[X] My Assistant

[edstrick]

tallbear: "....However, the Cassin Tour will be altered in early 2006 and these opportunities may go away while others may appear.....

Uh... Say WHAT?....is this a branch to an entirely different series of encounters than the second half of the primary mission that they've been designing in (necessarily) obsessive-compulsive detail for the last decade? Did they have to retarget to make a close flyby of a Vogon Mothership? Or did they find a spinning blue telephone call-box floating in Saturn orbit? <grin!>

[ugordan]

tallbear:  "....However, the Cassin Tour will be altered in early 2006 and these opportunities may go away while others may appear.....

Uh... Say WHAT?....is this a branch to an entirely different series of encounters than the second half of the primary mission that they've been designing in (necessarily) obsessive-compulsive detail for the last decade?  Did they have to retarget to make a close flyby of a Vogon Mothership?  Or did they find a spinning blue telephone call-box floating in Saturn orbit?  <grin!>

Maybe he's talking about the next phase in the mission where Cassini won't be in the ringplane anymore and hence not in a favorable position to do serendipous non-targeted flybys?

[pat]

Maybe he's talking about the next phase in the mission where Cassini won't be in the ringplane anymore and hence not in a favorable position to do serendipous non-targeted flybys?

The Cassini tour is indeed being changed from 2006 onwards. This is due to the Titan flyby altitudes being raised -- Titan's atmosphere is thicker than expected at the flyby altitudes. The change is intented have have a minimal impact on the Science----> the new trajectory is as close as possible to the previous tour.

[ugordan]

The Cassini tour is indeed being changed from 2006 onwards. This is due to the Titan flyby altitudes being raised -- Titan's atmosphere is thicker than expected at the flyby altitudes. The change is intented have have a minimal impact on the Science----> the new trajectory is as close as possible to the previous tour.

Yes, but what is the impact delta-V wise? While I'm at it, why don't the Cassini weekly status reports indicate any hints of remaining consumables, whether they be in kilograms, percent, deltaV, ANYTHING?
It would really be nice, I'm often wondering how long an extended mission Cassini might pull off one day since I keep hearing about these OTMs and unscheduled tweaks to the tour that expend several meters/s and somehow I get the feeling Cassini doesn't have that much fuel left onboard as is?

[JRehling]

I keep hearing about these OTMs and unscheduled tweaks to the tour that expend several meters/s and somehow I get the feeling Cassini doesn't have that much fuel left onboard as is?

I'd like to know the ballpark figures... a document predating SOI mentioned a very long life as being possible for Cassini... it will be 20 years from now before Cassini will be as old as Voyager 2 is today. If extended mission(s) lasted that long, then the original primary mission could one day be remembered as a small portion of the total cruise.

The history of NASA spacecraft is that most craft that don't fail early don't fail soon thereafter, either, and that lifetimes greatly beyond the posted "shelf life" as common. Presumably, the main issue here is the consumption of fuel, and I note that the Voyagers have great reserves left over: three-axis stabilization itself, in deep space, anyway, does not consume very much (which makes sense). Note that course modification and attitude control employ *two different* subsystems, so that this story should not impact the lifetime of Cassini in any direct way. Except that avoiding the torque of a close Titan flyby will certainly help!

Burning course modifying fuel of course, limits our ability to keep tweaking the trajectory, but Cassini will stay in Saturn orbit regardless. The hazard would be that the trajectory would eventually crash into something (Titan, if probability were to have its way) and we'd lack the delta-v to avoid it. But a long, semi-aimless life in an orbit that intersects that of Enceladus and that of Titan would give us good science indefinitely far into the future.

I have found at this link

http://www.ssd.rl.ac.uk/news/cassini/mission/ops.html

that Cassini is expected to burn "less than half" of its attitude control fuel in the primary mission. Well, 1% is "less than half", but if they mean less than and close to half, then we might expect only about 4-5 more years of life after the primary mission. On the other hand, it seems that it is pointing, not mere maintenance, that eats the fuel up -- my so-rusty-it's-dead rotational mechanics background says that you could run these operations with less fuel consumption if you were willing to limit the ability of the craft to swivel quickly on close flybys, and to pick and choose observational opportunities so that you got fewer observations per flyby, but a substantially higher number of flybys. I would certainly prefer to see a full RADAR map of Titan trickle in over 25 years than to map half of it in six years, then have Cassini be utterly dead. Not only to reap the most spatial coverage, but in recognition of the fact that Enceladus may have time-varying phenomena of interest (although maybe the fountains are constant in their output over long spans of time?), and Titan's weather is sure to change over the very long seasons: it would be great to get even sporadic observations through 2034 to get to see a whole Titan year take place. To sum up, I'd like to see a strategy of conservation that gives us long-term climate observations and steady progress in RADAR mapping of Titan, along with intermittent observations of Enceladus. Encounters with the other icy moons would continue to happen if only by accident.