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131.
Paul S. Wesson 《Space Science Reviews》1992,59(3-4):365-406
We ask about the nature and origin of the fundamental constants of astrophysics and particle physics, notably the speed of light c, the gravitational constant G, Planck's constant h, and the magnitude of the electron charge e. We consider general relativity and the theories of the electromagnetic, weak and strong interactions that make up the Standard Model; together with the Lagrangians of Einstein, Maxwell, Schrödinger, Klein-Gordon, Dirac, Proca, and Yang-Mills. Then we look in a more qualitative way at how the equations of physics are set up, their dimensional content, and the removal of constants from them by a suitable choice of units. We conclude with Hoyle and Narlikar, Jeffreys and McCrea that parameters like c, G, and h are merely manmade dimensional conversion constants. They arise because of our subjective view that mass, length, and time are different concepts. These constants can be removed in a manner analogous to the removal of the permittivity of free space
0 from electrodynamics, and none are really fundamental. The charge e is different, being the low-energy limit of a function related to properties of the vacuum, but because of this it is not a fundamental constant either. We suggest there are no constants which truly deserve to be called fundamental, and that an aim of physics ought to be to write down laws in which no constants appear. 相似文献
132.
Gordon Chin Scott Brylow Marc Foote James Garvin Justin Kasper John Keller Maxim Litvak Igor Mitrofanov David Paige Keith Raney Mark Robinson Anton Sanin David Smith Harlan Spence Paul Spudis S. Alan Stern Maria Zuber 《Space Science Reviews》2007,129(4):391-419
NASA’s Lunar Precursor Robotic Program (LPRP), formulated in response to the President’s Vision for Space Exploration, will
execute a series of robotic missions that will pave the way for eventual permanent human presence on the Moon. The Lunar Reconnaissance
Orbiter (LRO) is first in this series of LPRP missions, and plans to launch in October of 2008 for at least one year of operation.
LRO will employ six individual instruments to produce accurate maps and high-resolution images of future landing sites, to
assess potential lunar resources, and to characterize the radiation environment. LRO will also test the feasibility of one
advanced technology demonstration package. The LRO payload includes: Lunar Orbiter Laser Altimeter (LOLA) which will determine
the global topography of the lunar surface at high resolution, measure landing site slopes, surface roughness, and search
for possible polar surface ice in shadowed regions, Lunar Reconnaissance Orbiter Camera (LROC) which will acquire targeted
narrow angle images of the lunar surface capable of resolving meter-scale features to support landing site selection, as well
as wide-angle images to characterize polar illumination conditions and to identify potential resources, Lunar Exploration
Neutron Detector (LEND) which will map the flux of neutrons from the lunar surface to search for evidence of water ice, and
will provide space radiation environment measurements that may be useful for future human exploration, Diviner Lunar Radiometer
Experiment (DLRE) which will chart the temperature of the entire lunar surface at approximately 300 meter horizontal resolution
to identify cold-traps and potential ice deposits, Lyman-Alpha Mapping Project (LAMP) which will map the entire lunar surface
in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently
shadowed regions illuminated only by starlight. Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which will investigate
the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background
space radiation. The technology demonstration is an advanced radar (mini-RF) that will demonstrate X- and S-band radar imaging
and interferometry using light weight synthetic aperture radar. This paper will give an introduction to each of these instruments
and an overview of their objectives. 相似文献
133.
James C. Leary Richard F. Conde George Dakermanji Carl S. Engelbrecht Carl J. Ercol Karl B. Fielhauer David G. Grant Theodore J. Hartka Tracy A. Hill Stephen E. Jaskulek Mary A. Mirantes Larry E. Mosher Michael V. Paul David F. Persons Elliot H. Rodberg Dipak K. Srinivasan Robin M. Vaughan Samuel R. Wiley 《Space Science Reviews》2007,131(1-4):187-217
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was designed and constructed to withstand the harsh environments associated with achieving and operating in Mercury
orbit. The system can be divided into eight subsystems: structures and mechanisms (e.g., the composite core structure, aluminum
launch vehicle adapter, and deployables), propulsion (e.g., the state-of-the-art titanium fuel tanks, thruster modules, and
associated plumbing), thermal (e.g., the ceramic-cloth sunshade, heaters, and radiators), power (e.g., solar arrays, battery,
and controlling electronics), avionics (e.g., the processors, solid-state recorder, and data handling electronics), software
(e.g., processor-supported code that performs commanding, data handling, and spacecraft control), guidance and control (e.g.,
attitude sensors including star cameras and Sun sensors integrated with controllers including reaction wheels), radio frequency
telecommunications (e.g., the spacecraft antenna suites and supporting electronics), and payload (e.g., the science instruments
and supporting processors). This system architecture went through an extensive (nearly four-year) development and testing
effort that provided the team with confidence that all mission goals will be achieved.
Larry E. Mosher passed away during the preparation of this paper. 相似文献
134.
The Legislative Update column reports on President Bush's supplemental budget request for the war in Iraq, the formation of a defense caucus in the House of Representatives, stabilized funding for airport security, the Department of Homeland Security budget, NASA's budget request, funding for NASA's aeronautics program, and NASA's new authorization. NASA's FY04 budget request is $15.47 billion, less than 1% more than FY03. The aeronautics program budget request for FY04 is $959 million, a decrease of 8.5% from FY03. Congress is working to introduce a multiyear authorization for NASA during the 108th session. 相似文献
135.
The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) on the New Horizons Mission
Ralph L. McNutt Jr. Stefano A. Livi Reid S. Gurnee Matthew E. Hill Kim A. Cooper G. Bruce Andrews Edwin P. Keath Stamatios M. Krimigis Donald G. Mitchell Barry Tossman Fran Bagenal John D. Boldt Walter Bradley William S. Devereux George C. Ho Stephen E. Jaskulek Thomas W. LeFevere Horace Malcom Geoffrey A. Marcus John R. Hayes G. Ty Moore Mark E. Perry Bruce D. Williams Paul Wilson IV Lawrence E. Brown Martha B. Kusterer Jon D. Vandegriff 《Space Science Reviews》2008,140(1-4):315-385
The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto’s outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a “heavy comet” as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10 s of keV to ~1 MeV in a 160°×12° fan-shaped beam in six sectors for 1.5 kg and ~2.5 W. 相似文献
136.
Barton Paul Levenson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A semigray (shortwave and longwave) surface temperature model is developed from conditions on Venus, Earth and Mars, where the greenhouse effect is mostly due to carbon dioxide and water vapor. In addition to estimating longwave optical depths, parameterizations are developed for surface cooling due to shortwave absorption in the atmosphere, and for convective (sensible and latent) heat transfer. An approximation to the Clausius–Clapeyron relation provides water–vapor feedback. The resulting iterative algorithm is applied to three “super-Earths” in the Gliese 581 system, including the “Goldilocks” planet g (Vogt et al., 2010). Surprisingly, none of the three appear habitable. One cannot accurately locate a star’s habitable zone without data or assumptions about a planet’s atmosphere. 相似文献
137.
Marc S. Allen Paul L. Hertz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
NASA research programs offer many opportunities for productive partnerships with investigators in other countries. While spacecraft projects are complex and very expensive, there are other, lower-cost partnerships that can yield important scientific results and offer excellent opportunities for building up new space and Earth science programs and for training new researchers. 相似文献
138.
139.
Mourad Lazri Zohra Ameur Soltane Ameur Yacine Mohia Jean Michel Brucker Jacques Testud 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The ultimate objective of this paper is the estimation of rainfall over an area in Algeria using data from the SEVIRI radiometer (Spinning Enhanced Visible and Infrared Imager). To achieve this aim, we use a new Convective/Stratiform Rain Area Delineation Technique (CS-RADT). The satellite rainfall retrieval technique is based on various spectral parameters of SEVIRI that express microphysical and optical cloud properties. It uses a multispectral thresholding technique to distinguish between stratiform and convective clouds. This technique (CS-RADT) is applied to the complex situation of the Mediterranean climate of this region. The tests have been conducted during the rainy seasons of 2006/2007 and 2010/2011 where stratiform and convective precipitation is recorded. The developed scheme (CS-RADT) is calibrated by instantaneous meteorological radar data to determine thresholds, and then rain rates are assigned to each cloud type by using radar and rain gauge data. These calibration data are collocated with SEVIRI data in time and space. 相似文献
140.
U. Mukherjee B. Paul 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2774-2776
High Mass X-ray Binary Pulsars (HMXBP), in which the companion star is a source of supersonic stellar wind, provide a laboratory to probe the velocity and density profile of such winds. Here, we have measured the variation of the absorption column density along with other spectral parameters over the binary orbit for two HMXBP in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. In 4U 1538-52, we find the model corroborating the observations; whereas in GX 301-2, the stellar wind appears to be very clumpy and a smooth symmetric wind model seems to be inadequate in explaining the variation in column density. 相似文献