[X] My Assistant

[algorimancer]

Any showstoppers? I would envision something similar to the upcoming Mars Science Laboratory (RTG's are a given). Lot's colder on Titan... rough on lubricants, and parts would be brittle. Not sure whether the organics would pose a problem in the way of gumming up the works, but it doesn't seem likely at liquid methane temperatures. Smaller world, lower gravity, thick atmosphere... I'm inclined to think that a simple copy of the MSL, perhaps with some added insulation, would work just fine. The only alternative I've been hearing about is a balloon-borne probe, but that doesn't allow the same level of geologic prospecting.

[Guest_BruceMoomaw_*]

This particular note really belongs over in the Venus thread; but the presentations from the second VEXAG meeting have just arrived ( http://www.lpi.usra.edu/vexag/May2006/presentations.html ). In the one on the latest update of the Solar System Roadmap ( http://www.lpi.usra.edu/vexag/May2006/VEXAG_52006_ELLEN.pdf ), Ellen Stofan's group recommends that for the projected Flagship-class Venus Surface Explorer, an "air mobility platform with long traversing" is now "preferred over a surface rover" for Venus as well, logically enough. (Not only does it allow much longer traversing, but in the case of Venus it would also allow the vehicle to land, hastily take a look around and grab some samples for later digestion, and then take off again for the cooler upper atmosphere, thereby reducing its heat burden.)

The one other piece of real news from that particular presentation is that apparently Enceladus has now officially been added to the list of Solar System candidates that may be worthy of a Flagship mission (unless they're talking about a combined Titan/Enceladus mission).

[elakdawalla]

....The one other piece of real news from that particular presentation is that apparently Enceladus has now officially been added to the list of Solar System candidates that may be worthy of a Flagship mission (unless they're talking about a combined Titan/Enceladus mission).

My impression from Ellen's VEXAG presentation was that they were in fact talking about a combined mission.

--Emily

[djellison]

I wonder what sort of mission design you could do there.

A smaller spacecraft to visit Enc rides piggyback on the Titan orbiter which would I presume have a v.large HGA for radar and downlink. It could then act as a relay for the smaller craft.

Doug

[Guest_Richard Trigaux_*]

A smaller spacecraft to visit enceladus piggybacking on a larger ship to Titan?

Two remarks

-The small ship to Enceladus could be a stardust-like sampler harvesting enceladus dust and sending it back to Earth. This poses some constrains on the entry trajectory of the main probe into the Saturn system: to lauch the enceladus sample return in an hyperbolic trajectory to Enceladus and earth, and only after to brake to get in orbit into Saturn. Feasible I think.



-Once empty of fuel, the main ship could stay in orbit around Saturn, or even around Titan if this is possible. Even without fuel it still has RTG power and it could be used as a radio relay, GPS emitter, etc, for further missions, not to speak of course of a permanent observatory: a SAR swath every two hours!!

Eventually this could be a good end for Cassini too, but I don't know if it would have enough fuel to get satellized around Titan, or even in a safe orbit around Saturn.

[Guest_BruceMoomaw_*]

I can't help feeling, though, that this is one pair of targets that really don't get covered very well by a single large spacecraft -- at any rate, I can't think of any way to do so that isn't better done by two separate spacecraft. Time to exercise our ingenuity, I suppose.

Actually, one POSSIBLE way: a single Saturn orbiter drops off a lander (or, in Titan's case, a balloon) at one moon, and then puts itself into a Saturn orbit timed to be resonant with that moon's period of revolution -- so that it makes repeated flybys of the moon to serve as a com relay for the surface spacecraft. Then it modifies its orbit, drops off a lander at the other moon, and modifies its orbit to do the same thing in that case. (The main problem here might be that a Titan balloon will do a considerable amount of wandering over the surface, forcing the main craft to keep modifying its Titan flyby path on rather short notice to stay in touch with the balloon during its flyby passes. I mentioned earlier that Ralph Lorenz says that, as an initial relatively low-cost Titan mission, he'd rather have a nonlanding balloon for a detailed surface survey than he'd like a stationary lander.)

[Guest_Richard Trigaux_*]

Bruce, this is again the idea of a satellite which would serve only as a radio relay. Perhaps such a non-glorious mission will have to be launched, to save money for true science missions, in place of repeatedly lauch the same radio-large antenna-RTG gear. Such a satellite would also serve as a GPS emitter, very useful to precisely locate a lander or flyer.

[Guest_BruceMoomaw_*]

Well, NASA has decided that, for the next few decades, a pure comsat isn't even worthwhile at Mars unless it also does a lot of science studies. This argument is even stronger for the outer planets, since the time between science missions to any of them is so long that the chances are greatly diminished of a pure comsat lasting long enough to do relay duty for two different science missions.

A Saturn orbiter of the type I'm talking about, in addition to doing com relay duty for spacecraft at either or both moons, would presumably also itself do more detailed scientific studies of Titan -- and maybe of Enceladus and other parts of the Saturn system -- than Cassini has. (At a minimum, it would surely map more of Titan's surface, using radar and near-IR. Even if Cassini devotes all of the 15 or so additional Titan flybys it may be able to make during its extended mission to radar mapping, that will still mean that only about 40% of Titan's surface will have been radar-mapped -- which, on a world as varied as Titan has turned out to be, is an important deficit. And Cassini's coverage of Titan's surface in the optimum 2-micron window which only VIMS can use will also still be seriously limited by the end of the mission. I also wonder what it could do at both moons using a radar sounder.)

[Guest_Richard Trigaux_*]

Well, Bruce, I understand the argument.

... I also wonder what it could do at both moons using a radar sounder.)

What do you mean with a radar Sounder? something able to penetrate the ice? I don't know if this is possible, but if so, it would be wonderful. Even looking only some kilometres into Enceladus would perhaps make us able to see the the rising "hot" ice, and water flows if there are.

[Guest_BruceMoomaw_*]

A subsurface radar sounder (like the one proposed for Europa Orbiter) has also been talked about for a long time as an important instrument for understanding Titan, for reasons that should be obvious. At this point, I really don't think we will be able to understand that place without it.

As Ralph Lorenz points out, though, it will be difficult to do subsurface radar sounding at good resolution from an orbiter, simply because any Titan orbiter must stay at a very high altitude above Titan (1500-2000 km) just to keep that moon's vastly extended upper atmosphere from dragging it to its doom in a matter of a few days -- and if you use a radar wavelength long enough to penetrate into the surface of Titan, it will be very hard to distinguish those echoes which return late from very deep directly underneath the craft, and those echoes which return late from shallower depths at places off to one side of the orbiter's orbital path. At such high altitudes for the Titan orbiter, it will be hard to make the horizontal "footprint" of the sounder's downward beam narrow enough to minimize this problem. Therefore, Lorenz uses a subsurface radar sounder as one of his big selling points for a Titan balloon or powered aircraft.

[Guest_Richard Trigaux_*]

Yes Bruce, I understand that radar sounding Titan in the way you describe above would be very difficult, especially without any extra-large antenna. This is my domain, so I can just confirm. Some improvements may come though:
-scanning Titan surface could allow to apply a deconvolution to the information gathered, so this could better the discrimination of side features.
-they could design some extra-large antenna, in a stripline technology with emitting slots, made of a supple material which could be rolled and stored into the spacecraft. But usually such revolutionarry solutions are not retained (or if they are, they often don't work). Perhaps such antennas should be tested first into Earth TV satellites.

On the other hand, radar sounding Enceladus should be easy, as the distance of a meaningful pass is very short. But no radar on a small piggy-back small probe! So I imagine the following scenario:

-The craft enters Saturn system into an hyperbolic trajectory grazing at Enceladus.
-It observes Enceladus springs, radar probe them, image them, and scoop dusts with an aerogel
-it releases the aerogel capsule, still into its hyperbolic trajectory back to Earth
-It brakes like Cassini did and began a more conventional mission aimed at Titan.

perhaps this is not the right order of events, but it may look like that. For instance the aerogel capsule could be released before the Enceladus encounter, with the main ship at a safer distance. But in this case radar sounding is not so good.

[ljk4-1]

Has someone considered a Titan airship that would drop ministations
across the moon and then deposit some explosive charges a short
distance away to record the effects?

The ministations could also serve as weather stations for as long
as they can survive. Hopefully by the time such a mission arrives
at Titan, batteries will last much longer than Huygens did.

Or maybe they could get energy from the moon itself? Perhaps by
converting some of the local chemistry to fuel?

[Guest_Richard Trigaux_*]

Or maybe they could get energy from the moon itself? Perhaps by
converting some of the local chemistry to fuel?

Windmills!!

Green energy!

Nobody expected winds on Titan surface, due to the scarcity of solar energy. But there seems to be noticeable winds generated by tides on the atmosphere.

Are such winds really strong enough to run a wind mill? I don't know. And anyway it will have some drawbacks too. But if it works, it may be a very convenient source of energy for a local station, which could then last one or two years, at least as long as the buffer batteries hold. It's enough to catch titan quakes, if there are, or Titan meteorology.