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Posted by baalke on May 19, 2007, 12:06 pm
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Cassini Significant Events
for 05/09/07 - 05/15/07
The most recent spacecraft telemetry was acquired on Tuesday, May 15,
from
the Goldstone 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" web page located at
http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, May 9 (DOY 129):
An article on Cassini was included in the April publication of
"National
Geographic Explorer." This version of National Geographic is
distributed to
over one million school children ages 6 to 12, grades 2 through 6.
The
24-page magazine contains only three features each month and is
accompanied
by a teacher's guide.
Uplink Operations sent commands to the spacecraft today for a live
update to
modify the pointing vectors for the Titan 30 flyby to occur on
Saturday, May
12.
Thursday, May 10 (DOY 130):
On May 10th, the Radio Science (RSS) team performed ingress and egress
ionospheric/atmospheric Saturn occultations, and an egress only ring
occultation. The ingress occultation covered Saturn northern
latitudes
around 71 degrees, the highest latitude to be probed by radio signal
in both
the Cassini prime and proposed extended missions. The egress ring
occultation is one of two occultations that were especially designed
to view
the rings at an intermediate opening angle of about 15 degrees. The
next
opportunity will occur during orbit 46. Collectively, the occultations
provide important information about the atmosphere's thermal
structure, the
microwave absorbing species, the hydrogen-to-helium ratio, and the
winds of
Saturn. Composite Infrared Spectrometer (CIRS) and Ultraviolet
Imaging
Spectrograph (UVIS) Saturn limb observations, and Visual and Infrared
Mapping Spectrometer (VIMS) cylindrical mapping followed the RSS
occultations.
Mission Planning (MP) hosted a Titan Atmosphere Model Working Group
(TAMWG)
meeting today to review Titan atmospheric density results from the Ion
and
Neutral Mass Spectrometer (INMS), AACS, and Navigation teams for the
Titan
23 through 29 flybys. It was noted that the T29 density was
unusually high
compared to T19, which was at a similar altitude and latitude at
closest
approach. The T29 results are being reviewed for more data pertinent
to the
atmosphere model. Including T29, all the recent flybys appear to be
consistent with the current model.
A discussion of flyby altitudes for the proposed extended mission was
included in the meeting agenda. In general a case was made for being
somewhat aggressive in lowering flyby altitudes in order to increase
science
value. The TAMWG accepted the MP proposal of new extended mission
flyby
altitudes, although some specific passes may still be adjusted after
meeting
with the Project Manager. The next TAMWG meeting is scheduled for 15
October to review in particular the T36 pass, which will be the first
low
altitude pass so far in the southern hemisphere.
Friday, May 11 (DOY 131):
The spacecraft transitioned from reaction wheel to thruster attitude
control
today in order to support the third RPWS Whistler activity. In this
observation, performed over a downlink pass, the wheels are turned off
to
eliminate interference during the observation, then turned back on
before
the next activity begins.
Scientists have long known that the lower atmosphere of Saturn's moon
Titan
contains organic aerosols, or tholins, formed from simple organic
molecules,
such as methane and nitrogen. Researchers had thought these tholins
formed
at altitudes of several hundred kilometers, but new information
gathered by
three particle spectrometers aboard the Cassini spacecraft shows
tholin
formation happens in Titan's atmosphere at altitudes greater than
1,000
kilometers. The results also show tholins form differently than
previously
thought. Understanding how tholins form could provide valuable insight
into
the origin of life in the solar system. For more information on this
subject, see a news release at:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=3D746
Saturday, May 12 (DOY 132):
Cassini flew past Titan today for the 31st targeted encounter of the
prime
mission. [Recall that the number assigned to a Titan encounter, e.g.,
T30,
is always one less than the number of encounters that have occurred at
that
point due to the extra orbit and Titan flyby that were inserted in the
tour
as part of the solution to the Huygens receiver problem.] Closest
approach
occurred at 2007-132T20:05:28 Spacecraft Event Time, at an altitude of
960
km, and a speed of 6.2 km/sec. The latitude at closest approach was
68.9=B0 N.
SCO reported 345 g of hydrazine were used, and a peak thruster duty
cycle of
53.8 %.
Science for this flyby included RADAR high latitude Synthetic Aperture
RADAR
observations of a large, expansive dark area dubbed the "Caspian Sea"
in the
Fensal/Aaru region of Titan. This north polar feature stretches over
1,000
kilometers and is only slightly smaller than Earth's Caspian Sea. The
Ion
and Neutral Mass Spectrometer (INMS) 'rode-along' with RADAR to make
in-situ
observations of Titan's upper atmosphere, measuring neutral particles
and
ions, UVIS measured Titan's stratospheric temperatures, VIMS obtained
surface observations at small solar angles of the northern hemisphere,
and
ISS performed imaging between 620 m/pixel and 1 km/pixel at phase
angles
less than 30 degrees. For the complete mission description of the T30
flyby
link to:
http://saturn.jpl.nasa.gov/news/events/titan20070512/index.cfm
Monday, May 14 (DOY 134):
The final sequence development process for S31 is about half way
through and
negotiations for DSN allocations for this sequence are complete. As a
result, Science Planning was able to initiate the Science Allocation
Panel
(SAP) process and allocate additional available SSR data volume for
six
periods in S31 to the instrument teams. More SSR data volume means
more
science data. This is only the second time since the Stereo Launch
slips in
October of 2006 that the SAP process could be performed during the
background sequence development time frame. Kudos to the DSN
schedulers who
are still working very hard to return to their original schedule of
deliverables.
Tuesday, May 15 (DOY 135):
AACS Periodic Engineering Maintenance was completed today. This
activity,
performed every 90 days, exercises the Engine Gimbal Actuators, the
backup
reaction wheel assembly - or RWA-3 - and scrubs the Backdoor Assisted
Load
Format Injection Loader memory.
On the extended mission front (XM), having completed the Senior Review
in
February of this year, the flight team now awaits the final approval
from
NASA, expected after an Operations Review is completed later this
year. In
the mean time, XM planning activities must continue in order to be
ready by
the time the Prime Mission concludes on June 30, 2008. The
Segmentation
Working Group met today to complete negotiations for the periapsis
allocations. This determines which of the Orbiter Science Teams or
Target
Working Teams will be primary for science occurring at periapsis for
each of
the extended mission orbits. For trajectory design development,
tumble
densities and minimum Titan altitudes have been finalized, and tweaks
to the
proposed extended mission trajectory have been released for review.
Everything is on track.
The official and final port for the S33 Science Operations Plan Update
process occurred today. All science teams, SCO, and Navigation
delivered
their files. These have now been merged and the concatenated file
posted to
the data repository for the teams to review. This process will
conclude on
June 1. The final development process for this sequence will then
begin on
the following Monday.
Orbit Trim Maneuver (OTM) #110, the T30 cleanup maneuver scheduled for
May
15, 2007, has been cancelled. This was a benefit realized from the
T30 aim
point adjustment performed by OTM-109, and the relatively large size
of the
next OTM, #111. The estimate for OTM-110 was 0.125 m/s. The
following
maneuver #111 is a deterministic maneuver of about 5.6 m/s. Due
primarily
to the relatively large size of OTM-111, the cost of OTM-110
cancellation
was only 0.112 m/s.
FYI - Deterministic maneuvers must be performed, as they are part of
the
original trajectory design and are required to change the trajectory
to keep
the spacecraft on its designed path. Other maneuvers are
"statistical" and
are used to compensate for the statistical variations that are a
normal part
of the navigation process. Many maneuvers are a combination of both.
The
statistical maneuvers are the ones that are candidates for
cancellation.
Two news releases were posted on the Cassini Web site on May 16
concerning
Enceladus. The first article postulates that frictional heating may be
what
powers the geysers jetting out from the surface of Saturn's moon
Enceladus.
For the details link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=3D747.
The second article from Goddard Space Flight Center concerns the
opening and
closing of the cracks or "Tiger Stripes" on the surface of Enceladus.
Tides
generated by the gravitational effects of Saturn could control the
occurrence of the eruptions. For the full article link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=3D748
THIS WEEKEND:
Saturday and Sunday, May 19 and 20, JPL will open its doors for the
annual
open house event. The Cassini display will be on the mall as you
enter the
campus from the main gate. A full-scale model of the Huygens probe
and a
quarter scale model of the Cassini spacecraft will be at our booth
this
year. Some of the most recent images will be on display along with
the
themed exhibits Titan-The Most Earth-Like Body in the Solar System,
and
Enceladus-The Multi-Discipline Nature of Discovery. Trading cards are
back
this year along with bookmarks and other outreach handouts. The Moon
Walk-a
walk among the moons of Saturn, hugely popular last year, is back for
a
return engagement. Drop by and say hi to the Outreach Folks and other
Cassini Flight Team members who will be staffing the booth.
Wrap up:
Check out the Cassini web site at http://saturn.jpl.nasa.gov for the
latest
press releases and images.
The Cassini-Huygens mission is a cooperative project of NASA, the
European
Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a
division of the California Institute of Technology in Pasadena,
manages the
Cassini-Huygens mission for NASA's Science Mission Directorate,
Washington,
D=2EC. JPL designed, developed and assembled the Cassini orbiter.
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