# spacecraft with rotational artificial gravity

#### Tom Carson

How large would something like need to be? Compared to the Space Station?

#### Ittiz

big, look at the gateway foundation's stuff

#### Tom Carson

big, look at the gateway foundation's stuff
Looks pretty optimistic to me. I could not find what the approximate diameter would be. Are we talking 500 or 1,000 feet?

#### Ittiz

Based on the images and animations I've seen I'd say 500 meters to a kilometer in diameter. And yeah optimistic is a giant understatement. I actually think we won't know this stuff for sure until we start to actually experiment with rotating habitats in orbit. Something that hasn't gotten much attention yet because of the scale needed. Even though everyone just assumes it in all scifi for the last 60 years it seems.

#### Mental Avenger

I did some calculations on a vessel 200 ft diameter. IIRC a 200 ft diameter craft would only have to rotate at 3 rpm to achieve .38G Gravity (simulating Mars). Coriolis effects will be minimal in a 200 ft diameter ship. Remember, the crew will be sleeping about 1/3 of the time, and coriolis effect would be nil at that time. Of the remaining time, perhaps ½ would be at seated tasks, also reducing the effect. Even then, the differential between the head and the feet while standing would only be about .08 G at .5G.

newtons_laws

#### Mental Avenger

There have been many different designs for spacecraft providing artificial gravity.

The obvious design is a cylinder, with “down” being the outer hull.

Another design uses tethers to connect two or more modules. They start by being connected together as a single unit. Once underway and coasting, the module group can begin to slowly spun, with the tethers paying out until they reached their limit. They would be rotating about a common point. They could remain that way until it was necessary to begin deceleration. The advantage is small modules can be used to provide up to 1g while spinning slowly about a common center. The disadvantage is that transport of personnel or supplies between the modules would be extremely difficult.

newtons_laws

#### Tom Carson

I did some calculations on a vessel 200 ft diameter. IIRC a 200 ft diameter craft would only have to rotate at 3 rpm to achieve .38G Gravity (simulating Mars). Coriolis effects will be minimal in a 200 ft diameter ship. Remember, the crew will be sleeping about 1/3 of the time, and coriolis effect would be nil at that time. Of the remaining time, perhaps ½ would be at seated tasks, also reducing the effect. Even then, the differential between the head and the feet while standing would only be about .08 G at .5G.
I'm curious how sleeping and the coriolis effect are related?

#### Mental Avenger

I'm curious how sleeping and the coriolis effect are related?
The coriolis effect would be expressed in several ways in a non-accelerating rotating cylinder in space . First, if you throw an object along the direction of rotation, it won't react the way you think it should because is it crossing through different levels of gravity due to the fact that the path of the object is straight, while the field through which it passes is curved. That effect is more pronounced the smaller the diameter of the rotating field.

The second is the difference in gravity felt by different parts of your body as you stand. I believe that there would be noticeable effect while lying down. I have no information on that.

There may also be some Gyroscopic Precession involved in some directions.

#### EjmMissouri

I did some calculations on a vessel 200 ft diameter. IIRC a 200 ft diameter craft would only have to rotate at 3 rpm to achieve .38G Gravity (simulating Mars).
Can you show us the formula you used to do this calculation? I would like to see what the rpm would need to be for different diameters.

#### Mental Avenger

Can you show us the formula you used to do this calculation? I would like to see what the rpm would need to be for different diameters.
Sorry, that was over ten years ago when I was on SDC Uplink. I probably used ordinary math. I have hundreds of saved documents from those years, but most are just comments based upon my research, not any backup. Until I do further research, most my comments will be excerpts from those documents.

#### dr tom

Sorry, that was over ten years ago when I was on SDC Uplink. I probably used ordinary math. I have hundreds of saved documents from those years, but most are just comments based upon my research, not any backup. Until I do further research, most my comments will be excerpts from those documents.

Cool World did a nice 15-20 minute U-Tube on this.

A 200 ft wheel would work fine. Maybe Bigelow should be working on this.

The drum or cylinder idea might seem ideal but, as is demonstrated, is not particularly stable. If the cylinder length > 1.5 diameter ( I think it is 1.5) it may periodically flip end for end!

#### Mental Avenger

Cool World did a nice 15-20 minute U-Tube on this.

A 200 ft wheel would work fine. Maybe Bigelow should be working on this.

The drum or cylinder idea might seem ideal but, as is demonstrated, is not particularly stable. If the cylinder length > 1.5 diameter ( I think it is 1.5) it may periodically flip end for end!
Very interesting. That video at
confirms everything I wrote in that discussion over 10 years ago. Maybe they read my original comments. I will disagree with the cylinder flipping end over end. That handle in the video was not a cylinder. It was dramatically not symmetrical, with the T handle on one end. I would like to see the same experiment performed in space using a symmetrical cylinder. I do not know of any force that would make it flip.

Their conclusions seem to support a 200 ft diameter cylinder for a rotating spacecraft.

#### dr tom

Good point about the T handle! I'd like some input from someone with the rotational physics credentials to address the instabilities of wheel and cylinder configurations.

I'd like your tether suggestion to work, I've seen it in scifys. I just wonder though... Isn't there a major ship structural integrity issue? I think some of these ships are not much more than balloons owing much of their strength to pressurized fuel tanks.

If you have two ships tethered and spinning so as to achieve 1g, I think that is the equivalent of hanging each entire ship by a mount on the side of each vessel? Imagine a crane lifting a whole Starship by connecting to a D-Ring on its side.

Artificial gravity: I wish NASA would allocate some seed money to orbiting demo projects.

(I also wish NASA would quit wasting tax dollars building boosters and capsules!)

#### Mental Avenger

I'd like your tether suggestion to work, I've seen it in scifys. I just wonder though... Isn't there a major ship structural integrity issue? I think some of these ships are not much more than balloons owing much of their strength to pressurized fuel tanks.

If you have two ships tethered and spinning so as to achieve 1g, I think that is the equivalent of hanging each entire ship by a mount on the side of each vessel? Imagine a crane lifting a whole Starship by connecting to a D-Ring on its side.
The tether concept would be used to rotate two modules about a center mass, like the ship. The modules could be living quarters perhaps 10%-5% the mass of the actual ship. No need to spin up the entire structure, engines, fuel, and supplies.

#### teflonsteel

gravity can be handle by rotation. Other forms is by magnets.

#### Ken Fabian

Another design uses tethers to connect two or more modules. They start by being connected together as a single unit. Once underway and coasting, the module group can begin to slowly spun, with the tethers paying out until they reached their limit. They would be rotating about a common point. They could remain that way until it was necessary to begin deceleration. The advantage is small modules can be used to provide up to 1g while spinning slowly about a common center. The disadvantage is that transport of personnel or supplies between the modules would be extremely difficult.

I think this would be the simplest solution. I think Heinlein may have paired two ships like that in one of his stories (Space Family Stone maybe?).

No reason tether-paired modules/ships cannot be accelerated and decelerated in most directions whilst twirling - easiest in line with axis of course but tracking, synchronized drives should manage all but perpendicular to axis - the rolling mode. And even then maybe. Probably handle higher accelerations along the line of axis but maybe only lower accelerations when skewed.

I suggest tensile tubes to connect them rather than cables - or tubes in addition to cables; they would allow air filled access between them. Paired tubes would allow a circulating air flow between the modules. I don't know how very low temperatures effect tensile strength; cables may need heating.

I would avoid connecting more than 2 modules for simplicity and stability; not quite the same "three body problem" as The Three Body Problem but more than two is unstable whilst a pair should be inherently stable. More than 2 would need constant monitoring and adjustments to prevent instability. Probably manageable to have a midpoint module without much instability if it low mass - for zero gee and docking access.

Dr Tom -
I'd like your tether suggestion to work, I've seen it in scifys. I just wonder though... Isn't there a major ship structural integrity issue? I think some of these ships are not much more than balloons owing much of their strength to pressurized fuel tanks.

Any attempts to spin ships or stations to simulate gravity will require designing and building them to handle it.

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#### YetAnotherBob

Can you show us the formula you used to do this calculation? I would like to see what the rpm would need to be for different diameters.

A = w^2 * r
Where A is the acceleration due to gravity.
w is the angular velocity. In practice, just use 1/t where t is the time in seconds for a single revolution. Values of t <3 are known to cause problems with dizziness and balance. The ear has fluids that circulate. That's how our sense of balance works. Many experts now recommend values of t > 30 seconds. That gives a diameter of close to a kilometer.
r is the radius of the object. Half of the diameter is the radius in most instances.
This is first year college Physics for a STEM major.

#### egribble

The coriolis effect would be expressed in several ways in a non-accelerating rotating cylinder in space . First, if you throw an object along the direction of rotation, it won't react the way you think it should because is it crossing through different levels of gravity due to the fact that the path of the object is straight, while the field through which it passes is curved. That effect is more pronounced the smaller the diameter of the rotating field.

The second is the difference in gravity felt by different parts of your body as you stand. I believe that there would be noticeable effect while lying down. I have no information on that.

There may also be some Gyroscopic Precession involved in some directions.

#### egribble

This is what I undertand as well. That the minimum size will depend on the amount of discomfort a human will feel. My understanding is that there has not been adequate research.

#### YetAnotherBob

This is what I understand as well. That the minimum size will depend on the amount of discomfort a human will feel. My understanding is that there has not been adequate research.
Research in the 1960's indicated that it took around 3 seconds per rotation to minimize discomfort. Research since then, using rings large enough has upped this number significantly. It's now considered around 30 seconds in most reports, hence the 1 Km radius. But there are very few real studies using actual centrifuges. The '60's work for instance used only centrifuges where the subject was sitting in an acceleration couch.

#### ALSEY

Just stumbled upon this.

We know that humans need as close to 1G (Earth) gravity as possible, along with many other aspects of our unique home planet, in order to survive. Any deviations will negatively affect our physiology and may be deadly. The rotating environment seems to be the best solution at a certain RPM for the diameter.

Here's the problem I see with the development of any system, in my opinion, so PLEASE opine!

The future goals and efforts of our current space program, seem a bit misguided. By this, I mean focusing on Mars instead of our moon. I believe the best approach to developing living environments should be focused on using our moon as an intermediate, developmental launching pad to space. We're not that far away from the Moon, versus Mars, so resource supplies and rescues, if needed, would be more feasible.

We've seen the 'lava tubes' which would (theoretically) be ideal for establishing a lunar base, where we can develop and refine acquisition of the essential natural resources already present on the moon, like water and H3. The tubes can also protect against damage from space objects and radiation. Construction materials, equipment and tools can be developed on Earth and transported to the moon, where we can build and test prototypes for space travel, including ship parts or entire ships with rotating living environments. A rotating living environment must FIRST be constructed, tested and used for long-term living and working on the moon, before we can go any further into space. We must also determine what we can grow and harvest for food and also the best ways of waste management and recycling.

We must develop an extra-terrestrial resource acquisition program in order to venture far away from home. This may include setting up bases on other worlds in our solar system, such as the many moons of Saturn, for example. We must find resources and develop the techniques for mining them for fuel, water and food. Mining different elements and minerals, including those for whatever type of energy we'll need can't be ignored. This can help offset the cost by providing essentials. We certainly can't expect Earth to provide everything we'll need.

The core foundation for making all of this possible will be the rotating living environments and to make those environments simulate Earth as best as we can. At the same time, shielding our bodies from the destructive radiation which exists everywhere in space is ESSENTIAL. I've seen the coriolis effect mentioned in this forum. The only time the CE will be felt, is when ascending and descending. Slowing ascent and descent will minimize the affect perceived.

So many experiments, so many resources (including funding) and so much time will be needed, in order to make survival in space possible. This may take many generations to accomplish, but it may be well worth it.

ONLY when we can learn to survive and thrive on the Moon, can we even THINK about further ventures. Starting with Mars is a BIG MISTAKE. MOON FIRST, then Mars and then the Saturnian moons like Europa, Titan and Enceladus, for examples. Jupiter may simply be too dangerous to consider.

Human nature will drive us to explore and survive, maybe even beyond the death of our Sun. However, in order to preserve how we were created, we must understand ALL of the combined aspects of how our bodies have adapted and evolved and how all of the ecosystems on Earth have contributed to our existence and reproduction and we must simulate that environment to the best of our ability.

Even Earth's massive core and protective magnetic field, along with our large moon have an essential effect on most species on Earth, including us...on and on.... Everything must be considered and nothing can be overlooked.

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#### archiek-author

The coriolis effect would be expressed in several ways in a non-accelerating rotating cylinder in space . First, if you throw an object along the direction of rotation, it won't react the way you think it should because is it crossing through different levels of gravity due to the fact that the path of the object is straight, while the field through which it passes is curved. That effect is more pronounced the smaller the diameter of the rotating field.

The second is the difference in gravity felt by different parts of your body as you stand. I believe that there would be noticeable effect while lying down. I have no information on that.

There may also be some Gyroscopic Precession involved in some directions.
My puzzlement lies in how a thrown object, or any object floating in the air withing a rotating cylinder would react. The assumption by Mental Avenger is that a thrown object would be subject to gravity while in the air. Isn't the artificial gravity created by a cylinder only on the moving rotational portion of the cylinder. The air inside would not move towards the cylinder except for the currents created by interacting with the cylinder. The air would tend to equalize in pressure throughout the interior. Thus any object thrown would move in a straight line, except for air currents, until it impacted another internal surface.

#### Think twice

Very interesting. That video at
confirms everything I wrote in that discussion over 10 years ago. Maybe they read my original comments. I will disagree with the cylinder flipping end over end. That handle in the video was not a cylinder. It was dramatically not symmetrical, with the T handle on one end. I would like to see the same experiment performed in space using a symmetrical cylinder. I do not know of any force that would make it flip.

Their conclusions seem to support a 200 ft diameter cylinder for a rotating spacecraft.
You may have described something like this idea of mine in following above post. But in case not: Imagine a side loading washing machine drum. 2 ft Diameter, 1 foot depth/length. As all washing machines do it rotates along the depth/length axis which is parallel to its depth/ length. Like a sideways rotating drum. Now stretch it’s depth to 10 ft to accomadate length of sleeper. And enlarge its rotational diameter to let’s say 8 ft diameter to give more room above sleepers body to the other side of drum above horizontal sleeper.

You now have a Sleeping module bunk with artificial G. Kind of like an extended 8 ft deep washing machine drum. The sleeper crawls into pod through hole at end just as one loads a side loading washer machine and settles into lengthwise sleeping position and turns drum on. It rotates like a washing machine while the sleeper sleeps in artificial G. (Sleeper is lengthwise in the rotating pod. The pod rotates about its axis which is also along the length of the pod)
I suppose with a small diameter it would have significant coriolis. But it would be small and not have to deal with technical strains on frame of a rotating living pod in the 100s of meters

#### Ken Fabian

The sleeper crawls into pod through hole at end just as one loads a side loading washer machine and settles into lengthwise sleeping position and turns drum on. It rotates like a washing machine while the sleeper sleeps in artificial G. (Sleeper is lengthwise in the rotating pod. The pod rotates about its axis which is also along the length of the pod)

The problem of disorientation and nausea from the inner ear perceiving rotation - the mismatch with apparent lack of motion within the enclosed space - is why small diameter centrifuges aren't suitable and larger diameters are required. Rotating rooms and centrifuges have been used to mimic the rotation speeds; apparently even seasoned aircraft pilots who are normally unaffected by disorientation and nausea succumb when it goes on and on without letup.

Atlan0101

#### Think twice

The problem of disorientation and nausea from the inner ear perceiving rotation - the mismatch with apparent lack of motion within the enclosed space - is why small diameter centrifuges aren't suitable and larger diameters are required. Rotating rooms and centrifuges have been used to mimic the rotation speeds; apparently even seasoned aircraft pilots who are normally unaffected by disorientation and nausea succumb when it goes on and on without letup.
Yes that makes sense. Although I wonder if it’s possible these rotating rooms and small centrifuges problem was not the artificial G but the artificial G combined with an equally powerful earth G which confused the ear? Not forgetting that artificial G doesn’t get rid of earths gravity. Just adds a new gravitational vector. I imagine these test pods you mentioned were earth bound.
But it made me think of another possible design. The problem with larger diameter rotating artificial G pods ( like the 200+ meter disaster usually cited) are the strains on the structure. For instance the famous 2001 rotating space station would surely be impossible to build without it flying apart the minute it rotated. But how about a large enough ring structure, let’s say 100 meter diameter with sleeping pods that insert into the structure and go round and round on rails on the inside of the ring. Like cars on a circular rollercoaster. This way you get the large enough diameter rotation without having to build a structurally sound rotating wheel In space.

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