1,721,006 research outputs found
The Determination of Jupiter’s Angular Momentum from the Lense-Thirring Precession of the Juno Spacecraft
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MORE: an advanced tracking experiment for the exploration of Mercury with the mission BepiColombo
No full textPrecise microwave tracking of interplanetary spacecraft has been a crucial tool in solar system exploration. Range and range rate measurements, the main observable quantities in spacecraft orbit determination and navigation, have been widely used to refine the dynamical model of the solar system and to probe planetary interiors. Thanks to the use of Ka-band and multifrequency radio links, a significant improvement in microwave tracking systems has been demonstrated by the radio science experiments of the Cassini mission to Saturn. The Cassini radio system has been used to carry out the most accurate test of General Relativity to date. Further developments in the radio instrumentation have been recently started for the MORE experiment, selected for the ESA mission to Mercury, BepiColombo. MORE addresses the mission's scientific goals in geodesy, geophysics and fundamental physics. In addition, MORE will carry out a navigation experiment, aiming to a precise assessment of the orbit determination accuracies attainable with the use of the novel instrumentation. The key instrument is a Ka/Ka band digital transponder enabling a high phase coherence between uplink and downlink carriers and supporting a wideband ranging tone. The onboard instrumentation is complemented by a ground system based upon the simultaneous transmission and reception of multiple frequencies at X and Ka-band. The new wideband ranging system is designed for an end-to-end accuracy of 20 cm using integration times of a few seconds. Two-way range rate measurements are expected to be accurate to 3 micron/s, thanks to nearly complete cancellation or calibration of the propagation noise from interplanetary plasma and troposphere. We review the experimental configuration of the experiment and outline its scientific goals and expected results
Mass and interior of Enceladus from Cassini data analysis
No full textGravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be (1.0798±0.0016)× 10^20 kg, which implies a density of 1608.9±4kg*m^−3. For a core made of hydrated silicates with a density of 2500kg*m^−3 the core radius is about 190 km and the quadrupole moment C22 = 1.4×10^−3. If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin–orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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