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71.
J.C. Raymond 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(9):145-151
Ultraviolet spectra of supernova remnants obtained with the IUE satellite provide unique information concerning the shock conditions and elemental abundances in the optically bright filaments. High temperature species such as N V provide diagnostics for shock velocities above 100 km s?1, and strong lines of carbon and silicon in the IUE spectral range make it possible to study the destruction of refractory grains in shocked interstellar gas. Observations of a non-radiative shock at the edge of the Cygnus Loop provide constraints on the physics of the shock front itself. Most of the very young remnants whose optical spectra show anomalous elemental abundances are too highly reddened for IUE observations, but extensive observations of the Crab Nebula and a spectrum of the supernova remnant in NGC 4449 yield carbon to oxygen ratios from which the mass of the progenitor may be estimated. 相似文献
72.
In airline service the reliability of a system is more than the confirmed failures for the system; it is the total removal experience of the system. Thus, the reliability of a system lies not only in the piece part failure rates, but also in the capability to verify and isolate failures. The application of digital technology brings several significant reliability improvements to automatic flight control systems (AFCS) when compared to contemporary analog systems. These advantages are demonstrated by the experience of the digital air data computer (DADC) of the DC-10 and the digital AFCS of the JA-37 Viggen. Experience with this equipment is reviewed, and the results are interpreted in terms of projections for airline DAFCS reliability. The digital system built-in test implemented by a stored program and the central processor gives a system integrity and dispatch reliability unequaled by analog systems. This high-integrity self-test reduces removal rates by giving line personnel a trustworthy tool and more complete automatic test processes for verifying maintenance actions. Digital circuit technology is directly suitable to largescale integrated circuits (LSIC) which reduce piece part counts and improve LRU reliability. Digital circuits are less subject to drift and the attendant difficulty to detect failures. These factors, coupled with the inherent high-integrity self-test, provide the basis for a significant improvement in reliability by the use of a digital automatic flight control system. 相似文献
73.
Charles E. Schlemm II Richard D. Starr George C. Ho Kathryn E. Bechtold Sarah A. Hamilton John D. Boldt William V. Boynton Walter Bradley Martin E. Fraeman Robert E. Gold John O. Goldsten John R. Hayes Stephen E. Jaskulek Egidio Rossano Robert A. Rumpf Edward D. Schaefer Kim Strohbehn Richard G. Shelton Raymond E. Thompson Jacob I. Trombka Bruce D. Williams 《Space Science Reviews》2007,131(1-4):393-415
NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of
the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital
phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft
will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface
of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12°
field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis
due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority
of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes
XRS’s science objectives, technical design, calibration, and mission observation strategy. 相似文献
74.
The UK government's recent announcement that the British National Space Centre could not expect a budget increase has prompted much reaction in the press. The Chief Executive of British Aerospace, a leading company in the UK space industry, here offers his views on the country's future role in space. 相似文献