NASA Cassini Significant Events 09/17/2014 – 09/23/2014
Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 40.3 degrees from the planet’s equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Sept. 23 using the 70 meter diameter Deep Space Network (DSN) station in Spain. The spacecraft continues to be in an excellent state of health with all of its subsystems operating normally except for the instrument issues described at http://saturn.jpl.nasa.gov/news/significantevents/anomalies . Information on the present position of the Cassini spacecraft may be found on “Eyes on the Solar System”:
Wednesday, Sept. 17 (DOY 260)
While gathering speed towards a Friday periapsis, the Ultraviolet Imaging Spectrograph (UVIS) controlled the spacecraft’s orientation for close to twelve hours to scan Saturn’s thermosphere — the heated, thin upper atmosphere. Data from this observation will be useful for refining estimates of the gas density there to aid in planning Cassini’s 2017 proximal orbits.
Thursday, Sept. 18 (DOY 261)
The Composite Infrared Spectrometer (CIRS) took control of pointing for six hours to carry out a thermal survey of the rings. Next, UVIS mapped the rings to collect spectral data for about eight hours while the Imaging Science Subsystem (ISS), the Visible and Infrared Mapping Spectrometer (VIMS) and CIRS acquired data in ride-along mode.
Friday, Sept. 19 (DOY 262)
The flight team fired Cassini’s small rocket thrusters using commands created and uplinked near real time, for Orbit Trim Maneuver (OTM) 391. The commands caused the spacecraft to turn and burn hydrazine for 79 seconds, imparting the desired change in velocity of 85 millimeters per second to fine-tune the approach to Titan.
As soon as the OTM finished executing, VIMS observed a 4.5-hour occultation as the red giant star R Lyrae passed behind Saturn’s rings. This star is brighter in infrared light than the well-known star Vega (Alpha Lyrae) is in visible light. ISS and CIRS rode along. With the occultation complete, CIRS made another thermal survey of the rings; this one lasted four hours. Next, VIMS led ISS and CIRS in a 4.5-hour study of the region where Saturn’s shadow falls on the rings. Finally, ISS spent an hour re-targeting features known as “propellers” (http://go.usa.gov/YyGR) in the rings. Cassini passed through periapsis at 753,000 kilometers above Saturn’s cloud tops, going 30,911 kilometers per hour relative to the planet.
Four moons, which may have a potential for harboring some sort of life, appeared in NASA’s Astronomy Picture of the Day today. Two of them, the 5,152 kilometer diameter Titan, and the 504 kilometer wide Enceladus, are targets that Cassini regularly studies:
http://apod.nasa.gov/apod/ap140919.html
Saturday, Sept. 20 (DOY 263)
CIRS conducted a four-hour thermal survey of the rings, and then ISS pointed to the thin, detached F ring for nearly eight hours to make a movie. CIRS and VIMS observed as riders.
Sunday, Sept. 21 (DOY 264)
All of Cassini’s telescopic “eyes” turned to Titan as it loomed closer than the distance from Earth to our own Moon. CIRS controlled pointing today, studying Titan in the far- and mid-infrared parts of the spectrum, while ISS, UVIS, and CIRS rode along for various observations.
Meanwhile, back on Earth, equinox marked the beginning of spring in the southern hemisphere. Saturn is high in the sky from down under, where the (DSN) Canberra antenna complex tracked Cassini on five occasions during the week. Today’s NASA Astronomy Picture of the Day features Saturn’s own most recent equinox, which Cassini captured in 2009:
http://apod.nasa.gov/apod/ap140921.html
Monday, Sept. 22 (DOY 265)
On approach to Titan, UVIS observed an occultation of the bright blue star EtaUrsa Majoris while Cassini’s orbital motion made it pass behind the atmosphere in Titan’s southern hemisphere. Next, VIMS controlled pointing as Cassini flew inbound to its closest approach to Titan. CIRS then took command on the outbound leg, except for a 1.5 hour UVIS Titan observation halfway through the day. More details on this Titan T-105 encounter may be seen here:
http://saturn.jpl.nasa.gov/mission/flybys/titan20140922
The Cassini Spacecraft itself is one of Saturn’s moons, albeit a mechanical one bristling with instruments. An image featured today captures some of Saturn’s other satellites and rings:
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5095
Tuesday, Sept. 23 (DOY 266)
To allow for a complete playback of the Titan flyby data, Cassini spent an unusually long time today, 13 hours, with its 4-meter diameter high-gain antenna oriented towards the distant Earth, communicating with DSN’s 70-meter diameter stations in Australia and then Spain. After the playback completed, ISS turned back to monitor Titan’s northern latitudes to track clouds and their evolution as Titan’s northern summer approaches. ISS led all the other telescopic instruments for 10 hours of observations as Titan receded, and will continue with more on the following day. This week, the DSN communicated with and tracked Cassini on six occasions, using stations in Australia and Spain. A total of 172 individual commands were uplinked, and nearly 2,300 megabytes of telemetry data were downlinked at rates as high as 142,201 bits per second.
For a glossary of technical terms relating to these events, click the “full story” link on this page:
