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981.
982.
983.
E. Echer B.T. Tsurutani F.L. Guarnieri 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
In this article, we study fast shocks at CIR boundaries during an extended interval of 15 consecutive major high speed solar wind streams in 1992–1993. Ulysses was 4–5 AU from the sun. The Abraham-Schrauner shock normal method and the Rankine-Hugoniot relations were used to determine fast shock directions and speeds. Out of 33 potential CIR shocks, 14 were determined to be fast forward shocks (FSs) and 14 were fast reverse shocks (RSs). Of the remaining 5 events, 2 were forward waves and 3 were reverse waves. CIR edges at latitudes below ∼30o were, for the most part, bounded by fast magnetosonic shocks. The forward shocks were generally quasi-perpendicular (average θnBo = 67o). The reverse shocks were more oblique (average θnBo = 52o), but they extended to all angles. Both FSs and RSs had magnetosonic Mach numbers ranging from 1 to 5 or 6. The average Mach numbers were 2.4 and 2.6 for FSs and RSs, respectively. The shock Mach numbers were noted to generally decrease with increasing latitude. The non-shock events or waves were noted to occur preferentially at high (∼−30° to −35°) heliolatitudes where stream-stream interactions were presumably weaker. These results are consistent with expectations, indicating the general accuracy of the Abraham-Schrauner technique. 相似文献
984.
D. Kucharski T. Otsubo G. Kirchner F. Koidl 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The Graz 2 kHz Satellite Laser Ranging (SLR) measurements allow determination of the spin axis orientation of the geodetic satellite Ajisai. The high repetition rate of the laser makes it possible to determine the epoch time when the laser is pointing directly between two corner cube reflector (CCR) rings of the satellite. Identification of many such events during a few (up to 3) consecutive passes allows to state the satellite orientation in the celestial coordinate system. Six years of 2 kHz SLR data (October 2003–October 2009) delivered 331 orientation values which clearly show precession of the axis along a cone centered at 14h56m2.8s in right ascension and 88.512° in declination (J2000.0 celestial reference frame) and with an half-aperture angle θ of 1.405°. The spin axis precesses with a period of 117 days, which is equal to the period of the right ascension of the ascending node of Ajisai’s orbit. We present a model of the axis precession which allows prediction of the satellite orientation – necessary for the envisaged laser time transfer via Ajisai mirrors. 相似文献
985.
986.
F. Santoni F. Piergentili F. Graziani 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The nanosatellite UNICubeSAT is described, carrying a Broglio Drag Balance Instrument for neutral thermosphere density in situ measurements. The aim of the mission is to contribute to the development of accurate thermosphere models, achieving in situ, real time measurements of atmosphere density, that could be exploited for global atmosphere model validation and accurate short term (1–3 days) real time space weather forecasts. The satellite is inexpensive and swarms could be easily launched operating as a distributed sensor network to get simultaneous in situ local (not orbit averaged) measurements in multiple positions and orbit heights. The nanosatellite is based on the Cubesat standard architecture, weighing about 1 kg for 1-L volume. Atmospheric drag force is measured by the displacement of light plates exposed to the incoming particle flux seen by the spacecraft, applying the original three dimensional Broglio Drag Balance concept to a single nanosatellite axis. The instrument concept and its relation to the satellite bus is depicted, showing that many long term potential measurement error sources and biases can be removed in data processing if the spacecraft is spin stabilized. The expected accuracy in density measurements is 20%. The instrument cost is a fraction of that of accurate accelerometers. The onboard systems are based on commercial off the shelf components, in accordance with the short lifetime typical of aeronomy satellites. 相似文献
987.
G. Tobie B. Giese T. A. Hurford R. M. Lopes F. Nimmo F. Postberg K. D. Retherford J. Schmidt J. R. Spencer T. Tokano E. P. Turtle 《Space Science Reviews》2010,153(1-4):375-410
The surface morphology of icy moons is affected by several processes implicating exchanges between their subsurfaces and atmospheres (if any). The possible exchange of material between the subsurface and the surface is mainly determined by the mechanical properties of the lithosphere, which isolates the deep, warm and ductile ice material from the cold surface conditions. Exchanges through this layer occur only if it is sufficiently thin and/or if it is fractured owing to tectonic stresses, melt intrusion or impact cratering. If such conditions are met, cryomagma can be released, erupting fresh volatile-rich materials onto the surface. For a very few icy moons (Titan, Triton, Enceladus), the emission of gas associated with cryovolcanic activity is sufficiently large to generate an atmosphere, either long-lived or transient. For those moons, atmosphere-driven processes such as cryovolcanic plume deposition, phase transitions of condensable materials and wind interactions continuously re-shape their surfaces, and are able to transport cryovolcanically generated materials on a global scale. In this chapter, we discuss the physics of these different exchange processes and how they affect the evolution of the satellites’ surfaces. 相似文献
988.
989.
Alexander F. Zakharov Francesco De Paolis Gabriele Ingrosso Achille Nucita Asghar Qadir 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):2061-2063
General relativity (GR) can be probed by several tests in the weak gravitational field limit. On the contrary, very poor information exists about GR tests in strong gravitational fields. Here, we focus on the interaction of light rays with the strong gravitational field of a massive black hole and show that relativistic images may form. Hence, we calculate the shapes of shadows (mirages) forming just near BH horizons and discuss the possibility to estimate the black hole parameters (mass, spin and charge) by future astrometric missions. In 2007, the Radioastron space telescope will be launched and it will allow to evaluate those parameters for the black hole hosted at the center of our Galaxy. 相似文献
990.
We consider transfers with low thrust in an arbitrary field of forces. The modified method of transporting trajectory [1–4] is used for optimization of the transfers. The complexity of finding the transporting trajectory of a preset type can be the main obstacle to application of this method. This challenge is solved for the three-body problem in the Hill motion model. Numerical analysis of the method is performed using an example of the transfers to halo-orbits around the solar-terrestrial libration points. 相似文献