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991.
Blanc M. Bolton S. Bradley J. Burton M. Cravens T.E. Dandouras I. Dougherty M.K. Festou M.C. Feynman J. Johnson R.E. Gombosi T.G. Kurth W.S. Liewer P.C. Mauk B.H. Maurice S. Mitchell D. Neubauer F.M. Richardson J.D. Shemansky D.E. Sittler E.C. Tsurutani B.T. Zarka Ph. Esposito L.W. Grün E. Gurnett D.A. Kliore A.J. Krimigis S.M. Southwood D. Waite J.H. Young D.T. 《Space Science Reviews》2002,104(1-4):253-346
Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres.
These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's ‘intrinsic’
magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects
will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles
and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific
questions concerning the interaction of these two magnetospheres with their environment.
The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity
and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in
the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's
induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic
field of Titan.
Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition
to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss
what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards,
we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites,
which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps
the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between
dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics
is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the
magnetosphere and Saturn's upper atmosphere, and the source of Saturn's auroral emissions, including the kilometric radiation.
For each of these regions we identify the key scientific questions and propose an investigation strategy to address them.
Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible
to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all,
of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an
efficient strategy in which in situ measurements and remote sensing observations complement each other.
Saturn's magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission.
All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles
— are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting
aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems
form.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
P. A. J. de Korte J. A. M. Bleeker A. J. F. den Boggende G. Branduardi-Raymont A. C. Brinkman J. L. Culhane E. H. B. M. Gronenschild I. Mason S. P. McKechnie 《Space Science Reviews》1981,30(1-4):495-511
The instrument configuration and performance characteristics of the X-ray imaging telescopes on EXOSAT are described. The instrument comprises two fully independent Wolter I imaging telescopes. Each telescope can be used in either of two principal modes: (i) an imaging mode with either a position sensitive proportional counter or a channel multiplier array plate in the focal plane, (ii) a spectrometer mode which features a 500 lines/mm and/or a 1000 lines/mm transmission grating as dispersive element.Preliminary results from the calibration of the fully integrated experiment indicate an ultimate angular resolution of 8.5 arc sec full width at half maximum or 17.5 arc sec half-power beam width. The ultimate wavelength resolution in the spectrometer mode ranges from 1Å for wavelengths below 50Å, to 5Å at wavelengths near 300Å.A method for estimating the telescope performance is given which reasonably accounts for the influence of the X-ray source spectrum and the degree of interstellar absorption on the counting statistics.A comparison between EXOSAT and the EINSTEIN telescope in terms of band width/resolution and minimum source detectability shows an enhanced potential for EXOSAT relative to EINSTEIN for sources with T 107K and low column densities (< 4 × 1020cm–2) and a reduced potential for sources with hard, or heavily cut-off, spectra. 相似文献
993.
Minimum mean-square-error demodulators for pulse-frequency-modulated signals are considered. The optimum demodulator structure is found and a suboptimum one is proposed that may be implemented by standard circuitry. 相似文献
994.
The low-energy neutral atom imager for IMAGE 总被引:1,自引:0,他引:1
Moore T.E. Chornay D.J. Collier M.R. Herrero F.A. Johnson J. Johnson M.A. Keller J.W. Laudadio J.F. Lobell J.F. Ogilvie K.W. Rozmarynowski P. Fuselier S.A. Ghielmetti A.G. Hertzberg E. Hamilton D.C. Lundgren R. Wilson P. Walpole P. Stephen T.M. Peko B.L. Van Zyl B. Wurz P. Quinn J.M. Wilson G.R. 《Space Science Reviews》2000,91(1-2):155-195
The `Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) will be launched early in the year 2000. It will be the first mission dedicated to imaging, with the capability to determine how the magnetosphere changes globally in response to solar storm effects in the solar wind, on time scales as short as a few minutes. The low energy neutral atom (LENA) imager uses a new atom-to-negative ion surface conversion technology to image the neutral atom flux and measure its composition (H and O) and energy distribution (10 to 750 eV). LENA uses electrostatic optics techniques for energy (per charge) discrimination and carbon foil time-of-flight techniques for mass discrimination. It has a 90°×° field-of-view in 12 pixels, each nominally 8°×°. Spacecraft spin provides a total field-of-view of 90°×360°, comprised of 12×45 pixels. LENA is designed to image fast neutral atom fluxes in its energy range, emitted by auroral ionospheres or the sun, or penetrating from the interstellar medium. It will thereby determine how superthermal plasma heating is distributed in space, how and why it varies on short time scales, and how this heating is driven by solar activity as reflected in solar wind conditions. 相似文献
995.
ACTIVE SPACECRAFT POTENTIAL CONTROL 总被引:1,自引:0,他引:1
W. Riedler K. Torkar F. RÜDENAUER M. Fehringer A. Pedersen R. Schmidt R. J. L. Grard H. Arends B. T. Narheim J. Troim R. Torbert R. C. Olsen E. Whipple R. Goldstein N. Valavanoglou HUA Zhao 《Space Science Reviews》1997,79(1-2):271-302
Charging of the outer surface or of the entire structure of a spacecraft in orbit can have a severe impact on the scientific output of the instruments. Typical floating potentials for magnetospheric satellites (from +1 to several tens of volts in sunlight) make it practically impossible to measure the cold (several eV) component of the ambient plasma. Effects of spacecraft charging are reduced by an entirely conductive surface of the spacecraft and by active charge neutralisation, which in the case of Cluster only deals with a positive potential. The Cluster spacecraft are instrumented with ion emitters of the liquid-metal ion-source type, which will produce indium ions at 5 to 8 keV energy. The operating principle is field evaporation of indium in the apex field of a needle. The advantages are low power consumption, compactness and high mass efficiency. The ion current will be adjusted in a feedback loop with instruments measuring the spacecraft potential (EFW and PEACE). A stand-alone mode is also foreseen as a back-up. The design and principles of the operation of the active spacecraft potential control instrument (ASPOC) are presented in detail. Flight experience with a similar instrument on the Geotail spacecraft is outlined. 相似文献
996.
综述了中空纤维释放黏结剂的裂纹愈合及近期开发的机敏裂纹自愈合复合材料的研究进展。对后者微胶囊促使的机敏裂纹自愈合进行了详尽的阐述。其中包括愈合剂和催化剂的结构、微胶囊的形成和外表连接催化剂、愈合剂系统原位聚合反应、纯环氧树脂基体和复合材料中的裂纹自愈合、愈合效率及愈合复合材料微观表征等方面。一个典型的双相自愈合系统是包含于微胶囊中的二聚环戊二烯(DCPD),通过埋于环氧基体中的钌络合物催化剂进行开环转位聚合反应(ROMP),形成新的聚合物来愈合裂纹。在纯环氧树脂基体中,上述自愈合系统在室温下的愈合效率可高达90%,而在碳纤维复合材料中室温下的愈合效率大致是45%,在80℃可提高到80%。降冰片烯(Norbomene)及其衍生物具有同以上系统相似的自愈合功能。三聚呋喃和四聚马来酰亚胺可在无催化剂作用下,进行热可逆的、无终止的交联聚合反应,自动愈合裂纹。同时,对以上三种自愈合剂系统及复合材料的特点进行了比较。 相似文献
997.
The development of mathematical models suitable for minimum weight boost and buck-boost converter designs are presented. The facility of an augumented Lagrangian (ALAG) multiplier-based nonlinear programming technique is demonstrated for minimum weight design optimizations of boost and buck-boost power converters. ALAG-based computer simulation results for those two minimum weight designs are discussed. Certain important features of ALAG are presented in the framework of a comprehensive design example for boost and buck-boost power converter design optimization. The study provides refreshing design insight of power converters and presents such information as weight and loss profiles of various semiconductor components and magnetics as a function of the switching frequency. 相似文献
998.
Gray M. Hutchinson F. Ridgely D. Fruge F. Cooke D. 《IEEE transactions on aerospace and electronic systems》1969,(4):632-637
In the deployment of pulse Doppler (PD) radar, determination of phase and amplitude stability is the most difficult measurement problem. Unique requirements are placed on pulse and carrier stability so that the radar can perform in strong clutter. Because of subclutter visibility and sensitivity specifications, coherent noise, which is insignificant for noncoherent pulse radars, becomes extremely important. In solving the measurement problem, special support equipment was developed which is considered to have reached such a degree of refinement that it is probably one of the most technically advanced pieces of field test equipment supporting any operational radar. This paper discusses stability requirements, sources of instability, and the combination of techniques selected for verification of compliance of the PD radar with the stability requirements. The results of a program to develop special field support equipment to satisfy the measurement requirements are emphasized. Results of field experience and the special training required of military field personnel to enable them to effectively use this relatively complex support equipment are discussed. 相似文献
999.
O Iversen T-HRasmussen F Gmünder C Baggerud E L Kordyum V V Lozovaya M Tairbekov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):123-131
An experiment using plant protoplasts has been accepted for the IML-1 Space Shuttle mission scheduled for 1991. Preparatory experiments have been performed using both fast and slow rotating clinostats and in orbit to study the effect of simulated and real weightlessness on protoplast regeneration. Late access to the space vehicles before launch has required special attention since it is important to delay cell wall regeneration until the samples are in orbit. On a flight on Biokosmos 9 ("Kosmos-2044") in September 1989 some preliminary results were obtained. Compared to the ground control, the growth of both carrot and rapeseed protoplasts was decreased by 18% and 44% respectively, after 14 days in orbit. The results also indicated that there is less cell wall regeneration under micro-g conditions. Compared to the ground controls the production of cellulose in rapeseed and carrot flight samples was only 46% and 29% respectively. The production of hemicellulose in the flight samples was 63% and 67% respectively of that of the ground controls. In both cases all samples reached the stage of callus development. The peroxidase activity was also found to be lower in the flight samples than in the ground controls, and the number of different isoenzymes was decreased in the flight samples. In general, the regeneration processes were retarded in the flight samples with respect to the ground controls. From a simulation experiment for IML-1 performed in January 1990 at ESTEC, Holland, regenerated plants have been obtained. These results are discussed and compared to the results obtained on Biokosmos 9. Protoplast regeneration did not develop beyond the callus stage in either the flight or the ground control samples from the Biokosmos 9 experiment. 相似文献
1000.
Deep space environments for human exploration. 总被引:3,自引:0,他引:3
J W Wilson M S Clowdsley F A Cucinotta R K Tripathi J E Nealy G De Angelis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1281-1287
Mission scenarios outside the Earth's protective magnetic shield are being studied. Included are high usage assets in the near-Earth environment for casual trips, for research, and for commercial/operational platforms, in which career exposures will be multi-mission determined over the astronaut's lifetime. The operational platforms will serve as launching points for deep space exploration missions, characterized by a single long-duration mission during the astronaut's career. The exploration beyond these operational platforms will include missions to planets, asteroids, and planetary satellites. The interplanetary environment is evaluated using convective diffusion theory. Local environments for each celestial body are modeled by using results from the most recent targeted spacecraft, and integrated into the design environments. Design scenarios are then evaluated for these missions. The underlying assumptions in arriving at the model environments and their impact on mission exposures within various shield materials will be discussed. 相似文献