The most recent spacecraft telemetry was acquired on Tuesday, June
10, from the Goldstone, California tracking complex. The Cassini
spacecraft is in an excellent state of health and all subsystems are
operating normally. Information on the present position and speed of
the Cassini spacecraft may be found on the "Present Position" page
at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, June 4 (DOY 156)
This week begins by continuing to focus on ring science. During the
bulk of the week, the Magnetospheric and Plasma Science (MAPS)
instruments took advantage of opportunities to observe the auroras
and the processes driving them. In addition, a number of occultation
experiments were performed. On DOY 160, the Visual and Infrared
Mapping Spectrometer (VIMS) observed the occultation of the star
Gamma Cru with the Magnetospheric Imaging Instrument (MIMI),
Composite Infrared Spectrometer (CIRS) and Ultraviolet Imaging
Spectrograph (UVIS) riding along. On DOY 161, UVIS observed a solar
occultation. The solar occultation port boresight was centered on the
sun as it entered Saturn's atmosphere. The camera slit was aligned
tangent to Saturn's limb. On DOY 162, CIRS observed a stellar ring
occultation, and UVIS observed a stellar ring occultation on DOY 163
to close out the week.
Thursday, June 5 (DOY 157)
Today Uplink Operations sent commands to the spacecraft for the S41
live Mimas Inertial Vector Propagator (IVP) update, and commands to
modify Radio and Plasma Wave Science (RPWS) direction finding. Both
commands will execute on Sunday, June 8.
Saturn's F ring has long been of interest to scientists as its
features change on timescales from hours to years and it is probably
the only location in the solar system where large-scale collisions
happen on a daily basis. Understanding these processes helps
scientists understand the early stages of planet formation. A team of
scientists led from the UK has discovered that the rapid changes in
Saturn's F ring can be attributed to small moonlets colliding with
their constituent particles and causing perturbations. Images
obtained by Cassini in 2006 and 2007 show the formation and evolution
of a series of structures called "jets" that are the result of
collisions between small nearby moonlets and the core of the F ring.
A paper on these findings has been published in "Nature." Title: "The
determination of the structure of Saturn's F ring by nearby
moonlets." For the complete article about these findings link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=846
Friday, June 6 (DOY 158):
The Command Loss Timer was set back to the nominal 90 hours in the
background sequence today. It had been set to a value of five days
back on May 6 in order to accommodate potential Cassini DSN pass
losses should any problems arise during the Entry/Descent/Landing
phase of the Phoenix Mission.
The third DSS-47 proficiency test with Cassini using a Radio Science
Receiver (RSR) in Narrabri, Australia, was completed today. The ~2.5
hour track overlapped additional supports over Goldstone's DSS-25 and
Canberra's DSS-34 stations. The entire DSS-47 support was in 3-way
mode with DSS-25 providing the uplink.
Since the last Cassini Narrabri test on DOY 126, station personnel
have been running a series of tests to try to identify and repair the
source of two issues that were reported by the RSS team: Spurious
spectral spikes around the carrier and poor short- and long-term
frequency stability. One of the issues seems to have "gone away," and
the test today was unable to provide insight to the cause of the
other.
The next planned DSS-47 Cassini support is on DOY 168 during an RSS
Saturn atmospheric occultation. The occultation will also be covered
by Goldstone's DSS-25 and DSS-26 and Canberra's DSS-34 in addition to
the 70-m antennas at both sites, making it the first time ever four
antennas will be tracking Ka-band simultaneously! Previously the most
has been three antennas.
Saturday, June 7 (DOY 159):
This weekend the moon glides past several planetary waypoints, one of
which is Saturn. All you'll need to enjoy this show is a clear
evening sky. On Saturday, June 7, the crescent moon will be visible
just below Mars. On the 8th, the moon is closer to Saturn, forming a
little triangle with Regulus. And on the 9th, the waxing crescent is
higher still above Saturn, tracing an imaginary line along the
ecliptic plane. Over the next few weeks, Mars and Saturn draw closer
together. On July 10 and 11, both planets will be visible in the same
telescope field-of view. A star chart for Saturn and Mars can be
found at: http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=2109
Sunday, June 8 (DOY 160):
June 8 is noted for Saturn periapsis for Cassini, and for the fact
that it is the 383rd birthday of Giovanni Domenico Cassini. Born in
1625, Cassini, an Italian-French astronomer, discovered several of
Saturn's satellites: Iapetus, Rhea, Tethys and Dione. In 1675, he
discovered what is today called the "Cassini Division," the gap
between two of the main rings of Saturn.
Monday, June 9 (DOY 161):
Non-targeted flybys of Pan and Pandora occurred today.
A weeklong series of meetings has begun as part of the #45 PSG
meeting being held in Rome. The primary focus will be on the various
science discipline sessions, and on discussion of post Equinox
Mission activities.
An image of Saturn's rings from the "other side" is Astronomy Picture
of the Day today. In this instance, "other side" means 17 degrees
above the ring plane. Check it out at:
http://antwrp.gsfc.nasa.gov/apod/ap080609.html
Live IVP/ Live Movable Block (LMB) activities in S41 continued today
with the kickoff meeting for the third update process of the
sequence. The orbit determination solution will be released tomorrow,
and a go/no go given on Wednesday. If it's a go, the files will be
uplinked to the spacecraft on Friday. UPDATE: It's a go. Based on
analysis by Science Planning and concurrence from ISS, CIRS, VIMS and
UVIS, the Saturn and Mimas vectors will be updated and the Dione
vectors will not. The live movable block for RSS to execute on June
15 will also be updated.
The sequence leads for S42 currently have their hands full. After
receiving the Instrument Expanded Block (IEBs) files from the
instrument teams, the end result will be 15 loads to be sent to the
spacecraft for this sequence. Eight are for the Ion and Neutral Mass
Spectrometer (INMS) and the ISS load was large enough that it had to
be split in two. This is not counting getting the background sequence
up as well. This is a record for the number of IEBs to be uplinked.
This could also present some scheduling issues since the first uplink
track on DOY 177 only has three hours of usable uplink time, and the
second uplink track the next day has an RSS boresight calibration
resulting in one hour without telemetry.
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