Cassini Significant Events 12/23/09 - 01/05/10
The most recent spacecraft telemetry was acquired on Jan. 5 from the
Deep Space Network tracking complex at Madrid, Spain. 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, Dec. 23 (DOY 357)
Real time commands sent to the spacecraft today included Cosmic Dust
Analyzer (CDA) commands to increase the particle size threshold in
preparation for the G and E ring crossings over Christmas, uplink of
the DOY 359 Radio Science (RSS) Live Moveable Block, and spacecraft
maintenance commands to clear a Solid State Power Switch (SSPS) trip.
Thanks to the accurate execution of Orbit Trim Maneuver (OTM) #228,
accurate prediction of the bias delta-Vs, and a low delta-V
cancellation penalty, cancellation has been proposed for OTM-229 due
to execute on Dec. 24, Christmas Eve. Science Planning has analyzed
the pointing differences for the trajectory modeled with and without
the execution of OTM-229. Pointing differences are within acceptable
margins although the errors are slightly lower with the execution of
the maneuver, particularly for the RADAR observations at Titan
closest approach. In neither case are they sufficiently large to
argue for execution of the OTM. RADAR has agreed with this analysis
so OTM-229 has been cancelled.
The Cassini imaging team has created a video collection of "mutual
events," which occur when one moon passes in front of another, as
seen from the spacecraft. Scientists use mutual event observations to
refine their understanding of the dynamics of Saturn's moons. For the
full text and the videos go to:
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease2009121723/
and http://saturn.jpl.nasa.gov/video/videodetails/?videoID=206
Thursday, Dec. 24 (DOY 358)
Today was the fifth anniversary of the release of the Huygens Probe
from the Cassini Spacecraft. Three weeks later, the probe entered
the atmosphere and landed on Titan.
Friday, Dec. 25 (DOY 359)
Today Radio Science (RSS) successfully completed the S56 orbit 123
Saturn atmospheric and rings occultation experiment. The experiment
included ingress and egress ring occultations and an egress
atmospheric occultation.
This was the first in a set of three especially designed Cassini
orbits that capture optimized diametric ring occultations covering
the full ring system from ansa-to-ansa. The optimized geometry is
similar to that of another set implemented early in the prime mission
in 2005. The difference is that the rings are nearly closed during
the second set, while they were much more open during the first.
The ring-opening angle was 4.8 degrees compared with 20 to 23.5
degrees in 2005. The highly elongated path of the radio signals
through the rings enhances sensitivity to tenuous ring material
especially in the C ring and the Cassini Division, but causes the
signals to become noise-limited in other dense ring regions such as
most of the B ring, the opposite of the 2005 set. Thus, the two sets
nicely complement one another. The multiple occultations provide a
fair sampling of variations in profiles of various dynamical ring
features with observation longitude. The nearly 4.5 years time
difference between the two sets provided valuable information about
potential variability of Saturn's equatorial winds and other
atmospheric physical properties with time.
The main engine cover was closed today as a precautionary measure to
avoid dust hazards. It will be reopened tomorrow to complete the
55th in-flight cycle of the cover.
Saturday, Dec. 26 (DOY 360)
Non-targeted flybys of Tethys and Prometheus occurred today along
with an Imaging Science (ISS) ring propeller observation.
Sunday, Dec. 27 (DOY 361)
Today Cassini flew by Titan at an altitude of 955 km and a speed of 6
km/sec. Closest approach for Titan 64 occurred at 05:23 PM PST on
Dec. 27 (Dec. 28 GMT), latitude 82 degrees N. During this flyby,
RADAR got another view of the north polar lakes, providing an
opportunity to measure changes in lake size and other lake
characteristics. Other instruments utilized this opportunity to
sample the high northern atmosphere as well as to look for possible
seasonal changes.
The Ion and Neutral Mass Spectrometer (INMS) was prime on the inbound
leg of T64, and riding with RADAR outbound. This nearly north polar
flyby is critical when paired with T65, which will be nearly south
polar. Scientists are eager to take advantage of the opportunity to
view the north and south poles in close temporal proximity to compare
the atmosphere and the surface topography. This flyby will also help
study any seasonal variations that may have occurred in the north
since the early part of the prime mission.
RADAR observations included altimetry and ride-along Synthetic
Aperture Radar (SAR) with INMS inbound to Titan, SAR outbound, and
altimetry and hi-altitude SAR over northern polar lakes to perform
stereo and seasonal change detection. This was the only opportunity
to collect north polar SAR data in the extended mission.
This flyby allowed the Visual and Infrared Mapping Spectrometer
(VIMS) to acquire a mosaic of Titan between 160 and 300 deg longitude
at a resolution of 20 km/pixel. VIMS also monitored for mid-latitude
clouds and surveyed the evolution of the north polar hood.
The Composite Infrared Spectrometer (CIRS) obtained mid-northern
latitude composition and temperature vertical profiles.
ISS acquired a full-disk mosaic of Adiri and rode along with VIMS to
observe Adiri at higher resolution and to monitor clouds. ISS also
monitored Titan to track clouds and their evolution for an extra day
after the Titan encounter.
T64 was a north polar dusk flyby with a minimum altitude of 955 km.
In normal upstream conditions, Cassini would explore the north lobe
of Titan's magnetic tail, very close to the moon. Due to the location
of the point of closest approach, it was potentially important
regarding the detection of an intrinsic magnetic field, but not as
good as T70 will be. With adequate pointing of Magnetospheric and
Plasma Science (MAPS) instruments, Magnetometer data acquired during
this flyby will be extremely helpful in the identification of
escaping particles similar to those that could be seen in T63. If the
upstream conditions are similar to T63, T64 will be extremely
important to have an idea of the structure of Titan's magnetic tail
in the dusk sector.
The Magnetospheric Imaging Instrument measured energetic ion and
electron energy input to the atmosphere.
The Radio and Plasma Wave Science (RPWS) instrument measured thermal
plasmas in Titan's ionosphere and surrounding environment, searched
for lightning in Titan's atmosphere, and investigated the interaction
of Titan with Saturn's magnetosphere. For more information link to
the Cassini Web Site:
http://saturn.jpl.nasa.gov/mission/flybys/titan20091228/
Tuesday, Dec. 29 (DOY 363)
Rain in Spain, specifically rain and snow over the DSN complex near
Madrid, caused partial loss of the Titan 64 playback data on Dec. 28
and also during the repeated playback on Dec. 29. A memory readout
(MRO) to confirm that the AACS safe table update occurred as planned
was also lost. The MRO will be verified via real time command on Dec.
30. The Titan data that was lost is not recoverable.
Wednesday, Dec. 30 (DOY 364)
As development for OTM-230 gained momentum, it became apparent that
it could be combined at a minimal cost of about 0.1 m/s of main
engine propellant with OTM-231. Taking into consideration additional
factors of late updates to the maneuver design, availability of
personnel during the holiday period, and the weather at Madrid, it
made good sense to proceed with the combined OTMs. So, OTM-230 has
been cancelled.
A Cassini view of Saturn has made Time Magazine's 2009 'Year in
Pictures.' The image, released in September and dubbed 'The Rite of
Spring,' was a view of Saturn and the rings as the equinox crossing
occurred. For the complete article link
to:http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3661
Thursday, Dec. 31 (DOY 365)
Cassini Science at the conclusion of 2009 included MAPS observations
of Titan's clouds at low phase angles and at a closer distance than
many previous opportunities, UVIS mapped volatiles in the system in
the immediate neighborhood of Enceladus to test connections of
volatile changes to plume eruptions, and CIRS measured oxygen
compounds in Saturn's stratosphere as a function of latitude and took
data for a mid-IR temperature map of Saturn to determine upper
troposphere and tropopause temperature with spatial resolution of
about two degrees over multiple latitudes.
Friday, Jan. 1 (DOY 001)
The New Year began with a CIRS ring observation. This was followed
by a VIMS calibration using the Pleiades, and ISS led a Titan eclipse
observation with long exposures to search for auroras and lightning
on Titan in eclipse.
Saturday, Jan. 2 (DOY 002)
On Jan. 2, the INMS replacement heater experienced a solid-state
power switch (SSPS) trip. The fault protection response was to
command the switch OFF then ON, and then power OFF the INMS
instrument. This SSPS incident is the 28th such trip of these
switches since launch and occurred six weeks after trip #27. Since
the instrument was in a safe state and not currently involved in
collecting high value science, it was decided to send reset commands
next week.
Monday, Jan. 4 (DOY 004):
Orbit Trim Maneuver (OTM) #231 was performed today. This was the
apoapsis maneuver setting up for the Titan 65 encounter on Jan. 12.
The main engine burn began at 10:59 PM PST. Telemetry immediately
after the maneuver showed a burn duration of 47.08 seconds, giving a
delta-V of 8.046 m/s. All subsystems reported nominal performance
after the maneuver.
Tuesday, Jan. 5 (DOY 005)
INMS has looked at the initial telemetry after the uplink of reset
commands following the SSPS trip on Saturday. Initial turn-on has
been confirmed and the flight software load has been reset.
Everything looks good. The team will send an email tomorrow morning
when the MRO data has been processed. Instrument activation will
occur on Thursday.
