Sunday, February 17, 2013
Building a Space Station
Let's say you wanted to build a space station--- a big one. How big? Let's say one which would enable you to generate 1 g of artificial gravity. The size would be 1000 yards radius, and it would spin at 1 RPM. This would yield 1 earth gravity.
That only answers part of how big it should be. It is 2000 yards in diameter, since it has a 1000 yard radius. That doesn't tell us how big the livable part of it should be.
Let's imagine contructing one of these things before trying to answer that question. Let's start with a model to work with, such as a spoked bicycle wheel.
You could have spokes leading from the axle to the rim. On the rim is where you would build the livable part. It would correspond to the tire part of a bicycle wheel. Rather than a rubber tire, you would build your living quarters on top of the rim. It would be as large as the materials would support, if that is desired. It should be kept in mind that the weight of the thing would be massive considering that it would be over 3 miles in circumference. Perhaps it would be best to keep it as small as possible. Let's say enough for two levels--- a living level and a transit level. Thus, the structure could be kept simple, like a square. These could be welded together piece by piece as you construct your space station. I guesstimate about 14 feet in height would do for the two levels. If it is a square, then 14 by 14 will set the dimensions.
But how many spokes? In order to keep it even, let's say 1 spoke for every 10 degrees around the rim. That would make 36 spokes times two, as there would be two attached to the axle as per bicycle model.
But that may not be enough. As they rim will be over 3 miles in circumference, each spoke would be covering too much territory. We have 2000 yards diameter times pi, which yields a circumference of 6280 yards. That would yield 174.44 yards for each spoke. We are going to need many more spokes. If you divide by 10, then you would have 17 yards for each spoke, which is close to the size of the living space we are shooting for. That would mean 1 spoke for each degree of movement, or 360 spokes. Two spokes attach to the axle, so there would be 720 spokes total.
You could set the spokes side by side along the axle. Not exactly the same as in a bicycle, which are offset a bit from each other. That way, you attach the two together to make a rectangular living enclosure which would be 34 yards wide at the rim. Keeping it square, we could extend the size to 17 yards all around. It would thus be 17 yards tall, not just under 5. The idea is to make it as uniform as possible. Then everything could be taken up together in sheets of metal that could be welded into place as we build around the base of the rim.
I'm a little concerned about weight as this is a lot of metal.
But there's a lot of space now. Enough for four levels, not just two.
Back to the weight concern. I've done some calculations and the weight of the metal could get prohibitive. If we cut the thickness down to a minimum, the weight may be manageable ( let's suppose so, anyway).
Where would we get all the material? I'm thinking from the moon. It could be iron, which is freed of its oxygen and fashioned into the size sheets we want. It would be launched from the surface of the moon.
Since we need so much of the stuff, that means a lot of launches. You could use a mass driver that would fling it into cislunar space, which then be retrieved and taken to the construction site. Let's say you can do each node for about 50k pounds. That would mean about 360 launches for these alone. You would need a way to manage all this, of course. You would need a way to fabricate the sheets of iron, too. That implies a moon manufacturing site, plus capability to launch.
But back to the station: There would be six pieces for each node. Three for each spoke, as there are two spokes per degree, and welded together into three sides in turn welded together as mentioned above. As each spoke is constructed, it carries along its 3 pieces which are welded into place at its designated spot. That will leave an open area 17 yards tall, 34 yards wide along the rim and the roof. It would be open ended, as each are butted up against the next spoke's node.
Of course, this is all highly simplified. There are plenty of details to work out. One of these would be how would these pieces would fit in a circular object? You would have to compensate for the angles, somehow. I'd figure some kind of interface joint which would allow for the circularity to be compensated and keep to the rectangular modular design, which keeps the main pieces simple to make in a uniform way. It wouldn't be as pretty, but who cares?
What about other factors, like lighting? Could the roof be partly glass to let in the light? That would entail some additional engineering details for the other levels. Keep in mind that the metal is pretty thin in order to keep down weight. Maybe no natural light be used at all. This implies a maintenance schedule to keep replacing burned out lighting.
The inside living quarters and storage areas need to be built out once the superstructure is installed. These details can take care of those other matters just mentioned.
The weight of the space station would be be over 18 million pounds just for the nodes. The axle wasn't discussed.
The axle is where the interface with the outside takes place. It serves as the anchor for the revolving nodes as well. It must be very sturdy as a lot of force is being placed upon it.
A transit tube between the axle and the nodes will allow transport of supplies and personnel as needed. The transit tube could itself be a specially designed spoke.
More thought about those spokes. What would they be made of? I was thinking that they would be made of the stronger materials. It would be sent up in spools and unwound as it was being installed. However, how to keep it taut when the station wasn't spinning? The idea was to pay out the cable a few yards at a time through a metal sleeve. Each sleeve would attach the next sleeve and then pay out more cable. This would repeat until all 1000 yards are deployed. The metal sleeve keeps the cable taut until the station is spun up. The sleeves could be held in a compact way until ready to be used for deploying the cable. That's so you don't have to figure out a way to make 1000 yard long spokes.
How would these work in practice? I'm thinking the sleeves keep everything in place until the station is spun up. Then the forces will tend to pull apart from the center and that will tighten up the cables inside the sleeves.
Such a station as this could hold thousands of people. Would it need to be that big? Perhaps it could be made differently than what I've outlined here. There could be some sections that are lighted and used to grow plants, for example.
The more people, the more capability.
A bit more thought applied to this yields a more realistic design. It may be able to house 720 people. Instead of it being as big as I indicated, I had to downsize it considerably. It would be the same length around the rim, but the nodes would be pyamidal, thus saving materials. It would also be much smaller, saving weight. Even so, the weight would still be 50k lbs or so for each node. I made a drawing for a node to give an idea of what I'm thinking.