Cassini Tour Selection Dr. Kevin R. Grazier IS/SPE With Significant Viewgraph Assistance By: Linda Spilker Cassini Deputy Project Scientist July 26, 2005

KRG/LJS July 2005 History Tour was discussed in the Cassini Announcement of Opportunity (AO) Discussions about creating a “new tour” began at very first PSG meeting (in December, 1990) Tour was created after Cassini descope. Very Galileo-like in its character. –mostly updated tour for new Cassini arrival date

KRG/LJS July 2005 Tour Characteristics of –63 Orbits –33 Titan flybys 12 inbound, 21 outbound, 10 solar/earth occulations –4 targeted icy satellite flybys: Enceladus, Dione, Rhea, Iapetus –12 non-targeted flybys (d<50,000 km) –Saturn/ring occultations: 5 earth and sun during first 2 occultation sequences

KRG/LJS July 2005 Tour Trade Study PSG and Project agreed to a tour design trade study, scheduled between 1993 and 1996 Discipline Working Groups (Atmospheres, MAPS, Satellites, Rings) developed a list of tour geometry objectives and guidelines –DWG tour priorities generated over several PSG meetings –Finalized by DWGs at ESTEC PSG in May 1995 Tour design tool (STOCK) provided to teams –With software and excel spreadsheets Cassini scientists could design a Titan-only tour New orbit rotation technique identified (Titan 180 transfer)

KRG/LJS July 2005 Tour Design Considerations Titan flyby strategy Tour redesign implications of change in minimum altitude, number of flybys and occultations Extent of CCW rotation at beginning of tour Number of moderately inclined (20-50 deg) orbits and location during tour Extent of CW rotation toward magnetotail Maximum value of high inclination orbits Saturn and Rings sun/earth occultation geometry strategy Icy satellite flyby strategy for given tour rotation/inclination profile Tour strategy relative to horseshoe/tadpole trapped particle risk regions Ground system requirements

KRG/LJS July 2005 Selecting a Tour Orbiter workshop held in July, 1995 –3 IS-led interdisciplinary teams evaluated 8 classes of tours (38 Titan-only tours) –Identified driving requirements and suggested possible compromise tours At end of tour design trade study, 17 Titan-only tours (T1 – T17) were available for further study

KRG/LJS July 2005 Some Tours Looked Rather Familiar

KRG/LJS July 2005 Others…. Didn’t

KRG/LJS July 2005 Selecting a Tour At 8/96 PSG, added one class of tour for further study– T18 Three tours quickly emerged as favored:

KRG/LJS July 2005 T2 Quickly eliminated largely because of low science return.

KRG/LJS July 2005 T9 LOVED by MAPS, Rings, Titan (two 180 transfers; 51 Titan flybys)! Too difficult operationally (too many consecutive 16-day orbits)

KRG/LJS July 2005 The Winner Is: T18 At 3/99 PSG selected T18-1 as final tour Less science return than T9-1 Still difficult operationally, but we decided to “bite the bullet”. Since T18-1, there have been 4 major revisions and at least 14 minor.

KRG/LJS July 2005 Current Reference Tour 74 Orbits 45 Titan flybys 8 targeted icy satellite flybys: Phoebe, Enceladus (3), Dione, Rhea, Hyperion, Iapetus ~30 non-targeted flybys (d < 100,000 km) Many Saturn/ring occultation opportunities –Early, middle and late in tour One Titan 180 transfer One high inclination sequence at end of tour

KRG/LJS July 2005 Our Pre-launch Goals Scan Platform Working Group: 11/91 –Sequencing process must start early, before launch, if possible –Tour fully designed before SOI (minimizes impact of burnout, divorce, suicide, murder, etc. during tour)

KRG/LJS July 2005 Cassini Tour T18-5 Looking down from Saturn’s North Pole Outer dotted circle: Orbit of Iapetus Inner dotted circle: Orbit of Titan Sun along +X Axis – Plot shows phase Looking in Saturn’s Ring Plane Excursions in inclination different from Galileo All units in Rs

KRG/LJS July 2005 CASSINI TOUR T18-5 Orbit Insertion and Huygens Mission All units in Rs

KRG/LJS July 2005 CASSINI TOUR T18-5 Huygens Mission – Rev B Probe Release All units in Rs

KRG/LJS July 2005 CASSINI TOUR T18-5 Huygens Mission – Rev B Probe Mission All units in Rs

KRG/LJS July 2005 CASSINI TOUR T FEB 15 to 2005 SEP 07 Mid-Rev 3 to Mid-Rev 14 Occultation Sequences All units in Rs

KRG/LJS July 2005 CASSINI TOUR T FEB 15 to 2005 SEP 07 Mid-Rev 3 to Mid-Rev 14 Occultation Sequences All units in Rs

KRG/LJS July 2005 CASSINI TOUR T SEP 07 to 2006 JUL 22 Mid-Rev 14 to Mid-Rev 26 Magnetotail and Icy Satellites All units in Rs

KRG/LJS July 2005 CASSINI TOUR T SEP 07 to 2006 JUL 22 Mid-Rev 14 to Mid-Rev 26 Magnetotail and Icy Satellites

KRG/LJS July 2005 CASSINI TOUR T JUL 22 to 2007 JUN 30 Mid-Rev 26 to Mid-Rev Transfer: Rings and MAPS All units in Rs

KRG/LJS July 2005 CASSINI TOUR T JUL 22 to 2007 JUN 30 Mid-Rev 26 to Mid-Rev Transfer: Rings and MAPS

KRG/LJS July 2005 CASSINI TOUR T JUN 30 to 2007 AUG 31 Mid-Rev 47 to Mid-Rev 49 Iapetus Flyby Preparation/Icy Satellites All units in Rs

KRG/LJS July 2005 CASSINI TOUR T AUG 09 to 2007 SEP 14 Rev 49 Titan Gravity Assist and Iapetus Flyby All units in Rs

KRG/LJS July 2005 CASSINI TOUR T AUG 09 to 2007 SEP 14 Rev 49 Titan Gravity Assist and Iapetus Flyby

KRG/LJS July 2005 CASSINI TOUR T AUG 31 to 2008 JUL 01 Mid-Rev 49 to EOM High Inclination Revs: Rings and MAPS All units in Rs

KRG/LJS July 2005 CASSINI TOUR T AUG 31 to 2008 JUL 01 Mid-Rev 49 to EOM High Inclination Revs: Rings and MAPS