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Posted by: Phil Naranjo Sep 27 2012, 07:24 PM

I saw this article today: The Titan Lake In-situ Sampling Propelled Explorer (TALISE) proposes a sending an instrument-laden boat-probe to Saturn’s largest moon.

Read more: http://www.universetoday.com/97611/paddleboat-mission-to-titan-proposed/#ixzz27hR16wOH

I was under the impression that the liquid hydrocarbon lakes of Titan were highly viscous, more tar like? Prior to Cassini, I recall speculation by scientists that Titan might harbor giant waves.

--Phil

Posted by: djellison Sep 27 2012, 07:48 PM

Everything I've read suggests the lakes are ethane/menthane - not longer more tar like hydrocarbons.

Some of the SAR Topo passes have shown the surfaces to be mill-pond smooth.

Posted by: ngunn Sep 27 2012, 08:53 PM

The idea is just too good to give up on. C'mon everybody: TITAN BOAT, TITAN BOAT, TITAN BOAT . . .

Posted by: djellison Sep 27 2012, 09:16 PM

Seems like a lot of mass/complexity to do something that the winds are going to do to you anyway, right? I wish we had the budget to do TiME, CHopper and InSight.

Posted by: ngunn Sep 27 2012, 09:23 PM

Exactly my thought: mass, complexity and, not least, energy for a very inefficient propulsion system. But hey - let's keep the idea flying. NASA is not the world.

Posted by: Eyesonmars Sep 27 2012, 09:31 PM

The lakes of Titan cover only what ,1-2% of the surface? And being seasonal and the result of precipitation they can't be much else besides pure ethane or methane. So sampling these liquids wouldn't tell us much.

Posted by: ngunn Sep 27 2012, 10:04 PM

Earth's oceans are mostly water, but their minor constituents tell just about the whole story of what's going on on this planet now. Trace chemicals from geology and weather mainly, but there's agricultural chemicals, false eyelashes, plastic wrappers and pharmaceuticals in there too. Everything accumulates in bodies of liquid. It's reasonable to suppose that this also applies on Titan, given its weather system's ability to move stuff about.

EDIT: The large northern lakes are not seasonal if you mean by that they disappear once a year. There's too much liquid there. They may disappear and re-form over the longer timescales proposed by Aharonson (Croll-Milankovich cycles) but in my view that would not greatly diminish their value as science targets.

Posted by: stevesliva Sep 28 2012, 02:18 AM

Oh, I'm sure some mechanical engineer would love to figure out how to make an ASRG run a paddlewheel as well as an alternator.

Posted by: Fran Ontanaya Sep 28 2012, 03:10 AM

I think I read liquid methane would be half as viscous as water. Also I think the big waves theory was abandoned too. Forgive my bad memory if I'm wrong.

I'm curious about heat isolation, I wonder how much leakage would make the boat float on a pad of vaporized methane.

Posted by: mcaplinger Sep 28 2012, 04:20 AM

I guess you haven't heard of the carbon cycle on Titan. See http://www.kiss.caltech.edu/workshops/titan2010/presentations/aharonson.pdf for starters. The science goals of a Titan lake mission were rather well studied by the TiME Phase A study, alas not selected. See http://en.wikipedia.org/wiki/Titan_Mare_Explorer

Posted by: rlorenz Sep 28 2012, 07:57 AM

I saw their poster at EPSC yesterday. I'll restrain myself from critical comment but the paddle-wheel thing is rather cute, and in principle is a viable solution to locomotion in a tar-like environment.

ngunn summarizes the situation well : the situation is complex in that there is likely no single description applies to all bodies of liquid on Titan. The Croll-Milankovich cycle in the present epoch favors accumulation of methane/ethane in the north (which is where we see the large seas like Ligeia), so we may expect them to be rather fluid - hence sailing works fine there and you don't need paddles.

The south is drying out, consistent with paucity of liquid bodies seen in that hemisphere, and the rather shallow and possibly shrinking depth of the largest (but still somewhat small) lake, Ontario Lacus. We might expect Ontario to be more viscous than the northern seas and lakes, so a paddle-steamer might make more sense there than in the north. Which is just as well, since the seasonal geometry makes direct-to-earth communication progressively more difficult into the late 2020s from the northern polar regions, so for a 2030+ arrival timeframe Ontario makes more sense as a target.

Posted by: Eyesonmars Sep 28 2012, 01:00 PM

Thanks. I'm not aware of the supposed carbon cycle on Titan. I should have done some additional reading before making my comments. Apologies to all.

I don't make a living in these fields like the rest of you. But my observation as an interested and (relatively) informed but average Joe taxpayer is :
Why limit ourselves to a boat when we could have an aerial vehicle that could potentially sample the entire planet. I even remember reading somewhere that a balloon based vehicle could be designed such that multiple trips to the surface are possible, even liquid landings. ( complexity i guess)

Posted by: nprev Sep 28 2012, 03:08 PM

<Mod hat on> Apology accepted, and please also try to keep your comments on-topic for a given thread. Many alternative methods of exploring Titan have been extensively discussed in other threads on the Forum; I enourage you to explore a bit.

Posted by: Juramike Sep 28 2012, 03:31 PM

The idea of a self-propelled lake probe transecting across a Titan lake is pretty cool (!). The ability to selectively target the shoreline, or a bay or river inlet would provide the bonus of learning about the materials and composition of runoff or seeps. (Might even get lucky and sample during a storm-runoff event.)

Posted by: JRehling Sep 28 2012, 05:16 PM

Titan is unusually diverse as worlds go, and even a highly mobile mission would have trouble sampling half the major terrain types. One hitch is that the terrain types are considerably segregated by latitude and the cheap mobility of floating in the winds will move parallel to certain terrain type boundaries and thus not cross them, at least in a timely fashion.

A second hitch is that a lot of science depends upon touching the surface, so an aerial mission either has to do semi-remote sensing (km high, with still-considerable atmospheric interference; solar illumination has still been filtered by all the haze on the way down) or have some pretty complex moving parts to enable multiple descent/ascent stages. It's a tough cost/science trade off.

Some certainties are: No one mission is going to study all of Titan's interesting terrains in situ. There is no appetite for an immediate flagship-cost mission, so naturally we're seeing proposals for good missions at lower costs. Titan merits at least as about as many dedicated missions as Mars has received, but given the vastly greater distance, it looks like this is going to unfold on a timeline that's painfully slow. People are proposing missions that might return data while they are still alive.

Posted by: vjkane Sep 29 2012, 05:22 AM

I'll echo John Rehling's comments on Titan as a world deserving of many missions. In terms of landing, flying, or floating, it's also the easiest world to explore. On the down sides, it's distance means long flight times, plutonium power sources, and higher power communications systems, all of which means more dollars.

The ease of landing probably makes Titan cheaper to explore via a series of landers, flyers, floaters than with an orbiter (the opposite of Mars). A mission to map Titan in high resolution requires a high power communications system and a high capacity plutonium-based power system to match. Estimates come in at $1.5B up to many B's. A minimal lander mission would cost between $425M (TiME proposal team's assumed estimate) and somewhat greater than $1B (Decadal Survey estimate) for a lake lander, which represents one of the simpler missions. The AVIATR airplane mission (without a relay orbiter) was estimated to cost ~$750M. A simple relay orbiter (like that which is planned for the TALISE lake lander that started this thread) could be fairly cheap compared to a high capability orbiter, but I haven't seen estimates.

Net of all this, for much less than is proposed for NASA's Mars program, we could have a series of missions to Titan (although to be fair, the Titan craft would be less capable than the missions envisioned for Mars -- distance from Earth and the sun extracts its penalty).

TiME would have been a great mission to start a series of Titan missions. Let's hope the the TALISE proposers or another team finds the bucket of money to fly.

Posted by: TheAnt Sep 29 2012, 05:30 PM

That is what I started to think when they mentioned a hovercraft design. That a more or less constant heat leakage would be utilized to collect the methane and contain it under a skirt. So far I can say there's no immediate showstoppers to that idea.

Posted by: rlorenz Sep 30 2012, 12:45 AM

apart from it just not working quantitatively, you mean? Leaving aside the question of how much methane is in the liquid (the present models have it as only a minor constituent in the seas) I expect the condensation flux would be really high - you are essentially having to feed in power to keep the vapor out of equilibrium with the liquid. A good analogy is to watch how liquid nitrogen skitters across the floor when spilled on a lino floor - it does the air-cushion/leidenfrost thing, but the drops boil away in seconds. Hovercraft is just the same thing upside down. It would be a fun physics problem to actually calculate the flux needed on Titan (or Earth with water, for that matter) to support a given mass and/or area of vehicle, but I'd bet it turns out not to be practical.

Posted by: TheAnt Sep 30 2012, 02:23 PM

@rlorenz

Yes I said that with a bit of a reservation.

Since a mission like this would be a first in many ways, and one not the least important that it would be for traveling over a surface / liquid we do not know much about - or hardly anything! So the amount of methane / ethane might indeed be one such showstopper.

Here on Earth we use hovercrafts where conditions vary, and on Titan tholin foam could be problematic.

So I did favour the hovercraft by mentioning since it would overcome the problem that paddles or one propeller working in liquid might have. Being able to travel over various surfaces. Subsurface hydrocarbon could pose a threat by grounding the vehicle. Imagine the camera on this craft on Titan only seeing a perfectly clear surface but might risk getting stuck on such subsurface ice.
And again in favour of the hovercraft, it could potentially continue past the lake and study other locations and materials on one extended mission.

Oh yes I have experimented with liquid nitrogen also, one of us thought it might risk damaging the floor, but for the very reason you pointed out, it crates a cushion of gas so it do not actually touch the floor.

Bottom line is that it might not be practical, even with the low surface gravity.
But I do think that one having one active secondary propeller or turbine to crate lift complicate any design and a risk of a breakdown.
And not the least important, the power requirement for one such would make it unfeasible from the start.

So no I did not envision anything like this one for a Titan mission.

Posted by: atomoid Dec 13 2012, 02:12 AM

i imagine if a http://www.planetaryprobe.org/sessionfiles/session2/presentations/8_hall_tae.pdf inflation payload (if not the gondola itself, or why not both!?) could be structured to drop on its own parachute to float Huygens-style on one of the lakes, we'd get the best of both worlds..

Posted by: vjkane Dec 14 2012, 04:53 PM

The instrument suite proposed for the gondola is very different than the one proposed for the lake lander. The former focuses on remote sensing of the surface and sub-surface while the lake lander focuses on atmosphere/lake composition and lake properties.

Posted by: rlorenz Dec 15 2012, 02:26 PM

I have in fact (on a TV shoot for '95 Worlds and Counting') been on a hot air balloon that ditched briefly in Mono Lake since we were starting to drift away from shore and recovery on the other side would take too much time. Seeing water welling up around my feet in the wicker basket was interesting. We took off again briefly by a few feet and landed on a boat which could push us back to shore to resume filming.

Anyway, point being you can land a balloon rather safely on the surface of a lake, without carrying a parachute. Whether that is the best thing to do with a balloon is of course open to debate.