[X] My Assistant

[imran]

Whether this is a two-year extension or longer I'd still have to go with Titan. There is so much of this world which we don't understand and have only begun to unveil that it begs us to focus our attention on this dynamic world. Some important questions that may only be answered with additional flybys:

- What is the source of methane in the atmosphere?
- Are there any bodies of liquids on the surface?
- Is there active precipitation?
- Is Titan geologically active, i.e. cryvolcanism, tectonism, etc?
- What is the extent of the organics present?
- Is there an ammonia/water mixture under the surface?

[Guest_BruceMoomaw_*]

Looks like it's time for me to ask Bob Mitchell again about their possible alternative plans. While I was scrounging through my printed records last night (as one of my periodic spasmodic ofice cleanups), I ran across Mitchell's Jan. 29, 2001 reply to my question on the possible goals of an extended mission:

"[The most desirable goal for an extended mission] depends on which of the scientists you talk to...However, the prime target that seems to be least satisfactorily covered in the current prime tour by the investigators is Titan. On the other hand, by the time we're halfway through the prime mission, we may have made discoveries that will completely change what would be considered the prime targets."

Speak of the Devil. We're about halfway through the prime mission, and Enceladus has indeed upset the applecart. Beyond that, though, the main new conclusion seems to be that Titan's surface is even more varied, hard to understand, and therefore worthy of extensive mapping than had been expected. (I wonder if they'll emphasize using the VIMS more for that than the ISS cameras during the Extended Mission?) Beyond those two moons, the only target I can think of whose relative importance MIGHT possibly be increased by Cassini's observations so far is Hyperion, with its very odd surface.

[volcanopele]

Speak of the Devil. We're about halfway through the prime mission, and Enceladus has indeed upset the applecart. Beyond that, though, the main new conclusion seems to be that Titan's surface is even more varied, hard to understand, and therefore worthy of extensive mapping than had been expected. (I wonder if they'll emphasize using the VIMS more for that than the ISS cameras during the Extended Mission?) Beyond those two moons, the only target I can think of whose relative importance MIGHT possibly be increased by Cassini's observations so far is Hyperion, with its very odd surface.

I don't think the discoveries at Enceladus really change the extended mission strategy all that much. Yes, we will want to include more Enceladus flybys, at least a couple right over the south polar region, one to cover the still poorly mapped leading hemisphere, and at least a couple to do gravity measurements. But the driver for any tour will still be Titan. The question will be whether we want a longer extended mission in order to observe seasonal changes, which will mean fewer RADAR passes and perhaps fewer targeted Titan flybys in general to conserve fuel, or a shorter extended mission with more RADAR passes at the expense of observing seasonal changes.

I prefer meeting these camps halfway, a two year extended mission with a little bit of both Titan camps to allow enough time for at least 5 Enceladus passes and an additional Iapetus pass. This is smack in the middle of the hyperactive, one-year extended mission that RADAR would prefer, and the slower-paced, 4-year extended mission that the ORS folks may want.

In terms of ISS vs. VIMS, once again, we have already done that. Closer in, when ORS has the reins, VIMS is driving. Farther out, ISS is driving because it can get much of the visible surface at only a little lower resolution than VIMS up close.