Cassini Significant Events — for 07/07/05 – 07/13/05

Cassini Significant Events -- for 07/07/05 - 07/13/05

July 15, 2005

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired Wednesday, July 13, 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 .

Activities this week:

Thursday, July 7 (DOY 188):

The Sequence Team leads for S12 sent commands to the spacecraft today to patch the Ultraviolet Imaging Spectrograph (UVIS) instrument expanded block (IEB) #5, and to check some Cosmic Dust Analyzer (CDA) settings prior to the Enceladus encounter next week.

An encounter strategy meeting was held today for the Enceladus2 through Titan5 period. This includes Orbit Trim Maneuvers (OTM) 26, 27, and 28.
Topics for a strategy meeting include but are not limited to the Navigation schedule, deliveries, and reference trajectory, maneuver performance, staffing, targeted encounter summary, past encounters, predicted orbit determination accuracy, special events during the encounter, spacecraft consumables tracking, main engine assembly cover strategy, DSN coverage, first time events, backup and contingency planning, instrument status, and so on. Even though Cassini is now up to OTM-25, nothing is taken for granted and the preparation for each maneuver is carefully considered prior to approval.

Uplink Operations has released the merged products for OTM-25 with the currently executing S12 background sequence. These are the products that will be used by the flight team to do their checklists. The maneuver
approval meeting is scheduled for 7:00 am Friday of this week with uplink -- once approved -- beginning at 9:00 am Pacific time.

The S12 DOY Live Inertial Vector Propagator (IVP) update kick-off meeting was held this morning. Later in the day Navigation released the orbit determination solution for teams to review for this update. A go/no go meeting will be held tomorrow.

Friday, July 8 (DOY 189):

The S15 official port occurred today as part of the Science Operations Plan Update process. A program briefing will be held on the contents of this sequence on July 20.

At the Live IVP Update Decision Meeting this morning for Rhea and Enceladus, Science Planning and the driving instruments present recommended a "no-go" for the DOY 195 Update. As part of the standard update process, science planning along with each science team use the latest Navigation trajectory information to come up with a recommendation on whether the pointing update is needed or not. In this case, all teams felt the actual spacecraft trajectory did not deviate significantly from the planned trajectory used when the pointing design was submitted several months ago. Therefore, there was no need to perform any near real-time updates to spacecraft pointing.

OTM-25 was successfully completed on board the spacecraft today. This "Enceladus 2 approach maneuver," together with OTM-24, places the spacecraft on the proper trajectory for the July 14, 175 km targeted flyby of Enceladus.

The main engine (ME) burn began at 3:00 p.m. PDT. A "quick look" at telemetry immediately after the maneuver showed the burn duration was 2.1 sec, giving a delta-V of 0.33 m/s. This is the shortest ME burn to date. All subsystems reported nominal performance after the event. OTM-25 was the first use of the new Mission Sequence Subsystem (MSS) D11.0 OTM blocks and Maneuver Automation Software V5.0 software.

Saturday, July 9 (DOY 190):

Via commands in the background sequence, the Main Engine Cover was closed in preparation for dust hazard conditions around the Enceladus encounter on July 14. It will be opened again on August 2, the day before OTM-26.

Monday, July 11 (DOY 192):

The RADAR instrument was powered on to obtain distant full-disk radiometry of Titan. The next RADAR observation will be to participate in the Rhea non-targeted flyby on July 14.

Real-time commands were sent to the spacecraft for a modification to the CDA Enceladus flyby activities, and to send a trigger command for the RADAR scatterometry to be performed at Rhea.

An image advisory on Hyperion was released today. The image products released include a movie sequence and a 3D view. The views were acquired between June 9 and June 11, 2005, during Cassini's first brush with Hyperion. In both the movie and the 3D image, craters are visible on the moon's surface down to the limit of resolution, about 1 kilometer per pixel. The fresh appearance of most of these craters, combined with their high spatial density, makes Hyperion look something like a sponge. Both items are available for viewing at http://saturn.jpl.nasa.gov or http://www.nasa.gov/cassini.

With the Enceladus flyby happening this week, Cassini Outreach has updated the Enceladus moon and flyby pages. The links are:

Enceladus moon page:
http://saturn.jpl.nasa.gov/science/moons/enceladus/

Enceladus flyby page:
http://saturn.jpl.nasa.gov/news/events/enceladus20050802/index.cfm

Tuesday, July 12 (DOY 193):

Last week at the Titan Atmosphere Model Working Group (TAMWG) telecon, the key topic of discussion was the appropriate altitude for the upcoming T7 flyby in September. Because of variations in atmospheric density observed to date, there is no consensus model to predict the atmospheric density to be encountered at T7. Use of worst-case density values indicate that the T5 altitude of 1025 km may not be safe for T7 with its far southern hemisphere latitude of closest approach, and might lead to spacecraft loss of attitude control and safing. The closer the spacecraft (S/C) gets to Titan, the greater the atmospheric torque applied to the spacecraft. At some point the atmosphere becomes dense enough that the S/C cannot maintain its orientation while flying through it. Then it executes safing and has to find the sun in order to regain its proper orientation so that it can communicate with Earth again. Safing terminates the executing sequence, so all science observations planned between the safing activity and when the sequence is resumed are lost. By raising the flyby altitude we essentially eliminate any chance of this happening because the atmosphere will be thinner.

Following the TAMWG meeting, a follow-on meeting was held to discuss the operational issues related to making this change. There were concerns expressed about trying to accommodate changes for S13 when the sequence is so close to completion and there is limited time available to implement changes. S13 is currently in the final development phase with sequence approval scheduled for July 21, and uplink beginning on July 27. However, a schedule for product deliveries was developed that would allow the changes to be accommodated, and the decision was made to proceed with the change. As of today the target altitude for the T7 flyby has been officially raised from 1,025 to 1,075 km. An updated reference trajectory will be delivered on 20 July for teams to begin making the necessary adjustments to S13 and S14.

Commands were sent to the spacecraft today to enable Radio and Plasma Wave Science (RPWS) sounder operations and to load an Ion and Neutral Mass Spectrometer (INMS) flight software patch and instrument expanded block for Enceladus.

The S14 preliminary cycle 1 merged sequence products were released today for team review. These include files necessary for the live moveable block scheduled for that sequence. The cycle 2 products will be released on July 15 so that teams may check their pointing designs against the new reference trajectory to be released on July 20. Teams have only one chance in the cycle 2 phase to correct any flight rule violations or pointing designs caused by flying the new trajectory.

Wednesday, July 13 (DOY 194):

The S13 preliminary cycle 2 products were released today as part of sequence development. These included products for the background sequence, live moveable block (LMB) for DOY 214, and the combined background sequence and LMB.