Proximal Orbit Science Team (POST) Summary M. Evans Thursday Feb 12 th 2015

1. Proximal Orbit Science Team (POST) Summary M. Evans Thursday Feb 12th 2015 v2

2. Option 9 https://cassini.jpl.nasa.gov/projscimtg/fprox/POST_option_9_141210.pdf https://cassini.jpl.nasa.gov/projscimtg/fprox/option9_portrait_141210.pdf

3. The POST Periods The POST period times are absolute (not epoch relative) and will not change POST_periods_option_9_141210.pdf

4. Option 9 (141210). Description and Liens Rev 271 – This is a designated “cool” orbit. See the section on Cool Orbits. Observe Saturn polar regions inbound/outbound for CIRS/VIMS when their respective radiators are cooler (In approximately the 1-2 hrs from periapse periods). ISS does the PDT design for the entire -/+ 2 hrs period including the HGA to RAM period. Rev 272 – MAG to roll about an axis other than Z (i.e. X or Y). CDA to be consulted about secondary orientation/roll phase at RPX. MAG requests that periapse be done under RCS control. Will be using RCS for central 5 hrs. Rev 273 – RSS gravity pass, XBAND to Earth primary. MAG Range 1 calibration - rolling for 5 hours during the inbound portion (periapse -11:40 to -06:40). MAG Range 2&3 calibration – rolling for 5 hours centered on periapse. CDA to be consulted about secondary orientation/roll phase at RPX. Rev 274 – RSS gravity pass. XBAND to Earth primary. CDA to be consulted about secondary orientation. Rev 275 – RSS gravity pass. XBAND to Earth primary. CDA to be consulted about secondary orientation. Rev 276 – RADAR Rings on the inbound portion which then hands of at RPX -10 mins at HGA to RAM. At RPX +10 mins ISS Rings picks up at HGA to RAM. Coordination required regarding the choice of secondary for the HGA to RAM period. Rev 277 – ISS Rings on the inbound portion which then hands of at RPX -10 mins at HGA to RAM. At RPX +10 mins RADAR Rings picks up at HGA to RAM. Coordination required regarding the choice of secondary for the HGA to RAM period.

5. Rev 278 – RSS gravity pass. XBAND to Earth primary. CDA to be consulted about secondary orientation. Rev 279 – Joint INMS/CDA. NEG_X to RAM with secondary chosen for CDA. Rev 280 – RSS gravity pass. XBAND to Earth primary. CDA to be consulted about secondary orientation. Rev 281 – This is a designated “cool” orbit. See section on Cool Orbits. Observe Saturn polar regions inbound/outbound for CIRS/VIMS when their respective radiators are cooler. (In approximately the 1-2 hrs from periapse periods). ISS does the PDT design for the entire -/+ 2 hrs period including the HGA to RAM period. Rev 282 – UVIS Rings on the inbound portion which then hands of at RPX -10 mins at HGA to RAM. At RPX +10 mins RADAR Rings picks up at HGA to RAM. Coordination required regarding the choice of secondary for the HGA to RAM period. Rev 283 – Joint INMS/CDA. POS_X to COROT with secondary chosen for CDA. Rev 284 – RSS gravity pass, XBAND to Earth primary. MAG Range 1 calibration - rolling for 5 hours during the inbound portion (periapse -11:40 to -06:40). MAG Range 2&3 calibration – rolling for 5 hours centered on periapse. CDA to be consulted about secondary orientation and roll phase at RPX. Rev 285 – MAG to roll about an axis other than Z (i.e. X or Y). CDA to be consulted about orientation choice/roll phase at RPX. MAG requests that periapse be done under RCS control. Will be using RCS for central 5 hrs. Rev 286 – This is a designated “cold” orbit. See section on Cold Orbits. POST has explicitly allocated the time from periapse -1hr to periapse +7 hrs for auroral/Enceladus studies. VIMS and CIRS will negotiate the exact division of the time. The allowable heating in each of the VIMS/CIRS periods is subject to negotiation.

6. Rev 287 – Joint INMS/CDA. POS_X to COROT with secondary chosen for CDA. Rev 288 – INMS. POS_X to COROT secondary should be NEG_Z to Saturn for RADAR Saturn. Rev 289 – This is a designated “cold” orbit. See section on Cold Orbits. Since the periapse altitude is so low atmospheric drag and heating become a consideration. Its possible that constraints imposed by aerodynamic heating will prevent this orbit being truly cold and that it will be “cool” instead. This periapse will be made as cool as is practical. CIRS & VIMS observations are permitted but may be prevented by the necessity of adopting a non-science minimal heating (both aerodynamic and radiative) pointing profile. Rev 290 – RADAR. NEG_Z to Saturn. Secondary chosen for INMS (POS_X to COROT) Rev 291 – INMS. POS_X to COROT secondary should be NEG_Z to Saturn for RADAR Saturn. Rev 292 – INMS. POS_X to COROT secondary should be NEG_Y to Saturn for ISS Saturn.

7. Cold Orbits The rev 286 & 289 periapses have been designated by POST as “cold orbits”. At no time during the POST period may the CIRS radiator delta_T be more than 3K -- this restriction is superseded if M. Flasar approves a CIRS radiator heating profile that covers the entire POST period. At no time during the POST period may the VIMS radiator delta_T be more than TBD* -- this restriction is superseded if R. Brown approves a VIMS radiator heating profile that covers the entire POST period (*will be set once the new VIMS thermal code is available). POST 286 – only VIMS Prime Saturn and CIRS Prime Enceladus observations my be integrated by the TWT in this period POST 289 – During the S/PIE process POST recommends that any VIMS/CIRS Saturn/Rings PIEs have precedence in the ~6 hrs immediately following the POST period. No additional restrictions placed on integration. These requirements will likely affect the choice of inbound observations prior to the POST period. Heating during both the pre-POST TWT time and the pre-periapse POST time can be significant if using an ORS to Saturn science orientation. The POST cold orbit requirement has priority over a PIE and may prevent the PIE from being integrated as desired

8. Cool Orbits The rev 271 & 281 periapses have been designated by POST as “cool orbits”. At no time during the POST period may the CIRS radiator delta_T be more than 6K -- this restriction is superseded if M. Flasar approves a CIRS radiator heating profile that covers the entire POST period. At no time during the POST period may the VIMS radiator delta_T be more than TBD* -- this restriction is superseded if R. Brown approves a VIMS radiator heating profile that covers the entire POST period (*will be set once the new VIMS thermal code is available). POST 271 & 281 – During the S/PIE process POST recommends that any VIMS/CIRS Saturn/Rings PIEs have precedence in the ~6 hrs immediately following the POST period. No additional restrictions placed on integration. These requirements could affect the choice of inbound observations prior to the POST period. The POST cool orbit requirement has priority over a PIE and may prevent the PIE from being integrated as desired

9. Periapse passages to be performed using RCS Due to the spacecraft being close to or in the atmosphere it is a requirement that the final five periapses, 288-292, be performed using RCS. MAG has requested that the two periapses when it is performing non-Z axis calibration rolls, 272 & 285, also be done using RCS. Summary

10. Spacecraft orientations at the start and end of the POST periods The TWTs allocated the segments that include the POST periods will have to hand-off/pick up at the start/end of the POST allocated blocks of time at the desired pointings of the POST observations i.e. the TWTs are responsible for the turns to/from the POST observation attitudes in “their” time.

11. Remaining Issues • Concerns regarding rev 289. Our ability to achieve a “Cold Orbit” remains in doubt. Fallback position if we’re reduced to 1 cold orbit? Give 286 to INMS and then make one of the earlier INMS periapses a cold orbit instead (which one?) is an option. • CDA has an interest in the secondary orientations in eleven revs. 272-275 278-280 283-285 & 287. They have yet to sign off on the designs for a number of revs (which revs?) • MIMI has an in interest in the orientations for all revs. They need to analyse all 22 designs in order to determine if their requirements have been met. If they haven’t some rework may be necessary. • VIMS heating model. When this becomes available the current designs need to be run through it. If heating turns out to be unacceptable POST allocations may need to be reworked • All current designs to be run through CIRS heating model to identify additional serendipitous cool/cold orbits. • Status of period immediately following the rev 289 POST period i.e. periapse +1 hr to ~+7 hrs. The expectation is that VIMS/CIRS rings/atmospheres observations will be made. Do we leave this to the TWT allocated the segment or provide some formal guidance? Should PIE hours be used for CIRS/VIMS rings/Saturn during this time? • Exact timings of the 20 minute duration HGA to RAM dust hazard periods that are required in revs 271, 276, 277, 281 and 282. The CIMS entries are a little confused. Do we need to go down to the second level or is rounding to the nearest minute O.K.?