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

2. XXM Status Icy satellite observations executed since last team meeting
Rev 183 DOY March Rhea flyby for gravity
Rev 188 DOY April 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

3. Satellite Flyby Hiatus

4. Proximal Mission Phase Priorities
Two more potential Enceladus stellar occs in the future
One is equatorial
22 June :19 Rev 280 Mean anomaly = 116
The other requires a trajectory tweak – occ rayheight is currently 3000 km)
11 March :57 Rev 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)

5. 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

6. All Nav Studies

7. 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
>
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
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.

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

9. Case 7a

10. 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?

11. 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

12. 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

13. Backup

14. System Scans - Summary of Request
June 2012
OR August hr
August hr
August hr
January resume 4 per year 64 hr cadence

15. 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

16. 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

17. 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