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31.
32.
Tilman Spohn Mario H. Acuña Doris Breuer Matthew Golombek Ronald Greeley Alexander Halliday Ernst Hauber Ralf Jaumann Frank Sohl 《Space Science Reviews》2001,96(1-4):231-262
The evolution of Mars is discussed using results from the recent Mars Global Surveyor (MGS) and Mars Pathfinder missions together with results from mantle convection and thermal history models and the chemistry of Martian meteorites. The new MGS topography and gravity data and the data on the rotation of Mars from Mars Pathfinder constrain models of the present interior structure and allow estimates of present crust thickness and thickness variations. The data also allow estimates of lithosphere thickness variation and heat flow assuming that the base of the lithosphere is an isotherm. Although the interpretation is not unambiguous, it can be concluded that Mars has a substantial crust. It may be about 50 km thick on average with thickness variations of another ±50 km. Alternatively, the crust may be substantially thicker with smaller thickness variations. The former estimate of crust thickness can be shown to be in agreement with estimates of volcanic production rates from geologic mapping using data from the camera on MGS and previous missions. According to these estimates most of the crust was produced in the Noachian, roughly the first Gyr of evolution. A substantial part of the lava generated during this time apparently poured onto the surface to produce the Tharsis bulge, the largest tectonic unit in the solar system and the major volcanic center of Mars. Models of crust growth that couple crust growth to mantle convection and thermal evolution are consistent with an early 1 Gyr long phase of vigorous volcanic activity. The simplest explanation for the remnant magnetization of crustal units of mostly the southern hemisphere calls for an active dynamo in the Noachian, again consistent with thermal history calculations that predict the core to become stably stratified after some hundred Myr of convective cooling and dynamo action. The isotope record of the Martian meteorites suggest that the core formed early and rapidly within a few tens of Myr. These data also suggest that the silicate rock component of the planet was partially molten during that time. The isotope data suggest that heterogeneity resulted from core formation and early differentiation and persisted to the recent past. This is often taken as evidence against vigorous mantle convection and early plate tectonics on Mars although the latter assumption can most easily explain the early magnetic field. The physics of mantle convection suggests that there may be a few hundred km thick stagnant, near surface layer in the mantle that would have formed rapidly and may have provided the reservoirs required to explain the isotope data. The relation between the planform of mantle convection and the tectonic features on the surface is difficult to entangle. Models call for long wavelength forms of flow and possibly a few strong plumes in the very early evolution. These plumes may have dissolved with time as the core cooled and may have died off by the end of the Noachian. 相似文献
33.
相变材料微胶囊悬浮液在矩形小通道内层流流动传热的实验 总被引:1,自引:1,他引:1
本文进行了对比性的实验,以研究相变材料微胶囊(MEPCM)-水悬浮液在水力直径为2.71mm的矩形小通道内的层流流动传热性能.实验中用的MEPCM颗粒的平均粒径为4.97μm,与蒸馏水混合制备成质量浓度范围为0~20%的MEPCM-水悬浮液.对比性的实验是指,在相同的悬浮液质量流量和热力条件下,使用不同浓度的MEPCM悬浮液进行传热实验.实验发现,MEPCM悬浮液的冷却性能严重依赖于悬浮液的质量流量和悬浮液的质量浓度.质量浓度为5%的悬浮液在在整个质量流量范围内总是表现出比水好的冷却性能,它对应的是更低的壁面温度以及更好的传热系数.而对于更高质量浓度的悬浮液,在低质量流量的情况下,它们具有很好的冷却性能;而在高质量流量的情况下,它们表现出的冷却性能比水更差,它们对应更高的壁面温度以及更低的Nusselt数. 相似文献
34.
Dr. Wei Sun Frank Ellmers Andreas Winkler Herbert Schuff Manuel Julián Sansegundo Chamarro 《Acta Astronautica》2011,68(7-8):802-810
Hispasat Advanced Generation 1 (HAG1) is the first satellite using the SGEO platform, which is under the development in the ESA Artes-11 program. Since the last presentation in the IAC 2007, a European industrial consortium led by OHB has completed the mission and spacecraft design. The platform Preliminary Design Review has been carried out in May 2008. The customer for the first mission is a commercial operator—Hispasat. The contract was signed in December 2008 and the satellite will be launched in 2012. To give confidence to the customer, SGEO platform will use up to date flight proven technologies. HAG1 carries 20/24 Ku-band and 3/5 Ka-band transponders to provide commercial services. Some innovative payload technologies will also be flown on board of HAG1 to gain in-orbit heritage. SGEO has also been selected as the baseline platform for the ESA Data Relay Satellite (EDRS). Phase-A study has just kicked off in January 2009. The targeted launch date is 2013. Heinrich Hertz will also use the SGEO platform. Heinrich Hertz is funded by the German Space Agency (DLR) and provides flight opportunities for technologies and components developed by the German Space Industry. With the HAG1 contract in hand, and EDRS and Heinrich Hertz in the line, OHB with its partners has the confidence that it will be able to speed up the product development of the SGEO platform for potential customers in the commercial market. This paper will first present the updated platform design and the status of the product development will be followed with the introduction of innovative payload technologies on board the first mission—HAG1 and ended with the mission concepts of EDRS and Heinrich Hertz missions. 相似文献
35.
36.
Frank White 《Space Policy》1987,3(1)
The US National Commission on Space has recently issued its report, Pioneering the Space Frontier. As the US Founding Fathers laid down the basic principles which are the foundation of US society, the Commission has articulated certain basic principles which reflect the fundamental values of the American people. These principles lay the basis for the Commission's vision of space exploration and settlement and its benefits for the USA and all of humankind. 相似文献
37.
38.
The plasma physics of shock acceleration 总被引:1,自引:0,他引:1
The notion that plasma shocks in astrophysical settings can and do accelerate charged particles to high energies is not a new one. However, in recent years considerable progress has been achieved in understanding the role particle acceleration plays both in astrophysics and in the shock process itself. In this paper we briefly review the history and theory of shock acceleration, paying particular attention to theories of parallel shocks which include the backreaction of accelerated particles on the shock structure. We discuss in detail the work that computer simulations, both plasma and Monte Carlo, are playing in revealing how thermal ions interact with shocks and how particle acceleration appears to be an inevitable and necessary part of the basic plasma physics that governs collisionless shocks. We briefly describe some of the outstanding problems that still confront theorists and observers in this field. 相似文献
39.
Frank Verbunt 《Space Science Reviews》1982,32(4):379-404
This review presents an introduction to the theory of accretion disks. After explaining the importance of accretion disks in stellar X-ray sources, it considers observational and theoretical indications of the formation of accretion disks in close binary systems. The simple Shakura and Sunyaev model and its problems are discussed. A survey of other models that try to improve upon this model is given (in Table III), and critically discussed. 相似文献
40.
Significant size, weight, power and reliability improvements can be achieved in next generation avionics by the modular integration of similar functions into a fault tolerant reconfigurable architecture. The Integrated Communication Navigation Identification Avionics program (ICNIA), and ITT/TI Joint Venture, is accomplishing this task with a combination of modular circuit designs using VHSIC technology, improved packaging designs incorporating surface mount component technology and a modular two-level maintenance support concept for reduced life cycle cost. This article will concentrate on the modular packaging technology of the digital processor subsystem. 相似文献