排序方式: 共有29条查询结果,搜索用时 31 毫秒
21.
D. Oertel D. Spänkuch H. Jahn H. Becker-Ross W. Stadthaus J. Nopirakowski W. Döhler K. Schäfer J. Güldner R. Dubois V.I. Moroz V.M. Linkin V.V. Kerzhanovich I.A. Matsgorin A.N. Lipatov A.A. Shurupov L.V. Zasova E.A. Ustinov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(9):25-36
Fourier spectrometers for the investigation of infrared spectra of Venus were installed on the recent Soviet orbiters “Venera-15” and “Venera-16”. Many spectra with reliable absolute calibration were obtained in the 280–1500 cm?1 region with a spectral resolution of 5 cm?1 (ground based processing) and about 7 cm?1 (preoprocessed on board) and a spatial resolution of about 100 km at the Venusian cloud top level. Bands of CO2, H2O, H2SO4 and SO2 are identified. The 15 μm-CO2- fundamental band was used for retrieval of altitude dependent temperature profiles. There are significant differences in the cloud structure above 60 km for distinct regions of Venus, demonstrated by differences in the spectra. 相似文献
22.
The reasoning which led to the particular slot structure defined for the collision avoidance system specified by the Air Transportation Association Collision Avoidance System Technical Working Group is discussed. The objectives were to choose a slot length that would 1) minimize the probability of interference, 2) maximize the capacity of the information channel (as measured by the number of messages received in a unit of time). Interference can be manifested by the garbling of either the collision avoidance message or the synchronization signals. 相似文献
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24.
Beaty DW Clifford SM Borg LE Catling DC Craddock RA Des Marais DJ Farmer JD Frey HV Haberle RM McKay CP Newsom HE Parker TJ Segura T Tanaka KL 《Astrobiology》2005,5(6):663-689
In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be. 相似文献
25.
Conclusions Passive observation of the naturally occurring γ-ray and X-ray from the planets is potentially an important technique for
determining their gross chemical composition and on the basis of natural γ-radiation determining if the planetary surface
is composed of differential material. If the planet is not covered by a thick atmosphere then it is possible to map the distribution
of the most abundant elements on a scale of spatial resolution that is of the order of the altitude at which the observations
are made. Initial observations carried out from lunar orbit have shown that the flux levels are approximately as expected
and that the lunar surface is not characterized by any widespread distribution of acidic rocks in the region observed by the
Luna 10 spacecraft. 相似文献
26.
Starting from their FIRES proposal [1]the DLR makes a new approach in the design of a small satellite mission dedicated to hot spot detection and evaluation: the BIRD mission. The new approach is characterized by a strict design-to-cost philosophy. A two-channel infrared sensor system in combination with a Wide-Angle Optoelectronic Stereo Scanner (WAOSS) shall be the payload of a small satellite (80kg) considered for piggyback launch. So the launch is not a main cost driver as for other small satellite missions with dedicated launchers. The paper describes the mission objectives, the scientific payload, the spacecraft bus, and the mission architecture of a small satellite mission dedicated to the investigation of hot spots (forest fires, volcanic activities, burning oil wells or coal seams), of vegetation condition and changes and of clouds. The paper represents some results of a phase A study and of the progressing phase B. 相似文献
27.
Many observations of geomagnetic cutoff phenomena and their implications with respect to the dynamics of charged particles in the geomagnetic field are discussed. Störmer's analytic treatment of the motion of charged particles in a dipole field is briefly reviewed, as are the approximate treatments of charged particle motions, first developed by Alfvén, which were to find successful application to the more complex fields now known to exist in the magnetosphere. In conclusion, the present understanding of geomagnetic cutoffs, together with some remaining areas of uncertainty are examined. 相似文献
28.
Medium energy neutral atom (MENA) imager for the IMAGE mission 总被引:1,自引:0,他引:1
Pollock C.J. Asamura K. Baldonado J. Balkey M.M. Barker P. Burch J.L. Korpela E.J. Cravens J. Dirks G. Fok M.-C. Funsten H.O. Grande M. Gruntman M. Hanley J. Jahn J.-M. Jenkins M. Lampton M. Marckwordt M. McComas D.J. Mukai T. Penegor G. Pope S. Ritzau S. Schattenburg M.L. Scime E. Skoug R. Spurgeon W. Stecklein T. Storms S. Urdiales C. Valek P. van Beek J.T.M. Weidner S.E. Wüest M. Young M.K. Zinsmeyer C. 《Space Science Reviews》2000,91(1-2):113-154
The Medium Energy Neutral Atom (MENA) imager was developed in response to the Imaging from the Magnetopause to the Aurora for Global Exploration (IMAGE) requirement to produce images of energetic neutral atoms (ENAs) in the energy range from 1 to 30 keV. These images will be used to infer characteristics of magnetospheric ion distributions. The MENA imager is a slit camera that images incident ENAs in the polar angle (based on a conventional spherical coordinate system defined by the spacecraft spin axis) and utilizes the spacecraft spin to image in azimuth. The speed of incident ENAs is determined by measuring the time-of-flight (TOF) from the entrance aperture to the detector. A carbon foil in the entrance aperture yields secondary electrons, which are imaged using a position-sensitive Start detector segment. This provides both the one-dimensional (1D) position at which the ENA passed through the aperture and a Start time for the TOF system. Impact of the incident ENA on the 1D position-sensitive Stop detector segment provides both a Stop-timing signal and the location that the ENA impacts the detector. The ENA incident polar angle is derived from the measured Stop and Start positions. Species identification (H vs. O) is based on variation in secondary electron yield with mass for a fixed ENA speed. The MENA imager is designed to produce images with 8°×4° angular resolution over a field of view 140°×360°, over an energy range from 1 keV to 30 keV. Thus, the MENA imager is well suited to conduct measurements relevant to the Earth's ring current, plasma sheet, and (at times) magnetosheath and cusp. 相似文献
29.
Herbert I. M. Lichtenegger Helmut Lammer Yuri N. Kulikov Shahin Kazeminejad Gregorio H. Molina-Cuberos Rafael Rodrigo Bobby Kazeminejad Gottfried Kirchengast 《Space Science Reviews》2006,126(1-4):469-501
The heating of the upper atmospheres and the formation of the ionospheres on Venus and Mars are mainly controlled by the solar
X-ray and extreme ultraviolet (EUV) radiation (λ = 0.1–102.7 nm and can be characterized by the 10.7 cm solar radio flux).
Previous estimations of the average Martian dayside exospheric temperature inferred from topside plasma scale heights, UV
airglow and Lyman-α dayglow observations of up to ∼500 K imply a stronger dependence on solar activity than that found on
Venus by the Pioneer Venus Orbiter (PVO) and Magellan spacecraft. However, this dependence appears to be inconsistent with
exospheric temperatures (<250 K) inferred from aerobraking maneuvers of recent spacecraft like Mars Pathfinder, Mars Global
Surveyor and Mars Odyssey during different solar activity periods and at different orbital locations of the planet. In a similar
way, early Lyman-α dayglow and UV airglow observations by Venera 4, Mariner 5 and 10, and Venera 9–12 at Venus also suggested
much higher exospheric temperatures of up to 1000 K as compared with the average dayside exospheric temperature of about 270
K inferred from neutral gas mass spectrometry data obtained by PVO. In order to compare Venus and Mars, we estimated the dayside
exobase temperature of Venus by using electron density profiles obtained from the PVO radio science experiment during the
solar cycle and found the Venusian temperature to vary between 250–300 K, being in reasonable agreement with the exospheric
temperatures inferred from Magellan aerobraking data and PVO mass spectrometer measurements. The same method has been applied
to Mars by studying the solar cycle variation of the ionospheric peak plasma density observed by Mars Global Surveyor during
both solar minimum and maximum conditions, yielding a temperature range between 190–220 K. This result clearly indicates that
the average Martian dayside temperature at the exobase does not exceed a value of about 240 K during high solar activity conditions
and that the response of the upper atmosphere temperature on Mars to solar activity near the ionization maximum is essentially
the same as on Venus. The reason for this discrepancy between exospheric temperature determinations from topside plasma scale
heights and electron distributions near the ionospheric maximum seems to lie in the fact that thermal and photochemical equilibrium
applies only at altitudes below 170 km, whereas topside scale heights are derived for much higher altitudes where they are
modified by transport processes and where local thermodynamic equilibrium (LTE) conditions are violated. Moreover, from simulating
the energy density distribution of photochemically produced moderately energetic H, C and O atoms, as well as CO molecules,
we argue that exospheric temperatures inferred from Lyman-α dayglow and UV airglow observations result in too high values,
because these particles, as well as energetic neutral atoms, transformed from solar wind protons into hydrogen atoms via charge
exchange, may contribute to the observed planetary hot neutral gas coronae. Because the low exospheric temperatures inferred
from neutral gas mass spectrometer and aerobraking data, as well as from CO+
2 UV doublet emissions near 180–260 nm obtained from the Mars Express SPICAM UV spectrograph suggest rather low heating efficiencies,
some hitherto unidentified additional IR-cooling mechanism in the thermospheres of both Venus and Mars is likely to exist.
An erratum to this article can be found at 相似文献