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571.
A two-way, noncoherent spacecraft navigation technique has been developed to provide velocity accuracy comparable to that available from a deep space coherent transponder (0.1 mm/s). The technique is compatible with the normal tracking procedures of the Deep Space Network (DSN) ground stations and does not require the use of a highly stable oscillator on-board the spacecraft. The measurement technique, potential error sources, and test results obtained with prototype hardware are described 相似文献
572.
Using empirical velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models
of anisotropic ion temperatures in the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation
of high frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which can heat and accelerate ions differently depending
on their charge and mass. We find that it is possible to explain the observed high perpendicular temperatures and strong anisotropies
with relatively small amplitudes for the resonant waves. There is suggestive evidence for steepening of the Alfvén wave spectrum
between the coronal base and the largest heights observed spectroscopically. Because the ion-cyclotron wave dissipation is
rapid, even for minor ions like O5+, the observed extended heating seems to demand a constantly replenished population of waves over several solar radii. This
indicates that the waves are generated gradually throughout the wind rather than propagated up from the base of the corona.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
573.
574.
A method is substantiated to ensure energy security for the satellite communication systems (SCS) at a close position of the
radio interception receiver. This is done by lowering the carrier frequency down to f
0 = 60…80 MHz and by applying spaced measurements with n ≥ 4 receiving antennas. 相似文献
575.
A. V. Tavrov O. I. Korablev A. V. Rodin I. I. Vinogradov A. Yu. Trokhimovsky A. Yu. Ivanov L. V. Ksanfomaliti D. A. Orlov 《Cosmic Research》2011,49(2):99-109
In order to observe exoplanets we propose a space-based achromatic stellar coronagraph combined with a 0.8–1.5 m telescope.
We develop an achromatic common path interferometer for observing an exoplanet (a faint off-axis source) on the background
of a hoste star (bright axial source). An image of the star and its copy acquire an achromatic phase shift by 180° and interfere
in antiphase. The achromatic phase shift is caused by geometric phase in the scheme of a three-dimensional interferometer.
The interference process divides spatially the dark and light fields of the star image redirecting them to the opposite sides
of a beam splitter. The interference process does not weaken the image of a planet, with equal intensities it is redirected
to both sides of a beam splitter. The suggested scheme of common path interferometer ensures mechanical stability. The background
signal is experimentally demonstrated to be reduced by six orders of magnitude. 相似文献
576.
I. A. Galiullin 《Cosmic Research》2011,49(2):175-178
The constraints imposed on parameters of a force field and of a symmetrical gyrostat in it are determined, at which regular
precession of this gyrostat demonstrate Lyapunov stability (or, respectively, instability). 相似文献
577.
Kapoor R. Banerjee A. Tsihrintzis G.A. Nandhakumar N. 《IEEE transactions on aerospace and electronic systems》1999,35(3):819-834
We address the problem of detection of targets obscured by a forest canopy using an ultrawideband (UWB) radar. The forest clutter observed in the radar imagery is a highly impulsive random process that is more accurately modeled with the recently proposed class of alpha-stable processes as compared with Gaussian, Weibull, and K-distribution models. With this more accurate model, segmentation is performed on the imagery into forest and clear regions. Further, a region-adaptive symmetric alpha stable (SαS) constant false-alarm rate (CFAR) detector is introduced and its performance is compared with the Weibull and Gaussian CFAR detectors. The results on real data show that the SαS CFAR performs better than the Weibull and Gaussian CFAR detectors in detecting obscured targets 相似文献
578.
Possible consequences of collisions of natural cosmic bodies with the Earth’s atmosphere and surface are described. The methodological
basis of classification of consequences is the solution of meteor physics equations characterizing the trajectory of a body
in the atmosphere, namely, the dependence of the body’s velocity and mass on the flight altitude. The solution depends on
two dimensionless parameters characterizing the drag altitude and the role of mass loss by a meteoroid during its motion in
the atmosphere. Depending on values of these parameters, the degree of effect on the planetary surface considerably changes.
In particular, the conditions of cratering and meteorite fall on the planetary surface are obtained. The results are presented
in a simple analytical form. They quite match to the real events considered in the paper. Recommendations are given on further
investigations into the important problem of interaction of cosmic bodies with planetary atmospheres. 相似文献
579.
580.
B. A. Antuf’ev 《Russian Aeronautics (Iz VUZ)》2008,51(3):227-231
A problem on low vibrations of a thin spherical shell is considered. A solid of finite dimensions is discretely attached to the shell by means of an elastic rod system. The calculation examples are presented. 相似文献