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Let's say there are billions of asteroids in the galaxy, varying in size from baseballs to hunks of rock almost big enough to be dwarf planets. If someone wanted to set up a habitable location on one of the larger ones (house-sized or bigger), what kind of device and/or materials would be needed to give one of these asteroids a breathable synthetic atmosphere?

Here are some things to note:

• These asteroids will be used for a variety of purposes, ranging from small pawn shops to gigantic shopping malls to apartment complexes to maximum security prisons.


• Faster-than-light travel is used in this universe, allowing people and supplies to be moved across the galaxy in weeks rather than millions of years.


• Atmosphere must be similar to Earth. Earth-like gravity can be left up to handwavium.

You need to build a very robust greenhouse all around the asteroid, practically wrapping it (or the area you want to provide with atmosphere) into the structure.

If it is limited to hosting humans, you can make the greenhouse just a couple of meters high above the surface, provide adequate protection against micrometeorites and space radiation (a couple of meters of air won't stop any energetic radiation coming from space, like instead our earthly atmosphere does) and ensure that there is something providing air circulation (with very low gravity also convective motion will be limited, and you don't want to suffocate just because you were not moving and a bubble of CO2 formed around your head) and regeneration.

1. Hollow out asteroid.


2. Pump asteroid interior full of your favorite breathables until at your favorite pressure.

This could be done with our own tech and it is a good idea. Asteroids are already up there. They are fine radiation shielding. You could hollow them out with focused sunlight, letting the molten metal spill into space or have people with explosives and hammers do it 1800s style. It is not a particularly novel idea. https://www.earth.com/news/hollow-asteroids-generation-ships/

Any sufficiently advanced technology is indistinguishable from magic.

FTL implies a high tech level. It is not a big stretch to assume that possessing FTL technology also means you have gravity control. With gravity control, you can retain atmosphere even on a small asteroid.

So, whatever unobtanium you use use for FTL can also be the key to gravity control and atmospheric engineering. Or you may simply assume that you also have gravity control via an unrelated technology and possibly a separate unobtanium.

Expanding on some of the comments: if you are bestowing Earth-like gravity on these asteroids anyway, then your problem is more or less solved. Just dump an appropriate amount of Nitrogen, Oxygen, Argon, Carbon Dioxide, etc. into your weirdly heavy asteroid and the gravity will retain the atmosphere. If there is a strong radiation environment (e.g. from a nearby star) you will want to consider having a magnetic field or other radiation shielding, as an atmosphere won't cut it for high-energy particles.

If you want this to be remotely science-based you should probably focus on the "handwavium" that provides the gravity you are looking for. Not that you have to fully flesh it out, but it could be made to believably solve most of the issues in creating the setting you want. In addition, if you are considering an asteroid belt or field where there are various small settlements/facilities, you should consider the increased gravitational force between the asteroids. If a decent amount of the asteroids in the solar system's asteroid belt all of a sudden became Earth-like in mass, the belt would probably accrete into one large body (and have major interaction with Jupiter, possibly colliding).