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181.
David Arnas Daniel Casanova Eva Tresaco 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(11):3683-3695
4D Lattice Flower Constellations is a new constellation design framework, based on the previous 2D and 3D Lattice theories of Flower Constellations, that focus on the generation of constellations whose satellites can have different semi-major axis and still present a constellation structure that is maintained during the dynamic of the system. This situation can arise when dealing with satellites with very different instruments, or when it is of interest to coordinate two different constellations. In that sense, 4D Lattice Flower Constellations constitutes the most general representation of the Flower Constellation formulation. In addition, the effects of the perturbation are taken into account in order to generate distributions that maintain their initial design configuration under this perturbation for longer periods of time with a low fuel budget. Finally, examples of application are presented, showing the possibilities in satellite constellation design of this new approach. 相似文献
182.
Alex T. Chartier Cathryn N. Mitchell David R. Jackson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Data assimilation in conventional meteorological applications uses measurements in conjunction with a physical model. In the case of the ionised region of the upper atmosphere, the ionosphere, assimilation techniques are much less mature. The empirical model known as the International Reference Ionosphere (IRI) could be used to augment data-sparse regions in an ionospheric now-cast and forecast system. In doing so, it is important that it does not introduce systematic biases to the result. Here, the IRI model is compared to ionospheric observations from the Global Positioning System satellites over Europe and North America. Global Positioning System data are processed into hour-to-hour monthly averages of vertical Total Electron Content using a tomographic technique. A period of twelve years, from January 1998 to December 2009, is analysed in order to capture variations over the whole solar cycle. The study shows that the IRI model underestimates Total Electron Content in the daytime at solar maximum by up to 37% compared to the monthly average of GPS tomographic images, with the greatest differences occurring at the equinox. IRI shows good agreement at other times. Errors in TEC are likely due to peak height and density inaccuracies. IRI is therefore a suitable model for specification of monthly averages of Total Electron Content and can be used to initialise a data assimilation process at times away from solar maximum. It may be necessary to correct for systematic deviations from IRI at solar maximum, and to incorporate error estimation into a data assimilation scheme. 相似文献
183.
184.
Elyse J. Allender Csilla Orgel Natasha V. Almeida John Cook Jessica J. Ende Oscar Kamps Sara Mazrouei Thomas J. Slezak Assi-Johanna Soini David A. Kring 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):692-727
This study explores the Design Reference Mission (DRM) architecture developed by Hufenbach et al. (2015) as a prelude to the release of the 2018 Global Exploration Roadmap (GER) developed by the International Space Exploration Coordination Group (ISECG). The focus of this study is the exploration of the south polar region of the Moon, a region that has not been visited by any human missions, yet exhibits a multitude of scientifically important locations – the investigation of which will address long standing questions in lunar research. This DRM architecture involves five landing sites (Malapert massif, South Pole/Shackleton crater, Schrödinger basin, Antoniadi crater, and the South Pole-Aitken basin center), to be visited in sequential years by crew, beginning in 2028. Two Lunar Electric Rovers (LER) are proposed to be tele-robotically operated between sites to rendez-vous with crew at the time of the next landing. With engineering parameters in mind we explore the feasibility of tele-robotic operation of these LERs between lunar landing sites, and identify potential high interest sampling locations en-route. Additionally, in-depth sample collection and return traverses are identified for each individual landing site across key geologic terrains that also detail crew Extra-Vehicular Activity (EVA). Exploration at and between landing sites is designed to address a suite of National Research Council (2007) scientific concepts. 相似文献
185.
Environmental consequences of impact cratering events as a function of ambient conditions on Earth 总被引:1,自引:0,他引:1
Kring DA 《Astrobiology》2003,3(1):133-152
The end of the Mesozoic Era is defined by a dramatic floral and faunal turnover that has been linked with the Chicxulub impact event, thus leading to the realization that impact cratering can affect both the geologic and biologic evolution of Earth. However, the environmental consequences of an impact event and any subsequent biological effects rely on several factors, including the ambient environmental conditions and the extant ecosystem structures at the time of impact. Some of the severest environmental perturbations of the Chicxulub impact event would not have been significant in some periods of Earth history. Consequently, the environmental and biological effects of an impact event must be evaluated in the context in which it occurs. 相似文献
186.
Macromolecules derived from hydrogen cyanide (HCN) may be major components of the dark matter observed in bodies in the outer Solar System, which include comets and asteroids. HCN oligomers and polymers are readily formed at room temperature and react with water to produce polypeptides and alpha-amino acids or undergo pyrolysis to produce nitrogen heterocycles. Electron spin resonance (ESR) spectroscopy shows that HCN polymer mixtures contain a significant amount of long-lived organic free radicals that are primarily carbon-based. For comparison, we have also examined samples of tholins produced from experimental analogs of Titan aerosols, which has been shown by trace organic analysis to consist partly of HCN polymer. The "Titan tholin" exhibits at least two ESR signals that can be assigned to nitrogen- and carbon-centered radicals, although heating the sample eliminates the nitrogen centers and increases the signal from the carbon centers. This result suggests that the nitrogen-centered radicals may be thermodynamically less stable, but are kinetically trapped during the spark-discharge reactions that produce tholins from mixtures of gases such as methane and nitrogen. The results strongly support previous proposals of free radical mechanisms for HCN polymerization. 相似文献
187.
Swirl is used extensively in gas turbine combustors, principally as a means of controlling flame size, shape, stability and combustion intensity. Rapid progress has been made in recent years in the development of mathematical models of combustor swirl flows which simulate the processes of turbulence, combustion, fuel droplet sprays, radiation and pollutant formation, and solve the resulting equations via a computational procedure, which seeks an optimum path to the solution of the governing set of several simultaneous nonlinear partial differential equations. This paper looks at recent advances in the modeling of combustor swirl flows, its aim being to review the difficulties, discuss developments, demonstrate that useful predictions are already being made, and indicate in what areas further research may be useful. 相似文献
188.
David L 《Aerospace America》2002,40(4):36-8,41-3
Rising costs of the International Space Station prompted NASA to convene a panel of experts to assess the quality of ISS cost estimates and review program assumptions and requirements. The panel concluded that NASA was unable to accurately predict ISS costs or to support requests for increased funding for the ISS through 2006 and should maintain a U.S. core complete program with three-person crews with 6-month stays on the ISS. International response to the panel report was negative with space agencies from Japan, Russia, Canada, and Europe taking issue with the expected impact on ISS construction and use. 相似文献
189.
We present data on the solar irradiance as derived from a number of sources. An attempt was made to bring these data onto a uniform scale. The results are presented in Table IV and Figure 6. Summation of fluxes at all wavelengths yields a figure of 1357.826 W m-2 for the solar constant. Estimates are made of the solar flux variations due to flares, active regions (slowly varying component), solar rotation and the 11-year cycle.Solar activity does not produce a significant variation in the value of the solar constant. Nevertheless, variations in the X-ray and extreme ultraviolet portions of the solar flux may be several orders of magnitude during solar activity, especially at times of major flares. It is well established that these short wavelength flux enhancements cause significant changes in the terrestrial ionosphere. 相似文献
190.
David S. King 《Space Science Reviews》1980,27(3-4):519-527
The Cepheid-like pulsations of some of the R CrB stars should in principle make it possible to determine their masses and hence to place constraints on possible evolution scenarios. We briefly review the evidence for these pulsations and discuss the problem of how these low-mass, hydrogen-deficient carbon stars could have evolved to their present position in the H-R diagram. Linear and nonlinear pulsation calculations are reviewed. It is found that for these large luminosity to mass ratio (L/M) stars a region of pulsation instability extends considerably hotter than for normal high luminosity Cepheids. The envelopes of these models are so nonadiabatic that the identification of modes becomes very difficult since there is frequently no clearly defined nodal structure. For the most extreme L/M cases it is found that the models are unstable in the sense that they appear on the verge of ejecting the outer layers. 相似文献