叶片前缘有气膜孔的冲击冷却研究

为了确定涡轮叶片前缘阵列射流冲击到穿孔靶面的传热特性,本文采用六个放大比例的模型,进行了一系列的实验研究。在广泛的实际有兴趣的参数组合范围内,分别对各种模型,获得了压力损失和N_u数与射流雷诺数的关系式。这些组合参数包括:射流雷诺数,叶片前缘曲率半径与孔径的比,射孔间距与孔径的比以及射流冲击间隙与孔径的比。并利用实验数据,分析了各项几何参数的影响。     

Measuring the economic benefits of a national planetary protection policy to regulate future private space activities between Earth and Mars: Results of a contingent valuation survey in Greece

The emergence of private space actors may soon enable the growth of the novel market segments of space research and exploration, space resources utilization, and human access to space. The interdisciplinary field of Planetary Protection has to keep up with these advances. Planetary Protection is defined as a set of guidelines that aim to prevent the forward contamination of celestial bodies with biological material from Earth and the backward contamination of the terrestrial biosphere with extraterrestrial biological material. As space entrepreneurs acquire and develop the resources and competencies for commercial access to space, significant questions are expected to be raised in the future with respect to potential forward and backward contamination issues, particularly with respect to activities between Earth and Mars. Although such private activities do not seem to pose a serious Planetary Protection threat at the moment, certain preparatory steps need to be taken in order to prudently inform the relevant policy-making procedures. This work describes the application of the Contingent Valuation Method, a useful tool of the environmental economics discipline, with the aim of demonstrating a novel approach to estimate the economic valuation of the external benefits of preventing forward and backward contamination between Earth and Mars. Particularly, via a survey specifically developed for this purpose, a set of questions are used to elicit the perceived economic value that respondents place on the prevention of forward and backward contamination; the survey is administered to a national probability sample in Greece, and the generated data is processed through statistical analysis. The Contingent Valuation Method is a popular and well-established stated preference valuation technique; these techniques are often the more suitable choice for ex-ante valuations of future changes, and are currently the only known approach to capture all the aspects of the economic value of non-market goods. Through an initial proof-of-concept in Greece, the goal of this work is to provide useful insights on the expected external benefits of a national Planetary Protection policy to regulate future private space activities between Earth and Mars, and to encourage a larger-scale application of this tool in other countries around the world.     

An engineering model of Titan surface winds for Dragonfly landed operations

Winds near the ground on Titan for the Dragonfly landing site (near Selk crater, 10°N) for the mid-2030s (Titan late southern summer, L_s ~ 310°) are estimated for mission design purposes. Prevailing winds due to the global circulation are typically 0.5 m/s, and do not exceed 1 m/s. Local terrain-induced flows such as slope winds appear to be similarly capped at 1 m/s. At various landing sites and times, these two contributions will vectorially combine to yield steady winds (for part of a Titan day, Tsol) of up to 2.0 m/s, but typically less – the slope wind component will be small in the mid-morning. In early afternoon, as on Earth and Mars, solar-driven convection in the planetary boundary layer will cause wind fluctuations of the order of 0.1 m/s, varying with a typical timescale of ~1000 s. Occasionally this convection organizes into coherent ‘dust devil’ vortices: detectable vortices with speeds of 1 m/s are predicted about once per Titan day. We have introduced the convective velocity scale combined with the advection time of PBL cells as a metric to derive the frequency of occurrence of gusts associated with convective vortices (‘dust devils’). Maximum possible vortex winds on Titan of 2.8 m/s may be expected only once per 40 Tsols, and define the maximum wind (4.8 m/s at 10 m height) that Dragonfly must tolerate without damage. The applicability of different wind combinations, scaled to the height of relevant Dragonfly components above the ground (e.g. the maximum corresponds to 3.9 m/s at 1.3 m height) by a logarithmic wind profile, to Dragonfly design and operations are discussed.     

Planet temperatures with surface cooling parameterized

A semigray (shortwave and longwave) surface temperature model is developed from conditions on Venus, Earth and Mars, where the greenhouse effect is mostly due to carbon dioxide and water vapor. In addition to estimating longwave optical depths, parameterizations are developed for surface cooling due to shortwave absorption in the atmosphere, and for convective (sensible and latent) heat transfer. An approximation to the Clausius–Clapeyron relation provides water–vapor feedback. The resulting iterative algorithm is applied to three “super-Earths” in the Gliese 581 system, including the “Goldilocks” planet g (Vogt et al., 2010). Surprisingly, none of the three appear habitable. One cannot accurately locate a star’s habitable zone without data or assumptions about a planet’s atmosphere.     

Viability of bacterial spores exposed to hydrazine

For the purposes of planetary protection, a series of experiments were performed to answer a long-standing question about the potential of bacterial contamination of interplanetary spacecraft from liquid hydrazine. Spores of Bacillus atrophaeus (ATCC No. 9372, also known as Bacillus subtilis var. niger, and BSN) were exposed to hydrazine and survivors were enumerated using the NASA standard planetary protection pour plate assay. Results indicate that bulk hydrazine rocket propellant may be considered free of living bacterial cells for planetary protection compliance.     

Might astronauts one day be treated like return samples?

The next time humans set foot on the Moon or another planet, will we treat the crew like we would a sample return mission when they come back to Earth? This may seem a surprising or even provocative question, but it is one we need to address. The hurdles and hazards of sending humans to Mars – for example, the technology constraints and physiological and psychological challenges – are many; but let us not forget the need to protect populations and environments from the risk of contamination [United Nations, treaty on principles governing the activities of states in the exploration and use of outer space, including the Moon and other celestial bodies (the “Outer Space Treaty”) referenced 610 UNTS 205 - resolution 2222(XXI) of December 1966].     

Achievements of Space Scientific Experiments Aboard SJ-8 Satellite

As scientific experiment payloads, microgravity experiments of fluid physics, life science,combustion science, physics and accelerator measurement were conducted on board the Chinese recoverable satellite SJ-8 during 18-day orbital flight. The experimental payloads and an experiment support system constituted the microgravity experiment system of the flight mission. This article has presented the briefs of the scientific achievements of these space experiments, the composition and performance of the Microgravity Experimental System (MES) and the general picture of the overall flight mission, respectively.      

An ethical approach to planetary protection

What hazards might biological contamination pose to planets, comets and other celestial bodies visited by probes launched from Earth? What hazards might returning probes pose to Earth and its inhabitants? What should be considered an acceptable level of risk? What technologies, procedures and constraints should be applied? What sort of attitude has to be chosen concerning human crews, who themselves could become both contaminated victims and contaminating agents? The vast issue of planetary protection must, more than ever, spark ethical debate. Space treaty, COSPAR recommendations offer borders and context for this reflection, which has to be introduced in the actual humanist: never has been anthropocentrism so practical and concerned, in the same time, by the next generations, because of the historical character of life. At least an ethics of risk is necessary (far from the myth of zero-risk) for all the three types of contamination: other celestial bodies (forward contamination), Earth (backward contamination) and astronauts.     

Characterizing bedrock lithologies using Small Crater Rims and Ejecta Probing (SCREP)

This paper describes the rationale, methodology, and importance of focusing on the rim and proximal ejecta of small (<5 km in diameter), immature impact craters to explore an underlying crustal lithology. Small Crater Rim and Ejecta Probing (SCREP) describes a methodology and application program that extracts bedrock spectral and compositional information from a remote sensing image. Extracted data can yield the pristine lithologies of a planetary crust that would otherwise be obscured by the products of space weathering processes. SCREP was developed with lunar data, specifically Clementine multispectral image mosaics, therefore the technique is discussed in this context. However, its application to other airless solar system bodies is apparent. Knowledge of the pristine bedrock compositions of a planetary crust provides insight into geological surface processes, which can be used to refine models of planetary interiors and their evolution.     

基于OMLHD的仿真模型验证方法

当仿真因子数目较多,而真实系统观测数据相对稀少时,仿真模型的验证工作难以进行.针对仿真因子空间庞大,对应于每一组仿真因子配置,有且仅有对真实系统在相应工作条件下的一次观测这一极端情形,提出一种基于最优拉丁超立方设计(OMLHD,Orthogonal-Maximin Latin Hypercube Designs)的仿真模型验证方法.利用仿真验证试验的优化设计技术对仿真因子配置进行筛选,合理的选择、安排验证试验；采用p值分析方法解决验证试验中的数据一致性分析问题；基于逆概率分布定理的思想,对各组验证试验一致性分析结果进行综合分析.以某导弹制导仿真模型验证为例,对方法的性能进行了讨论.结果表明该方法能够实现在整个因子空间上对仿真模型的可信性进行验证的目的.