To overcome the shortcomings of the traditional measurement error calibration methods for spaceflight telemetry, tracking and command(TT&C) systems, an online error calibration method based on low Earth orbit sate...To overcome the shortcomings of the traditional measurement error calibration methods for spaceflight telemetry, tracking and command(TT&C) systems, an online error calibration method based on low Earth orbit satellite-to-ground doubledifferential GPS(LEO-ground DDGPS) is proposed in this study. A fixed-interval smoother combined with a pair of forward and backward adaptive robust Kalman filters(ARKFs) is adopted to solve the LEO-ground baseline, and the ant colony optimization(ACO) algorithm is used to deal with the ambiguity resolution problem. The precise baseline solution of DDGPS is then used as a comparative reference to calibrate the systematic errors in the TT&C measurements, in which the parameters of the range error model are solved by a batch least squares algorithm. To validate the performance of the new online error calibration method, a hardware-in-the-loop simulation platform is constructed with independently developed spaceborne dual-frequency GPS receivers and a Spirent GPS signal generator. The simulation results show that with the fixed-interval smoother, a baseline estimation accuracy(RMS, single axis) of better than 10 cm is achieved. Using this DDGPS solution as the reference, the systematic error of the TT&C ranging system is effectively calibrated, and the residual systematic error is less than 5 cm.展开更多
With the development of the transportation industry, the effective guidance of aircraft in an emergency to prevent catastrophic accidents remains one of the top safety concerns. Undoubtedly, operational status data of...With the development of the transportation industry, the effective guidance of aircraft in an emergency to prevent catastrophic accidents remains one of the top safety concerns. Undoubtedly, operational status data of the aircraft play an important role in the judgment and command of the Operational Control Center(OCC). However, how to transmit various operational status data from abnormal aircraft back to the OCC in an emergency is still an open problem. In this paper, we propose a novel Telemetry, Tracking,and Command(TT&C) architecture named Collaborative TT&C(CoTT&C) based on mega-constellation to solve such a problem. CoTT&C allows each satellite to help the abnormal aircraft by sharing TT&C resources when needed, realizing real-time and reliable aeronautical communication in an emergency. Specifically, we design a dynamic resource sharing mechanism for CoTT&C and model the mechanism as a single-leader-multi-follower Stackelberg game. Further, we give an unique Nash Equilibrium(NE) of the game as a closed form. Simulation results demonstrate that the proposed resource sharing mechanism is effective, incentive compatible, fair, and reciprocal. We hope that our findings can shed some light for future research on aeronautical communications in an emergency.展开更多
Spaceflight and ground-based microgravity analog experiments have suggested that microgravity can affect microbial growth and metabolism. Although the effects of microgravity and its analogs on microorganisms have bee...Spaceflight and ground-based microgravity analog experiments have suggested that microgravity can affect microbial growth and metabolism. Although the effects of microgravity and its analogs on microorganisms have been studied for more than 50 years, plausible conflicting and diverse results have frequently been reported in different experiments, especially regarding microbial growth and secondary metabolism. Until now, only the responses of a few typical microbes to microgravity have been investigated; systematic studies of the genetic and phenotypic responses of these microorganisms to microgravity in space are still insufficient due to technological and logistical hurdles. The use of different test strains and secondary metabolites in these studies appears to have caused diverse and conflicting results. Moreover, subtle changes in the extracellular microenvironments around microbial cells play a key role in the diverse responses of microbial growth and secondary metabolisms. Therefore, "indirect" effects represent a reasonable pathway to explain the occurrence of these phenomena in microorganisms. This review summarizes current knowledge on the changes in microbial growth and secondary metabolism in response to spaceflight and its analogs and discusses the diverse and conflicting results. In addition, recommendations are given for future studies on the effects of microgravity in space on microbial growth and secondary metabolism.展开更多
Satellite constellations are promising in enabling the global Internet.However,the increasing constellation size also complicates tracking,telemetry and command(TT&C)systems.Traditional groundbased and space-based...Satellite constellations are promising in enabling the global Internet.However,the increasing constellation size also complicates tracking,telemetry and command(TT&C)systems.Traditional groundbased and space-based approaches have encountered significant obstacles due to,e.g.,the limited satellite visible arc and long transmission delay.Considering the fast development of intersatellite communications,synergy among multiple connected satellites can be exploited to facilitate TT&C system designs.This leads to networked TT&C,which requires much less predeployed infrastructures and even performs better than traditional TT&C systems.In this paper,we elaborate system characteristics of networked TT&C compared with traditional ground-based and spacebased TT&C,and propose the unique security challenges and opportunities for networked TT&C,which includes secure routing and trust mechanisms.Furthermore,since networked TT&C is a novel scenario with few relevant researches,we first investigate the current researches on secure routing and trust mechanisms for traditional terrestrial and satellite networks,and then accordingly deliver our security perspectives considering the system characteristics and security requirements of networked TT&C.展开更多
The whole airspace phased array telemetry,track and command(TT&C)system is regarded as the development tendency of next generation TT&C system,and the distribution of the antenna units and the beamforming tech...The whole airspace phased array telemetry,track and command(TT&C)system is regarded as the development tendency of next generation TT&C system,and the distribution of the antenna units and the beamforming technology have sparked wide interest in this field.A method for antenna distribution is proposed based on the linear subarrays technology.A symmetrical truncated cone conformal array is composed of the linear subarrays placed on the generatrix.The impact of truncated cone bottom radius and elevation angle on beamforming are studied and simulated.Simulation results verify the system design.展开更多
When analyze the uncertainty of the cost and the schedule of the spaceflight project, it is needed to know the value of the schedule-cost correlation coefficient. This paper deduces the schedule distribution, consider...When analyze the uncertainty of the cost and the schedule of the spaceflight project, it is needed to know the value of the schedule-cost correlation coefficient. This paper deduces the schedule distribution, considering the effect of the cost, and proposes the estimation formula of the correlation coefficient between the in（schedule） and the cost. On the basis of the fact and Taylor expansion, the relation expression between the schedule-cost correlation coefficient and the in-schedule-cost correlation coefficient is put forward. By analyzing the value features of the estimation formula of the in-schedule-cost correlation coefficient, the general rules are proposed to ascertain the value of the schedule-cost correlation coefficient. An example is given to demonstrate how to approximately amend the schedule-cost correlation coefficient based on the historical statistics, which reveals the traditional assigned value is inaccurate. The universality of this estimation method is analyzed.展开更多
[ Objective] To explore the effects of spaceflight on the second-generation seeds of alfalfa and provide a theoretical basis for mutation breeding. [Method] The seeds of Medicago stavia L. lines no. 1, no. 2 and no. 4...[ Objective] To explore the effects of spaceflight on the second-generation seeds of alfalfa and provide a theoretical basis for mutation breeding. [Method] The seeds of Medicago stavia L. lines no. 1, no. 2 and no. 4 were carried into space by the Shijian-8 seed breeding satellite for a 15-d spaceflight treatment. After returning to the ground, seedlings were transplanted to field. Traits of the second-generation seeds of alfalfa were evaluated. [Result] The 1 000-grain weight of the second-generation seeds were 5% -9% significantly higher than that the control （P 〈 0.05）. The germination rate, seedling weight, shoot length and root length were significantly increased （P 〈 0.05）. The hard seed rate and the rate of moldy seeds were significantly decreased （ P 〈 0.05）. However, the rate of dead seeds was increased. [ Conclusion] Spaceflight treatment has positive mutagenic effects on the second-generation seeds of alfalfa.展开更多
Highly relativistic speeds are desirable for interstellar travel. Relativistic time dilation would reduce the subjective duration of the trip for the travelers, so that they can cover galaxy-scale distances in a reaso...Highly relativistic speeds are desirable for interstellar travel. Relativistic time dilation would reduce the subjective duration of the trip for the travelers, so that they can cover galaxy-scale distances in a reasonable amount of personal time. Unfortunately, as spaceship velocities approach the speed of light, interstellar hydrogen H, although only present at a density of approximately 1.8 atoms/cm3, turns into intense radiation that would quickly kill passengers and destroy electronic instrumentation. In addition, the energy loss of ionizing radiation passing through the ship’s hull represents an increasing heat load that necessitates large expenditures of energy to cool the ship. Stopping or diverting this flux, either with material or electromagnetic shields, is a daunting problem. Going slow to avoid severe H irradiation sets an upper speed limit of v ~ 0.5 c. This velocity only gives a time dilation factor of about 15%, which would not substantially assist galaxy-scale voyages. Diffuse interstellar H atoms are the ultimate cosmic space mines and represent a formidable obstacle to interstellar travel.展开更多
Currently, TT&C of spacecraft is performed by a ground system. Because more and more spacecrafts are launched into orbits, it is difficult for the ground system to meet the TT&C requirements of the spacecrafts...Currently, TT&C of spacecraft is performed by a ground system. Because more and more spacecrafts are launched into orbits, it is difficult for the ground system to meet the TT&C requirements of the spacecrafts. To explore a new, effective and economical TT&C mode is absolutely necessary. A method is proposed to use SGBM mode in TT&C spacecrafts in low earth orbits, here. Firstly, the principle of the mode is discussed; secondly, the system to simulate the mode is designed; thirdly, the relative issues to use the mode are indicated; fourthly, the experimental results (simulation) to apply the mode to TT&C spacecrafts are analyzed; and finally dawn is the main conclusion of the method.展开更多
An interference mitigation for acquisition method,based on both energy center and spectrum symmetry detection,has been proposed as a possible solution to the problem of signal acquisition susceptibility to continuous-...An interference mitigation for acquisition method,based on both energy center and spectrum symmetry detection,has been proposed as a possible solution to the problem of signal acquisition susceptibility to continuous-wave interference(CWI)in unified carrier telemetry,tracking,and command(TT&C)systems.With subcarrier modulation index as a priori condition,the existence of CWI is determined by comparing the energy center with the symmetric center.In the presence of interference,the interference frequency point is assumed and culled;sequentially,the spectral symmetry is used to verify whether the signal acquisition is realized.Theoretical analysis,simulations,and experimental results demonstrate that the method can realize the acquisition of the main carrier target signal with an interference-to-signal ratio of 31 dB,which represents an improvement over the existing continuous-wave interference mitigation for acquisition methods.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos. 60904090 and 61401389)the National Science Foundation for Distinguished Young Scholars of China (No. 61525403)+1 种基金the Joint Fund of the Ministry of Education of China (No. 6141A02033310)the Fundamental Research Funds for the Central Universities, China (No. 2018QNA4053).
文摘To overcome the shortcomings of the traditional measurement error calibration methods for spaceflight telemetry, tracking and command(TT&C) systems, an online error calibration method based on low Earth orbit satellite-to-ground doubledifferential GPS(LEO-ground DDGPS) is proposed in this study. A fixed-interval smoother combined with a pair of forward and backward adaptive robust Kalman filters(ARKFs) is adopted to solve the LEO-ground baseline, and the ant colony optimization(ACO) algorithm is used to deal with the ambiguity resolution problem. The precise baseline solution of DDGPS is then used as a comparative reference to calibrate the systematic errors in the TT&C measurements, in which the parameters of the range error model are solved by a batch least squares algorithm. To validate the performance of the new online error calibration method, a hardware-in-the-loop simulation platform is constructed with independently developed spaceborne dual-frequency GPS receivers and a Spirent GPS signal generator. The simulation results show that with the fixed-interval smoother, a baseline estimation accuracy(RMS, single axis) of better than 10 cm is achieved. Using this DDGPS solution as the reference, the systematic error of the TT&C ranging system is effectively calibrated, and the residual systematic error is less than 5 cm.
基金supported by the National Natural Science Foundation of China under Grant 62131012/61971261。
文摘With the development of the transportation industry, the effective guidance of aircraft in an emergency to prevent catastrophic accidents remains one of the top safety concerns. Undoubtedly, operational status data of the aircraft play an important role in the judgment and command of the Operational Control Center(OCC). However, how to transmit various operational status data from abnormal aircraft back to the OCC in an emergency is still an open problem. In this paper, we propose a novel Telemetry, Tracking,and Command(TT&C) architecture named Collaborative TT&C(CoTT&C) based on mega-constellation to solve such a problem. CoTT&C allows each satellite to help the abnormal aircraft by sharing TT&C resources when needed, realizing real-time and reliable aeronautical communication in an emergency. Specifically, we design a dynamic resource sharing mechanism for CoTT&C and model the mechanism as a single-leader-multi-follower Stackelberg game. Further, we give an unique Nash Equilibrium(NE) of the game as a closed form. Simulation results demonstrate that the proposed resource sharing mechanism is effective, incentive compatible, fair, and reciprocal. We hope that our findings can shed some light for future research on aeronautical communications in an emergency.
基金supported by the China Manned Space Engineering Program(CMSE,921–2)the National Program on Key Basic Research Project(973 Program,No.2014CB744400)the General Financial Grant from the China Postdoctoral Science Foundation(No.2016 M602971)
文摘Spaceflight and ground-based microgravity analog experiments have suggested that microgravity can affect microbial growth and metabolism. Although the effects of microgravity and its analogs on microorganisms have been studied for more than 50 years, plausible conflicting and diverse results have frequently been reported in different experiments, especially regarding microbial growth and secondary metabolism. Until now, only the responses of a few typical microbes to microgravity have been investigated; systematic studies of the genetic and phenotypic responses of these microorganisms to microgravity in space are still insufficient due to technological and logistical hurdles. The use of different test strains and secondary metabolites in these studies appears to have caused diverse and conflicting results. Moreover, subtle changes in the extracellular microenvironments around microbial cells play a key role in the diverse responses of microbial growth and secondary metabolisms. Therefore, "indirect" effects represent a reasonable pathway to explain the occurrence of these phenomena in microorganisms. This review summarizes current knowledge on the changes in microbial growth and secondary metabolism in response to spaceflight and its analogs and discusses the diverse and conflicting results. In addition, recommendations are given for future studies on the effects of microgravity in space on microbial growth and secondary metabolism.
基金supported by the National Natural Science Foundation of China under Grant 61971261/62131012Technology Project of the State Grid Corporation of China under Grant 5400202255158A-1-1-ZN。
文摘Satellite constellations are promising in enabling the global Internet.However,the increasing constellation size also complicates tracking,telemetry and command(TT&C)systems.Traditional groundbased and space-based approaches have encountered significant obstacles due to,e.g.,the limited satellite visible arc and long transmission delay.Considering the fast development of intersatellite communications,synergy among multiple connected satellites can be exploited to facilitate TT&C system designs.This leads to networked TT&C,which requires much less predeployed infrastructures and even performs better than traditional TT&C systems.In this paper,we elaborate system characteristics of networked TT&C compared with traditional ground-based and spacebased TT&C,and propose the unique security challenges and opportunities for networked TT&C,which includes secure routing and trust mechanisms.Furthermore,since networked TT&C is a novel scenario with few relevant researches,we first investigate the current researches on secure routing and trust mechanisms for traditional terrestrial and satellite networks,and then accordingly deliver our security perspectives considering the system characteristics and security requirements of networked TT&C.
文摘The whole airspace phased array telemetry,track and command(TT&C)system is regarded as the development tendency of next generation TT&C system,and the distribution of the antenna units and the beamforming technology have sparked wide interest in this field.A method for antenna distribution is proposed based on the linear subarrays technology.A symmetrical truncated cone conformal array is composed of the linear subarrays placed on the generatrix.The impact of truncated cone bottom radius and elevation angle on beamforming are studied and simulated.Simulation results verify the system design.
基金This project was supported by Weapon System Advanced Research Foundation(51419010204KG01) and National ScienceFoundation of China(70272002).
文摘When analyze the uncertainty of the cost and the schedule of the spaceflight project, it is needed to know the value of the schedule-cost correlation coefficient. This paper deduces the schedule distribution, considering the effect of the cost, and proposes the estimation formula of the correlation coefficient between the in（schedule） and the cost. On the basis of the fact and Taylor expansion, the relation expression between the schedule-cost correlation coefficient and the in-schedule-cost correlation coefficient is put forward. By analyzing the value features of the estimation formula of the in-schedule-cost correlation coefficient, the general rules are proposed to ascertain the value of the schedule-cost correlation coefficient. An example is given to demonstrate how to approximately amend the schedule-cost correlation coefficient based on the historical statistics, which reveals the traditional assigned value is inaccurate. The universality of this estimation method is analyzed.
基金supported by the grants of the National Key Technology R&D Program (2008BADB3B04 )Basic Science and Research Special Fund for the State Level and Public Scientific Research Institute (Grassland Research Institute,Chinese Academy of Agricultural Sciences) (2007-1-02)
文摘[ Objective] To explore the effects of spaceflight on the second-generation seeds of alfalfa and provide a theoretical basis for mutation breeding. [Method] The seeds of Medicago stavia L. lines no. 1, no. 2 and no. 4 were carried into space by the Shijian-8 seed breeding satellite for a 15-d spaceflight treatment. After returning to the ground, seedlings were transplanted to field. Traits of the second-generation seeds of alfalfa were evaluated. [Result] The 1 000-grain weight of the second-generation seeds were 5% -9% significantly higher than that the control （P 〈 0.05）. The germination rate, seedling weight, shoot length and root length were significantly increased （P 〈 0.05）. The hard seed rate and the rate of moldy seeds were significantly decreased （ P 〈 0.05）. However, the rate of dead seeds was increased. [ Conclusion] Spaceflight treatment has positive mutagenic effects on the second-generation seeds of alfalfa.
文摘Highly relativistic speeds are desirable for interstellar travel. Relativistic time dilation would reduce the subjective duration of the trip for the travelers, so that they can cover galaxy-scale distances in a reasonable amount of personal time. Unfortunately, as spaceship velocities approach the speed of light, interstellar hydrogen H, although only present at a density of approximately 1.8 atoms/cm3, turns into intense radiation that would quickly kill passengers and destroy electronic instrumentation. In addition, the energy loss of ionizing radiation passing through the ship’s hull represents an increasing heat load that necessitates large expenditures of energy to cool the ship. Stopping or diverting this flux, either with material or electromagnetic shields, is a daunting problem. Going slow to avoid severe H irradiation sets an upper speed limit of v ~ 0.5 c. This velocity only gives a time dilation factor of about 15%, which would not substantially assist galaxy-scale voyages. Diffuse interstellar H atoms are the ultimate cosmic space mines and represent a formidable obstacle to interstellar travel.
文摘Currently, TT&C of spacecraft is performed by a ground system. Because more and more spacecrafts are launched into orbits, it is difficult for the ground system to meet the TT&C requirements of the spacecrafts. To explore a new, effective and economical TT&C mode is absolutely necessary. A method is proposed to use SGBM mode in TT&C spacecrafts in low earth orbits, here. Firstly, the principle of the mode is discussed; secondly, the system to simulate the mode is designed; thirdly, the relative issues to use the mode are indicated; fourthly, the experimental results (simulation) to apply the mode to TT&C spacecrafts are analyzed; and finally dawn is the main conclusion of the method.
基金Supported by the National Natural Science Foundation of China(61401026)
文摘An interference mitigation for acquisition method,based on both energy center and spectrum symmetry detection,has been proposed as a possible solution to the problem of signal acquisition susceptibility to continuous-wave interference(CWI)in unified carrier telemetry,tracking,and command(TT&C)systems.With subcarrier modulation index as a priori condition,the existence of CWI is determined by comparing the energy center with the symmetric center.In the presence of interference,the interference frequency point is assumed and culled;sequentially,the spectral symmetry is used to verify whether the signal acquisition is realized.Theoretical analysis,simulations,and experimental results demonstrate that the method can realize the acquisition of the main carrier target signal with an interference-to-signal ratio of 31 dB,which represents an improvement over the existing continuous-wave interference mitigation for acquisition methods.
