NASA Cassini Significant Events for 04/01/09 – 04/07/09
The most recent spacecraft telemetry was acquired on Apr. 7 from the Deep Space Network tracking complex at Goldstone, California. 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, April 1 (DOY 091)
With the successful execution of Orbit Trim Maneuver (OTM) #186 on Mar. 29, targeting for the Titan 52 flyby is assured and OTM-186a is not required. OTM-186a has been cancelled.
An encounter strategy meeting was held today to cover the period between April 4 and April 20, Titan flybys T52 and T53, and maneuvers 188-190.
Upon a recommendation from Navigation, the Spacecraft Operations Office is planning to update two Main Engine (ME) maneuver parameters in AACS Flight Software in order to keep performance better aligned with actual physics. The first parameter is the Accelerometer (ACC) Scale Factor. This has been patched four times since launch with the most recent correction occurring in July 2006. The second parameter is a change to the ME tail-off impulse. This will correct a small – about 3 mm/sec – but persistent underburn condition. This parameter has not been updated before. These patches will go through testing in the Integrated Test Laboratory the week of Apr. 6. The first OTM targeted to use the new parameters is #192 on Apr. 28, a fairly large ME maneuver estimated at 2.2 m/sec.
Thursday, April 2 (DOY 092)
A kick-off meeting was held today for the final sequence development process for S51.
The Cassini Plasma Spectrometer had prime pointing control for a magnetosphere survey. The Magnetometer then performed a six hour calibration roll, followed by the acquisition of an optical navigation image and a downlink pass to transmit the data back to Earth.
Friday, April 3 (DOY 093):
Members of the Spacecraft Telecommunications Team updated Cassini’s Radio Frequency Subsystem Best Lock Frequency (BLF) today. The free running voltage controlled oscillator frequency had drifted about 3.5 kHz off the commanded DSN BLF over the past two years. The commanded DSN BLF now is within 0.5kHz of the free running frequency.
Cassini passed by Titan (T52) at an altitude of 4150 km and a speed of 5.8 km/sec. The latitude at closest approach was 2.8 degrees S and occurred at approximately 7:58 PM PDT. Unlike other flybys, this encounter was set up with only one maneuver: a combined post-flyby cleanup/Titan approach maneuver, executed on March 29. Due to the short interval between T51 and T52, the Navigation team had scheduled four different opportunities for this important maneuver to insure its execution.
The T52 egress atmospheric occultation was one of the highest priority RSS occultations of the extended mission. It was the first Cassini occultation to probe Titan near-equatorial latitudes, while the ingress occultation probed mid-northern latitudes. The occultations will shed more light on latitudinal variability of the electron density profile of the ionosphere, temperature and pressure profile, extinction profile, and small scale-structure of the neutral atmosphere. The RSS occultations are the only Cassini observations able to map the thermal structure of the atmosphere down to the surface with high spatial resolution. They require implementation of critical pointing to steer the spacecraft during the observations to keep track of the radio signal as it bends through the atmosphere. To maximize chances of success, the pointing design was updated and radiated to Cassini the week before execution of the experiment.
The T52 inbound bi-static scattering observation probed for the first time high-northern latitude regions of Titan’s surface. The outbound bi- static measurements probed the mid-southern latitude region. The incidence angle for both sides was close to the Brewster angle range of likely surface compositions. Same- and cross-polarized components of the quasi- specular surface echo will provide information about the dielectric constant and physical state of the surface region probed.
Both T52 RSS experiments were successful. Real-time bi-static echoes were detected from two surface regions not probed before by RSS, and high quality occultation data were acquired.
Solar and stellar occultations by Titan are the most valuable Titan observations for the Ultraviolet Imaging Spectrograph (UVIS) because they provide detailed vertical profiles of nitrogen in the Extreme Ultraviolet channel during solar occultation and hydrocarbons, HCN, and aerosols in the Far Ultraviolet channel during stellar occultations. In T52, UVIS took advantage of a very slow occultation, among the slowest in Cassini’s extended mission, to probe Titan’s polar vortex region. These profiles probe altitudes between 300 km and 2400 km, which fill the gap between CIRS and the Ion and Neutral Mass Spectrometer (INMS) measurements. Much of the chemistry and aerosol formation occurs in this vertical region. Observations taken over the course of the mission will collectively provide coverage at many latitudes and local times and these will be used to study meridional and local time gradients in the upper atmosphere. Knowledge of these gradients is important for understanding the meridional circulation and other dynamical and chemical processes. For more information on the T52 flyby go to: http://saturn.jpl.nasa.gov/files/20090403_titan_mission_description.pdf and http://saturn.jpl.nasa.gov/mission/flybys/titan20090403/
Monday, April 6 (DOY 096):
The Target Working Team (TWT)/ Orbiter Science Team (OST) integrated products for S54, covering orbits 119 through 121, were delivered today. The integrated products are in their final form and no re-integration is planned. The next step in sequence development, Science Operations Plan (SOP) implementation, will kick off on Apr. 20. Between now and then, the instrument teams will be working on pointing designs for the sequence. TWT/OST teams deliver integrated sequence products for the extended mission about every five weeks.
While touring the Saturn system in 2008, Cassini enabled great scientific studies and observations. Listed below are the top 10 science highlights of the year as selected by the Cassini science teams.
- Positive identification of liquid ethane in a lake on Titan
- Polar storms on Saturn
- Strong inference of a liquid water layer in Titan’s interior
- The likelihood of dusty rings around Rhea
- The possibility of plate-tectonic-like spreading in the Enceladus south polar region
- Water vapor jets inside the plume of gas leaving Enceladus
- Moonlet population in and around the F ring
- New insights into Saturn’s aurora
- Three belts of sub-moonlets in the A ring (propellers)
- Six month-old lightning storm shatters record for longevity
For all the details link to: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20090330/
Tuesday, April 7 (DOY 097):
Due to the excellent accuracy of Orbit Trim Maneuver (OTM) #186 on Sunday, Mar. 29, OTM-188, the T52 cleanup maneuver scheduled for April 7, 2009, was cancelled. Since OTM-189 is a fairly large deterministic maneuver of about 7 m/s, it is possible to combine 188 and 189 with a delta V penalty of only 22 mm/sec.
The seventh edition of the Cassini Scientist for a Day contest has begun. This national essay contest is for U.S. students in grades 5-12. This year students may select from one of three available targets: Dione, Prometheus/the Rings of Saturn, or Janus/Epimetheus, and write a 500- word essay on why they think that studying their selected target will yield the best science results. Essay contest entries must be received by April 30, 2009, at 12:00 noon Pacific Daylight Time. For more information link to: http://saturn.jpl.nasa.gov/education/scientistforaday7thedition/intro/
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
