This study involved simulations and experiments aimed at assessing the efficacy of a tether net in encapsulating space debris.The tether net was modeled as a spring–mass–damper system considering the influence of ae...This study involved simulations and experiments aimed at assessing the efficacy of a tether net in encapsulating space debris.The tether net was modeled as a spring–mass–damper system considering the influence of aerodynamic and gravitational forces and the occurrence of debris collisions.To examine the influence of collision position and size disparity between the debris and the net on debris capture status,the entanglement nodes of the net were identified.Experiments were conducted to evaluate the wrapping capabilities of the tether net,focusing specifically on debris capture.Subsequently,the results were compared with those of the numerical simulation.In the experiments,radio frequency identification was used to identify the entanglement points of the tether net.Previous studies have indicated that the ideal collision point for capturing debris using a tether net with the debris intended to be captured is located at the center of the net.However,the experimental results of this study revealed that a collision position that is slightly shifted from the center of the tether net is more advantageous for capturing debris in terms of tether net entanglement.展开更多
The Tethered Space Net Robot(TSNR)is an innovative solution for active space debris capture and removal.Its large envelope and simple capture method make it an attractive option for this task.However,capturing maneuve...The Tethered Space Net Robot(TSNR)is an innovative solution for active space debris capture and removal.Its large envelope and simple capture method make it an attractive option for this task.However,capturing maneuverable debris with the flexible and elastic underactuated net poses significant challenges.To address this,a novel formation control method for the TSNR is proposed through the integration of differential game theory and robust adaptive control in this paper.Specifically,the trajectory of the TSNR is obtained through the solution of a real-time feedback pursuit-evasion game with a dynamic target,where the primary condition is to ensure the stability of the TSNR.Furthermore,to minimize tracking errors and maintain a specific configuration,a robust adaptive formation control scheme with Artificial Potential Field(APF)based on a Finite-Time Convergent Extended State Observer(FTCESO)is investigated.The proposed control method has a key advantage in suppressing complex oscillations by a new adaptive law,thus precisely maintaining the configuration.Finally,numerical simulations are performed to demonstrate the effectiveness of the proposed scheme.展开更多
The increasing accumulation of space debris threatens the integrity and functionality of satellites and complicates orbital operations.This paper constructs an advanced rigid-flexible coupling dynamic model for tether...The increasing accumulation of space debris threatens the integrity and functionality of satellites and complicates orbital operations.This paper constructs an advanced rigid-flexible coupling dynamic model for tethered satellite systems,tailored to enhance space debris management.Utilizing the nodal position finite element method,the model significantly improves the precision of simulating tether dynamics and captures the complex interactions involving satellite and debris attitude dynamics.This advancement allows for detailed examination of potential tether entanglements and provides crucial data for optimizing deorbiting processes.To overcome the limitations of conventional control techniques,a robust adaptive sliding mode control strategy is developed.This approach is specifically designed to manage the unpredictable conditions of the low-Earth orbit and ensure precise satellite attitude control,critical for successful debris removal.Validated through extensive numerical simulations,our model and control strategy demonstrate substantial improvements in operational reliability and safety,significantly enhancing the success rate of deorbiting missions.展开更多
Dynamic analysis of the tethered satellite system(TSS)can provide a fundamental guideline to the evaluation of performance and robust design of the system examined.Uncertainties inherited with the parameters would ind...Dynamic analysis of the tethered satellite system(TSS)can provide a fundamental guideline to the evaluation of performance and robust design of the system examined.Uncertainties inherited with the parameters would induce unexpected variation of the response and deteriorate the reliability of the system.In this work,the effect of uncertain mass of the satellites on the deployment and retrieval dynamics of the TSS is investigated.First the interval mode is employed to take the variation of mass of satellite into account in the processes of deployment and retrieval.Then,the Chebyshev interval method is used to obtain the lower and upper response bounds of the TSS.To achieve a smooth and reliable implementation of deployment and retrieval,the nonlinear programming based on the Gauss pseudospectral method is adopted to obtain optimal trajectory of tether velocity.Numerical results show that the uncertainties of mass of the satellites have a distinct influence on the response of tether tension in the processes of deployment and retrieval.展开更多
Small molecule inhibitors have dominated the pharmaceutical landscape for a long time as the primary therapeutic paradigm targeting pathogenic proteins.However,their efficacy heavily relies on the amino acid compositi...Small molecule inhibitors have dominated the pharmaceutical landscape for a long time as the primary therapeutic paradigm targeting pathogenic proteins.However,their efficacy heavily relies on the amino acid composition and spatial constitution of proteins,rendering them susceptible to drug resistance and failing to target undruggable proteins.In recent years,the advent of targeted protein degradation(TPD)technology has captured substantial attention from both industry and academia.Employing an event-driven mode,TPD offers a novel approach to eliminate pathogenic proteins by promoting their degrada-tion,thus circumventing the limitations associated with traditional small molecule inhibitors.Hydropho-bic tag tethering degrader(HyTTD)technology represents one such TPD approach that is currently in the burgeoning stage.HyTTDs employ endogenous protein degradation systems to induce the degrada-tion of target proteins through the proteasome pathway,which displays significant potential for medical value.In this review,we provide a comprehensive overview of the development history and the reported mechanism of action of HyTTDs.Additionally,we delve into the physiological roles,structure-activity re-lationships,and medical implications of HyTTDs targeting various disease-associated proteins.Moreover,we propose insights into the challenges that necessitate resolution for the successful development of HyTTDs,with the ultimate goal of initiating a new age of clinical treatment leveraging the immense po-tential of HyTTDs.展开更多
Tethered Space Net Robot(TSNR)is considered to be a promising approach for space debris removal,and accordingly it is also an interesting control problem due to its time-varying disturbances caused by an elastic and f...Tethered Space Net Robot(TSNR)is considered to be a promising approach for space debris removal,and accordingly it is also an interesting control problem due to its time-varying disturbances caused by an elastic and flexible net and a main connected tether.In this situation,the control scheme should be robust enough,low-frequency,and finite-time convergent in presence of external disturbances.In this paper,a robust controller with an advanced adaptive scheme is proposed.To improve robustness,the disturbance is skillfully involved in the adaptive scheme.It is strictly proven that the closed-loop system can converge to the desired trajectory in finite time in both reaching and sliding processes.Based on the theoretical proof,adaptive gains and corresponding dynamic stability characteristics are further discussed.Finally,the efficiency of the proposed control scheme is numerically proven via a TSNR.The proposed control scheme utilizes small and continuous control forces to compensate for the disturbance efficiently and track the desired trajectory quickly.展开更多
For mitigating the libration angle fluctuation of the tethered satellite system,this paper discusses how to make the uniform velocity-deceleration separation scheme achieve the best effect.First,a judgment condition i...For mitigating the libration angle fluctuation of the tethered satellite system,this paper discusses how to make the uniform velocity-deceleration separation scheme achieve the best effect.First,a judgment condition is established to determine the tether state by comparing the tether length and the relative distance of the sub-satellite and the parent satellite.Based on the tethered satellite system dynamics equation and Clohessy-Wiltshire equation,dynamic models are given for four cases of tether states.Second,the influence of the uniform velocity-deceleration separation scheme on the libration angle is analyzed by taking the libration angle at the separation ending time and the mean absolute value of the libration angle as index functions.Then,the optimality problem of the uniform velocity-deceleration separation scheme is formulated as an optimization problem with constraints,and an approximate solution algorithm is given by combining the back propagation neural network and Newton-Raphson method of multiple initial values.Finally,the effectiveness of the proposed method is verified by a numerical simulation.展开更多
Rh/SiO2 catalysts with tethered-phosphines with different alkyl spacer lengths have been prepared,tested and characterized.Lengthening the alkyl spacer of the tethered-phosphine improved the flexibility of tethered-ph...Rh/SiO2 catalysts with tethered-phosphines with different alkyl spacer lengths have been prepared,tested and characterized.Lengthening the alkyl spacer of the tethered-phosphine improved the flexibility of tethered-phospine,promoted the formation of active species and enhanced the activity of hydroformylation over other tethered-phosphine modified Rh/SiO2 catalysts.展开更多
This paper presents a novel design for a Dyson-Harrop CubeSat aimed at harvesting energy from the solar wind. Unlike current photovoltaic-based satellite energy generation, the Dyson-Harrop satellite generates energy ...This paper presents a novel design for a Dyson-Harrop CubeSat aimed at harvesting energy from the solar wind. Unlike current photovoltaic-based satellite energy generation, the Dyson-Harrop satellite generates energy based on the photoelectric effect, which has the potential to achieve significantly higher efficiency than current photovoltaic technology. The proposed CubeSat system consists of three main components: a tether unit, an energy harvesting unit, and the central 3U CubeSat body. The tether unit generates a cylindrical magnetic field along its main tether,effectively concentrating electrons from the solar wind to the energy harvesting unit. The energy harvesting unit includes a spherical electron receiver, functioning as a capacitor, which attracts electrons from the solar wind, as well as an annular flat solar sail that captures photons in the solar wind to eject electrons via the photoelectric effect, resulting in an electric current in the system.The Dyson-Harrop CubeSat is shown to be highly efficient as an energy-generation system, producing approximately 1 kW of power by a 3U CubeSat. This energy can be transmitted via microwave beams to other spacecraft or ground stations on the Earth. It is important to note that this estimation is based on first-principle estimations, and thorough theoretical analysis and experimental validation are required to confirm the feasibility of the concept.展开更多
The concept of tethered satellite system （TSS） promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and...The concept of tethered satellite system （TSS） promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and interesting problems related to their dynamics, control, and physical implementation. Over the past decades, this exciting topic has attracted significant attention from many researchers and gained a vast number of analytical, numerical and experimental achievements with a focus on the two essential aspects of both dynamics and control. This review article presents the historic background and recent hot topics for the space tethers, and introduces the dynamics and control of TSSs in a progressive manner, from basic operating principles to the state-of-the-art achievements.展开更多
Tethered satellite systems（TSSs） have attracted significant attention due to their potential and valuable applications for scientific research. With the development of various launched on-orbit missions, the deploym...Tethered satellite systems（TSSs） have attracted significant attention due to their potential and valuable applications for scientific research. With the development of various launched on-orbit missions, the deployment of tethers is considered a crucial technology for operation of a TSS. Both past orbiting experiments and numerical results have shown that oscillations of the deployed tether due to the Coriolis force and environmental perturbations are inevitable and that the impact between the space tether and end-body at the end of the deployment process leads to complicated nonlinear phenomena. Hence, a set of suitable control methods plays a fundamental role in tether deployment. This review article summarizes previous work on aspects of the dynamics, control, and ground-based experiments of tether deployment. The relevant basic principles, analytical expressions, simulation cases, and experimental results are presented as well.展开更多
For the study of the non-linear response of inclined tethers subjected to parametric excitation in submerged floating tunnels, a theoretical model for coupled tube-tether vibration is developed. Upon the assumption th...For the study of the non-linear response of inclined tethers subjected to parametric excitation in submerged floating tunnels, a theoretical model for coupled tube-tether vibration is developed. Upon the assumption that the static equilibri- um position of the tether is a quadratic parabola, the governing differential equations of the tether motion are derived by use of the Hamihon principle. An approximate numerical solution is obtained by use of Galerkin method and Runge-kutta method. The results show that, when the static equilibrium position of the tether is assumed to be. a quadratic parabola, the tether sag effect on its vibration may be reflected; the tether sag results in the asymmetry of tether vibration amplitude ; for the reduction of the tether amplitude, the buoyant unit weight of the tether should approach to zero as far as possible during the design.展开更多
This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionl...This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionless form. Further, a decoupled PD controller is proposed, and the local stability of the controller is analyzed by linearization technique. Parametric studies of the dynamics and de-spin control of a massive target are conducted to characterize the dynamic process of de-spin with the proposed control law. It is shown that the massive target can be de-span by a single and small space tug with limited thrust within finite time. The thrust tangent with the tether de-spins the target while the thrust normal to the tether prevents the tether from winding up the target. The tether length has a positive contribution to the de-spin of a target. The longer tether leads to a faster de-spin process.展开更多
The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital ...The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.展开更多
A mathematical equation for vibration of submerged floating tunnel tether under the effects of earthquake and parametric excitation is presented. Multi-step Galerkin method is used to simplify this equation and the fo...A mathematical equation for vibration of submerged floating tunnel tether under the effects of earthquake and parametric excitation is presented. Multi-step Galerkin method is used to simplify this equation and the fourth-order Runge-Kuta integration method is used for numerical analysis. Finally, vibration response of submerged floating tunnel tether subjected to earthquake and parametric excitation is analyzed in a few numerical examples. The results show that the vibration response of tether varies with the seismic wave type; the steady maximum mid-span displacement of tether subjected to seismic wave keeps constant when parametric resonance takes place; the transient maximum mid-span displacement of tether is related to the peak value of input seismic wave acceleration.展开更多
For the study of the parametric vibration response of submerged floating tunnel tether under random excitation, a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel ...For the study of the parametric vibration response of submerged floating tunnel tether under random excitation, a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up. Subsequently, vibration response of tether in the tether-tube system is analyzed by Monte Carlo method. It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation, the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether; the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases; owing to the damping force of water, the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air; increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether; the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.展开更多
Tethered cord syndrome is a progressive disease with a typically insidious onset in infants and children, and which can lead to persistent progress of neurological deficits and a high rate of disability without timely...Tethered cord syndrome is a progressive disease with a typically insidious onset in infants and children, and which can lead to persistent progress of neurological deficits and a high rate of disability without timely intervention. The purpose of this study was to investigate the curative effect of microsurgery in children with different types of tethered cord syndrome. In this study, we analyzed 326 patients with tethered cord syndrome, aged from 2 months to 14 years old, who were followed for 3-36 months after microscopic surgery. Based on clinical manifestations and imaging findings, these patients were classified into five types： tight ilium terminale （53 cases）, lipomyelome- ningocele （55 cases）, lipomatous malformation （124 cases）, postoperative adhesions （56 cases）, and split cord malformation （38 cases）. All patients underwent microsurgery. Curative effects were measured before and 3 months after surgery by Spina Bifida Neurological Scale based on sensory and motor functions, reflexes, and bladder and bowel function. The results showed that Spina Bifida Neurological Scale scores improved in all five types after surgery. Overall effective rates in these patients were 75%. Effective rates were 91% in tight ilium terminale, 84% in lipomyelomeningocele, 65% in lipomatous malformation, 75% in postoperative adhesion, and 79% in split cord mal- formation. Binary logistic regression analysis revealed that types of tethered cord syndrome （lipoma-type or not） and symptom duration before surgery were independent influencing factors of surgical outcome. These results show that therapeutic effect is markedly different in patients with different types of tethered cord syndrome. Suitable clinical classification for tethered cord syndrome will be helpful in predicting prognosis and guiding treatment. This trial has been registered in the Chinese Clinical Trial Registry （registration number： ChiCTR1800016464）.展开更多
文摘This study involved simulations and experiments aimed at assessing the efficacy of a tether net in encapsulating space debris.The tether net was modeled as a spring–mass–damper system considering the influence of aerodynamic and gravitational forces and the occurrence of debris collisions.To examine the influence of collision position and size disparity between the debris and the net on debris capture status,the entanglement nodes of the net were identified.Experiments were conducted to evaluate the wrapping capabilities of the tether net,focusing specifically on debris capture.Subsequently,the results were compared with those of the numerical simulation.In the experiments,radio frequency identification was used to identify the entanglement points of the tether net.Previous studies have indicated that the ideal collision point for capturing debris using a tether net with the debris intended to be captured is located at the center of the net.However,the experimental results of this study revealed that a collision position that is slightly shifted from the center of the tether net is more advantageous for capturing debris in terms of tether net entanglement.
基金supported by the National Natural Science Foundation of China(Nos.62222313,62173275,62327809,62303381,and 62303312)in part by the China Postdoctoral Science Foundation(No.2023M732225).
文摘The Tethered Space Net Robot(TSNR)is an innovative solution for active space debris capture and removal.Its large envelope and simple capture method make it an attractive option for this task.However,capturing maneuverable debris with the flexible and elastic underactuated net poses significant challenges.To address this,a novel formation control method for the TSNR is proposed through the integration of differential game theory and robust adaptive control in this paper.Specifically,the trajectory of the TSNR is obtained through the solution of a real-time feedback pursuit-evasion game with a dynamic target,where the primary condition is to ensure the stability of the TSNR.Furthermore,to minimize tracking errors and maintain a specific configuration,a robust adaptive formation control scheme with Artificial Potential Field(APF)based on a Finite-Time Convergent Extended State Observer(FTCESO)is investigated.The proposed control method has a key advantage in suppressing complex oscillations by a new adaptive law,thus precisely maintaining the configuration.Finally,numerical simulations are performed to demonstrate the effectiveness of the proposed scheme.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.62173107 and 12202058)the Young Elite Scientists Sponsorship Program by Beijing Association for Science and Technology(Grant No.BYESS2023344).
文摘The increasing accumulation of space debris threatens the integrity and functionality of satellites and complicates orbital operations.This paper constructs an advanced rigid-flexible coupling dynamic model for tethered satellite systems,tailored to enhance space debris management.Utilizing the nodal position finite element method,the model significantly improves the precision of simulating tether dynamics and captures the complex interactions involving satellite and debris attitude dynamics.This advancement allows for detailed examination of potential tether entanglements and provides crucial data for optimizing deorbiting processes.To overcome the limitations of conventional control techniques,a robust adaptive sliding mode control strategy is developed.This approach is specifically designed to manage the unpredictable conditions of the low-Earth orbit and ensure precise satellite attitude control,critical for successful debris removal.Validated through extensive numerical simulations,our model and control strategy demonstrate substantial improvements in operational reliability and safety,significantly enhancing the success rate of deorbiting missions.
基金supported by the National Natural Science Foundation of China(Grant No.U21B2075)。
文摘Dynamic analysis of the tethered satellite system(TSS)can provide a fundamental guideline to the evaluation of performance and robust design of the system examined.Uncertainties inherited with the parameters would induce unexpected variation of the response and deteriorate the reliability of the system.In this work,the effect of uncertain mass of the satellites on the deployment and retrieval dynamics of the TSS is investigated.First the interval mode is employed to take the variation of mass of satellite into account in the processes of deployment and retrieval.Then,the Chebyshev interval method is used to obtain the lower and upper response bounds of the TSS.To achieve a smooth and reliable implementation of deployment and retrieval,the nonlinear programming based on the Gauss pseudospectral method is adopted to obtain optimal trajectory of tether velocity.Numerical results show that the uncertainties of mass of the satellites have a distinct influence on the response of tether tension in the processes of deployment and retrieval.
基金supported by grants from the National Natural Science Foundation of China(Nos.82103978,81874286)the Natural Science Foundation of Jiangsu Province(No.BK20210423)“Double-First-Class”University Project(Nos.CPU 2018PZQ02,CPU 2018GY07).
文摘Small molecule inhibitors have dominated the pharmaceutical landscape for a long time as the primary therapeutic paradigm targeting pathogenic proteins.However,their efficacy heavily relies on the amino acid composition and spatial constitution of proteins,rendering them susceptible to drug resistance and failing to target undruggable proteins.In recent years,the advent of targeted protein degradation(TPD)technology has captured substantial attention from both industry and academia.Employing an event-driven mode,TPD offers a novel approach to eliminate pathogenic proteins by promoting their degrada-tion,thus circumventing the limitations associated with traditional small molecule inhibitors.Hydropho-bic tag tethering degrader(HyTTD)technology represents one such TPD approach that is currently in the burgeoning stage.HyTTDs employ endogenous protein degradation systems to induce the degrada-tion of target proteins through the proteasome pathway,which displays significant potential for medical value.In this review,we provide a comprehensive overview of the development history and the reported mechanism of action of HyTTDs.Additionally,we delve into the physiological roles,structure-activity re-lationships,and medical implications of HyTTDs targeting various disease-associated proteins.Moreover,we propose insights into the challenges that necessitate resolution for the successful development of HyTTDs,with the ultimate goal of initiating a new age of clinical treatment leveraging the immense po-tential of HyTTDs.
基金supported by the National Natural Science Foundation of China(Nos.62222313 and 62173275)。
文摘Tethered Space Net Robot(TSNR)is considered to be a promising approach for space debris removal,and accordingly it is also an interesting control problem due to its time-varying disturbances caused by an elastic and flexible net and a main connected tether.In this situation,the control scheme should be robust enough,low-frequency,and finite-time convergent in presence of external disturbances.In this paper,a robust controller with an advanced adaptive scheme is proposed.To improve robustness,the disturbance is skillfully involved in the adaptive scheme.It is strictly proven that the closed-loop system can converge to the desired trajectory in finite time in both reaching and sliding processes.Based on the theoretical proof,adaptive gains and corresponding dynamic stability characteristics are further discussed.Finally,the efficiency of the proposed control scheme is numerically proven via a TSNR.The proposed control scheme utilizes small and continuous control forces to compensate for the disturbance efficiently and track the desired trajectory quickly.
基金supported by the National Key R&D Program of China(2018YFA0703800)the National Natural Science Foundation of China(62173030)the Beijing Natural Science Foundation(4222050).
文摘For mitigating the libration angle fluctuation of the tethered satellite system,this paper discusses how to make the uniform velocity-deceleration separation scheme achieve the best effect.First,a judgment condition is established to determine the tether state by comparing the tether length and the relative distance of the sub-satellite and the parent satellite.Based on the tethered satellite system dynamics equation and Clohessy-Wiltshire equation,dynamic models are given for four cases of tether states.Second,the influence of the uniform velocity-deceleration separation scheme on the libration angle is analyzed by taking the libration angle at the separation ending time and the mean absolute value of the libration angle as index functions.Then,the optimality problem of the uniform velocity-deceleration separation scheme is formulated as an optimization problem with constraints,and an approximate solution algorithm is given by combining the back propagation neural network and Newton-Raphson method of multiple initial values.Finally,the effectiveness of the proposed method is verified by a numerical simulation.
基金financially supported by the National Natural Science Foundation of China(21273227,20903090)~~
文摘Rh/SiO2 catalysts with tethered-phosphines with different alkyl spacer lengths have been prepared,tested and characterized.Lengthening the alkyl spacer of the tethered-phosphine improved the flexibility of tethered-phospine,promoted the formation of active species and enhanced the activity of hydroformylation over other tethered-phosphine modified Rh/SiO2 catalysts.
基金supported by the Discovery grant(No.RGPIN-2024-06290)the CREATE grant(No.504156)of the Natural Sciences and Engineering Research Council of Canada.
文摘This paper presents a novel design for a Dyson-Harrop CubeSat aimed at harvesting energy from the solar wind. Unlike current photovoltaic-based satellite energy generation, the Dyson-Harrop satellite generates energy based on the photoelectric effect, which has the potential to achieve significantly higher efficiency than current photovoltaic technology. The proposed CubeSat system consists of three main components: a tether unit, an energy harvesting unit, and the central 3U CubeSat body. The tether unit generates a cylindrical magnetic field along its main tether,effectively concentrating electrons from the solar wind to the energy harvesting unit. The energy harvesting unit includes a spherical electron receiver, functioning as a capacitor, which attracts electrons from the solar wind, as well as an annular flat solar sail that captures photons in the solar wind to eject electrons via the photoelectric effect, resulting in an electric current in the system.The Dyson-Harrop CubeSat is shown to be highly efficient as an energy-generation system, producing approximately 1 kW of power by a 3U CubeSat. This energy can be transmitted via microwave beams to other spacecraft or ground stations on the Earth. It is important to note that this estimation is based on first-principle estimations, and thorough theoretical analysis and experimental validation are required to confirm the feasibility of the concept.
基金the National Natural Science Foundation of China(10672073)the Innovation Fund for Graduate Students,Nanjing University of Aeronautics and Astronautics
文摘The concept of tethered satellite system （TSS） promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and interesting problems related to their dynamics, control, and physical implementation. Over the past decades, this exciting topic has attracted significant attention from many researchers and gained a vast number of analytical, numerical and experimental achievements with a focus on the two essential aspects of both dynamics and control. This review article presents the historic background and recent hot topics for the space tethers, and introduces the dynamics and control of TSSs in a progressive manner, from basic operating principles to the state-of-the-art achievements.
基金funded by the National Natural Science Foundation of China (11672125, 11732006)the Civil Aerospace Pre-research Project of China (D010305)+1 种基金the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures (Nanjing University of Aeronautics and Astronautics, MCMS-0116K01)the Fundamental Research Funds for the Central Universities (NS2016009)
文摘Tethered satellite systems（TSSs） have attracted significant attention due to their potential and valuable applications for scientific research. With the development of various launched on-orbit missions, the deployment of tethers is considered a crucial technology for operation of a TSS. Both past orbiting experiments and numerical results have shown that oscillations of the deployed tether due to the Coriolis force and environmental perturbations are inevitable and that the impact between the space tether and end-body at the end of the deployment process leads to complicated nonlinear phenomena. Hence, a set of suitable control methods plays a fundamental role in tether deployment. This review article summarizes previous work on aspects of the dynamics, control, and ground-based experiments of tether deployment. The relevant basic principles, analytical expressions, simulation cases, and experimental results are presented as well.
基金supported by the Program for New Century Excellent Talents in University of China(Grant No.NCET-06-0270)the National Natural Science Foundation of China (Grant No.50578032)
文摘For the study of the non-linear response of inclined tethers subjected to parametric excitation in submerged floating tunnels, a theoretical model for coupled tube-tether vibration is developed. Upon the assumption that the static equilibri- um position of the tether is a quadratic parabola, the governing differential equations of the tether motion are derived by use of the Hamihon principle. An approximate numerical solution is obtained by use of Galerkin method and Runge-kutta method. The results show that, when the static equilibrium position of the tether is assumed to be. a quadratic parabola, the tether sag effect on its vibration may be reflected; the tether sag results in the asymmetry of tether vibration amplitude ; for the reduction of the tether amplitude, the buoyant unit weight of the tether should approach to zero as far as possible during the design.
基金supported by the Discovery Grant(No.RGPIN-2018-05991)of the Natural Sciences and Engineering Research Council of Canada
文摘This paper investigates the dynamics and de-spin control of a massive target by a single tethered space tug in the post-capture phase. The dynamic model of the tethered system is derived and simplified to a dimensionless form. Further, a decoupled PD controller is proposed, and the local stability of the controller is analyzed by linearization technique. Parametric studies of the dynamics and de-spin control of a massive target are conducted to characterize the dynamic process of de-spin with the proposed control law. It is shown that the massive target can be de-span by a single and small space tug with limited thrust within finite time. The thrust tangent with the tether de-spins the target while the thrust normal to the tether prevents the tether from winding up the target. The tether length has a positive contribution to the de-spin of a target. The longer tether leads to a faster de-spin process.
基金supported by the National Natural Science Foundation of China(Nos.11002068 and11202094)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(No.0113Y01)the Priority Academic Program of Jiangsu Higher Education Institutions
文摘The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.
基金supported by the National Natural Science Foundation of China (Grant No. 51108224)the Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province (Grant No. BS2010HZ005)
文摘A mathematical equation for vibration of submerged floating tunnel tether under the effects of earthquake and parametric excitation is presented. Multi-step Galerkin method is used to simplify this equation and the fourth-order Runge-Kuta integration method is used for numerical analysis. Finally, vibration response of submerged floating tunnel tether subjected to earthquake and parametric excitation is analyzed in a few numerical examples. The results show that the vibration response of tether varies with the seismic wave type; the steady maximum mid-span displacement of tether subjected to seismic wave keeps constant when parametric resonance takes place; the transient maximum mid-span displacement of tether is related to the peak value of input seismic wave acceleration.
基金supported by the Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province (Grant No. BS2010HZ005)
文摘For the study of the parametric vibration response of submerged floating tunnel tether under random excitation, a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up. Subsequently, vibration response of tether in the tether-tube system is analyzed by Monte Carlo method. It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation, the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether; the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases; owing to the damping force of water, the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air; increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether; the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.
基金supported by the Science Foundation of Military Medical Research and Clinical Research Foundation of PLA General Hospital in China,No.2016FC-CXYY-1006(to AJS)a grant from the Application of Clinical Features of Capital City of Science and Technology Commission in China,No.Z171100001017140(to AJS)
文摘Tethered cord syndrome is a progressive disease with a typically insidious onset in infants and children, and which can lead to persistent progress of neurological deficits and a high rate of disability without timely intervention. The purpose of this study was to investigate the curative effect of microsurgery in children with different types of tethered cord syndrome. In this study, we analyzed 326 patients with tethered cord syndrome, aged from 2 months to 14 years old, who were followed for 3-36 months after microscopic surgery. Based on clinical manifestations and imaging findings, these patients were classified into five types： tight ilium terminale （53 cases）, lipomyelome- ningocele （55 cases）, lipomatous malformation （124 cases）, postoperative adhesions （56 cases）, and split cord malformation （38 cases）. All patients underwent microsurgery. Curative effects were measured before and 3 months after surgery by Spina Bifida Neurological Scale based on sensory and motor functions, reflexes, and bladder and bowel function. The results showed that Spina Bifida Neurological Scale scores improved in all five types after surgery. Overall effective rates in these patients were 75%. Effective rates were 91% in tight ilium terminale, 84% in lipomyelomeningocele, 65% in lipomatous malformation, 75% in postoperative adhesion, and 79% in split cord mal- formation. Binary logistic regression analysis revealed that types of tethered cord syndrome （lipoma-type or not） and symptom duration before surgery were independent influencing factors of surgical outcome. These results show that therapeutic effect is markedly different in patients with different types of tethered cord syndrome. Suitable clinical classification for tethered cord syndrome will be helpful in predicting prognosis and guiding treatment. This trial has been registered in the Chinese Clinical Trial Registry （registration number： ChiCTR1800016464）.
