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1.
This paper provides an overview of a system for providing reliable, ongoing, timely situational awareness services to satellite operators. Such services would include close approach warnings, warnings of potential radio frequency interference, and other offerings designed to help make operators aware of possible threats to the safe operation of their spacecraft and measures they can take to lessen these threats. The paper discusses current trends, proposes operational requirements, and speculates on the type of organization that may emerge to provide space traffic control services. It highlights how the detailed information required for such services may affect the evolution of the use of space. 相似文献
2.
Laser-Raman imagery is a non-intrusive, non-destructive analytical technique, recently introduced to Precambrian paleobiology, that can be used to demonstrate a one-to-one spatial correlation between the optically discernible morphology and kerogenous composition of permineralized fossil microorganisms. Made possible by the submicron-scale resolution of the technique and its high sensitivity to the Raman signal of carbonaceous matter, such analyses can be used to determine the chemical-structural characteristics of organic-walled microfossils and associated sapropelic carbonaceous matter in acid-resistant residues and petrographic thin sections. Here we use this technique to analyze kerogenous microscopic fossils and associated carbonaceous sapropel permineralized in 22 unmetamorphosed or little-metamorphosed fine-grained chert units ranging from approximately 400 to approximately 2,100 Ma old. The lineshapes of the Raman spectra acquired vary systematically with five indices of organic geochemical maturation: (1) the mineral-based metamorphic grade of the fossil-bearing units; (2) the fidelity of preservation of the fossils studied; (3) the color of the organic matter analyzed; and both the (4) H/C and (5) N/C ratios measured in particulate kerogens isolated from bulk samples of the fossil-bearing cherts. Deconvolution of relevant spectra shows that those of relatively well-preserved permineralized kerogens analyzed in situ exhibit a distinctive set of Raman bands that are identifiable also in hydrated organic-walled microfossils and particulate carbonaceous matter freed from the cherts by acid maceration. These distinctive Raman bands, however, become indeterminate upon dehydration of such specimens. To compare quantitatively the variations observed among the spectra measured, we introduce the Raman Index of Preservation, an approximate measure of the geochemical maturity of the kerogens studied that is consistent both with the five indices of organic geochemical alteration and with spectra acquired from fossils experimentally heated under controlled laboratory conditions. The results reported provide new insight into the chemical-structural characteristics of ancient carbonaceous matter, the physicochemical changes that accompany organic geochemical maturation, and a new criterion to be added to the suite of evidence by which to evaluate the origin of minute fossil-like objects of possible but uncertain biogenicity. 相似文献
3.
Thompson William B. Valiquette Carolyn M. Bennett Bonnie H. Sutherland Karen T. 《Spatial Cognition & Computation》1999,1(3):291-321
Map-based navigation in outdoor terrain lacking man-made structures or other highly distinctive landmarks can produce severe localization problems. This paper presents an approach to navigation which implements high level geometric reasoning and matching strategies based on those used by skilled human navigators. This approach, which is demonstrated on a real example involving imagery of mountainous terrain obtained with a video camera and USGS map data, is designed to avoid many of the pitfalls occurring when an attempt is made to navigate by modeling the environment mathematically. It exploits feature attributes which cannot be easily expressed quantitatively but are central to the successful human navigation process. 相似文献
4.
Mahaffy P.R. Donahue T.M. Atreya S.K. Owen T.C. Niemann H.B. 《Space Science Reviews》1998,84(1-2):251-263
The Galileo Probe Mass Spectrometer measurements in the atmosphere of Jupiter give D/H = (2.6 ± 0.7) × 10-5 3He/4He = (1.66 ± 0.05) × 10-4These ratios supercede earlier results by Niemann et al. (1996) and are based on a reevaluation of the instrument response at high count rates and a more detailed study of the contributions of different species to the mass peak at 3 amu. The D/H ratio is consistent with Voyager and ground based data and recent spectroscopic and solar wind (SW) values obtained from the Infrared Spectroscopic Observatory (ISO) and Ulysses. The 3He/4He ratio is higher than that found in meteoritic gases (1.5 ± 0.3) × 10-4. The Galileo result for D/H when compared with that for hydrogen in the local interstellar medium (1.6 ± 0.12) × 10-5 implies a small decrease in D/H in this part of the universe during the past 4.55 billion years. Thus, it tends to support small values of primordial D/H - in the range of several times 10-5 rather than several times 10-4. These results are also quite consistent with no change in (D+3He)/H during the past 4.55 billion years in this part of our galaxy. 相似文献
5.
This paper reviews our present knowledge about elemental and isotopic ratios in the Giant Planets and Titan. These parameters
can provide key information about the formation and evolution of these objects. Element abundances, especially after the results
of the Galileo Probe Mass Spectrometer in Jupiter, strongly support the formation model invoking an initial core formation
(Mizuno, 1980; Pollack et al., 1996). They also suggest that solar composition icy planetesimals (SCIPs) brought the heavy elements to Jupiter. The Jupiter
value of D/H appears to be representative of the protosolar value, while the D/H enrichment observed on Uranus and Neptune
is consistent with the formation scenario of these planets. The 15N/14N measurement in Jupiter seems to be representative of its protosolar value. Future measurements are expected to come from
the Cassini and Herschel space mission, as well as the ALMA submillimeter observatory.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Cassini Imaging Science: Instrument Characteristics And Anticipated Scientific Investigations At Saturn 总被引:1,自引:0,他引:1
Carolyn C. Porco Robert A. West Steven Squyres Alfred Mcewen Peter Thomas Carl D. Murray Anthony Delgenio Andrew P. Ingersoll Torrence V. Johnson Gerhard Neukum Joseph Veverka Luke Dones Andre Brahic Joseph A. Burns Vance Haemmerle Benjamin Knowles Douglas Dawson Thomas Roatsch Kevin Beurle William Owen 《Space Science Reviews》2004,115(1-4):363-497
The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35∘ across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5∘ across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 μ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn’s many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising.This revised version was published online in July 2005 with a corrected cover date. 相似文献
7.
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
8.
M. Combes V. I. Moroz J. F. Crifo J. P. Bibring N. Coron J. Crovisier T. Encrenaz N. F. Sanko A. Grigoriev D. Bockele-Morvan R. Gispert C. Emerich J. M. Lamarre F. Rocard V. A. Krasnopolsky T. Owen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(12):127-131
Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H2O and CO2 molecules have been detected with production rates of 1030 s−1 and 1.5 1028 s−1 respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H2O 0.2. OH emission and H2O - ice absorption might also be present in the spectra. 相似文献
9.
10.
Jeremie Lasue Nicolas Mangold Ernst Hauber Steve Clifford William Feldman Olivier Gasnault Cyril Grima Sylvestre Maurice Olivier Mousis 《Space Science Reviews》2013,174(1-4):155-212
In this paper, we review current estimates of the global water inventory of Mars, potential loss mechanisms, the thermophysical characteristics of the different reservoirs that water may be currently stored in, and assess how the planet’s hydrosphere and cryosphere evolved with time. First, we summarize the water inventory quantified from geological analyses of surface features related to both liquid water erosion, and ice-related landscapes. They indicate that, throughout most of Martian geologic history (and possibly continuing through to the present day), water was present to substantial depths, with a total inventory ranging from several 100 to as much as 1000 m Global Equivalent Layer (GEL). We then review the most recent estimates of water content based on subsurface detection by orbital and landed instruments, including deep penetrating radars such as SHARAD and MARSIS. We show that the total amount of water measured so far is about 30 m GEL, although a far larger amount of water may be stored below the sounding depths of currently operational instruments. Finally, a global picture of the current state of the subsurface water reservoirs and their evolution is discussed. 相似文献