I first was thinking centripetal force on a circular ship, but performing external maintenance would be extremely difficult due to the force pushing the person or robot off.

Would a spherical vessel be able to produce gravity with a mass at the center that spins? Would it work on a conventional barge style ship if it was below the bottommost habitable level?

Any other feasible solutions?

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    $\begingroup$ possible duplicate of What's the most logical shape for my city in space (space station)? $\endgroup$ – Cort Ammon Mar 6 '15 at 6:43
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    $\begingroup$ Performing maintenance on the outside of a ship that is spinning in such a way as to provide 1g acceleration is exactly as difficult as performing maintenance on the ceiling of a building when you're hanging off of it. We do this now using cables and harnesses to hold us there, freeing our hands to do the real work. $\endgroup$ – iAdjunct Oct 31 '15 at 15:03

I'm not sure I understand your second paragraph, but I think I can answer your question anyway. There are three options to get 'create' gravity:

  • A planet-sized mass at the center of your ship. Not really feasible.
  • Some 'technobabble' device beyond the understanding of present-day science. I think you don't want that.
  • A spinning section.

Regarding the third option, you can select different shapes.

  1. Most of the ship doesn't spin, but there are pods at the end of long arms.
  2. Most of the ship doesn't spin, but there is a ring rotating outside.
  3. Most of the ship doesn't spin, but there is a ring rotating inside.
  4. The entire ship spins around the axis.
  5. The ship consists of two parts, connected by a tether. They spin around a common center of gravity.

The felt gravity depends on the spin radius and the rotation speed. Too many rpm and you get problems with coriolis force. Too much radius and your ship gets large/heavy.

A spherical ship would be consistent wih 3. or 4. but either way you don't get much living space at maximum gravity. OTOH, you don't have to keep the fuel tanks or cargo holds under gravity. They can go into the center of the ship.

Here are some more explanations and pics. www.projectrho.com

  • $\begingroup$ The first option could be feasible, depending on your interpretation. $\endgroup$ – KSmarts Mar 6 '15 at 21:36
  • $\begingroup$ Doesn't mass increase with velocity? if the mass spun wouldn't it accrue more mass, thus creating a larger gravitational field? and it would only need an earth-sized mass if it were an earth-sized ship. $\endgroup$ – Damien Andre Mar 7 '15 at 5:57
  • $\begingroup$ @DamienAndre Mass does increase with velocity, but you'd need the mass to spin fantastically fast (at a minimum - I don't know if this would really work for a spinning, uniform sphere). The earth has 5.972*10^24 kg of mass. To get the relativistic effects to increase, say, 100 tons to that, you'd need to accelerate something to so close to the speed of light that it'd probably be easier just to build a new planet. $\endgroup$ – Darth Wedgius Apr 11 '15 at 6:25

A solution I don't see being offered her is acceleration. If your ship accelerates at 1g, then everyone in the ship will experience that as effective gravity, oriented so that your engines are "down".

This won't work if you need to spend a lot of time on the ship while in orbit or docked, but if the majority of your time is spent travelling and you can sustain that acceleration over time, it will work.

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    $\begingroup$ The fuel requirements would be extraordinary for interstellar travel. If you could convert matter to kinetic energy perfectly (which you can't) you would need to shed 90% of your mass to maintain the acceleration for about three years (that is three years of proper time). $\endgroup$ – M.Herzkamp Mar 6 '15 at 9:58
  • $\begingroup$ Yeah, you'd need something like a Bussard Ramjet or a Zero Point Energy trap. Keep in mind though that you could get away without accelerating at a full 1g. I assume humans would be healthy at say, .5g, and that would extend the distance you can travel substantially. $\endgroup$ – Dan Smolinske Mar 6 '15 at 15:24

The spherical vessel will only have gravity towards the mass. (and unless their was a high mass their would not be a lot of it). The spinning of the mass would not create a force on the ship unless the ship spun with it.

  • $\begingroup$ According to General Relativity, a spinning mass will have a different "gravitational field" than a resting mass. However, it won't necessarily be directed towards the center of mass. $\endgroup$ – M.Herzkamp Mar 6 '15 at 10:05

This isn't my field, but the exchange between o.m. and Shion got me thinking. When o.m. says that you would need a planet-sized mass, that isn't correct, right? Gravitational force is a function of mass vs the square of the distance. So, if you want earth-like gravity at the outer sections of a ship centered around a massive object, and your ship's radius is 1/100,000 that of the earth (so about 63m), then your massive object would only need to be 1/10,000,000,000 that of the earth.

Now, I seem to recall reading something about the concept of inducing a black hole with a relatively small mass by compressing it to a tiny size. The context involved scientists using a nano-scale black hole as a perfect mass to energy converter. In other words, something that would let you turn anything into energy, by feeding in mass and capturing the energy that gets ejected back out. So, perhaps, in theory, you could create a tiny black hole with the mass of a smallish asteroid and build a ship around it. The event horizon would be too small to see, let alone be a danger, but you would have to figure out how to move it along with the ship, without any part of the ship being close enough to be damaged by it's gravity. This would also make maintenance an issue, as the closer you get to it, the more intense the gravity gets. From 1G at your main deck at 63m, you get 4G halfway to the black hole at 31.5m, and 16G halfway from there at 15.75m.

Another concern with this idea is that it makes your ship incredibly massive for its size, which means you need a lot more fuel than you otherwise would. That said, if you can also use the black hole as an energy source by feeding it with whatever material you can get your hands on, it may not be too bad. Haven't done any math on this though.


While I'm not a physics expert, I read in some journals that gravity is basically created when you have something with huge mass. Basically, if you are to stand on a piece of rock thrice bigger than you in space, you will feel an attraction, because the rock has gravity. Many people do not know that celestial bodies actually exert gravity on each other.

As o.m. mentioned, you need a planet sized mass in the center of your ship to create gravity. But you don't actually need a planet sized mass. An asteroid sized mass is more than enough to create gravity. It's not the size that matters, it's the volume of mass itself. Black holes exert a greater gravity than stars of the same size (not that we know exactly how big black holes are) because all its volume of mass collapsed into a singularity making a superdense mass.

All the moons of the planets also create gravity. It may be small, instead of 1g, you get 0.5g or 0.6g, but it's still gravity. How about Mars then?

The answer? Dark matter/god particles whatever you can thing of. If you want to coin a new term such as 'nucleonic' (my term, take it and i'll throw you into a singularity) it's fine too. Your problem will be how to get it to work and how to contain it. You can simply use electical power to activate the matter, and you can simply say that it's placed under the floor. Obviously this is easy to maintain than rotating sections.

Obviously I'm not saying that there is 'dark matter' inside Earth.

Personally, I dislike rotating sections, because even with future technologies the necessity of weekly, even daily maintenance is horrendous. You not only to have to take care of the moving parts, these moving parts are also sections vulnerable to space radiation. Sure, it's a lower level tech, but it's a hassle to maintain.

In one of the episodes of "the outer limits", they show a dark particle that can't be quantified and and looks just like a normal asteroid causing a malfunction in hyperspace drive, trapping two human ships and an alien ship inside the gravity field.

  • $\begingroup$ I think a couple of times where you say "volume of the mass" you mean "density of the mass". Also, Mars is smaller than Earth. And there would be no need to have rotating sections of the ship requiring moving parts and joins - just rotate the entire ship. $\endgroup$ – Turophile Mar 6 '15 at 7:29
  • $\begingroup$ Oops, I wonder why I thought Mars is bigger than Earth. Strange... fixed. The reason I mentioned rotating parts is because the amount of thrust needed to constantly keep the whole ship rotating would quickly reduce the supplies needed for maneuver and braking. Some would say that once something rotates in space, it will keep rotating forever, but I have not seen any evidence of that actually happening, at least nothing that rotates constantly forever. $\endgroup$ – Shion Mar 6 '15 at 7:35
  • $\begingroup$ @Shion In addition to tumbling rocket stages, there are a multitude of spin-stabilized satellites including Pioneer 10 and 11, Lunar Prospector, Galileo, and the various Mars landers (while they were in transfer orbit). They all maintain their spin rate without propulsion, since there is no friction in space. $\endgroup$ – 2012rcampion Mar 6 '15 at 15:16

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