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251.
John R. Solin 《IEEE transactions on aerospace and electronic systems》2006,42(4):1437-1445
The era of hardening military satellites against nuclear events, lasers, and high-power microwaves, appears to have come to an end. A case is made here for maintaining rudimentary nuclear, laser, and high-power microwave (HPM) hardening requirements in order to protect against developing third world threats. The third world nuclear threat is well known. Less appreciated is the fact that third world laser and microwave threats have changed radically in the past few years 相似文献
252.
The original design by J. A. Simpson of the neutron monitor enabled continuous monitoring of the primary cosmic-ray flux by
ground-based recordings of the nucleonic component with only a rather simple correction for atmospheric effects. Simpson (1957)
extended the original pile to the 12 counter IGY neutron monitor which was deployed in a world wide network during the International
Geophysical Year 1957/8. The desirability for monitors with higher counting rates became evident soon afterwards. Subsequently
the NM64 super neutron monitor was designed by H. Carmichael for deployment in time for the International Quiet Sun Year 1964.
Using unusually large 10BF3 proportional counters made at Chalk River, Hatton and Carmichael (1964) studied comprehensively the experimental design of
the NM64. Consequently the efficiency of neutron counters to record evaporation neutrons produced in the lead of a monitor
increased from 1.9% for the IGY to 5.7% for the NM64, an increase of 3.3 times the counting rate per unit area of lead producer.
During the years much attention was given to the neutron multiplicity spectrum in neutron monitors. This spectrum is related
to the energy spectrum of the nucleonic component incident on the neutron monitor, but is only weakly dependent on the spectrum
of galactic cosmic rays at the top of the atmosphere. Contrary to galactic cosmic rays, solar flare protons and neutrons are
observed predominantly as single counts per interaction, in multiplicity 1, because of the softness of solar flare particle
energy spectra. Neutron monitors have also been specially designed to record solar neutrons with increased sensitivity. Newly
developed 3He counters with a largely reduced thermal neutron absorption mean free path should lead to improved efficiency in recording
primary cosmic radiation. Design criteria are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
253.
254.
Alan Drysdale Takashi Nakamura Neil Yorio John Sager Ray Wheeler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Plant lighting is a critical issue for cost effectiveness of bioregenerative systems. A plant lighting system using sunlight has been investigated and compared to systems using electrical lighting. Co-generation of electricity and use of in situ resource utilization (ISRU) were also considered. The fixed part of equivalent system mass was found to be reduced by factors of from 3.1 to 3.9, according to the mission assumptions. The time-dependent part of equivalent system mass was reduced by a smaller value, of about 1.05. Cost effectiveness of bioregeneration has been compared to the cost of shipping food. Break-even times for different Lunar and Mars missions were generally in the order of 2–10 years, and were quite sensitive to the assumptions. There is significant scope for future refinement of these values, and work is ongoing. 相似文献
255.
The James Webb Space Telescope 总被引:4,自引:0,他引:4
Jonathan P. Gardner John C. Mather Mark Clampin Rene Doyon Matthew A. Greenhouse Heidi B. Hammel John B. Hutchings Peter Jakobsen Simon J. Lilly Knox S. Long Jonathan I. Lunine Mark J. Mccaughrean Matt Mountain John Nella George H. Rieke Marcia J. Rieke Hans-Walter Rix Eric P. Smith George Sonneborn Massimo Stiavelli H. S. Stockman Rogier A. Windhorst Gillian S. Wright 《Space Science Reviews》2006,123(4):485-606
The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next decade into orbit around the second Earth–Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m.The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations.To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities. 相似文献
256.
257.
The Lunar Reconnaissance Orbiter (LRO) was implemented to facilitate scientific and engineering-driven mapping of the lunar surface at new spatial scales and with new remote sensing methods, identify safe landing sites, search for in situ resources, and measure the space radiation environment. After its successful launch on June 18, 2009, the LRO spacecraft and instruments were activated and calibrated in an eccentric polar lunar orbit until September 15, when LRO was moved to a circular polar orbit with a mean altitude of 50 km. LRO will operate for at least one year to support the goals of NASA’s Exploration Systems Mission Directorate (ESMD), and for at least two years of extended operations for additional lunar science measurements supported by NASA’s Science Mission Directorate (SMD). LRO carries six instruments with associated science and exploration investigations, and a telecommunications/radar technology demonstration. The LRO instruments are: Cosmic Ray Telescope for the Effects of Radiation (CRaTER), Diviner Lunar Radiometer Experiment (DLRE), Lyman-Alpha Mapping Project (LAMP), Lunar Exploration Neutron Detector (LEND), Lunar Orbiter Laser Altimeter (LOLA), and Lunar Reconnaissance Orbiter Camera (LROC). The technology demonstration is a compact, dual-frequency, hybrid polarity synthetic aperture radar instrument (Mini-RF). LRO observations also support the Lunar Crater Observation and Sensing Satellite (LCROSS), the lunar impact mission that was co-manifested with LRO on the Atlas V (401) launch vehicle. This paper describes the LRO objectives and measurements that support exploration of the Moon and that address the science objectives outlined by the National Academy of Science’s report on the Scientific Context for Exploration of the Moon (SCEM). We also describe data accessibility by the science and exploration community. 相似文献
258.
The neutron monitor provides continuous ground-based recording of the hadronic component in atmospheric secondary radiation
which is related to primary cosmic rays. Simpson (1948) discovered that the latitude variation of the secondary hadronic component
was considerably larger than the muon component suggesting the response of a neutron monitor is more sensitive to lower energies
in the primary spectrum. The different methods of determining the neutron monitor response function of primary cosmic rays
are reviewed and discussed including early and recent results. The authors also provide results from a new calculation (Clem,
1999) including angle dependent yield functions for different neutron monitor types which are calculated using a simulation
of cosmic ray air showers combined with a detection efficiency simulation for different secondary particle species. Results
are shown for IGY and NM64 configurations using the standard 10BF3 detectors and the new 3He detectors to be used in the Spaceship Earth Project (Bieber et al., 1995). The method of calculation is described in detail and the results are compared with measurements and previous calculations.
A summary of future goals is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
259.
Space Science Reviews - 相似文献
260.
We review results about protoplanetary disk models, protoplanet migration and formation of giant planets with migrating cores.
We first model the protoplanetary nebula as an α–accretion disk and present steady state calculations for different values
of α and gas accretion rate through the disk. We then review the current theories of protoplanet migration in the context
of these models, focusing on the gaseous disk–protoplanet tidal interaction. According to these theories, the migration timescale
may be shorter than the planetary formation timescale. Therefore we investigate planet formation in the context of a migrating
core, considering both the growth of the core and the build–up of the envelope in the course of the migration.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献