[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!>

[Guest_AlexBlackwell_*]

NASA Considering Extending Cassini Mission Through 2010
By Jefferson Morris
Aerospace Daily & Defense Report
12/27/2005 08:57:09 AM

[ugordan]

It's nice to hear an official word on an extended mission, but I'm wondering:

"If we put together a tour that would look very much like what we're doing now - a Titan flyby every month or so and an icy satellite flyby stuck in here and there - then another two years would probably about run us out of fuel," he [Mitchell] said.

How does that cope with this:

Propellant and extended mission: we expect to have nearly 60% of our hydrazine left at the end of the nominal mission. This, along with the quoted biprop numbers, could be used to support an extended mission for 1 year or 10; it all depends on how we use it.

That's gotta be some eventful extended mission if they intend to spend all their hydrazine on the short end of the above estimate, 2 years...

[Guest_AlexBlackwell_*]

That's gotta be some eventful extended mission if they intend to spend all their hydrazine on the short end of the above estimate, 2 years...

As one might expect, the EM options have varying degrees of propellant intensivity. There are Titan-only tours, tours that have targeted icy satellite encounters from high orbital inclination, etc. It all depends on the EM option that is selected and the propellant margin level (and level of risk) the Project decides to accept. Bob Mitchell and "canis minor" may be referring to two entirely different options, which would not be too surprising at this juncture.

[ugordan]

Unless something completely surprising crops up in the near future and throws a curve-ball at us once again, I'd expect the priority targets for an extended mission would be (in order of decreasing importance): Titan, Enceladus, Iapetus.
Iapetus is an expensive target to reach, orbiting quite far away from Saturn so I don't think there'd be more than one (if any!) additional flybys in the extended mission.
Personally, I'd set up a mission phase where Cassini's orbital period would be in resonance with Enceladus' and get several repeated flybys and gravity runs to get a better understanding of this enigmatic moon. Any extended time periods spent near the rings and in the E ring itself would probably be slightly risky so I'd set up that phase at the end of the extended mission. The obvious trouble would be the resonance - you couldn't have a low one, such as 3:1, that would imply lowering your apoapse below Titan's orbit, a big no-no.
Then there's Titan - obviously even if we had 100 more flybys, we'd still have unmapped territories and competing observations to be done.
So much to do... so little fuel...

All in all, I'm looking forward to seeing what the mission folks will devise.

[volcanopele]

A few things I should note: first, in order to accomplish the icy satellite flybys, we have to descend from the high inclination orbit we have at the end of the nominal mission to Saturn's equatorial plane, and that will take lots o' hydrazine, especially if we want to do it quickly. We could stay up to continue to monitor the rings, but that would also require hydrazine, as we would naturally decrease in inclination over time.

[Guest_AlexBlackwell_*]

A few things I should note: first, in order to accomplish the icy satellite flybys, we have to descend from the high inclination orbit we have at the end of the nominal mission to Saturn's equatorial plane, and that will take lots o' hydrazine, especially if we want to do it quickly.

I do know that one of the tour trades Cassini MP revisited during the EM brainstorming process was: "Targeted icy satellite opportunities available during inclined orbits." Another one was: "How to obtain low latitude diametric Titan RSS occultations." I know the former is propellant-intensive; I'm not sure about the latter, though, if I remember correctly, RSS did lose a Titan occultation (equatorial?) earlier in the tour due to a trajectory tweak.

Of course, concentrating on Enceladus flybys (from a low inclination orbit) is popular for an extended mission, which is similar to the Galileo Europa Mission. It'll be interesting to see what happens.

[Bob Shaw]

One of the serendipitous aspects of even the current Cassini orbital campaign has been the 'unplanned' encounters - are there any 'interesting' extended missions? I'm thinking, perhaps, of Enceladus/Titan opportunities, odd things which might happen on the flip-side...

Bob Shaw

[nprev]

One of the serendipitous aspects of even the current Cassini orbital campaign has been the 'unplanned' encounters - are there any 'interesting' extended missions? I'm thinking, perhaps, of Enceladus/Titan opportunities, odd things which might happen on the flip-side...

Bob Shaw

I hope one option being considered for the extended mission is to get in one more good pass at Iapetus in addition to the solitary scheduled close encounter. Hopefully, Titan could be used to de-pump the spacecraft back into an inner icy moon sequence thereafter with minimal propellant usage.

Iapetus really needs at least medium-resolution global coverage (if that's not planned already; don't know the geometry of the 2007 pass). Who wants to sit through another Mariner 10/what's-on-the-other-side-of-Caloris-Basin situation for who knows how long? I want to see what's on the opposite side of that ridge!

[Guest_BruceMoomaw_*]

I pretty much take for granted that an extended mission will include lots more Titan flybys, several of Enceladus, a second one of Iapetus, and probably one of Mimas. Beyond that, it's anybody's guess -- and I imagine it will depend on what interesting phenomena they see during their long-term observations of Saturn, its rings and its magnetosphere, as well as what we see on the remainder of Titan.

[The Messenger]

Those can be at 950 mostly because they are over the polar regions where the atmosphere is much thinner at that altitude.  Also interesting is that they're exploring the possibility of flying through or near the plumes of Enceladus.

This is good, because it will nail down whether or not the anomally is truly connected with the molecular head count...Good that is, if the margin is great enough to counter the torque without compromising the mission.

If I am reading Emily's table correctly, the first 950km flyby will be T16 on July 22, 2006.

[tasp]

I'm not smart enough to do the math on this so if impractical or unmeritorious, mea culpa.

Iapetus is not so far off of being in a 1 to 5 resonance with Titan, and is one of the larger satellites of Saturn and is very distant to boot.

What if....

Cassini is put in a ~79.3 day orbit of Saturn and makes a couple of (fairly identical trajectory wise) succesive flybys of Iapetus. One pass could be devoted to photographic scrutiny, and the other could have the radar instrument examine the same ground track as the photo series. (nice if the path crossed the edge of Cassini Regio and over the equatorial ridge structure)

My thoughts are that bringing all the crafts sensors to bear on the dark stain and the ridge structure might yield enough data to verify one or some (or none!) of the many theories as to what happened to this amazing moon.

Additionally (crossing my fingers here) in view of Iapetus' mass and remoteness from Saturn, would allow a sufficient gravity assist to get back to a close approach to Titan to resume the Titan resonant orbits as seen in the rest of mission?

(I'm thinking an orbit that synchronizes to Iapetus doesn't go back to Titan unless you 'do something', like utilize Iapetus, to get back to Titan's proximity to resume orbit mods there.)

{are you having fun watching me squirm at the narrow confines of my intellect? }

[tasp]

What the heck, might as well drop this one in too:

At the conclusion of the Cassini mission, have the craft crater in Cassini Regio.

Hopefully a future mission can photograph the crater (shades of Ranger 7!) and perhaps some more clues as to the dark stain can be gleaned?

Perhaps the dark coating is very thin, Cassini might blast quite a hole in it and reveal quite an acreage of white material beneath.

Maybe its' thick and the crater barely pierces the black stuff.

Maybe the coating is thin, and slowly reforms over time (years? centuries?).

Worth a shot?

[edstrick]

I wouild assume a major science opportunity during an extended mission would be ring observations in 2009 when the spring equinox occurs and the sun passes directly through the orbital plane of the rings. The grazing illumination should better reveal vertical structure of the rings, including vertically extended dust hazes, out-of-plane wave structures, overall ring warp due to satellite tides, etc. I would assume the highest value observations would be from high inclinatin orbit, more or less over a pole at the extended moment the sun (3 arcmin diameter, approx) goes through the ring plane.

Volcanopele: What's the discussion on science merits of different observations during the solar ringplane crossing period, and effects on extended tour plans?

[tallbear]

A few things I should note: first, in order to accomplish the icy satellite flybys, we have to descend from the high inclination orbit we have at the end of the nominal mission to Saturn's equatorial plane, and that will take lots o' hydrazine, especially if we want to do it quickly.  We could stay up to continue to monitor the rings, but that would also require hydrazine, as we would naturally decrease in inclination over time.

depends upon which sats have priority ... during revs 6 thru 14 the ring plance crossing occured righte close to 4.0 Rs which is great for Enceladus... and those orbits were inclinded in the 20'ish degree range to optimize for RSS OCCs. Studies are in place to see what sorts of orbits are required for what satellites and if any satellite flybys require
an EQ orbit. ... and there are lots of events that can not be viewed in EQ orbits so the pressure is on ..... all these EM studies and discussions are in their infancy .... so don't expect more than specualtion for ages.( Feb 2007 with a fair HINT at the naure of the Tour out in Aug 2006) ,....

[tallbear]

I wouild assume a major science opportunity during an extended mission would be ring observations in 2009 when the spring equinox occurs and the sun passes directly through the orbital plane of the rings.  The grazing illumination should better reveal vertical structure of the rings, including vertically extended dust hazes, out-of-plane wave structures, overall ring warp due to satellite tides, etc.  I would assume the highest value observations would be from high inclinatin orbit, more or less over a pole at the extended moment the sun (3 arcmin diameter, approx) goes through the ring plane. 

Volcanopele:  What's the discussion on science merits of different observations during the solar ringplane crossing period, and effects on extended tour plans?

Rings folk definitely want to be out of the ring plane for the equinox passage period and also for the Prometheus - F-Ring collision / interaction that falls late in 2009. To be honest... Rings folk have little desire to get into the Ring Plane <G> .... but these Geometric events are in the Rings High Priority listings.