Tuesday, June 14, 2011

On Hydrogen and Hohmann Transfers

On some nights, if you know where to look in the sky, if you're out in the middle of the Atlantic or somewhere the light pollution isn't too bad, you can see a bright flash of color, green then yellow then orange into red. Sometimes it even starts in green or blue before working it's way down the sequence. A negligent poet once described them as nature's fireworks, which is completely wrong, since there's nothing at all natural about them. But the best the rest of us can come up with is "bursts of colored light in the sky which serve a purpose other than simply being pretty", but that completely wrecks the scansion. University English Departments tell us they're working on it.

I've been considering the economic aspects of the Terrible Secret of Space, namely what resources we need and where you get them. It's a thorny problem, and in some ways it can't be broken down into component questions. Especially because any analysis of these questions bears on what number and what type of warships can be produced, and therefor the combat aspects of the game as well.

Let's take an example; Hydrogen. Where do you get hydrogen in the solar system?
Potential sources:
Splitting water
Collecting it from Jupiter
Collecting it from the Sun
Breaking it off of hydrocarbons

Now, we don't want to get too much of it at the bottom of a gravity well; too inefficient. So boosting earth water into orbit for hydrolosis is possible, but we don't want that as the main supply. Rather than get water from Earth's oceans, we could get ice from Europa (smaller gravity well) or the rings of Saturn. We can say there's infrastructure out that far if we need to, but let's take a look at the other options.

Jupiter's atmosphere is largely composed of hydrogen. It should be possible to skim off some of the higher atmosphere. Sort of a reverse gravitational slingshot effect; you lose energy but you fill up your fuel tanks on your way through. You don't have to worry about Jupiter's gravity well either; since you're starting at the top you aren't losing much energy going down and back out again. You could also do this with other gas giants, or even the sun, assuming your shields can stand that close to the sun. In the Mote in God's Eye, the book which I lifted the shields from, a spaceship makes a trip inside a gas giant, so it might be possible. I'm going with awesome, but not economical. If you're not diving into the sun, there might be a way to collect the charged particles of the solar wind, combine them into hydrogen and use that as a fuel source.

The last option, hydrocarbons, is pretty speculative. I mean, it's not that different than boosting water for splitting, if more efficient by mass. But hey, it's possible we'll find hydrocarbons in the sky. There's an assumption that these things are only produced by life forms, but I'm not sure how true that is cosmically. Carbon and hydrogen exist in great abundance in the universe, I should think we'd be surprised if it didn't ever come together otherwise. Then again, I really don't know enough about chemistry to really say much about it. So if all else fails I guess we could Word of God a stellar source of hydrocarbons into the system. A lot of all else would have to fail though.

Let's move on to the other half of the problem for now. There are going to be asteroid miners, there have to be asteroid miners. Presumably they're out there mining metals to send back in to the orbital factories. But how exactly do they ship the materials? Again we have to pay attention to the laws of commerce to make sure this works the way we want it to. Barring the interplanetary transit network, the most energy efficient way to get from one orbit to another is a Hohmann transfer. It has the great advantage of only requiring you to accelerate once at the start and decelerate once at the end, saving immensely on gas.

Hohmann transfers have two problems; one is that it takes a very long time to switch orbits (in college I remember calculating that it took two hundred some days to get from Earth to Mars this way), and the other is that you can only leave at certain times. (Once you got to mars, you'd have to wait the better part of a martian year to return on another Hohmann transfer.) On the first issue, a couple hundred days isn't much of a problem; getting the materials a known number of days from now just requires more planning on the part of the manufacturies in question. Not something we have to concern ourselves with. Er... with which we have to concern ourselves.

Only certain launch dates being allowed gives us a bigger problem. I'd have to figure out where certain asteroids are at each point in the game, work back to the previous hohmann transfer window, and figure from there when Earth will receive it's goods. A lot of calculation, which I'm not particularly eager to do. It gets worse if you realize that I'd have to do the same calculations for materials from any other source in the solar system; the mines of Mercury, for example.

If it was a spaceship moving along these transfers, it'd carry an engine along to do the accelerating. We could lash engines to the rocks, but that adds a lot of difficulty and expense to the mining. It'd be a lot easier if you could set up a cannon in the belt and fire the rocks down with that. But you'd need something to decelerate once you got to Earth orbit. The good news is, we already have an in game system for decelerating large rocks; the Langston field.

Supposing you had a large Langston field generator up in orbit. You've got an asteroid coming in, which needs to be stopped before it can be stripped of it's metals. So you maneuver your asteroid or your shield so that the former strikes the latter. The shield stops the asteroid's momentum, giving off the energy as heat and light. You move the asteroid away from the shield with some sort of tug boat, and you're ready to collect another. Neat as that.

Next question: why do we have only one of these catcher's mitts? Let's say we had fifty two of them, spaced evenly in Earth's orbit around the Sun. The reason why Hohmann transfers have required windows to start them is that you need to connect your orbit with the target planet's orbit, if you get there but the Earth is several months out you've got nowhere to land. But if you're just targeting the orbital path itself, you could launch one off whenever, and get it caught on whatever mitt is available at the time. The orbital factories get dragged around the sun with the Earth, and they'd pass a mitt every week. That means a consistent influx of new raw materials. Best of all, I don't have to calculate a thing.

It gets even better; your Langston field doesn't just catch huge chunks of silicate, it also stops things like radiation. In particular, I'm thinking of the solar wind. The solar wind is a stream of charged particles from the sun, mostly protons and electrons. As long as you have a Langston field in the solar system, it's going to be absorbing these particles. So we invent a scoop, which will swish through the field every so often, combining the charged particles into hydrogen. In addition to the function of asteroid catching, we can use these stations to collect hydrogen to fuel the fusion engines of the orbital factories as they swing past every year.

Even more than that, every warship in the game is going to have one of these field generators on board. If we also equip them with a scoop, we never need to worry about refueling them; they'll subsist off of the gleanings of the solar wind. As someone who's never liked the upkeep of manually refueling spaceships in games, I'm pretty happy about that.

The other consequences of this system are Here's another thought; what about using Langston fields for re-entry? Take a place in Arizona, middle of the desert in case something goes wrong. Put up a number of shields so that a patch of desert acts as a great catcher's mitt. You can drop things from orbit, land them on the shield and collect them from there. It might work for raw materials, but I can't imagine that the deceleration would be very pleasant for persons or manufactured goods.

Also? We now have established the existence of multiple rock throwers in the asteroid belt, which could easily be re purposed as weapons. I'm not at all unhappy with this development.

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