首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   53篇
  免费   0篇
航空   21篇
航天技术   10篇
航天   22篇
  2021年   1篇
  2017年   1篇
  2015年   1篇
  2014年   4篇
  2012年   3篇
  2011年   8篇
  2010年   2篇
  2009年   3篇
  2008年   3篇
  2007年   6篇
  2006年   2篇
  2004年   1篇
  2003年   2篇
  2002年   2篇
  2001年   1篇
  2000年   1篇
  1999年   1篇
  1993年   4篇
  1990年   1篇
  1989年   1篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1982年   1篇
  1968年   1篇
排序方式: 共有53条查询结果,搜索用时 15 毫秒
11.
    
This paper examines the relationship between public sector objectives in the Earth observation data market and the economic interests of Earth observation data procedures. The Earth observation data market is treated as a particular example of an information market and the economic incentives created by the cultural characteristics of the market, particularly in Europe, are considered to assess the implications for data pricing policies. The analysis focuses upon implications of the vertical and horizontal linkages in the Earth observation industrial participation chain which includes space segment suppliers, space agencies and operators, data intermediaries and end users. A rebalancing of administrative and market decisions is proposed that would result in a shift in the allocation of public resources from space agencies and data intermediaries to data users whose activities are deemed to be in the widest public interest.  相似文献   
12.
The Mars Program Plan includes an integrated and coordinated set of future candidate missions and investigations that meet fundamental science objectives of NASA and the Mars Exploration Program (MEP). At the time this paper was written, these possible future missions are planned in a manner consistent with a projected budget profile for the Mars Program in the next decade (2007-2016). As with all future missions, the funding profile depends on a number of factors that include the exact cost of each mission as well as potential changes to the overall NASA budget. In the current version of the Mars Program Plan, the Astrobiology Field Laboratory (AFL) exists as a candidate project to determine whether there were (or are) habitable zones and life, and how the development of these zones may be related to the overall evolution of the planet. The AFL concept is a surface exploration mission equipped with a major in situ laboratory capable of making significant advancements toward the Mars Program's life-related scientific goals and the overarching Vision for Space Exploration. We have developed several concepts for the AFL that fit within known budget and engineering constraints projected for the 2016 and 2018 Mars mission launch opportunities. The AFL mission architecture proposed here assumes maximum heritage from the 2009 Mars Science Laboratory (MSL). Candidate payload elements for this concept were identified from a set of recommendations put forth by the Astrobiology Field Laboratory Science Steering Group (AFL SSG) in 2004, for the express purpose of identifying overall rover mass and power requirements for such a mission. The conceptual payload includes a Precision Sample Handling and Processing System that would replace and augment the functionality and capabilities provided by the Sample Acquisition Sample Processing and Handling system that is currently part of the 2009 MSL platform.  相似文献   
13.
14.
In 1996, the National Research Council's Committee on Risk Characterization argued convincingly for the implementation of more participatory approaches to improve policy making by incorporating a wide range of stakeholder values and concerns in policy decisions. Guidance about how to best carry out such an approach in an agency like NASA is less clear. To address this gap, this paper discusses how the use of a structured approach to involve expert and non-expert stakeholders in policy making can improve the quality of stakeholder involvement and resulting decisions for space policy making at NASA. Supporting this discussion are results from two recent experiments. One compared the quality and type of participants’ input in a conventional stakeholder workshop with that of a more structured participatory process. The results from this experiment showed that a structured decision approach leads to more thoughtful and better-informed decisions. A second experiment showed that structured, participatory decision processes can help to legitimize space policy decisions after they have been implemented, leading to future benefits for the space agency.  相似文献   
15.
Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust transport can generate atmospheric electricity via contact electrification or "triboelectricity." In convective structures such as dust devils and dust storms, grain stratification leads to macroscopic charge separations and gives rise to an overall electric dipole moment in the aeolian feature, similar in nature to the dipolar electric field generated in terrestrial thunderstorms. Previous numerical simulations indicate that these storm electric fields on Mars can approach the ambient breakdown field strength of approximately 25 kV/m. In terrestrial dust phenomena, potentials ranging from approximately 20 to 160 kV/m have been directly measured. The large electrostatic fields predicted in martian dust devils and storms can energize electrons in the low pressure martian atmosphere to values exceeding the electron dissociative attachment energy of both CO2 and H2O, which results in the formation of the new chemical products CO/O- and OH/H-, respectively. Using a collisional plasma physics model, we present calculations of the CO/O- and OH/H- reaction and production rates. We demonstrate that these rates vary geometrically with the ambient electric field, with substantial production of dissociative products when fields approach the breakdown value of approximately 25 kV/m. The dissociation of H2O into OH/H- provides a key ingredient for the generation of oxidants; thus electrically charged dust may significantly impact the habitability of Mars.  相似文献   
16.
Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of the interaction of the solar radiation with the solar-sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The dependence of the thickness of solar sail on temperature and on wavelength of the electromagnetic spectrum of solar radiation is investigated. Physical processes of the interactions of photons, electrons, protons and α-particles with sail material atoms and nuclei, and inflation fill gas molecules are analyzed. Calculations utilized conservative assumptions with the highest values for the available cross sections for interactions of solar photons, electrons and protons with atoms, nuclei and hydrogen molecules. It is shown that for high-energy photons, electrons and protons the beryllium sail is mostly transparent. Sail material will be partially ionized by solar UV and low-energy solar electrons. For a hollow-body photon sail effects including hydrogen diffusion through the solar-sail walls, and electrostatic pressure is considered. Electrostatic pressure caused by the electrically charged sail’s electric field may require mitigation since sail material tensile strength decreases with elevated temperature. It also can substitute inflation-gas pressure loss due to gas diffusion and perforation by micrometeoroids impact to keep the sail inflated.  相似文献   
17.
The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS.  相似文献   
18.
The spin periods of accreting neutron stars in binary systems with Be star primaries are shown to depend more strongly on periastron distance than apastron distance. This is interpreted as showing that neutron stars spin-up on shorter timescales than they spin-down. The pulse and orbital periods of V 0332+53 suggest that the optical counterpart of this source is a Be star.  相似文献   
19.
The Sun?s gravity focus at >550 AU is of interest to astrophysicists including SETI scientists, researchers seeking to image extra-solar planets and others. One method for an extra-solar probe to reach the Sun?s inner gravity focus within a human working lifetime (less than 50 years) is to combine solar and nuclear propulsion techniques. Here, we present a non-optimized probe concept including state-of-the-art solar-sail, radioisotope-electric propulsion and giant-planet gravity assists. Application of radioisotope propulsion allows some cross range capability during and after the powered and cruise phases of the flight to >600 AU. Such a capability is likely necessary to fully utilize the solar gravitational lens effect for SETI and astrophysical observations.  相似文献   
20.
Current technologies could support the deployment of strategic defences that are effective, affordable and stabilizing. With recent developments in space-based interceptors, in particular, it no longer seems to be a question of whether the technologies could be deployed, but whether one wants to deploy them. Missile attacks could not yet be rendered ineffective, but this goal can be approached in stages. The author examines the range of limited applications and describes the financial and technological demands posed by each.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号