As humanity ventures deeper into space,our challenges become increasingly complex.Space medicine,once confi ned to ensuring the health and safety of astronauts on low-Earth orbit missions,is now tasked with ensuring t...As humanity ventures deeper into space,our challenges become increasingly complex.Space medicine,once confi ned to ensuring the health and safety of astronauts on low-Earth orbit missions,is now tasked with ensuring the health and safety of astronauts embarking on extended missions to the Moon,Mars,and beyond.Th e advancement of space medicine and the conduct of in-orbit medical experiments not only determine the boundaries of human exploration of the cosmos but also provide new insights that can benefi t human health on Earth.展开更多
3D printing technology can realize the rapid fabrication of complicated structures with short production chain,which just meet the requirements for space manufacturing in the future.This Special Issue features the cut...3D printing technology can realize the rapid fabrication of complicated structures with short production chain,which just meet the requirements for space manufacturing in the future.This Special Issue features the cutting-edge 3D printing technologies considering the space environment,focusing on the experimental validation and simulation on the 3D printing process and structural technologies,including whole process chain from raw materials,structural design,process,equipment,as well as functional verification.展开更多
The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-d...The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-dimension collision-free trajectory planning is the prerequisite to ensure airspace security.However,the timely information of surrounding situation is difficult to acquire by UAVs,which further brings security risks.As a mature technology leveraged in traditional civil aviation,the Automatic Dependent Surveillance-Broadcast(ADS-B)realizes continuous surveillance of the information of aircraft.Consequently,we leverage ADS-B for surveillance and information broadcasting,and divide the aerial airspace into multiple sub-airspaces to improve flight safety in UAV trajectory planning.In detail,we propose the secure Sub-airSpaces Planning(SSP)algorithm and Particle Swarm Optimization Rapidly-exploring Random Trees(PSO-RRT)algorithm for the UAV trajectory planning in law-altitude airspace.The performance of the proposed algorithm is verified by simulations and the results show that SSP reduces both the maximum number of UAVs in the sub-airspace and the length of the trajectory,and PSO-RRT reduces the cost of UAV trajectory in the sub-airspace.展开更多
The energetic particle detector on China's space station can determine the energy, flux, and direction of medium-and highenergy protons, electrons, heavy ions, and neutrons within the path of the station's orb...The energetic particle detector on China's space station can determine the energy, flux, and direction of medium-and highenergy protons, electrons, heavy ions, and neutrons within the path of the station's orbit. It also assesses the linear energy transfer(LET)spectra and radiation dose rates generated by these particles. Neutron detection is a significant component of this work, utilizing a new type of Cs_(2)LiYCl_(6): Ce scintillator material along with plastic scintillators as sensors. In-orbit testing has demonstrated the efficient identification of space neutrons and gamma rays(n/γ). This data plays a crucial role in supporting manned space engineering, scientific research, and other related fields.展开更多
Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetar...Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetary defense strategy. Different from those conducted asteroid flyby missions, in the 12th China Trajectory Optimization Competition (CTOC-12), a NEAs flyby trajectory design problem using reusable probes that depart from a Lunar Distant Retrograde Orbit (DRO) station in the cislunar space was released. The objective was flyby to as many NEAs as possible using up to 20 probes within a total of 10 years. The ∑ team proposed a solution that can explore 47 NEAs using 11 probes, ranking the first in the competition. In this paper, the methods and results from the winning team are introduced, including mission analysis and preliminary design, and low-energy transfer trajectory optimization. In particular, a round-trip trajectory is divided into three phases: deep space transfer, indirect transfer between the Earth to DRO, and DRO phasing and rendezvous. With the combination of global optimization and local optimization algorithms, the required velocity increments to change the orbital planes are effectively reduced, thus increasing the number of the explored NEAs. The final solution of our team is presented and the results are compared with those of the top three teams. The competition demonstrates that the regularization of flyby missions from the cislunar space to explore NEAs with the potential impact risks to the Earth is the feasible and promising.展开更多
Graphene-copper(Gr-Cu)composites exhibit significant potential for industrial applications.Among the methods for fabricating Gr-Cu composites,the in-situ growth method stands out as a simple yet effective approach.How...Graphene-copper(Gr-Cu)composites exhibit significant potential for industrial applications.Among the methods for fabricating Gr-Cu composites,the in-situ growth method stands out as a simple yet effective approach.However,graphene converted from liquid or solid molecules by the traditional in-situ growth method often exhibits numerous defects,thereby reducing its effectiveness in enhancing the electrical properties of the composites.To address this issue,we developed an innovative and efficient method,referred to as the“confinedparallel-space in-situ growth(CPS)method,”to grow highquality graphene and fabricate high-conductivity Gr-Cu composites.Oleic acid was chosen as the small molecular carbon source and confined between copper sheets obtained by rolling dendritic copper powder.This carbon source underwent conversion into oriented,high-quality graphene in the confined space at high temperature.The high-quality graphene sheets serve as continuous electron transport channels,significantly improving the conductivity of the composite.The composite prepared by the CPS method(CPS-composite)demonstrates unique conductivity,exceeding that of standard annealed copper at temperatures above 40℃and notably outperforming it by 3.2%at160℃.In addition,compared to the composite with a similar carbon content prepared by the traditional in-situ growth method,the yield strength of the CPS-composite increased by 23.6%,while the strengthening efficiency of graphene improved by 146.6%,achieving an ultrahigh value of 489 at a carbon volume fraction of 0.086 vol%.The CPS method emerges as a novel strategy for fabricating high-performance,low-cost,and large-scale graphene-copper composites using small molecular carbon sources,making it suitable for industrial production.展开更多
In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a s...In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a star point positioning algorithm based on the capsule network whose input and output are both vectors. First, a PCTL (Probability-Coordinate Transformation Layer) is designed to represent the mapping relationship between the probability output of the capsule network and the star point sub-pixel coordinates. Then, Coordconv Layer is introduced to implement explicit encoding of space information and the probability is used as the centroid weight to achieve the conversion between probability and star point sub-pixel coordinates, which improves the network’s ability to perceive star point positions. Finally, based on the dynamic imaging principle of star sensors and the characteristics of near-space environment, a star map dataset for algorithm training and testing is constructed. The simulation results show that the proposed algorithm reduces the MAE (Mean Absolute Error) and RMSE (Root Mean Square Error) of the star point positioning by 36.1% and 41.7% respectively compared with the traditional algorithm. The research results can provide important theory and technical support for the scheme design, index demonstration, test and evaluation of large dynamic star sensors in near space.展开更多
The increasing complexity of on-orbit tasks imposes great demands on the flexible operation of space robotic arms, prompting the development of space robots from single-arm manipulation to multi-arm collaboration. In ...The increasing complexity of on-orbit tasks imposes great demands on the flexible operation of space robotic arms, prompting the development of space robots from single-arm manipulation to multi-arm collaboration. In this paper, a combined approach of Learning from Demonstration (LfD) and Reinforcement Learning (RL) is proposed for space multi-arm collaborative skill learning. The combination effectively resolves the trade-off between learning efficiency and feasible solution in LfD, as well as the time-consuming pursuit of the optimal solution in RL. With the prior knowledge of LfD, space robotic arms can achieve efficient guided learning in high-dimensional state-action space. Specifically, an LfD approach with Probabilistic Movement Primitives (ProMP) is firstly utilized to encode and reproduce the demonstration actions, generating a distribution as the initialization of policy. Then in the RL stage, a Relative Entropy Policy Search (REPS) algorithm modified in continuous state-action space is employed for further policy improvement. More importantly, the learned behaviors can maintain and reflect the characteristics of demonstrations. In addition, a series of supplementary policy search mechanisms are designed to accelerate the exploration process. The effectiveness of the proposed method has been verified both theoretically and experimentally. Moreover, comparisons with state-of-the-art methods have confirmed the outperformance of the approach.展开更多
This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moo...This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.展开更多
Space laser communication(SLC)is an emerging technology to support high-throughput data transmissions in space networks.In this paper,to guarantee the reliability of high-speed SLC links,we aim at practical implementa...Space laser communication(SLC)is an emerging technology to support high-throughput data transmissions in space networks.In this paper,to guarantee the reliability of high-speed SLC links,we aim at practical implementation of low-density paritycheck(LDPC)decoding under resource-restricted space platforms.Particularly,due to the supply restriction and cost issues of high-speed on-board devices such as analog-to-digital converters(ADCs),the input of LDPC decoding will be usually constrained by hard-decision channel output.To tackle this challenge,density-evolution-based theoretical analysis is firstly performed to identify the cause of performance degradation in the conventional binaryinitialized iterative decoding(BIID)algorithm.Then,a computation-efficient decoding algorithm named multiary-initialized iterative decoding with early termination(MIID-ET)is proposed,which improves the error-correcting performance and computation efficiency by using a reliability-based initialization method and a threshold-based decoding termination rule.Finally,numerical simulations are conducted on example codes of rates 7/8 and 1/2 to evaluate the performance of different LDPC decoding algorithms,where the proposed MIID-ET outperforms the BIID with a coding gain of 0.38 dB and variable node calculation saving of 37%.With this advantage,the proposed MIID-ET can notably reduce LDPC decoder’s hardware implementation complexity under the same bit error rate performance,which successfully doubles the total throughput to 10 Gbps on a single-chip FPGA.展开更多
In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator esti...In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator estimates are motivated by the study of well-posedness results for some models in incompressible fuid mechanics.展开更多
The China Space Station Telescope(CSST) is primarily designed for large-scale multi-color imaging and seamless spectroscopic survey, while also accommodating observations with an integral field spectrograph(IFS), mult...The China Space Station Telescope(CSST) is primarily designed for large-scale multi-color imaging and seamless spectroscopic survey, while also accommodating observations with an integral field spectrograph(IFS), multichannel imaging, direct imaging of exoplanets, and terahertz-band observations. It is scheduled to be launched in about 2 yr. The telescope is equipped with a variety of terminal instruments. It has important scientific missions but limited observation time, so it is suggested to develop a 2.5 m coaxial telescope that will be co-orbiting with the space station. This additional telescope will mainly focus on time-domain surveys and IFS surveys. Its development budget is lower than the current 2 m off-axis telescope, CSST, but it offers superior system performance. Within the limited operational lifespan of the space station, it can significantly enhance the existing survey efficiency. Like the CSST, this telescope will be able to do multi-color imaging survey, and time-domain surveys are also under consideration.展开更多
It is widely known that the hypervelocity impact of orbital debris can cause serious damage to spacecraft,and enhancing the impact resistance is the great concern of spacecraft shield design.This paper provides a comp...It is widely known that the hypervelocity impact of orbital debris can cause serious damage to spacecraft,and enhancing the impact resistance is the great concern of spacecraft shield design.This paper provides a comprehensive overview of advances in the development of bumper materials for spacecraft shield applications.In particular,the protective mechanism and process of the bumper using different materials against hypervelocity impact are reviewed and discussed.The advantages and disadvantages of each material used in shield were discussed,and the performance under hypervelocity impact was given according to the specific configuration.This review provides the useful reference and basis for researchers and engineers to create bumper materials for spacecraft shield applications,and the contemporary challenges and future directions for bumper materials for spacecraft shield were presented.展开更多
This study presents an achievement of laser cooling of alkaline-earth atoms in the Chinese Space Station’s strontium(Sr)atomic space optical clock.The system’s core components,physical unit,optical unit,and electric...This study presents an achievement of laser cooling of alkaline-earth atoms in the Chinese Space Station’s strontium(Sr)atomic space optical clock.The system’s core components,physical unit,optical unit,and electrical unit,have a total volume of 306 L and a total mass of 163.8 kg.These compact and robust units can overcome mechanical vibrations and temperature fluctuations during space launch.The laser sources of the optical unit are composed of diode lasers,and the injection locking of slave lasers is automatically performed by a program.In the experiment,a blue magneto-optical trap of cold atoms was achieved,with the atom numbers estimated to be approximately(1.50±0.13)×10^(6) for 87Sr and(8.00±0.56)×10^(6) for 88Sr.This work establishes a foundation for atomic confinement and high-precision interrogation in space-based optical clocks and expands the frontiers of cold atom physics in microgravity.展开更多
China scheduled to complete the assembly of the T-shaped Tiangong Space Station in 2022,and will enter a new stage of utilization.There are more than 20 experiment racks inside the modules,and more than 50 external on...China scheduled to complete the assembly of the T-shaped Tiangong Space Station in 2022,and will enter a new stage of utilization.There are more than 20 experiment racks inside the modules,and more than 50 external onboard payloads mounting spaces,which will support large-scale science and technology experiments during the operation.The development of internal experiment racks and external research accommodations approved during the construction has been completed,of which 4 racks in Tianhe core module,including High Microgravity Level research Rack(HMLR)and Container-less Materials Processing Rack(CMPR),have finished on-orbit tests;while other racks in Wentian and Mengtian experiment modules are under comprehensive ground tests.The Chinese Space Survey Telescope(CSST)has advanced much in the last two years with 24 pre-launch research projects funded and 4 joint science center built in preparation for CSST’s future scientific observations and operations.The systematic research planning for China’s Space Station(CSS)during 2022-2032 is updated with the researches classified into four important areas:space life sciences and human research,microgravity physical sciences,space astronomy and Earth science,and new space technologies and applications.According to the planning,more than 1000 experiments are expected to perform in CSS during the operating period.Overall,the CSS utilization missions are proceeding as planned,which will contribute to the major scientific or application output and have a positive impact on the quality of life on Earth.展开更多
Chinese Space Station(CSS)has been fully deployed by the end of 2022,and the facility has entered into the application and development phase.It has conducted scientific research projects in various fields,such as spac...Chinese Space Station(CSS)has been fully deployed by the end of 2022,and the facility has entered into the application and development phase.It has conducted scientific research projects in various fields,such as space life science and biotechnology,space materials science,microgravity fundamental physics,fluid physics,combustion science,space new technologies,and applications.In this review,we introduce the progress of CSS development and provide an overview of the research conducted in Chinese Space Station and the recent scientific findings in several typical research fields.Such compelling findings mainly concern the rapid solidification of ultra-high temperature alloy melts,dynamics of fluid transport in space,gravity scaling law of boiling heat transfer,vibration fluidization phenomenon of particulate matter,cold atom interferometer technology under high microgravity and related equivalence principle testing,the full life cycle of rice under microgravity and so forth.Furthermore,the planned scientific research and corresponding prospects of Chinese space station in the next few years are presented.展开更多
The Strategic Priority Program(SPP)on Space Science,which is under the leadership of the Chinese Academy of Sciences(CAS),has established China’s space science satellite series from scratch.A number of major scientif...The Strategic Priority Program(SPP)on Space Science,which is under the leadership of the Chinese Academy of Sciences(CAS),has established China’s space science satellite series from scratch.A number of major scientific achievements have been made by the first phase of the Program(SPPⅠ),while SPPⅡhas been currently being implemented.The future development of space science needs urgent top-level planning and advanced layout to clarify the overall goal and investment portfolio from 2025 to 2030.We will briefly introduce the initiative and possible space science missions of SPPⅢ,including the preparatory work which already started in July 2021.Following the effective administrative tradition since SPPⅠ,National Space Science Center(NSSC,CAS)is responsible for the whole procedure,including soliciting,assessment,and implementation of SPPⅢ.Brief information on the 13 candidate missions will be described,including missions in the fields of astronomy&astrophysics,exoplanets,heliophysics and planetary&Earth science,respectively.展开更多
Existing orthogonal space-time block coding(OSTBC)schemes for backscatter communication systems cannot achieve a full transmission code rate when the tag is equipped with more than two antennas.In this paper,we propos...Existing orthogonal space-time block coding(OSTBC)schemes for backscatter communication systems cannot achieve a full transmission code rate when the tag is equipped with more than two antennas.In this paper,we propose a quasi-orthogonal spacetime block code(QOSTBC)that can achieve a full transmission code rate for backscatter communication systems with a four-antenna tag and then extend the scheme to support tags with 2i antennas.Specifically,we first present the system model for the backscatter system.Next,we propose the QOSTBC scheme to encode the tag signals.Then,we provide the corresponding maximum likelihood detection algorithms to recover the tag signals.Finally,simulation results are provided to demonstrate that our proposed QOSTBC scheme and the detection algorithm can achieve a better transmission code rate or symbol error rate performance for backscatter communication systems compared with benchmark schemes.展开更多
Since 2011,the Chinese Academy of Sciences(CAS)has implemented the Strategic Priority Program on Space Science(SPP).A series of scientific satellites have been developed and launched,such as Dark Matter Particle Explo...Since 2011,the Chinese Academy of Sciences(CAS)has implemented the Strategic Priority Program on Space Science(SPP).A series of scientific satellites have been developed and launched,such as Dark Matter Particle Explorer(DAMPE),Quantum Experiments at Space Scale(QUESS),Advanced Space-based Solar Observatory(ASO-S),Einstein Probe(EP),and significant scientific outcomes have been achieved.In order to plan the future space science missions in China,CAS has organized the Chinese space science community to conduct medium and long-term development strategy studies,and summarized the major scientific frontiers of space science as“One Black,Two Dark,Three Origins and Five Characterizations”.Five main scientific themes have been identified for China’s future breakthroughs,including the Extreme Universe,Space-Time Ripples,the Panoramic View of the Sun and Earth,the Habitable Planets,and Biological&Physical Science in Space.Space science satellite missions to be implemented before 2030 are proposed accordingly.展开更多
基金supported by the National Natural Science Foundation of China(T2192933).
文摘As humanity ventures deeper into space,our challenges become increasingly complex.Space medicine,once confi ned to ensuring the health and safety of astronauts on low-Earth orbit missions,is now tasked with ensuring the health and safety of astronauts embarking on extended missions to the Moon,Mars,and beyond.Th e advancement of space medicine and the conduct of in-orbit medical experiments not only determine the boundaries of human exploration of the cosmos but also provide new insights that can benefi t human health on Earth.
文摘3D printing technology can realize the rapid fabrication of complicated structures with short production chain,which just meet the requirements for space manufacturing in the future.This Special Issue features the cutting-edge 3D printing technologies considering the space environment,focusing on the experimental validation and simulation on the 3D printing process and structural technologies,including whole process chain from raw materials,structural design,process,equipment,as well as functional verification.
基金supported by the National Key R&D Program of China(No.2022YFB3104502)the National Natural Science Foundation of China(No.62301251)+2 种基金the Natural Science Foundation of Jiangsu Province of China under Project(No.BK20220883)the open research fund of National Mobile Communications Research Laboratory,Southeast University,China(No.2024D04)the Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001).
文摘The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-dimension collision-free trajectory planning is the prerequisite to ensure airspace security.However,the timely information of surrounding situation is difficult to acquire by UAVs,which further brings security risks.As a mature technology leveraged in traditional civil aviation,the Automatic Dependent Surveillance-Broadcast(ADS-B)realizes continuous surveillance of the information of aircraft.Consequently,we leverage ADS-B for surveillance and information broadcasting,and divide the aerial airspace into multiple sub-airspaces to improve flight safety in UAV trajectory planning.In detail,we propose the secure Sub-airSpaces Planning(SSP)algorithm and Particle Swarm Optimization Rapidly-exploring Random Trees(PSO-RRT)algorithm for the UAV trajectory planning in law-altitude airspace.The performance of the proposed algorithm is verified by simulations and the results show that SSP reduces both the maximum number of UAVs in the sub-airspace and the length of the trajectory,and PSO-RRT reduces the cost of UAV trajectory in the sub-airspace.
基金This mission was supported by the China Manned Space Office。
文摘The energetic particle detector on China's space station can determine the energy, flux, and direction of medium-and highenergy protons, electrons, heavy ions, and neutrons within the path of the station's orbit. It also assesses the linear energy transfer(LET)spectra and radiation dose rates generated by these particles. Neutron detection is a significant component of this work, utilizing a new type of Cs_(2)LiYCl_(6): Ce scintillator material along with plastic scintillators as sensors. In-orbit testing has demonstrated the efficient identification of space neutrons and gamma rays(n/γ). This data plays a crucial role in supporting manned space engineering, scientific research, and other related fields.
基金supported by the Special Funding Project for Space Debris and Near-Earth Asteroids Defense Research, China (No. KJSP2023020303)Beijing Municipal Science and Technology Commission, China (No. Z181100002918004)the Youth Innovation Promotion Association, Chinese Academy of Sciences (No. 2022146)
文摘Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetary defense strategy. Different from those conducted asteroid flyby missions, in the 12th China Trajectory Optimization Competition (CTOC-12), a NEAs flyby trajectory design problem using reusable probes that depart from a Lunar Distant Retrograde Orbit (DRO) station in the cislunar space was released. The objective was flyby to as many NEAs as possible using up to 20 probes within a total of 10 years. The ∑ team proposed a solution that can explore 47 NEAs using 11 probes, ranking the first in the competition. In this paper, the methods and results from the winning team are introduced, including mission analysis and preliminary design, and low-energy transfer trajectory optimization. In particular, a round-trip trajectory is divided into three phases: deep space transfer, indirect transfer between the Earth to DRO, and DRO phasing and rendezvous. With the combination of global optimization and local optimization algorithms, the required velocity increments to change the orbital planes are effectively reduced, thus increasing the number of the explored NEAs. The final solution of our team is presented and the results are compared with those of the top three teams. The competition demonstrates that the regularization of flyby missions from the cislunar space to explore NEAs with the potential impact risks to the Earth is the feasible and promising.
基金financially supported by Harbin Ship Boiler and Turbine Research Institute Stability Support Project and Heilongjiang Province Young Scientific and Technological Talent Lift Project(No.2023QNTJ)
文摘Graphene-copper(Gr-Cu)composites exhibit significant potential for industrial applications.Among the methods for fabricating Gr-Cu composites,the in-situ growth method stands out as a simple yet effective approach.However,graphene converted from liquid or solid molecules by the traditional in-situ growth method often exhibits numerous defects,thereby reducing its effectiveness in enhancing the electrical properties of the composites.To address this issue,we developed an innovative and efficient method,referred to as the“confinedparallel-space in-situ growth(CPS)method,”to grow highquality graphene and fabricate high-conductivity Gr-Cu composites.Oleic acid was chosen as the small molecular carbon source and confined between copper sheets obtained by rolling dendritic copper powder.This carbon source underwent conversion into oriented,high-quality graphene in the confined space at high temperature.The high-quality graphene sheets serve as continuous electron transport channels,significantly improving the conductivity of the composite.The composite prepared by the CPS method(CPS-composite)demonstrates unique conductivity,exceeding that of standard annealed copper at temperatures above 40℃and notably outperforming it by 3.2%at160℃.In addition,compared to the composite with a similar carbon content prepared by the traditional in-situ growth method,the yield strength of the CPS-composite increased by 23.6%,while the strengthening efficiency of graphene improved by 146.6%,achieving an ultrahigh value of 489 at a carbon volume fraction of 0.086 vol%.The CPS method emerges as a novel strategy for fabricating high-performance,low-cost,and large-scale graphene-copper composites using small molecular carbon sources,making it suitable for industrial production.
文摘In order to solve the problem that the star point positioning accuracy of the star sensor in near space is decreased due to atmospheric background stray light and rapid maneuvering of platform, this paper proposes a star point positioning algorithm based on the capsule network whose input and output are both vectors. First, a PCTL (Probability-Coordinate Transformation Layer) is designed to represent the mapping relationship between the probability output of the capsule network and the star point sub-pixel coordinates. Then, Coordconv Layer is introduced to implement explicit encoding of space information and the probability is used as the centroid weight to achieve the conversion between probability and star point sub-pixel coordinates, which improves the network’s ability to perceive star point positions. Finally, based on the dynamic imaging principle of star sensors and the characteristics of near-space environment, a star map dataset for algorithm training and testing is constructed. The simulation results show that the proposed algorithm reduces the MAE (Mean Absolute Error) and RMSE (Root Mean Square Error) of the star point positioning by 36.1% and 41.7% respectively compared with the traditional algorithm. The research results can provide important theory and technical support for the scheme design, index demonstration, test and evaluation of large dynamic star sensors in near space.
基金co-supported by the National Natural Science Foundation of China(No.12372045)the Guangdong Basic and Applied Basic Research Foundation,China(No.2023B1515120018)the Shenzhen Science and Technology Program,China(No.JCYJ20220818102207015).
文摘The increasing complexity of on-orbit tasks imposes great demands on the flexible operation of space robotic arms, prompting the development of space robots from single-arm manipulation to multi-arm collaboration. In this paper, a combined approach of Learning from Demonstration (LfD) and Reinforcement Learning (RL) is proposed for space multi-arm collaborative skill learning. The combination effectively resolves the trade-off between learning efficiency and feasible solution in LfD, as well as the time-consuming pursuit of the optimal solution in RL. With the prior knowledge of LfD, space robotic arms can achieve efficient guided learning in high-dimensional state-action space. Specifically, an LfD approach with Probabilistic Movement Primitives (ProMP) is firstly utilized to encode and reproduce the demonstration actions, generating a distribution as the initialization of policy. Then in the RL stage, a Relative Entropy Policy Search (REPS) algorithm modified in continuous state-action space is employed for further policy improvement. More importantly, the learned behaviors can maintain and reflect the characteristics of demonstrations. In addition, a series of supplementary policy search mechanisms are designed to accelerate the exploration process. The effectiveness of the proposed method has been verified both theoretically and experimentally. Moreover, comparisons with state-of-the-art methods have confirmed the outperformance of the approach.
文摘This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1005000)the National Natural Science Foundation of China(Grant No.62101308 and 62025110).
文摘Space laser communication(SLC)is an emerging technology to support high-throughput data transmissions in space networks.In this paper,to guarantee the reliability of high-speed SLC links,we aim at practical implementation of low-density paritycheck(LDPC)decoding under resource-restricted space platforms.Particularly,due to the supply restriction and cost issues of high-speed on-board devices such as analog-to-digital converters(ADCs),the input of LDPC decoding will be usually constrained by hard-decision channel output.To tackle this challenge,density-evolution-based theoretical analysis is firstly performed to identify the cause of performance degradation in the conventional binaryinitialized iterative decoding(BIID)algorithm.Then,a computation-efficient decoding algorithm named multiary-initialized iterative decoding with early termination(MIID-ET)is proposed,which improves the error-correcting performance and computation efficiency by using a reliability-based initialization method and a threshold-based decoding termination rule.Finally,numerical simulations are conducted on example codes of rates 7/8 and 1/2 to evaluate the performance of different LDPC decoding algorithms,where the proposed MIID-ET outperforms the BIID with a coding gain of 0.38 dB and variable node calculation saving of 37%.With this advantage,the proposed MIID-ET can notably reduce LDPC decoder’s hardware implementation complexity under the same bit error rate performance,which successfully doubles the total throughput to 10 Gbps on a single-chip FPGA.
文摘In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator estimates are motivated by the study of well-posedness results for some models in incompressible fuid mechanics.
文摘The China Space Station Telescope(CSST) is primarily designed for large-scale multi-color imaging and seamless spectroscopic survey, while also accommodating observations with an integral field spectrograph(IFS), multichannel imaging, direct imaging of exoplanets, and terahertz-band observations. It is scheduled to be launched in about 2 yr. The telescope is equipped with a variety of terminal instruments. It has important scientific missions but limited observation time, so it is suggested to develop a 2.5 m coaxial telescope that will be co-orbiting with the space station. This additional telescope will mainly focus on time-domain surveys and IFS surveys. Its development budget is lower than the current 2 m off-axis telescope, CSST, but it offers superior system performance. Within the limited operational lifespan of the space station, it can significantly enhance the existing survey efficiency. Like the CSST, this telescope will be able to do multi-color imaging survey, and time-domain surveys are also under consideration.
基金supported by National Natural Science Foundation of China(Grant Nos.12202068,12202087)China National Space Administration Preliminary Research Project(Grant Nos.KJSP2023020201,KJSP2020010402).
文摘It is widely known that the hypervelocity impact of orbital debris can cause serious damage to spacecraft,and enhancing the impact resistance is the great concern of spacecraft shield design.This paper provides a comprehensive overview of advances in the development of bumper materials for spacecraft shield applications.In particular,the protective mechanism and process of the bumper using different materials against hypervelocity impact are reviewed and discussed.The advantages and disadvantages of each material used in shield were discussed,and the performance under hypervelocity impact was given according to the specific configuration.This review provides the useful reference and basis for researchers and engineers to create bumper materials for spacecraft shield applications,and the contemporary challenges and future directions for bumper materials for spacecraft shield were presented.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB35010202)the National Natural Science Foundation of China(Grants No.62275268)。
文摘This study presents an achievement of laser cooling of alkaline-earth atoms in the Chinese Space Station’s strontium(Sr)atomic space optical clock.The system’s core components,physical unit,optical unit,and electrical unit,have a total volume of 306 L and a total mass of 163.8 kg.These compact and robust units can overcome mechanical vibrations and temperature fluctuations during space launch.The laser sources of the optical unit are composed of diode lasers,and the injection locking of slave lasers is automatically performed by a program.In the experiment,a blue magneto-optical trap of cold atoms was achieved,with the atom numbers estimated to be approximately(1.50±0.13)×10^(6) for 87Sr and(8.00±0.56)×10^(6) for 88Sr.This work establishes a foundation for atomic confinement and high-precision interrogation in space-based optical clocks and expands the frontiers of cold atom physics in microgravity.
文摘China scheduled to complete the assembly of the T-shaped Tiangong Space Station in 2022,and will enter a new stage of utilization.There are more than 20 experiment racks inside the modules,and more than 50 external onboard payloads mounting spaces,which will support large-scale science and technology experiments during the operation.The development of internal experiment racks and external research accommodations approved during the construction has been completed,of which 4 racks in Tianhe core module,including High Microgravity Level research Rack(HMLR)and Container-less Materials Processing Rack(CMPR),have finished on-orbit tests;while other racks in Wentian and Mengtian experiment modules are under comprehensive ground tests.The Chinese Space Survey Telescope(CSST)has advanced much in the last two years with 24 pre-launch research projects funded and 4 joint science center built in preparation for CSST’s future scientific observations and operations.The systematic research planning for China’s Space Station(CSS)during 2022-2032 is updated with the researches classified into four important areas:space life sciences and human research,microgravity physical sciences,space astronomy and Earth science,and new space technologies and applications.According to the planning,more than 1000 experiments are expected to perform in CSS during the operating period.Overall,the CSS utilization missions are proceeding as planned,which will contribute to the major scientific or application output and have a positive impact on the quality of life on Earth.
文摘Chinese Space Station(CSS)has been fully deployed by the end of 2022,and the facility has entered into the application and development phase.It has conducted scientific research projects in various fields,such as space life science and biotechnology,space materials science,microgravity fundamental physics,fluid physics,combustion science,space new technologies,and applications.In this review,we introduce the progress of CSS development and provide an overview of the research conducted in Chinese Space Station and the recent scientific findings in several typical research fields.Such compelling findings mainly concern the rapid solidification of ultra-high temperature alloy melts,dynamics of fluid transport in space,gravity scaling law of boiling heat transfer,vibration fluidization phenomenon of particulate matter,cold atom interferometer technology under high microgravity and related equivalence principle testing,the full life cycle of rice under microgravity and so forth.Furthermore,the planned scientific research and corresponding prospects of Chinese space station in the next few years are presented.
基金Supported by Strategic Priority Research Program of the Chinese Academy of Sciences(XDA15060102)。
文摘The Strategic Priority Program(SPP)on Space Science,which is under the leadership of the Chinese Academy of Sciences(CAS),has established China’s space science satellite series from scratch.A number of major scientific achievements have been made by the first phase of the Program(SPPⅠ),while SPPⅡhas been currently being implemented.The future development of space science needs urgent top-level planning and advanced layout to clarify the overall goal and investment portfolio from 2025 to 2030.We will briefly introduce the initiative and possible space science missions of SPPⅢ,including the preparatory work which already started in July 2021.Following the effective administrative tradition since SPPⅠ,National Space Science Center(NSSC,CAS)is responsible for the whole procedure,including soliciting,assessment,and implementation of SPPⅢ.Brief information on the 13 candidate missions will be described,including missions in the fields of astronomy&astrophysics,exoplanets,heliophysics and planetary&Earth science,respectively.
基金supported by Beijing Municipal Natural Science Foundation(L222002)the Natural Science Foundation of China(U22B2004).
文摘Existing orthogonal space-time block coding(OSTBC)schemes for backscatter communication systems cannot achieve a full transmission code rate when the tag is equipped with more than two antennas.In this paper,we propose a quasi-orthogonal spacetime block code(QOSTBC)that can achieve a full transmission code rate for backscatter communication systems with a four-antenna tag and then extend the scheme to support tags with 2i antennas.Specifically,we first present the system model for the backscatter system.Next,we propose the QOSTBC scheme to encode the tag signals.Then,we provide the corresponding maximum likelihood detection algorithms to recover the tag signals.Finally,simulation results are provided to demonstrate that our proposed QOSTBC scheme and the detection algorithm can achieve a better transmission code rate or symbol error rate performance for backscatter communication systems compared with benchmark schemes.
基金Supported by Consultation and Evaluation Program on Academic Divisions of the Chinese Academy of Sciences(2022-DX02-B-007)。
文摘Since 2011,the Chinese Academy of Sciences(CAS)has implemented the Strategic Priority Program on Space Science(SPP).A series of scientific satellites have been developed and launched,such as Dark Matter Particle Explorer(DAMPE),Quantum Experiments at Space Scale(QUESS),Advanced Space-based Solar Observatory(ASO-S),Einstein Probe(EP),and significant scientific outcomes have been achieved.In order to plan the future space science missions in China,CAS has organized the Chinese space science community to conduct medium and long-term development strategy studies,and summarized the major scientific frontiers of space science as“One Black,Two Dark,Three Origins and Five Characterizations”.Five main scientific themes have been identified for China’s future breakthroughs,including the Extreme Universe,Space-Time Ripples,the Panoramic View of the Sun and Earth,the Habitable Planets,and Biological&Physical Science in Space.Space science satellite missions to be implemented before 2030 are proposed accordingly.
