Cassini Significant Events 06/27/07 - 07/02/07

July 6, 2007

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired on Monday, July 1, from the Canberra tracking complex. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" web page located at

Wednesday, June 27 (DOY 178):

The sequence leads for S33 held a simulation coordination meeting to make final plans to test the Iapetus flyby and solar conjunction period sequences in the Integrated Test Laboratory. The Iapetus test will begin this Friday and conclude the following Monday. The conjunction test will then begin on Tuesday and conclude on July 9.

A "critical" ring plane crossing occurred on June 27, 2007. A crossing is designated critical if there is a possibility of damage to the main engine as a result of dust impacts. As preventive measures, the high gain antenna was turned to the ring particle ram direction, the backup SSA was powered on, and the main engine cover deployed for the 33rd time since launch. The cover will be opened June 28, right before the T33 flyby.

Non-targeted flybys of Tethys, Methone, and Mimas occurred today. Passing by Tethys at an altitude of 18,945 km, Cassini got a "close-up" look at the large crater Odysseus, which is 450 kilometers in diameter, and Ithaca Chasma, a canyon that is four times as long as Earth's Grand Canyon. Scientists are studying how this canyon formed and whether Tethys was active in the past. Scientists also obtained close-up images of dark patches and took data to understand what the surface is made of. Scientists would like to learn if Tethys is pure water ice, or if it's contaminated with dark material rich in organics, like the material that covers the dark side of Iapetus.

The beautiful VIMS "neon" image of Saturn is Astronomy Picture of the Day today. 

A delivery coordinating meeting was held today for the updated Command Database which will be used in conjunction with the delivery of Mission Sequence Subsystem (MSS) D13 next week, and CDS Flight Software Version 10 in late summer of 2007.

Thursday, June 28 (DOY 179):

AACS performed an update to the B branch thruster parameters with real time commands today. These updates are performed periodically to keep the on-board flight software parameters in line with actual hydrazine tank pressures.

Non-targeted flybys of Enceladus, Prometheus, Epimetheus, and Rhea occurred today. In addition to the Tethys science mentioned above, the Composite Infrared Spectrometer obtained an observation of Mimas crossing the solar eclipse exit, the Imaging Science Subsystem performed global color mapping of Mimas and Enceladus, and RADAR performed scatterometry and radiometry measurements of Mimas and Rhea. 

Friday, June 29 (DOY 180):

The Aftermarket Process for S36, orbits 54 - 57, began today. This five-week process will address proposed changes that require re-integration of the segments contained in the S36 sequence.

Today Cassini flew past Titan for the T33 flyby. Closest approach occurred at 16:59:46 UTC, at an altitude of 1,932 kilometers above the surface and at a speed of 6.2 kilometers per second. The latitude at closest approach was 8.1° N.

Science highlights for the encounter:

Cassini Plasma Spectrometer

T33 is an upstream encounter. Though some CAPS scientists find wake encounters more desirable, the upstream encounter allows a very good comparison to wake encounters such as T9. There was good CAPS pointing for measuring magnetospheric interactions, with co-rotation in view from closest approach-2 hours to closest approach+1 hour. There were no turns during this interval, allowing for very stable CAPS pointing during this period. The team anticipates a good data set for ionosphere and upstream interactions.

Ultraviolet Imaging Spectrograph (UVIS)

The team obtained spectral images of Titan in the EUV and FUV during day side and night side scans to map the aurora and day glow, to map hydrocarbon absorption, and to measure scattering and absorption by aerosols in the stratosphere.

Composite Infrared Spectrometer (CIRS)

CIRS performed high spectral resolution measurements of the atmosphere.

Visual and Infrared Mapping Spectrometer (VIMS)

VIMS obtained a global composition map at nearly full illumination and monitored for cloud motion and formation. It also searched for spectral signatures of dune fields, liquid hydrocarbons, and water and methane frost

Imaging Science Subsystem (ISS)

ISS performed high-resolution (120-240 m/pixel) imaging of the equatorial bright-dark boundary around 1° N, 215-210° W (low phase angle coverage - 20-15°), and regional-scale (240-500 m/pixel) mapping of the equatorial bright-dark boundary around 1° N, 210° W (very low phase angle ~13°).

On DOY 180-181, Cassini Radio Science (RSS) completed the Titan 33 gravity observation. This flyby was one of three devoted to Titan gravity science in the prime mission in order to determine the gravity field of Titan and investigate Titan's internal structure and mass distribution. The observation consisted of three segments: an inbound segment, a segment through closest approach, and an outbound segment. The first two gravity flybys earlier in the mission, T11 and T22, were both when Titan was near apoapsis in its orbit around Saturn and provided consistent values of J2 and C22. T33 occurred with Titan near its periapsis and provided the first opportunity to determine a preliminary value of Titan's Love number. The final determination of the Love number is expected to tell whether or not Titan has an internal ocean.

So what's a Love number you ask? The mass repartitioning of a body induced by tides is usually described by a set of dimensionless numbers called "Love numbers," which express the flexibility of the planet. The value of the k-Love number will be much larger if the core is liquid than if it is solid. Observational constraints on this k-Love number would allow the physical state of the core to be determined, and in the case of Titan, determine if there is an internal ocean.

Monday, July 2 (DOY 183):

July 1 marked the third anniversary of Cassini Saturn Orbit Insertion in 2004.

A delivery coordination meeting was held today for Version D13 of the Mission Sequence Subsystem (MSS). This delivery is based on the most recently delivered version of the command database.  Sequences S35 and later will point to use D13 in the Science Operations Plan Update (SOPU) and Science and Sequence Update processes (SSUP). Earlier sequences that are in execution or finishing SOPU/SSUP will stay pointed to version D12.1.