Space centerfuges. How big should we make them?

[DerpenWolf]

Ok so I'm wondering what the ideal size would be for a spacecraft centrifuge, including large (space station) and small sizes (interplanetary craft). So here are a few questions I have based on the topic:

- What RPM will feel comfortable for the passenger (I'm guessing that sitting in a)?

- What RPM(s) is most appropriate for making sure everything remains structurally sound?

- What minimum % of gravity (I KNOW ITS NOT A GRAVITATIONAL PULL) do you think would be needed to help keep the astronaut(s) healthy?

- What sizes/RPM would you think work best for a large and small spacecraft?

[Nuke]

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm

bigger and slower is better in terms of crew comfort. but for a space craft having a 1km ring is impractical. you can do with less gravity or have to go through some conditioning to deal with a smaller centrifuge. for example if you have a 120m radius centrifuge and are ok with 0.5g, you get by with that. of course this is all theoretical with some of the data for human comfort levels being attained with science.

1. 2-6 rpm (lower is better)

2. dont exceed 1g and you shouldn't have to worry about breaking it, however more gravity->more structure->more mass.

3. this varies widely, dont exceed earth normal (unless your landing on a high g world and need to condition for it), and at some point at the lower end, walking would become difficult (such as what happened on moon walks). if i were to take a guess id say 0.5g, its a nice round number (in the range of what science people think) and allows for a smaller centrifuge. but you dont know till you try it.

4. depends on what kind of ship or station you are doing. a civilian station might want to be 1km across and 0.95rpm (close to 1g). a large civilian ship might have 120m radius @ 1.93rpm for close to half a g. a military ship might want to be compact to keep size and weight down and require conditioned crew, 25m @ 5 rpm for a little more than 2/3s a g.

Edited December 12, 2014 by Nuke

[trekkie_]

I think determining the size of one should be based on a factor of the average human height. Basically though, the smallest size possible that allows comfortable gravity simulation, but the further away from the center of the spin the better, to a point anyways. Ideally, 100% of earths gravity should always be the aim, but 80-90% would probably be a good compromise.

RPM would be based on the size of the rotating structure and its distance from the center, so it's not a fixed number.

[Guest]

Centrifuge must be big enough to fit dr. Zoidberg within.

[Nibb31]

- Comfort is subjective. While some people might be confortable in a spinning habitat, others might get dizzy or nauseous. The same is true for microgravity itself. So whether microgravity or centrifuge-induced is preferable might depend on the individual. Some people might prefer one or the other.

- This depends on the structure, obviously. If you design the structure to be able to bear the load that it is designed to bear, then it should be able to bear that load, shouldn't it? One thing is for sure, you wouldn't want one of those silly rotation joints that you see in science fiction movings. It simply adds a whole lot of complexity and possibility for failure. You would rather rotate the entire ship, like in Interstellar.

- We don't know. Artificial gravity might even be detrimental compared to microgravity. You might suffer from equilibrium and internal ear problems, causing motion sickness.

- The sizes and RPM depend on how much artificial gravity you would need, if you need it. The smaller the vehicle, the faster it has to spin, obviously, and the more negative effects you get due to the Coriolis effect.

The truth is, we don't really know the answers to any of these questions, because there has been no proper experimentation in artificial gravity. We can only extrapolate based on what we do know from operating centrifuges in Earth gravity. We don't know whether 0.1G is enough to avoid most microgravity problems, or whether you need 0.3 or simply 1G.

We do know that a centrifuge adds a lot of complexity, cost, and risk. We also know that astronauts have been able to live and work in microgravity for extended periods. We also know that we can use medication and exercice to fight most of the detrimental effects of microgravity. So for the moment, nobody is considering artificial gravity as an actual necessity in the foreseeable future.

Edited December 12, 2014 by Nibb31

[sgt_flyer]

maybe try to avoid the additional complexity of centrifuges : simply 'deploy' the hab module from the space ship atop of a truss or a cable, with a counterweight made of other spacecraft systems the other way, and make the whole spacecraft spin on itself. (so no need of bearings, and no need to spacebuild a huge circular structure)

the only thing to address in these cases is how to maintain the antenna's alignement towards earth

[RuBisCO]

I edited the wiki for this years ago.

You need a radius of 224 m to achieved earth gravity at 2 rpms, more rpms and Coriolis effect on the inner ear becomes noticeable.

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

[Nibb31]

I edited the wiki for this years ago.

You need a radius of 224 m to achieved earth gravity at 2 rpms, more rpms and Coriolis effect on the inner ear becomes noticeable.

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

[Citation needed]

[Nuke]

[Citation needed]

spincalc gives me green lights all the way down for those numbers. there are citations on that page for the various tolerable ranges. though we dont have any idea what kind of data we would get from a centrifuge operating in orbit.

if you could somehow rig up an airbus beluga as vomit comet you could build a centrifuge inside its hold for some tests. the cargo hold has a diameter of about 7.1 meters (7.62 for the super guppy turbine and 8.38 for the dream lifter), which while not ideal is probibly adequate for a couple human guinea pigs to go for a spin. just pad up the interior for safety reasons. i dont think you would get a whole lot of data but you might get a general idea. for science!

Edited December 12, 2014 by Nuke

[Nibb31]

Yes, the numbers compute. My question is with the noticeable inner-ear effects claim. I don't think we have any experience of a 224m centrifuge operating at 2 rpm in microgravity (even on Earth, I don't know if there are any experimental centrifuges that big)

[RuBisCO]

[Citation needed]

Well there are different studies on that, google is your friend.

[MrZayas1]

I've never understood centrifuges too much, I understand the concept, RPMS and all that, but how do you induce the gravity? If you are floating, and it starts spinning then you will either hit a wall or be just perfectly placed to watch everything around you spin while you get dizzier than a drunk man. Maybe strap yourself in? Other than that, what happens when you jump? Do you fall down, or do you slide sideways? Would love an answer, I have always wondered about this.

[Wanderfound]

A lot bigger than you think.

See http://www.brandeis.edu/graybiel/publications/docs/187_sensmotor_adpt_highrotation.pdf

Undersized (as in, "not as big as a small town") rotational habitats are intensely nauseogenic.

[RuBisCO]

I've never understood centrifuges too much, I understand the concept, RPMS and all that, but how do you induce the gravity? If you are floating, and it starts spinning then you will either hit a wall or be just perfectly placed to watch everything around you spin while you get dizzier than a drunk man. Maybe strap yourself in? Other than that, what happens when you jump? Do you fall down, or do you slide sideways? Would love an answer, I have always wondered about this.

Does these help visualize it?

[Skyler4856]

Wouldn't the ideal range for g load be less than one? One reason that is most readily available is caloric load required

[MrZayas1]

Does these help visualize it?

Yes they help me visualize it, thanks for showing me how it works, but I don't think astronauts would appreciate bouncing around for like 3-4 minutes hitting there heads on things while gravity sets in, is there any possible way to mitigate this?

[Wanderfound]

Yes they help me visualize it, thanks for showing me how it works, but I don't think astronauts would appreciate bouncing around for like 3-4 minutes hitting there heads on things while gravity sets in, is there any possible way to mitigate this?

Sit down and do up your seatbelt as it spins up. Or hold on tight to the ladder if you're moving from the hub to the wheel.

It's not that big an issue.

[Rakaydos]

For the record, a "Halo" style orbital station with a Million KM radius and a 24 hour rotation (for a proper day-night cycle) generate just over .5g

[lincourtl]

Other than that, what happens when you jump? Do you fall down, or do you slide sideways?

There are two fictitious forces at play. Centrifugal force which pushes you to the outside, and the Coriolis effect which is at 90 degrees to the rotation axis, and the direction of motion. So if you run in the direction of rotation, the Coriolis effect will make you feel slightly heavier, while if you run counter the direction of motion, you'll feel slightly lighter. If you jump, on your way "up" will be pushed forward (toward the direction of rotation) a bit, and on your way "down" you'll be pushed a little backwards.

And yeah, this plays havoc with your sense of balance. It's not too bad at all at low rotational speeds, but it's unlikely your inner ear could compensate at higher rotational speeds.

On edit: Wiki explains the Coriolis effect really well. And there's an animated GIF, so bonus. http://en.wikipedia.org/wiki/Coriolis_effect

Edited December 13, 2014 by lincourtl

[NERVAfan]

I edited the wiki for this years ago.

You need a radius of 224 m to achieved earth gravity at 2 rpms, more rpms and Coriolis effect on the inner ear becomes noticeable.

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

Maybe so, but it's not clear to me that "noticeable" equates to bad (or that it even would remain noticeable after a while -- often continuous stimuli, like noise or smells, stop being noticed). You adapt to zero-g (stop feeling nauseous) after a while, the same would probably happen to this.

OTOH, I don't think it's actually necessary for near-term stuff. Valeri Polyakov spent 14 months in microgravity on Mir and apparently was able to walk out of the capsule upon landing; it's only 8 months to Mars.

And IIRC current ISS exercise stuff is dramatically better for bone loss than what they had then; IIRC it's near zero (though there are still some visual effects etc.)

So we don't need it for Mars IMO.

[bm92]

If you built a 'ring world' with a radius of 100Km around Mars, spincalc suggest angular velocity of 0.002357 rpm (about 7 hrs for 1 rev) - how much would this reduce the coriolis effect?  What would be an acceptable reduction for human comfort and even lower for human noticability?  How big would the ring need to be to achieve these values?  Would you still feel anything walking or jumping tangentially to the rotation or along the direction of rotation?

[Wjolcz]

Why not take 2 ships, a crewed one and a tanker, tie them together with a cable and spin to 1G? Even if the cable fails and snaps both ships can continue the trip on their own or re-rendezvous and reconnect the cable.

If the ship can whithstand 1G standing on a launchpad on Earth then it can be used to simulate 1G without the complexity of a centrifuge.

[linuxgurugamer]

30 minutes ago, Wjolcz said:

Why not take 2 ships, a crewed one and a tanker, tie them together with a cable and spin to 1G? Even if the cable fails and snaps both ships can continue the trip on their own or re-rendezvous and reconnect the cable.

If the ship can whithstand 1G standing on a launchpad on Earth then it can be used to simulate 1G without the complexity of a centrifuge.

Well, to start, the stresses may not be the same.  Then you have the issue of spinning up and back down.  Midcourse corrections will be difficult. To say the least.  Finally, if the cable breaks. The tanker and ship will be on diverging courses, both of which will be sure to miss the target.

[kerbiloid]

And the cable elasticity turns it into yoyo.

[tomf]

4 hours ago, linuxgurugamer said:

Well, to start, the stresses may not be the same.  Then you have the issue of spinning up and back down.  Midcourse corrections will be difficult. To say the least.  Finally, if the cable breaks. The tanker and ship will be on diverging courses, both of which will be sure to miss the target.

For midcourse correction you would just cancel the spin, wind the cable in and reconnect the halves, perform the burn and then spin up again.

If you use a 1000m cable that the two halves have a relative velocity of 100m/s, it should be perfectly possible for the two parts to use their OMS to rendevous, hook up again and resume tumbling.