# How does a spacecraft function despite it's own (non-centrifugal) artificial gravity?

Haven't done shipbuilding in a while so let me start simple. Sci-fi spacecrafts all tend to have some unexplained method of generating artificial gravity, which keeps the crew nice and cozy. The more realistic ships use centrifugal force for this but mine uses the good old "handwavium" to generate its gravity.

The gravitational core of the ship is placed right in the centre, surrounded by the machinery which gives it its properties as well as the foundation of the ship. Because of this the ship will be radially designed, perhaps spherical or disk-shaped to equally distribute the force. The idea I am going with has the core serve two functions: first at 'low' intensity it serves to keep the crew grounded. At higher intensities (a fraction of the suns mass) it serves for warp travel. This second application is rather problematic but you don't have to answer it.

However, this is not my only concern. The ship is quite large, approximately one kilometre in diameter to house its closed ecosystem and machinery. Due to its mass it cannot enter into an atmosphere, instead relying on shuttles for short distance transportation. These smaller ships also serve for mining operations to refuel using asteroids and repair or expand the ship.

My question is how this type of ship would function in ordinary conditions. The best answer should take into account these factors:

1. The ship has to maintain its structural integrity
2. There is propulsion, with exhaust
3. The ship has shuttles
• Point one. Why does the ship have to spin at all if it has a device on board that generates an artificial gravitational field sufficient to provide 'near Earth' comfort levels for the crew?
– Mon
Commented Feb 9, 2022 at 21:57
• Does the artificial gravity force reduce with distance the same way that real gravity does (ie inverse square relationship)? Commented Feb 9, 2022 at 22:00
• The other 2 points? Why does it have to have an exhaust (apart from heat) if it uses a gravity drive for propulsion. It wouldn't need a rocket engine except on approach to a planet, station or ship for orbital insertion/docking when the main drive would have to be off. Point 3? As long as the main drive is off during shuttle launch/docking the ships internal field shouldn't be a problem because you've already stated the internal G field is <1. As long as the shuttles engines generate >1G of thrust they can 'escape' the local G field using their onboard engines. Or just turn it off briefly.
– Mon
Commented Feb 9, 2022 at 22:19
• I have this daemon of which I will tell you nothing except that it imparts on random objects an acceleration similar to Earth's gravitational acceleration. I won't tell you if it obeys an inverse law, an inverse square law, an inverse cube law or, truly, if it extends constant to infiinity and beyond. Now, although I have this nifty device imparting an acceleration on random objects, I don't really want it to do so, and I am asking how to have my device not impart an acceleration on a random subset of objects. And then I will ask you what color is ice cream in the range of this device. Commented Feb 9, 2022 at 22:21
• What exhaust? I thought it had some kind of warp-drive, what exhaust does it produce? At present there are just too many simultaneous questions. Needs narrowing. Commented Feb 10, 2022 at 1:08

Disclaimer: science does not provide artificial gravity

Remark about your tags: you want to bend space time to your liking. Alas, there is no actual science based way to do that, like there is no FTL travel. There is only science fiction about artificial gravity. The centrifugal solution is the only one plausible in a science-based way.

Suppose artificial gravity could have a limited range

Your opening: "The more realistic ships use centrifugal force for this but mine uses the good old "handwavium" to generate its gravity."

Voilà.. You could circumvent the whole issue with "extra" mass influencing everything else, by letting your folks develop an artificial gravitational field with a limited range. It will not affect the space-time gradient far away, it would be felt only inside the anti-gravity container, where your ship either hangs, or levitates.

Mount things outside

You'll have to mount the propulsion outside on the 1km construct, firmly mounted somewhere on the hull of the container. Inside the container, where your ship is, the gravitational field generated would make propulsion a waste of energy. Your ship could hover inside, and e.g. not feel deadly acceleration of the entire construct.

You need the shuttles to be mounted outside too.. provide for an elevator or a bridge, to enter the shuttles from the ship.

# Structural Integrity

This is likely built similarly to bridges and buildings, which regularly withstand the effects of gravity (citation needed) and shear forces (which would be generated as the spacecraft maneuvers, even with gentle acceleration).

If you spin to cancel out the gravitational force, you are also producing weightlessness for your crew. Not only could this be counterclockwise, it will certainly be counterproductive! This is also ignoring some oddities induced by Coriolis effects. Best not to spin, IMHO.

Let's also address some of the issues about being too close or too far from the core. If the core is producing gravity which obeys something like Newton's law of gravitation, slight changes in height will produce dramatic effects on the gravitational force experienced. People close in will experience dramatic changes in blood pressure (and weight) between their feet and head. Possibly leading to light headedness and fainting.

On the other end (literally), people too far away will experience little gravitational effect. This kinda negates the benefits of having artificial gravity. Some tricky engineering and distributing the sources of gravity around can lead to some interesting things, like nearly uniform gravity across all levels. Read on to propulsion to find out more!

# Propulsion

Assuming regular rockets and some gravity producing wire or tube, this craft can take advantage of some mathematical field shenanigans to cancel out the artificial gravity outside the ship. This doesn't negate things like newton's laws (or the tyranny of the rocket equation), but it will allow exhaust to be safely propelled away from the ship.

Since you are generating gravity, you can attempt an Alcubierre Drive for 'FTL' propulsion. This would mean the ability to increase and decrease gravity in front and back of the vehicle. Consider secondary 'gravitational drive cores' fore and aft for this effect.

# Docking: 0-G docking or Landing?

Assuming you can cancel out the gravitational field outside of the ship, dock like a normal 0-G environment. (Slowly match speeds and drift together!) Otherwise, anything docking with the ship really means 'landing' on the ship. Landing could look like many things, like SpaceX's rockets touching down, a ball hitting the surface (not suggested), or a space shuttle touching down.

In any case, consider the use of standard docking systems in case the gravity field generator breaks. Just because there is gravity now doesn't mean there isn't gravity later, or that the gravity would prevent air from escaping the ship.

If there are secondary fore/aft gravity generation cores, these could be turned on to 'low' to produce a 0-g environment for docking purposes.

• If the artificial gravity falls off in an inverse squared (or even inverse) relationship then "No" to your first point - in a spinning ship people and objects close to the core will be strongly affected by the "gravity" and barely affected by centrifugal force, at large radius the core's effect will be trivial and centrifugal force significant, with nasty tidal effects. See this xkcd what if for some consequences what-if.xkcd.com/68 Commented Feb 9, 2022 at 22:43
• @KerrAvon I assumed people inhabited the "nice" area where these effects would cancel out. You are not wrong about some very extreme effects when outside this zone. It certainly does not counteract my conclusion about rotation: it does not really help at all. I'll add to my answer. Commented Feb 9, 2022 at 23:13

I have to concur that while you are waving your hands about the gravity production you can simply keep waving them to excuse any extra issues as well.

Building a spaceship with the structural integrity to withstand a comfortable [for the crew] artificial gravity field shouldn't an issue because modern rocket launches run to 3 gees and the equipment has to tolerate that plus have a built in margin of safety.

Rocket exhaust will almost certainly be travelling faster than the ships' escape velocity in order to provide meaningful propulsive force. If this is not true for some reason then the simplest solution is to map the likely fall of particulate and strategically plate the ship with charged attractor units that hold material to the hull until it can be scrubbed off during vessel maintenance.

Building a vehicle that can launch out of a 1 gee well is something humans have been doing since the late 1950s. Shuttle launch points will need to be specially shielded against thermal/radioactive spill over and for particulate contamination containment so it doesn't cloud sensors but all of that is manageable. The lack of an atmosphere helps with particulate because the exhaust doesn't undergo chaotic interactions with other material so it's path is more predictable.

• +1 for suggesting to keep handwaving. It is actually quite practical- the less you say about it, the less people will get angry over bad science. Really, unless it is critical to plot, gaming, or whatever your ultimate purpose is (like, I donno, having fun), let sleeping dogs lie! Commented Feb 9, 2022 at 23:54

You have an Alcubierre drive.

https://en.wikipedia.org/wiki/Alcubierre_drive

Rather than exceeding the speed of light within a local reference frame, a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel.

The graphic is meant to show how bending space works with the Alcubierre drive. The ship moves away from stretched space and towards contracted space. Bending space is also how gravity "wells" work. Mass tells space how to curve. If you can curve space through negative energy shenanigans Alcubierre-style, you have something besides mass telling space how to curve. The curve of space is how you get gravity.

And then of course you use your same space-bending powers to propel your ship. A fine question on this stack dealt with using Alcubierre drives slower than light.
Alcubierre Drive without FTL?

With gravity on, the ship will be drawn towards the center of the ship where space is compressed. Engineers have had millenia of experience designing structures that do not crumple because they are being drawn downwards by gravity. I envision a spherical suspension bridge.

Propulsion: Alcubierre style. As regards "exhaust", come to a halt in such a way that any objects entrained in your wake that continue on your same trajectory run into a large and durable object, like a star.

Docking etc. If you can bend the space inside your ship for gravity and outside the ship for propulsion you can gravity your way into the docking bay. I envision those hand held maze puzzles with a little ball where you tilt the maze so the ball rolls where you want it. Except in 3d and there are no walls to arrest your motion.

Maybe there could be tugboats?

Since you are planning to use a warp drive and faster than light travel, whilst (I assume) you still want to keep causality it would seem that relativity is dead along with most of modern physics. This is fine for science fiction, but having killed off physics you can hardly expect much in the way of reasoned arguments based on real physics.

It would probably be more believable if you introduce some strange side effects like an area of the ship where gravity is repulsive rather than attractive. But make sure you understand how this effect would work in your world, what the implications are and use it consistently! Consistent and well thought out effects like this can help suspend disbelief.