THE RESONANT FREQUENCIES OF CAVITIES IN A MAGNETOIONIC MEDIUM

1964 ◽  
Vol 42 (1) ◽  
pp. 90-102 ◽  
Author(s):  
K. G. Budden
Keyword(s):  
Plasma Frequency ◽  
Space Vehicle ◽  
Boundary Region ◽  
Plasma Sheath ◽  
Space Vehicles ◽  
Isotropic Plasma ◽  
Resonant Frequencies ◽  
Characteristic Frequencies ◽  
Spherical Mass ◽  
Electron Gyrofrequency

The resonant frequencies for a hollow cylindrical or spherical cavity in a magnetoionic medium are derived using a simple model in which the boundary of the cavity is sharp and the medium outside it is homogeneous and loss free, but anisotropic. The effects of electron temperature and of nonlinearity are ignored. The problem is complementary to a similar problem treated by Herlofsen (1951), who discussed the resonant frequencies of a uniform cylindrical or spherical mass of isotropic plasma surrounded by a vacuum. It is found that the resonant frequencies are not equal to the characteristic frequencies of the plasma as usually described by the formulae X = 1, X = 1 ± Y, but are more complicated functions of the plasma frequency and the electron gyrofrequency. It is concluded that, for a plasma sheath or cavity of any structure, with a sharp or gradual boundary region, the resonant frequencies will in general differ from the characteristic frequencies of the undisturbed plasma. For a cylindrical cavity the resonant frequencies depend upon the angle between the axis of the cavity and the constant magnetic field. The results may have applications to the interpretation of plasma "spikes" observed with space vehicles, and to the theory of the radar cross section of a space vehicle within the ionosphere.

SCATTERING FROM A CYLINDER COATED WITH AN INHOMOGENEOUS DIELECTRIC SHEATH

1963 ◽  
Vol 41 (1) ◽  
pp. 143-151 ◽  
Author(s):  
C. Yeh ◽  
Z. A. Kaprielian
Keyword(s):  
Dielectric Constant ◽  
Scattering Problem ◽  
Plane Waves ◽  
Space Vehicle ◽  
Plasma Sheath ◽  
Scattering Coefficients ◽  
Average Value ◽  
Inhomogeneous Dielectric ◽  
Specific Variation ◽  
Plane Wave Scattering

As a space vehicle re-enters the atmosphere, a plasma sheath, surrounding the vehicle, is generated. It is well known that the sheath is inhomogeneous. However, to make this problem suitable for theoretical analysis, most investigators make the assumption that the sheath is homogeneous. To investigate the validity of this assumption, the idealized problem of the scattering of plane waves by a conducting cylinder coated with a stratified dielectric sheath is considered. The wave equation is separated using the vector wave-function method of Hansen and Stratton. It is then applied to the plane-wave scattering problem. The backscattering cross section is defined and obtained. Analytical expressions for the scattering coefficients of a thin inhomogeneous sheath are also given. Numerical computations are carried out for a specific variation of the dielectric sheath: i.e., ε(r) = ε0α/k0r, where α is a constant, k02 = ε2 με0, and ε0 is the free-space dielectric constant. Results are compared with the homogeneous sheath problem; the dielectric constant of the homogeneous sheath is taken to be the average value of that for the inhomogeneous sheath. It is found that in general rather distinct differences are observed except when the sheath is very thin.

Relativistic synchronization of onboard clocks of navigation space vehicles with the aid of intersatellite measurements

2021 ◽  
pp. 56-66
Author(s):  
Nikolay N. Vasilyuk ◽  
Alexander P. Chervonkin
Keyword(s):  
Proper Time ◽  
Space Vehicle ◽  
Relativistic Correction ◽  
Point Of View ◽  
Space Vehicles ◽  
Satellite Measurements ◽  
Clock Drift ◽  
Coordinate Time ◽  
Upper Limit ◽  
Unambiguous Interpretation

The problem of the synchronization of onboard clocks of navigation satellites has considered from a relativistic point of view using the concept of “coordinate simultaneity”. This concept allows an unambiguous interpretation of the synchronization results within the framework of general relativity. The algorithm of intersatellite measurements processing has formulated in terms of a proper time of a space vehicle and the coordinate time of a reference frame. Rules of transformation between coordinate and proper time scales have indicated. An analytical expression has obtained for the periodic relativistic correction to the estimated value of the relative clock drift. This correction has expressed in terms of the coordinate time of a ground observer. The value of this correction exceeds the acceptable synchronization error and should be taken into account for the inter-satellite measurements processing. The error of the relativistic correction determination has calculated. This error provides an upper limit for the period of uploading of ephemeris data on the board of the space vehicle.

On the theory of plasma–sheath resonance in a non-uniform plasma

1999 ◽  
Vol 61 (3) ◽  
pp. 469-488 ◽  
Author(s):  
NOBORU TANIZUKA ◽  
JOHN E. ALLEN
Keyword(s):  
Resonant Frequency ◽  
Plasma Frequency ◽  
Inhomogeneous Plasma ◽  
Plasma Sheath ◽  
Entire System ◽  
Local Resonance ◽  
Uniform Plasma

Calculations are presented on the phenomenon of plasma–sheath resonance in an inhomogeneous plasma. In certain cases, this resonance coincides with a local resonance occurring in the plasma, the local plasma frequency being equal to the resonant frequency of the entire system. The theory does not describe the mechanism of absorption, but does predict the magnitude of the power involved. Some limitations of the theory are discussed.

Small amplitude transverse wave propagation in a weakly Langmuir turbulent plasma

1969 ◽  
Vol 3 (4) ◽  
pp. 593-601
Author(s):  
N. Bel ◽  
J. Heynaerts
Keyword(s):  
High Frequency ◽  
Small Amplitude ◽  
Cold Plasma ◽  
Plasma Frequency ◽  
Turbulent Plasma ◽  
Distribution Functions ◽  
Isotropic Plasma ◽  
Particle Correlation ◽  
Special Cases ◽  
Corrective Term

The high frequency conductivity tensor of an isotropic plasma is derived taking into account particle correlations at the lowest consistent order in the parameter ωp/ω these correlations describe a weakly Langmuir turbulent plasma. Two special cases are investigated in which the two-particle correlation function is related to the turbulent electrostatic field spectrum. Particular distribution functions and spectra are considered and approximate dispersion relations are derived in both cases in ‘the cold plasma limit’. The importance of the corrective term is discussed in terms of three dimensionless parameters measuring the strength of the turbulence, the shape of the spectrum, and the frequency. The effect could be important for frequencies not too far from the plasma frequency.

Observations of ELF (extremely low frequency) signatures arising from space vehicle disturbances of the ionosphere

1991 ◽  
Vol 69 (8-9) ◽  
pp. 959-965 ◽  
Author(s):  
Jack Y. Dea ◽  
William Van Bise ◽  
Elizabeth A. Rauscher ◽  
Wolfgang-M. Boerner
Keyword(s):  
Geomagnetic Field ◽  
San Diego ◽  
Low Frequency ◽  
Space Vehicle ◽  
Lower Ionosphere ◽  
Space Vehicles ◽  
Extremely Low Frequency ◽  
Evanescent Fields ◽  
Hydromagnetic Waves

We report on observations of extremely low-frequency (ELF) signatures during exit or reentry of space vehicles through the ionosphere. The two modes regularly observed gave signals that peaked at 5.6 and 11.2 Hz. The evidence points to the lower ionosphere, i.e., the D- and E-layers, as the generator of these signals. The measurements were performed using ground-based multiturn coil sensors located in Reno and San Diego. The nature of these signals is unclear at present but it is surmised that we are detecting either the evanescent fields of hydromagnetic waves traveling in the ionosphere or the oscillating geomagnetic field associated with these hydromagnetic waves.

Theoretical cross-spectrum of the microfield measured by two small dipoles in a warm isotropic plasma

1977 ◽  
Vol 17 (2) ◽  
pp. 201-231 ◽  
Author(s):  
R. Pottelette ◽  
C. Chauliaguet ◽  
L. R. O. Storey
Keyword(s):  
Magnetic Field ◽  
Thermal Equilibrium ◽  
Plasma Frequency ◽  
Debye Length ◽  
Resonance Peak ◽  
Isotropic Plasma ◽  
Main Resonance ◽  
Mutual Impedance ◽  
Cross Spectrum ◽  
Electron Density And Temperature

We suggest that the electron density and temperature of a plasma could be determined by immersing two small dipole antennae in it, and by measuring, as a function of frequency, the cross-spectrum of the random signals that they receive. When the plasma is in thermal equilibrium, this spectrum is related simply, by Nyquist's theorem, to the real part of the mutual impedance of the two antennae. We have studied the case where, in addition, the plasma is collisionless and no magnetic field is present. The spectrum has a main resonance peak slightly above the plasma frequency, while for still higher frequencies it exhibits oscillations, the amplitudes of which decrease as one moves away from the plasma frequency. The main resonance peak becomes sharper, but smaller, as the distance between the antennae becomes large compared with the Debye length.

Optimal Space Trajectories—A Review of Published Work

1968 ◽  
Vol 72 (686) ◽  
pp. 141-146 ◽  
Author(s):  
D. J. Bell
Keyword(s):  
Gravitational Field ◽  
General Theory ◽  
Optimal Trajectory ◽  
Space Vehicle ◽  
Two Dimensions ◽  
Performance Criteria ◽  
Space Vehicles ◽  
Optimal Space Trajectories ◽  
End Conditions ◽  
Optimal Space

The problem of transferring a space vehicle between two points in a given gravitational field such that the minimum amount of fuel is used has been called the fundamental navigational problem of astronautics. In such a problem it may be required to find the optimum thrust magnitude and thrust direction which yields a minimum fuel trajectory. Furthermore, certain end conditions may be specified which the optimal trajectory must satisfy. In a large number of published papers the velocity of the vehicle is supposed known both at the beginning of the transfer and at the end whereas the time taken to complete the manoeuvre may or may not be given. Also, other performance criteria have been chosen besides minimum fuel. For example, minimum time of transit or maximum orbital altitude at perigee. Papers mentioned in this review deal mainly with flight in two dimensions apart from those sections on general theory. Furthermore, all space vehicles considered are assumed to have a fixed exhaust velocity unless otherwise stated.

Excitation of Electrostatic Fields in a Plasma by Transverse Electromagnetic Waves

1971 ◽  
Vol 49 (24) ◽  
pp. 3221-3226 ◽  
Author(s):  
M. P. Bachynski ◽  
B. W. Gibbs
Keyword(s):  
Electromagnetic Wave ◽  
Incident Wave ◽  
Electromagnetic Waves ◽  
Plasma Frequency ◽  
Incident Field ◽  
Isotropic Plasma ◽  
Electrostatic Fields ◽  
Plane Transverse ◽  
Dielectric Coefficient ◽  
Transverse Electromagnetic

An experiment has been conducted in which a plane transverse electromagnetic wave is incident from free space on a layer of isotropic plasma at small angles (0–12°) of incidence. Strong longitudinal electrostatic fields are observed within the plasma in the regions where the radian frequency of the incident wave equals the plasma frequency when the electric vector of the incident field is in the plane of incidence. Only weak longitudinal electrostatic fields are observed if the incident electric field is perpendicular to the plane of incidence. The observed phenomenon appears consistent with the field growth in a region where the dielectric coefficient of a plasma becomes zero.

Intelligent Techniques for Star-Pattern Recognition

2003 ◽  
Author(s):  
Lalitha Paladugu ◽  
Marco P. Schoen ◽  
Brian G. Williams
Keyword(s):  
Good Accuracy ◽  
Attitude Determination ◽  
Space Vehicle ◽  
Field Of View ◽  
Space Vehicles ◽  
Neural Network Approach ◽  
Star Pattern ◽  
The Neural Network ◽  
Star Pattern Recognition

This work presents the study of two different approaches for the attitude determination of space vehicles. The Neural Network approach is based on a simple Kohonen network, where the characteristics of a star distribution within the Field Of View (FOV) are matched against an on-board stored star map. The second approach utilizes a Genetic Algorithm (GA). The GA minimizes the discrepancy between the characteristics of the stars inside the FOV and a candidate FOV selected from the star map. Preliminary simulations indicate that both approaches work well and deliver good accuracy in determining the bore sight direction of the space vehicle with respect to the star map.

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