Habitat clusters

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Destructionator
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Habitat clusters

Post by Destructionator » Sun Jun 06, 2010 4:06 am

My opus magnum sci-fi epic (I'm just a regular Frank Herbert) up in the literature forum is actually the first time I've seriously pondered the layout of the habitat clusters. Previously, I was just like "yeah, they're there, and they're clustered". Now, I have a bit of a plan.

There's three levels to a group of space habitats, on a physical level:

a) The individual hab. It would consist of the living area, its agricultural ring(s), and any zero-G industrial shops or captured asteroid floating around in its general area. Aside from angular momentum tending to an annoying burn being necessary to stay pointed at the sun in the long term, they should be fairly self-sufficient.

b) A pair of habs. To solve the annoying gyroscope problem, a simple and cheap fix is to tether a habitat to its twin. During construction, they can spin each other up, and after construction, they keep the same angular inertia, with a net zero internal rotation, meaning they point to the sun forever with minimal maintenance.

Transit between a pair is very easy, but aside from that and being tethered for physics, they aren't any more intertwined than any other random pair of individual habs among the cluster.



c) A cluster of pairs. This is the new thing. Physics suggests that habitats should be paired, but there's no such thing with a cluster. Clusters form for "people" reasons; people want to be close together perhaps for economic advantages (easier transit and trade), or perhaps for tribal reasons (be close to your friends so if needed, they can bail you out of trouble OR, be close to your enemies so you can keep them under control), or any other reason why people would like short, easy travel times.

I've been thinking about what physics would suggest for this layout. I'm growing to like the idea of a polygon ring - that is, a bunch of pairs arranged in vaguely a circle, but the connection between any two neighbors is a straight line, instead of a curve like you'd get in a proper circle.

The reason comes back to what we saw in the early one space travel segment in the story (that is new as of me typing this), which is in turn, taken from an idea Dr. O'Neill proposed in his book, The High Frontier.

(His idea was applying to cylinders tethered together, but I will be applying it to the whole cluster here. He also would have made the shuttles simpler than my own - not having an engine nor crew at all - but I'm putting them there in case of mistakes and to correct for different habitat sizes across the cluster. The former case could be avoided by having emergency vehicles on call to rescue people who have an accident; it should be rare anyway, so this works. But rockets would definitely be needed in a cluster with varying habitats... of course, if all are the same model, you could avoid that.)

Anyway, the idea is to use the habitat's rotation to provide you with your initial speed, and the destination habitat's rotation to provide you with your stopping speed. Your kinetic energy is borrowed from the habitat's rotational energy, so it costs your vehicle nothing - no energy, no propellant.

In the case of moving to a tethered twin habitat, you then give that energy right back to the habitat system when you stop! Thus, we have high speed, yet extremely efficient travel. In the case of going outside the pair, this would slowly change the rotation of the two habs. But, assuming about equal travel all around the cluster, it will all balance out. And, even if it doesn't, the mass of a shuttle is many millions of times less than that of the habitat, so the problem is slight anyway, and can be corrected by rocket burns if it gets big enough to worry about over time.

(This is exactly the same as launching something from the Earth's equator. The launching spacecraft is borrowing some rotational energy from the planet to get going. In theory, if millions upon quadrillions of spacecraft were launched in this manner, the Earth would lose all its angular momentum and stop rotating! But, in practice, it isn't a concern since Earth is fucking massive. In a space habitat, the mass difference brings it down, but you'd still think about it, since they depend on angular inertia being precise to keep the sun shining in through its mirrors.)



Anyway, taking this mode of transportation, how would we lay out the cluster to take advantage of it? Well, the straight line ring is it! You want to orient the habitats such that the next hab on the trip is tangent to the last's rotation.

Let me draw a picture:

Image

The black lines represent the physical tethers between habitat pairs. The green arrows are the direction of rotation of the individual habs, and the red lines show tangent lines - the path a space car could take for easy travel between pairs. The angle here is if you were the sun looking at the cluster. (The reason for this is so the sun shines right into the mirrors on the end caps.) This has some minor orbital implications, but the size of the cluster is virtually nothing compared to the distance to the sun. Might - might - be an issue in Earth orbit though. Worst case, they tether the ring together (meh), or just simply burn every so often to stay in formation.

Also, note that this picture isn't remotely to scale. The twin habitats of a pair might be as much as 50 miles apart - and if you assume 4 miles wide, you can see the scale really break down here. But, it does serve to illustrate the motion involved.


The habitats are all arranged so the pairs point in<->out with the center of the cluster ring for the main reason of keeping the traffic lanes relatively clear. With this layout, you have a steady two way connection between the inner portion of the ring, and a separate two way connection with the outer part of the ring.

These inter-part connections would have very little in the way of intra-pair connections, which would follow an extension of the red lines. Notice how there's only one arrow on the inside of the two circles: they have the same motion there. If you release at a 45 degree angle while moving toward the inside, you'll fly across, and reach the other cylinder at a relative stop to its location. If this was to scale, I'm thinking the lines for inside and outside wouldn't line up, but in this picture, they basically do.

The same thing works for inter-pair connections. See how the green arrow at the leaving point is the same direction as at the receiving point in all the cases? That's your ticket to free travel.


What you get here is a kind of two way highway, with every adjacent habitat easily accessible from its friends. From the one at the very bottom of the image, you can do the diagonal up to get to its tethered twin.


There's more cool to the ring layout. You have those diagonal lines, but there's also straight lines right across the cluster! Like the inner circle at the bottom to the inner circle at the top. Boom.

You can go almost anywhere from anywhere, without burning any propellant.


Next time someone says "habitats suck because space travel is hella hard", think about this result!


The next thing is scaling it up. How many routes can we get without hitting each other? My gut says a diameter of about 400 miles with 20 pairs will give you a big set. You can have over 50 miles between each one, so each angle should be free. But I'll have to draw a real scale model, or do some detailed math to determine for sure. BTW, this gives a population for the cluster of ~ 400 million assuming Island III size and density for each, with no part of it being more than 400 miles away from any other part.

But, this is about what I'm running with in the story. Releasing from a 4 mile wide cylinder across the 400 mile gap is about a 1 hour ride, no propellant needed. (Though, the destination hab in the story is smaller than the origin, so they will have to do a small burn to match speed. You'll see.)

But yeah, 400 million people, all no more than 1 hour or so away from anyone else, at zero cost. So much for space being a pain, eh?



Final question here: how did the body get discovered? Everybody leaving would have the same speed right? Well, the key here is there are more like 20 pairs instead of the 4 in my illustration here, and they are not all the same size, so speeds change. There's a lot more routes out there. Details beyond that get into spoiler territory, so I'll leave it a here for now. You'll see soon enough.


On, one last thing. What about transit between clusters? Easy - instead of taking the tangent toward the center of your ring, launch toward the outside. Harder to get to another cluster than somewhere inside your cluster though, which will have some meaning when it comes to immigration and warfare.


Gotta go, I'll come back to this later, and should be able to draw an actual map!
Last edited by Destructionator on Sun Jun 06, 2010 4:49 am, edited 1 time in total.
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Re: Habitat clusters

Post by Destructionator » Sun Jun 06, 2010 4:35 am

Afterthought: either a gyro or a little tiny wee bit of propellant will be needed, or you could get a twist as you leave (which is what Dr O'Neill proposed). The reason is you have to do a 180 degree roll to meet up with the destination; you'll be upside down relative to it without that roll. At least in the case of intra-pair transits.

For inter-pair, it shouldn't be required in a lot of cases. Only if you go from the inner ring to the outer ring do you need it I think.

But, this is just a small rotation; still a tiny expense.

side note: even without the rotational velocity, the expense of traveling around a habitat cluster is tiny. I'll post the tech specs for the space car and space hummer in a while and explain the reasoning behind the prices.

oh and the energy of a space car traveling such? ~80 megajoules for 4.5 tons launched from a large hab. If you smashed into a habitat, it'd cause some minor damage. To prevent this, you'd probably see traffic control radars keeping an eye on approaching things (also serves to watch for accidents too), and maybe police tugs going to fix the vector.

seriously one last thing, you might be able to add another "ring" outside this one. Just like this setup, but a larger radius of the circle. Go too much and the orbital issues will surely arise, and there might be traffic problems even with the relatively simple case.
His Certifiable Geniusness, Adam D. Ruppe (My 'verse)
Marle: Lucca! You're amazing!
Lucca: Ain't it the truth! ... Oh, um...I mean...
Marle: Enough with the false modesty! You have a real gift! I would trade my royal ancestry for your genius in a heartbeat!

"I still really hate those pompous assholes who quote themselves in their sigs." -- Me

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Re: Habitat clusters

Post by Destructionator » Fri Jun 11, 2010 4:31 pm

Another thing to put in the ring will be laser stations. On the habitat endcaps, or perhaps floating right in front of it, are laser communication sending/receiving stations.

One points up and down (on the diagram) to talk to your twin. The others can point left and right. to talk to your partners in the ring. There may be yet more connecting multiple clusters together.

Laser communication can provide good bandwidth and latency without needing a physical connection between them. Since the straight line is wanted for transportation, the laser works on the same principle. Regular radio would be fine too, but the laser seems even better.


A message can fly around the ring, or might have stations pointing to individual habitats for a speed boost. Flying round trip around the ring has a light speed lag of single digit miliseconds; quite negligble, but the electronics at the sending/receiving stations may add to that, so a direct path is surely a bit faster than the round trip.

But, the speed of this network would certainly be excellent. In addition to easy transport, the ring setup provides for easy real-time communication all around.



Now, inside the habitat, you have two options to connect: one is to run wires to your house, or to wireless stations all around, just like we do today.

Another is to have a shared wireless connection. It could be in the end cap (Dr O'Neill proposed this in The High Frontier). The shape of the cap might be shaped to act like a dish to help boost the signal, but it needn't be too fancy.

The distance is no more than 20 miles for people in most habs, and will be a straight line in many cases. A simple roof dish could do the job.

More reliable though, I'm imagining, would be relay stations that talk to the main endcap. So every so often, you see a pole with a microwave antenna on it, pointed straight to the endcap. It picks it up and repeats the signal for local wi-fi. It might also use poles and wired links to the main station.


However it is done, a pretty simple system can do the job and provide fast wireless network to almost all points in the cluster, to all other points. The inside ones have the fast internet/laser links, and stations or ships outside can use regular radio links to easily connect.


These outside radio signals that the ships (and zero-g stations) would probably be intermittant inside the habitat; the hab's hull would block the signal, but it could probably get in through the windows. But, the hab is rotating, so you won't get it reliably.

The main antenna would be on the outside, in the non-rotating section, and there might be some on the surface of the hull too. Still, this would be mainly for outsiders connecting to the net, so it needn't get directly inside. If someone wants to run a private radio antenna, he might need to get permits to open a hole in the hull in a few locations, and have a relay station outside for a reliable link. Probably not common, since the shared internet works better anyway.

(of course, if you're an ISP, you'd go ahead and do the hassle anyway. or maybe buy those laser stations at the end cap. Private ISPs might try to cater to specialised needs that the public net is too slow for; the private laser stations can do a direct connection somewhere with a lot more bandwidth available. Then, you'd just need to run the connection to your house - a rooftop dish talking to the endcap would probably have the cheapest installation.)
His Certifiable Geniusness, Adam D. Ruppe (My 'verse)
Marle: Lucca! You're amazing!
Lucca: Ain't it the truth! ... Oh, um...I mean...
Marle: Enough with the false modesty! You have a real gift! I would trade my royal ancestry for your genius in a heartbeat!

"I still really hate those pompous assholes who quote themselves in their sigs." -- Me

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