So I'm building a skyhook on Titan...
March 1, 2010 1:20 PM   Subscribe

I working on a piece of fiction, and I would like very specific, esoteric information about Saturn's moon Titan. Who should I ask? What is a good source?

I've checked NASA, JPL, and wikipedia. I am interested in the specifics of orbiting spaceships around Titan, the effects of it's atmosphere at orbital distances, and I have a lot of questions about a potential space elevator on Titan. Most of my concerns are very specific in order for the setting to be realistic.
posted by fuq to Science & Nature (14 answers total) 6 users marked this as a favorite
You could always give outlining your actual questions here a shot...
posted by Artw at 1:29 PM on March 1, 2010

Wikipedia's article has most of what we probably know about Titan's atmosphere. This graphic is pretty awesome. Turns out its atmosphere is actually about 1.5 times as dense as Earth's. Which is weird, considering it only weighs a fraction as much.

I think what you're looking for is less information about Titan per se than information about orbital mechanics, atmospherics and fluid dynamics. Once you know how orbits work, you can take those general equations and plug Titan's information into them.

If that's beyond you, you need to contact an aerospace engineer. This is the sort of thing my aero buddies geek out about.
posted by valkyryn at 1:31 PM on March 1, 2010 [1 favorite]

There are some links to reports about possible future Titan missions here. I agree with Artw - ask specific questions, and we'll give them a shot.
posted by lukemeister at 1:42 PM on March 1, 2010

Response by poster: You could always give outlining your actual questions here a shot...

What is an optimal orbital altitude and how fast would things need to be moving? It is possible to use the atmosphere for lift, like with balloons or helicopters? Would a large collection of vessels be more likely to be in the upper atmosphere, or in a higher orbit? How far away can an orbit be maintained. What special qualities does the upper atmosphere of Titan have, and how would that affect a vessel? If there were ships floating in the atmosphere, how high could they get, what are the delta-v requirements?

Is it even possible to build a space elevator on Titan, given it's slow rotation? Which direction would it face? Would it go toward Saturn or trail behind Titan or what? How long would it need to be and what sort of counterweights or facilities could be stuck on it? What's the deal with lagrange points on something like Titan?

Yeah, I've checked Atomic Rockets. Most of this is simple, I think, but I don't know the math.
posted by fuq at 1:47 PM on March 1, 2010

What is an optimal orbital altitude?

Why do you want to orbit the planet? Observation? Commerce? Bombing? What will you be observing, buying or bombing? A few more details would really help.
posted by Ironmouth at 2:26 PM on March 1, 2010

You may want to read about the Cassini-Huygens mission, if you haven't already.
posted by Lobster Garden at 2:28 PM on March 1, 2010

You may want to reach out to James Nicoll, who writes about this kind of stuff on Usenet from time to time.
posted by Chrysostom at 2:31 PM on March 1, 2010

Response by poster: Why do you want to orbit the planet? Observation? Commerce? Bombing? What will you be observing, buying or bombing? A few more details would really help.

Commerce. Titan's surface is MacGuffin-rich. No one wants to live on the surface because it's so unpleasent, but space travel is advanced so there is a "frontier town" in orbit. There is a space elevator because it needs to break to provide impetus for an story.
posted by fuq at 2:37 PM on March 1, 2010 [1 favorite]

Depending on how you envision your space elevator to work and how this orbiting town is supposed to orbit, you might be interested in something like a geostationary orbit of the town so that it orbits in sync with the hypothetical space elevator which I presume is tied to the surface of Titan somehow. It's fairly straight forward to calculate a rough orbital distance for a geostationary orbit (there is only one fixed distance that will work for this type of orbit... for earth it is 35785 km above the equator. If this is what you're interested in, feel free to me-mail me and I could quickly hash out a number for you.

Then again, you might have a totally different vision of how a space elevator works and want something different.
posted by Diplodocus at 2:47 PM on March 1, 2010 [1 favorite]

Most of the questions you're asking can be answered via knowledge of Titan's atmosphere as a function of altitude. The Huygens Atmospheric Structure Instrument (HASI) was designed to measure this; it sat on board the Huygens probe as it fell into Titan's atmosphere in 2005. I wasn't able to quickly find a published scholarly reference, but this PDF includes a density profile of Titan's atmosphere as a function of altitude. (See page 6.)

Honestly, you might try just e-mailing one or two of the HASI team members and asking them if they or one of their students would be willing to help run a calculation or two. Be up-front that you can't pay them for their time (if you can't), but that you'd be happy to acknowledge their assistance in the finished product. Full-fledged professors might not feel like they had enough time to help you out, but graduate students might have more spare time, and this is exactly the kind of thing that physicists love to think about and run back-of-the-envelope calculations for. Hell, I'd run a few of those calculations myself if I didn't have to prepare for a talk tomorrow.
posted by Johnny Assay at 2:48 PM on March 1, 2010 [1 favorite]

This isn't specific to your particular needs, but the Na(tional)No(vel)Wri(ting)Mo(nth) website has forums that its writers use to ask questions about this sort of thing. Not sure if it's active during this part of the year (NaNoWriMo is November) but I'm sure your questions for outside novels would be welcome.
posted by i_am_a_fiesta at 2:57 PM on March 1, 2010

Interesting. I study astronautics, though I'm not an expert on planetary science. valkyryn's right, I could geek out on this pretty seriously. Unfortunately, I don't have time at the moment to go as deeply as I'd like. But for a start:

Ironmouth is right - optimal altitude for an orbit depends on what you want to do in it. Regardless, you want to be high enough to minimize atmospheric drag. If you're at low altitudes, you make many passes over the surface relatively quickly at close range. Good if you want to see details, but you get a limited slice of the surface to see at a time, and you also pass in and out of range with any ground communication stations quickly. If you're farther out, you see more of the surface at once, but any observations are probably less detailed. It might be desirable to put yourself in an orbit that will match your orbital period to the rotational period of Titan. For Earth, this is called a geosynchronous orbit, and a geostationary orbit is a special (circular, zero inclination) case of this where the satellite stays above the exact same point on the ground at all times. This is handy for things like TV broadcasting satellites, so your ground antennas don't have to keep changing their angles to stay pointed at them.

Depending on how strong the pull of Saturn's gravity is at Titan (I don't have time to run numbers at the moment), you may need to take it into account when calculating orbits and such. If you're staying pretty close to Titan, you could probably get an okay first approximation by pretending Saturn has no effect at all. (The same way you can do pretty good Earth orbit calculations while ignoring the Sun.) If you do care about exactly what Saturn's doing, then you have a three-body problem, and that's trickier to handle.

The surface atmospheric pressure on Titan is about 1.5 times that of Earth - Wikipedia says the same as being 5 meters underwater on Earth. Gravity is low, and the atmosphere is thick, so it should be great for flying vehicles like balloons or airplanes. It's cold, though, and you have to worry about poisonous hydrogen cyanide gas.

I don't know enough about space elevator physics to address that aspect of your questions.

There are Lagrange points in the Saturn-Titan system. (Tangentially related, a couple of Saturn's moons actually carry additional little satellites along at their L4 and L5 points.) What do you want to do there?
posted by sigmagalator at 3:21 PM on March 1, 2010 [2 favorites]

As I understand it, if you want to build a traditional space elevator you want your entire system set up so that it's center of gravity is in a geostationary orbit, but given that Titan is tidally locked, I think you could put the center of gravity in Titans L1 point and let any of Saturn's gravitational effect work in your favor.
posted by Kid Charlemagne at 4:08 PM on March 1, 2010 [2 favorites]

No one wants to live on the surface because it's so unpleasent, but space travel is advanced so there is a "frontier town" in orbit.

One of the classic "frontier town"s in the region of Saturn is the story (and mentions in other stories, particularly Ophiuchi Hotline) by John Varley where "pairs" of humans and plant-like symbiotes float around in the rings. This seems like a more plausible frontier type setting to me, because of the larger space, more available raw materials and hidey-holes. It's also probably pretty easy to get from there to Titan, although I don't know the gravitational potential in the area of the rings.

Your spacers could zip around in one- or two-man ships and live off the water and other matter of the mountain-sized ring rocks, zipping back and forth to Titan and having shootouts or whatever.

There is a space elevator because it needs to break to provide impetus for an story.

Oh. Well, in that case.
posted by DU at 6:52 PM on March 1, 2010

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