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51.
Space Science Reviews - 相似文献
52.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
53.
Two methods of calculating the resultant vector and principal moment of light pressure forces, having an effect on a spacecraft
with a composite solar sail, are compared. The first method is based on analytical formulas obtained without regard to shading
of some parts of the sail by others. The second method uses a detailed geometrical model of the sail, which allows one to
take such shading into account. Some part of photons falling on a sail is supposed to be reflected from it in a mirror manner,
while the others are completely absorbed. The range of variation of sail orientation parameters with respect to incident solar
light streams, where the first method turns out to be accurate enough, is found. 相似文献
54.
根据TeamSAI和Ascend公司的最新数据,2009年世界航空运输维修市场(MRO)将比2008年增长1.4%,达到457亿美元.如果不考虑材料和劳动力成本上涨等因素,2009年MRO市场实际将比2008年的451亿美元降低2.3%. 相似文献
55.
The organization principles of constructing the European system of warning about dangerous situations in the outer space are
considered in the paper. 相似文献
56.
57.
Hauke Hussmann Frank SohlJürgen Oberst 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Key information on Europa’s interior can be gained by monitoring tidally-induced surface deformations from orbiting and landed spacecraft. Such observations would provide constraints on the thickness and rheology of Europa’s ice and liquid water layer, being thus an important tool to characterize basic physical properties of the satellite’s putative subsurface water ocean. Focusing on the outer ice-I layer we will present relations between the interior of Europa and key tidal parameters that can be retrieved from an instrument suite monitoring tidally-induced changes of local gravity, tilt, latitude and strain at the surface. A most promising approach would involve laser altimetry and gravitational field observations from an orbiting spacecraft combined with monitoring of tidally-induced gravity and tilt changes at the surface. However, tidal measurements at the surface may be significantly impeded by instrumental drift, instrument coupling to the surface, local sources of noise and the presumably short life-time of the instruments due to the harsh radiation environment. 相似文献
58.
59.
Bela G. Fejer 《Space Science Reviews》2011,158(1):145-166
The low latitude ionosphere is strongly affected by several highly variable electrodynamic processes. Over the last two decades
ground-based and satellite measurements and global numerical models have been extensively used to study the longitude-dependent
climatology of low latitude electric fields and currents. These electrodynamic processes and their ionospheric effects exhibit
large ranges of temporal and spatial variations during both geomagnetic quiet and disturbed conditions. Numerous recent studies
have investigated the short term response of equatorial electric fields and currents to lower atmospheric transport processes
and solar wind-magnetosphere driving mechanisms. This includes the large electric field and current perturbations associated
with arctic sudden stratospheric warming events during geomagnetic quiet times and highly variable storm time prompt penetration
and ionospheric disturbance dynamo effects. In this review, we initially describe recent experimental and numerical modeling
results of the global climatology and short term variability of quiet time low latitude electrodynamic plasma drifts. Then,
we examine the present understanding of equatorial electric field and current perturbation fields during periods of enhanced
geomagnetic activity. 相似文献
60.
Transfers with a low thrust are considered under constraints imposed on the thrust vector direction. These constraints can be caused by peculiarities of the attitude control system and the mode of stabilization of a spacecraft, and, in the general case, they are functions of the time and state vector. The constraints specified by equalities and inequalities are investigated. It is shown that the optimal thrust is directed along the projection of the Lawden’s primer vector onto the restricting set. 相似文献