2003 Vol. 23, No. 4
2003, 23(4): 241-247.
Abstract:
A method called complete Orthogonal Function Series Expansion (OFSE) in Hilbert space is proposed to solve the non-dissipative torsional Alfvén wave in coronal loops. Every base function corresponds to an intrinsic angular frequency wn of every magnetic field line in coronal loops. Torsional Alfvén wave resonance of a magnetic field line in coronal loops comes out when the driven angular frequency equals to its intrinsic angular frequency. With the method, we present a new form of Torsional Alfvén wave evolution solution with two-footpoint driven boundary condition. There exists a resonant term in the solution, from which it could be found that: near the resonant place with an angular frequency w,a discontinuity profile appears at times t equal to the multiples of n/w and a 1/x discontinuity profile appears at times t equal to the odd multiples of n/(2w). It is also found that the wave amplitude at resonant place increases linearly with time and the slope is proportional to Alfvén wave speed, inverse proportional to loop length and independent of driven frequency.
A method called complete Orthogonal Function Series Expansion (OFSE) in Hilbert space is proposed to solve the non-dissipative torsional Alfvén wave in coronal loops. Every base function corresponds to an intrinsic angular frequency wn of every magnetic field line in coronal loops. Torsional Alfvén wave resonance of a magnetic field line in coronal loops comes out when the driven angular frequency equals to its intrinsic angular frequency. With the method, we present a new form of Torsional Alfvén wave evolution solution with two-footpoint driven boundary condition. There exists a resonant term in the solution, from which it could be found that: near the resonant place with an angular frequency w,a discontinuity profile appears at times t equal to the multiples of n/w and a 1/x discontinuity profile appears at times t equal to the odd multiples of n/(2w). It is also found that the wave amplitude at resonant place increases linearly with time and the slope is proportional to Alfvén wave speed, inverse proportional to loop length and independent of driven frequency.
2003, 23(4): 248-255.
Abstract:
The process of magnetic reconnection in the collisionless plasma and distributions of particles in different positions are studied based on two-dimensional particle simulation. It is found that the procedure of the magnetic reconnection saturates at t=14.8 Ωi-1 after a phase of linear growth, and the difference between the ion and electron dynamics in the diffusion region gives rise to in-plane (Hall) currents, which produces an out-of-plane By field with a quadrupolar structure. The velocity distributions of ion and electron deviate from the initial Maxwell distribution and are characterized by non-local multi-component distributions with high anisotropy, which is consistent with the observations of Seon and Onsager. At the same time the electron acceleration and heating take place near the X-type region, so the electron distribution shows a high-energy tail in the electron energy distribution. At last, we find that outgoing flux velocity of the electrons near the X point is higher than that of the ions. The flux velocity of the electrons is about 2 Alfvén speed, while the flux velocity of the ions is about 1 Alfvén speed.
The process of magnetic reconnection in the collisionless plasma and distributions of particles in different positions are studied based on two-dimensional particle simulation. It is found that the procedure of the magnetic reconnection saturates at t=14.8 Ωi-1 after a phase of linear growth, and the difference between the ion and electron dynamics in the diffusion region gives rise to in-plane (Hall) currents, which produces an out-of-plane By field with a quadrupolar structure. The velocity distributions of ion and electron deviate from the initial Maxwell distribution and are characterized by non-local multi-component distributions with high anisotropy, which is consistent with the observations of Seon and Onsager. At the same time the electron acceleration and heating take place near the X-type region, so the electron distribution shows a high-energy tail in the electron energy distribution. At last, we find that outgoing flux velocity of the electrons near the X point is higher than that of the ions. The flux velocity of the electrons is about 2 Alfvén speed, while the flux velocity of the ions is about 1 Alfvén speed.
2003, 23(4): 256-261.
Abstract:
Atmospheric angular spectrum is one of the significant features of the atmospheric radio scatterrers. Echoes scattered from the electron irregularities in the mesosphere and lower thermosphere can be used to measure horizontal winds and electron densities with the MF radar at Wuhan. Configured with spaced antenna mode and full correlation analysis techniques, Wuhan MF radar can measure the life time and scale of the irregularities routinely as well. Using these data, the atmospheric angular spectrum can be estimated with both a spectral width method and a space correlation method. The former method gives the upper limit of the angular spectrum, while the latter gives estimations close to the true angular spectrum. The observational data on February 9, 2001 are used to estimate the angular spectrums with these two methods.Results show that the angular spectrum increase slightly with increasing height with a minimum of 6 at 68km and a maximum of 11 at 90km. Its mean value is 9.2.Data at 86km level from Feb. 4 to 10, 2001 are used to give mean daily variations that have a maximum in the daytime and minimum in the nighttime.
Atmospheric angular spectrum is one of the significant features of the atmospheric radio scatterrers. Echoes scattered from the electron irregularities in the mesosphere and lower thermosphere can be used to measure horizontal winds and electron densities with the MF radar at Wuhan. Configured with spaced antenna mode and full correlation analysis techniques, Wuhan MF radar can measure the life time and scale of the irregularities routinely as well. Using these data, the atmospheric angular spectrum can be estimated with both a spectral width method and a space correlation method. The former method gives the upper limit of the angular spectrum, while the latter gives estimations close to the true angular spectrum. The observational data on February 9, 2001 are used to estimate the angular spectrums with these two methods.Results show that the angular spectrum increase slightly with increasing height with a minimum of 6 at 68km and a maximum of 11 at 90km. Its mean value is 9.2.Data at 86km level from Feb. 4 to 10, 2001 are used to give mean daily variations that have a maximum in the daytime and minimum in the nighttime.
RAYLEIGH LIDAR AND RADIOSOND OBSERVATIONS OF DENSITY AND TEMPERATURE IN MIDDLE ATMOSPHERE OVER WUHAN
2003, 23(4): 262-268.
Abstract:
Vertical distributions of atmosphereic density and temperature over Wuhan (30.5N, 114.4E) from ground to 65km have been obtained by Rayleigh Scattering Lidar with high temporal and special resolution and radiosondes. A method to derive the density and temperature from the photon counts collected by lidar is described briefly. The density and temperature profiles agree very well with MSISE-90 atmosphere model and the temperature difference between the derived profiles and model were less than 3 K near the stratospause. The errors involved in the derived values are presented and analyzed. Preliminary analysis of temperature variations in a night revealed fluctuations with characteristics resembling those large-scale gravity waves.
Vertical distributions of atmosphereic density and temperature over Wuhan (30.5N, 114.4E) from ground to 65km have been obtained by Rayleigh Scattering Lidar with high temporal and special resolution and radiosondes. A method to derive the density and temperature from the photon counts collected by lidar is described briefly. The density and temperature profiles agree very well with MSISE-90 atmosphere model and the temperature difference between the derived profiles and model were less than 3 K near the stratospause. The errors involved in the derived values are presented and analyzed. Preliminary analysis of temperature variations in a night revealed fluctuations with characteristics resembling those large-scale gravity waves.
2003, 23(4): 269-277.
Abstract:
The upper troposphere/lower stratosphere (UT/LS), as a special region, lies between 8 and 25 km altitude. Because most of ozone column resides in the lower stratosphere, small change in ozone abundance could have a large impact on climate and the surface UV flux. The tropopause, as an interface or transition zone between the well mixed, ozone-poor upper troposphere and the stratified, ozone rich lower stratosphere, has its seasonal and long-term variation trends which in turn could lead to a direct and evident effect on the distribution of atmospheric ozone and its column abundance. This work simulated the impact of tropopause variation on the distribution of ozone in UT/LS with a two-dimensional model named SOCRATES (Simulation Of Chemistry, Radiation, And Transport of Environmentally important Species). The model, developed in the Division of Atmospheric Chemistry of NCAR, is one coupling chemical, radiative, and dynamical processes. Its domain and resolution are 0-120 km and 1 km in vertical and 85S-85N and 5?in horizontal. Model simulation results show that the annual cycle of the tropopause height has remarkable impact on the ozone distribution in the UT/LS. The local change of ozone can be more than 10%. When the tropopause is increased by 1 km in winter in middle latitudes of Northern Hemisphere, the impact on ozone distribution is evident and the local change of ozone can be more than 6%. However the impact on total ozone is relatively small, less than 5 Dobson units. This is much less than the statistic results between tropopause height and total ozone from data analysis.
The upper troposphere/lower stratosphere (UT/LS), as a special region, lies between 8 and 25 km altitude. Because most of ozone column resides in the lower stratosphere, small change in ozone abundance could have a large impact on climate and the surface UV flux. The tropopause, as an interface or transition zone between the well mixed, ozone-poor upper troposphere and the stratified, ozone rich lower stratosphere, has its seasonal and long-term variation trends which in turn could lead to a direct and evident effect on the distribution of atmospheric ozone and its column abundance. This work simulated the impact of tropopause variation on the distribution of ozone in UT/LS with a two-dimensional model named SOCRATES (Simulation Of Chemistry, Radiation, And Transport of Environmentally important Species). The model, developed in the Division of Atmospheric Chemistry of NCAR, is one coupling chemical, radiative, and dynamical processes. Its domain and resolution are 0-120 km and 1 km in vertical and 85S-85N and 5?in horizontal. Model simulation results show that the annual cycle of the tropopause height has remarkable impact on the ozone distribution in the UT/LS. The local change of ozone can be more than 10%. When the tropopause is increased by 1 km in winter in middle latitudes of Northern Hemisphere, the impact on ozone distribution is evident and the local change of ozone can be more than 6%. However the impact on total ozone is relatively small, less than 5 Dobson units. This is much less than the statistic results between tropopause height and total ozone from data analysis.
2003, 23(4): 278-285.
Abstract:
By using International Geomagnetic Reference Field (IGRF), the paper computes the drift of South Atlantic Anomaly (SAA) region at several altitudes lower than 1 000 km for the interval of 1970-2000. The results show that the center of the SAA moves 4°-6° towards west, while the center of the SAA no more than 1° towards the north. The extent of the SAA in the year 2000 includes that of the SAA in 1970 and its coverage extends with some scale in both latitude and longitude directions. The value of geomagnetic field strength at the center of SAA in 2000 is lower than that in 1970. The biggest scale for the decrease in geomagnetic field strength at the center of the SAA is no more than 3.87% for the altitudes lower than 1000 km. It is enough to use internal field for the altitudes lower than 1000 km, so the results are reliable. The charged particles with energy higher than 10 MeV mainly distribute in the SAA region for low altitudes based on AP8 Model, but the model was just suit for epoch 1960 to 1970. Because the kinetic properties of a charged particle are almost completely decided by the properties of the geomagnetic field at altitudes lower than 1000 km, so we can know the charged particles with energy higher than 10 MeV still distribute in SAA region. The space distribution configuration of charged particles with high energy should basically be consistent with the space distribution configuration of the geomagnetic field for low altitudes. The space configuration of the SAA region in low altitudes can be considered as the criterion of the space configuration of radiation belt protons with energy higher than 10 MeV.
By using International Geomagnetic Reference Field (IGRF), the paper computes the drift of South Atlantic Anomaly (SAA) region at several altitudes lower than 1 000 km for the interval of 1970-2000. The results show that the center of the SAA moves 4°-6° towards west, while the center of the SAA no more than 1° towards the north. The extent of the SAA in the year 2000 includes that of the SAA in 1970 and its coverage extends with some scale in both latitude and longitude directions. The value of geomagnetic field strength at the center of SAA in 2000 is lower than that in 1970. The biggest scale for the decrease in geomagnetic field strength at the center of the SAA is no more than 3.87% for the altitudes lower than 1000 km. It is enough to use internal field for the altitudes lower than 1000 km, so the results are reliable. The charged particles with energy higher than 10 MeV mainly distribute in the SAA region for low altitudes based on AP8 Model, but the model was just suit for epoch 1960 to 1970. Because the kinetic properties of a charged particle are almost completely decided by the properties of the geomagnetic field at altitudes lower than 1000 km, so we can know the charged particles with energy higher than 10 MeV still distribute in SAA region. The space distribution configuration of charged particles with high energy should basically be consistent with the space distribution configuration of the geomagnetic field for low altitudes. The space configuration of the SAA region in low altitudes can be considered as the criterion of the space configuration of radiation belt protons with energy higher than 10 MeV.
2003, 23(4): 286-293.
Abstract:
The Deep Space 3 is a proposed mission by NASA within the New Millennium Program. This paper primarily studies the relative state parameters autonomous determination of three satellites formation of the Deep Space 3 using inter-satellite relative measurements of like-GPS carrier phase and a ranging code onboard. To validate this inter-satellite relative measurements technique, various kinds of measurement projects and the accuracy of measure were researched. Firstly, the inter-satellites relative measurements system model of three satellites formation was built. Secondly, various kinds of measurement projects were simulated using high accurate pseudorange and carrier phase onboard. The single different phase bias was initialized with more epochs of pseudorange and phase observations during the relative attitude rotation among the satellites and the optimal initializing projection was investigated. Lastly, the results of simulation/covariance analysis were given.
The Deep Space 3 is a proposed mission by NASA within the New Millennium Program. This paper primarily studies the relative state parameters autonomous determination of three satellites formation of the Deep Space 3 using inter-satellite relative measurements of like-GPS carrier phase and a ranging code onboard. To validate this inter-satellite relative measurements technique, various kinds of measurement projects and the accuracy of measure were researched. Firstly, the inter-satellites relative measurements system model of three satellites formation was built. Secondly, various kinds of measurement projects were simulated using high accurate pseudorange and carrier phase onboard. The single different phase bias was initialized with more epochs of pseudorange and phase observations during the relative attitude rotation among the satellites and the optimal initializing projection was investigated. Lastly, the results of simulation/covariance analysis were given.
2003, 23(4): 294-298.
Abstract:
Based on self-developed software, a GPS real-time attitude determination system is built using GPS OEM boards as basic hardware. The Hardware structure is simple and the cost of system is low. The attitude determination software solve a series of technical problems such as data receiving, decoding and synchronizing, carrier phase ambiguity resolution, system kinematic calibration. Validated by static and kinematic experiments, the system run stably and has well dynamic performance. The mean square error of attitude can be less than 0.3? when baseline length be 1.2m around. So the system can act as navigation equipment or as regulator of navigation equipment.
Based on self-developed software, a GPS real-time attitude determination system is built using GPS OEM boards as basic hardware. The Hardware structure is simple and the cost of system is low. The attitude determination software solve a series of technical problems such as data receiving, decoding and synchronizing, carrier phase ambiguity resolution, system kinematic calibration. Validated by static and kinematic experiments, the system run stably and has well dynamic performance. The mean square error of attitude can be less than 0.3? when baseline length be 1.2m around. So the system can act as navigation equipment or as regulator of navigation equipment.
2003, 23(4): 299-305.
Abstract:
The fault diagnosis of satellites is a difficult problem due to the complex and unique of structure and control of satellite and the presence of multi-excite sources. Generally, one satellite fault mode is relative to many symptom variables. These variables comprise a set, called the primary symptom set of the fault mode. If each variable in the primary symptom set is necessary to the fault diagnosis? The answer is "no".That is, some variables in the set are redundancy variables. Current reasoning method of fault diagnosis uses all of the variables of primary symptom set to diagnose fault. Because of the redundancy variables in the set, the reasoning method is usually complicated. The redundancy variables not only give no contributions to the fault diagnosis, but also affect the accuracy of the fault diagnosis. So, the methods that can remove the redundancy variables in the primary set should be found. Rough set is a kind of advanced uncertainty reasoning theory. It has several advantages. One of them is to be used to simplify and optimize the sets, which have redundancy variables. Based on Rough set, a new method of satellite fault diagnosis is proposed in this paper. This method removes the redundancy variables in the primary symptom set of satellite fault mode firstly. The remainder variables comprise a set, called the reduction symptom set of satellite fault mode. Then, on condition that the diagnosis accuracy is guaranteed, the proposed method only uses the variables in the reduction symptom set to diagnose fault. The diagnosis reasoning is relatively simpler, because it uses fewer variables to diagnose fault. The content of this paper is organized as following: Firstly, the shortage of current methods of satellite fault diagnosis and the necessity of applying Rough set to satellite fault diagnosis are analyzed. Secondly, the theoretical method of Rough set for diagnosing satellite fault is briefly studied. Thirdly, the practical application of the method is given. Finally, the proposed method is discussed and the conclusions of this paper are given. It is shown that the method proposed in this paper is effective for satellite fault diagnosing.
The fault diagnosis of satellites is a difficult problem due to the complex and unique of structure and control of satellite and the presence of multi-excite sources. Generally, one satellite fault mode is relative to many symptom variables. These variables comprise a set, called the primary symptom set of the fault mode. If each variable in the primary symptom set is necessary to the fault diagnosis? The answer is "no".That is, some variables in the set are redundancy variables. Current reasoning method of fault diagnosis uses all of the variables of primary symptom set to diagnose fault. Because of the redundancy variables in the set, the reasoning method is usually complicated. The redundancy variables not only give no contributions to the fault diagnosis, but also affect the accuracy of the fault diagnosis. So, the methods that can remove the redundancy variables in the primary set should be found. Rough set is a kind of advanced uncertainty reasoning theory. It has several advantages. One of them is to be used to simplify and optimize the sets, which have redundancy variables. Based on Rough set, a new method of satellite fault diagnosis is proposed in this paper. This method removes the redundancy variables in the primary symptom set of satellite fault mode firstly. The remainder variables comprise a set, called the reduction symptom set of satellite fault mode. Then, on condition that the diagnosis accuracy is guaranteed, the proposed method only uses the variables in the reduction symptom set to diagnose fault. The diagnosis reasoning is relatively simpler, because it uses fewer variables to diagnose fault. The content of this paper is organized as following: Firstly, the shortage of current methods of satellite fault diagnosis and the necessity of applying Rough set to satellite fault diagnosis are analyzed. Secondly, the theoretical method of Rough set for diagnosing satellite fault is briefly studied. Thirdly, the practical application of the method is given. Finally, the proposed method is discussed and the conclusions of this paper are given. It is shown that the method proposed in this paper is effective for satellite fault diagnosing.
2003, 23(4): 306-312.
Abstract:
This paper discusses path planning of the free-floating double arms space manipulators under the tiny gravity envioronment. Combination the condition of conservations of momentum and angular momentum, the text gives out the formula to compute the dynamics singularities and the zero disturbance maps of the robotic system. Using the dynamics singularities and the zero disturbance maps,we can develop a way to save the expensive space feul resources through path planning.
This paper discusses path planning of the free-floating double arms space manipulators under the tiny gravity envioronment. Combination the condition of conservations of momentum and angular momentum, the text gives out the formula to compute the dynamics singularities and the zero disturbance maps of the robotic system. Using the dynamics singularities and the zero disturbance maps,we can develop a way to save the expensive space feul resources through path planning.
2003, 23(4): 313-320.
Abstract:
Contributions on attitude of small satellite have mainly placed emphasize on control system, such as system design, method of control, control algorithms, mathematical model, attitude simulation and the like, but few papers have been published on the relation between attitude stabilization and mass center of small satellites. This paper analyzes effect of the displacement of mass center on attitude of small satellites from the view of structure design and dynamical balancing in light of ellipsoid of kinetic energy and motion equation. The motion equation in this paper is deduced from Lagrange equation of second kind, and represented in terms of matrix to benefit solving the equation by computer and also to make the equation concise. By the equation, the numerical simulations of attitude are carried out for a 50kg small satellite corresponding to different initial angular velocities and different displacements of mass center. The effect of displacement of mass center on stability of motion of small satellites is also analyzed. The simulations and analysis show that one or several optimal displacement of mass center exists both for attitude stabilization and stability of motion. This paper aims at providing reference for structure design, attitude control, as well as for determining the precision of dynamic balancing.
Contributions on attitude of small satellite have mainly placed emphasize on control system, such as system design, method of control, control algorithms, mathematical model, attitude simulation and the like, but few papers have been published on the relation between attitude stabilization and mass center of small satellites. This paper analyzes effect of the displacement of mass center on attitude of small satellites from the view of structure design and dynamical balancing in light of ellipsoid of kinetic energy and motion equation. The motion equation in this paper is deduced from Lagrange equation of second kind, and represented in terms of matrix to benefit solving the equation by computer and also to make the equation concise. By the equation, the numerical simulations of attitude are carried out for a 50kg small satellite corresponding to different initial angular velocities and different displacements of mass center. The effect of displacement of mass center on stability of motion of small satellites is also analyzed. The simulations and analysis show that one or several optimal displacement of mass center exists both for attitude stabilization and stability of motion. This paper aims at providing reference for structure design, attitude control, as well as for determining the precision of dynamic balancing.
Office system
Scan Wechat
Readers and readers can bind WeChat official account to experience new functions of mobile terminals
E-mail Alerts RSSCopyright Information
bimonthly Founded in 1981
Sponsor：CAS
Sponsored by：NSSC, CAS; CSSR
Publisher：Science Press
ISSN：ISSN 0254-6124
CN：CN 11-1783/V
Editor chief：WU Ji
Counselor：Gu YiDong
Deputy-chief-editor：
CAO Jinbin
FALANGA Maurizio (Switzerland)
FU Suiyan KANG Qi
LIN Baojun LIN Yangting
SHI Jiancheng YANG Huigen
YANG Zhen ZHANG Shuangnan
NoticeMore>>
Top DownloadMore>>
- Study on Geoeffectiveness of Interplanetary Coronal Mass Ejections by Support Vector Machine ormalsize
- Finite Time Control of Space Robot with Elastic Base and Flexible Arms
- Design of VHF System Spaceborne SVOMormalsize
- Solar Wind Parameters and Auroral Hemispheric Power of Magnetic Storm during ICME
- Model and Impact Risk Assessment of Meteoroid for Marsormalsize
- Transport Time for the Geomagnetic Storm Caused by CME
Top ViewMore>>
- Study on Geoeffectiveness of Interplanetary Coronal Mass Ejections by Support Vector Machine ormalsize
- Principle and Accuracy Problems of Gravitational Redshift Experiments in Space
- Prediction of High-energy Electron Flux of Geosynchronous Orbit Based on Empirical Mode Decomposition
- Transport Time for the Geomagnetic Storm Caused by CME
- Global Space Weather Roadmap and Its Enlightenment to China
- Model and Impact Risk Assessment of Meteoroid for Marsormalsize
Top High in fiveMore>>
- Development and Prospect of Hyperspectral Imager and Its Application
- Progress of China's Lunar Exploration (2011-2020)
- Mission Planning for Small Satellite Constellations Based on Improved Genetic Algorithm
- Orbit Performances Validation for CFOSAT Scatterometer
- GNSS-R Sea Surface Wind Speed Inversion Based on Tree Model Machine Learning Method
- A Modulation Recognition Algorithm Based on Wavelet Transform Entropy and High-order Cumulant for Satellite Signal Modulation
Download CenterMore>>
Contact Us
Address：North-Star Times Tower, No.8 Beichendong Road, Chaoyang District, Beijing, China
Postcode：100190
Telephone：010-62582788
