From: Jet Propulsion Laboratory
Posted: Tuesday, May 27, 2014
Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 44.3 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on May 21 using one of the 34-meter diameter Deep Space Network stations at Goldstone, California. Except for the 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 "Eyes on the Solar System"
Cassini continued its plunge toward Saturn and then whipped around through periapsis on Thursday. Outbound from the planet, the spacecraft flew close by Titan on Saturday and conducted a wide range of compelling science experiments as part of the T-101 encounter. Two Radio Science experiments yielded their data in real time, and data from the other observations were recorded on the spacecraft and then played back in telemetry on the following day. As always, this encounter took advantage of Titan's momentum and gravitation to change the shape of Cassini's orbit around Saturn. The spacecraft's orbital period decreased from 35.8 to 31.9 days, and the inclination increased from 40.7 to 44.3 degrees above Saturn's equatorial plane.
Wednesday, May 14 (DOY 134)
The flight team prepared commands based on the latest radiometric tracking data from the Deep Space Network (DSN) and uplinked them to the spacecraft to perform Orbit Trim Maneuver (OTM) 379. The commands turned the spacecraft and fired its small rocket thrusters for 17 seconds, producing the desired change in velocity of 22 millimeters per second. This fine-tuned the flight path for an accurate Titan T-101 flyby distance on Saturday of 2,993.8 kilometers above the shrouded moon's surface.
The Ultraviolet Imaging Spectrograph (UVIS) spent nearly 15 hours conducting a Saturn south polar auroral observation, with the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) riding along.
Telemetry showed that the Magnetometer instrument (MAG) had quit communicating over the spacecraft's internal data bus. Commands were prepared to reset it and its bus-interface unit. Cassini's Program Manager and Project Scientist met in Columbia, Maryland with other Cassini scientists, independent reviewers, and NASA officials to review plans for the final three years of the Cassini Solstice Mission.
Thursday, May 15 (DOY 135)
UVIS conducted two observations of Saturn's south polar auroral region totaling 20 hours. CIRS, VIMS, and the Imaging Science Subsystem (ISS) took data in ride-along mode during the first one, and CIRS and VIMS participated in the second. During these observations, the spacecraft passed through periapsis of its Saturn orbit #204 at a height of 686,254 km above Saturn's cloud-tops, going 32,902 kilometers per hour relative to the planet.
Using one of the 34-meter diameter DSN stations in California, the flight team uplinked commands which Cassini's science instruments will expand to support the next 10-week command sequence, S84. After a round-trip light time of two hours, 28 minutes, telemetry from the spacecraft confirmed that each of the 7,356 individual commands had been received and properly stored.
Friday, May 16 (DOY 136)
As the distance to Titan decreased to around the distance from Earth to our Moon, CIRS began monitoring temperatures on Titan's surface and within its atmosphere, with ISS and VIMS riding along. When this three hour, 45 minute-observation finished, ISS spent 50 minutes acquiring a mosaic of the northern latitudes on Titan's leading hemisphere; CIRS and VIMS participated.
Next, UVIS took advantage of a "stellar" opportunity to observe the bright blue star Eta Ursae Majoris (also known as Alkaid) as Titan slowly passed in front of it. The other telescopic instruments CIRS, ISS, and VIMS acquired data as well, as ride-alongs. This ingress-occultation experiment lasted three hours. Together with the subsequent egress observation, it will provide data to discern high-resolution vertical profiles of nitrogen, hydrocarbons, haze, and temperatures in Titan's complex atmosphere. A graphic simulation depicts the stellar ingress here: http://go.usa.gov/88pF
The flight team sent realtime commands to reset the MAG bus interface unit. Later, telemetry confirmed that the instrument had returned to normal operation.
Saturday, May 17 (DOY 137)
UVIS continued to lead the other telescopic instruments in a five hour, 15 minute-observation of Titan in the extreme-ultraviolet part of the spectrum while the bright blue star Eta Ursae Majoris lingered in occultation. As the star reappeared in egress from behind the giant moon, UVIS and the other instruments observed it for another four and one-half hours. By the time these observations were complete, the distance to Titan had shrunk to less than 65,000 kilometers and the T-101 encounter was fully under way. Further details, including an animation of the Radio Science Titan Occultation experiment, may be found here:
During the Radio Science bistatic observation, the spacecraft beamed its Ka-band (32 GHz), X-band (8 GHz), and S-band (2GHz) radio signals toward Titan at angles that were calculated to scatter and reflect off the surface towards Earth. Indeed, the DSN stations participating in Australia received specular reflections of all three frequencies in real time; these will provide valuable insights into the nature of Titan's surface. Following this, the spacecraft turned to point its optical instruments toward Titan again.
Sunday, May 18 (DOY 138)
Cassini's telescopes remained trained on Titan as it receded into the distance. CIRS monitored Titan's surface and atmospheric temperatures, and measured trace gases as a function of altitude above the surface in observations lasting a total of 13 hours; ISS, CIRS, and VIMS participated at different times.
Monday, May 19 (DOY 139)
ISS conducted three observations in its ongoing Titan monitoring campaign for a total of seven hours with CIRS and VIMS riding along. Next, UVIS turned the spacecraft to study Saturn's aurora for 6.3 hours to build long movies; CIRS and VIMS participated as riders.
An image of Saturn's moon Tethys from late last year was featured today: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5027. Cassini will have several closer flybys of Tethys in 2015.
Tuesday, May 20 (DOY 140)
Early in the morning, the flight team sent Cassini a file of 10,113 commands comprising the S84 background sequence, which will go active next Saturday to begin controlling the spacecraft's activities over the next 10 weeks. Telemetry showed that all were properly received.
ISS, VIMS and CIRS made another Titan monitoring campaign observation; by now, the distance had grown to 1.3 million kilometers. UVIS looked back at Saturn to observe the northern aurora for 13 hours, 30 minutes with CIRS and VIMS also taking data.
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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