Cassini Update - June 7, 2008
- From: baalke@xxxxxxxxxxxxx
- Date: Fri, 6 Jun 2008 09:01:06 -0700 (PDT)
Cassini Significant Events
for 05/28/08 - 06/03/08
The most recent spacecraft telemetry was acquired on Tuesday, June 3,
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, May 28 (DOY 149)
On Wednesday, May 28, Cassini flew by Titan for the 45th targeted
flyby
of that satellite at an altitude of 1400 km, and a speed of 6.3 km/
sec.
Closest approach occurred at approximately 01:42 AM PDT at a latitude
of
12.4 degrees N. Spacecraft Operations (SCO) reported that 891g of
hydrazine were used to support this flyby. To view the Mission
Description PDF file, images, and additional information, link to:
http://saturn.jpl.nasa.gov/news/events/titan20080528/index.cfm
T44 is the last Titan flyby of the original four-year tour. If Titan
were a planet, it would likely stand out as the most important planet
in
the solar system after Earth for humans to explore. Titan is about the
size of a terrestrial planet (It's diameter is 76% of Mars'
diameter.),
it has a dense atmosphere of nitrogen and methane, and a surface
covered
with organic material. It is Titan that is arguably Earth's sister
world
and the Cassini-Huygens mission considers Titan among its highest
priorities. The following material was extracted from the mission
description and goes into detail on the science obtained from this
last
flyby.
RADAR altimetry at T44 was close to an area known as Hotei, over an
area
that was imaged with Synthetic Aperture RADAR (SAR) during T43. The
SAR
swath sweeps northwest across Xanadu, over the Shangri-La dunefields
and
onto Dilmun. The SAR imaged the southern edge of Xanadu, which shows a
sharp boundary in microwave emissivity that is not presently
understood.
The SAR data is hoped to yield information on Xanadu's large-scale
topography, as well as the influence of Xanadu on regional wind
patterns
as revealed in the dunes, and a partial overlap with T13 SAR may give
stereo information and refined estimates of Titan's rotation
state.
Because of the higher altitude of this flyby, the spacecraft was above
most of the ionosphere, so the Ion and Neutral Mass Spectrometer INMS
performed exospheric observations. The team will use these
observations
to identify what chemical compounds are escaping from Titan's
atmosphere, looking at both altitude and the difference between the
northern and southern hemispheres.
The Composite Infrared Spectrometer (CIRS) continued to extend spatial
and temporal coverage of Titan, from low-spectral resolution disk maps
to high spectral resolution nadir and limb integrations. Getting good
time-resolution is important because the team is looking for seasonal
changes in the stratosphere, especially the expected break-up of the
northern polar vortex in northern spring. In a rare occurrence, during
the T44 targeted Titan flyby, CIRS observed the rings of Saturn.
Usually, the Titan observations are considered more compelling during
the flybys since the geometries and opportunities are so spectacular,
so
this rings observation was unique. CIRS measured the mean thermal
gradient across Saturn's many-particle-thick rings by executing radial
scans of Saturn's main rings A, B, and C, over multiple illumination
geometries including phase, spacecraft inclination, and solar
elevation
on the lit and unlit sides of the rings.
Visual and Infrared Mapping Spectrometer (VIMS) observations
concentrated on determining time scales for cloud formation and
dissipation.
The T44 flyby geometry showed a half-illuminated Titan as Cassini
approached and receded. On approach, the Imaging Science Subsystem
(ISS)
carried out night-side imaging for photometry and searched for
lightning
and aurora. ISS also acquired a regional-scale map of Hotei Arcus, its
highest-resolution observation of this region to date. Outbound, ISS
saw
portions of Belet and Adiri and territory to the north, capturing
global
and full-disk mosaics. As the geometries of the T41 through T44 flybys
were very similar, ISS had opportunities to detect clouds in this
region
every few weeks.
As Titan is out "in front" of Saturn, the T41 through T44 flybys put
the
spacecraft in an ideal location to have another opportunity for the
Radio and Plasma Wave Science (RPWS) instrument to observe Titan
outside
of Saturn's magnetosphere, in shocked solar wind ahead of the
magnetosheath as happened on T32. The instrument team was interested
in
duplicating the flyby geometry to look for shorter time-scale
phenomena
in Titan's plasma environment. This series of four flybys, especially
T41 through T43, offered that opportunity.
Thursday, May 29 (DOY 150)
This was quite a heavy week in terms of software deliveries both for
ground and flight software. The Cassini Archive Tracking System V5.1
modified internal formulas and database queries, the SCO Flight
Software
Development System (FSDS) V2.22 among other changes added an Enceladus
plume density model, additional Titan mass properties files for
extended
mission, a new reference trajectory ephemeris file, and added new
capabilities to FSDS to facilitate operational processes. Navigation
delivered the T2.6 version of the Maneuver Operations Program Set
(MOPS)/ Maneuver Automation Software (MAS) and MOPS utility software,
as
well as incremental enhancements to other software sets. Finally, the
Cosmic Dust Analyzer (CDA) delivered V12.2 of its instrument flight
software (FSW). The FSW contains a correction for Enceladus flybys in
high-speed mass spectra mode.
The sequence leads for S42 reported this week that the uplink windows
for this FSW have been set for DOY-190 and 191. The FSW checkout on
DOY-194 and the first ring plane crossing (RPX) demo on DOY-196 have
been combined into one sequence to facilitate uplinking. DOY-201 has
been tentatively set for the CDA/CDS S&ER2 TLM mode test but there are
some details still to be worked. Finally, a second RPX demo is
scheduled
for DOY-203 and a RPX science real-time activity is set for DOY-217.
Uplink windows for activities executing after DOY 191 will be selected
at a later date.
The Project Change Control Board (PCCB) reviewed and approved an
Engineering Change Request that lays out the maintenance and upgrade
plans for ISS and VIMS software at the Multi-Mission Image Processing
Laboratory for the next delivery.
At this time two live update approval and uplink processes are running
concurrently. Today, a go was given for the Live Inertial Vector
Propagator (IVP) update and Radio Science (RSS) Live Movable Block
(LMB)
for DOY-153. Tomorrow those files will be uplinked to the spacecraft.
Also tomorrow, a kick-off meeting will be held for Live Update #2 for
Saturn and Mimas on DOY-160. On Sunday, the DOY-153 updates will
execute.
Friday, May 30 (DOY 151):
Due to the fact that Orbit Trim Maneuver (OTM) #159 coming up on June
23
is a large deterministic maneuver of over 12 m/s, and the team had a
very much on-target flyby of Titan 44, it appears that OTM-158 is not
required to maintain the spacecraft on the reference trajectory. There
is also a small predicted delta v saving if the maneuver is not
performed. Science planning has reviewed the "no maneuver" trajectory
and determined that there is no negative impact to science if the
maneuver is cancelled. Therefore, OTM-158 has been cancelled.
Sequence leads sent commands to the spacecraft this week for RPWS
direction finding, S41 RSS occultation ingress LMB, S41 Live IVP
update,
a Reaction Wheel (RWA) bias to execute over the OTM-158 prime pass,
and
an additional RWA bias for the OTM-158 backup pass.
Saturday, May 31 (DOY 152):
The S40 sequence concluded and S41 began execution today at
2008-152T04:27:00 SCET. The sequence will run for 31 days and conclude
on July 1. During that time there will be no targeted encounters.
There
will however be 16 non-targeted flybys, one each of Pallene, Pandora,
Epimetheus, Enceladus, and Atlas, two each of Janus, Pan, Titan, and
Prometheus, and three of Methone. Two OTMs are scheduled, numbered 158
and 159.
Members of Cassini Outreach gave presentations on Cassini and the Mars
Phoenix lander, and located Saturn and Mars in the heavens for 120
attendees to observe at a Joshua Tree National Park public star party
on
May 31.
Sunday, June 1 (DOY 153):
Non-targeted flybys of Pallene and Janus occurred today.
The Main Engine (ME) cover, open since March 24, was closed today
right
after the OTM-158 prime uplink pass for a dust hazard. The plan is for
the cover to remain closed for two more dust hazards occurring on June
9
and 16. The cover will be reopened June 17. This will be cycle #39 for
the ME cover.
Science activities today included VIMS and CIRS combining to design
two
back-to-back stellar occultations, ISS recorded a short auroral movie
and RSS observed an occultation ingress of Saturn's ionosphere and
atmosphere to measure vertical profiles of electron density in the
ionosphere, and density, pressure, and temperature in the neutral
atmosphere. CIRS obtained stratospheric thermal structure at the RSS
occultation points. At the end of the day, all the Optical Remote
Sensing instruments combined for an Enceladus observation.
The Navigation Team participated today in one of two outreach
activities
occurring over the next two weeks. For a number of years, the Nav Team
has participated in the Consortium for Undergraduate Research
Experience
(CURE) program. Since the summer of 1999, California State University
of
Los Angeles together with the Jet Propulsion Laboratory and four local
community colleges, Los Angeles City College, East Los Angeles
College,
Los Angeles Southwest College, and Pasadena City College have
collaborated to offer a community based, year round, National Science
Foundation funded REU program known as CURE. The objectives of the
CURE
program are to recruit, train, and retain underrepresented minorities
in
the fields of science and engineering. The CURE program offers
qualified
students an opportunity to experience all aspects of a scientific
research project. The general area of research is astronomy utilizing
the Table Mountain Observatory (TMO) operated by JPL as the
observational research base. Students learn the basics of
observational
astronomy, telescope operation, data reduction and analysis, and very
importantly the students also learn to report their findings in
academic
settings. Students also prepare reports consisting of journal
articles,
oral presentations and poster papers that are presented at various
conferences including the American Astronomical Society (AAS) and the
Astronomical Society of the Pacific (ASP) annual meetings.
Monday, June 2 (DOY 154):
Another important milestone occurred today in the implementation of
the
Cassini extended mission. The final integrated S46 sequence segments,
which include orbits 94 through 99, were delivered today. S46
executes
from Nov. 26, 2008 through Jan. 9, 2009. Between now and then, the
Science Operations Plan process (SOP) and Science and Sequence Update
Process must be completed in order to create a sequence that then can
be
approved and flown on the spacecraft. As of today, scientists will
begin
working on their pointing designs for the sequence. The final Cassini
DSN station requests for the November through January time frame will
be
delivered to the DSN schedulers on June 4.
Development of S44 continues with AACS performing the end-to-end
pointing analysis on the port #2 merged product delivered last week.
AACS is also performing the first Reaction Wheel Assembly Bias
Optimization Tool (RBOT) analysis. A series of RBOT meetings will be
held over the next two weeks.
Tuesday, June 3 (DOY 155):
The first input port as part of the SOP Implementation Process for S45
occurred today. It's been quite a busy week for Science Planning.
Based on analysis by Science Planning, and concurrence from the ISS
team, the ISS Saturn vector live update on DOY-161 will not be
performed. However, based on recommendations from SP, CIRS and UVIS,
the
Mimas vector for the CIRS observation on DOY-106 will be updated.
Current plans are to hold a command approval meeting for the files on
Thursday, June 5, and send them up to the spacecraft the same day.
Cassini has used its Integrated Test Laboratory (ITL) since the very
early design stages. Today the ITL Lead gave a presentation open to
all
Laboratory personnel on "What Is Cassini Doing With a System Testbed
at
This Stage of the Mission?" The ITL is a high-fidelity
hardware-in-the-loop testbed. It uses Attitude and Articulation
Control
Subsystem (AACS) and Command and Data Subsystem (CDS) hardware (H/W),
as
well as high-fidelity simulations of other spacecraft subsystems and
signals, and occasionally Cassini instrument H/W. System testbeds like
the Cassini ITL are often considered to be primarily for use in the
Final Design and Fabrication phase and the System Assembly,
Integration
& Test and Launch phase of a mission, but the Cassini ITL has proven
to
be an essential component of an extremely successful Operations and
Sustainment phase. The presentation outlined the role of the Cassini
ITL
since Cassini's launch, through cruise, orbit insertion at Saturn,
probe
release at Titan, and throughout its prime mission tour and on into
extended mission.
A dozen Cassini scientists participated in three teleconferences today
with students whose essays reached the final judging round in the
Cassini Scientist for a Day contest. About 300 students from all over
the U.S. got the chance to quiz scientists on anything related to
Cassini and space exploration - including the three images that
Cassini
will take on June 10. For the contest, students were tasked with
choosing which of three possible images would bring the most science.
Winners will be announced on June 16. For more information on the
contest, visit: http://saturn.jpl.nasa.gov/education/scientist/
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.C. JPL designed, developed and assembled the Cassini orbiter.
.
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