This paper proposes an optimal maneuver strategy to improve the observability of angles-only rendezvous from the perspective of relative navigation.A set of dimensionless relative orbital elements(ROEs)is used to para...This paper proposes an optimal maneuver strategy to improve the observability of angles-only rendezvous from the perspective of relative navigation.A set of dimensionless relative orbital elements(ROEs)is used to parameterize the relative motion,and the objective function of the observability of anglesonly navigation is established.An analytical solution of the optimal maneuver strategy to improve the observability of anglesonly navigation is obtained by means of numerical analysis.A set of dedicated semi-physical simulation system is built to test the performances of the proposed optimal maneuver strategy.Finally,the effectiveness of the method proposed in this paper is verified through the comparative analysis of the objective function of the observability of angles-only navigation and the performances of the angles-only navigation filter under different maneuver schemes.Compared with the cases without orbital maneuver,it is concluded that the tangential filtering accuracy with the optimal orbital maneuver at the terminal time is increased by 35%on average,and the radial and normal filtering accuracy is increased by 30%on average.展开更多
Multiple unmanned aerial vehicles(UAVs)cooperative operation is the main form for UAVs fighting in battlefield,and multi-UAV mission rendezvous is the premise of cooperative reconnaissance and attack missions.We propo...Multiple unmanned aerial vehicles(UAVs)cooperative operation is the main form for UAVs fighting in battlefield,and multi-UAV mission rendezvous is the premise of cooperative reconnaissance and attack missions.We propose a rendezvous control strategy,which divides the rendezvous process into two parts:The loose formation rendezvous and the close formation rendezvous.In the first stage,UAVs are supposed to reach the specific target locations simultaneously and form a loose formation.A distributed control strategy based on first-order consensus algorithm is presented to achieve this goal.Then the second stage is designed based on the second-order consensus algorithm to complete the transition from the loose formation to the close formation.This process needs the speeds and heading angles of UAVs to reach an agreement.Besides,control algorithms with a virtual leader are proposed,by which the formation states can reach a specific value.Finally,simulation results show that the control algorithms are capable of realizing the mission rendezvous of multi-UAV and the consistence of UAVs′final states,which verify the effectiveness and feasibility of the designed control strategy.展开更多
A strategy for spacecraft autonomous rendezvous on an elliptical orbit in situation of no orbit information is developed. Lawden equation is used to describe relative motion of two spacecraft. Then an adaptive gain fa...A strategy for spacecraft autonomous rendezvous on an elliptical orbit in situation of no orbit information is developed. Lawden equation is used to describe relative motion of two spacecraft. Then an adaptive gain factor is introduced, and an adaptive control law for auton- omous rendezvous on the elliptical orbit is designed using Lyapunov approach. The relative motion is proved to be ultimately bounded under this control law, and the final relative position error can achieve the expected magnitude. Simulation results indicate that the adaptive control law can realize autonomous rendezvous on the elliptical orbit with relative state information only.展开更多
The rendezvous procedure combines an endoscopic technique with percutaneous transhepatic biliary drainage(PTBD).When a selective common bile duct cannulation fails,PTBD allows successful drainage and retrograde access...The rendezvous procedure combines an endoscopic technique with percutaneous transhepatic biliary drainage(PTBD).When a selective common bile duct cannulation fails,PTBD allows successful drainage and retrograde access for subsequent rendezvous techniques.Traditionally,rendezvous procedures such as the PTBDassisted over-the-wire cannulation method,or the parallel cannulation technique,may be available when a bile duct cannot be selectively cannulated.When selective intrahepatic bile duct(IHD) cannulation fails,this modified rendezvous technique may be a feasible alternative.We report the case of a modified rendezvous technique,in which the guidewire was retrogradely passed into the IHD through the C2 catheter after end-to-end contact between the tips of the sphincterotome and the C2 catheter at the ampulla's orifice,in a 39-year-old man who had been diagnosed with gallbladder carcinoma with a metastatic right IHD obstruction.Clinically this procedure may be a feasible and timesaving technique.展开更多
This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs.A barrier Lyapunov function is used to ensure the constraints ...This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs.A barrier Lyapunov function is used to ensure the constraints of states,so that the computational singularity of the inverse matrix in control command can be avoided,while a linear auxiliary system is introduced to handle with the adverse effect of actuator saturation.The tuning rules for designing parameters in control command and auxiliary system are derived based on the stability analysis of the closed-loop system.It is proved that all closed-loop signals always keep bounded,the prescribed constraints of relative pose tracking errors are never violated,and the pose tracking errors ultimately converge to small neighborhoods of zero.Simulation experiments validate the performance of the proposed robust saturated control strategy.展开更多
BACKGROUND In patients with large stones in the common bile duct(CBD),advanced treatment modalities are generally needed.Here,we present an interesting case of a huge CBD stone treated with electrohydraulic lithotrips...BACKGROUND In patients with large stones in the common bile duct(CBD),advanced treatment modalities are generally needed.Here,we present an interesting case of a huge CBD stone treated with electrohydraulic lithotripsy(EHL)by the percutaneous approach and rendezvous endoscopic retrograde cholangiography(ERC)using a nasal endoscope.CASE SUMMARY A 91-year-old woman underwent ERC for a symptomatic large CBD stone with a diameter of 50 mm.She was referred to our institution after the failure of lithotomy by ERC,and after undergoing percutaneous transhepatic biliary drainage.We attempted to fragment the stone by transhepatic cholangioscopy using EHL.However,the stones were too large and partly soft clay-like for lithotripsy.Next,we attempted lithotomy with ERC and cholangioscopy by the rendezvous technique using a nasal endoscope and achieved complete lithotomy.No complication was observed at the end of this procedure.CONCLUSION Cholangioscopy by rendezvous technique using a nasal endoscope is a feasible and safe endoscopic method for removing huge CBD stones.展开更多
A closed-form solution to the angles-only initial relative orbit determination(IROD)problem for space rendezvous with non-cooperated target is developed,where a method of hybrid dynamics with the concept of virtual fo...A closed-form solution to the angles-only initial relative orbit determination(IROD)problem for space rendezvous with non-cooperated target is developed,where a method of hybrid dynamics with the concept of virtual formation is introduced to analytically solve the problem.Emphasis is placed on developing the solution based on hybrid dynamics(i.e.,Clohessy-Wiltshire equations and two-body dynamics),obtaining formation geometries that produce relative orbit state observability,and deriving the approximate analytic error covariance for the IROD solution.A standard Monte Carlo simulation system based on two-body dynamics is used to verify the feasibility and evaluate the performance proposed algorithms.The sensitivity of the solution accuracy to the formation geometry,observation numbers is presented and discussed.展开更多
Despite the ongoing decrease in the frequency of complications after hepatectomy, biliary fistulas still occur and are associated with high morbidity and mortality rates. Here, we report on an unusual technique for ma...Despite the ongoing decrease in the frequency of complications after hepatectomy, biliary fistulas still occur and are associated with high morbidity and mortality rates. Here, we report on an unusual technique for managing biliary fistula following left hepatectomy in a patient in whom the right posterior segmental duct joined the left hepatic duct. The biliary fistula was treated with a combined radiologic and endoscopic procedure based on the "rendezvous technique". The clinical outcome was good, and reoperation was not required.展开更多
High-specific-impulse electric propulsion technology is promising for future space robotic debris removal in sun-synchronous orbits.Such a prospect involves solving a class of challenging problems of low-thrust orbita...High-specific-impulse electric propulsion technology is promising for future space robotic debris removal in sun-synchronous orbits.Such a prospect involves solving a class of challenging problems of low-thrust orbital rendezvous between an active spacecraft and a free-flying debris.This study focuses on computing optimal low-thrust minimum-time many-revolution trajectories,considering the effects of the Earth oblateness perturbations and null thrust in Earth shadow.Firstly,a set of mean-element orbital dynamic equations of a chaser(spacecraft)and a target(debris)are derived by using the orbital averaging technique,and specifically a slow-changing state of the mean longitude difference is proposed to accommodate to the rendezvous problem.Subsequently,the corresponding optimal control problem is formulated based on the mean elements and their associated costate variables in terms of Pontryagin’s maximum principle,and a practical optimization procedure is adopted to find the specific initial costate variables,wherein the necessary conditions of the optimal solutions are all satisfied.Afterwards,the optimal control profile obtained in mean elements is then mapped into the counterpart that is employed by the osculating orbital dynamics.A simple correction strategy about the initialization of the mean elements,specifically the differential mean true longitude,is suggested,which is capable of minimizing the terminal orbital rendezvous errors for propagating orbital dynamics expressed by both mean and osculating elements.Finally,numerical examples are presented,and specifically,the terminal orbital rendezvous accuracy is verified by solving hundreds of rendezvous problems,demonstrating the effectiveness of the optimization method proposed in this article.展开更多
The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In additio...The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pressure force. In general, the cone angle can change from 0° to 90°. However, in practical applications, a large cone angle may reduce the efficiency of solar radiation pressure force and there is a strict requirement on the attitude control. Usually, the cone angle range is restricted less more than an acute angle (for example, not more than 40°) in engineering practice. In this paper, the time-optimal transfer trajectory is designed over a restricted range of the cone angle, and an indirect method is used to solve the two point boundary value problem associated to the optimal control problem. Relevant numerical examples are provided to compare with the case of an unrestricted case, and the effects of different maximum restricted cone angles are discussed. The results indicate that (1) for the condition of a restricted cone-angle range the transfer time is longer than that for the unrestricted case and (2) the optimal transfer time increases as the maximum restricted cone angle decreases.展开更多
Aimed at the problem of final translation of space rendezvous for the applications such as docking,inspection and tracking,optimal straight-line guidance algorithm based on pulse/continuous low-thrust in the context o...Aimed at the problem of final translation of space rendezvous for the applications such as docking,inspection and tracking,optimal straight-line guidance algorithm based on pulse/continuous low-thrust in the context of Clohessy-Wiltshire dynamics is proposed.Two modes of guidance strategy:varying-speed and fixed-speed approaching scheme for V-bar and R-bar approach by using constant/finite low-thrust propulsion respectively are studied,and the corresponding fuel-optimal conditions are obtained.Numerical simulation is conducted to verify and test the proposed algorithms.The results show that there is generally no different between the fuel consumptions by using the two different approaching modes for V-bar case.However,the conclusion for Rbar case is different that the using of continuous low-thrust cost more fuel and transfer time.展开更多
As the number of space objects(SO)increases,collision avoidance problem in the rendezvous tasks or reconstellation of satellites with SO has been paid more attention,and the dangerous area of a possible collision shou...As the number of space objects(SO)increases,collision avoidance problem in the rendezvous tasks or reconstellation of satellites with SO has been paid more attention,and the dangerous area of a possible collision should be derived.In this paper,a maneuvering method is proposed for avoiding collision with a space debris object in the phasing orbit of the initial optimal solution.Accordingly,based on the plane of eccentricity vector components,relevant dangerous area which is bounded by two parallel lines is formulated.The axises of eccentricity vector system pass through the end of eccentricity vector of phasing orbit in the optimal solution,and orientation of axis depends on the latitude argument where a collision will occur.The dangerous area is represented especially with the graphical dialogue,and it allows to find a compromise between the SO avoiding and the fuel consumption reduction.The proposed method to solve the collision avoidance problem provides simplicity to calculate rendezvous maneuvers,and possibility to avoid collisions from several collisions or from“slow”collisions in a phasing orbit,when the protected spacecraft and the object fly dangerously close to each other for a long period.展开更多
Energy conservation is becoming the main critical issue in wireless sensor network and also the main research area for most of the researchers. For improving the energy efficiency, sink mobility is used with constrain...Energy conservation is becoming the main critical issue in wireless sensor network and also the main research area for most of the researchers. For improving the energy efficiency, sink mobility is used with constrain path in wireless sensor network. In order to solve these optimization problems, inter cluster Ant Colony Optimization Algorithm (ACO) is used with mobile sink (MS) and rendezvous nodes (RN). The proposed algorithm will improve 30% more network lifetime than the existing algorithm and prompts high accurate delivery of packets in highly dense network.展开更多
At 1:36 am on November 3,China's Shenzhou 8 unmanned spaceship and Tiangong 1 space lab spacecraft accomplished the country's first space docking procedure and coupling in space at more than 343km above Earth&...At 1:36 am on November 3,China's Shenzhou 8 unmanned spaceship and Tiangong 1 space lab spacecraft accomplished the country's first space docking procedure and coupling in space at more than 343km above Earth's surface,marking a great leap in China's space program.展开更多
When the clock struck midnight on February 23 this year, my flight left from Cairo to Beijing and I was about to start a lO-month program organized by China Public Diplomacy Association.
This paper proposes a fast calculation method to solve all mission opportunities for orbital interception and orbital rendezvous under the impulse-magnitude constraint.Different from the existing search methods,the pr...This paper proposes a fast calculation method to solve all mission opportunities for orbital interception and orbital rendezvous under the impulse-magnitude constraint.Different from the existing search methods,the proposed method does not need to solve Lambert's problem in the whole process.Three cases are considered for either departure time or transfer time being free,or both being free.For fixed departure time,the feasible windows of transfer time are obtained by solving a single-variable nonlinear equation only of terminal true anomaly.Similarly,for fixed interception(or rendezvous)time,the feasible windows of departure time are obtained.For free departure time and free transfer time,all mission opportunities are obtained by using a onedimensional search strategy.The hyperbolic-transfer and the multiple-revolution cases are also analyzed.Numerical results show that the proposed method is superior to the typical pork-chop plot method and the two-dimensional launch window method in computational time.展开更多
Relative navigation is crucial for spacecraft noncooperative rendezvous,and angles-only navigation using visible and infrared cameras provides a feasible solution.Herein,an angles-only navigation algorithm with multis...Relative navigation is crucial for spacecraft noncooperative rendezvous,and angles-only navigation using visible and infrared cameras provides a feasible solution.Herein,an angles-only navigation algorithm with multisensor data fusion is proposed to derive the relative motion states between two noncooperative spacecraft.First,the design model of the proposed algorithm is introduced,including the derivation of the state propagation and measurement equations.Subsequently,models for the sensor and actuator are introduced,and the effects of various factors on the sensors and actuators are considered.The square-root unscented Kalman filter is used to design the angles-only navigation filtering scherne.Additionally,the Clohessy-Wiltshire terminal guidance algorithm is introducedto obtain the theoretical relative motion trajectories during the rendezvous operations of two noncooperative spacecraft.Finally,the effectiveness of the proposed angles-only navigation algorithm is verified using a semi-physical simulation platform.The results prove that an optical navigation camera combined with average accelerometers and occasional orbital maneuvers is feasible for spacecraft noncooperative rendezvous using angles-only navigation.展开更多
基金supported by the China Aerospace Science and Technology Corporation 8th Research Institute Industry-University-Research Cooperation Fund(SAST 2020-019)。
文摘This paper proposes an optimal maneuver strategy to improve the observability of angles-only rendezvous from the perspective of relative navigation.A set of dimensionless relative orbital elements(ROEs)is used to parameterize the relative motion,and the objective function of the observability of anglesonly navigation is established.An analytical solution of the optimal maneuver strategy to improve the observability of anglesonly navigation is obtained by means of numerical analysis.A set of dedicated semi-physical simulation system is built to test the performances of the proposed optimal maneuver strategy.Finally,the effectiveness of the method proposed in this paper is verified through the comparative analysis of the objective function of the observability of angles-only navigation and the performances of the angles-only navigation filter under different maneuver schemes.Compared with the cases without orbital maneuver,it is concluded that the tangential filtering accuracy with the optimal orbital maneuver at the terminal time is increased by 35%on average,and the radial and normal filtering accuracy is increased by 30%on average.
基金jointly granted by the Science and Technology on Avionics Integration Laboratorythe Aeronautical Science Foundation(2016ZC15008)
文摘Multiple unmanned aerial vehicles(UAVs)cooperative operation is the main form for UAVs fighting in battlefield,and multi-UAV mission rendezvous is the premise of cooperative reconnaissance and attack missions.We propose a rendezvous control strategy,which divides the rendezvous process into two parts:The loose formation rendezvous and the close formation rendezvous.In the first stage,UAVs are supposed to reach the specific target locations simultaneously and form a loose formation.A distributed control strategy based on first-order consensus algorithm is presented to achieve this goal.Then the second stage is designed based on the second-order consensus algorithm to complete the transition from the loose formation to the close formation.This process needs the speeds and heading angles of UAVs to reach an agreement.Besides,control algorithms with a virtual leader are proposed,by which the formation states can reach a specific value.Finally,simulation results show that the control algorithms are capable of realizing the mission rendezvous of multi-UAV and the consistence of UAVs′final states,which verify the effectiveness and feasibility of the designed control strategy.
基金supported by the National Natural Science Foundation of China (10702003)
文摘A strategy for spacecraft autonomous rendezvous on an elliptical orbit in situation of no orbit information is developed. Lawden equation is used to describe relative motion of two spacecraft. Then an adaptive gain factor is introduced, and an adaptive control law for auton- omous rendezvous on the elliptical orbit is designed using Lyapunov approach. The relative motion is proved to be ultimately bounded under this control law, and the final relative position error can achieve the expected magnitude. Simulation results indicate that the adaptive control law can realize autonomous rendezvous on the elliptical orbit with relative state information only.
文摘The rendezvous procedure combines an endoscopic technique with percutaneous transhepatic biliary drainage(PTBD).When a selective common bile duct cannulation fails,PTBD allows successful drainage and retrograde access for subsequent rendezvous techniques.Traditionally,rendezvous procedures such as the PTBDassisted over-the-wire cannulation method,or the parallel cannulation technique,may be available when a bile duct cannot be selectively cannulated.When selective intrahepatic bile duct(IHD) cannulation fails,this modified rendezvous technique may be a feasible alternative.We report the case of a modified rendezvous technique,in which the guidewire was retrogradely passed into the IHD through the C2 catheter after end-to-end contact between the tips of the sphincterotome and the C2 catheter at the ampulla's orifice,in a 39-year-old man who had been diagnosed with gallbladder carcinoma with a metastatic right IHD obstruction.Clinically this procedure may be a feasible and timesaving technique.
基金supported in part by the National Natural Science Foundation of China(61903025)the Fundamenta Research Funds for the Central Universities(FRF-GF-18-028B)the China Scholarship Council(201906465028)
文摘This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs.A barrier Lyapunov function is used to ensure the constraints of states,so that the computational singularity of the inverse matrix in control command can be avoided,while a linear auxiliary system is introduced to handle with the adverse effect of actuator saturation.The tuning rules for designing parameters in control command and auxiliary system are derived based on the stability analysis of the closed-loop system.It is proved that all closed-loop signals always keep bounded,the prescribed constraints of relative pose tracking errors are never violated,and the pose tracking errors ultimately converge to small neighborhoods of zero.Simulation experiments validate the performance of the proposed robust saturated control strategy.
文摘BACKGROUND In patients with large stones in the common bile duct(CBD),advanced treatment modalities are generally needed.Here,we present an interesting case of a huge CBD stone treated with electrohydraulic lithotripsy(EHL)by the percutaneous approach and rendezvous endoscopic retrograde cholangiography(ERC)using a nasal endoscope.CASE SUMMARY A 91-year-old woman underwent ERC for a symptomatic large CBD stone with a diameter of 50 mm.She was referred to our institution after the failure of lithotomy by ERC,and after undergoing percutaneous transhepatic biliary drainage.We attempted to fragment the stone by transhepatic cholangioscopy using EHL.However,the stones were too large and partly soft clay-like for lithotripsy.Next,we attempted lithotomy with ERC and cholangioscopy by the rendezvous technique using a nasal endoscope and achieved complete lithotomy.No complication was observed at the end of this procedure.CONCLUSION Cholangioscopy by rendezvous technique using a nasal endoscope is a feasible and safe endoscopic method for removing huge CBD stones.
基金the Natural Science Foundation of China(11802119)the National Postdoctoral Program for Innovative Talents(BX201700304)Fundamental Research Funds for Central Universities(NT2019023).
文摘A closed-form solution to the angles-only initial relative orbit determination(IROD)problem for space rendezvous with non-cooperated target is developed,where a method of hybrid dynamics with the concept of virtual formation is introduced to analytically solve the problem.Emphasis is placed on developing the solution based on hybrid dynamics(i.e.,Clohessy-Wiltshire equations and two-body dynamics),obtaining formation geometries that produce relative orbit state observability,and deriving the approximate analytic error covariance for the IROD solution.A standard Monte Carlo simulation system based on two-body dynamics is used to verify the feasibility and evaluate the performance proposed algorithms.The sensitivity of the solution accuracy to the formation geometry,observation numbers is presented and discussed.
文摘Despite the ongoing decrease in the frequency of complications after hepatectomy, biliary fistulas still occur and are associated with high morbidity and mortality rates. Here, we report on an unusual technique for managing biliary fistula following left hepatectomy in a patient in whom the right posterior segmental duct joined the left hepatic duct. The biliary fistula was treated with a combined radiologic and endoscopic procedure based on the "rendezvous technique". The clinical outcome was good, and reoperation was not required.
基金supported by the National Key Research and Development Project(Grant No.2018YFB1900605)the Key Research Program of Chinese Academy of Sciences(Grant No.ZDRW-KT-2019-1).
文摘High-specific-impulse electric propulsion technology is promising for future space robotic debris removal in sun-synchronous orbits.Such a prospect involves solving a class of challenging problems of low-thrust orbital rendezvous between an active spacecraft and a free-flying debris.This study focuses on computing optimal low-thrust minimum-time many-revolution trajectories,considering the effects of the Earth oblateness perturbations and null thrust in Earth shadow.Firstly,a set of mean-element orbital dynamic equations of a chaser(spacecraft)and a target(debris)are derived by using the orbital averaging technique,and specifically a slow-changing state of the mean longitude difference is proposed to accommodate to the rendezvous problem.Subsequently,the corresponding optimal control problem is formulated based on the mean elements and their associated costate variables in terms of Pontryagin’s maximum principle,and a practical optimization procedure is adopted to find the specific initial costate variables,wherein the necessary conditions of the optimal solutions are all satisfied.Afterwards,the optimal control profile obtained in mean elements is then mapped into the counterpart that is employed by the osculating orbital dynamics.A simple correction strategy about the initialization of the mean elements,specifically the differential mean true longitude,is suggested,which is capable of minimizing the terminal orbital rendezvous errors for propagating orbital dynamics expressed by both mean and osculating elements.Finally,numerical examples are presented,and specifically,the terminal orbital rendezvous accuracy is verified by solving hundreds of rendezvous problems,demonstrating the effectiveness of the optimization method proposed in this article.
基金supported by the National Natural Science Foundation of China(11272004 and 11302112)China’s Civil Space Funding
文摘The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pressure force. In general, the cone angle can change from 0° to 90°. However, in practical applications, a large cone angle may reduce the efficiency of solar radiation pressure force and there is a strict requirement on the attitude control. Usually, the cone angle range is restricted less more than an acute angle (for example, not more than 40°) in engineering practice. In this paper, the time-optimal transfer trajectory is designed over a restricted range of the cone angle, and an indirect method is used to solve the two point boundary value problem associated to the optimal control problem. Relevant numerical examples are provided to compare with the case of an unrestricted case, and the effects of different maximum restricted cone angles are discussed. The results indicate that (1) for the condition of a restricted cone-angle range the transfer time is longer than that for the unrestricted case and (2) the optimal transfer time increases as the maximum restricted cone angle decreases.
基金State Key Laboratory of Satellite Navigation System and Equipment Technology(CEPNT-2017KF-02)the Natural Science Foundation of China(11802119)Fundamental Research Funds for Central Universities(NT2019023)。
文摘Aimed at the problem of final translation of space rendezvous for the applications such as docking,inspection and tracking,optimal straight-line guidance algorithm based on pulse/continuous low-thrust in the context of Clohessy-Wiltshire dynamics is proposed.Two modes of guidance strategy:varying-speed and fixed-speed approaching scheme for V-bar and R-bar approach by using constant/finite low-thrust propulsion respectively are studied,and the corresponding fuel-optimal conditions are obtained.Numerical simulation is conducted to verify and test the proposed algorithms.The results show that there is generally no different between the fuel consumptions by using the two different approaching modes for V-bar case.However,the conclusion for Rbar case is different that the using of continuous low-thrust cost more fuel and transfer time.
基金This work is supported and funded by NSFC(Natural Science Foundation of China)[No.51905272].
文摘As the number of space objects(SO)increases,collision avoidance problem in the rendezvous tasks or reconstellation of satellites with SO has been paid more attention,and the dangerous area of a possible collision should be derived.In this paper,a maneuvering method is proposed for avoiding collision with a space debris object in the phasing orbit of the initial optimal solution.Accordingly,based on the plane of eccentricity vector components,relevant dangerous area which is bounded by two parallel lines is formulated.The axises of eccentricity vector system pass through the end of eccentricity vector of phasing orbit in the optimal solution,and orientation of axis depends on the latitude argument where a collision will occur.The dangerous area is represented especially with the graphical dialogue,and it allows to find a compromise between the SO avoiding and the fuel consumption reduction.The proposed method to solve the collision avoidance problem provides simplicity to calculate rendezvous maneuvers,and possibility to avoid collisions from several collisions or from“slow”collisions in a phasing orbit,when the protected spacecraft and the object fly dangerously close to each other for a long period.
文摘Energy conservation is becoming the main critical issue in wireless sensor network and also the main research area for most of the researchers. For improving the energy efficiency, sink mobility is used with constrain path in wireless sensor network. In order to solve these optimization problems, inter cluster Ant Colony Optimization Algorithm (ACO) is used with mobile sink (MS) and rendezvous nodes (RN). The proposed algorithm will improve 30% more network lifetime than the existing algorithm and prompts high accurate delivery of packets in highly dense network.
文摘At 1:36 am on November 3,China's Shenzhou 8 unmanned spaceship and Tiangong 1 space lab spacecraft accomplished the country's first space docking procedure and coupling in space at more than 343km above Earth's surface,marking a great leap in China's space program.
文摘When the clock struck midnight on February 23 this year, my flight left from Cairo to Beijing and I was about to start a lO-month program organized by China Public Diplomacy Association.
基金supported in part by the National Natural Scientific Foundation of China(No.11772104)the Key Research and Development Plan of Heilongjiang Province,China(No.GZ20210120)the Fundamental Research Funds for the Central Universities,China.
文摘This paper proposes a fast calculation method to solve all mission opportunities for orbital interception and orbital rendezvous under the impulse-magnitude constraint.Different from the existing search methods,the proposed method does not need to solve Lambert's problem in the whole process.Three cases are considered for either departure time or transfer time being free,or both being free.For fixed departure time,the feasible windows of transfer time are obtained by solving a single-variable nonlinear equation only of terminal true anomaly.Similarly,for fixed interception(or rendezvous)time,the feasible windows of departure time are obtained.For free departure time and free transfer time,all mission opportunities are obtained by using a onedimensional search strategy.The hyperbolic-transfer and the multiple-revolution cases are also analyzed.Numerical results show that the proposed method is superior to the typical pork-chop plot method and the two-dimensional launch window method in computational time.
基金supported by the China Aerospace Science and Technology Corporation Eighth Research Institute Industry-University-Research Cooperation Fund(SAST 2020-019).
文摘Relative navigation is crucial for spacecraft noncooperative rendezvous,and angles-only navigation using visible and infrared cameras provides a feasible solution.Herein,an angles-only navigation algorithm with multisensor data fusion is proposed to derive the relative motion states between two noncooperative spacecraft.First,the design model of the proposed algorithm is introduced,including the derivation of the state propagation and measurement equations.Subsequently,models for the sensor and actuator are introduced,and the effects of various factors on the sensors and actuators are considered.The square-root unscented Kalman filter is used to design the angles-only navigation filtering scherne.Additionally,the Clohessy-Wiltshire terminal guidance algorithm is introducedto obtain the theoretical relative motion trajectories during the rendezvous operations of two noncooperative spacecraft.Finally,the effectiveness of the proposed angles-only navigation algorithm is verified using a semi-physical simulation platform.The results prove that an optical navigation camera combined with average accelerometers and occasional orbital maneuvers is feasible for spacecraft noncooperative rendezvous using angles-only navigation.