Let's put a sailboat on Titan

Apr 16, 2014 by Michael Habib, Universe Today
Images from the Cassini mission show river networks draining into lakes in Titans north polar region. Credit: NASA/JPL/USGS.

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn's largest moon, is the only natural satellite known to house a thick atmosphere. It's surface, revealed in part by the Cassini probe, is sculpted by lakes and rivers. There is interest in exploring Titan further, but this is tricky from orbit because seeing through the thick atmosphere is difficult. Flying on Titan has been discussed around the web (sometimes glibly), and this was even one of the subjects treated by the immensely popular comic, XKCD.

However, there remains the problem of powering propulsion. The for flight are quite minimal on Titan, so might work. But Titan also presents an alternative: sailing.

With all those lakes and rivers, exploring Titan with a surface ship might be a great way to see much of the moon. The vehicle wouldn't be sailing on water, though. The lakes on Titan are composed of liquid methane. The challenge is therefore making the vessel buoyant: liquid methane is only 45% as dense as liquid water. This means we would need a lot of displacement. A deep, hollow hull could do this, however, and it turns out that the has an advantage that helps make up for the low density: it is much less viscous than water.

Reynolds number is proportional to the ratio of density to viscosity, and it turns out that friction drag on a hull is inversely proportional to Re. While Titan's seas and lakes have only 45% the density of water, they also have only 8% of the viscosity. This means that the Titan sailing vessel would only experience about 26% of the friction drag as its Earth equivalent. [Yacht designers have found that the friction drag is about equal to 0.075/(log(Re)-2)^2)]. That leaves us room to make the hull deeper (important to compensate for the density as above), and longer (if we want a longer waterline, which will make the bow waves longer and improve maximum speed).

An illustration showing how a sailboat mission to Titan might land and become operational. Credit: Estevan Guzman for Universe Today.

The sail itself would get less wind, on average, on Titan than Earth. Average wind speeds on Titan seem to be about 3 meters/s, according to Cassini, though it might be higher over the lakes. Average wind speed over Earth oceans is closer to 6.6 meters/s. But, the Titan atmosphere is also about 4x denser than Earth's, and both lift and drag are proportional to fluid density. All told, this means that the total fluid force on the sail will be about 83% of what you'd get on Earth, all else being equal, which could be sufficient. There would be a premium on sail efficiency and size, and so we might have to take advantage of the low-friction hull to examine shapes with more stability that can house a larger, taller (and presumably high aspect ratio) sail.

Let’s put a sailboat on Titan
Titan Mare Explorer. Credit: NASA/JPL

This is all quite speculative, of course, but it provides a fun exercise and perhaps provides inspiration as we imagine tall-sailed robotic vessels silently cruising the lakes of Titan.

Explore further: Cassini sheds light on Titan's second largest lake, Ligeia Mare

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HannesAlfven
1.1 / 5 (7) Apr 16, 2014
Re: "The vehicle wouldn't be sailing on water, though. The lakes on Titan are composed of liquid methane."

Science is not just a matter of applying mathematics. One of the reasons why we use philosophy in science is to question our assumptions. The statements above favor the former over the latter, for the observations suggest the HYPOTHESIS that there are methane lakes, based upon a worldview which itself is based upon assumptions and inferences.

In philosophy of science, there is the problem of unconceived alternatives. In this case, we don't know the many ways in which we might have misled ourselves into thinking that there are methane lakes.

This problem pops up all of the time in cosmology. But, in most cases, there is no harm to it, because this is usually just people playing with equations on a computer. But, once you take your worldview and attempt to fund it, then philosophy starts to matter a lot.

So, how do we question our assumptions?
HannesAlfven
1 / 5 (7) Apr 16, 2014
Well, the easiest thing we can do -- when our intention is to engage an issue on its philosophical terms -- is to listen to the critics. In this instance, Wal Thornhill has written extensively on this specific issue. At http://www.holosc...ntists/, he lists out the numerous assumptions which go into this inference for methane lakes on Titan.

Wal suggests in very clear terms, from an alternative worldview based upon an electrical cosmology, that these "lakes" appear like glass because they are the result of electrical machining.

Now, the thing is this: What has typically happened in the past is that Wal's predictions would be dismissed. And that's even the case when they turn out to be correct (as in the Deep Impact mission). But, the scientists on this mission might want to consider that this time could be different, for there are tens of thousands of people who know what the Electric Universe is this time around. And they will all be watching.
HannesAlfven
1 / 5 (8) Apr 16, 2014
And there remains many years -- at least 15, from what I'm seeing -- for the public to learn yet more about what plasmas are, and why they might be machining Titan to have a glassy surface. That's a lot of time for the awareness to rise yet further. The Thunderbolts channel is currently at 3.6 million views on YouTube since 2008.

So, is Wal right? The first instinct, when people see his site, is to attempt to debunk his work. But, based upon many years of observing these patterns, it's clear that people do not imagine that they need to learn electrical cosmology in order to argue against it.

And this suggests that a crisis in public confidence in astrophysics and cosmology, based upon the failure to listen and learn from their best critics, and manifested by a colossally expensive failure, may simply be inevitable.

After all, there is no excuse for refusing to question assumptions, when you have critics that are explaining in great detail why & how your mission is going to fail.
Shootist
3.9 / 5 (7) Apr 16, 2014
lights appear to be on.

nobody's home.
alfie_null
1 / 5 (1) Apr 17, 2014
My first thought is I'd have a lot of concern about grounding the vessel. It wouldn't be much use in exploring the land - we would probably avoid approaching the shore too closely. If accompanied by submersible sensors, it would, however, provide a great opportunity for exploring the bottom of the sea.
FineStructureConstant
not rated yet Apr 17, 2014
Present indications are that the lakes are fairly shallow - the Wikipedia quotes depths less than 8 meters for Ontario Lacus, and at least 8 meters (the radar doesn't sense any greater depths) for Ligeia Mare. So sensing the lake bottoms should not present any insurmountable problems.

I'm wondering if the "coracle" shape is the best for such a craft - am I missing something here (apart from those pesky electric machine thunderbolt thingummies, that is ;-))?
barakn
3.7 / 5 (3) Apr 17, 2014
The southwestern shore of Ontario Lacus was observed to retreat 9-11 km between 2005 and 2009. That's right - Hannes's "glass" drained like water in a bathtub or evaporated like a pot of water on a hot stove. Wal has been fairly quiet about Titan since 2007, Hannes. Unlike you, he could see the writing on the wall.
Sinister1812
5 / 5 (2) Apr 19, 2014
Would they call it the Titan-ic? And would it hit a methane iceberg?
barakn
5 / 5 (2) Apr 23, 2014
Hannes finally saw the handwriting too.