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, and use my code, Isaac Arthur.

Before we build cities among the stars, we'll build factories on the moon.

Our first real step from Earthbound to interplanetary.

Building tomorrow's industry under an alien sky.

It's one thing to dream about gleaming starships or bustling motion metropolis, but before

we ever get there, we have to match the far more humble art of building useful things off

earth. Otherwise, we're forever paying an invisible yet immense tax on every product we loft into

the void, tribute to the tyrannical rocket equation, which demands staggering amounts of fuel just

to send up tiny payloads, and even more to land them on another world.

On top of that, anything we build on Earth has we sturdy not to withstand our gravity, making

it bulkier and heavier, and tough enough to survive the punishing gauntlet of atmospheric

exit at blistering speeds need to reach orbit.

There's only so large or delicate we can make such things.

Survey kilogram of material we can mine, forge, or assemble in a place with low gravity and no atmosphere saves us dearly,

and each lunar weld or extrusion brings us one bold step closer to truly opening the final

frontier. A satellite I build on the moon from structural materials made there does not need

to be able to survive Earth's gravity or a high G launch through Earth's atmosphere, just

the gentler conditions on the moon, and later in space, making it cheaper to build and even cheaper

to launch than the already immense fuel savings from launching from the Moon as opposed

...