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| Titel |
Juno observation of Io Plasma Torus |
| VerfasserIn |
Daniele Durante, Luciano Iess, Paolo Tortora, Marco Zannoni |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146279
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| Publikation (Nr.) |
 EGU/EGU2017-10296.pdf |
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| Zusammenfassung |
| Juno is currently orbiting Jupiter in a highly eccentric, 53.5-day orbit, with a perijove altitude
of about 4000 km. Radio science measurements are acquired during selected perijove passes
for about eight hours across closest approach to determine the gravity field and the interior
structure of Jupiter. The gravity determination is obtained by fitting precise range rate
measurements (3 μm/s over a time scale of 1000 s) through predictions obtained from a
dynamical model of the spacecraft.
The Juno, X band uplink, X band downlink, radio system at 7.2-8.4 GHz is
complemented by a Ka band system devised for the radio science investigation. During
dedicated perijove passes, the onboard Ka band frequency translator (KaT) locks into a Ka
band uplink signal at 34 GHz and retransmit it coherently to ground at 32 GHz. This radio
system configuration, used on Dec. 11, 2016 during the third perijove pass (PJ3) and
planned for all gravity orbits, allows a 75% calibration of dispersive contributions in
the Ka signal, such as the Io plasma torus. During PJ1 (Aug 27, 2016), a direct
measurement of plasma contribution in the downlink leg can was possible by transmitting
two downlink signals at X and Ka band coherent with a common uplink X band
signal.
The data collected during PJ01 and PJ03 show a clear signature associated to the Io
plasma torus. Doppler data points can be integrated and related to a plasma path delay, or a
TEC profile, along the Earth-Juno line-of-sight Due to the geometry of the orbit (polar, close
to face on as seen from the Earth), the radio link crosses the Io plasma torus during all gravity
science measurements. The associated delay, although small at Ka band, should be calibrated
in order to obtain a more accurate gravity estimation. In turn, the calibration data available in
all gravity passes can be profitably used to obtain a good sampling of the plasma
environment in the torus. This work will present the methods adopted in the data
analysis and the characterization of the Io torus from the first Juno perijove passes. |
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