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.

Our progress in the field of rocketry this last decade has been amazing, but to reach a

future in which millions can travel to and from orbit every day, we will need freeways and

train tracks to space itself.

So today we are going to be looking at a space launch system, the tethered ring, that is

a cousin to the mass driver, orbiter ring, and Lofstrom Loop, three of our favorite active

support launch systems.

Now, each of those has its own episode in our Upward Bound series that you can watch for

details, and it seemed right that the tethered ring should get its own episode in our Upward Bound series, that you can watch for details, and it

seemed right that the tethered rings should get its own episode too. It's a fantastic idea

for hanging a non-rocket-based launch system in the upper atmosphere that could make launch

cost orbit around Earth as Cheba's air travel around Earth, and indeed could make travel

around Earth a lot

faster and cheaper, too. If you haven't seen any of those episodes, they are not prerequisites

to understand today's topic, but a basic understanding of them is helpful to understand how the

tethered ring works, as is an understanding of active support, so we will cover them briefly today as a prelude

to the tethered ring.

It might be helpful to think of the active support in a tethered ring as a system for simply

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