[X] My Assistant

[Del Palmer]

The flyby mission description is now up.

1,300 km altitude, southern hemisphere, outbound. ISS and VIMS will observe Ontario Lacus.

[volcanopele]

The T38 flyby is now the top story on the Cassini website. You might notice a disconnect between the description the header images uses, "Cassini's Search for Subsurface Ocean Continues," and the goals of the flyby: to image Ontario Lacus. Originally, the T38 encounter was to be a "gravity pass", with the Radio Science team having time at closest approach and at other times in the encounter to measure the gravitational field of Titan. Combined with three other passes in the nominal mission, the interior structure and the thickness of Titan's internal ocean could be discerned. After the discovery of Ontario Lacus, it became important to determine whether it was in fact a lake filled with liquid methane. Cassini's trajectory during T38 takes it directly over Ontario Lacus. The VIMS team successfully argued for a change in the T38 sequence to make it an ORS pass, giving prime targeting control to VIMS during C/A. However, many internal documents have not been updated to reflect that change (including my copy of the timeline, as you can tell from the CICLOPS looking ahead page, which still mentions the non-C/A RSS passes).

Which might explain why the graphic used on the Cassini homepage says that this pass will continue the search for an internal ocean.

[rlorenz]

VP - it wasnt just the VIMS team.
One of your ISS colleagues close to me was also among the chorus (including myself) that
argued for T38 being used for ISS and VIMS to observe Ontario, it being a particularly good
opportunity to do so. (Radar will hit it in XM, hopefully with both SAR and altimetry - the illumination
will be poorer then, but we dont need no stinkin sunshine...).

A major factor in this re-assignment was the calculation (once all the
details of ground station availability etc. were in and the error correlation matrices calculated) was that
the incremental value of the flyby towards the gravity field (and tidal variation thereof) determination
was in fact rather small. RSS will get better results from T45 in XM (assuming XM gets approved)

The T38 flyby is now the top story on the Cassini website. You might notice a disconnect between the description the header images uses, "Cassini's Search for Subsurface Ocean Continues," and the goals of the flyby: to image Ontario Lacus. Originally, the T38 encounter was to be a "gravity pass", with the Radio Science team having time at closest approach and at other times in the encounter to measure the gravitational field of Titan. Combined with three other passes in the nominal mission, the interior structure and the thickness of Titan's internal ocean could be discerned. After the discovery of Ontario Lacus, it became important to determine whether it was in fact a lake filled with liquid methane. Cassini's trajectory during T38 takes it directly over Ontario Lacus. The VIMS team successfully argued for a change in the T38 sequence to make it an ORS pass, giving prime targeting control to VIMS during C/A. However, many internal documents have not been updated to reflect that change (including my copy of the timeline, as you can tell from the CICLOPS looking ahead page, which still mentions the non-C/A RSS passes).

Which might explain why the graphic used on the Cassini homepage says that this pass will continue the search for an internal ocean.