[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_BruceMoomaw_*]

EcdentricAnomaly is, I believe, overlooking the point of my argument -- which is not that Iapetus' escape velocity is much lower than Titan's (which of course it is), but that it's much harder to use repeated gravity-assist flybys to previously get Cassini into an orbit close to Iapetus' in order to minimize flyby speed during the insertion burn. Indeed, in the case of Titan you can use not only gravity-assist flybys but also aerobraking for that purpose -- and so, if they don't think insertion into orbit around the moon is practical for Titan, it's certainly not for Iapetus.

[EccentricAnomaly]

EcdentricAnomaly is, I believe, overlooking the point of my argument -- which is not that Iapetus' escape velocity is much lower than Titan's (which of course it is), but that it's much harder to use repeated gravity-assist flybys to previously get Cassini into an orbit close to Iapetus' in order to minimize flyby speed during the insertion burn.  Indeed, in the case of Titan you can use not only gravity-assist flybys but also aerobraking for that purpose -- and so, if they don't think insertion into orbit around the moon is practical for Titan, it's certainly not for Iapetus.

I'm not referring to escape velocity...

In order to capture you need to first get rid of your hyperbolic excess velocity (i.e. your v-infinity). You cannot lower your v-infinity wrt Titan with repeated flybys... Cassini's will always be around 6 km/s wrt Titan. The only way to get rid of that is via aerobraking or maneuvers. Aerobraking is impractical as Cassini is not designed to dip low enough into the atmosphere to get much of an effect at such a high velocity. And there is no way to get rid of that much energy with Cassini's on board DV.

For various geometric reasons, Cassini's Iapetus v-infinity is around 2 km/s. Given a very high apoapsis ( > 200 RS), a maneuver of around 100 m/s or so could bring that v-infinity down to 0 km/s (a parabola). And then maybe some sort of Lissajous orbit would be possible that would give a low orbit insertion DV. But such a scenario may just barely be possible using all of Cassini's on board DV (as of today, giving up the rest of the prime mission), and would require a Phd Thesis amount of work into the trajectory design... So getting into Iapetus orbit isn't practical, but I'd say it just might be possible.

[EccentricAnomaly]

Orbiting Phoebe might also me possible... but its lower gravity would make staying in orbit much harder than at Iapetus.