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11.
Numerical simulations of energy depositions in the middle and upper solar chromosphere result in ejection of chromospheric material into the corona and heating of the chromospheric gas. These simulations may be capable of describing some of the features seen by the soft X-ray telescope on board theYohkoh satellite. 相似文献
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13.
Until pristine samples can be returned from cometary nuclei, primitive meteorites represent our best source of information
about organic chemistry in the early solar system. However, this material has been affected by secondary processing on asteroidal
parent bodies which probably did not affect the material now present in cometary nuclei. Production of meteoritic organic
matter apparently involved the following sequence of events: Molecule formation by a variety of reaction pathways in dense
interstellar clouds; Condensation of those molecules onto refractory interstellar grains; Irradiation of organic-rich interstellar-grain
mantles producing a range of molecular fragments and free radicals; Inclusion of those interstellar grains into the protosolar
nebula with probable heating of at least some grain mantles during passage through the shock wave bounding the solar accretion
disc; Agglomeration of residual interstellar grains and locally produced nebular condensates into asteroid-sized planetesimals;
Heating of planetesimals by decay of extinct radionuclides; Melting of ice to produce liquid water within asteroidal bodies;
Reaction of interstellar molecules, fragments and radicals with each other and with the aqueous environment, possibly catalysed
by mineral grains; Loss of water and other volatiles to space yielding a partially hydrated lithology containing a complex
suite of organic molecules; Heating of some of this organic matter to generate a kerogen-like complex; Mixing of heated and
unheated material to yield the meteoritic material now observed. Properties of meteoritic organic matter believed to be consistent
with this scenario include: Systematic decrease of abundance with increasing C number in homologous series of characterisable
molecules; Complete structural diversity within homologous series; Predominance of branched-chain isomers; Considerable isotopic
variability among characterisable molecules and within kerogen-like material; Substantial deuterium enrichment in all organic
fractions; Some fractions significantly enriched in nitrogen-15; Modest excesses of L-enantiomers in some racemisation-resistant
molecules but no general enantiomeric preference. Despite much speculation about the possible role of Fischer-Tropsch catalytic
hydrogenation of CO in production of organic molecules in the solar nebula, no convincing evidence for such material has been
found in meteorites. A similarity between some meteoritic organics and those produced by Miller-Urey discharge synthesis may
reflect involvement of common intermediates rather than the operation of electric discharges in the early solar system. Meteoritic
organic matter constitutes a useful, but not exact, guide to what we shall find with in situ analytical and sample-return
missions to cometary nuclei.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Leslie A. Young S. Alan Stern Harold A. Weaver Fran Bagenal Richard P. Binzel Bonnie Buratti Andrew F. Cheng Dale Cruikshank G. Randall Gladstone William M. Grundy David P. Hinson Mihaly Horanyi Donald E. Jennings Ivan R. Linscott David J. McComas William B. McKinnon Ralph McNutt Jeffery M. Moore Scott Murchie Catherine B. Olkin Carolyn C. Porco Harold Reitsema Dennis C. Reuter John R. Spencer David C. Slater Darrell Strobel Michael E. Summers G. Leonard Tyler 《Space Science Reviews》2008,140(1-4):93-127
The New Horizons spacecraft will achieve a wide range of measurement objectives at the Pluto system, including color and panchromatic maps, 1.25–2.50 micron spectral images for studying surface compositions, and measurements of Pluto’s atmosphere (temperatures, composition, hazes, and the escape rate). Additional measurement objectives include topography, surface temperatures, and the solar wind interaction. The fulfillment of these measurement objectives will broaden our understanding of the Pluto system, such as the origin of the Pluto system, the processes operating on the surface, the volatile transport cycle, and the energetics and chemistry of the atmosphere. The mission, payload, and strawman observing sequences have been designed to achieve the NASA-specified measurement objectives and maximize the science return. The planned observations at the Pluto system will extend our knowledge of other objects formed by giant impact (such as the Earth–moon), other objects formed in the outer solar system (such as comets and other icy dwarf planets), other bodies with surfaces in vapor-pressure equilibrium (such as Triton and Mars), and other bodies with N2:CH4 atmospheres (such as Titan, Triton, and the early Earth). 相似文献
15.
Flow corridors are a new class of trajectory-based airspace which derives from the next generation air transportation system concept of operations. Reducing the airspace complexity and increasing the capacity are the main purposes of the en-route corridor. This paper analyzes the collision risk-capacity tradeoff using a combined discrete–continuous simulation method. A basic two-dimensional en-route flow corridor with performance rules is designed as the operational environment. A second-order system is established by combining the point mass model and the proportional derivative controller together to simulate the self-separation operations of the aircrafts in the corridor and the operation performance parameters from the User Manual for the Base of Aircraft Data are used in this research in order to improve the reliability. Simulation results indicate that the aircrafts can self-separate from each other efficiently by adjusting their velocities,and rationally setting the values of some variables can improve the rate and stability of the corridor with low risks of loss of separation. 相似文献
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17.
Andrew J. Ball Michael E. Price Roger J. Walker Glyn C. Dando Nigel S. Wells John C. Zarnecki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We describe a Mars ‘Micro Mission’ for detailed study of the martian satellites Phobos and Deimos. The mission involves two ∼330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988–89) failed to realise its full potential. Many questions remain concerning the moons’ origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA’s Aurora programme. 相似文献
18.
Jean Claude Uwamahoro John Bosco Habarulema Dalia Buresova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(10):3102-3118
A statistical evaluation of storm-time total electron content (TEC) modelling techniques over various latitudes of the African sector and surrounding areas is presented. The source of observational TEC data used in this study is the Global Navigation Satellite Systems (GNSS), specifically the Global Positioning Systems (GPS) receiver networks. For each selected receiver station, three different storm-time models based on empirical orthogonal functions (EOF) analysis, non-linear regression analysis (NLRA) and Artificial neural networks (ANN), were implemented. Storm-time GPS TEC data used for both development and validation of the models was selected based on the storm criterion of nT or to take into account both coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs) driven storms, respectively. To make an independent test of the models, storm periods considered for validation were excluded from datasets used during the implementation of the models and results are compared with observations, monthly median values, and International Reference Ionosphere (IRI-2016) predictions. Considering GPS TEC as reference, a statistical analysis performed over six storm periods reserved for validation revealed that ANN model is about 10%, 26%, and 58% more accurate than EOF, NLRA, and IRI models, respectively. It was further found that, EOF model performs 15%, and 44% better than NLRA, and IRI models, respectively, while NLRA is 25% better than IRI. On the other hand, results are also discussed referring to the background ionosphere represented by monthly median TEC (MM TEC) and statistics are provided. Moreover, strengths and weaknesses of each model are highlighted. 相似文献
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20.
John M. Logsdon 《Space Policy》1987,3(2)
This response to Alex Roland's article, ‘Priorities in space for the USA’, argues that his analysis and conclusions are based on shaky historical evidence. Professor Roland's interpretation of NASA's priorities since 1959 is challenged, and it is pointed out that the manned spaceflight programme has widespread support in the USA. The most important issue, raised by the article but not treated extensively enough, is whether the pursuit of the widely accepted emphasis on manned spaceflight is a large-scale societal mistake. 相似文献