From: Jet Propulsion Laboratory
Posted: Thursday, April 24, 2014
Cassini is orbiting Saturn with a 35.8-day period in a plane inclined 40.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 8 using one of the 34-meter diameter Deep Space Network (DSN) stations at Madrid, Spain. 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":
The week's highlight was the closest encounter of the Titan kind remaining in the mission plan. Named T-100, it was Cassini's 101st targeted flyby of the 5,150-kilometer diameter moon. Due to the exchange of orbital momentum between Titan and the spacecraft, Cassini came away with a precisely planned increase in orbital period and decrease in inclination. But it also marked the start of a "pi transfer," the final one in the planned mission. The transfer is called "pi" because it results in a shift of pi radians (180 degrees) in the location of future Titan encounters. Previous encounters have been occurring on the sunward side of Saturn; from now on they will occur on its anti-sunward side.
Wednesday, April 2 (DOY 092)
The Imaging Science Subsystem (ISS) took charge of pointing the spacecraft to make a 1.5-hour Titan cloud monitor observation, with the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) also taking data ("riding along"). The Cassini navigation team then used ISS for 1.5 hours to take images of Saturn's satellite Dione against a field containing recognizable background stars for the purpose of optical navigation. ISS then spent nearly nine hours taking images of Saturn to compile the third and final part of a movie of the planet's northern polar vortex. VIMS rode along.
Thursday, April 3 (DOY 093)
VIMS controlled pointing for 13.5 hours, with ISS and CIRS riding, making a map of Saturn's northern hemisphere. Evidence of an ocean below the surface of Saturn's small moon Enceladus was the subject of a news release today:
Friday, April 4 (DOY 094)
During a DSN tracking period, the flight team uplinked commands to execute Orbit Trim Maneuver (OTM)-376, which turned the spacecraft and fired its small thrusters for 51 seconds, producing the desired change in velocity of 54 millimeters per second to fine-tune the approach to Titan. After the OTM, the Ultraviolet Imaging Spectrograph (UVIS) spent 13.5 hours observing Saturn in the extreme- and far-ultraviolet parts of the spectrum.
Saturday, April 5 (DOY 095)
ISS pointed to Saturn's brightly lit northern hemisphere and tracked atmospheric features for five hours to determine wind velocities, with UVIS and VIMS riding along. CIRS then measured oxygen compounds -- water and carbon dioxide -- in Saturn's stratosphere as a function of latitude for six hours, with UVIS riding along.
Sunday, April 6 (DOY 096)
ISS made another five-hour Saturn wind measurement. Next, Saturn's largest satellite took center stage, and observations of it continued for the rest of the day while the target loomed larger. By midnight, Titan was closer to Cassini than the distance from Earth to our Moon (which is smaller than Titan).
NASA's Astronomy Picture of the Day featured Enceladus's southern crevasses, known as the "tiger stripes" today: http://apod.nasa.gov/apod/ap140406.html
Monday, April 7 (DOY 097)
Today's T-100 encounter occurred on the sunward side of Saturn; as planned, the spacecraft reacted with its thrusters to maintain a prescribed attitude profile as the upper reaches of atmosphere introduced a predicted amount torque on the spacecraft's body. By midday Cassini's distance to Titan's surface had shrunk to only 963 kilometers, and the spacecraft had turned to place the Ion and Neutral Mass Spectrometer in the best position to directly sense the oncoming matter. Further details of today's encounter may be found on the T-100 web page:
To celebrate the Cassini mission's final pi transfer, which started today, flight team members took the opportunity to do a "pie transfer," bringing various sorts of pies to the main conference room to enjoy and share. Cassini's pi transfer will end with the T-101 encounter on May 17.
The hazy world Titan, with lakes visible near its north pole, is the subject of an image featured today:
Tuesday, April 8 (DOY 098)
CIRS led observations of the fast-receding Titan to gather data on the thermal structure of its stratosphere, while ISS rode along to take images and VIMS rode along to take cubes. Finally, Cassini turned to point its high-gain antenna dish squarely towards Earth and communicated with DSN stations, first in California and then in Spain, for a total of 11.25 hours. In addition to precise radiometric tracking for navigation purposes, the ones and zeroes of telemetry from Cassini returned 100% of the science observations stored onboard during the T-100 flyby.
Visit the JPL Cassini home page for more information about the Cassini Project:
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