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by Dennis M. Myers, 08/3/2019
When I started putting together the worlds that humans inhabit in the Corporate Federation, I found that Luna might be an exception. What I mean is, we might start colonizing it before we get really good at using resources mined in space to construct orbital habitats. Thing is, once we start building those, we won't ever stop. They will give us a variety of gravitational levels, even within the same habitat, they'll have plenty of light anywhere in the habitable zone of the solar system, and with their enclosed spaces, they will be much easier to keep habitable than a toxic chemical trap like Mars. (Not to mention the dust!)
Luna may well get the full colonization treatment, simply because once we start, we won't stop. Once habitats are built, we'll populate them, then push them out to wherever we want to go.
The curious thing I found is that most people seem to assume that the O'Neill cylinder is going to be the default shape. Sure, there other shapes as well, but I found a paper that did a lot of actual math. The problem with a single O'Neill cylinder is that it's inherently unstable. That's why you always see them as a pair. Counter-rotating within a stable frame. From an economic standpoint, you have to build two at a time. Seems to me like it could be prohibitive, especially if you need to show a profit sooner, rather than later.
The Kalpana proposal looks at different shapes, and shows that a single drum shape is far more stable, and you don't need an enclosing steady frame. You can just rotate the whole thing. The only fiddly bits are where you have ships dock at the axis. Kalpana class habitats are smaller, and cheaper to build. They are scalable, too. There is a website with quite a few images that show what one might look like. I have to admit, I used this site for my reference, along with the math from the paper to create Kigyo Station, Endurance Halo, Croydon Ring, and many of the other habitats in my story. Most are variations on the theme, with a few cylinders scattered in for good measure.
The first complicated part came when I was putting together Kigyo. I needed to know what it was like inside, get a feel for the perspective. It has several levels inside the drum, so I needed to know the gravity for each. I researched the equations I needed, and found some online calculators to help. I started with one gee at the bottom level. I also studied the images at Spacehabs and realized that each level was capable of supporting a three story structure. So I played with that as well. I wasn't happy with my initial results, and realized that since many of the people would be from Mars, perhaps they had a lower gravity. When I ran the calculations for .5g at the lowest level, something magical happened. The second story of the third level had nearly exactly Mars normal gravity. Bingo. Now I knew where Elliot had his main living quarters. Lunar normal was up on Level 7, but that's so close to the center, there are some serious side-effects. I haven't had a chance to work that into the story, yet. Maybe in the third book.
Endurance Halo was another habitat I did for the second book. It's actually the same size as Kigyo, but where Kigyo is all open space with corporate suites along the sides, Endurance Halo has nine full decks. The lowest deck connects to the drum hulls, while the inner decks are all suspended, allowing them a bit of give. While the population of Kigyo is around 3,000, there are over 20,000 people living on Endurance Halo. It's a little crowded, but no more so that of an suburban setting. Kigyo is quiet, peaceful. You have to go looking for those few hidden night spots. The Halo has an open market with a polka band playing in the center. Small shops through the whole area. There's even a carnival we get to explore. Kigyo is a very controlled environment. The gentle smells of flowers abound. The Halo smells like people and food, and everything else.
The really cool thing about the drum shape is that it can be expanded. Want those nice bug dual O'Neill cylinders? Start with a single drum. Get your profit first. Then build another drum right next door, counter rotating. Connect them with a frame, then you can add new segments as you have the budget. But by starting with the one segment, you are already way ahead. The biggest adjustment to the Kalpana design I see in that is the radiator. You will still need to dump excess heat, but their design for the fin might interfere with your picturesque dual cylinder design. You will probably want to mount that on a connecting structure, or come up with some other solution. You will need to dump the extra heat.
And I digress. I'll link to the paper I read down below, and of course, the images are all links to Spacehabs.com. Bryan Versteeg has done some amazing work there. Check it out.
Another great resource I've used is Science & Futurism With Isaac Arthur (SFIA). His YouTube channel has a lot to say on many topics, and I've watched nearly all of them.