexible formation reconfiguration capabilities. The technologies demonstrated within SAFE are considered as key precursors of future distributed satellite systems for unrivaled remote sensing and space exploration.

Saturation attack based route planning and threat avoidance algorithm for cruise missiles

According to the characteristic of cruise missiles,navigation point setting is simplified,and the principle of route planning for saturation attack and a concept of reference route are put forward.With the help of the shortest-tangent idea in route-planning and the algorithm of back reasoning from targets,a reference route algorithm is built on the shortest range and threat avoidance.Then a route-flight-time algorithm is built on navigation points.Based on the conditions of multi-direction saturation attack,a route planning algorithm of multi-direction saturation attack is built on reference route,route-flight-time,and impact azimuth.Simulation results show that the algorithm can realize missiles fired in a salvo launch reaching the target simultaneously from different directions while avoiding threat.

Impact Point Prediction and Lateral Correction Analysis of Two-dimensional Trajectory Correction Projectiles

Compared with the one-dimensional trajectory correction technology which adjusts longitudinal range, not only does the two-dimensional trajectory correction technology adjust the force in velocity direction, but also need to modulate the lateral force or trajectory (perpendicular to the vertical plane of fire direction). Therefore, the structure of control cabin of two-dimensional trajectory correction projectile (TDTCP) is more complicated than that of one-dimensional trajectory correction projectile (ODTCP). To simplify the structure of control cabin of TDTCP and reduce the cost, a scheme of adding a damping disk to the control cabin of ODTCP has been developed recently. The damping disk is unfolded at the right moment during its flight to change the ballistic drift of spin stabilized projectile. For this technical scheme of TDTCP, a fast and accurate impact point prediction method based on extended Kalman filter is presented. An approximate formula for predicting the ballistic drift and trajectory correction quantity is deduced. And the lateral correction capability for different fire angles and its influencing factors are analyzed. All the work is valuable for further research.

Research on SINS Error Recursive Model of Ballistic Missile

The strap-down inertial navigation system (SINS) error of ballistic missile is generated by the mutual influence of gyroscope and accelerometer, and the recursive model is completely different from that of gimbaled INS. In the paper, a discrete error recursive model was obtained by studying the applied SINS error model of ballistic missile, and the discrete Kalman filtering simulation based on the model was carried out. The simulated results show that the model can depict the SINS error exactly and provide the advantages for research on integrated guidance and improved hit accuracy.

Guidance Law Design Under Impact Angle Constraint Based on Nussbaum-type Gain Technique

Aiming at the guidance problem under impact angle constraint for homing missile against ground targets,a new adaptive robust nonlinear terminal guidance law was proposed in this paper.According to nonlinear kinetic relationship between the missile and target in vertical plane,a mathematic model was formulated while the motion of target and the system structure perturbation were regarded as limited disturbances.Based on the ideas of zeroing the rate of line-of-sight(LOS)angle and the impact angular tracking error,a nonlinear control strategy was contrived to obtain adaptive robust guidance law by adopting Nussbaum-type gain technique under a desired impact angle.The stability of guidance system in finite time is strictly proven by using Lyapunov stability theory.Finally,the numerical simulation verifies the effectiveness of the proposed scheme.

PATH FOLLOWING GPS-BASED CONTROL OF SMALL-SIZE ROBOTIC UNMANNED BLIMP

Robotic unmanned blimps own an enormous potential for applications in low-speed and low-altitude exploration, surveillance, and monitoring, as well as telecommunication relay platforms. To make lighter-than-air platform a robotic blimp with significant levels of autonomy, the decoupled longitude and latitude dynamic model is developed, and the hardware and software of the flight control system are designed and detailed. Flight control and navigation strategy and algorithms for waypoint flight problem are discussed. A result of flight experiment is also presented, which validates that the flight control system is applicable and initial machine intelligence of robotic blimp is achieved.

H_∞-Mixed Sensitivity Design of Roll Channel of Bank-to-Turn Autopilot for Small Diameter Bomb

According to requirements of the bank-to-turn (BTT) control for a small diameter bomb (SDB), the robust design problem for the roll autopilot was studied by H∞-mixed sensitivity control method. A roll channel dynamics model was established. Considering the couple between the yaw and roll channel as uncertain disturbance, the roll autopilot was designed using dual-loop scheme which takes a linear quadratic regulator (LQR) as inner-loop, to ensure the control effect of the certain part in model, and an H∞-mixed sensitivity control as outer-loop, to restrain coupling disturbance and strengthen the system's robust performance. The dynamic tracking performance and the robustness for the parameter disturbance of the roll controller were analyzed. The simulated results show that the roll control system functions better and robustly.

A Novel Sliding-mode Guidance Law Based on Lie-group Method

Although the channel-decoupling assumption is often used in design of three-dimensional guidance laws, it loses its rationality for aircrafts with strong kinematics coupling because body rotation arises. To overcome this trouble, a novel guiding method was proposed based on Lie-group. After a model of 3D guidance is formulated using vectors, the precision guidance with ending angular constraints can be transformed into a problem involving the relation between directional angles and rotational angular velocities of certain vectors. When the guidance model is imposed a SO(3)-based description, a novel 3D sliding mode guidance law with ending angular constraints can be developed via Lie-group control method and variable structure control theory. Finally, the feasibility and performance of the guidance law were shown by simulating the examples.

Modeling and Simulation for Gliding Missile with Large Aspect Ratio

An improved STT (skid to turn) autopilot was developed to solve the problem of roll control saturation for the gliding missile with large aspect ratio. A lateral acceleration feedback was introduced in the roll channel of the autopilot to ensure that the roll angle could closely follow the lateral acceleration,so that the sideslip angle and the roll rudder deflection could be reduced,and the roll control saturation was avoided. A six-DOF ( degree of freedom) nonlinear simulation model was set up. The simulation results indicate that the model and the control scheme are effective.

Cascaded navigation control for agricultural vehicles tracking straight paths

In precision agriculture(PA),an agricultural vehicle navigation system is essential and the navigation control accuracy is important in this system.As straight path tracking is the major operating mode of agricultural vehicles on large fields,a cascaded navigation control method for straight path tracking is proposed in this study.Firstly,a cascaded navigation control structure for the agricultural vehicle was discussed.Based on this structure,the navigation control task was decomposed into two cascaded control tasks,namely,the path tracking control task and the steering control task.Secondly,a relative kinematics model of agricultural vehicles was deduced,and an optimal Proportional-Derivative(PD)method based on the deduced model was developed in the path tracking control task.Then,an improved PD method based on a transition process was proposed in the steering control task to enhance the performance of the steering control subsystem.Finally,the effectiveness and the superiority of the proposed method were verified by a series of experiments.Results of the experimental data analysis show that mean value of the lateral position deviation is 0.02 m and standard deviation of the lateral position deviation is 0.04 m,which proves that the proposed method has achieved satisfactory effects on the straight path tracking of agricultural vehicles.

End-to-end Mars entry,descent,and landing modeling and simulations for Tianwen-1 guidance,navigation,and control system

On May 15,2021,the Tianwen-1 lander successfully touched down on the surface of Mars.To ensure the success of the landing mission,an end-to-end Mars entry,descent,and landing(EDL)simulator is developed to assess the guidance,navigation,and control(GNC)system performance,and determine the critical operation and lander parameters.The high-fidelity models of the Mars atmosphere,parachute,and lander system that are incorporated into the simulator are described.Using the developed simulator,simulations of the Tianwen-1 lander EDL are performed.The results indicate that the simulator is valid,and the GNC system of the Tianwen-1 lander exhibits excellent performance.

Photothermally induced liquid gate with navigation control of the fluid transport

The ability to control multiphase flows is essential for applications such as microvalves,chemical analyses,mi-croreactors,and multiphase separators.Furthermore,more specific controls,including the positional naviga-tion control of fluids under steady-state pressures,will improve the development of these applications.Here,we present a fundamentally new photothermally induced liquid gating system that allows light-controlled con-tactless fluid transport and gas/liquid separations at designated locations,with seconds response times,under constant pressures.Experiments and theoretical calculations demonstrate the stability of our system and its novel regulation mechanism,which is based on a photothermally induced liquid-reconfigurable gate with a change in the surface/interfacial tension and Marangoni flow redistribution of the gating liquid at the illuminated location.This regulation mechanism with positional navigation properties requires neither mechanical parts nor complex accessories and can further enable the miniaturization and integration of various engineering processes.Our ap-plication demonstrations confirm the potential of this system in fields of smart valves,multiphase separations,multiphase microreactors,and beyond.

Imaginary filtered hindsight experience replay for UAV tracking dynamic targets in large-scale unknown environments

As an advanced combat weapon,Unmanned Aerial Vehicles(UAVs)have been widely used in military wars.In this paper,we formulated the Autonomous Navigation Control(ANC)problem of UAVs as a Markov Decision Process(MDP)and proposed a novel Deep Reinforcement Learning(DRL)method to allow UAVs to perform dynamic target tracking tasks in large-scale unknown environments.To solve the problem of limited training experience,the proposed Imaginary Filtered Hindsight Experience Replay(IFHER)generates successful episodes by reasonably imagining the target trajectory in the failed episode to augment the experiences.The welldesigned goal,episode,and quality filtering strategies ensure that only high-quality augmented experiences can be stored,while the sampling filtering strategy of IFHER ensures that these stored augmented experiences can be fully learned according to their high priorities.By training in a complex environment constructed based on the parameters of a real UAV,the proposed IFHER algorithm improves the convergence speed by 28.99%and the convergence result by 11.57%compared to the state-of-the-art Twin Delayed Deep Deterministic Policy Gradient(TD3)algorithm.The testing experiments carried out in environments with different complexities demonstrate the strong robustness and generalization ability of the IFHER agent.Moreover,the flight trajectory of the IFHER agent shows the superiority of the learned policy and the practical application value of the algorithm.

Powered-descent landing GNC system design and flight results for Tianwen-1 mission

The powered-descent landing(PDL)phase of the Tianwen-1 mission began with composite backshell–parachute(CBP)separation and ended with landing-rover touchdown.The main tasks of this phase were to reduce the velocity of the lander,perform the avoidance maneuver,and guarantee a soft touchdown.The PDL phase overcame many challenges:performing the divert maneuver to avoid collision with the CBP while simultaneously avoiding large-scale hazards;slowing the descent from approximately 95 to 0 m/s;performing the precise hazard-avoidance maneuver;and placing the lander gently and safely on the surface of Mars.The architecture and algorithms of the guidance,navigation,and control system for the PDL phase were designed;its execution resulted in Tianwen-1’s successful touchdown in the morning of 15 May 2021.Consequently,the Tianwen-1 mission achieved a historic autonomous landing with simultaneous hazard and CBP avoidance.

Guidance law with impact time and impact angle constraints

A novel closed-form guidance law with impact time and impact angle constraints is pro- posed for salvo attack of anti-ship missiles, which employs missile＇s normal acceleration （not jerk） as the control command directly. Firstly, the impact time control problem is formulated as tracking the designated time-to-go （the difference between the designated impact time and the current flight time） for the actual time-to-go of missile, and the impact angle control problem is formulated as tracking the designated heading angle for the actual heading angle of missile. Secondly, a biased proportional navigation guidance （BPNG） law with designated heading angle constraint is constructed, and the actual time-to-go estimation for this BPNG is derived analytically by solving the system differential equations. Thirdly, by adding a feedback control to this constructed BPNG to eliminate the time-to-go errorthe difference between the standard time-to-go and the actual time-to-go, a guidance law with adjustable coefficients to control the impact time and impact angle simultaneously is developed. Finally, simulation results demonstrate the performance and feasibility of the proposed approach.

Ground-based low altitude hovering technique of Hayabusa2

The asteroid explorer Hayabusa2 carries multiple rovers and separates them to land on an asteroid surface.One of these rovers,called MASCOT,was developed under the international cooperation between the Deutsches Zentrum f¨ur Luft-und Raumfahrt and the Centre National d’Etudes Spatiales.This rover was designed to be separated to land and perform several missions on an asteroid surface.To support these missions,the mother ship Hayabusa2 must separate this rover at a low altitude of approximately 50 m and hover at approximately 3 km after separation to achieve are liable communication link with MASCOT.Because the on-board guidance,navigation,and control(GNC)does not have an autonomous hovering function,this hovering operation is performed by ground-based control.This paper introduces the GNC operation scheme for this hovering operation and reports on its flight results.