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/
---
To unsubscribe from Cassini Spacecraft Updates, send a message to
leave-cassini-27602O@xxxxxxxxxxxxxxxxx
---
Visit the JPL Cassini home page for more information about the Cassini
Project: <http://saturn.jpl.nasa.gov/>
