Hello, SFIA audio listeners. In this month's Nebula exclusive, Big Alien Theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content,

check out go.nebola.t.v.tv slash Isaac Arthur.

In order to succeed in space, we must be able to produce as much as possible on-site,

or in-situ, but what are the most critical resources to harvest, and how do we do it?

We are discussing ISRU, or in-situ resource utilization, which includes the collection,

processing, storing, and use of materials found or manufactured on other astronomical

bodies, such as the Moon, or Mars, or asteroids, or even the Sun itself.

So they will be looking at eight broad categories of ISSU, providing shelter, extraction

of volatiles, regular-lith processing, energy production, manufacturing construction, agriculture,

propellant production, and starlifting.

And we'll go over them in that order, because I feel it loosely represents your priority list,

as for instance shelter and extraction of volatiles are what you need to avoid almost immediately

dine from a lack of protection from radiation and vacuum, and get air and water to breathe

and drink. And speaking of drinks, you might want to grab one and a snack to enjoy for today's episode.

You will have brought those on your journey and presumably have some reserves, but they are

your thinnest and shortest margin. You cannot live long without either.

Alternatively, I've put starlifting at the end because while it is your ultimate ISRU option,

short of something probably

impossible like raw matter and energy production right out of the quantum foam or vacuum,

but also requires truly epic engineering and infrastructure to get going.

...