XXM Status, Priorities, Plans, and Activities Icy Satellite Science C. J. Hansen, A. Hendrix June 2013

XXM Status Icy satellite observations executed since last team meeting Rev 183 DOY068 March 9 Rhea flyby for gravity Rev 188 DOY118 April 28 Dione occultation Enceladus plume observations Mimas PIEs Upcoming observations in next 6 months Low phase observations of Mimas, Enceladus, Tethys and Dione Iapetus gamma Ori occultation We have no PIEs in 2014

Satellite Flyby Hiatus

Proximal Mission Phase Priorities Two more potential Enceladus stellar occs in the future One is equatorial 22 June 2017 01:19 Rev 280 Mean anomaly = 116 The other requires a trajectory tweak – occ rayheight is currently 3000 km) 11 March 2016 11:57 Rev 233 Mean anomaly = 220 The other main priority for UVIS are the Dione stellar occ opportunities MAG sees mass-loading in the magnetosphere at ~7 kg/sec (Enceladus supplies ~200 kg/sec) Dione plume won’t go as high or lose as much gas (escape velocity is higher because Dione is larger, gravity higher)

Overview of Nav effort to restore Occ* UVIS/SOST requested study to determine if the Enceladus plume occultation could be restored on Rev 233 Nav agreed to take a look at what the consequences of restoring the Enceladus occ would be Delta-v Ripples to tour Nav (P. Valerino) presented initial study results and options at the April 8th MP Forum Purpose of May 7th MP forum was to gather initial feedback from the science teams * From Emily’s MP presentation and notes

All Nav Studies

April 8th MP Forum Recap Trajectory DV cost (m/s)  Post-T117 inclination (deg) Min. Polar crossing limb altitude * (km) T115 altitude Achieves T116 UVIS, T117 RSS, and T117 Enceladus occultation Comments 110818   15.0 > 2473.0 3817.4 T116 UVIS, T117 RSS occultations only Case 4 1.14 16.235 24.28 3550.4 Yes T115, T122, T123, T125 float Case 7 0.67 16.295 29.71 3530.2 All flybys float (T109-T125) Nav (P. Valerino) presented several options for tour tweaks that would enable an Enceladus plume occultation on Rev 233 Varied post-T117 inclination and allowed various flybys to float https://cassini.jpl.nasa.gov/mp/forum/Encel_Study_MP_Forum_130408_rev1_LRS.pdf Discussion at the forum identified Cases 4 and 7 as the strongest cases TWT/OST/DWGs were asked to review these cases NOTE: DV cost does not include xyz targeting that will be required Oct 2007 (T36-T37), Encel occ xyz targeting DV cost 0.7 m/s in ops (1.3 m/s in statistical analysis) * Table from “Rev 233 Enceladus Occultation Study”, P. Valerino, April 8, 2013.

T117 Enceladus Occultation Geometry Case 4 – T115, T122, T123, T125 float (time and altitude) 110818 reference trajectory Minimum limb altitude : -12.2888 km Polar crossing altitude* : 24.2829 km * Min. limb (polar crossing) must be between 15-40 km to achieve occultation * Slide from “Rev 233 Enceladus Occultation Study”, P. Valerino, April 8, 2013.

Case 7a

DWG Feedback MAPS Essentially none Not very sensitive to timing changes Concerned about an EN auroral footprint observation (DOY 046) Back-to-back with SOST PIE Want to shift PIE in MAPS segment (Rev 244) Frank thinks this is managable Concerned about time and effort to evaluate tweaks No preference between Case 4 and 7 RINGS Case 4 and 7 similar Degradations to RSS and VIMS science Compromise between VIMS and RSS to trade observing time to preserve science Does not solve Rev 231 (DOY 028) VIMS occ, still lost Can NAV tweak Rev 231 VIMS del-Vir occ back in? Should have process for tweaks/ new discoveries SATURN No preference between case 4 and 7 Tweak is not a big impact to SATURN TOST T115 change (~250km) is no impact to CIRS T122 change is acceptable for RSS gravity T117 and T119 occ changes have no impact T116 – larger effect on stellar occs, but changes are manageable T118 no impact SOST Prefer Case 4 Occ is slightly closer to the limb (~5 km) Case 7 is acceptable Small phase angle observations of icy moons affected Level 2 goal Higher priority is EN occ Can NAV move Case 7 closer to limb?

Discussion and Next Steps Complete Nav study Conduct additional statistical analysis for xyz-targeting See if Rev 231 Del-Vir occ is recoverable - No Look at moving Case 7 EN occ closer to limb - Yes NAV will focus studies on Case 7 since no strong preferences were noted for either case Provide one trajectory spk (Case 7 variant) for June PSG PSG gives go or no-go on tweak If go, final decision in October after weighing potential ∆V cost trades between this tweak and proximal orbits redesign If approved, include tweak in Jan 2014 and March 2014 reference trajectory releases

Reference Trajectory Schedule April 2013 Discuss Enceladus occultation with scientists May 2013 Gather initial feedback from science teams June 2013 Release of Enceladus occultation study for Summer PSG June/July 2013 Release of proximal orbits trade space October 2013 PSG decides on proximal orbit and approves Enceladus occultation trajectory January 2014 Preliminary release of reference trajectory March 2014 Final release of reference trajectory; covers remainder of tour

Backup

System Scans - Summary of Request 167-168 17 June 2012 OR 169-170 2 August 2012 256 hr 196-197 5 August 2013 256 hr 206-207 3 August 2014 256 hr 211-212 25 January 2015 resume 4 per year 64 hr cadence

Hello Helene! Helene is Dione’s leading co-orbital; one of 4 of Saturn’s moons in the Lagrangian L4 point Phoebe-size: 36 x 32 x 30 km Sub-Saturnian side 36x32x30 km (like Phoebe), imaged June 18 from 7000 km

XXM Planning Status Requested PIEs for all occultations by: Dione and Tethys Look for volatiles being released, supplying E ring Rhea Look for rings or other evidence of volatile release 15 occs requested 8 in as occ PIEs 2 “in” SOST but in conflict 4 out 1 not scheduled yet Iapetus in apoapsis Rev 196 Now looking at occs in proximal orbit

Solstice Mission Enceladus Flybys All Enceladus flyby’s in XXM have executed except E21 E20 and E22 are relatively distant flybys on Rev 223 and Rev 228, resp., in 2015