Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

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

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check out go.nebula.tv slash Isaac Arthur and use my code, Isaac Arthur.

From Hammer Habitat to Tethereded designs, today we explore the ingenious ways to bring some

gravitas to the final frontier.

Over the last few months, we've been deep diving into various types of rotating space habitats

designed to provide spin gravity to their occupants, ideally allowing families, communities,

and even entire ecosystems to dwell in space. Since we recently explored how centrifugal force

simulates gravity, we won't repeat that here. However, today's habitat design closely resembles the classic

human centrifuges used to acclimate pilots and astronauts to high G forces. These centrifuges are

designed for one person at a time, whereas hammer habitats aim to achieve something similar

on a larger scale. Space habitats like the O'Neill-Near-Bron-Wille,

Stanford Taurus, and Bernersphere all aimed spent gravity for large populations and expansive areas.

In contrast, tethered habitats and hammer habitats are about achieving the minimum structural requirements

to provide gravity for a crew or a living space.

As we'll see today, these designs can scale to very large structures and offer practical

modularity, potentially making them the most common type of space habitat, particularly

aboard spacecraft or mobile facilities.

But why focus on these designs?

We don't yet know the limits of human or ecological tolerance for gravity variance and rotation rates.

However, we have reason to believe that two rotations per minute, RPM, is probably acceptable,

...