Cassini Significant Events 04/15/2015 – 04/21/2015

Cassini is currently orbiting Saturn with a 28-day period in a plane inclined 0.3 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 21 using one of the 34-meter diameter Deep Space Network stations in Australia. 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.

If Saturn appears to be some strange and different planet, when viewing the latest raw images from Cassini (http://saturn.jpl.nasa.gov/photos/raw), perhaps it's because the vast system of rings all but disappears when viewed edge-on or nearly so. With Cassini now orbiting near the planet's equator, the rings often appears as a single thin line, if they're visible at all. Even the rings' familiar broad shadows across the planet's haze were scarcely seen this week, since Cassini has been mostly on the night side, coasting outbound from Saturn towards an April 25 apoapsis passage.

Wednesday, April 15 (DOY 105)

With Cassini out beyond Saturn's vast, diffuse E ring today -- this is the ring that the tiny moon Enceladus creates and sustains with its geysers -- the Imaging Science Subsystem (ISS) took control of spacecraft pointing for 15.5 hours to observe that ring, edge-on while it was backlit by sunlight. This is a viewing angle that causes fine particles to become visible. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) observed as well, in ride-along mode. Both before and after this observation, ISS made a two-minute storm-watch observation on Saturn, which by now was 1.7 million kilometers away. Often done before and/or after other observations when long spacecraft turns are not required, there were nine quick storm-watch observations in total this week.

Thursday, April 16 (DOY 106)

ISS and VIMS performed a 90-minute observation in the Titan monitoring campaign; the hazy planet-like moon was 1.6 million kilometers from Cassini's telescopes. The observation was repeated on the following day, and again on Saturday and on Sunday; the distance to Titan varied only a small amount during the interval.

Friday, April 17 (DOY 107)

Following a nine-hour tracking and communications session via the Deep Space Network (DSN), the spacecraft remained in an Earth-pointed attitude for 15 hours while the direct-sensing Magnetospheric and Plasma Science (MAPS) instruments collected data about the spacecraft's immediate environment. Late in the day, and now 2.5 million kilometers from Saturn, the Ultraviolet Imaging Spectrograph (UVIS) began an 11-hour observation of the planet's polar aurorae; time enough to watch one complete rotation of the oblate gas giant. CIRS and VIMS observed while riding along.

Saturday, April 18 (DOY 108)

UVIS led CIRS and VIMS in another 11-hour Saturn auroral observation today, and a 12.25-hour one on the following day.

Sunday, April 19 (DOY 109)

Perhaps Saturn's moon Rhea is what a satellite in the outer solar system is "supposed" to look like: no geysers, no lakes, no atmospheres or active volcanoes. Just an ancient, heavily cratered surface is to be seen in an image featured this week:
/resources/16184 .

Monday, April 20 (DOY 110)

In response to commands prepared and uplinked near real time, the spacecraft turned and fired its small, hydrazine-fed rocket thrusters for 44 seconds to perform Orbit Trim Maneuver (OTM) 408. This OTM provided a 47-millimeter-per-second change in Cassini's velocity, to set up the desired timing and flyby altitude for Titan encounter T-111, which will occur on May 7.

Tuesday, April 21 (DOY 111)

UVIS began another observation of Saturn’s aurorae, with CIRS and VIMS riding along. This one lasted 31 hours. The distance from Cassini to Saturn reached three million kilometers today.

The flight team began the task of installing commands on board Cassini today that will operate its science instruments in support of the next 10-week command sequence. Using the newest of the DSN's ground stations, a 34-meter diameter dish in Australia, mission controllers sent a total of 7,252 instrument commands from four files. After a round-trip travel time of 152 minutes at the speed of light, telemetry confirmed that each was properly stored for later use. The S89 background command sequence will be uplinked on April 29 and begin controlling Cassini on May 1.

During the past week, the Deep Space Network communicated with and tracked Cassini on six occasions, using stations in Australia. A total of 7,404 individual commands were uplinked, and about 1,479 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

This illustration shows Cassini's position on April 21: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=4&day=21&year=2015&hour=23&minute=55&fovmul=1&rfov=40&bfov=30&brite=1&showsc=1&showac=1 .

Milestones spanning the whole orbital tour are listed here: http://saturn.jpl.nasa.gov/mission/saturntourdates .

Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
http://saturn.jpl.nasa.gov/mission/presentposition/ .