News | September 18, 2013
Cassini Significant Events 09/11/2013 - 09/17/2013
Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 51.9 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Sept. 17 using one of the 34-meter diameter Deep Space Network stations at Canberra, Australia. Except for some science instrument issues described in previous reports (for more information search the Cassini website for CAPS and USO), the spacecraft continues to be in an excellent state of health with all of its subsystems operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
The main event this week was Thursday's Titan T94 flyby at 1400 kilometers altitude. Cassini's optical remote-sensing instruments and direct-sensing instruments carried out science observations, while the encounter provided a gravity-assist boost to reshape the spacecraft's orbit according to plan. Orbital inclination was brought down by 1.5 degrees and the period was increased by eight days.
Wednesday, Sept. 11 (DOY 254)
As Titan loomed closer, Cassini turned to train its optical remote-sensing instruments on it. The Composite Infrared Spectrometer (CIRS) led the encounter's observations by obtaining information on the stratosphere's thermal structure.
Thursday, Sept. 12 (DOY 255)
As the spacecraft encountered Titan, the optical instruments carried out their planned observations as described on the T94 Flyby page:
Meanwhile, with closest approach occurring on Titan's dayside, Cassini's direct-sensing instruments studied the diffusion of Saturn's magnetic field at low Titan altitudes and low solar zenith angles. The Magnetospheric Imaging Instrument (MIMI) measured energetic ion and electron energy being input to the atmosphere. The Radio and Plasma Wave Science subsystem (RPWS) measured thermal plasmas in the ionosphere and surrounding environment, and searched for lightning.
Twelve hours after closest approach, Cassini turned to point its high-gain antenna toward Earth. An hour and a half later, the 70-meter aperture Deep Space Network (DSN) station at Canberra, Australia locked onto Cassini's signal and began to decipher T94 telemetry data coming from the spacecraft's solid-state recorder. At the same time, the DSN station transmitted a continuous uplink signal for navigation and sent some routine realtime commands from the Cassini flight team. This DSN period ended after seven and a half hours.
Friday, Sept. 13 (DOY 256)
The 70-meter DSN station at Madrid, Spain tracked Cassini for three hours in downlink-only mode today, capturing more of the data recorded onboard during the T94 science observations. Then the spacecraft turned away from Earth to allow the Imaging Science Subsystem (ISS) look back at Titan and monitor its clouds. This was followed by another two-way session with the 70-meter DSN station in Australia. After eight and one quarter hours the entire T94 telemetry data playback was complete with no data lost. The science teams who had designed the T94 observations now had all the results in hand. There were a total of six DSN sessions this week for routine tracking and communications.
The navigation team iterated Cassini's orbit model using Doppler-shift and ranging data from the DSN passes following T94, and determined the correction needed to adhere to the intended Saturn-tour trajectory. The flight team created commands to achieve this correction with Orbit Trim Maneuver (OTM)-359, and transmitted them to the spacecraft during tonight's DSN pass. The commands are timed to execute on Sunday night.
Saturday, Sept. 14 (DOY 257)
CIRS performed a far-infrared map of Saturn’s southern hemisphere to determine the atmospheric and ionospheric thermal structure. ISS then performed an observation in the Satellite Orbit Campaign, looking at small objects orbiting close to the planet.
Sunday, Sept. 15 (DOY 258)
ISS created a fifteen-hour, low-resolution movie of the narrow F-Ring. The day concluded with execution of the T94 trajectory cleanup maneuver OTM-359.
Monday, Sept. 16 (DOY 259)
With Titan at a distance of 1.4 million kilometers, ISS, CIRS and the Visible and Infrared Mapping Spectrometer (VIMS) performed an observation in the Titan monitoring campaign. ISS then looked back at the irregular moon Tarvos, the small dark object described last week, and studied it for 13.5 hours.
An image featured today shows one of the F ring's many peculiarities:
Tuesday, Sept. 17 (DOY 260)
The Ultraviolet Imaging Spectrograph (UVIS) began its yearly campaign to study Saturn’s magnetosphere by starting a 37-hour mosaic scan, imaging oxygen in the vicinity of the Saturn disk.
Observing at longer wavelengths, you can view more deeply into Saturn's atmosphere. A Cassini Science League feature released today discusses the results of using Cassini's Radar instrument in its passive microwave-radiometer mode, which is sensitive to radiation coming from deep within Saturn at 2.2 centimeters wavelength: