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.tv slash Isaac Arthur and use my code, Isaac Arthur.

This episode is brought to you by Brilliant.

Interstellar space is beyond enormous.

In order to travel between the stars, we will need the power of the stars.

So today we'll be taking a look at spaceship proportion focusing on fusion-based drives,

and we'll be looking at both

the various possible fusion drive systems and what they would really mean in practical terms.

In that regard we will discuss the possible speed such ships might obtain and what sort of

cost we might see for passengers or cargo, both for interplanetary travel and for interstellar

travel, though for the latter especially,

we will have to be rather speculative. This is not our first time discussing fusion as a power

source, so we will skim over some of the basic function and economic impacts that we explore

in our fusion power and impact of nuclear fusion episodes, but we have several different

fusion drive scenarios and each will look very

different. The key ones we will consider for today will be fusion torch drives versus fusion

powered ion drives, the Bussarred Ramjet, Deuterium-based fusion, helium-3 fusion, plain hydrogen

fusion, and post-fusion, which is essentially shooting hydrogen bombs out behind a ship.

The last one, Pulse Fusion, is the only one we currently have the technology for, and folks

are not overly anxious to construct a ship to Mars or Alpha Centauri that would leave Earth's

...