NASA Cassini Significant Events for 02/23/06 – 03/01/06
The most recent spacecraft telemetry was acquired Wednesday, March 1, from the Goldstone tracking stations. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” web page located at http://saturn.jpl.nasa.gov/operations/present-position.cfm .
Thursday, February 23 (DOY 054):
A very nice image of the big storm on Saturn is Astronomy Picture of the Day today.
Cassini Outreach and Saturn Observation Campaign members participated in Community Science Night at La Fetra Elementary School in Glendora, California. Over 200 students, their families, and teachers attended. In addition to a school science fair, attendees all received Saturn and the moons of Saturn lithographs, and had access to excellent views of Saturn and other night sky objects through three telescopes.
Friday, February 24 (DOY 055):
Uplink Operations and the Spacecraft Operations Office sent commands to the spacecraft to mask, and then unmask the z-sigma ratio fault protection monitor prior to the Titan 11 flyby. This strategy was first employed for the Titan 10 flyby on January 15, to prevent Titan appearing as an unexpectedly bright body as it passed across the field of view of the Stellar Reference Unit.
A non-targeted flyby of the satellite Helene occurred today.
Saturday, February 25 (DOY 056):
At periapse, Cassini came within 337,000 km of Saturn. On the inbound leg, the Composite Infrared Spectrometer (CIRS) performed limb sounding of the planet in the mid-infrared to obtain stratospheric thermal structure with especially good vertical resolution. The Radio and Plasma Wave Science (RPWS) instrument looked for lightning whistlers and the fine temporal structure of any Saturn electrostatic discharges that were detected. After periapse, the Visible and Infrared Mapping Spectrometer (VIMS) made a thermal map of the night side of Saturn and then watched for lightning. The Ultraviolet Imaging Spectrometer (UVIS) observed with both extreme ultraviolet (EUV) and far ultraviolet (FUV) during this observation.
Beginning Thursday, and running through today, Cassini Outreach participated in a national conference in Louisville, Kentucky, put on by the National After School Association. The outreach team hosted a workshop on ‘Reading, Writing, and Rings’ (RWR) to 30 attendees, and distributed RWR information and bookmarks at the NASA/JPL booth throughout the event.
Monday, February 27 (DOY 058):
The Titan 11 (T11) encounter was an outbound flyby of Titan with an altitude at closest approach of 1,813 km. The small solar phase angle approach was excellent for the Optical Remote Sensing (ORS) instruments. Activities at Titan began with a VIMS mapping of the Saturn-facing side of Titan searching for mid-latitude transient clouds and monitoring the surface for haze and photometric changes. Riding along, CIRS obtained information on trace constituents in Titan’s stratosphere, UVIS measured in both EUV and FUV, and the Imaging Science Subsystem (ISS) provided context imaging.
ISS followed with a global-scale mosaic of the hemisphere covering the equatorial region from Fensal/Quivira/Aztlan to Aaru, and Tsegihi in the south. Another mosaic ranged from the regional scale to high resolution and included the southern part of Aztlan, the eastern part of Shiwanni Virgae, and Elba Facula. Since these observations covered regions where a number of Radar swaths terminate, they will be useful in the development of the geodetic control network that is used to correlate co-ordinates on the flat image with their actual location on the spherical planetary body.
The focus then shifted to the Radio Science Subsystem (RSS). This was the first of four coordinated gravity field passes – the others occurring in T22, T33, and T38 – to determine the low degree coefficients of Titan’s gravity field. This knowledge may help to answer the question of whether Titan possesses an internal ocean. The four passes require disparate geometries: two of these flybys must occur when Titan is near periapse along its orbit around Saturn and two flybys – of which T11 was one – must occur when Titan is close to its apoapse. For each of these two pairs, one flyby must be on a nearly equatorial orbit with respect to Titan as was T11, and the other on an orbit with an inclination as large as possible. Radio Science also had two Gravity Science Enhancement (GSE) passes occurring after the flyby. The GSE passes are crucial to de-correlate Titan’s mass from the distance at closest approach.
After the Radio Science experiment, UVIS made a slow scan across Titan’s visible hemisphere to form spectral images. These observations in the EUV-FUV wavelength will provide insight into atmospheric composition and structure. Following this, a CIRS far-infrared nadir composition map of CH4, HCN, and CO in Titan’s stratosphere was performed. Trace constituents in the stratosphere may also have been detected.
For the Magnetospheric and Plasma Science instruments, T11 included an equatorial wake passage differentiated from previous wake encounters by being near Saturnian midnight, where a special dynamic plasma environment is expected. Cassini passed directly through the wake at an intermediate altitude in comparison to T9, which was a distant wake passage.
Tuesday, February 28 (DOY 059):
The Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference this week was a presentation by a Huygens Surface Science Package co-Investigator and dealt with the ongoing analysis and science results from the probe data.
Radar carried out a radiometric calibration using the objects M17, Cass A, Taurus A and Orion as microwave sources for collection of radiometry data.
Wednesday, March 1 (DOY 060):
Orbit trim maneuver (OTM) 53 was performed today. This is the cleanup maneuver from the T11 encounter. The Reaction Control Subsystem burn began at 11:00 PM Pacific Time. A “quick look” after a Reaction Wheel Assembly (RWA) bias following the maneuver showed the burn duration was 291.5 seconds, giving a delta-V of approximately 269.64 mm/s, including everything up through the RWA bias. Upon returning to Earth-point after the maneuver, red alarms were received indicating that the helium latch valve driver “A” solid-state power switch had tripped. It was off at the time so there was no effect. All other subsystems reported nominal performance after the event.
A delivery coordination meeting was held today for version 3.0 of the Reaction Wheel Assembly Bias Optimization Tool (RBOT). RBOT is designed to compute the bias, accomplish momentum management, and optimize consumption of resources for the reaction wheels.
Last week it was determined that Orbit Trim Maneuver 52 would be cancelled. Once that determination was made, it was possible to also cancel the Cosmic Dust Analyzer (CDA) decontamination mini-sequence scheduled for today. The CDA instrument team is concerned about contamination from the main engine. If we use the main engine, then a decontamination is performed, otherwise it’s not.
Wrap up:
Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images.
