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Revealing the Lord of the Rings
27 May, 2005
Cassini Radio Science
appreciation for the Deep Space Network
The 3rd of May, 2005 was a memorable day for the Cassini Radio
Science Team. After nearly 15 years of planning, the first Cassini
Saturn atmosphere and rings occultation finally took place.
An occultation occurs when
the Cassini spacecraft passes behind the planet and/or the rings
as seen from Earth. By passing radiowaves through Saturn's rings,
details of their particle size, structure and composition can
be determined by analysing the data received by the antennas
of the Deep Space Network (DSN).
Despite a complicated configuration
involving the first ever three-wavelength downlinks occultation
(S-, X- and Ka-band), right-hand and left-hand polarisation where
available, multiple stations including the first use of Ka-band
on Deep Space Station 34 (DSS-34) at the Canberra Deep Space
Communciation Complex (CDSCC), special and demanding pointing
requirements at Ka-band, and the use of 14 open-loop receiver
channels simultaneously, to name a few, the experiment was a
great success.
 Sizing up the Rings
Each radio wavelength
is sensitive to different populations of ring particle material.
When the particle diameter is a small fraction of the wavelength,
it becomes essentially invisible in measurements at this wavelength.
Roughly speaking, when the red, green, and blue lines are nearly
coincident, the particles sizes in that ring region exceed about
5cm in diameter. When the red line (S-band) clearly separates
from the other two lines, the main size population contains particles
smaller than 5cm in diameter, and when the green (X-band) and
blue (Ka-band) lines also separate, the size population includes
particles smaller than about 1cm diameter.
The Deep Space Network, the
bigger part of the Radio Science instrument, performed practically
flawlessly, thanks to the planning, preparation, and practice
on the part of a large team of DSN personnel at JPL and at the
stations in Canberra (Australia), Madrid (Spain), and Goldstone
(California, USA).
The Cassini Radio Science Team
expressed its sincere appreciation and gratitude to the personnel
and management of the three Deep Space Communication Complexes
for their outstanding support, noting that their attentive interest
in the Cassini Radio Science observations had a significant impact
on this very important mission science goal.
A second occultation experiment
was also successfully completed on 21 May. There are also six
more occultation experiments planned for this calendar year,
and more planned throughout the remainder of the Cassini mission.
A NASA press
release on the experiment including images generated from radio
occultation data can be found here...>>
Article
compiled from messages and reports from the Cassini Radio Science
Subsystem Team and the Radio Science Systems Group.
Thanks also to Graham Baines from the Canberra Complex for additional
information and support. |
