Potential

Take a guess

After we now solved the "How?", let's start thinking more practically. Does the asteroid belt even contain enough asteroids for us to build Space Habs out of them? Before breaking down the answer to this question, let's guess. What do you think?

How big of a diameter does an asteroid need to have for us to be able to build a Space Habitat the same land mass as the earth out of it's containing materials? Think about it for a second before revealing the answer if you like 🤔.

Actual material cost

First of all, we'll do the calculation for the result you just revealed. A relatively recent summer study from NASA estimated that for a habitat with a living space of 0.68 km², you would roughly need 10 million tons of material. Since 0.68 km² is 680.000 m², you just have to divide the 10 million tons by 680.000 to get the amount of mass necessary to construct and shield one square meter of living space, which is

$\dfrac{10.000.000 t}{680.000m²} ~= 15$ $t/m²$

Earth has a surface area of 510.000.000 km² of which just 29.2% is land, the rest of it being covered by vast oceans. This leaves us with around 150.000.000 km² of habitable area that we need to supply within our Space Hab to make it habitable for equally as much humans as Earth. 150.000.000 km² equals to 150.000.000.000.000 m² (150 trillion square meters). So now we know both the amount of mass necessary to create one square meter of habitable living space and the amount of square meters necessary, meaning we can simply multiply them to get the amount of mass necessary to build an earth-sized Space Habitat.

$150.000.000.000.000$ $m²$ $*$ $15$ $t$ = $2.250.000.000.000.000$ $t$

Creating our asteroid

Now that we know the amount of mass necessary to build an earth-sized Space Habitat, it's time to make an asteroid out of it so we can understand the result we've been given earlier. For this example, we'll use the biggest asteroid in the Solar System, Ceres. Ceres is so big that it is actually classified as a dwarf planet. It's density is roughly 2 tons/m³. Using Ceres as a point of orientation, this would mean that our 2.25 quadrillion tons condensed into an object with similar density as Ceres would hold 2 tons per m³, giving this resulting object a volume of 1.125 quadrillion m³.

We now have an object with a volume of 1.125 quadrillion m³ and a mass of 2.25 quadrillion tons. Let's put this volume into a sphere and check for it's diameter.

The formula to calculate a sphere's diameter based on it's volume is:

$D =\sqrt[3]{\cfrac{6 * V}{π} }$

So now we can insert our volume:

$D =\sqrt[3]{\cfrac{6 * 1.125.000.000.000.000m^3}{π} }$

= 129.038 meters = 129 kilometers.

Apart from all of these numbers looking gigantic, it would "only" need one asteroid with a diameter of 129 kilometers to recreate equally as much living space as available on earth in a Space Habitat.

Full Potential

The preceding calculation purely tried to solve the size - well, the diameter to be precise - of an asteroid capable of being reconstructed into an earth-sized Space Habitat. How many of those could we really build, though?

Rest assured, this calculation is easier than the earlier ones. Let's start by checking out how many we could build by just harvesting Ceres. Ceres has a total mass of 940.000.000.000.000.000 tons. Since we need 2.250.000.000.000.000 tons for 1 Space Habitat, all we need to do is divide the mass of Ceres by the necessary mass for a Space Habitat to find out how many we can build.

$\cfrac{940.000.000.000.000.000t}{2.250.000.000.000.000t} = 422,56$

Just by harvesting Ceres, we could build over 420 (🥦) earth-sized Space Habitats!

Since Ceres only makes up roughly a third of the mass in the asteroid belt, it can be assumed that over 1.200 earth-sized Space Habitats can be built by harvesting our Solar System's asteroid belt, creating living space for multiple trillions of people at a time.

Summary

As you can see, there is no reason for us to leave our Solar System in the near of even somewhat distant future. Assuming Space Habitats don't come with issues nobody has yet, in the year 2023, thought about, it's save to say they will be one of the biggest contributors to the growth of our species for a long time. Ultimately, they will remain it forever, since even if we get access to other solar systems, most of it's new inhabitants will live in similar space colonies aswell.

However, one question remains: How are we going to power 1.200 of these Space Habitats? Let's find a way to do so in the next chapter.

Additional Resources

1.
Although I took a different approach for my calculations, Robert Walker has a great article about the potential of Space Habitats, which I took a TON of inspiration from.