[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?

[Bart]

I just looked up the formulas and did the calculations myself and it looks like a circularizing a Titan/Mimas osculating orbit takes a delta-V of 2.7 km/s, whereas converting a Titan/Mimas osculating orbit to an Iapetus/Mimas osculating orbit takes 3.6 km/s. Obviously, these orbits are oversimplifications, but I think it illustrates the point that circularizing the orbit is not that hard.

As far as where to get that delta-V, the theoretical max that you could get from a Titan-assist is 11 km/s, but I know they're not actually using anywhere near that much.

As an aside, surely someone has compiled the delta-V from each Cassini-Titan flyby somewhere? This would be a really neat addition to one of the 'Saturn Tour' pages like the one on the Cassini homepage, or Emily's much better one.

Bart

EDIT: Ok, I just looked at Emily's page to get a rough idea of the gravity assist magnitudes for the mission so far and it looks like most of them are in the range of 200-600 m/s. This means it would take several passes to circularize the orbit, but probably less than 10.

[ugordan]

As far as where to get that delta-V, the theoretical max that you could get from a Titan-assist is 11 km/s

11 km/s ???
How in the world did you come up with that figure?

[Bart]

11 km/s ???
How in the world did you come up with that figure?

According to the Wikipedia entry (taken, I believe, originally from the Cassini website anyway), the maximum delta-V for a gravity assist maneuver is twice the orbital speed of the assisting body. In the case of Titan, the orbital velocity is 5.5 km/s. Obviously you're only going to approach this value in very specific circumstances, but it does provide an upper bound.

Bart

[ugordan]

According to the Wikipedia entry (taken, I believe, originally from the Cassini website anyway), the maximum delta-V for a gravity assist maneuver is twice the orbital speed of the assisting body. In the case of Titan, the orbital velocity is 5.5 km/s. Obviously you're only going to approach this value in very specific circumstances, but it does provide an upper bound.

A very unrealistic upper bound! Those specific circumstances being:
* Reversing your incoming direction, that is -- following a parabolic trajectory in Titan's reference frame. Not very useful since it implies you're standing still w/ respect to Titan's infinity and following precisely in Titan's orbit from Saturn's viewpoint.
* Assuming you already have a nonzero v-infinity (obviously always true since you're orbiting Saturn, not Titan), you need to fly very close to Titan's center of mass for it to bend the trajectory that much (to get very close to a parabola, not hyperbola). Which basically means flying well below its atmosphere and surface -- not doable.

For all purposes, that upper bound is probably more than an order of magnitude higher than what's realistically doable, especially taking into account the pretty large radius the flybys need to be done -- a consequence of Titan's small density and very extensive atmosphere.