Energy law of similitude for laser propulsion refers to the law that there is an optimum nozzle configuration for the largest value of impulse coupling coefficient at certain incident laser energy. A dimensionless factor combined with incident laser energy, nozzle configuration parameters and working gas parameters is introduced. Energy law of similitude is established by means of theoretical analysis, experimental study and numerical simulation of radiation gas-dynamics. The qualitative results obtained from theoretical analysis are verified by experimental and numerical results. Physical meaning and engineering application of dimensionless factor and energy law of similitude are analyzed. Results indicate that impulse coupling coefficient has a maximum value with dimensionless factor of about 0.4; impulse coupling coefficient is independent of incident laser energy when dimensionless factor is constant. Conclusions and recognitions acquired in this article can not only present optimum nozzle configurations for the present laser energy level, but also provide a good guide for the optimum nozzle configuration design once the laser energy is amplified to a high level. 相似文献
NASA’s Stardust mission collected dust from the coma of Comet Wild-2 on January 2nd, 2004, by direct capture into aerogel cells that flew through the dust coma at ∼6 km/s. Stardust collected several hundred comet particles >10 μm in size. These comet samples were delivered to Earth on January 15th, 2006. We developed a facility at the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, NY, USA) for the in-situ characterization of ∼10 μm particles collected in aerogel. These analytical instruments allow us to perform extensive chemical, mineralogical, and size-frequency characterization of particles captured in aerogel. These analyses are conducted without any invasive extraction, minimizing the possibility of contamination or particle loss during preparation. This facility was used to determine the chemical composition, the oxidation state, the mineralogy and to provide an indication of the grain size of the Wild-2 particles before they were removed from the aerogel. This information provides a catalog of particle types, allowing a more reasoned allocation of the particles to subsequent investigators based on a relatively detailed knowledge of the chemical composition and mineralogy of each particle. These measurements allowed a comparison of the chemical and mineralogical properties of the Wild-2 particles with other types of extraterrestrial materials, including interplanetary dust particles and meteorites. The success of in-situ analysis for Wild 2 particles demonstrates that synchrotron-based facilities will be important for the analysis of particles collected in aerogel on future earth-orbiting satellites and spacecraft. 相似文献
We present a forward modelling technique for calculating the surface X-ray spectra for a variety of lunar terrains. Our calculations considered variations in solar fluxes from solar quiescent condition to large flare activity (M1 flare), and expected elemental concentrations in the target, as well as yield, instrumental, and viewing geometry parameters for X-ray induced fluorescence from the lunar surface. Additionally, we present estimates of anticipated XRF signals from prominent Kα lines observable by a collimated 14 cm2 X-ray detector from a 100 km lunar orbit with ∼20 km spatial resolution. Our results show that Mg, Al and Si characteristic Kα lines can be observed for all solar conditions. The Ca Kα lines line can be differentiated from a fixed background during more energetic solar conditions such as C1 and M1 flares, whereas Ti and Fe lines are identifiable only during C1 and M1 solar flare conditions for Apollo 12 site composition. Both the Kα X-ray intensity ratios of Mg/Si and Al/Si correlate well with concentration ratios of Mg/Si and Al/Si, respectively, for B1 and M1 solar conditions. The Kα X-ray intensity ratios of Fe/Si and Ca/Si correlates with concentration ratios of Fe/Si and Ca/Si, respectively, for M1 solar condition. In principle, the modelling technique outlined here can be used to determine absolute elemental abundances (Mg, Al, Si, Ca, Ti and Fe) from X-ray spectra measured during recent and future lunar missions. 相似文献