primarscources (primarscources) wrote,

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methane on titan

hydrocarbon deposits have been discovered on Titan, a moon of Saturn. had a discussion as to whether or not we ought to mine the hydrocarbons from Titan, apparently assuming some readers would take objection to this clearly non-conservationist approach at getting energy. however, they overlooked a simple fact, which i, having a degree in physics, illuminated for them. here was my post:

Mining hydrocarbons on a moon of Saturn should not be made illegal. There's no reason for such a law. However, there are some issues of practicality to consider.

Hauling 10 million kilograms of methane (the hydrocarbon with the highest energy density) a distance of 9 astronomical units with a constant 0.1 G of acceleration for the first half of the trip, and a constant 0.1 G of deceleration on the second half would take 27 days to complete. The maximum speed (halfway through) would be 1,149,000 meters per second. It would require a minimum of 1.32 * 10^19 Joules of energy to send the material to earth at this acceleration.

Here's the catch: The amount of potential energy contained within the 10,000,000 kilograms of methane is only 5.56 * 10^14 Joules, less than 1% of what we used to haul it. Oh dear. Looks like we need to slow down our spaceship to save energy.

Let's try quickly accelerating up to 30,000 meters per second, coasting, and decelerating back to a stop at the end to save time. Now our trip time is up to 520 days, but our energy usage (assuming 100% efficiency, which is rather optimistic) is down to only 4.5 * 10^15 Joules. Of course, we need to carry the weight of all the rocket fuel, so that adds more energy input. Then there's the production of rocket fuel to consider. Also, rockets aren't 100% efficient at converting potential energy into mechanical energy. So we need to slow down our ship even further.

Let's try accelerating up to 3,000 meters per second, coasting, then decelerating back to a stop at the end. Our trip time now expands to 14.2 years. However, our energy requirement is (with 100% efficiency and massless rocket fuel) is down to 4.5 * 10^13 Joules. Now we're only using 8% of the energy we get back from the methane. It's a really long time to wait, though. In those 14.2 years, we could harvest FAR more energy from other sources, without the huge investment in spaceship technology.

2. If we instead build a base on Saturn's moon, and use methane to power the base, we still need an oxidizing agent (like oxygen). Where do we find oxygen? Oh yeah, it's back on Earth. Darn.

In short, harvesting methane (or any hydrocarbon) from Titan is a waste of time and money. I'm sure NASA has already realized this. Have you?
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