Artificial Gravity from Rotation

[sanman]

Since Man's physique tends to atrophy in the absence of the force of gravity, the idea of a rotating vessel or station has been suggested to counter this.

What level of artificial gravity is suggested as most suitable to keep astronauts healthy on prolonged space missions? 1G? 0.5G? 0.2G? 1.5G? 2G? How much?

Furthermore, what would be the most practical and effective design for a rotating station or vessel? Space Wheel? Barrel? Coil? Sphere? What?

Should a space vessel meant to travel somewhere have a different shape than a space station meant to only stay in orbit? Or will whatever shape that works for one automatically work for the other?

What size/diameter should the vessel/station be? What curvature gradient should it have?

[Hop_David]

Since Man's physique tends to atrophy in the absence of the force of gravity, the idea of a rotating vessel or station has been suggested to counter this.

What level of artificial gravity is suggested as most suitable to keep astronauts healthy on prolonged space missions? 1G? 0.5G? 0.2G? 1.5G? 2G? How much?

Furthermore, what would be the most practical and effective design for a rotating station or vessel? Space Wheel? Barrel? Coil? Sphere? What?

Should a space vessel meant to travel somewhere have a different shape than a space station meant to only stay in orbit? Or will whatever shape that works for one automatically work for the other?

What size/diameter should the vessel/station be? What curvature gradient should it have?

Largely unknown.

Lampyridae posted some good links a while back:

http://chamberland.blogspot.com/2006/07/dangers-of-artificial-gravity.html

http://www.graybiel.brandeis.edu/history/walthamnews.html

http://www.graybiel.brandeis.edu/history/finalfrontier.html

http://www.ncbi.nlm.nih.gov/pubmed/14501105

http://jn.physiology.org/cgi/reprint/80/2/546.pdf

DiZio and Lackner are pioneering this research. DiZio is such an appropriate name, though!

Clicking the top of that quote will also take you to an earlier thread that covered this topic.

[scienceguy]

Meliga et. al. (2005) found that 10 out of 16 people subjected to 23 rpm at a 2 m radius (head at center of rotation) for 30 to 40 minutes got motion sickness. Young et. al. (2001) and Elias et al. (2007) found something similar. All of these studies used 2 m as a rotation radius! If only someone had used 3 m! Then we would have one more data point!

Anyway, with these 3 data points, “very” motion sick at 0 m, “some” motion sickness at 2 m (after around 30-40 min) and “no” motion sickness at infinite radius, I tried to draw a graph and extrapolate. The graph I drew uses a “motion sickness index” of 0-10, 0 meaning no sickness, 5 meaning “some” and 10 meaning “very sick”. I used 1000 m for “infinite” radius.

As you can see from the graph, anything 100 m or more leads to almost no motion sickness. Of course, this graph is very roughly estimated from only 3 data points.


References

P. Z. Elias∗, T. Jarchow, L. R. Young (2007) Modeling sensory conflict and motion sickness in artificial gravity. Acta Astronautica 62: 224-231.

P. Meliga, H. Hecht∗, L. R.Young and F. W. Mast (2005) Artificial gravity—head movements during short-radius centrifugation: Influence of cognitive effects. Acta Astronautica 56: 859-866.

L. R. Young, H. Hecht, L. E. Lyne, K. H. Sienko, C. C. Cheung, J. Kavelaars (2001) Artificial Gravity: Head Movements During Short radius Centrifugation. Acta Astronautica 49: 215-226.

[sanman]

Hi, thanks for that!

So assuming the 100m radius is the optimal tradeoff for minimum size without motion sickness, then we are talking about a ~200m diameter  space station or spacecraft.

That size of space station would have to be assembled in pieces then, with a considerable number of launches.

To minimize the number of launches, how about just a simple linear design having a 200m length? It would have to spin end-over-end, like a cheerleader's baton.

Is that a feasible design? The endpoints could be the sleeping quarters for the crew, and could perhaps provide 1.2G just to give slightly extra exertion to their muscles.

[scienceguy]

Hi, thanks for that!

So assuming the 100m radius is the optimal tradeoff for minimum size without motion sickness, then we are talking about a ~200m diameter  space station or spacecraft.

That size of space station would have to be assembled in pieces then, with a considerable number of launches.

To minimize the number of launches, how about just a simple linear design having a 200m length? It would have to spin end-over-end, like a cheerleader's baton.

Is that a feasible design? The endpoints could be the sleeping quarters for the crew, and could perhaps provide 1.2G just to give slightly extra exertion to their muscles.

I don't know if that's a feasible design; I'm not an aerospace engineer.

Like you said, you would want a minimum number of launches, so I agree that a "baton"-shaped structure would minimize that.

[hop]

To minimize the number of launches, how about just a simple linear design having a 200m length? It would have to spin end-over-end, like a cheerleader's baton.

Tethers have also been proposed.

1.2G just to give slightly extra exertion to their muscles.

Most certainly you want to push the envelope in the other direction. If say 1/3 G with lots of exercise will do the trick, the whole thing gets a lot easier.

[MickQ]

While people usually associate Artifical Gravity with the  classic  2001 : A Space Odyssey  station, in reality, that kind of structure is probably further away than a manned landing on Pluto.  IMHO.

The idea of the cheerleaders baton design seems more practical from both economic and engineering perspectives.  I think that the whole craft need not be pressurized, only the occupied outer modules.  My idea is for a central hub with telescoping truss arms extending out in 2, 3 or 4 directions, depending on the mission requirements, with a module at the end of each arm.  Inhabited sections could be in one module, nuclear power in another, rovers and landers in another etc.

Telescoping the arms would vary the induced gravity for the same spin rate.  For a Mars mission the craft could be spun up to provide close to 1G when leaving Earth.  During the transit the arms would be gradually pulled in to wind the gravity down to 1/3G before arriving at Mars and the reverse happens on the return trip.

Does this work for anyone ?

Mick.

[kkattula]

Surely it would be far easier to slow the spin rate than telescope the arm length?

Why put anything except crew hab in a spun section?

[SimonFD]

Telescoping the arms would vary the induced gravity for the same spin rate.  For a Mars mission the craft could be spun up to provide close to 1G when leaving Earth.  During the transit the arms would be gradually pulled in to wind the gravity down to 1/3G before arriving at Mars and the reverse happens on the return trip.

We see what happens when ice skaters pull their arms in during a spin.....the rotation speeds up, so you'd need to counter this with some kind of thruster. If you need thrusters anyway, why complicate things with telescopic arms.

[Lampyridae]

Since Man's physique tends to atrophy in the absence of the force of gravity, the idea of a rotating vessel or station has been suggested to counter this.

What level of artificial gravity is suggested as most suitable to keep astronauts healthy on prolonged space missions? 1G? 0.5G? 0.2G? 1.5G? 2G? How much?

NASA tends to go with 0.25g as the minimum. Lower than that, with short radii, you wind up in zero gee if you walk against the direction of spin.

Furthermore, what would be the most practical and effective design for a rotating station or vessel? Space Wheel? Barrel? Coil? Sphere? What?

The most practical for small crews is a cylindrical module on a stick, with the floors arranged skyscraper style and a counterweight such as nuke reactor on the other end of the stick.

Should a space vessel meant to travel somewhere have a different shape than a space station meant to only stay in orbit? Or will whatever shape that works for one automatically work for the other?

It doesn't really matter. Drives like VASIMIR produce such low thrust that structure is hardly affected.

What size/diameter should the vessel/station be? What curvature gradient should it have?

15m radius with 4RPM and 0.25g is touted by NASA as being the smallest feasible. I reckon you could go smaller, have higher RPM and/or g levels.

[Lampyridae]

While people usually associate Artifical Gravity with the  classic  2001 : A Space Odyssey  station, in reality, that kind of structure is probably further away than a manned landing on Pluto.  IMHO.

The idea of the cheerleaders baton design seems more practical from both economic and engineering perspectives.  I think that the whole craft need not be pressurized, only the occupied outer modules.  My idea is for a central hub with telescoping truss arms extending out in 2, 3 or 4 directions, depending on the mission requirements, with a module at the end of each arm.  Inhabited sections could be in one module, nuclear power in another, rovers and landers in another etc.

Telescoping the arms would vary the induced gravity for the same spin rate.  For a Mars mission the craft could be spun up to provide close to 1G when leaving Earth.  During the transit the arms would be gradually pulled in to wind the gravity down to 1/3G before arriving at Mars and the reverse happens on the return trip.

Does this work for anyone ?

Mick.

Many designs using ion / VASIMIR propulsion resemble yours. Except for the telescoping bit, that's not needed. Just use propellant to spin up / down.

The whole thing may would rotate, with fuel tanks at the CoG. Only the comms and nav assembly need be despun.

[kevin-rf]

Why does everyone always say you need propellant to spin down?

You don't!

A gyro (reaction wheel) or set of gyro's perpendicular to the axis of rotation will stop the rotation. No need to waste reaction mass.

Also, com and nav do not need to be despun. A properly designed phased array antenna can handle the rotation with zero moving parts.

[sanman]

Gyro wheel sounds cool, because it can be solar powered. So I presume that a very small wheel can compensate for its low mass by turning very rapidly?

Also, wouldn't the wheel have to be placed in the exact center of the space station's axis of rotation? How would you be able to tell where that was, exactly? Because it even might change slightly, depending on where people move around.

[mlorrey]

Gyro wheel sounds cool, because it can be solar powered. So I presume that a very small wheel can compensate for its low mass by turning very rapidly?

Also, wouldn't the wheel have to be placed in the exact center of the space station's axis of rotation? How would you be able to tell where that was, exactly? Because it even might change slightly, depending on where people move around.

Ok since we're generally agreed on a baton architecture, with a nuke at one end and cylindrical hab at the other, then since a gyro is generally going to be dead mass, you might as well put it to good use in other things, so make the gyro out of depleted uranium as a radiation shadow shield.

[thomson]

What level of artificial gravity is suggested as most suitable to keep astronauts healthy on prolonged space missions? 1G? 0.5G? 0.2G? 1.5G? 2G? How much?

Largely unknown.

Shouldn't this start with departure gravity (1G for Earth) and slowly increase/decrease to match destination (0.4G for Mars)? Possibly match destination some time before arrival to ease body adaptation process while still en route.

[JDCampbell]

Why does everyone always say you need propellant to spin down?

You don't!

A gyro (reaction wheel) or set of gyro's perpendicular to the axis of rotation will stop the rotation. No need to waste reaction mass.

Also, com and nav do not need to be despun. A properly designed phased array antenna can handle the rotation with zero moving parts.

What about docking issues?

[TyMoore]

The trouble with using gyro wheels is that it needs to store all of the angular momentum of the larger rotating structure, in a comparatively small package. To keep it light, it must spin at tremendous speed. Still you're talking about several tons of otherwise dead weight.

Also, what happens when the flywheel nears saturation (approaches maximum speed) and can't store anymore angular momentum? You need a way to bleed off that angular momentum, and you can only do that with thrusters.

And what about redundancy--what happens if a flywheel 'fails?'

Flywheels are good for comparatively small angular momentum changes required for slow, careful angular displacements, which is why they are used on many spacecraft these days. But using them to spin up or spin down a manned, artificical gravity spacecraft sounds like an awful lot of momentum. I'd have to do some calculations to see how much momentum this is likely to be...I can only say now, it is a bunch!

Momentum must be conserved.

[SpacexULA]

Crazy idea, but I have to say it.

Why not use your water storage as a component of your flywheel?

When you leave you have 4-5 donuts full of frozen fresh water, over the course of the mission you empty the donuts, and then fill them back with the unprocessed parts of the urine and other water wastes.

You should have ruffly the same amount of water in the tanks thoughout the mission, in case of solar flare you shut down the flywheel and crawl inside the donut, and it allows your flywheel to weigh tons, but not add considerably to the weight of the mission.

[Lampyridae]

Crazy idea, but I have to say it.

Why not use your water storage as a component of your flywheel?

When you leave you have 4-5 donuts full of frozen fresh water, over the course of the mission you empty the donuts, and then fill them back with the unprocessed parts of the urine and other water wastes.

You should have ruffly the same amount of water in the tanks thoughout the mission, in case of solar flare you shut down the flywheel and crawl inside the donut, and it allows your flywheel to weigh tons, but not add considerably to the weight of the mission.

Slosh issues when spinning up. How do you freeze it evenly enough? Also, urine / wastes will create precipitates and inhomogeneities (wow spelled that right first time!) that unbalance the doughnut. But that is good thinking, perhaps some kind of cargo could be used, or simply spin up an empty spent stage.

Best to use water for radiation shielding, spin the whole craft up. I have a link somewhere about an AG + VASIMIR + transhab Mars mission drawn up by NASA. That's probably the best way to do it.

Here it is:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070023306_2007019854.pdf

[sanman]

Well, now that I think about it, the "flywheel" doesn't have to be a dead mass - it could be some mass of useful equipment performing other useful duties, as long as it meets the criteria for flywheel usage.

It would then probably have to be solid-state equipment, without any moving parts to disturb/complicate the flywheel spin operation. The mass would have to be uniformly distributed radially, etc. The equipment has to be able to withstand rotational forces and still function.

Maybe your flywheel could be a large dish antenna, providing high-bandwidth communication with Earth.

Suppose you were on a voyage using some kind of VASIMR or ion-propulsion which provides prolonged thrust for the duration of the voyage? Spinning that propulsion unit along its thrust axis would ensure that the thrust is perfectly symmetrically centered around that axis, thus alleviating the need for any potential discrete course corrections due to any asymmetries/imperfections in the thrust. That spinning propulsion unit is then serving as a flywheel.