Aiming at the interception problem of noncooperative evader spacecraft adopting random maneuver strategy in one-to-one orbital pursuit-evasion problem,an interception strategy with decision-making training mechanism f...Aiming at the interception problem of noncooperative evader spacecraft adopting random maneuver strategy in one-to-one orbital pursuit-evasion problem,an interception strategy with decision-making training mechanism for the pursuer based on deep reinforcement learning is proposed.Its core purpose is to improve the success rate of interception in the environment with high uncertainty.First of all,a multi-impulse orbit transfer model of pursuer and evader is established,and a modular deep reinforcement learning training method is built.Second,an effective reward mechanism is proposed to train the pursuer to choose the impulse direction and impulse interval of the orbit transfer and to learn the successful interception strategy with the optimal fuel and time.Finally,with the evader taking a random maneuver decision in each episode of training,the trained decision-making strategy is applied to the pursuer,the corresponding interception success rate of which is further analyzed.The results show that the pursuer trained can obtain universal and variable interception strategy.In each round of pursuit-evasion,with random maneuver strategy of the evader,the pursuer can adopt similar optimal decisions to deal with high-dimensional environments and thoroughly random state space,maintaining high interception success rate.展开更多
For the challenging problem that a spacecraft approaches a tumbling target with non-cooperative maneuver,an anti-saturated proximity control method is proposed in this paper.First,a brand-new appointed-time convergent...For the challenging problem that a spacecraft approaches a tumbling target with non-cooperative maneuver,an anti-saturated proximity control method is proposed in this paper.First,a brand-new appointed-time convergent performance function is developed via exploring Bézier curve to quantitatively characterize the transient and steady-state behaviors of the pose tracking error system.The major advantage of the proposed function is that the actuator saturation phenomenon at the beginning can be effectively reduced.Then,an anti-saturated pose tracking controller is devised along with an adaptive saturation compensator.Wherein,the finite-time stability of both the pose and its velocity error signals are guaranteed simultaneously in the presence of actuator saturation.Finally,2 groups of illustrative examples are organized and verify that the close-range proximity is effectively realized even with unknown target maneuver.展开更多
This paper discusses the modeling and solving of orbital pursuit-evasion games(OPEGs)under J_(2)perturbation.The optimal long-range maneuver method under J_(2)perturbation is designed,and it is proved that the effect ...This paper discusses the modeling and solving of orbital pursuit-evasion games(OPEGs)under J_(2)perturbation.The optimal long-range maneuver method under J_(2)perturbation is designed,and it is proved that the effect of eccentricity can be ignored when transfer times and theΔV budgets are fixed.It is discovered that when the inclination between the initial and target orbit is equal and is between 10°and 25°,the whole maneuver process can be simplified to a fixed-inclination transfer.Subsequently,a long-term OPEG model is provided under the assumption of fixed inclination,zero eccentricity,and impulsive thrust.Winning conditions of OPEGs under J_(2)perturbation are then carefully derived,with long-time OPEG(J_(2)dominated)and short-time OPEG(traditional)separated,and typical tactics of both sides formulated and verified.These studies are further extended to the“Arrival time matching game”for maintaining/avoiding resonant arrival time under J_(2)perturbation,and the advantages and disadvantages of both sides are analyzed.The models and strategies obtained in this paper can be potentially used in practical applications of OPEGs,especially for evaders that have low thrust-weight ratios and are weak in traditional short-term OPEGs.展开更多
Collision probability is employed for evaluating whether there will be a dangerous encounter between 2 space objects.The fidelity of the collision probability mainly depends on the accuracies of orbit prediction and c...Collision probability is employed for evaluating whether there will be a dangerous encounter between 2 space objects.The fidelity of the collision probability mainly depends on the accuracies of orbit prediction and covariance prediction for the space objects.In this paper,the collision probability between the Tsinghua Gravitation and Atmosphere Science Satellite,Q-Sat,and the space debris with a North American Aerospace Defense Command ID of 49863 on 2022 January 18 was calculated.The 2 objects approached each other dangerously close and the event was reported.First,the atmospheric density model is modified by a dynamic approach-based inversion to improve the accuracy of orbit prediction for the Q-Sat.Next,predictions of position error covariance are carried out.Orbits of the next 24 hours are predicted,and the predicted orbits are compared with the actual orbits of the Q-Sat.Backpropagation neural network was trained for predicting the position error covariance.For the space debris,the 2-line element data are employed.Orbit predictions for the space debris are also conducted and compared with the actual orbit.Another backpropagation neural network for predicting the position error covariance for the space debris is trained.Using the covariances from the backpropagation neural network,the error ellipsoids of the 2 objects are established.The error ellipsoids are later projected to the encounter plane to calculate the collision probability.Different from the reports from other institutes,the closest distance between the Q-Sat and the space debris calculated by the current method was 2.71 km.The collision probability was 1.16×10−11.It was not a dangerous encounter event.The onboard precise orbit determination device enabled improved orbit determination precision and orbit prediction accuracy,which is important for space safety management.展开更多
Along with the rapid development of space technology,extraterrestrial exploration has gradually tended to further-distanced and longer-termed planet exploration.As the first step of an attempt for humans to build a pe...Along with the rapid development of space technology,extraterrestrial exploration has gradually tended to further-distanced and longer-termed planet exploration.As the first step of an attempt for humans to build a perpetual planet base,building a lunar base by in situ resource utilization(ISRU)will drastically reduce the reliance of supplies from Earth.Lunar resources including mineral resources,water/ice resources,volatiles,and solar energy will contribute to the establishment of a lunar base for long-term life support and scientific exploration missions,although we must consider the challenges from high vacuum,low gravity,extreme temperature conditions,etc.This article provides a comprehensive review of the past developing processes of ISRU and the latest progress of several ISRU technologies,including in situ water access,in situ oxygen production,in situ construction and manufacture,in situ energy utilization,and in situ life support and plant cultivation on the Moon.Despite being able to provide some material and energy supplies for lunar base construction and scientific exploration,the ISRU technologies need continuous validation and upgrade to satisfy the higher requirements from further lunar exploration missions.Ultimately,a 3-step development plan for lunar ISRU technologies in the next decade is proposed,which consists of providing technological solutions,conducting technical verification on payloads,and carrying out in situ experiments,with the ultimate aim of establishing a permanent lunar station and carrying out long-term lunar surface scientific activities.The overview of ISRU techniques and our suggestions will provide potential guidance for China’s future lunar exploration missions.展开更多
After more than 7 years of development,the Tianzhou cargo spacecraft(TZ),a space station cargo transfer spacecraft,was successfully launched on 2017 April 20.The TZ is robotic spacecraft that is designed to support Ch...After more than 7 years of development,the Tianzhou cargo spacecraft(TZ),a space station cargo transfer spacecraft,was successfully launched on 2017 April 20.The TZ is robotic spacecraft that is designed to support China space station operation by transporting pressurized cargo,unpressurized cargo,large cargo,propellant,and other supplies.The vehicle is equipped with the crew specifications necessary for astronauts to unload pressurized cargo.TZ can be utilized for a variety of commercial,engineering,scientific,or other proposed activities once its primary mission is complete.TZ is China's first dedicated space cargo transport spacecraft,but the safety designs for crew activities are also particular to TZ.Newly developed technologies were applied to enable high-efficiency cargo shipment.Its development was carried out under the policy of adopting flight-proven technologies to enhance the reliability and safety of a mission.The success of the flight test of the TZ-1 cargo spacecraft marked the perfect end of the mission of the China Space Laboratory and laid the foundation for the smooth implementation of the manned space station project.As a novel manned spacecraft,TZ-1 has broken through key technologies such as cargo transportation,propellant replenishment,and fully autonomous rapid rendezvous and docking.TZ has the characteristics of high transport efficiency,multitasks,and strong self-control ability.The paper describes the phylogeny,main technical schemes,and technological achievements of China TZ.展开更多
This paper proposed a new attitude determination method for low-orbit spacecraft.The attitude prediction accuracy is greatly improved by adding the unmodeled environmental torque to the dynamic equation.Specifically,t...This paper proposed a new attitude determination method for low-orbit spacecraft.The attitude prediction accuracy is greatly improved by adding the unmodeled environmental torque to the dynamic equation.Specifically,the environmental torque extraction algorithm based on extended Kalman filter and series extended state observer is introduced,and the unmodeled part of dynamic is identified through the inverse dynamic model.Then,the collected data are analyzed and trained by a backpropagation neural network,resulting in an attitude-torque mapping network with compensation ability.The simulation results show that the proposed feedback attitude prediction algorithm can outperform standard methods and provide a high accurate picture of prediction and reliability with discontinuous measurement.展开更多
The tethered TSAR(tomographic synthetic aperture radar)system is a group of tethered SAR satellites that can be rapidly deployed and provide a stable baseline for 3-dimensional topographic mapping and moving target de...The tethered TSAR(tomographic synthetic aperture radar)system is a group of tethered SAR satellites that can be rapidly deployed and provide a stable baseline for 3-dimensional topographic mapping and moving target detection.Successful deployment is critical for TSAR tethered system.This paper discusses the deployment strategy for a 3-body chain-type tethered satellite system in a low-eccentric elliptical orbit.Two deployment strategies are discussed.Then,the tension on the tether is used to deploy it to the desired length and suppress its sway motion,resulting in an underactuated and input-constrained system.Hierarchical sliding mode control(HSMC)with anti-windup technology is employed to overcome the above challenges.In addition,the proposed approach includes the use of a disturbance observer to estimate the second derivative signal and a robust differentiator to estimate the sliding surfaces of the unacted subsystem.Finally,the effectiveness of the proposed deployment strategy is verified by MATLAB/Simulink.展开更多
Countermeasures in weightlessness are a predominant technique for long-term residency in space.Head-down bed rest(HDBR)has long been used to simulate the physiological effects of spaceflight and test the efficacy of c...Countermeasures in weightlessness are a predominant technique for long-term residency in space.Head-down bed rest(HDBR)has long been used to simulate the physiological effects of spaceflight and test the efficacy of countermeasures.In 2019,the Astronaut Center of China(ACC)has held a 90-d HDBR on the effects of exercises’intervention.Thirty-six subjects were recruited and randomized into 5 intervention groups:(a)control,(b)aerobic exercises,(c)resistance exercises,(d)concurrent aerobic and lower load resistance exercises,and(e)concurrent aerobic and high-load resistance exercises.Moreover,exercise interventions were performed in supine or 6°head-down tilt.They were provided with plain medical,psychological,and nutritional supports during the experiment.In addition,cardiovascular and pulmonary functions,muscle strength,bone density,and neuro-immune-endocrine functions were assessed over time.Subjects were monitored by clinical evaluations,psychological assessments,and nutritional status evaluations.All subjects spent 138 d in the bed rest study laboratory and received 2 follow-up tests per 3 months in the home recovery period.It was found that exercises in the 4 groups were effective interventions for aerobic capacity compared with control.The resistance exercises or concurrent aerobic and high-load resistance exercises improved isometric maximal voluntary contraction.However,the protection against bone loss still needs further exploration.Appropriate psychosocial and nutrition support techniques are worth to be reinforced.展开更多
Impact craters are one of the most important landforms on the lunar surface,playing a crucial role in the formation and later evolution of the Moon.For example,as a primary source of remote sensing observations and lu...Impact craters are one of the most important landforms on the lunar surface,playing a crucial role in the formation and later evolution of the Moon.For example,as a primary source of remote sensing observations and lunar samples,lunar regolith is predominantly composed of impact ejecta.Based on their morphologies,lunar impact craters with increasing sizes can be classified into simple craters,complex craters,and multiring basins,and they play different roles in lunar evolution.In our study,we conducted numerical simulations of the South Pole-Aitken basin and the Orientale basin on the lunar surface,as well as the Aristarchus complex crater and the Zhinyu simple crater.The resultant effects of them are further analyzed.Because Zhinyu crater is relatively close to the Chang’e-4 landing site,while Aristarchus crater is relatively close to the Chang’e-5 landing site,their simulation results have direct significance for interpreting the corresponding exploration data from both missions.The numerical simulation results demonstrate that the formation of large basins not only affects the subsurface structure within the basin but also significantly disturbs the surrounding geological layers.Complex and simple craters mainly disturb the subsurface layers within the crater,but complex craters can cause uplift of the underlying strata.These impact processes dominate the primary geological framework of the lunar surface,depositing ejecta materials of varying thicknesses from different depths,which has important implications for future sample collection missions.In conclusion,impact processes are one of the primary driving forces in the lunar evolution.展开更多
Considering the demand of distributed satellite clusters for high-speed information communication in the future,this paper establishes a laser network model based on optical multibeam antenna.At present,there are stil...Considering the demand of distributed satellite clusters for high-speed information communication in the future,this paper establishes a laser network model based on optical multibeam antenna.At present,there are still some networking and reconstruction problems,such as network connectivity,duration,and stability.To address them,the paper develops a multiobjective optimization model for the laser networking of distributed satellite clusters,which aims to maximize network connectivity and network duration and minimize the perturbation of the network connection matrix.The model is constructed under the constraints of multibeam antenna capability,the visibility of satellites in clusters,and network connectivity.From the perspectives of the optimization effect and timeliness of the optimization algorithm,a deep reinforcement learning algorithm is proposed,which is based on a double-layer Markov decision model,to meet the needs of on-orbit intelligent networking and dynamic reconstruction of distributed satellite clusters.Simulation results show that the algorithm features flexible architecture,excellent networking performance,and strong real-time performance.When the optimization results are similar,the proposed algorithm outperforms the nonsorted genetic algorithm II algorithm and the particle swarm optimization algorithm in terms of solution speed.展开更多
As a manned spacecraft operating in orbit for a long time,a space station embodies a country’s scientific and technological strength comprehensively.Building a space station is the final target of the 3-step strategy...As a manned spacecraft operating in orbit for a long time,a space station embodies a country’s scientific and technological strength comprehensively.Building a space station is the final target of the 3-step strategy of China’s manned space program.This paper introduces the design of the Tiangong space station in terms of its design principles,overall scheme,building process,and special system design.On this basis,the paper analyzes and summarizes the technical characteristics of the Tiangong space station in the aspects of system design and optimization,the large proportion of new technologies,the excellent cost-effectiveness ratio,and the high safety and efficiency of the crew’s residence.Finally,it discusses the future application and development of the Tiangong space station.展开更多
Satellite communication is an indispensable part of future wireless communications given its global coverage and long-distance propagation.In satellite communication systems,channel acquisition and energy consumption ...Satellite communication is an indispensable part of future wireless communications given its global coverage and long-distance propagation.In satellite communication systems,channel acquisition and energy consumption are two critical issues.To this end,we investigate the tradeoff between the total energy efficiency(TEE)and minimum EE(MEE)for robust multigroup multicast satellite communication systems in this paper.Specifically,under the total power constraint,we investigate the robust beamforming aimed at balancing the TEE-MEE,so as to achieve the balance between the fairness and total performance on the system EE.For this optimization problem,we first model the balancing problem as a nonconvex problem while deriving its approximate closed-form average user rate.Then,the nonconvex problem is handled by solving convex programs sequentially with the help of the semidefinite relaxation and the concave-convex procedure.In addition,depending on the solution rank value,Gaussian randomization and eigenvalue decomposition method are applied to generate the feasible solutions.Finally,simulation results illustrate that the proposed approach can effectively achieve the balance between the TEE and MEE,thus realizing a tradeoff between fairness and system EE performance.It is also indicated that the proposed robust approach outperforms the conventional baselines in terms of EE performance.展开更多
Since the 1990s,the existence of water-ice in the permanent shadow areas of the lunar polar regions and the problem of water in the early lunar period have become the hot spot of international lunar exploration.This p...Since the 1990s,the existence of water-ice in the permanent shadow areas of the lunar polar regions and the problem of water in the early lunar period have become the hot spot of international lunar exploration.This paper analyzes the research progress and existing problems of lunar water-ice detection in recent years.Based on the analysis of expected foreign lunar water-ice exploration missions,the major scientific problems of lunar water-ice are analyzed.From different exploration methods,this paper tentatively puts forward the scientific tasks,payload configuration,functional requirements,and possible scientific outputs of water-ice in China's future lunar exploration projects,which can provide reference for future lunar exploration missions.展开更多
Today,the discussion about colonizing different planets has shifted from the"IF"mode to the"WHEN"mode,and the substantial large group of humans living for a long time in an isolated,hostile,and enc...Today,the discussion about colonizing different planets has shifted from the"IF"mode to the"WHEN"mode,and the substantial large group of humans living for a long time in an isolated,hostile,and enclosed environment is about to become a reality.Thus,the space-related healthcare methodologies should shift as well from a small number of selected persons to much more extensive groups with much less health homogeneity.Moreover,the development of human colonies,first on the Moon and later on Mars,will be a game changer in allthat we know and use to see in space travel and eventually in space health.Humans will leave Earth but will carry human society's health patterns,adjusted to the environment.The foundation for space epidemiology modeling can be set today and should attract the attention of the epidemiological and space research communities.展开更多
Many studies have shown that spaceflight causes oxidative stress and induces brain disorder in astronauts,but the counter measurements are lacking.Increasing evidence demonstrated that hydrogen can act as a therapeuti...Many studies have shown that spaceflight causes oxidative stress and induces brain disorder in astronauts,but the counter measurements are lacking.Increasing evidence demonstrated that hydrogen can act as a therapeutic antioxidant.In this study,rats were treated with or without about 5%hydrogen under hindlimb unloading or normal conditions for 28 d.We assessed rat’s brain function by open-field test,step-down passive avoidance test,the neurotransmitter’s level detected by liquid chromatography with tandem mass spectrometry,and Nissl and hematoxylin-eosin staining analysis.We also assessed the oxidative damage by changes of malondialdehyde level,the ratio of reduced glutathione to oxidized glutathione,and superoxide dismutase and catalase activity.Glucose metabolism disorder was disclosed through glucose metabolomic analysis.The underlying mechanism of the effects of hydrogen was analyzed by mRNA sequencing and detecting mRNA and protein levels.Our data showed that hindlimb unloading caused oxidative damage and glucose metabolism disorder in brain tissues and decreased brain function in rats.Hydrogen inhalation reduced oxidative damage,ameliorated glucose metabolism disorder,and alleviated the dysfunction of rat brain function.Peroxisome-proliferator-activated receptor gamma coactivator 1αand brain-derived neurotrophic factor,the key regulators of glucose metabolism and brain function,were obviously affected.This research confirms the protective effect of hydrogen inhalation on declining brain function under hindlimb unloading conditions and discloses the underlying mechanism,which provides a potential strategy for astronauts’health.展开更多
The mixed terrains of terramechanics research are mainly composed of static stones and loose soil.The movement behavior of stones is often ignored while analyzing the influence of the wheel’s traction performance cau...The mixed terrains of terramechanics research are mainly composed of static stones and loose soil.The movement behavior of stones is often ignored while analyzing the influence of the wheel’s traction performance caused by mixed terrain.When a wheel is in contact with the movable stone and with the loose soil at the same time,the residual soil model,therefore,is proposed to simulate the change of the contact force between the wheel and the remaining loose soil caused by the failure of the loose soil in the area covered by stone.The plastic homogeneous soil mechanics model is proposed based on the soil’s mechanical properties.It is used for simulating the reaction force provided by soil to the moving stones.These mechanical models are compiled into the simulation programs,which are called by Adams to calculate the contact forces and moments of the planetary rover’s wheels in the mixed terrain with the movable stone and loose soil.Carrying out soil bin tests under the same experimental conditions,the comparative analysis of the simulation and experiment for a wheel in contact with 4 types of stones shows that the comparison results are in good agreement,which can verify the effectiveness of the proposed models to an extent.展开更多
With the increasing number of satellites being launched in China,the demand for Telemetry,Tracking,and Command(TT&C)resources is also increasing.Because of the global coverage and resource requirements of TT&C...With the increasing number of satellites being launched in China,the demand for Telemetry,Tracking,and Command(TT&C)resources is also increasing.Because of the global coverage and resource requirements of TT&C management,this paper proposes a TT&C scheme based on the Global Short-Message Communication System(GSMCS)of the BeiDou-3 Navigation Satellite System(BDS-3).The system composition,workflow,and functions of satellite TT&C are analyzed using the GSMCS of BDS-3.Through the coverage analysis of the Medium Earth Orbit(MEO)constellation of BDS-3,scheme’s applicability is pointed out,and the correctness of the analysis results is verified via simulation.The value range of the link distance is derived by calculating the range of the distance variation between any 2 satellites in the BDS-3 MEO constellation and combining the intersatellite routing scheme.The calculation results show that the response time range of the autonomous request management application of in-orbit satellites based on the GSMCS of BDS-3 is 1.407 to 2.448 s.This can meet the requirements of TT&C service.展开更多
A reinforcement learning-based approach is proposed to design the multi-impulse rendezvous trajectories in linear relative motions.For the relative motion in elliptical orbits,the relative state propagation is obtaine...A reinforcement learning-based approach is proposed to design the multi-impulse rendezvous trajectories in linear relative motions.For the relative motion in elliptical orbits,the relative state propagation is obtained directly from the state transition matrix.This rendezvous problem is constructed as a Markov decision process that reflects the fuel consumption,the transfer time,the relative state,and the dynamical model.An actor-critic algorithm is used to train policy for generating rendezvous maneuvers.The results of the numerical optimization(e.g.,differential evolution)are adopted as the expert data set to accelerate the training process.By deploying a policy network,the multi-impulse rendezvous trajectories can be obtained on board.Moreover,the proposed approach is also applied to generate a feasible solution for many impulses(e.g.,20 impulses),which can be used as an initial value for further optimization.The numerical examples with random initial states show that the proposed method is much faster and has slightly worse performance indexes when compared with the evolutionary algorithm.展开更多
The multiple signal classification method for direction-of-arrival estimation is widely applied in practical scenarios.However,the multiple signal classification method with planar array requires 2-dimensional on-grid...The multiple signal classification method for direction-of-arrival estimation is widely applied in practical scenarios.However,the multiple signal classification method with planar array requires 2-dimensional on-grid spectrum searches,which would lead to the grid mismatch and high computational complexity.Therefore,a high-precision fast direction-of-arrival estimation method for planar array is proposed.In the proposed method,a 2-stage grid search approach over the 2-dimensional spectrum is firstly applied to obtain a quick coarse estimation of direction of arrival.Then,the estimation of higher precision is achieved via a quadratic surface fitting method.Simulation results verified the effectiveness of the proposed method.展开更多
基金supported by the National Natural Science Foundation of China(grant nos.62073102 and 62203145).
文摘Aiming at the interception problem of noncooperative evader spacecraft adopting random maneuver strategy in one-to-one orbital pursuit-evasion problem,an interception strategy with decision-making training mechanism for the pursuer based on deep reinforcement learning is proposed.Its core purpose is to improve the success rate of interception in the environment with high uncertainty.First of all,a multi-impulse orbit transfer model of pursuer and evader is established,and a modular deep reinforcement learning training method is built.Second,an effective reward mechanism is proposed to train the pursuer to choose the impulse direction and impulse interval of the orbit transfer and to learn the successful interception strategy with the optimal fuel and time.Finally,with the evader taking a random maneuver decision in each episode of training,the trained decision-making strategy is applied to the pursuer,the corresponding interception success rate of which is further analyzed.The results show that the pursuer trained can obtain universal and variable interception strategy.In each round of pursuit-evasion,with random maneuver strategy of the evader,the pursuer can adopt similar optimal decisions to deal with high-dimensional environments and thoroughly random state space,maintaining high interception success rate.
基金supported by the National Natural Science Foundation of China(Grant Nos.62003371 and 62103446)Outstanding Youth Fund of Hunan Provincial Natural Science(Grant No.2022JJ20081)+1 种基金Funding of Science and Technology on Aerospace Flight Dynamics Laboratory(Grant No.KJW-6142210210306)Central South University Innovation-Driven Research Program(Grant No.2023CXQD066).
文摘For the challenging problem that a spacecraft approaches a tumbling target with non-cooperative maneuver,an anti-saturated proximity control method is proposed in this paper.First,a brand-new appointed-time convergent performance function is developed via exploring Bézier curve to quantitatively characterize the transient and steady-state behaviors of the pose tracking error system.The major advantage of the proposed function is that the actuator saturation phenomenon at the beginning can be effectively reduced.Then,an anti-saturated pose tracking controller is devised along with an adaptive saturation compensator.Wherein,the finite-time stability of both the pose and its velocity error signals are guaranteed simultaneously in the presence of actuator saturation.Finally,2 groups of illustrative examples are organized and verify that the close-range proximity is effectively realized even with unknown target maneuver.
基金supported by the National Natural Science Foundation of China(No.12172288)the National Key Basic Research Program of China:Gravitational Wave Detection Project(No.2021YFC2202601 and No.2021YFC2202603).
文摘This paper discusses the modeling and solving of orbital pursuit-evasion games(OPEGs)under J_(2)perturbation.The optimal long-range maneuver method under J_(2)perturbation is designed,and it is proved that the effect of eccentricity can be ignored when transfer times and theΔV budgets are fixed.It is discovered that when the inclination between the initial and target orbit is equal and is between 10°and 25°,the whole maneuver process can be simplified to a fixed-inclination transfer.Subsequently,a long-term OPEG model is provided under the assumption of fixed inclination,zero eccentricity,and impulsive thrust.Winning conditions of OPEGs under J_(2)perturbation are then carefully derived,with long-time OPEG(J_(2)dominated)and short-time OPEG(traditional)separated,and typical tactics of both sides formulated and verified.These studies are further extended to the“Arrival time matching game”for maintaining/avoiding resonant arrival time under J_(2)perturbation,and the advantages and disadvantages of both sides are analyzed.The models and strategies obtained in this paper can be potentially used in practical applications of OPEGs,especially for evaders that have low thrust-weight ratios and are weak in traditional short-term OPEGs.
基金supported by the National Natural Science Foundation of China under grant numbers 11872034 and U20B2056the Manned Space Engineering Project of China under grant number 010201Beijing Natural Science Foundation under grant number 1224039.
文摘Collision probability is employed for evaluating whether there will be a dangerous encounter between 2 space objects.The fidelity of the collision probability mainly depends on the accuracies of orbit prediction and covariance prediction for the space objects.In this paper,the collision probability between the Tsinghua Gravitation and Atmosphere Science Satellite,Q-Sat,and the space debris with a North American Aerospace Defense Command ID of 49863 on 2022 January 18 was calculated.The 2 objects approached each other dangerously close and the event was reported.First,the atmospheric density model is modified by a dynamic approach-based inversion to improve the accuracy of orbit prediction for the Q-Sat.Next,predictions of position error covariance are carried out.Orbits of the next 24 hours are predicted,and the predicted orbits are compared with the actual orbits of the Q-Sat.Backpropagation neural network was trained for predicting the position error covariance.For the space debris,the 2-line element data are employed.Orbit predictions for the space debris are also conducted and compared with the actual orbit.Another backpropagation neural network for predicting the position error covariance for the space debris is trained.Using the covariances from the backpropagation neural network,the error ellipsoids of the 2 objects are established.The error ellipsoids are later projected to the encounter plane to calculate the collision probability.Different from the reports from other institutes,the closest distance between the Q-Sat and the space debris calculated by the current method was 2.71 km.The collision probability was 1.16×10−11.It was not a dangerous encounter event.The onboard precise orbit determination device enabled improved orbit determination precision and orbit prediction accuracy,which is important for space safety management.
基金supported by the National Key Research and Development Program of China(grant no.2021YFA0717200).
文摘Along with the rapid development of space technology,extraterrestrial exploration has gradually tended to further-distanced and longer-termed planet exploration.As the first step of an attempt for humans to build a perpetual planet base,building a lunar base by in situ resource utilization(ISRU)will drastically reduce the reliance of supplies from Earth.Lunar resources including mineral resources,water/ice resources,volatiles,and solar energy will contribute to the establishment of a lunar base for long-term life support and scientific exploration missions,although we must consider the challenges from high vacuum,low gravity,extreme temperature conditions,etc.This article provides a comprehensive review of the past developing processes of ISRU and the latest progress of several ISRU technologies,including in situ water access,in situ oxygen production,in situ construction and manufacture,in situ energy utilization,and in situ life support and plant cultivation on the Moon.Despite being able to provide some material and energy supplies for lunar base construction and scientific exploration,the ISRU technologies need continuous validation and upgrade to satisfy the higher requirements from further lunar exploration missions.Ultimately,a 3-step development plan for lunar ISRU technologies in the next decade is proposed,which consists of providing technological solutions,conducting technical verification on payloads,and carrying out in situ experiments,with the ultimate aim of establishing a permanent lunar station and carrying out long-term lunar surface scientific activities.The overview of ISRU techniques and our suggestions will provide potential guidance for China’s future lunar exploration missions.
基金supported by China Manned Space Engineering Office.
文摘After more than 7 years of development,the Tianzhou cargo spacecraft(TZ),a space station cargo transfer spacecraft,was successfully launched on 2017 April 20.The TZ is robotic spacecraft that is designed to support China space station operation by transporting pressurized cargo,unpressurized cargo,large cargo,propellant,and other supplies.The vehicle is equipped with the crew specifications necessary for astronauts to unload pressurized cargo.TZ can be utilized for a variety of commercial,engineering,scientific,or other proposed activities once its primary mission is complete.TZ is China's first dedicated space cargo transport spacecraft,but the safety designs for crew activities are also particular to TZ.Newly developed technologies were applied to enable high-efficiency cargo shipment.Its development was carried out under the policy of adopting flight-proven technologies to enhance the reliability and safety of a mission.The success of the flight test of the TZ-1 cargo spacecraft marked the perfect end of the mission of the China Space Laboratory and laid the foundation for the smooth implementation of the manned space station project.As a novel manned spacecraft,TZ-1 has broken through key technologies such as cargo transportation,propellant replenishment,and fully autonomous rapid rendezvous and docking.TZ has the characteristics of high transport efficiency,multitasks,and strong self-control ability.The paper describes the phylogeny,main technical schemes,and technological achievements of China TZ.
基金supported by the National Natural Science Foundation of China(no.11822205 and 11772167).
文摘This paper proposed a new attitude determination method for low-orbit spacecraft.The attitude prediction accuracy is greatly improved by adding the unmodeled environmental torque to the dynamic equation.Specifically,the environmental torque extraction algorithm based on extended Kalman filter and series extended state observer is introduced,and the unmodeled part of dynamic is identified through the inverse dynamic model.Then,the collected data are analyzed and trained by a backpropagation neural network,resulting in an attitude-torque mapping network with compensation ability.The simulation results show that the proposed feedback attitude prediction algorithm can outperform standard methods and provide a high accurate picture of prediction and reliability with discontinuous measurement.
基金sponsored by the National Natural Science Foundation of China(grant number 62173273)the Natural Science Basic Research Plan in Shaanxi Province of China(grant number 2020JC-19).
文摘The tethered TSAR(tomographic synthetic aperture radar)system is a group of tethered SAR satellites that can be rapidly deployed and provide a stable baseline for 3-dimensional topographic mapping and moving target detection.Successful deployment is critical for TSAR tethered system.This paper discusses the deployment strategy for a 3-body chain-type tethered satellite system in a low-eccentric elliptical orbit.Two deployment strategies are discussed.Then,the tension on the tether is used to deploy it to the desired length and suppress its sway motion,resulting in an underactuated and input-constrained system.Hierarchical sliding mode control(HSMC)with anti-windup technology is employed to overcome the above challenges.In addition,the proposed approach includes the use of a disturbance observer to estimate the second derivative signal and a robust differentiator to estimate the sliding surfaces of the unacted subsystem.Finally,the effectiveness of the proposed deployment strategy is verified by MATLAB/Simulink.
基金supported by the China Manned Space Flight Engineering Advance Research Program(grant number HY-5)the Foundation of State Key Laboratory of Space Medicine Fundamentals and Application(grant number SMFA18A01)a Space Medical Experiment grant(grant number HYZHXM01001).
文摘Countermeasures in weightlessness are a predominant technique for long-term residency in space.Head-down bed rest(HDBR)has long been used to simulate the physiological effects of spaceflight and test the efficacy of countermeasures.In 2019,the Astronaut Center of China(ACC)has held a 90-d HDBR on the effects of exercises’intervention.Thirty-six subjects were recruited and randomized into 5 intervention groups:(a)control,(b)aerobic exercises,(c)resistance exercises,(d)concurrent aerobic and lower load resistance exercises,and(e)concurrent aerobic and high-load resistance exercises.Moreover,exercise interventions were performed in supine or 6°head-down tilt.They were provided with plain medical,psychological,and nutritional supports during the experiment.In addition,cardiovascular and pulmonary functions,muscle strength,bone density,and neuro-immune-endocrine functions were assessed over time.Subjects were monitored by clinical evaluations,psychological assessments,and nutritional status evaluations.All subjects spent 138 d in the bed rest study laboratory and received 2 follow-up tests per 3 months in the home recovery period.It was found that exercises in the 4 groups were effective interventions for aerobic capacity compared with control.The resistance exercises or concurrent aerobic and high-load resistance exercises improved isometric maximal voluntary contraction.However,the protection against bone loss still needs further exploration.Appropriate psychosocial and nutrition support techniques are worth to be reinforced.
基金supported by National Key Research and Development Program of China(2022YFF0503100)the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)+1 种基金National Natural Science Foundation of China(Grant Nos.41972321 and L2224032)Chinese Academy of Sciences(XK2022DXC004).
文摘Impact craters are one of the most important landforms on the lunar surface,playing a crucial role in the formation and later evolution of the Moon.For example,as a primary source of remote sensing observations and lunar samples,lunar regolith is predominantly composed of impact ejecta.Based on their morphologies,lunar impact craters with increasing sizes can be classified into simple craters,complex craters,and multiring basins,and they play different roles in lunar evolution.In our study,we conducted numerical simulations of the South Pole-Aitken basin and the Orientale basin on the lunar surface,as well as the Aristarchus complex crater and the Zhinyu simple crater.The resultant effects of them are further analyzed.Because Zhinyu crater is relatively close to the Chang’e-4 landing site,while Aristarchus crater is relatively close to the Chang’e-5 landing site,their simulation results have direct significance for interpreting the corresponding exploration data from both missions.The numerical simulation results demonstrate that the formation of large basins not only affects the subsurface structure within the basin but also significantly disturbs the surrounding geological layers.Complex and simple craters mainly disturb the subsurface layers within the crater,but complex craters can cause uplift of the underlying strata.These impact processes dominate the primary geological framework of the lunar surface,depositing ejecta materials of varying thicknesses from different depths,which has important implications for future sample collection missions.In conclusion,impact processes are one of the primary driving forces in the lunar evolution.
文摘Considering the demand of distributed satellite clusters for high-speed information communication in the future,this paper establishes a laser network model based on optical multibeam antenna.At present,there are still some networking and reconstruction problems,such as network connectivity,duration,and stability.To address them,the paper develops a multiobjective optimization model for the laser networking of distributed satellite clusters,which aims to maximize network connectivity and network duration and minimize the perturbation of the network connection matrix.The model is constructed under the constraints of multibeam antenna capability,the visibility of satellites in clusters,and network connectivity.From the perspectives of the optimization effect and timeliness of the optimization algorithm,a deep reinforcement learning algorithm is proposed,which is based on a double-layer Markov decision model,to meet the needs of on-orbit intelligent networking and dynamic reconstruction of distributed satellite clusters.Simulation results show that the algorithm features flexible architecture,excellent networking performance,and strong real-time performance.When the optimization results are similar,the proposed algorithm outperforms the nonsorted genetic algorithm II algorithm and the particle swarm optimization algorithm in terms of solution speed.
基金supported by China Manned Space Engineering Office.
文摘As a manned spacecraft operating in orbit for a long time,a space station embodies a country’s scientific and technological strength comprehensively.Building a space station is the final target of the 3-step strategy of China’s manned space program.This paper introduces the design of the Tiangong space station in terms of its design principles,overall scheme,building process,and special system design.On this basis,the paper analyzes and summarizes the technical characteristics of the Tiangong space station in the aspects of system design and optimization,the large proportion of new technologies,the excellent cost-effectiveness ratio,and the high safety and efficiency of the crew’s residence.Finally,it discusses the future application and development of the Tiangong space station.
基金supported by the National Natural Science Foundation of China under Grant 62341110the Key Technologies R&D Program of Jiangsu(Prospective and Key Technologies for Industry)under Grants BE2022067 and BE2022067-5,the Jiangsu Province Basic Research Project under Grant BK20192002+2 种基金the Fundamental Research Funds for the Central Universities under Grants 2242021R41148 and 2242022k60007the Young Elite Scientist Sponsorship Program by China Institute of Communicationssupported by the National Natural Science Foundation of China under Grant U2233216.
文摘Satellite communication is an indispensable part of future wireless communications given its global coverage and long-distance propagation.In satellite communication systems,channel acquisition and energy consumption are two critical issues.To this end,we investigate the tradeoff between the total energy efficiency(TEE)and minimum EE(MEE)for robust multigroup multicast satellite communication systems in this paper.Specifically,under the total power constraint,we investigate the robust beamforming aimed at balancing the TEE-MEE,so as to achieve the balance between the fairness and total performance on the system EE.For this optimization problem,we first model the balancing problem as a nonconvex problem while deriving its approximate closed-form average user rate.Then,the nonconvex problem is handled by solving convex programs sequentially with the help of the semidefinite relaxation and the concave-convex procedure.In addition,depending on the solution rank value,Gaussian randomization and eigenvalue decomposition method are applied to generate the feasible solutions.Finally,simulation results illustrate that the proposed approach can effectively achieve the balance between the TEE and MEE,thus realizing a tradeoff between fairness and system EE performance.It is also indicated that the proposed robust approach outperforms the conventional baselines in terms of EE performance.
基金supported by the National Key R&D Program of China(Grant No.2020YFE0202100).
文摘Since the 1990s,the existence of water-ice in the permanent shadow areas of the lunar polar regions and the problem of water in the early lunar period have become the hot spot of international lunar exploration.This paper analyzes the research progress and existing problems of lunar water-ice detection in recent years.Based on the analysis of expected foreign lunar water-ice exploration missions,the major scientific problems of lunar water-ice are analyzed.From different exploration methods,this paper tentatively puts forward the scientific tasks,payload configuration,functional requirements,and possible scientific outputs of water-ice in China's future lunar exploration projects,which can provide reference for future lunar exploration missions.
文摘Today,the discussion about colonizing different planets has shifted from the"IF"mode to the"WHEN"mode,and the substantial large group of humans living for a long time in an isolated,hostile,and enclosed environment is about to become a reality.Thus,the space-related healthcare methodologies should shift as well from a small number of selected persons to much more extensive groups with much less health homogeneity.Moreover,the development of human colonies,first on the Moon and later on Mars,will be a game changer in allthat we know and use to see in space travel and eventually in space health.Humans will leave Earth but will carry human society's health patterns,adjusted to the environment.The foundation for space epidemiology modeling can be set today and should attract the attention of the epidemiological and space research communities.
基金supported by Advanced Space Medico-Engineering Research Project of China(no.2015SY54A0503)the National Natural Science Foundation of China(31630038,81830061,and 82192882).
文摘Many studies have shown that spaceflight causes oxidative stress and induces brain disorder in astronauts,but the counter measurements are lacking.Increasing evidence demonstrated that hydrogen can act as a therapeutic antioxidant.In this study,rats were treated with or without about 5%hydrogen under hindlimb unloading or normal conditions for 28 d.We assessed rat’s brain function by open-field test,step-down passive avoidance test,the neurotransmitter’s level detected by liquid chromatography with tandem mass spectrometry,and Nissl and hematoxylin-eosin staining analysis.We also assessed the oxidative damage by changes of malondialdehyde level,the ratio of reduced glutathione to oxidized glutathione,and superoxide dismutase and catalase activity.Glucose metabolism disorder was disclosed through glucose metabolomic analysis.The underlying mechanism of the effects of hydrogen was analyzed by mRNA sequencing and detecting mRNA and protein levels.Our data showed that hindlimb unloading caused oxidative damage and glucose metabolism disorder in brain tissues and decreased brain function in rats.Hydrogen inhalation reduced oxidative damage,ameliorated glucose metabolism disorder,and alleviated the dysfunction of rat brain function.Peroxisome-proliferator-activated receptor gamma coactivator 1αand brain-derived neurotrophic factor,the key regulators of glucose metabolism and brain function,were obviously affected.This research confirms the protective effect of hydrogen inhalation on declining brain function under hindlimb unloading conditions and discloses the underlying mechanism,which provides a potential strategy for astronauts’health.
文摘The mixed terrains of terramechanics research are mainly composed of static stones and loose soil.The movement behavior of stones is often ignored while analyzing the influence of the wheel’s traction performance caused by mixed terrain.When a wheel is in contact with the movable stone and with the loose soil at the same time,the residual soil model,therefore,is proposed to simulate the change of the contact force between the wheel and the remaining loose soil caused by the failure of the loose soil in the area covered by stone.The plastic homogeneous soil mechanics model is proposed based on the soil’s mechanical properties.It is used for simulating the reaction force provided by soil to the moving stones.These mechanical models are compiled into the simulation programs,which are called by Adams to calculate the contact forces and moments of the planetary rover’s wheels in the mixed terrain with the movable stone and loose soil.Carrying out soil bin tests under the same experimental conditions,the comparative analysis of the simulation and experiment for a wheel in contact with 4 types of stones shows that the comparison results are in good agreement,which can verify the effectiveness of the proposed models to an extent.
基金funded by the Beijing Science and Technology Major Project of China,grant number Z18110400290000.
文摘With the increasing number of satellites being launched in China,the demand for Telemetry,Tracking,and Command(TT&C)resources is also increasing.Because of the global coverage and resource requirements of TT&C management,this paper proposes a TT&C scheme based on the Global Short-Message Communication System(GSMCS)of the BeiDou-3 Navigation Satellite System(BDS-3).The system composition,workflow,and functions of satellite TT&C are analyzed using the GSMCS of BDS-3.Through the coverage analysis of the Medium Earth Orbit(MEO)constellation of BDS-3,scheme’s applicability is pointed out,and the correctness of the analysis results is verified via simulation.The value range of the link distance is derived by calculating the range of the distance variation between any 2 satellites in the BDS-3 MEO constellation and combining the intersatellite routing scheme.The calculation results show that the response time range of the autonomous request management application of in-orbit satellites based on the GSMCS of BDS-3 is 1.407 to 2.448 s.This can meet the requirements of TT&C service.
基金supported in part by the Key Research and Development Plan of Heilongjiang Province under Grant GZ20210120.
文摘A reinforcement learning-based approach is proposed to design the multi-impulse rendezvous trajectories in linear relative motions.For the relative motion in elliptical orbits,the relative state propagation is obtained directly from the state transition matrix.This rendezvous problem is constructed as a Markov decision process that reflects the fuel consumption,the transfer time,the relative state,and the dynamical model.An actor-critic algorithm is used to train policy for generating rendezvous maneuvers.The results of the numerical optimization(e.g.,differential evolution)are adopted as the expert data set to accelerate the training process.By deploying a policy network,the multi-impulse rendezvous trajectories can be obtained on board.Moreover,the proposed approach is also applied to generate a feasible solution for many impulses(e.g.,20 impulses),which can be used as an initial value for further optimization.The numerical examples with random initial states show that the proposed method is much faster and has slightly worse performance indexes when compared with the evolutionary algorithm.
文摘The multiple signal classification method for direction-of-arrival estimation is widely applied in practical scenarios.However,the multiple signal classification method with planar array requires 2-dimensional on-grid spectrum searches,which would lead to the grid mismatch and high computational complexity.Therefore,a high-precision fast direction-of-arrival estimation method for planar array is proposed.In the proposed method,a 2-stage grid search approach over the 2-dimensional spectrum is firstly applied to obtain a quick coarse estimation of direction of arrival.Then,the estimation of higher precision is achieved via a quadratic surface fitting method.Simulation results verified the effectiveness of the proposed method.
