From: Jet Propulsion Laboratory
Posted: Sunday, October 20, 2013
Cassini is orbiting Saturn with a 47.9-day period in a plane inclined 49.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on October 16 using the 70-meter diameter Deep Space Network station at Goldstone, California. 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 of the Cassini spacecraft may be found on the "Present Position" page at:
This week Cassini was navigated past Titan at a low enough altitude for its direct-sensing instruments to encounter the upper atmosphere. This flyby also provided the gravity assist needed to increase the spacecraft's Saturn-orbit period from 31.9 to 47.9 days, and to decrease the orbit's inclination from 51.9 to 49.7 degrees.
Wednesday, Oct. 9 (DOY 282)
The Deep Space Network (DSN) carried out a ten-hour session for two-way digital communications and radiometric tracking with Cassini today using the 70-meter diameter station in Australia. This was one of six DSN tracks this week.
Thursday, Oct. 10 (DOY 283)
The Imaging Science Subsystem (ISS) drove spacecraft pointing to reacquire and track the orbits of known "propeller" features (http://go.usa.gov/YyGR) in Saturn's rings, while the other optical remote-sensing (ORS) instruments "rode along" to take data as well. The Visible and Infrared Mapping Spectrometer (VIMS) made a two-minute Saturn storm-watch observation, and then, in an effort to obtain more ring latitude and phase angle coverage, observed the sunlit side of the rings for seven hours, with ISS, the Composite Infrared Spectrometer (CIRS), and the Ultraviolet Imaging Spectrograph (UVIS) riding along. ISS performed another observation in the satellite orbit campaign and then spent two hours creating a full-color image of the Saturn system using its wide-angle camera, while VIMS also observed. The day concluded with Orbit Trim Maneuver 361, which turned the spacecraft and fired the small rocket thrusters for twelve seconds, providing a change in velocity of eighteen millimeters per second. This refined the spacecraft's trajectory on approach to the Titan T-95 flyby.
Friday, Oct. 11 (DOY 284)
ISS led another satellite orbit observation, VIMS did another quick storm-watch and then CIRS stared at the sunlit side of the rings for nine hours to obtain spectra in the thermal infrared and study ring particle composition. ISS finished the day with another propeller observation with UVIS also participating.
The flight team uplinked the instrument-expanded block commands that will be used by the S81 sequence starting on Oct. 23. All 9434 individual commands were confirmed onboard via telemetry after a round-trip light time of three hours.
Saturday, Oct. 12 (DOY 285)
ISS monitored Titan for eight hours, tracking clouds and their evolution at high northern latitudes, which is important to do as summer approaches in the northern hemisphere. CIRS then observed the rings, part of a campaign to obtain thermal phase curves of the lit rings at phase angles up to 90 degrees; today's observation filled in one of the less common geometries.
Sunday, Oct. 13 (DOY 286)
CIRS made mid-infrared nadir and limb maps of Titan, now looming larger, in order to retrieve vertical and meridional distributions of temperature and minor gas abundances. ISS rode along to track clouds at high northern latitudes. VIMS also observed, acquiring low spatial-resolution images of Titan's northern polar area where long integration times were used to map the lake areas.
Cassini passed through periapsis in its Saturn orbit, going 23,864 kilometers per hour relative to the planet, at a range of 1.19 million kilometers, nearly the distance to Titan's orbit. After Saturn periapsis, ISS acquired a mosaic of high northern latitudes on Titan's leading hemisphere, an area of Titan's surface not yet well observed. Finally, the Radar instrument began microwave radiometry observations of Titan.
Monday, Oct. 14 (DOY 287)
The Titan encounter T-95 executed today. The T-95 flyby page may be found at:
Radar continued its radiometry observations while inbound, and then proceeded to operate in its active remote-sensing modes during the flyby to obtain synthetic-aperture imaging and altimetry data. For the hour around closest approach, attitude control was commanded to switch from reaction wheels to thrusters for increased control authority over atmosphere-generated torques. At closest approach, which was 961 kilometers above Titan's surface, the Ion and Neutral Mass Spectrometer was the prime instrument, making in-situ measurements of Titan's upper atmosphere. Outbound from closest approach, Radar operated in its active scatterometry and altimetry modes and its passive radiometry mode.
From the perspective of the Magnetometer instrument, T-95 is almost identical to T-94: a high inclination, low altitude flyby in the noon sector of Saturn's magnetosphere. With closest approach on the dayside, Cassini was able to study the diffusion of the external magnetic field at low altitudes and low solar zenith angles. At the end of the day, CIRS again made nadir and limb maps of Titan in the mid-infrared, with ISS and VIMS riding along.
Tuesday, Oct. 15 (DOY 288)
ISS monitored Titan for an extra day after the encounter, looking at high southern latitudes now where winter is approaching. VIMS rode along to look for clouds and to monitor the evolution of the southern polar vortex.
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