Tour Re-planning and Upcoming Observations C. J. Hansen 25 July 2005

Tour Tweaks Tour changes for icy satellite science Tour changes for Titan atmosphere / safe mode avoidance Extended mission budget

Tour Tweaks for Icy Satellite Science “Tethys Tweak” NAV / SOST realized that with the expenditure of some delta-v (7 – 8 m/sec) we could change a ~30,000 km flyby of Tethys into a 1500 km flyby (Rev 15, September 24) This also brought the Rev 15 Mimas closest approach down from 118,000 km to ~70,000 km Although there was an impact to RADAR Saturn science, the Project Scientist weighed in and recommended the change We also ended up with a different star for our ICYEXO observation A substantial amount of re-integration of the sequence took place, including moving OTM-38 To save delta-v the targeted Hyperion flyby in Rev 15 was also affected: periapse was lowered from 1000 km down to 510 km

Tour Tweaks for Icy Satellite Science (cont.) Enceladus “Tweak” At the Rev 3 Enceladus flyby MAG detected draping of the magnetic field lines around Enceladus – this magnetic field signature is consistent with the presence of an atmosphere At the Rev 4 Enceladus flyby the MAG team detected an odd distortion of the field at closest approach In order to understand the Rev 4 data and to determine whether Enceladus potentially has an intrinsic or induced field the MAG team requested that the Rev 11 Enceladus flyby altitude be lowered to 175 km The NAV team was able to accommodate the MAG request for < 2m/sec and saved our ICYEXO observation (star changed from alpha Cma to gamma Ori) The EN011 flyby took place July 14 and the science results were well worth the changes!

Titan’s Atmosphere vs. Tour At the Ta flyby INMS and AACS derived quite different atmospheric densities UVIS collected stellar occ data on Tb and the Huygens HASI instrument measured deceleration; both teams came up with different density results The T5 flyby yielded yet another set of densities from AACS and INMS Within a single instrument different flyby geometries have given factors of 2 variation – difficult to sort out temporal and latitudinal and local time differences The bottom line is attitude control thruster authority and what is a safe altitude for Titan flybys –> 950 km seems to be out of the question, but should we go to 975, 1000, or 1025 km?

Comparison of Derived Densities

T7 After deliberation at the TAMWG, the project decided to raise the T7 closest approach flyby altitude T7 was at 1025 km Chance of entering safe mode judged to be 20-30 % Altitude will be raised to 1075 km Flying by at southerly latitude (67 south) RADAR prime at closest approach (worst attitude for control authority) Lowers T6 altitude by ~123 km (was 3758 km)

A series of 950 km flybys commences with T16

Impact to Extended Mission The project has been using delta-v fairly liberally It is worth considering what the impact to the extended mission may be

Bi-Propellant Budget

Upcoming Events Series of Saturn and ring occultations Titan Flybys Start April 14, end Aug. 20 Titan Flybys T6 August 22 T7 Sept. 7 T8 Oct. 28 T9 Dec. 26 UVIS HDAC experiment T10 Jan. 15 UVIS Solar Occultation

Occultation Orbits

Upcoming opportunities to observe Saturn’s icy satellites: Mimas Aug. 2 62,711 km Mimas Sept. 23 69,944 Tethys Sept. 24 1,500 Hyperion Sept. 26 510 Dione Oct. 11 500 Enceladus Oct. 12 49,126 Rhea Nov. 26 500

Aftermarket Process

Aftermarket Process Many levels of changes Internal to team, e.g. data distribution Internal to working groups, e.g. pointing changes Science-wide, e.g. tour modifications Project “accounting” system hasn’t really been necessary Many tour modifications have actually come along after the aftermarket process ended

TOST Categories of Changes No project visibility required Changes to distribution of bits internal to team’s data volume TOST “assisted” (facilitation with aftermarket process) Prime-rider coordination (mosaic layout, dwell time) Mutually agreed upon changes to prime instruments that don’t affect the secondary axis, at times not at closest approach TOST agreement required Changes to overall observation goals Changes to secondary axis Mutually agreed upon swaps of prime instrument at closest approach (e.g. T3 -T12) PSG approval required Changes to allocation of closest approach time

TOST Adaptability Schedule Flyby Previews  ~2 weeks before each flyby Reports on T0, Ta, Tb,T3, T4 and T5 were covered in flyby previews. Biweekly TOST meetings are opportunities for minor tweaking of observation designs. Workshop #1  Oct 2005 T6 + 6 wks Identify preliminary requests for changes to T13 to T19. Workshop #2  Feb 2006 T10 + 5 wks Discuss discoveries, instrument performance and review science priorities based on results from first 10 flybys. Select T20 option. Workshop #3  June 2006 After T14 Identify requests to T21 to T38.   Select T32 option. Workshop #4  Feb 2007 After T24 Half-way point on prime mission (T22 is Dec. 06). Detailed discussions on objectives of extended mission Titan science. Workshop #5  July 2007  After T34 Identify requests for changes to T39 to T44.   Select flyby type for T44

Negative Data Margin We have been dramatically under-utilizing SSR space Within TOST horrific wailing occurred over 25 Mb, yet we are often >200 Mb under in actuality All science planning margin for TOST playback has been released (~70 Mb) DSN changes for T7 were even greater: we (TOST) decided to allow –54 Mb Repercussion is that if SSR fills up we will lose data at the end just before the playback Project was unwilling to allow negative SSR margin