Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 46.5 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on June 25 using one of the 34-meter diameter Deep Space Network (DSN) 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"
This week Cassini's top scientists and managers are attending the 63rd Project Science Group meeting at the European Space Research and Technology Center in Noordwijk, The Netherlands. Over and above "routine" science working groups and presentations, steps are being taken in planning the F-Ring and Proximal Orbits phase, which will begin in November 2016, and will bring the mission to a finale in late 2017.
Wednesday, June 18 (DOY 169)
Today the Titan T-102 encounter executed flawlessly. Coming within 3,658.6 kilometers of the surface of the 5,150-km diameter clouded moon, Cassini turned so that its dish-shaped high-gain antenna (HGA) would project three downlink signals towards the enigmatic surface in such a way that the DSN might be able to pick up the scattered returns; the Radio Science Subsystem (RSS) team expects to tease out scientific results from the signals through post-processing of this "bistatic" experiment.
Going behind Titan, the spacecraft then turned to aim its signals toward Titan's limb where atmospheric refraction would bend them towards Earth. For this part of the intricate dance, the spacecraft picked up a highly stable reference signal from the DSN just as Cassini's turn to Earth completed. Cassini then used that uplink signal to generate its precise-frequency, pure-tone downlink signals and send them back through Titan's atmosphere. Results from this important "occultation" experiment will allow RSS to realize direct measurements of structures, winds, and temperatures in Titan's atmosphere and ionosphere.
The next part had the spacecraft's HGA facing lakes on Titan's surface at the angle that would produce specular (mirror-like) reflections in the direction of Earth. Indeed, the strong specular reflections seen in real time from this second bistatic part will yield more information about those lakes of liquid hydrocarbons and the surrounding terrain.
Although they were taking a back seat during closest approach, Cassini's telescopes and their optical remote-sensing instruments, as well as the direct-sensing magnetospheric and plasma science instruments, made extensive observations during the overall encounter. Their data were later played back in telemetry -- the ones and zeroes carrying images, spectra, and other results.
The Imaging Science Subsystem (ISS) monitored Titan as it receded, while the Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) took data in ride-along mode. By day's end Saturn's largest satellite was more than 240,000 kilometers from the fast-moving spacecraft. Next, CIRS observed the sunlit side of the rings for ten hours in the thermal infrared part of the spectrum, to study ring particle composition. VIMS and ISS rode along.
Friday, June 20 (DOY 171)
ISS controlled spacecraft pointing for 19.5 hours to lead an observation of Saturn's shadow on the very distant, inclined Phoebe ring, as CIRS and VIMS rode along. When this observation wrapped up, VIMS made a two-minute storm-watch observation of Saturn.
Saturday, June 21 (DOY 172)
The Navigation Team used ISS to take images of Saturn's small, active moon Enceladus against the background stars for optical navigation purposes. The Ultraviolet Imaging Spectrograph (UVIS) then observed the fourth-magnitude blue star Gamma Columbae for 10.3 hours as it came out from behind Saturn's atmosphere and made a pass behind each of the rings. CIRS also rode along to take data. Finally, VIMS and ISS made another quick storm-watch observation of Saturn.
Orbit Trim Maneuver (OTM) 383 was commanded in real time. This post-T-102 trajectory clean-up maneuver turned the spacecraft and fired the small thrusters for 41 seconds in order to provide the desired 45 millimeters-per-second change in velocity.
Sunday, June 22 (DOY 173)
Following the OTM, ISS turned the spacecraft to watch the F ring for 15 hours, which covered one full revolution of its particles around Saturn. The observation will be compiled into a low resolution movie of the narrow, complicated ring.
NASA's Astronomy Picture of the Day featured a series of three ultraviolet images showing Saturn's ever-changing south-polar aurora. As evident from the position of the planet's shadow on the rings, the images were taken from Earth's vicinity, where the Hubble Space Telescope provided the view.
CIRS watched the sunlit rings again in the thermal infrared, studying ring particle composition, this time with only VIMS taking data as a ride-along. Following this, VIMS controlled pointing for 7.7 hours to observe the fifth-magnitude red star L2 Puppis as it was entering occultation by the rings.
A news feature online today describes how the nitrogen that makes up most of Titan's atmosphere may have come in from Oort-cloud comets:
CIRS made the third observation this week of the sunlit rings with VIMS riding along; this one lasted four hours. VIMS then turned to watch L2 Puppis as it exited its ring occultation. ISS then took control for a one-hour observation in the satellite orbit campaign, looking at small objects near the planet. VIMS finished up the week with another two-minute storm watch.
Since next Monday will be the tenth anniversary of Cassini's entry into Saturn orbit, a news feature was published to mark the occasion: