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I want to have air and STP (standard temperature and pressure) around my spaceship.

Other properties:

  1. Objects can enter and exit it without bumping into any kind of a barrier? In fact, there doesn't seem to be anything between the air and the vacuum of space.
  2. The barrier, or whatever that keeps the air in there, is resilient to damage and malfunction.
  3. It consumes the least amount of power.

How can I have essentially a miniature atmosphere around my spaceship?

Note: Pretty much all comments and the answer are out-of-context now, thanks to my editing, just to clear up any confusion.

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    $\begingroup$ Worldbuilding is focused on fictional worlds of the OP's creation. Science Fiction & Fantasy is focused on commercial fictional worlds like Star Wars, Star Trek, and Jimmy Neutron. We usually migrate or close questions about other people's worlds because you, the OP, don't have control over the rules. $\endgroup$ – JBH May 12 at 20:49
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    $\begingroup$ @user535733 I didn't expect the Spannish Inquisition to show up here. $\endgroup$ – Mephistopheles May 12 at 21:00
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    $\begingroup$ From the help center, "Worldbuilding Stack Exchange is a site for designers, writers, artists, gamers and enthusiasts to get help creating imaginary worlds." You're not creating anything. You're modifying someone else's world. (Not even that, you're just trying to explain someone else's world.) Is there a problem asking this over at Science Fiction & Fantasy? There might be (and probably is) a canonical answer that trumps what you'd get here, even if we did consider this on-topic for our site. $\endgroup$ – JBH May 12 at 21:11
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    $\begingroup$ Nope, see my comment for Incognito's question. I think it's time for the community to decide for/against the issue of third-party worlds, so I opened a Meta discussion about it. $\endgroup$ – JBH May 12 at 22:01
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    $\begingroup$ @Mephistopheles - Nobody expects the Spanish Inquisition! $\endgroup$ – elemtilas May 13 at 0:57
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While you have the science-based tag on this question, the answer is "you can't."

All sorts of hand-waving can be done if you don't require hard science, but while you do, there's no practical way to meet your "Objects can enter and exit it without bumping into any kind of a barrier" requirement. There are no barriers which will confine gas molecules while allowing larger objects to pass through unimpeded.

There is a completely impractical way, in using a small black hole, but there's no way for humans to stay alive within a few hundred metres of a black hole that is science-based. Neutronium won't stay confined in a spaceship-sized quantity, it will just turn into very hot gas, otherwise known as exploding.

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    $\begingroup$ I think what you're saying, in essence, is that the air is kept in by a handwavium field for the purposes of television? :P $\endgroup$ – Arkenstein XII May 12 at 22:25
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    $\begingroup$ @ArkensteinXII: No. I'm saying that there is likely no explanation within the TV series, because the programme-makers have no bothered to produce one. The "handwavium field" is a rationalisation produced by you. $\endgroup$ – John Dallman May 13 at 6:29
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An atmosphere at STP is just a bunch of gas molecules bouncing off each other. On Earth they are prevented from flying off into space (most of the time) by gravity. You need some other force acting on the gas molecules that try and bounce away from your space ship.

There is no current way to do this known to science, especially not with your caveats.

Our only two options are to use electromagnetic or gravitational fields to apply our force.

It might be possible to have a dense layer of ionized gas molecules held between two very strong electric fields. When non-ionized gas molecules bump into the "trapped" ones, they would just bounce back into the containment area.

But oops, gas molecules don't always collide and can move right past each other, and do so many millions of times per second. This means our ionized barrier layer needs to be dense enough to stop almost every molecule from escaping, which would definitely be noticeable. Similar to how a balloon's skin or an aquarium's walls are noticeable.

Even if that was possible it would be insanely complex to have two perfectly counter-balanced electromagnetic fields held in a spherical shape, and would not be "energy friendly".

You could simplify that approach by ionizing ALL of the gas molecules in your atmosphere, removing their electrons. Then a single, extremely strong negative electric field would attract all the positively charged gas to your ship. This would present a whole slew of problems, from interfering with electronics and communications to degrading the material of your spaceship as electrons are forcibly ripped from them. This is not a viable idea by any means.

Another theoretical way to do this is with artificial gravity fields. Right now the only way we know how to generate gravitational fields is with a lot of mass. Having a super dense point of mass, such as a small black hole or a neutron star, could create the required field strength to trap an atmosphere, but would also collapse any possible support structure you tried to build around it. This would be super impractical to haul around as well, since a glass shell around your ship would weigh far less than a literal black hole.

TLDR:

Electromagnetic fields: No way to do it reliably, cheaply, and in an unnoticeable way.

Gravitational fields: No way to do it without literally being planet sized.

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    $\begingroup$ the last sentence of your answer is THE answer. The spaceship has to be planet sized, or to be more precise, Earth-sized. It also has to have a centrally distributed mass which matches Earth's mass. Only then will it keep a STP atmosphere with the appearance of a matter-permeable barrier between the air and the vacuum. After 4 billion years in service, this approach to proven to be extremely resilient to both damage and malfunction; and it expends no known energy towards atmospheric maintenance. You've provided a perfect answer! +1 $\endgroup$ – Henry Taylor May 15 at 22:53
  • $\begingroup$ You could also mimic gravitational fields through the effects of rotation. $\endgroup$ – nick012000 May 16 at 3:18
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    $\begingroup$ @nick012000 not in this case. Rotation gives you artificial gravity, but this force is outwards. Your astronauts are getting pushed against the outer wall of the spaceship, which keeps them on the floor. Without the hull, no artificial gravity, but the hull will retain atmosphere regardless if it rotates. $\endgroup$ – Whitecold May 16 at 6:57
  • $\begingroup$ @Whitecold Think a giant ring with the “inside” edge open to space, and retaining walls a few hundred miles tall on the sides. $\endgroup$ – nick012000 May 16 at 10:47
  • $\begingroup$ @HenryTaylor Even Earth is losing its atmosphere due to solar wind (and other effects) so it too small to be an answer ;-) $\endgroup$ – ADS May 18 at 11:42
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A gas torus

It depends on your proposed narrative context but this scenario was addressed by Larry Niven in his novel "The Integral Trees" (1984) and it's sequel "The Smoke Ring" (1987).

The setting is a biosphere (biotorus?) that has developed in a gas torus orbiting a neutron star.

There is a gas torus around Io and others suspected around Europa and Enceladus. While these are not at gas pressures sufficient to sustain life observations of the Enceladus torus suggest an abundance of O+, OH+, H2O+ and H3O+.

In the answer to this question L Dutch suggests that such a torus would not develop a life sustaining ecology but the astrophysics is good.

Why would there be a biosphere? While abiogenesis may not be the answer terraforming might be as could a 'seeding' process.

Up to your creative spirit and the milleau you are developing.

There is a Wikipedia article here

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You build a giant ring with walls a few hundred miles high on either side, then spin it up to 1G of rotational gravity. This will mimic the experience of being on a planet, allowing you to leave the inside of the ring open to space.

Of course, this would result in significant force loadings on all of the structural components in question, which would likely exceed the ultimate load strengths of any known material, though I haven't done the maths on them.

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  • $\begingroup$ This won't work. There's no applied force keeping molecules from bouncing "up" and over your walls. The atmosphere will expand and fill all the space it can. Since it has a large area exposed to vacuum, it will never stop leaking out. $\endgroup$ – abestrange May 16 at 17:26
  • $\begingroup$ @abestrange “There’s no applied force” Centripetal force. I know it’s an “illusion” that occurs as a result of reference frames, but when you’re in that reference frame, it acts like a real force. $\endgroup$ – nick012000 May 17 at 0:41
  • $\begingroup$ So from the frame of reference of a molecule bouncing around near the "top" of your confinement walls, what actual forces are going to be involved with pushing that atom back into the walls? It is going to be bouncing in a random direction until it hits something or a force acts on it. When you experience artificial gravity due to the rotation of the station, normal and frictional forces are accelerating you. Your momentum makes that illusion work. Unbound air molecules will not have the same effect. There will be no real applied force acting on them. They will escape over time. $\endgroup$ – abestrange May 17 at 14:34
  • $\begingroup$ @abestranger The air would be rotating along with the station, or else you’d have a permanent wind in the opposite direction from the rotation- and maybe there’s some big baffles dividing the station into sections to make sure it continues to do so. As a result, it would be concentrated towards the floor of the station the same way it’s concentrated towards the ground on Earth, with the walls going up to and above the Karman Line. $\endgroup$ – nick012000 May 17 at 22:47
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Build a spaceship as massive as a planet. Let gravity do the job. This system consumes no power.

You can simulate gravity on a smaller spaceship by accelerating your spaceship. One way is to spin your spaceship as nick012000 recommended. Another method is to continually accelerate your spaceship. You'll be doing this already if you're simulating 1G gravitation in addition to standard temperature and pressure.

Unfortunately, the simulated gravity system requires tall walls many miles high. (Or a powerful artificial gravity strong enough to crush a human being.) Exactly how high depends on how much air you'll tolerate leaking out.

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