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711.
Vitali Braun A. LüpkenS. Flegel J. GelhausM. Möckel C. KebschullC. Wiedemann P. Vörsmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Today’s space debris environment shows major concentrations of objects within distinct orbital regions for nearly all size regimes. The most critical region is found at orbital altitudes near 800 km with high declinations. Within this region many satellites are operated in so called sun-synchronous orbits (SSO). Among those, there are Earth observation, communication and weather satellites. Due to the orbital geometry in SSO, head-on encounters with relative velocities of about 15 km/s are most probable and would thus result in highly energetic collisions, which are often referred to as catastrophic collisions, leading to the complete fragmentation of the participating objects. So called feedback collisions can then be triggered by the newly generated fragments, thus leading to a further population increase in the affected orbital region. This effect is known as the Kessler syndrome. 相似文献
712.
M. E. Wiedenbeck 《Space Science Reviews》2013,176(1-4):35-46
The spectra of galactic cosmic rays that are observed inside the heliosphere result from the interaction of the spectra present in the local interstellar medium with the structured but turbulent magnetic field carried by the solar wind. Observational tests of solar modulation theory depend on comparisons between spectra inside and outside the heliosphere. Our knowledge of the local interstellar spectra are indirect, using extrapolations of interplanetary spectra measured at high energies where solar modulation effects are minimal and modeling of the physical processes that occur during particle acceleration and transport in the interstellar medium. The resulting estimates of the interstellar spectra can also be checked against observations of the effects that cosmic rays have on the chemistry of the interstellar medium and on the production of the diffuse galactic gamma-ray background. I review the present understanding of the local galactic cosmic-ray spectra, emphasizing the constraints set by observations and the uncertainties that remain. 相似文献
713.
Pascal Willis Hervé Fagard Pascale Ferrage Frank G. Lemoine Carey E. Noll Ron Noomen Michiel Otten John C. Ries Markus Rothacher Laurent Soudarin Gilles Tavernier Jean-Jacques Valette 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
DORIS is one of the four space-geodetic techniques participating in the Global Geodetic Observing System (GGOS), particularly to maintain and disseminate the Terrestrial Reference Frame as determined by International Earth rotation and Reference frame Service (IERS). A few years ago, under the umbrella of the International Association of Geodesy, a DORIS International Service (IDS) was created in order to foster international cooperation and to provide new scientific products. This paper addresses the organizational aspects of the IDS and presents some recent DORIS scientific results. It is for the first time that, in preparation of the ITRF2008, seven Analysis Centers (AC’s) contributed to derive long-term time series of DORIS stations positions. These solutions were then combined into a homogeneous time series IDS-2 for which a precision of less than 10 mm was obtained. Orbit comparisons between the various AC’s showed an excellent agreement in the radial component, both for the SPOT satellites (e.g. 0.5–2.1 cm RMS for SPOT-2) and Envisat (0.9–2.1 cm RMS), using different software packages, models, corrections and analysis strategies. There is now a wide international participation within IDS that should lead to future improvements in DORIS analysis strategies and DORIS-derived geodetic products. 相似文献
714.
A model of the main support of the aircraft landing gear is presented and its dynamics is studied using the equations for the distributed motion of a wheel equipped with a brake. Stability of the support wheel rolling motion is analyzed and the brake parameter values which may cause stability loss are found. The results of numerical experiments are presented. 相似文献
715.
The volume finite element in the form of hexahedron with nodal unknowns as components of the displacement vector and stress
tensor has been developed to analyze the shells of revolution. The displacement vector components for the inner point of the
finite element and the components of its stress tensor are expressed through the nodal unknowns using the method of vector
and tensor fields interpolation by the trilinear shape functions; that provides taking into account the finite element displacement
as a whole solid. The variational principle in a mixed formulation is applied to form the matrix of hexahedron deformation.
The efficiency of the proposed method for approximating the values being sought as vector and tensor fields in comparison
with the traditional method for approximating the values being sought as scalar fields is confirmed by a numerical example. 相似文献
716.
The paper presents a technique of calculating the life for gas turbine engine parts in a low cycle area based on the influence coefficients taking into account analytical and operational factors. A statistical method is used to determine the influence coefficients. 相似文献
717.
A. Lukaszczyk R. Williamson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Non-governmental organizations (NGOs) play a unique role in international affairs, providing access to resources, expertise, and assistance to supplement State resources. Sometimes the diplomatic skills and unofficial access of NGOs to policymakers through Track Two diplomacy can move a previously stalled critical issue forward and assist policymakers from different countries to find common ground outside official channels. Because they work outside of official channels, they are not bound by State policy that may inhibit negotiations between States. Some also have a convening power that sometimes makes it possible for State representatives to meet discipline experts and each other for informal discussions on issues of mutual interest. Finally, NGOs can draw attention to issues that may be overlooked or avoided by State organizations. 相似文献
718.
A comparison of temporal profiles of low-energy ion intensity and magnetic field magnitude in different periods of solar activity
in the outer heliosphere is carried out using the data of the Voyager 1 and Voyager 2 spacecraft. It is shown that temporal, spectral, and statistical characteristics of particle fluxes and magnetic field in
the heliospheric regions before and after the terminal shock in 2002–2008 had similar dynamics in different hemispheres. This
similarity allowed one to assume that, in the region of the inner heliospheric boundary, a quasistable spatial structure existed
moving together with the terminal shock in accordance with the solar wind pressure, as well as, probably, under the action
of the interstellar medium. It was revealed that the spatial dimensions of most details of this structure are less on Voyager 2, which, probably, is due to variation of the solar activity level, difference in latitude of spacecraft disposition, and
also the influence of the interstellar magnetic field. 相似文献
719.
I. Antonenko G.R. Osinski M. Battler M. Beauchamp L. Cupelli A. Chanou R. Francis M.M. Mader C. Marion E. McCullough A.E. Pickersgill L.J. Preston B. Shankar T. Unrau D. Veillette 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Remote robotic data provides different information than that obtained from immersion in the field. This significantly affects the geological situational awareness experienced by members of a mission control science team. In order to optimize science return from planetary robotic missions, these limitations must be understood and their effects mitigated to fully leverage the field experience of scientists at mission control. 相似文献
720.
Kh. Karami S. Ghader A. Raeen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the present work values of peak electron density (NmF2) and height of F2 ionospheric layer (hmF2) over Tehran region at a low solar activity period are compared with the predictions of the International Reference Ionosphere models (IRI-2001 and IRI-2007). Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran from July 2006 to June 2007 are used to perform the calculations. Formulations proposed by and are utilized to calculate the hmF2. The International Union of Radio Science (URSI) and International Radio Consultative Committee (CCIR) options are employed to run the IRI-2001 and IRI-2007 models. Results show that both IRI-2007 and IRI-2001 can successfully predict the NmF2 and hmF2 over Tehran region. In addition, the study shows that predictions of IRI-2007 model with CCIR coefficient has closer values to the observations. Furthermore, it is found that the monthly average of the percentage deviation between the IRI models predictions and the values of hmF2 and NmF2 parameters are less than 10% and 21%, respectively. 相似文献