TOWARDS AN INTEGRATED SCIENTIFIC AND SOCIAL CASE FOR HUMAN SPACE EXPLORATION     

I. A. Crawford 《Earth, Moon, and Planets》2004,94(3-4):245-266

I will argue that an ambitious programme of human space exploration, involving a return to the Moon, and eventually human missions to Mars, will add greatly to human knowledge. Gathering such knowledge is the primary aim of science, but science’s compartmentalisation into isolated academic disciplines tends to obscure the overall strength of the scientific case. Any consideration of the scientific arguments for human space exploration must therefore take a holistic view, and integrate the potential benefits over the entire spectrum of human knowledge. Moreover, science is only one thread in a much larger overall case for human space exploration. Other threads include economic, industrial, educational, geopolitical and cultural benefits. Any responsibly formulated public space policy must weigh all of these factors before deciding whether or not an investment in human space activities is scientifically and socially desirable.  相似文献   

The peculiar cooling flow cluster RX J0820.9+0752     

C. M. Bayer-Kim  C. S. Crawford  S. W. Allen  A. C. Edge  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2002,337(3):938-952

  相似文献   

Constraining the source regions of lunar meteorites using orbital geochemical data          下载免费PDF全文

A. Calzada‐Diaz  K. H. Joy  I. A. Crawford  T. A. Nordheim 《Meteoritics & planetary science》2015,50(2):214-228

Lunar meteorites provide important new samples of the Moon remote from regions visited by the Apollo and Luna sample return missions. Petrologic and geochemical analysis of these meteorites, combined with orbital remote sensing measurements, have enabled additional discoveries about the composition and age of the lunar surface on a global scale. However, the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite. Here, we investigate the link between meteorite and source region on the Moon using the Lunar Prospector gamma ray spectrometer remote sensing data set for the elements Fe, Ti, and Th. The approach has been validated using Apollo and Luna bulk regolith samples, and we have applied it to 48 meteorites excluding paired stones. Our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites. Basaltic and intermediate Fe regolith breccia meteorites are found to have the best constrained potential launch sites, with some impact breccias and pristine mare basalts also having reasonably well‐defined potential source regions. Launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element, such as Mg, will probably be required to identify potential source regions for these.  相似文献   

Summer circulation of the waters in Queen Charlotte sound     

W.R. Crawford  W.S. Huggett  M.J. Woodward  P.E. Daniel 《大气与海洋》2013,51(4):393-413

Abstract

An extensive set of measurements of currents, winds, subsurface pressures and water properties was undertaken in the summer of 1982 in Queen Charlotte Sound on the west coast of Canada. At most observation sites the summer‐averaged currents are found to be about 10 cm s^?1, smaller than the tidal currents but comparable to the standard deviation of the non‐tidal currents. The strongest average flow was the outflow of surface water past Cape St James at the northwestern corner of the Sound. During strong winds from the north or northwest a strong outflow of near‐surface fresher water was also observed over Cook Bank in the south. Eddies dominate the motion in the interior of the Sound, as shown by the behaviour of a near‐surface drifter that remained in mid‐Sound for 40 days before a storm pushed it into Hecate Strait. The disorganized, weak currents in the central Sound will likely allow surface waters or floating material to remain there for periods of several weeks in summer.

Empirical orthogonal function analyses of fluctuating currents, subsurface pressures and winds reveal that a single mode explains most of the wind and pressure variance but not the current variance. The first two pressure modes represent two distinct physical processes. The first mode is a nearly uniform, up‐and‐down pumping of the surface, while the second mode tilts across the basin from east to west, likely due to geostrophic adjustment of wind‐driven currents. This mode also tilts from south to north, owing to along‐strait wind stress. Most contributions to the first mode currents come from meters near shore or the edge of a trough. Coherence is high between these second mode pressures and first mode currents and winds, and lower but still significant between first mode pressures and first mode currents and winds. It is therefore difficult to predict the behaviour of currents in Queen Charlotte Sound in summer from pressure measurements at a single site, but the difference in sea‐level across Hecate Strait is a more reliable indicator.  相似文献   

The Parkes Multibeam Pulsar Survey – VI. Discovery and timing of 142 pulsars and a Galactic population analysis     

D. R. Lorimer  A. J. Faulkner  A. G. Lyne  R. N. Manchester  M. Kramer  M. A. McLaughlin  G. Hobbs  A. Possenti  I. H. Stairs  F. Camilo  M. Burgay  N. D'Amico  A. Corongiu  F. Crawford 《Monthly notices of the Royal Astronomical Society》2006,372(2):777-800

We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of  30 000 ± 1100  potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc². Adopting the Tauris & Manchester beaming model, this translates to a total of  155 000 ± 6000  active radio pulsars in the Galaxy above this luminosity limit. Using a pulsar current analysis, we derive the birth rate of this population to be  1.4 ± 0.2  pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scaleheight with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scaleheight of 330 pc. Surveys underway at Parkes and Arecibo are expected to improve the knowledge of the radial distribution outside the solar circle, and to discover several hundred new pulsars in the inner Galaxy.  相似文献   

Photometry: New techniques,an introduction     

David L. Crawford 《Experimental Astronomy》1994,5(1-2):49-53

In most fields of observational astronomy, the new techniques we have now and are developing offer great potentials for more and better data, and thus to increased understanding of the universe about us. Photometry, as perhaps the most fundamental of all the observational tools, is no exception. The next years will be most exciting, but we must always be aware of the potential pitfalls involved with new technology. In fact, the new technologies must be handled with great care in order to insure that our data is really first class. New generation small telescopes can be a great asset, offering great complementarity to the new large telescopes and to space astronomy.Operated by AURA, Inc. under cooperative agreement with the National Science Foundation, Washington D.C.  相似文献   

Powerful, obscured active galactic nuclei among X-ray hard, optically dim serendipitous Chandra sources     

P. Gandhi  C. S. Crawford  A. C. Fabian  R. M. Johnstone 《Monthly notices of the Royal Astronomical Society》2004,348(2):529-550

  相似文献   

Submillimetre observations of z > 6 quasars     

Ian Robson  Robert S. Priddey  Kate G. Isaak  Richard G. McMahon 《Monthly notices of the Royal Astronomical Society》2004,351(2):L29-L33

  相似文献   

An analytic method to determine future close approaches between satellites   总被引：6，自引：0，他引：6  

Felix R. Hoots  Linda L. Crawford  Ronald L. Roehrich 《Celestial Mechanics and Dynamical Astronomy》1984,33(2):143-158

The calculation of the times of future close approaches between pairs of satellites has been formulated using analytical techniques. The resulting analytical equations are solved using numerical iterative techniques similar to solving Kepler's equation. A solution is obtained in a very efficient manner by use of a series of prefilters which eliminate many cases from further consideration. The method is valid for all values of eccentricities less than one and all relative geometries between the two orbits. This approach produces results in a very efficient and reliable manner.  相似文献   

A deep Chandra observation of the cluster environment of the  z= 1.786  radio galaxy 3C 294     

A. C. Fabian  J. S. Sanders  C. S. Crawford  S. Ettori 《Monthly notices of the Royal Astronomical Society》2003,341(3):729-738

  相似文献