▪ Abstract A review of planetary-entry gas dynamics is presented. Evolution of a blunt-body flowfield from a free molecular flow environment to a continuum environment is described. Simulations of near-wake flow phenomena, important for defining aerobrake payload environments, are also discussed. Some topics to be highlighted include aerodynamic coefficient predictions with emphasis on high-temperature gas effects; surface heating and temperature predictions for thermal protection system (TPS) design in a high-temperature, thermochemical nonequilibrium environment; and thermochemical models required for numerical flow simulation. Recent applications involving atmospheric entry into Jupiter (Galileo), Mars (Pathfinder and Global Surveyor), and a planned mission in which dust from the tail of a comet will be returned to Earth (Stardust) will provide context for this discussion.
Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA/JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800˚C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.
The accuracy and complexity of solving multicomponent gaseous diffusion using the detailed multicomponent equations, the Stefan-Maxwell equations, and two commonly used approximate equations have been examined in a two part study. Part I examined the equations in a basic study with specified inputs in which the results are applicable for many applications. Part II addressed the application of the equations in the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) computational code for highspeed entries in EarthÕs atmosphere. The results showed that the presented iterative scheme for solving the Stefan-Maxwell equations is an accurate and effective method as compared with solutions of the detailed equations. In general, good accuracy with the approximate equations cannot be guaranteed for a species or all species in a multi-component mixture. ÒCorrectedÓ forms of the approximate equations that ensured the diffusion mass fluxes sum to zero, as required, were more accurate than the uncorrected forms. Good accuracy, as compared with the StefanMaxwell results, were obtained with the ÒcorrectedÓ approximate equations in defining the heating rates for the three Earth entries considered in Part II.
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