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351.
352.
The bandwidth of adaptive arrays with tapped delay lines behind the elements is examined. Such processing offers improved bandw over that attainable with quadrature hybrid processing. The performance of a two-element array with four types of processing (equarature hybrids, single delay lines, 3-tap delay lines, and 5-tap delay lines) is compared. It is shown that with half-wavelength element spacing, a quadrature hybrid and single delay-line processor are inadequate at 10-percent bandwidth. A 3-tap processor is adeq however, up to 40-percent bandwidth. 相似文献
353.
J.-P. Delaboudiniere R.A. Stern A. Maucherat F. Portier-Fozzani W.M. Neupert J.B. Gurman R.C. Catura J.R. Lemen L. Shing G.E. Artzner J. Brunaud A.H. Gabriel D.J. Michels J.D. Moses B. Au K.P. Dere R.A. Howard R. Kreplin J.M. Defise C. Jamar P. Rochus J.P. Chauvineau J.P. Marioge F. Clette P. Cugnon E.L. Van Dessel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2231-2237
The SOHO (SOlar and Heliospheric Observatory) satellite was launched on December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14th 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (Extreme ultraviolet Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Å images the chromosphere and the base of the transition region at a temperature of 5 − 8 × 104 K; the Fe IX–X filter at 171 Å images the corona at a temperature of 1.3 × 106 K; the Fe XII filter at 195 Å images the quiet corona outside coronal holes at a temperature of 1.6 × 106 K; and the Fe XV filter at 284 Å images active regions with a temperature of 2.0 × 106 K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection. 相似文献
354.
Charles F. Lillie Charles W. Hord Kevin Pang David L. Coffeen James E. Hansen 《Space Science Reviews》1977,21(2):159-181
The Voyager Photopolarimeter Experiment is designed to determine the physical properties of particulate matter in the atmospheres of Jupiter, Saturn, and the Rings of Saturn by measuring the intensity and linear polarization of scattered sunlight at eight wavelengths in the 2350–7500 Å region of the spectrum. The experiment will also provide information on the texture and probable composition of the surfaces of the satellites of Jupiter and Saturn and the properties of the sodium cloud around Io. During the planetary encounters a search for optical evidence of electrical discharges (lightning) and auroral activity will also be conducted. 相似文献
355.
This paper presents an overview of the identification and selection process of experiments and payloads for manned space flight missions, emphasizing the scope and magnitude of the problem of doing activity planning and the need for a methodology to assure timely flight and appropriate spacecraft design. Conclusions and results derived from the past several years are presented together with an analysis of the current procedure for defining activity for the space station. 相似文献
356.
On-board/in-flight checkout of future aerospace systems will necessitate a fundamental departure from today's design and checkout activities. The interrelationship of checkout, incorporated into prime vehicular functions, man as a subsystem, and standardization Of hardware/software must be considered as a functional and integral entity if the efforts of today's long-range planning are to become tomorrow's reality. This paper will describe future systems checkout, maintenance and support considerations, and actions and tentative measures necessary for implementation. The realization of the implementation of these concepts into functional elements will depend, accurately and economically, upon the degree of government perceptiveness and the extent of industrial support. 相似文献
357.
Avdeev S Bidoli V Casolino M De Grandis E Furano G Morselli A Narici L De Pascale MP Picozza P Reali E Sparvoli R Boezio M Carlson P Bonvicini W Vacchi A Zampa N Castellini G Fuglesang C Galper A Khodarovich A Ozerov Y Popov A Vavilov N Mazzenga G Ricci M Sannita WG Spillantini P 《Acta Astronautica》2002,50(8):511-525
The phenomenon of light flashes (LF) in eyes for people in space has been investigated onboard Mir. Data on particles hitting the eye have been collected with the SilEye detectors, and correlated with human observations. It is found that a nucleus in the radiation environment of Mir has roughly a 1% probability to cause an LF, whereas the proton probability is almost three orders of magnitude less. As a function of LET, the LF probability increases above 10 keV/micrometer, reaching about 5% at around 50 keV/micrometer. 相似文献
358.
J. P. Cox J. C. Wheeler C. J. Hansen D. S. King A. N. Cox S. W. Hodson 《Space Science Reviews》1980,27(3-4):529-535
The radial pulsations of very luminous, low-mass models (L/M 104, solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadiabatic. We find that there are in some cases at least one extra (strange) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars. 相似文献
359.
McEneaney W.M. Fitzpatrick B.G. Lauko I.G. 《IEEE transactions on aerospace and electronic systems》2004,40(4):1191-1216
A command and control (C/sup 2/) problem for military air operations is addressed. Specifically, we consider C/sup 2/ problems for air vehicles against ground-based targets and defensive systems. The problem is viewed as a stochastic game. We restrict our attention to the C/sup 2/ level where the problem may consist of a few unmanned combat air vehicles (UCAVs) or aircraft (or possibly teams of vehicles), less than say, a half-dozen enemy surface-to-air missile air defense units (SAMs), a few enemy assets (viewed as targets from our standpoint), and some enemy decoys (assumed to mimic SAM radar signatures). At this low level, some targets are mapped out and possible SAM sites that are unavoidably part of the situation are known. One may then employ a discrete stochastic game problem formulation to determine which of these SAMs should optimally be engaged (if any), and by what series of air vehicle operations. We provide analysis, numerical implementation, and simulation for full state-feedback and measurement feedback control within this C/sup 2/ context. Sensitivity to parameter uncertainty is discussed. Some insight into the structure of optimal and near-optimal strategies for C/sup 2/ is obtained. The analysis is extended to the case of observations which may be affected by adversarial inputs. A heuristic based on risk-sensitive control is applied, and it is found that this produces improved results over more standard approaches. 相似文献
360.