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.

Inter-satellite Link Topology Design and Relative Navigation for Satellite Clusters

A distributed relative navigation approach via inter-satellite sensing and communication for satellite clusters is proposed. The inter-satellite link(ISL)is used for ranging and exchanging data for the relative navigation,which can improve the autonomy of the satellite cluster. The ISL topology design problem is formulated as a multi-objective optimization problem where the energy consumption and the navigation performance are considered. Further,the relative navigation is performed in a distributed fashion,where each satellite in the cluster makes observations and communicates with its neighbors via the ISL locally such that the transmission consumption and the computational complexity for the navigation are reduced. The ISL topology optimization problem is solved via the NSGA-Ⅱ algorithm,and the consensus Kalman filter is used for the distributed relative navigation. The proposed approach is flexible to varying tasks,with satellites joining or leaving the cluster anytime,and is robust to the failure of an individual satellite. Numerical simulations are presented to verify the feasibility of the proposed approach.

Parametric message passing-based relative navigation in joint tactical information distribution system

Relative navigation is a key feature in the joint tactical information distribution system（JTIDS）.A parametric message passing algorithm based on factor graph is proposed to perform relative navigation in JTIDS.First of all,the joint posterior distribution of all the terminals＇ positions is represented by factor graph.Because of the nonlinearity between the positions and time-of-arrival（TOA） measurement,messages cannot be obtained in closed forms by directly using the sum-product algorithm on factor graph.To this end,the Euclidean norm is approximated by Taylor expansion.Then,all the messages on the factor graph can be derived in Gaussian forms,which enables the terminals to transmit means and covariances.Finally,the impact of major error sources on the navigation performance are evaluated by Monte Carlo simulations,e.g.,range measurement noise,priors of position uncertainty and velocity noise.Results show that the proposed algorithm outperforms the extended Kalman filter and cooperative extended Kalman filter in both static and mobile scenarios of the JTIDS.

Relative Navigation of Long-Range Non-Cooperative Targets Based on Monocular Sequence Images

Along with the increase of the number of failed satellites,plus space debris,year by year,it will take considerable manpower and resources if we rely just on ground surveillance and early warning.An alternative effective way would be to use autonomous long-range non-cooperative target relative navigation to solve this problem.For longrange non-cooperative targets,the stereo cameras or lidars that are commonly used would not be applicable.This paper studies a relative navigation method for long-range relative motion estimation of non-cooperative targets using only a monocular camera.Firstly,the paper provides the nonlinear relative orbit dynamics equations and then derives the discrete recursive form of the dynamics equations.An EKF filter is then designed to implement the relative navigation estimation.After that,the relative"locally weakly observability"theory for nonlinear systems is used to analyze the observability of monocular sequence images.The analysis results show that by relying only on monocular sequence images it has the possibility of deducing the relative navigation for long-range non-cooperative targets.Finally,numerical simulations show that the method given in this paper can achieve a complete estimation of the relative motion of longrange non-cooperative targets without conducting orbital maneuvers.

Cooperative Angles-Only Relative Navigation Algorithm for Multi-Spacecraft Formation in Close-Range

As to solve the collaborative relative navigation problem for near-circular orbiting small satellites in close-range under GNSS denied environment,a novel consensus constrained relative navigation algorithm based on the lever arm effect of the sensor offset from the spacecraft center of mass is proposed.Firstly,the orbital propagation model for the relative motion of multi-spacecraft is established based on Hill-Clohessy-Wiltshire dynamics and the line-of-sight measurement under sensor offset condition is modeled in Local Vertical Local Horizontal frame.Secondly,the consensus constraint model for the relative orbit state is constructed by introducing the geometry constraint between the spacecraft,based on which the consensus unscented Kalman filter is designed.Thirdly,the observability analysis is done and the necessary conditions of the sensor offset to make the state observable are obtained.Lastly,digital simulations are conducted to verify the proposed algorithm,where the comparison to the unconstrained case is also done.The results show that the estimated error of the relative position converges very quickly,the location error is smaller than 10m under the condition of 10−3 rad level camera and 5m offset.

Angles-only relative navigation in highly elliptical orbits

For angles-only relative navigation system only measures line-of-sight information,there are inherent problems in the ability to determine the range between Chaser and Target. Angles-only relative navigation is an attractive alternative for inspecting or rendezvous with noncooperative target,if adequate accuracy can be achieved. Angles-only relative navigation model considering J2 perturbation is presented for tracking and rendezvous with noncooperative target in highly elliptical orbit. Impulsive out-of-plane maneuvers of the Chaser are used to improve the navigation accuracy. The first impulse burns in cross-track directions to change the orbit inclination of the Chaser. The second impulse burns after one orbit period to change the orbit of the Chaser back. The simulation results show that the relative navigation system without maneuvers can't correct the initial state errors,while impulsive out-ofplane maneuvers of the Chaser improves the navigation accuracy. Angles-only relative navigation with chaser vehicle maneuvers to improve observability is effective when the spacecrafts are in highly elliptical orbits.

Second-order divided difference filter for vision-based relative navigation

A second-order divided difference filter (SDDF) is derived for integrating line of sight measurement from vision sensor with acceleration and angular rate measurements of the follower to estimate the precise relative position,velocity and attitude of two unmanned aerial vehicles (UAVs).The second-order divided difference filter which makes use of multidimensional interpolation formulations to approximate the nonlinear transformations could achieve more accurate estimation and faster convergence from inaccurate initial conditions than standard extended Kalman filter.The filter formulation is based on relative motion equations.The global attitude parameterization is given by quarternion,while a generalized three-dimensional attitude representation is used to define the local attitude error.Simulation results are shown to compare the performance of the second-order divided difference filter with a standard extended Kalman filter approach.

Relative navigation for satellite formation flight using a continuous-discrete converted measurement Kalman filter

The present paper develops an approach of relative orbit determination for satellite formation flight.Inter-satellite measurements by the onboard devices of the satellite were chosen to perform this relative navigation,and the equations of relative motion expressed in the Earth Centered Inertial frame were used to eliminate the assumption of the circular reference orbit.The relative orbit estimation was achieved through a continuous-discrete converted measurement Kalman filter design,in which the measurements were transformed to the inertial frame to avoid the linearization error of the observation equation.In addition,the situation of the coarse measurement period(only microwave radar measurements are available)existing was analyzed.The numerical simulation results verify the validity of the navigation approach,and it has been proved that this approach can be applied to the formation with an elliptical reference orbit.

Evaluation of global navigation satellite system spoofing efficacy

The spoofing capability of Global Navigation Satellite System(GNSS)represents an important confrontational capability for navigation security,and the success of planned missions may depend on the effective evaluation of spoofing capability.However,current evaluation systems face challenges arising from the irrationality of previous weighting methods,inapplicability of the conventional multi-attribute decision-making method and uncertainty existing in evaluation.To solve these difficulties,considering the validity of the obtained results,an evaluation method based on the game aggregated weight model and a joint approach involving the grey relational analysis and technique for order preference by similarity to an ideal solution(GRA-TOPSIS)are firstly proposed to determine the optimal scheme.Static and dynamic evaluation results under different schemes are then obtained via a fuzzy comprehensive assessment and an improved dynamic game method,to prioritize the deceptive efficacy of the equipment accurately and make pointed improvement for its core performance.The use of judging indicators,including Spearman rank correlation coefficient and so on,combined with obtained evaluation results,demonstrates the superiority of the proposed method and the optimal scheme by the horizontal comparison of different methods and vertical comparison of evaluation results.Finally,the results of field measurements and simulation tests show that the proposed method can better overcome the difficulties of existing methods and realize the effective evaluation.

Rolling velocity and relative motion of particle detector in local granular flow

The velocity of a particle detector in granular flow can be regarded as the combination of rolling and sliding velocities.The study of the contribution of rolling velocity and sliding velocity provides a new explanation to the relative motion between the detector and the local granular flow.In this study,a spherical detector using embedded inertial navigation technology is placed in the chute granular flow to study the movement of the detector relative to the granular flow.It is shown by particle image velocimetry(PIV)that the velocity of chute granular flow conforms to Silbert’s formula.And the velocity of the detector is greater than that of the granular flow around it.By decomposing the velocity into sliding and rolling velocity,it is indicated that the movement of the detector relative to the granular flow is mainly caused by rolling.The rolling detail shown by DEM simulation leads to two potential mechanisms based on the position and drive of the detector.

Reference satellite selection method for GNSS high-precision relative positioning

Selecting the optimal reference satellite is an important component of high-precision relat/ve positioning because the reference satellite directly influences the strength of the normal equation. The reference satellite selection methods based on elevation and positional dilution of precision （PDOP） value were compared. Results show that all the above methods cannot select the optimal reference satellite. We introduce condition number of the design matrix in the reference satellite selection method to improve structure of the normal equation, because condition number can indicate the ill condition of the normal equation. The experimental results show that the new method can improve positioning accuracy and reliability in precise relative positioning.

A study on dual quaternion based cooperative relative navigation of multiple UAVs with monocular vision-inertial integration

This paper addresses a cooperative relative navigation problem for multiple aerial agents,relying on visual tracking information between vehicles.The research aims to investigate a sensor fusion architecture and algorithm that leverages partially available absolute navigation knowledge while exploiting collaborative visual interaction between vehicles in mission flight areas,where satellite navigation-denied regions are irregularly located.To achieve this,the paper introduces a new approach to defining the relative poses of cameras and develops a corresponding process to secure the relative pose information.This contrasts with previous research,which simply linearized the relative pose information of aircraft cameras into navigation states defined in an absolute coordinate system.Specifically,the target pose in relative navigation is defined,and the pose of the camera and feature points are directly derived using dual quaternion representation,which compactly represents both translation and rotation.Furthermore,a mathematical model for the relative pose of the camera is derived through the dual quaternion framework,enabling an explicit pose formulation of relative navigation.The study investigates navigation performance in typical mission flight scenarios using an in-house high-fidelity simulator and quantitatively highlights the contributions of the proposed scheme by comparing the navigation error performance.Consequently,the proposed method demonstrates to have navigation accuracy in decimeter level even in GNSS-denied environments and an improved 3D Root Mean Square(RMS)error by30%smaller than the conventional absolute navigation framework.

Research on the strategy of angles-only relative navigation for autonomous rendezvous

This paper considers the problem of angles-only relative navigation for autonomous rendezvous. Methods for determining degree of observability （DO0） and latent range information of orbital maneuver are proposed for analyzing and enhancing the precision of relative position and velocity estimation. The equations of angles-only relative navigation are set forth on the con- dition that optical camera is the only viable sensor for relative measurement, and expressions for the DO0 of relative navigation are obtained by using the Newton iterative method. The latent range information of orbital maneuver is analyzed, which is employed to enhance the DOO of angles-only relative navigation. Simulation result shows that DOO is effective to describe the observability level of relative position and velocity, and the latent range information is useful in enhancing the DOO of the angles-only relative navigation.

Review of space relative navigation based on angles-only measurements

Relative navigation is a key enabling technology for space missions such as on-orbit servicing and space situational awareness.Given that there are several special advantages of space relative navigation using angles-only measurements from passive optical sensors,angles-only relative navigation is considered as one of the best potential approaches in the field of space relative navigation.However,angles-only relative navigation is well-known for its range observability problem.To overcome this observability problem,many studies have been conducted over the past decades.In this study,we present a comprehensive review of state-of-the-art space relative navigation based on angles-only measurements.The emphasis is on the observability problem and solutions to angles-only relative navigation,where the review of the solutions is categorized into four classes based on the intrinsic principle:complicated dynamics approach,multi-line of sight(multi-LOS)approach,sensor offset center-of-mass approach,and orbit maneuver approach.Then,the fight demonstration results of angles-only relative navigation in the two projects are briefly reviewed.Finally,conclusions of this study and recommendations for further research are presented.

Highly reliable relative navigation for multi-UAV formation flight in urban environments

Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely maintain a fairly close distance between UAVs and to achieve inner-system collision avoidance.However,Global Navigation Satellite System(GNSS)measurements are vulnerable to erroneous signals in urban canyons,which could potentially lead to catastrophic consequences.Accordingly,on the basis of performing relative positioning with double differenced pseudoranges,this paper develops an integrity monitoring framework to improve navigation integrity(a measure of reliability)in urban environments.On the one hand,this framework includes a fault detection and exclusion scheme to protect against measurement faults.To accommodate urban scenarios,spatial dependence in the faults are taken into consideration by this scheme.On the other hand,relative protection level is rigorously derived to describe the probabilistic error bound of the navigation output.This indicator can be used to evaluate collision risk and to warn collision danger in real time.The proposed algorithms are validated by both simulations and flight experiments.Simulation results quantitatively reveal the sensitivity of navigation performance to receiver configurations and environmental conditions.And experimental results suggest high efficiency and effectiveness of the new integrity monitoring framework.

Observability Analysis and Navigation Algorithm for Distributed Satellites System Using Relative Range Measurements

The problem of navigation for the distributed satellites system using relative range mea- surements is investigated. Firstly, observability for every participating satellites is analyzed based on the nonlinear Keplerian model containing J2 perturbation and the nonlinear measurements. It is proven that the minimum number of tracking satellites to assure the observability of the distributed satellites system is three. Additionally, the analysis shows that the J2 perturbation and the nonlinearity make little contribution to improve the observability for the navigation. Then, a quasi-consistent extended Kalman filter based navigation algorithm is proposed, which is quasi-consistent and can provide an on- line evaluation of the navigation precision. The simulation illustrates the feasibility and effectiveness of the proposed navigation algorithm for the distributed satellites system.

Global precision analysis of carrier phase relative positioning in BeiDou navigation satellite system and United States global positioning system

In this paper, we derived a high-efficiency formula for calculating the precision of carrier phase relative positioning,analyzed the various factors that affect the positioning accuracy using the carrier phase, and proposed the concept of using a frequency dilution of precision to describe the quantitative effect of different frequency combinations on the positioning precision. To this end, we computed and plotted the global spatial distribution map of the relative positioning dilution of precision for single-day solution, half-hour solution, and single-epoch solution of the global positioning system(GPS), regional Beidou navigation satellite system(BDS2), future global Beidou navigation satellite system(BDS3), and their fusion systems.Using processing software with autonomous intellectual property rights(GCN and VENUS/ARSNet), we solved the measurement data and examined the positioning precision of the single-day solution and single-epoch solution of GPS and BDS2.The analysis demonstrated that the B1/B2 frequency positioning precision of BDS2 was better than that of L1/L2 frequency positioning of GPS, but the positioning precision of the BDS2 is worse than that of GPS over most of the service region of the BDS2. Further, the positioning precision of BDS3 is better than that of GPS in the Asia-Pacific region, while it is the opposite in other regions. Based on these conclusions, we put forth some optimization recommendations regarding the signal frequency of the navigation system and GPS measurement standards to serve as references for optimizing the system performance and formulating standards.

Ranging-aided relative navigation of multi-platforms

This paper proposes a relative attitude and distance estimation algorithm based on pairwise range measurements between vehicles as well as inertial measurement of each platform. The solution of Wahba＇s Problem is introduced to compute the relative attitude between multi-platforms with the sampled pairwise ranges, in which the relative distance estimation is derived and the estimation error distributions are analyzed. An extended Kalman filter is designed to fuse the estimated attitude and distance with the inertial measurement of each platform. The relative poses between platforms are determined without any external aided measurement. To show this novelty, a real testbed is constructed by our research lab. And the experiment results are positive.

混合式惯性导航系统平台转动控制算法设计

混合式惯性导航系统(HINS)通过误差调制可以有效提高惯性导航系统的独立导航精度。传统三框架HINS平台转动控制算法能够控制旋转平台实现相对参考系(地理系或惯性系)稳定,但在此基础上叠加误差调制转动时会出现奇异点,使得旋转平台无法按预定方案旋转。针对出现奇异点的问题,分析了HINS在不同导航模式下旋转平台在转动过程中相应坐标系之间的转换关系,并以控制旋转平台达到指定位置为控制目标,利用四元数进行控制指令解算,设计了一种基于坐标系转换关系的四元数旋转平台转动控制算法。通过相应的仿真及实验进行验证,结果表明:所提算法避免了计算框架指令角位置信息时出现奇异点,使得三框架HINS能够按预定方案旋转。

Accurate Indoor Navigation System Using Human-Item Spatial Relation

Indoor navigation has received much attention by both industry and academia in recent years. To locate users, a number of existing methods use various localization algorithms in combination with an indoor map, which require expensive infrastructures deployed in advance. In this study, we propose the use of existing indoor objects with attached RFID tags and a reader to navigate users to their destinations, without the need for any additional hardware. The key insight upon which our proposal is based is that a person＇s movement has an impact on the frequency shift values collected from indoor objects when they near a tag. We leverage this local human-item spatial relation to infer the user＇s position and then navigate the user to the desired destination step by step. We implement a prototype navigation system, called Roll Caller, and conduct a comprehensive range of experiments to examine its performance.