From: Jet Propulsion Laboratory
Posted: Tuesday, June 3, 2008
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/
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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