Spacecraft orbit evasion is an effective method to ensure space safety. In the spacecraft’s orbital plane, the space non-cooperate target with autonomous approaching to the spacecraft may have a dangerous rendezvous....Spacecraft orbit evasion is an effective method to ensure space safety. In the spacecraft’s orbital plane, the space non-cooperate target with autonomous approaching to the spacecraft may have a dangerous rendezvous. To deal with this problem, an optimal maneuvering strategy based on the relative navigation observability degree is proposed with angles-only measurements. A maneuver evasion relative navigation model in the spacecraft’s orbital plane is constructed and the observability measurement criteria with process noise and measurement noise are defined based on the posterior Cramer-Rao lower bound. Further, the optimal maneuver evasion strategy in spacecraft’s orbital plane based on the observability is proposed. The strategy provides a new idea for spacecraft to evade safety threats autonomously. Compared with the spacecraft evasion problem based on the absolute navigation, more accurate evasion results can be obtained. The simulation indicates that this optimal strategy can weaken the system’s observability and reduce the state estimation accuracy of the non-cooperative target, making it impossible for the non-cooperative target to accurately approach the spacecraft.展开更多
For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlin...For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlinear iteration.However,due to the complex underwater environment,the sound speed changes with time and space,and then the acoustic propagation path is actually a curve,which inevitably causes some errors to the traditional distance intersection positioning algorithm.To reduce the position error caused by the uncertain underwater sound speed,a new time of arrival(TOA)intersection underwater positioning algorithm of LBL system is proposed.Firstly,combined with the vertical layered model of the underwater sound speed,an implicit positioning model of TOA intersection is constructed through the constant gradient acoustic ray tracing.And then an optimization function based on the overall TOA residual square sum is advanced to solve the position parameters for the underwater target.Moreover,the particle swarm optimization(PSO)algorithm is replaced with the tra-ditional nonlinear least square method to optimize the implicit positioning model of TOA intersection.Compared with the traditional distance intersection positioning model,the TOA intersec-tion positioning model is more suitable for the engineering practice and the optimization algorithm is more effective.Simulation results show that the proposed methods in this paper can effectively improve the positioning accuracy for the underwater target.展开更多
Inspired by increasing demand of advanced pulsed power capacitors,the development of lead-free dielectric ceramic capacitors with high energy storage density and temperature-insensitive performance are extremely cruci...Inspired by increasing demand of advanced pulsed power capacitors,the development of lead-free dielectric ceramic capacitors with high energy storage density and temperature-insensitive performance are extremely crucial.Herein,the lead-free relaxor ferroelectric ceramics based on(1-x)(Na_(0.5)Bi_(0.5))0.6Sr_(0.4)TiO_(3-x)Sr_(0.7)La_(0.2)ZrO_(3)[abbreviated as(1-x)NBST-xSLZ]are prepared by the solid-state reaction route.The large recoverable energy density(Wrec)of 3.45 J/cm^(3) and efficiency(h)of 90.1%are simultaneously realized in 0.86NBST-0.14SLZ ceramic due to increased breakdown strength.Furthermore,both the Wrec and h of 0.86NBST-0.14SLZ ceramic display superior of thermal stability(20e180C),frequency stability(1e1000 Hz),and cycle stability(10^(4))within a satisfactory range of variation.In addition,the 0.86NBST-0.14SLZ ceramic can also achieve a large current density(CD)of 625 A/cm^(2),an ultrahigh power density(PD)of 50 MW/cm^(3) and a fast discharge rate(t0.90)of 160.8 ns at 160 kV/cm.These results demonstrate that the 0.86NBST-0.14SLZ ceramic could be a highly competitive and ecofriendly relaxor ferroelectric material for next-generation pulsed power capacitors.展开更多
基金supported by the National Key R&D Program of China (2020YFA0713502)the Special Fund Project for Guiding Local Scientific and Technological Development (2020ZYT003)+1 种基金the National Natural Science Foundation of China (U20B2055,61773021,61903086)the Natural Science Foundation of Hunan Province (2019JJ20018,2020JJ4280)。
文摘Spacecraft orbit evasion is an effective method to ensure space safety. In the spacecraft’s orbital plane, the space non-cooperate target with autonomous approaching to the spacecraft may have a dangerous rendezvous. To deal with this problem, an optimal maneuvering strategy based on the relative navigation observability degree is proposed with angles-only measurements. A maneuver evasion relative navigation model in the spacecraft’s orbital plane is constructed and the observability measurement criteria with process noise and measurement noise are defined based on the posterior Cramer-Rao lower bound. Further, the optimal maneuver evasion strategy in spacecraft’s orbital plane based on the observability is proposed. The strategy provides a new idea for spacecraft to evade safety threats autonomously. Compared with the spacecraft evasion problem based on the absolute navigation, more accurate evasion results can be obtained. The simulation indicates that this optimal strategy can weaken the system’s observability and reduce the state estimation accuracy of the non-cooperative target, making it impossible for the non-cooperative target to accurately approach the spacecraft.
基金supported by the National Natural Science Foundation of China(61903086,61903366,62001115)the Natural Science Foundation of Hunan Province(2019JJ50745,2020JJ4280,2021JJ40133)the Fundamentals and Basic of Applications Research Foundation of Guangdong Province(2019A1515110136).
文摘For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlinear iteration.However,due to the complex underwater environment,the sound speed changes with time and space,and then the acoustic propagation path is actually a curve,which inevitably causes some errors to the traditional distance intersection positioning algorithm.To reduce the position error caused by the uncertain underwater sound speed,a new time of arrival(TOA)intersection underwater positioning algorithm of LBL system is proposed.Firstly,combined with the vertical layered model of the underwater sound speed,an implicit positioning model of TOA intersection is constructed through the constant gradient acoustic ray tracing.And then an optimization function based on the overall TOA residual square sum is advanced to solve the position parameters for the underwater target.Moreover,the particle swarm optimization(PSO)algorithm is replaced with the tra-ditional nonlinear least square method to optimize the implicit positioning model of TOA intersection.Compared with the traditional distance intersection positioning model,the TOA intersec-tion positioning model is more suitable for the engineering practice and the optimization algorithm is more effective.Simulation results show that the proposed methods in this paper can effectively improve the positioning accuracy for the underwater target.
基金supported by the National Nature Science Foundation of China(Grant No.51902167)Zhejiang Province Nature Science Foundation of China(Grant No.LY21E020002)+1 种基金Ningbo Nature Science Foundation of China(Grant No.2019A610001)Key Laboratory of Engineering Dielectrics and Its Application(Harbin University of Science and Technology),Ministry of Education.
文摘Inspired by increasing demand of advanced pulsed power capacitors,the development of lead-free dielectric ceramic capacitors with high energy storage density and temperature-insensitive performance are extremely crucial.Herein,the lead-free relaxor ferroelectric ceramics based on(1-x)(Na_(0.5)Bi_(0.5))0.6Sr_(0.4)TiO_(3-x)Sr_(0.7)La_(0.2)ZrO_(3)[abbreviated as(1-x)NBST-xSLZ]are prepared by the solid-state reaction route.The large recoverable energy density(Wrec)of 3.45 J/cm^(3) and efficiency(h)of 90.1%are simultaneously realized in 0.86NBST-0.14SLZ ceramic due to increased breakdown strength.Furthermore,both the Wrec and h of 0.86NBST-0.14SLZ ceramic display superior of thermal stability(20e180C),frequency stability(1e1000 Hz),and cycle stability(10^(4))within a satisfactory range of variation.In addition,the 0.86NBST-0.14SLZ ceramic can also achieve a large current density(CD)of 625 A/cm^(2),an ultrahigh power density(PD)of 50 MW/cm^(3) and a fast discharge rate(t0.90)of 160.8 ns at 160 kV/cm.These results demonstrate that the 0.86NBST-0.14SLZ ceramic could be a highly competitive and ecofriendly relaxor ferroelectric material for next-generation pulsed power capacitors.
