[X] My Assistant

[volcanopele]

I've seen plans four a four year mission for Cassini. What happens after this? Crash it into Saturn like they did with Galileo or an extended mission? I'd like to see it in orbit around Titan but that doesn't seem likely since it ends in a near polar orbit around Saturn.

I haven't heard much, but as far as I have heard, the discussion seems to be centered around just continuing the Cassini mission as it is now. Maybe get a few more icy satellite flybys, particularly of Tethys, which doesn't have a targeted flyby during the nominal mission. My hope is that, given the limited amount of hydrazine left at the end of the mission, that Cassini would at least get additional flybys of Titan over areas not well covered during the nominal mission like near 270W.

[Guest_BruceMoomaw_*]

Robert Mitchell told me a couple of years ago that the single highest priority for an extended mission is getting more coverage of Titan's surface. Beyond that, it's a safe bet that targeted flybys of Mimas and Tethys would be on the agenda (the primary mission actually has one very good untargeted Tethys flyby, but none of Mimas), surely a second one of Iapetus, and perhaps one of Janus and/or Epimetheus (are they really rubble piles, as the vague density data we have up to now suggests?)

It's interesting to speculate on whether they might eventually decide to aerobrake Cassini into a polar orbit around Titan for a really thorough mapping of that world -- although it would be difficult. All this, however, naturally depends on whatever unpredictable new discoveries they make during the primary mission.

[YesRushGen]

It's interesting to speculate on whether they might eventually decide to aerobrake Cassini into a polar orbit around Titan for a really thorough mapping of that world -- although it would be difficult....

Now that would be really neat! I'd imagine it wouldn't be really hard to do either.

1. At the end of Cassini's primary mission, we are in a near polar orbit about Saturn. We'd need an "equitorialization campaign," using Titan flyby's to place Cassini back in a co-planar orbit with Titan.

2. Depending on the resulting Titan co-planar orbit, we probably need to pump down (or pump up) Cassini's orbit using additional Titan flybys. Each one will lower the required capture delta-V to enter Titan's orbit. (Similar maneuver was planned for the aborted Europa Orbiter mission) Using this resonant encounter technique, we could probably get the required capture delta-V down to 100m/s or less. (Titan's gravity actually HELPS us with this)

3. The big one: Capture into Titan orbit. Do we use precious fuel for this? Or do we chance the FIRST EVER TRIED aerocapture manuever? Either way, we should enter an eccentric orbit with the maximum allowable Apoapsis.

4. From here, we just need to make shallow passes in Titan's thin upper atmosphere to gradually reduce the Apoapsis to the height of the target orbit.

5. After the target Apoapsis is reached, we will need a Periapsis raise burn at the next Apoapsis to bring the orbit out of the atmosphere and make it circular.

We have to consider how to orient Cassini during the atmospheric passes. My guess is to use point the HGA in the direction of travel. That will have the effect of protecting the rest of the spacecraft. (Similar to initial ring plane crossing) But the big question here is whether or not the HGA can stand the heating caused by the passes. As long as we're only hitting the outer fringe, it should probably be ok.

What could be easier?!?!

[djellison]

I challenge you to pulling that off in Orbiter www.orbitersim.com

Doug

[alan]

Aerocapture shouldn't be necessary. They may be able to finesse it using the L1 librating point like they did with the Genesis.

[alan]

An interesting article describing libration points chaotic orbits etc from discover magazine
http://www.findarticles.com/p/articles/mi_...i_55926787/pg_2

[djellison]

It shouldnt be that hard to essentially 'match' titan's orbit with Cassini - and then it's a tiny ammount of delta V to drop into orbit around Titan

Doug

[YesRushGen]

I challenge you to pulling that off in Orbiter www.orbitersim.com

Doug

Oh, I'm an Orbiter regular, no doubt about that. It is a good challenge, though!

Is this challenge with the stock Delta Glider, or with the Cassini add-on that's been released?

(err.. I dunno if the Cassini add-one models any atmospheric behaviors. I may be wrong on this, but I think that spacecraft in Orbiter have to be programmed to decelerate due to atmospheric interaction.)