Cassini Significant Events 04/14/05 - 04/20/05

April 22, 2005

(Source: JPL)

Activities this week:

The Titan 5 targeted encounter occurs on Saturday April 16.

Remember how I have been saying for the last two weeks that the flight team would be pulling off three Orbit Trim Maneuvers in 10 days? Well, that was until we cancelled one! Read on for more

Thursday, April 14:

Today there was an untargeted flyby of Saturn's satellite Pan.

The Main Engine cover was closed beginning around 11:00 PM Pacific Time for about 20 hours as a dust hazard avoidance precaution. The next time we close the cover is in about two weeks on April 29. The cover will then remain closed until our next maneuver in July.

Uplink Operations (ULO) radiated commands to the spacecraft to trigger the RADAR Instrument Expanded Block program for their Titan 5 Scatterometry and Radiometry observations.

Development for tour sequence S11 continued this week with a sequence change request (SCR) approval meeting. All seven SCRs were approved and are now being implemented by their respective teams.

Friday, April 15:

Untargeted flybys of Epimetheus, Mimas, and Calypso occurred today.

The Navigation team has announced that OTM-23, the T5 cleanup maneuver, is now a candidate for cancellation. It is possible that the maneuver required would be so small as to be negligible. DSN
tracks at Madrid on Sunday and Goldstone on Monday will be used to obtain the necessary information to make a decision.

Since this is the first time a cleanup maneuver has been a candidate for cancellation, a preliminary cancellation meeting will be held on Monday afternoon. The final decision will be made at the maneuver approval meeting on Tuesday morning. ULO was scheduled to uplink a live Inertial Vector Propagator (IVP) update the week after OTM-23, and a live moveable block the week after that. Since these two activities affect instrument pointing, and since OTMs affect pointing as well, Science Planning will be investigating the impact of cancellation on these two events. The results will be incorporated into the decision to cancel at the meeting on Tuesday.

Saturday, April 16:

The Titan 5 (T5) targeted flyby occurred today at the lowest altitude thus far of 1025 kilometers, and is the first low altitude pass in the tour for which the Ion and Neutral Mass Spectrometer (INMS) is the prime instrument.

T5 is important for determining the minor neutral and ion densities, and is a critical first step in sampling the global composition of the thermosphere and ionosphere, and the thermal structure as a function of local time and latitude under varying magnetospheric input conditions.

T5 also provides a second good look at the sub-Saturn hemisphere, including the first high-resolution - less than 250 m/pixel - coverage by the Imaging Science Subsystem (ISS) over the sub-Saturn region. This will be first good look ISS has had at the quasi-circular ~1000 km diameter feature, perhaps associated with an impact structure. ISS will also continue global monitoring and surface mapping coverage, wide-angle camera (WAC) photometry of haze properties, and a WAC movie of clouds in ride-along with Ultraviolet Imaging Spectrograph (UVIS). Eighteen hours before closest approach there is an outreach image opportunity of Saturn rise/set over Dione.

For this flyby UVIS will be obtaining an EUVFUV spectral image that is part of a series to map Titan's atomic emissions, acetylene distribution and haze properties.

The Cassini Plasma Spectrometer (CAPS) team reported that the T5 encounter is the first low altitude flyby with prime or otherwise excellent pointing for +-25 minutes. This will allow CAPS to sound the polar (74 deg) ionosphere to altitudes well below the ionospheric peak, and to study the plasma environment around the Titan/magnetosphere interaction. The high latitude of closest approach means Cassini will be flying through the Alfven currents which couple Titan to the magnetosphere. Finally, CAPS will continue to take high resolution data, with prime pointing, outbound to 120 Titan radii, observing the distant signatures of the Titan interaction, such as pickup ions escaping Titan's atmosphere.

Members of the Saturn Observation Campaign conducted over 60 special events honoring Astronomy Day today. Locally, Cassini Outreach held three Saturn Observing sessions reaching 950 attendees this week alone.

Monday, April 18:

An image of Enceladus and Saturn's rings edge on is today's Astronomy Picture of the Day.

Tuesday, April 19:

It's official. Orbit Trim Maneuver 23 has been cancelled.
reviewed the latest orbit determination and maneuver solution this
morning and confirmed yesterday's tentative decision.

Each time an OTM is cancelled you can expect to see that ULO uplinked Reaction Wheel Assembly (RWA) bias commands. This is because the bias that would have been included with the OTM commands needs to be performed anyway, and is now sent up as a separate activity.

Along with commands to perform an RWA bias ULO uplinked commands for a Magnetospheric Imaging Instrument (MIMI) motor test.

Wednesday, April 20:

Four SCRs were approved as part of S12 sequence development. Teams are now in the process of implementing the changes.

The Radio Science Team hosted a very exciting meeting where they described the purpose of the RSS Saturn Equatorial Occultations and the data they expect to receive after the activities that will execute on May 2-3.

Wrap up:

The most recent spacecraft telemetry was acquired Wednesday from the Goldstone tracking station. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally. Check out the Cassini web site at for the latest press releases and images.

Recently Cassini Outreach has been receiving requests for information on science results as part of the weekly significant events report. The purpose of the Cassini "SigEs" is to give a report of activities that occurred that week. But not to worry. Your questions were passed on to the Program Manager. He provided the following information:

The things that we have learned from these observations are, to some extent, available now in the literature. A literature search would show most of them. Probably the two most readable journals are Science and Nature, which have featured us a few times since SOI. Another avenue for people who really want to get serious about this is to refer them to the Planetary Data System. We have a big data release headed there this coming July, and more to follow on a quarterly basis. Anyone seriously interested in the raw data and how to access it should get in touch with Outreach who will refer them to the appropriate individuals.

The new moons page for the Cassini website is now online