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21.
In view of potential application as a construction material on the lunar surface the mechanical integrity of sulfur concrete was evaluated after being subjected to simulated temperature cycles. Here, small cubes of sulfur concrete were repeatedly cycled between room (20 °C) and liquid nitrogen (−191 °C) temperatures after which they, and non-cycled cubes, were evaluated by compression testing. The compression strength of the non-cycled samples averaged ∼35 MPa (5076 psi) before failing whereas the cycled samples fractured at about 7 MPa (1015 psi). Microscopic examination of the fracture surfaces from the cycled samples showed clear de-bonding of the sulfur from the aggregate whereas it was seen adhering in those non-cycled. Based on a simple analysis it was concluded that the large strength discrepancy between cycled and non-cycled samples is due to differences between the coefficients of thermal expansion of the materials constituting the concrete.  相似文献   
22.
Measurements of solar total irradiance and its variability   总被引:1,自引:0,他引:1  
The development of electrically self calibrated cavity pyrheliometric instrumentation that occurred in the early 20th century provided the technological base for experiments to detect variability of the solar total irradiance. Experiments from ground based observatories, aircraft and balloons during the 1st half of the 20th century were unable to achieve sufficient accuracy or long term precision to unambiguously detect irradiance variations of solar origin. Refinements in pyrheliometric technology during the 1960's and 1970's and the accessibility of extended experimental opportunities above the Earth's atmosphere in recent years have provided the first direct observations of solar total irradiance variability and provided the cornerstone observations of a long term database on solar irradiance. A program of solar irradiance monitoring has evolved to sustain the database over at least 22 years, corresponding to a single cycle of solar magnetic activity, and the shortest well identified cycle of climate variation. Direct links between total irradiance variations, solar magnetic activity and the solar global 5 min oscillation phenomena have been derived from recent space flight observations by the SMM/ACRIM I experiment.  相似文献   
23.
Recent Cluster observations have strongly supported the existence of meso-scale structure in the magnetotail current sheet. In our study, a magnetohydrodynamic simulation event study exhibited current sheet behavior comparable to that seen in the Cluster observations. Geotail and DoubleStar observations also show that the simulation is providing a realistic representation of the magnetosphere during the period of interest; that is, when the current sheet evidently becomes bifurcated. The magnetohydrodynamic simulation allows us to place the local observations into a global contest. It shows that the observations can be explained in terms of localized reconnection tailward of the Cluster location and the formation of a flux rope nearby. The simulation also features wave-like structure across the current sheet.  相似文献   
24.
Some of the considerations in the design of the telescope for FIRST are discussed. It is pointed out that instruments that operate at submillimetre wavelengths need to be analyzed with techniques derived from both the Radio and Optical/IR traditions. The issue of emissivity of reflector surfaces is also discussed.  相似文献   
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Space tourism is the term commonly used to refer to ordinary members of the public buying tickets to travel to space and back, but has recently become more broadly associated with “any commercial activity offering customers direct or indirect experience with space travel”. The nascent commercial human spaceflight market presents a challenge to regulators with regard to the potential certification and licensing of the flight vehicles and their use (both within and outside the atmosphere), from the perspective of the operator, the flight participants, and third parties who might be affected by the operations. The UK is currently reviewing the issues posed by this emerging sector and its licensing/certification authorities are considering how best to balance their statutory responsibilities with the need to facilitate the development of this new industry and the favour positioning of UK players, eliminating unnecessary regulatory barriers to participation.  相似文献   
27.
    
This paper describes and analyzes the economics of a power relay system that takes advantage of recent technological advances to implement a system that is economically viable. A series of power relay systems are described and analyzed which transport power ranging from 1,250 megawatts to 5,000 megawatts, and distribute it to receiving sites at transcontinental distances.

Two classes of systems are discussed—those with a single reflector and delivering all the power to a single rectenna, and a second type which has multiple reflectors and distributes it to 10 rectenna sites, sharing power among them. It is shown that when offering electricity at prices competitive to those prevalent in developed cities in the US that a low IRR is inevitable, and economic feasibility of a business is unlikely. However, when the target market is Japan where the prevalent electricity prices are much greater, that an IRR exceeding 65% is readily attainable. This is extremely attractive to potential investors, making capitalization of a venture likely.

The paper shows that the capital investment required for the system can be less than $1 per installed watt, contributing less than 0.02 $/KW-hr to the cost of energy provision. Since selling prices in feasible regions range from 0.18 to over 030 $/kW-hr, these costs are but a small fraction of the operating expenses. Thus a very large IRR is possible for such a business.  相似文献   

28.
Hartmann  Lee  Ciesla  Fred  Gressel  Oliver  Alexander  Richard 《Space Science Reviews》2017,212(1-2):813-834
Space Science Reviews - We review the general theoretical concepts and observational constraints on the distribution and evolution of water vapor and ice in protoplanetary disks, with a focus on...  相似文献   
29.
    
The coaxial compound helicopter has two possible strategies for heading control: collective differential and rudder deflection. A flight dynamics model is developed to assess the effect of different heading control strategies. This includes the trim characteristics, steady flight performance,controllability, and manoeuvrability. The trim study demonstrates that heading control strategies are less influential on trim results, and the steady flight performance is also not significantly affected by the heading control strategy adopted. The controllability analysis shows although heading bandwidth and phase delay results at various speeds with different heading control strategies are all satisfied, the control derivative of the collective differential decreases as speed increases, and its heading aggressive agility is degraded into Level 3 in high-speed flight. In addition, using collective differential would lead to severe heading-rolling coupling as forward speed increases. On the contrary, the control derivative and aggressive agility of the rudder deflection is improved with forward speed, and there is no evidence of heading-rolling coupling. Finally, the transient turn MissionTask-Element(MTE) is utilized to investigate the heading manoeuvre characteristics in different heading control strategies, which indicates that the collective differential would add the amplitude of control input and the power consumption during this MTE.  相似文献   
30.
    
The electron and ion beams which have been detected on many rockets and satellites are of particular interest because beam particles carry information about both the ionosphere and the magnetosphere out to the distant tail. Stability analyses have shown that even the most dramatic beams have evolved until the particle distribution functions are only weakly unstable. The shortest plasma wave growth lengths in the auroral region are usually comparable to the size of an arc. The resulting clearest electron beams generally are relatively minor features of distribution functions which are dominated by plateaus, loss cones, broad or stretched out field aligned features, and hot or cold isotropic components. The true electron beams therefore represent a small fraction of the total electron number density. Ion beams carry a much larger fraction of all ions, but also are only weakly unstable. The electron beams seen at low altitudes can drive whistlers (both electromagnetic and electrostatic, including lower hybrid waves) and upper hybrid waves, which may be particularly intense near electron gyroharmonics. Ion beams can drive low frequency electromagnetic waves that are related to gyrofrequencies of several ion species as well as ion acoustic and electrostatic ion cyclotron waves. These latter waves can be driven both by the drift of ion beams relative to cold stationary ions and by the drift of electrons relative to either stationary or drifting ions. Abrupt changes or boundaries in the electron and ion velocity space distribution functions (e.g. beams and loss cones) have been analyzed to provide information about the plasma source, acceleration process, and regions of strong wave-particle interactions. Fluid analyses have shown that upgoing ion beams carry a great deal of momentum flux from the ionosphere. This aspect of ion beams is analyzed by treating the entire acceleration region as a black box, and determining the forces that must be applied to support the upgoing beams. This force could be provided by moderate energy (10's of eV) electrons which are heated near the lower border of the acceleration region. It is difficult to use standard particle detectors to measure the particles which carry electric current in much of the magnetosphere. Such measurements may be relatively easy within upgoing ion beams because there is some evidence that few of the hard-to-measure cold plasma particles are present. Therefore, ion beam regions may be good places to study fluid or MHD properties of magnetospheric plasmas, including the identification of current carriers, a study of current continuity, and some aspects of the substorm and particle energization processes. Finally, some of the experimental results which would be helpful in an analysis of several magnetospheric problems are summarized.  相似文献   
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