Manned Landing On Titan, Issues & Answers? Options

[Juramike]

Combustion is not my field but I'd be surprised if 2%, or even the saturation level of 5% or so methane would be a sufficient concentration to support combustion with oxygen, especially starting from cryogenic temperatures.

I'd be more concerned with higher hydrocarbons and other organic brought in by the astronauts. Some of that stuff might melt as it gets warmer and could support combustion inside the living module. For example, hexane (solid at Titan's temperatures) might get tracked in on the astronauts boots or clothing, and it will volatilize and support combustion quite nicely in a 20% O2/N2 environment. (Diethyl ether would be even more impressive)

-Mike

[nprev]

Eek. So, outside-only booties & gloves stowed in the outermost airlock might be a very good idea, then? (Don't know what to do if anybody fell down outside & got this stuff on their suit, though...maybe an entire overgarment is the answer?)

EDIT: Got it! One stage of the ingress process should be pure N2 @ 300K to evaporate all this crap over a suitable (ta-da, da!) interval, then purge it out...afterwards, normal re-entry.

EDIT2: The process of going back inside is going to be a LOT like standard military chemical warfare decontamination procedures; gee, what fun.

[tty]

20 % O2 would seem excessive (and probably unhealthy) at 1,6+ atmospheres. 10 % should be enough for breathing as well as decreasing fire risks and the quantity of oxygen needed.

As for leaks from an overpressure habitat it seems likely to me that small leaks might well be self-sealing since the water and the CO2 in the interior atmosphere would freeze instantly at Titanian temperatures.

[nprev]

Hey, that's a great point about self-sealing leaks, tty! Guess that periodic inspections/maintenance would catch these so the crew could spackle them over.

Hot wiring faults to the outside are still worrisome, though. Might be best to have all that stuff completely outside the main habitat with its own power supply and an RF link to the inside, and THAT thing would have to have some serious ground-fault interrupt protection.

[Juramike]

Hydrocarbon solvents have a very low electical conductivity. Flowing hydrocarbon solvents (like methane, I suppose, but more OSHA data exists for hexanes) tend to build up static charges.

I wonder if a methane rain event on the outside of the habitat would build really impressive levels of static charge? In the "natural" environment, I also wonder if methane flowing along a Titan river stream might also build up an impressive static load.

"Solvents and fuels produced from petroleum (e.g., benzene, toluene, mineral spirits, gasoline, jet fuel) can build up a charge when they are poured or flow through hoses. They tend to hold a charge because they cannot conduct electricity well enough to discharge when in contact with a conducting material, like a metal pipe or container, that is grounded. When enough of a charge is built up, a spark may result. If the vapour concentration of the liquid in air is in the "flammable range" and the spark has enough energy, a fire or explosion can result."

Source: http://www.ccohs.ca/oshanswers/prevention/...ble_static.html

Since there is no oxygen in Titan's atmosphere, fire or explosion is not an option. But could "ground lightning" or spark discharges occur in the flowing streams?

-Mike

[nprev]

Think that would depend on the composition of the surrounding terrain, which is probably water ice with a lot of organic impurities (my guess is that on Titan H2O takes the role of SiO2 on Earth). Liquid water on Earth is significantly conductive only when it has dissolved salts or metallic ions, IIRC; don't know about ice. If the channels are carved out of good insulators, though, there well might be a good-sized charge in the fluid (and maybe also the atmosphere itself at times?)

Scary thought, though; in addition to grounding the hell out of the habitat, surface explorers may well have to have conductive suits with grounding straps dragging on the "soil" to avoid being zapped! (I have a mental image of spacesuits with dragging tails, but it's almost too stupid-looking to bear...beats blowing up, or frying the suit electronics, or even being electrocuted, though.)

Anyone else getting surprised at how un-easy surface exploration of Titan may turn out to be? That nice, thick atmosphere seems to have led to a false sense of security...

[dvandorn]

All in all, though, Nick, Titan offers more of the raw materials humans would need to create a self-sustaining colony than just about any other body in the Solar System (except for Earth).

There are all the elements we need to survive -- specifically, carbon, hydrogen, oxygen and nitrogen -- in great abundance. The only thing in short supply is a good power source. Yes, if you crack enough oxygen from the water ice you'd be able to burn a lot of the hydrocarbons, but that burning would generate less energy than what you'd need to crack that much oxygen out, I fear.

The one thing we'd need to import from Earth is a good energy source to make Titan a good place for human habitation. Unfortunately, the only thing I can think of that would work well there would be nuclear energy, and you don't want to have to transport megatons of fissile materials all the way out to Saturn! (You think you have issues with the anti-nuke crowd *now*...)

-the other Doug

[tty]

Yes, if you crack enough oxygen from the water ice you'd be able to burn a lot of the hydrocarbons, but that burning would generate less energy than what you'd need to crack that much oxygen out, I fear.

On the other hand heat engines should be very effective on Titan because of the very low ambient temperature. It will take some exotic engineering to make full use of heat engines where the cold end is at 90 K, but the end result might be spectacular. Think of a steam turbine, then you use the waste heat from the condenser to heat the habitat, then you use the waste heat from the habitat to run a carbon dioxide based stirling engine then you use the waste heat from that to run a methane based stirling engine....

Unfortunately, the only thing I can think of that would work well there would be nuclear energy, and you don't want to have to transport megatons of fissile materials all the way out to Saturn!

Why not? Uranium-based reactor fuel is almost completely harmless until it has been irradiated.

[dvandorn]

...you don't want to have to transport megatons of fissile materials all the way out to Saturn!

Why not? Uranium-based reactor fuel is almost completely harmless until it has been irradiated.

I was actually thinking about the extremely high mass of fissile materials. Takes a lot more energy to send a cubic mile of uranium to Saturn than sending a cubic mile of, say, lithium batteries.

-the other Doug

[djellison]

Takes a lot more energy to send a cubic mile of uranium to Saturn than sending a cubic mile of, say, lithium batteries.

You're not looking at that the right way. How much energy does it take to send, say, 1 MWhr of energy in the form of Uranium. Now how much energy does it take to send 1 MWhr of energy in the form of Li cells? You are assuming 1 kg of battery provides the same amount of energy as 1 kg of Uranium.

Doug

[dvandorn]

Oh, I understand -- uranium has a higher potential energy density than a lithium battery. I'm just thinking in terms of logistics. Any plan that requires bringing along enough fissile materials to support a manned base is going to be harder to accomplish (in terms of just getting everything to Titan and setting it up) than a plan that can actually draw enough power for its operations from indigenous sources.

Titan is just so energy-poor... you'd need to cover hundreds of square kilometers of landscape with solar cells to get anything useful at that distance from the Sun and through that thick haze. And you just can't extract heat out of a system that doesn't have any...

-the other Doug

[djellison]

Any plan that requires bringing along enough fissile materials to support a manned base is going to be harder to accomplish (in terms of just getting everything to Titan and setting it up) than a plan that can actually draw enough power for its operations from indigenous sources.

Not really, no. It's entirely dependent on the mass of a small reactor compared to the mass of whatever equipment and resources you bring along to use 'indigenous' sources (such as taking O2 to burn local material) I would also have thought the former would be simpler and more reliable. That one would be heavier than another is not certain.
Doug

[ngunn]

Has anyone mentioned 'hydro'power? All you need is a lake on a hilltop - or one with tides. There could be 'geo'thermal possibilities too, and wind power.

[nprev]

All in all, though, Nick, Titan offers more of the raw materials humans would need to create a self-sustaining colony than just about any other body in the Solar System (except for Earth).

-the other Doug

Oh, I completely agree; think Clarke got it exactly right in Imperial Earth...Titan will someday be the equivalent of Saudi Arabia just because most of the rest of the Solar System is so volatile-poor and because it's cheap in terms of energy to lift the materials off.

The energy generation problem is thorny, though, and I don't see any practical alternatives at all to fission reactors at this point. Hopefully by the time we get there to stay--thinking about 200 years from now--we'll have solved the fusion power problem in a cheap and highly portable fashion; no worries then!

EDIT: Doug's comment about importing O2 got me thinking. Maybe all we really need is a "seed" energy source, and by this I mean something to establish an initial energy generation process that's used to fire off another process using indigenious resources which in turn becomes self-sustaining...sort of like striking a match. (Sorry for the generality.)

[Juramike]

Nigel nailed it! There are lots of really good energy sources on Titan:

Wind - wind speeds low but fairly steady, but atmosphere is thicker than on Earth. And dunes give a great indicator of funneling of winds from topographical features. (Double Bonus, we can use dune features visible NOW to select best places for wind farms!)

"Hydro" - If any of the polar streams are flowing at rates even close to those predicted by dimension, there's a massive potential for methane fluid flow.

Geothermal - Findind a fairly recent crater could allow you to trap residual heat from liquid water-ammonia. Also, there might be circulating fluids down deep (molten water-ammonia? molten organics?). Water has good heat capacity due to it's phase change energy. (It releases lots of heat on crystallization)

Chemical - There may be natural organic ore bodies that could be useful for energy production. For example (and I'm speaking off the top of my head - someone would need to look at the energies to see if it would be useful), a deposit of pyridinium N-oxides might be equivalent of a fuel deposit on Earth. (Pyridinium N-oxide could be used as an oxidant). There could be other potential reactant bodies lying around (or easily mined) that are prevented from reacting due to kinetic barriers from normal Titan conditions. Add a catalyst, or enough heat to overcome the barrier, and bingo, you've got an energy source. (Maybe not as impressive as fire, but any exothermic reaction helps!)

Finally, what are then energies involved in splitting water, taking the oxygen, then burning hydrocarbon? (This might be "carbon neutral" on Titan - since you are swapping one IR absorber for another)

What are the energies for:

H2O --> H2 + O2 [uphill]
O2 + CH4 --> CO2 + H2O [downhill]
H2 + C2H4 (or C2H4) + cat --> C2H6 [downhill]


Titan has oodles of potential energy sources. We've got evidence of wind (Huygens drift and dunes), evidence for permanently flowing liquids is tanalizingly close, and exploitable chemical and geothermal sources will require more research and examination. (So surface exploration serves two roles: science and energy prospecting).

-Mike