There’s A Lot of Space in, er, Space

Last time I discussed the terraformation of the inner planets and of the Moon, which I think might happen more along the lines of an art project rather than a necessity. An uploaded human can live just as easily in the vacuum of space as on the surface of the Earth.

But planets are actually quite small compared to the size of the solar system. Whenever you see a representation of the solar system, you’ll usually see something like this: a large sun with large planets orbiting around it, with the gaps between planets only a few times larger than the planets itself. But, in reality, the solar system is a bunch of specks orbiting another very bright speck, with vast amounts of space in between. Roughly one million Earths lined up would stretch across the diameter of the entire solar system.

So what if we were to fill that space up as much as we could with places people could live, namely, space habitats? The idea of space habitats goes back decades. It was found in the 1970’s that even simple materials like steel and glass could be used to create giant space stations that could support thousands, if not millions of people in space. In the future, we’d be more likely to use more advanced materials like carbon fiber or even carbon nanotubes, which are lighter and stronger, and so allow for more habitats to be constructed per unit mass.

Let’s assume a typical space habitat is a cylindrical shell 10 km long and 2 km wide. It is so shaped in order to be rotated to produce artificial gravity. At this size 1 g of acceleration could be maintained by rotating the habitat at a little under one rotation per minute. Inside, this will produce a livable space of about 62.8 km2. I estimate that the average human needs about 500 m2 of space for a comfortable living space and area to grow food and other necessities, and accounting for future advances in the technology necessary to create those things. This leads to the habitat being able to support about 125,000 people.

Let’s also assume that the hull’s thickness is 10 meters, and that the average density of the hull is 2000 kg/m3 (made primarily of composite materials). At this size, and accounting for the mass of the air that will fill the inner volume, a single habitat will mass about 1.5 trillion kg.

This is way too large to launch from Earth, even if launched piece by piece and assembled on site. But there are vast quantities of resources in the asteroid belt and they are out of the deep gravity well that makes things so difficult to get into space from Earth. The total mass of the asteroid belt is estimated to be around 3 x 1021 kg. A quick bit of division shows that this amount of matter could be used to construct 2 billion space habitats. At 125,000 per habitat, that’s enough room to support 250 trillion people. That’s old fashioned biological humans, mind you, not the shiny brand-new uploaded humans that severely reduce demand on resources.

Even if we were to admit that A) not every single gram of asteroid material is usable and B) we might want to keep some asteroids around for posterity, it still leaves the potential to support trillions of humans relatively close by.

Of course, why bother terraforming Mars, or moving to a space habitat, if you’re uploaded and can have whatever you want in virtual space (including living on a terraformed Mars or inside a space habitat)? I think, given the vast number of people that exist, and will likely exist in the future, there will be supporters for all of these possibilities, and we’ll undertake them all, not just one to the exclusion of the others.

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