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.

[hop]

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.

This makes the design of both more expensive. High speed flywheels have particular requirements, and even at low speeds balance is going to be critical.

Spinning up to a few RPM is a very modest dV. For example, in the 15m / 4RPM case, the outer part is traveling at about 6.3 m/s. Unless you need to spin up and down every day, KISS says just use a rocket.

[kevin-rf]

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.

No you do not. A gyro (any spinning mass) has a resistance to turning end over end. Placing a gyro with an axis rotation perpendicular the larger rotating structures axis of rotation with experience a force that will slow down the structures rotation over time. The larger the gyro, the larger this force is, but a small force will over time also stop the structures rotation. A five pound gyro will given enough time stop any structure. It does not have to be a multi-tonne monster.

It is really an issue of how fast do you really need to despin.

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.

I am not talking storing energy in flywheels, or using them for spinup.

[Pedantic Twit]

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.

No you do not. A gyro (any spinning mass) has a resistance to turning end over end. Placing a gyro with an axis rotation perpendicular the larger rotating structures axis of rotation with experience a force that will slow down the structures rotation over time. The larger the gyro, the larger this force is, but a small force will over time also stop the structures rotation. A five pound gyro will given enough time stop any structure. It does not have to be a multi-tonne monster.

It is really an issue of how fast do you really need to despin.

But where does all of the poor angular momentum go? 

[sanman]

Yeah, that's actually a pretty interesting effect then.

So then does it only work one way? If you keeping spinning your perpendicular gyro/flywheel, and it slows down the rotation of the vehicle, then what happens if you suddenly halt the gyro/flywheel spin? Surely the missing vehicle rotation doesn't return, does it?

Somebody better explain this to me, otherwise it sounds like you're defying the conventional laws of physics, and causing momentum to be destroyed.

Does this have anything to do with frame-dragging, btw?

[drbobguy]

I don't know why more people don't think of using tethers.  One of the great important points of on-orbit engineering is that tensile strength is much lighter than compressive strength.

So say we have a 1,000 kg spacecraft.  Stick a 100kg weight out at 1km with a tether, and then spin the whole thing up with a reaction control system.  Effective rotation radius: 100m (based on the center of gravity).

Also, I don't think you need gyroscopes for rotation, unless spinning up and down is a common thing.  Rotational velocities are low for this kind of thing (in comparison to the delta V required for a manned mission somewhere).  And presumably the whole point of having a rotating spacecraft is because there is a long, uninterrupted mission.  So just use an RCS for the spin up and spin down (e.g. after the earth departure burn and before entering Mars orbit).

[ddunham]

No you do not. A gyro (any spinning mass) has a resistance to turning end over end. Placing a gyro with an axis rotation perpendicular the larger rotating structures axis of rotation with experience a force [...]

Yes.

that will slow down the structures rotation over time.

It seems to me you are ignoring precession. The gyro will not simply slow the exterior rotation down over time (like a directly opposing force such as friction would).  The angular momentum has to go somewhere.
--
Darren

[go2mars]

Aside from tethers, the most obvious solution is posted here:

http://forum.nasaspaceflight.com/index.php?topic=9733.30

[mlorrey]

Yeah, that's actually a pretty interesting effect then.

So then does it only work one way? If you keeping spinning your perpendicular gyro/flywheel, and it slows down the rotation of the vehicle, then what happens if you suddenly halt the gyro/flywheel spin? Surely the missing vehicle rotation doesn't return, does it?

Somebody better explain this to me, otherwise it sounds like you're defying the conventional laws of physics, and causing momentum to be destroyed.

Does this have anything to do with frame-dragging, btw?

You don't halt the flywheel spin, you store the angular momentum in it until you need it again. So, for instance, when you escape earth orbit, you use the flywheel to spin the vehicle up to its artificial gravity inducing speed at the G level you want by causing the previously still flywheel to spin up in the opposing direction. Once you are ready to insert into Mars orbit, you use the same spun up flywheel to spin down the structure by dumping the flywheel's counter rotating angular momentum into the structure. Same process on the return trip.

[sanman]

What TyMoore was talking about, was that if the gyroscope's axis of rotation was perpendicular to the axis of rotation of the spacecraft, saying it could halt the rotation of the spacecraft because the gyroscope resists a change to its axis of rotation.

Does that really work?

[MickQ]

When I proposed the telescopic arm idea I was thinking of a more robust and re-usable vehicle than two tin cans and a piece of string.  Tethers are OK for a technology demonstrator or maybe a one-off special purpose mission but for  a more permanent work around to the gravity problem I feel a more permanent type of design/method/solution etc is required.

By telescoping the various arms different masses of the various modules could be balanced around the central hub.  These modules could comprise 1. Control and accomodation,  2. nuclear power,  3. hydroponic garden,  4. mission specific equipment  etc.

I know there may be no need to spin anything but the permanently occupied module but we know how to grow plants in gravity a lot better than in zero G and what can it hurt by spinning all the rest as well ?  It seems to me that it would be easier to spin the whole craft rather than one portion of it.

Sooner or later we will go to Mars, because it is there, and we will likely go more than once.  We will also go to the outer planets and moons, because they are there.  Multiple re-use or multi year, long term missions really need a substantial space vehicle.    All IMHO of course.

Mick.

[mlorrey]

What TyMoore was talking about, was that if the gyroscope's axis of rotation was perpendicular to the axis of rotation of the spacecraft, saying it could halt the rotation of the spacecraft because the gyroscope resists a change to its axis of rotation.

Does that really work?

Conservation of angular momentum says that you could reduce the vehicles rotation but what would happen would be that it would be translated into rotation about the axis of the gyroscope, although the gyroscope could then counter that rotation. Accomplishing this would result in a significant amount of multiaxis tumbling in the spacecraft that you would want to avoid.

I personally recommend making a drum of depleted uranium to act both as a shadow shield for the nuclear reactor and as a flywheel for the artificial gravity. It's axis would be parallel to the vehicles axis of rotation (it doesn't need to be positioned at its center of gravity to do its job)

[GraphGuy]

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.

Spin up using a gyro and give it lots of your momentum so that your craft rotates.  Once your craft is up to speed, eject the gyro so that it floats away.  Momentum is conserved just in two disconnected bodies.

Fast gyro failure in the center of your ship is incredibly bad.  Keep spare gyros for spin down/ respinning as the mission requires.

[HappyMartian]

Astronaut Muscles Waste in Space   Thursday, August 19, 2010

"The destructive effects of extended weightlessness to skeletal muscle - despite in-flight exercise - pose a significant safety risk for future manned missions to Mars and elsewhere in the Universe."

See:  http://www.spaceref.com/news/viewpr.html?pid=31469

Cheers!

Edited.

[JohnFornaro]

It has always seemed to me that a lot of effort could be saved by building in rotation base artificial gravity from the very beginning.  One very important factor can be immediately eliminated from the short term engineering problem.  Yes, there would be a mass penalty, but it seems to me that the human penalty which we already know of is outweighed.  YMMV.

[alexterrell]

Aside from tethers, the most obvious solution is posted here:

http://forum.nasaspaceflight.com/index.php?topic=9733.30

That uses a Sea Dragon with a 25 metre diameter.

You could get an inflatable 50 diameter torus into a SDHLV, complete with spinning wheels.

What you can't get in to the 80 tons or so is sufficient shielding. 4mm of fibre is not reassuring enough.

[alexterrell]

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.
......

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.

Do you have a source for this (as it's rather fundamental to the future of human space-flight)?

[aero]

NASA tends to go with 0.25g as the minimum.

Is that a construction constraint or is that a human health constraint? Yes, the answer is very important because Mercury, Earth,  Mars and Venus are the only places in the solar system with gravity greater than 0.25g excluding the gas giants. And we can't colonize Mercury or Venus so that leaves us with Mars and Mars only as a target planet to colonize.
http://www.exploratorium.edu/ronh/weight/index.html (Use 100 %)

[orbitjunkie]

NASA tends to go with 0.25g as the minimum.

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.

Do you have a source for this (as it's rather fundamental to the future of human space-flight)?

Here is one (older, from 2002) source that disagrees.
http://selenianboondocks.com/2010/06/agnep2/
Click the link at the bottom of the post to the JSC slides. Slide 6 basically states that 1g is 'required' since there is no data for other gees and obtaining such data would be expensive.

I guess the thinking is, why go to the trouble of building one rotating station when you may discover that it doesn't accomplish what you hoped it would? Just build one for what you know will work. A simple solution to that, of course, would be design one for research purposes that could go up to 1 gee but modify it's rotation rate. Do multiple long-term studies there.

[Proponent]

FWIW I recall attending a lecture by researcher from the University of Birmingham (England) several years ago.  I recall him saying that at least 1/3 G was needed for significant health benefit.  Mars being just at that level, it was unclear what the long-term implications of stays on its surface were.

[AGStoddard]

Hello - Long time lurker on NASASpaceflight who has finally decided to join in on the discussion.  While I've been following the discussion regarding DIRECT for years, this topic finally prompted me to post as I have been contemplating this very subject for some time now.

Given what we know about the degenerative effects of long-term exposure to Zero-G, it seems to me that one of the pre-requisites for a robust BEO exploration program is a much better understanding of how to mitigate these effects with artificial gravity. We need to have solid, experimentally based data on what g-loads are required to mitigate the bone-lose, muscle-loss, and other deterioration that occurs in zero-g.  We need to understand what rotational rates are acceptable to humans, and what they can become accustomed to.  We need to understand the "real" life impact of prolonged living in a rotating AG environment - i.e. impact between pro-grade and retro-grade motion, gravity gradients, station support in non-zero-G, the sleeping vs exercising impacts/benefits of AG, etc.

As such, I believe one of the first missions for the SLS (if even that is required) should be deployment in LEO of a "small", "inexpensive" artificial gravity research station that would allow us to vary the key parameters of rotational AG and test the physiological impacts over extended periods - relative to the known impacts of zero-g and the expected requirements of prolonged manned missions.  Now, small and inexpensive are, or course, relative.  But what I have in mind is a tether based station that would be comprised primarily of a Bigelow type habitation module with airlock and docking module, a counterweight, and a "central" hub consisting mainly of a cable-spool/winch system that could be used to reel/unreel the hab and counter-weight to various diameters.

This system would allow you to test the impact of multiple G-loads, based upon multiple combinations of rotational speed and system diameter.  Such data would, I believe be invaluable in the design of MTV's and other, extended duration habitation modules for Beyond-Earth Exploration.

I'd be interested in your thoughts and comments, as I am working on fleshing out this concept into a more detailed design over the next days and weeks.

[kkattula]

...
I'd be interested in your thoughts and comments, as I am working on fleshing out this concept into a more detailed design over the next days and weeks.

I think it's a very good idea.

Of course I also think J-130 (SLS Lite? whatever...) needs some big but inexpensive payloads for the first few years. So I'd build a big, dumb, 2001-like wheel station out steel segments produced in a shipyard.

[rklaehn]

...
I'd be interested in your thoughts and comments, as I am working on fleshing out this concept into a more detailed design over the next days and weeks.

I think it's a very good idea.

Of course I also think J-130 (SLS Lite? whatever...) needs some big but inexpensive payloads for the first few years. So I'd build a big, dumb, 2001-like wheel station out steel segments produced in a shipyard.

I think it would be premature to build a 2001 style station until we find out how much gravity is required to prevent bone loss etc. and how much coriolis force is tolerable. So the first mission should require no assembly and preferably be launched on an existing launch vehicle.

A bigelow sundancer module connected to a counterweight/propulsion module by a deployable boom/tether could be launched fully outfitted and still fit on a Delta IV heavy or maybe even an Atlas V 551. The counterweight would contain enough propellant to spin/despin the entire assembly multiple times, so docking could happen in zero gravity.

Once you have figured out the optimum parameters (radius, rotation rate) for the station you could build a 2001 style station out of a ring of of bigelow ba330 modules. That would create demand for both the SLS and the bigelow stations.

[Xinvoker]

We need to have solid, experimentally based data on what g-loads are required to mitigate the bone-lose, muscle-loss, and other deterioration that occurs in zero-g. 

100% agree. It's an absolutely critical knowledge.
A mini-station capable of various Gees like the one you propose would be a great way to get this information. Not only we need this for future space stations and manned missions to Mars, but we need to know if the 0.38g of Mars is viable in the long term.

It's interesting that NASA went after AG as early as 1966 with Gemini 11, yet here we are today, AG still being an "Advanced Concept"! 

[IsaacKuo]

I agree that a spin gravity physiological research station is a good idea.  However, I think it should use I.S.S. based hardware and use as much commonality with I.S.S. hardware/procedures as possible to minimize costs.  Also, it should fly in the I.S.S.'s orbit, perhaps a few minutes ahead or behind it, so it's possible to travel from one to the other if necessary to transfer people or supplies.

The station should consist of mainly of ATV based modules--four on one end and two on the other end, to simulate Lunar gravity on the heavy side and Mars gravity on the light side.  Between them is a 120m long truss, so it spins end-over-end at 2rpm.

The reason to use a truss instead of a tether is so that the station can de-spin two or three times a year in order to dock with ATV supply ships.  The procedure is:

1) De-spin (using the ATV thrusters).

2) The two old ATV ships undock and leave (this leaves 3 MSS modules on the lunar side and 1 MSS mdoule on the Mars side)

3) The two new ATV ships dock.

4) Re-spin (using the ATV thrusters).

This means the station doesn't spin for a few hours as the trash-laden old ATV ships undock and the new supply-laden ATV ships dock.  This costs a small amount of fuel, but eliminates any need for a complex system for docking or undocking while spinning.

The old ATV ships can travel to the I.S.S., where suitable waste can be exploited for water using the I.S.S.'s more sophisticated recycling systems.

[Warren Platts]

I recall him saying that at least 1/3 G was needed for significant health benefit.

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

A simple way to get a third data point would be to set up a research station on the Moon.

Anyways, there's no crisis. We know that humans can withstand months to a year or more with no permanent ill effects. For the foreseeable future humans will be limited to short duration trips in space. A brand new space station just to test for the effects of weightlessness isn't worth it for NASA right now. It would make a good project for the second-tier space powers, however.

[JohnFornaro]

I think it would be premature to build a 2001 style station...

Well, I think we should start building it.  You don't need to say "money" in your response.  I know. 

Dang.  I worked out the numbers, but I can't remember exactly.  About 900m in diameter, about 1rpm equals dang near 1g.  The station is a clock, deliberately kept accurately rotating.  In fact, you could have a Moon and and Earh window, with a clock superimposed on the stable images.  The rotation speed is slow enough not to impose vertigo.  The two pieces are held with a tether at first, which is slowly expanded into the ring structure.

My argument is three fold.  Completely eliminate a subject from the near term need for study.  Get tourists up there in a comfortable fashion.  It is permanent. 

Don't use the word "money" in your response.

[rklaehn]

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

A simple way to get a third data point would be to set up a research station on the Moon.

I wouldn't call building a research station on the moon simple. And even if you do it, you just have one more data point (~0rpm, 0.16g). An artificial gravity research station could be done with a single launch of an EELV, and it would allow you to investigate the complete space between 0g and 1g and between, say, 1rpm and 10rpm.

Anyways, there's no crisis. We know that humans can withstand months to a year or more with no permanent ill effects. For the foreseeable future humans will be limited to short duration trips in space. A brand new space station just to test for the effects of weightlessness isn't worth it for NASA right now. It would make a good project for the second-tier space powers, however.

I disagree. If we want to build more permanent space habitats we need to know how much gravity is enough and what rpm is tolerable.

I think it would be premature to build a 2001 style station...

Well, I think we should start building it.  You don't need to say "money" in your response.  I know. 

If a heavy lifter becomes available, the US should immediately take advantage of it by building a 2001 style space station. That would be a good way to provide payloads for the heavy lifter, and be very impressive (you could call it demonstrating leadership in space to sell it to congress...)

But before building such a huge station, you should first fly a small mission to investigate what the optimum parameters are. Just a small habitable volume (bigelow sundancer), a variable-length deployable truss like this, and a counterweight with a propulsion system and enough propellant to spin the whole structure up and despin it a few dozen times for docking.

Dang.  I worked out the numbers, but I can't remember exactly.  About 900m in diameter, about 1rpm equals dang near 1g.  The station is a clock, deliberately kept accurately rotating.  In fact, you could have a Moon and and Earh window, with a clock superimposed on the stable images.  The rotation speed is slow enough not to impose vertigo.  The two pieces are held with a tether at first, which is slowly expanded into the ring structure.

There is this very nice web-based tool called spincalc to calculate parameters of artificial gravity space stations.

[alexterrell]

I disagree. If we want to build more permanent space habitats we need to know how much gravity is enough and what rpm is tolerable.

The design requirements of spin rate are even more improtant, given a = w^2 r.

GK O'Neil assumed 1g and 1 rpm for the Stanford Torus. This required a radius of 1km. For us now, very big, except with tethers.

However, it appears that most humans can take 4rpm, so that makes the radius about 60m.

Assume further that Mars gravity is acceptable - that makes the radius 24m. That's within the reach of SDHLV inflatables.

[kkattula]

Bigelow modules, ATVs?  Those are all zero-g modules. Absolutely not what you want in a rotating station.

I'm not suggesting a 900m 1g wheel straight up.  The point of a much smaller wheel is to test varying g and rpm to find out both what's tolerable and effective.

All the data we have is for small radii in a 1g field. A say 50m wheel running for months at 0.1, 0.2, 0.4 and maybe even 1 g could answer a lot of questions.

[rklaehn]

However, it appears that most humans can take 4rpm, so that makes the radius about 60m.

A 120m deployable boom should be almost a commercial off the shelf item nowadays: the ISS solar arrays use a 30m inflatable and retractable truss. And the SAR boom from STS-99 had a length of 60m.

The load on the truss would be almost exclusively tensional. The main purpose of the truss would be to keep the structure rigid when it is despun for docking or undocking. When spinning, the tension could be held by a tether inside the truss.

Bigelow modules, ATVs?  Those are all zero-g modules. Absolutely not what you want in a rotating station.

Why not? The ATV goes up on an Ariane V, so it is capable of withstanding significantly more than 1g. And a bigelow module inflated to 1 bar (14.5psi) will be almost as rigid as a car tire, so it will not deform significantly under 1g.

I'm not suggesting a 900m 1g wheel straight up.  The point of a much smaller wheel is to test varying g and rpm to find out both what's tolerable and effective.

All the data we have is for small radii in a 1g field. A say 50m wheel running for months at 0.1, 0.2, 0.4 and maybe even 1 g could answer a lot of questions.

But why a wheel? Even if you insist on using a completely rigid structure, a barbell-shaped station would be much lighter for a large radius.

[Proponent]

But before building such a huge station, you should first fly a small mission to investigate what the optimum parameters are. Just a small habitable volume (bigelow sundancer), a variable-length deployable truss like this, and a counterweight with a propulsion system and enough propellant to spin the whole structure up and despin it a few dozen times for docking.

Here's a discussion of just that concept, complete with proposal from kfsorensen.

[Proponent]

I recall him saying that at least 1/3 G was needed for significant health benefit.

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

I don't remember; I suspect he referred to bed-rest studies done at varying tilts.  That would hardly be conclusive of course, and I fully agree more research is needed.

[Warren Platts]

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

A simple way to get a third data point would be to set up a research station on the Moon.

I wouldn't call building a research station on the moon simple. And even if you do it, you just have one more data point (~0rpm, 0.16g). An artificial gravity research station could be done with a single launch of an EELV, and it would allow you to investigate the complete space between 0g and 1g and between, say, 1rpm and 10rpm.

We're going to the Moon anyway. The effects of 1/6 g will be studied by default, "for free" as it were. What if it turns out that 1/6 g is acceptable? We already know that 0 g is acceptable for 6 months  to a year a time--there are no permanent side effects.

Also, you can't launch your station and the people on it in one EELV; therefore it can't be done with a single launch of an EELV.

Anyways, there's no crisis. We know that humans can withstand months to a year or more with no permanent ill effects. For the foreseeable future humans will be limited to short duration trips in space. A brand new space station just to test for the effects of weightlessness isn't worth it for NASA right now. It would make a good project for the second-tier space powers, however.

I disagree. If we want to build more permanent space habitats we need to know how much gravity is enough and what rpm is tolerable.

But that's just it. We neather want nor need more space stations nor more permanent space stations. We already have ISS.

[rklaehn]

But before building such a huge station, you should first fly a small mission to investigate what the optimum parameters are. Just a small habitable volume (bigelow sundancer), a variable-length deployable truss like this, and a counterweight with a propulsion system and enough propellant to spin the whole structure up and despin it a few dozen times for docking.

Here's a discussion of just that concept, complete with proposal from kfsorensen.

Thanks for the link. I missed it for some reason.

It's not very detailed, but at least it confirms that a transhab style inflatable hab is fine in a 1g environment.

I think an initial facility could be done much simpler though: For starters:
- use simple thrusters for spinup and spindown.
- use multiple fixed solar arrays instead of tracking solar arrays
- have a boom in addition to the tether to avoid having to deal with tether dynamics when unspun

You could also use an ATV full of trash coming from the ISS as a counterweight. That gives you a nice ~20t counterweight for free. Have a dummy docking cone on one side of the deployable boom that the ATV can automatically dock to prior to the boom extension. The ATV would then vent its remaining propellants, depressurize and "passivize" itself.

[rklaehn]

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

A simple way to get a third data point would be to set up a research station on the Moon.

I wouldn't call building a research station on the moon simple. And even if you do it, you just have one more data point (~0rpm, 0.16g). An artificial gravity research station could be done with a single launch of an EELV, and it would allow you to investigate the complete space between 0g and 1g and between, say, 1rpm and 10rpm.

We're going to the Moon anyway. The effects of 1/6 g will be studied by default, "for free" as it were. What if it turns out that 1/6 g is acceptible? We already know that 0 g is acceptible for 6 months  to a year a time--there are no permanent side effects.

There are currently no plans to go to the moon. If "we" go to the moon, it will happen significantly after 2020. A simple rotating space station could be launched before 2015.

Also, we know that 0g is acceptable for one year for highly trained astronauts that follow a time-consuming exercise regime. If you want ordinary people to be able to live in space at some point, that is not enough. And if you want to do a mission to mars, phobos or an asteroid that lasts 2 to 3 years that is also not enough.

Also, you can't launch your station and the people on it in one EELV; therefore it can't be done with a single launch of an EELV.

I said that you could launch the station on a single EELV. The crews would obviously be launched in manned dragons or a boeing CST100.

I disagree. If we want to build more permanent space habitats we need to know how much gravity is enough and what rpm is tolerable.

But that's just it. We neather want nor need more space stations nor more permanent space stations. We already have ISS.

First of all, you don't get to decide what "we" want. I want more permanent space stations. And so does mr. bigelow and the other people posting on this thread.

Second, ISS is a station that is specifically designed to study zero gravity. It is completely unusable to study artificial gravity.

This thread is about "Artificial gravity from rotation". If you think that this is not needed and we should rather wait until 2025 when we might have a moon base, you are on the wrong thread.

[Lampyridae]

I recall him saying that at least 1/3 G was needed for significant health benefit.

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

I don't remember; I suspect he referred to bed-rest studies done at varying tilts.  That would hardly be conclusive of course, and I fully agree more research is needed.

We do have a lot of RPM research, and that shows that rotation rates of up to 10RPM are feasible. 5RPM appears well within limits for most people, and that makes a significant difference in rotation radius to 4RPM.

There is also hypergravity research with ~30RPM, and studies of "cosmonauts" who lived in a huge centrifuge for about a month.

Bed rest studies seem to indicate that bone loss is steady and permanent, governed by the equation:

Bone density = genetic baseline - (%gravity X Time) + (%gravity x Original)

So Mars would see a 0.6% bone density loss per year (with exercise)and would probably wind up at a constant 50-60% density, just above the critical threshold for fracture risk. Inertia however remains constant, so it would be higher. You could run on a tilted track on Mars or the moon to get higher g levels.

[alexterrell]

I recall him saying that at least 1/3 G was needed for significant health benefit.

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

I don't remember; I suspect he referred to bed-rest studies done at varying tilts.  That would hardly be conclusive of course, and I fully agree more research is needed.

We do have a lot of RPM research, and that shows that rotation rates of up to 10RPM are feasible. 5RPM appears well within limits for most people, and that makes a significant difference in rotation radius to 4RPM.

There is also hypergravity research with ~30RPM, and studies of "cosmonauts" who lived in a huge centrifuge for about a month.

Bed rest studies seem to indicate that bone loss is steady and permanent, governed by the equation:

Bone density = genetic baseline - (%gravity X Time) + (%gravity x Original)

So Mars would see a 0.6% bone density loss per year (with exercise)and would probably wind up at a constant 50-60% density, just above the critical threshold for fracture risk. Inertia however remains constant, so it would be higher. You could run on a tilted track on Mars or the moon to get higher g levels.

That's good info (thanks) but I don't see how you can evaluate the effects of exercise from bed rest studies.

If on Mars an 80kg person goes jogging with a 120kg backpack, won't that be just as good as jogging on Earth?

The other point of note, is that long term, humans will need to reproduce off Earth. Lots of animal experiments need to be done before that can happen.

[Hop_David]

So Mars would see a 0.6% bone density loss per year (with exercise)and would probably wind up at a constant 50-60% density, just above the critical threshold for fracture risk.

At that rate, it'd take about 85 years to reach 60% density.

.994^85 = ~.6

[JohnFornaro]

But why a wheel? Even if you insist on using a completely rigid structure, a barbell-shaped station would be much lighter for a large radius.

It starts out as a barbell, maybe even tether based, spokes and rim added incrementally.  The key thing, as I see it, is to start out at 1g, 1rpm.  Eliminate those other lines of inquiry.

True, we'll get to the Moon eventually.  But I see the hotel rooms also being a part of the space station from the beginning.  Even after we do get to the Moon, some vacations will still be less expensive than others.

See also:

http://forum.nasaspaceflight.com/index.php?topic=17823.msg437451#msg437451

http://forum.nasaspaceflight.com/index.php?topic=20529.msg547349#msg547349

http://forum.nasaspaceflight.com/index.php?topic=17264.msg422774#msg42277

[Warren Platts]

We're going to the Moon anyway. The effects of 1/6 g will be studied by default, "for free" as it were. What if it turns out that 1/6 g is acceptible? We already know that 0 g is acceptible for 6 months  to a year a time--there are no permanent side effects.

There are currently no plans to go to the moon. If "we" go to the moon, it will happen significantly after 2020. A simple rotating space station could be launched before 2015.

You're dreamin' if you think a rotating space station can be launched before 2015. We'll be lucky to get a simple, prototype propellant depot in orbit by 2015: (a) the technology isn't ready; (b) there's no pressing need, and hence no plans for one.

Also, we know that 0g is acceptable for one year for highly trained astronauts that follow a time-consuming exercise regime. If you want ordinary people to be able to live in space at some point, that is not enough. And if you want to do a mission to mars, phobos or an asteroid that lasts 2 to 3 years that is also not enough.

Thank you for making my point: 0g is acceptable for highly trained astronauts: that's who NASA sends up there; it is not NASA's job to enable ordinary people to live in space: it is not in the best interest of the US of A to subsidize colonies that are eventually going to rebel against us. As for Mars/Phobos, how do you know that humans cannot withstand 2 to 3 years of weightlessness with no permanent side effects? It's never been done before. So far, the world record holder isn't walking around with a cane, as far as I know.

I disagree. If we want to build more permanent space habitats we need to know how much gravity is enough and what rpm is tolerable. . . . you don't get to decide what "we" want. I want more permanent space stations. And so does mr. bigelow and the other people posting on this thread.

I'm merely pointing out the obvious: that NO ONE has a pressing need to make artificial gravity: not NASA, and not Bigelow. Therefore, neither NASA nor Bigelow is going to fund an artificial gravity spin station. For an outfit like the European Space Agency, however, a spin gravity research station would be an excellent initial project to cut their teeth on.

[rklaehn]

It starts out as a barbell, maybe even tether based, spokes and rim added incrementally.  The key thing, as I see it, is to start out at 1g, 1rpm.  Eliminate those other lines of inquiry.

But why 1rpm? Just because Gerard K. O'Neill used 1rpm for his island one design does not mean that it is optimal. According to Lampyridae 5rpm is well within limits for most people. And going with higher rpm is extremely helpful in reducing the size of the station.

1g at 1rpm will only be possible with tethers for the next decade or two, since it requires a radius of 900m. But tethers have a lot of complicated dynamics, especially when spinning up and despinning. At 5rpm you only need 35m radius, which is easily doable using a truss/tether combo or even rigid spokes.

So the difference between 1rpm and 5rpm is the difference between something we might do in the year 2050 and something we could start designing right now and launch before 2015.

By the way: even if we are capable of building km long structures in space at some point, there will always be situations where a lower radius is preferable. A 35m radius artificial gravity section could be integrated into even the smallest interplanetary spacecraft.

[rklaehn]

You're dreamin' if you think a rotating space station can be launched before 2015. We'll be lucky to get a simple, prototype propellant depot in orbit by 2015: (a) the technology isn't ready; (b) there's no pressing need, and hence no plans for one.

Can you please stop stating your opinions as factual statements? It is slightly annoying even when jim does it, but he is 99.95% right.

What technology in particular is not ready? The only missing technology I can identify is an affordable way to get the crews to the station. A deployable rigid truss of 60m length has been flown with STS-99. And spinning up rigid structures using thrusters gets done almost every time a satellite gets launched.

[AGStoddard]

But before building such a huge station, you should first fly a small mission to investigate what the optimum parameters are. Just a small habitable volume (bigelow sundancer), a variable-length deployable truss like this, and a counterweight with a propulsion system and enough propellant to spin the whole structure up and despin it a few dozen times for docking.

Here's a discussion of just that concept, complete with proposal from kfsorensen.

I'm not having any success connecting to your link - do you have a specific web address?

[AGStoddard]

Lots of good discussion, which is fantastic. 

For those that don't feel studying AG is a high priority (Warren et. al.), I'm trying to understand if your argument is one of lack of NEED, or lack or URGENCY.  Given the well documented adverse physiological impacts of Zero-G, and the desire of most of us on these forums for humanity to eventually live and explore in space - which will require stays of years in sub 1-G environments, I fail to understand how this can be something that doesn't need to be researched. 

IF we can agree on that, then it becomes a question of a) how best to conduct that research, and b) how urgent that research is, in terms of time-frame and devotion of resources relative to other research and exploration projects.

Starting with b), I believe we must, realistically, have a solid understanding of how to mitigate Zero-G impacts before we can even adequately PLAN for missions to Mars.  Could we over-engineer the whole thing with a huge centrifuge, or have the crew exercise for 4 hours every day on the way out, on the planet, and on the way back? Yes.  Is that a safe and efficient approach that maximizes our resource investment and that is repeatable for multiple missions - no.

We also know that rigorous research into this question will take years - by definition.  If we want to study the impact of various G-loads and spin rates on mitigating Zero-G deterioration, we will need to devote many months of study (likely 3-6) at each of the various spin/radius combinations that we may want to investigate.  That's likely something like 3, 4, and 5 RPMs at various radii generating from .16 to .38 to .5 G's 

That would translate to a minimum of 2 years of study, and possibly as many as 4.  Since I, personally, would like to see us get to Mars in my lifetime, I'd like to see us get started on the research sooner rather than later, so we can complete it by 2020 and get started on the Mars mission planning!

[AGStoddard]

I think it would be premature to build a 2001 style station...

Well, I think we should start building it.  You don't need to say "money" in your response.  I know. 

Dang.  I worked out the numbers, but I can't remember exactly.  About 900m in diameter, about 1rpm equals dang near 1g.  The station is a clock, deliberately kept accurately rotating.  In fact, you could have a Moon and and Earh window, with a clock superimposed on the stable images.  The rotation speed is slow enough not to impose vertigo.  The two pieces are held with a tether at first, which is slowly expanded into the ring structure.

My argument is three fold.  Completely eliminate a subject from the near term need for study.  Get tourists up there in a comfortable fashion.  It is permanent. 

Don't use the word "money" in your response.

Without using the "M" word in response (which we all know, in reality, would end the discussion immediately), I can think of 2 important reasons.  The first is - as others have pointed out - why 1-G?  In building this type of structure, with specific plans to make it "permanent", you are committing to a given design.  Are you sure that tourists really want 1 G?  Actually, I would argue that tourists are likely to want Zero-G.  You may be building the world's biggest White Elephant.  Secondly, by designing up front for 1-G and 1 RPM, you are likely massively over-engineering your station.  This means you are wasting time and resources - for what may well be a sub-par solution.

Don't get me wrong.  I LOVE the concept of a 2001 style station, and I sincerely hope to see one, and hopefully visit one, during my lifetime.  And, in case Jim is lurking on this thread, before he says such a station is not realistic and not required - I don't care.  Ferrari's are not realistic and not required, but they exist, and I'm glad they do, and I hope to drive one of those before I die, too!

But creating such a station, and doing it right, will be one of the greatest construction efforts in the history of mankind - dwarfing the ISS construction effort, even with Heavy Lift.  When we do it, we need to get it right, and we have a lot to learn before we are ready to do it right.

[JohnFornaro]

But why 1rpm?

Because the station is also a clock, as I see it.  Along with eliminating gravity as a problem to be dealt with, we maintain the international language of music time, which everyone who is interested in this understands.  More terrestrial familiarity.

I prefer a rigid structure, but perhaps tethers are appropriate in the ealy stages.  De-spinning should not be part of the engineering.  Once it starts rotating, all construction happens at that leisurely pace.  Faster rotation speeds will make it harder to construct new sections.  It never stops rotating.  Above about 5rpm, 24/7, tourists start getting queasy, and laundry bills start getting significant.  The tourists "are likely to want Zero-G" on the way up and back, sure.  This is totally personal, but I would want 1G after I got there.  Of course I may be the weirdo here.

This means you are wasting time and resources - for what may well be a sub-par solution.

I would say that the par solution is, by default, 1G.  If we're going back to stay, this eliminates completely any mal-effects.  Subsequent stations can be established on different specifications.  Also, remember that saying [cough]resources[cough] is kinda like using the "M-word".2:31 PM 8/24/2010

At 5rpm you only need 35m radius, which is easily doable...

Well.  None of it is easy.  Certainly a smaller station should be easier to construct than a larger station.  It is not my personal choice to explore that size and rotation speed.

So the difference between 1rpm and 5rpm is the difference between something we might do in the year 2050 and something we could start designing right now and launch before 2015.

This is pretty much totally incorrect reasoning.  The design of either station can be started "right now".  Size, in and of itself, is not the barrier to the start of design.  Launching any completely independent habitable structure with rotational AG before 2015 is purely speculative and not a valid means of comparison either, other than to generally point out the obvious:  Smaller tends to be quicker than larger.

A 35m radius artificial gravity section could be integrated into even the smallest interplanetary spacecraft.

There's no question in my mind that smaller rotational AG solutions are appropriate for different scenarios.  I'm just personally interested in the big one.  This is one of those estimated .05 situations where Jim is wrong.  IOW, John 1, Jim 9900, undecided 4.  But who's counting?

The only missing technology I can identify is an affordable way to get the crews to the station.

That, and the friggin' trusses and all.  But you're right, I think.  If ever there was a technical problem sovlable by our current technical skills, this is it. 

Not only do we not use the "M-word" in this chat, we also do not use the term "closed cycle environmental system".  If we have the former, then we have the way to get crews, cargo and environment to and from the station.  Without the former, the discussion stays safely here on Earth, obviating the need for tempermental outbursts such as:

It is not in the best interest of the US of A to subsidize colonies that are eventually going to rebel against us.

Which is why the eventuality is planned for in the early stages.  Note that Britain gave back an incredibly wealthy colony to China a few years back, right on a 99 year schedule.  The only shots fired were scotch whiskey.  Long term political treaties and other arrangements can be made to happen, but that has nothing to do with rotational AG.

[rklaehn]

Are you sure that tourists really want 1 G?  Actually, I would argue that tourists are likely to want Zero-G.

I agree with your general point. But I think we can take it for granted that after a day of messing around in Zero-G, tourists and researchers will appreciate the comfort of a non-zero-g toilet and shower.

That, and the friggin' trusses and all.  But you're right, I think.  If ever there was a technical problem sovlable by our current technical skills, this is it. 

I don't think the truss is a problem if you limit the radius. Very large (60m) deployable and retractable trusses have been flown in space. And for a barbell shaped station you only need one truss.

[mlorrey]

Are you sure that tourists really want 1 G?  Actually, I would argue that tourists are likely to want Zero-G.

I agree with your general point. But I think we can take it for granted that after a day of messing around in Zero-G, tourists and researchers will appreciate the comfort of a non-zero-g toilet and shower.

Yeah, I can see people trying out a zero g toilet exactly once, and getting totally turned off by the idea of having to perform "fecal decapitation", except for maybe the roughing it crowd who doesn't mind wiping with leaves when they go camping.

That, and the friggin' trusses and all.  But you're right, I think.  If ever there was a technical problem sovlable by our current technical skills, this is it. 

I don't think the truss is a problem if you limit the radius. Very large (60m) deployable and retractable trusses have been flown in space. And for a barbell shaped station you only need one truss.

Yeah, imho the only real component that needs development is a soft pressurized tube to connect the hub to the rim modules, but thats really just a modification of transhab existing tech.

[rklaehn]

I don't think the truss is a problem if you limit the radius. Very large (60m) deployable and retractable trusses have been flown in space. And for a barbell shaped station you only need one truss.

Yeah, imho the only real component that needs development is a soft pressurized tube to connect the hub to the rim modules, but thats really just a modification of transhab existing tech.

For a KISS initial artificial gravity research station you would despin for docking, so you would not need any pressurized tubes. But in the long term pressurized transhab/bigelow tubes would be extremely useful.

I wonder if bigelow aerospace has some conceptual designs...

[Proponent]

I'm not having any success connecting to your link - do you have a specific web address?

If you're on L2, just look for the thread entitled "Tether-Based Variable-Gravity Research Facility Concept" under the "Constellation to Future Plan Transition" sub-forum.

Anyway, I googled it and came up with this link:

http://www.artificial-gravity.com/JANNAF-2005-Sorensen.pdf .

[hop]

Are you sure that tourists really want 1 G?  Actually, I would argue that tourists are likely to want Zero-G.

I agree with your general point. But I think we can take it for granted that after a day of messing around in Zero-G, tourists and researchers will appreciate the comfort of a non-zero-g toilet and shower.

Maybe. The transition in either direction appears to be quite uncomfortable for many people, and can take several days. A shower and a proper toilet sound good, but not so much if the price is a of day severe back pain and nausea.  Multiple frequent transitions may reduce this to an acceptable level, or not. We don't know.

Most astros, including tourists to date report that they really like zero G, once adapted. I wouldn't count on the novelty wearing of in the first couple days, especially given that a high percentage of people feel really ill in those first days.

[Warren Platts]

Lots of good discussion, which is fantastic. 

For those that don't feel studying AG is a high priority (Warren et. al.), I'm trying to understand if your argument is one of lack of NEED, or lack or URGENCY.  Given the well documented adverse physiological impacts of Zero-G, and the desire of most of us on these forums for humanity to eventually live and explore in space - which will require stays of years in sub 1-G environments, I fail to understand how this can be something that doesn't need to be researched. 

IF we can agree on that, then it becomes a question of a) how best to conduct that research, and b) how urgent that research is, in terms of time-frame and devotion of resources relative to other research and exploration projects.

That's a good way of putting the issue: I agree that there's a need for AG; however, there is no urgency. For ISS, there's no problem since astronauts are limited to 6 month tours of duty. A permanently manned lunar base would have similar tours of duty, at least at first, and there is natural gravity on the Moon. The only possible practical application for AG in the foreseeable future (within next 40-50 years) would be for trips to Mars that could be expected to last for 2 or 3 years. Quite likely, astronauts can do 2 or 3 year trips without AG that result in no permanent side effects. We don't know, because we've never tried: fact is, for 2 or 3 year stays we have exactly 1 data point: 0 rotations at 1g. Perhaps the thing to do would be to find a couple of volunteers willing to stay at the ISS for a 3 year stint, and see what happens. If there are no permanent side effects, then bone loss is not a showstopper for Mars missions. Also, the possibility of drug treatments to reduce bone loss remains an open question. These are questions that can be answered at ISS without the need for a brand new space station that's going to cost billions to construct, and then more billions to maintain on annual basis.

Starting with b), I believe we must, realistically, have a solid understanding of how to mitigate Zero-G impacts before we can even adequately PLAN for missions to Mars.  Could we . . . have the crew exercise for 4 hours every day on the way out, on the planet, and on the way back? Yes.  Is that a safe and efficient approach that maximizes [sic] our resource investment and that is repeatable for multiple missions - no.

It would be repeatable, just like going to ISS is repeatable. There is measureable bone loss, and then the astronaut recovers once he or she is back on Earth. Also, the above approach would minimize the resource investment because the cost associated with AG development and deployment is eliminated. At current budget levels, going to Mars is going to be a shoe-string operation; AG is a nice-to-have frill.

We also know that rigorous research into this question will take years - by definition.  If we want to study the impact of various G-loads and spin rates on mitigating Zero-G deterioration, we will need to devote many months of study (likely 3-6) at each of the various spin/radius combinations that we may want to investigate.  That's likely something like 3, 4, and 5 RPMs at various radii generating from .16 to .38 to .5 G's 

That would translate to a minimum of 2 years of study, and possibly as many as 4.  Since I, personally, would like to see us get to Mars in my lifetime, I'd like to see us get started on the research sooner rather than later, so we can complete it by 2020 and get started on the Mars mission planning!

You're underestimating the time, and you're not mentioning the cost at all. Right now, we know that the risks associated with 6 months to a year of total weightlessness are acceptable: if we could safely extrapolate that knowledge to 2 or 3 years, we would, but we don't because we can't. To simulate the effects of a Mars mission, you've got to have the simulation last as long as the Mars mission. Similarly, if you want 9 data points, you're looking at an 18-year program that's going to cost $20 billion USD in total, assuming it can be constructed for 2% the cost of ISS and be maintained for half the cost of ISS. I got news for ya: if you really want to die happy, such an AG station is probably going to result in the opposite effect....

[Lampyridae]

I recall him saying that at least 1/3 G was needed for significant health benefit.

But why 1/3? There is no experimental basis to say that. We have 2 data points: 1 g and zero g.

I don't remember; I suspect he referred to bed-rest studies done at varying tilts.  That would hardly be conclusive of course, and I fully agree more research is needed.

We do have a lot of RPM research, and that shows that rotation rates of up to 10RPM are feasible. 5RPM appears well within limits for most people, and that makes a significant difference in rotation radius to 4RPM.

There is also hypergravity research with ~30RPM, and studies of "cosmonauts" who lived in a huge centrifuge for about a month.

Bed rest studies seem to indicate that bone loss is steady and permanent, governed by the equation:

Bone density = genetic baseline - (%gravity X Time) + (%gravity x Original)

So Mars would see a 0.6% bone density loss per year (with exercise)and would probably wind up at a constant 50-60% density, just above the critical threshold for fracture risk. Inertia however remains constant, so it would be higher. You could run on a tilted track on Mars or the moon to get higher g levels.

That's good info (thanks) but I don't see how you can evaluate the effects of exercise from bed rest studies.

If on Mars an 80kg person goes jogging with a 120kg backpack, won't that be just as good as jogging on Earth?

The other point of note, is that long term, humans will need to reproduce off Earth. Lots of animal experiments need to be done before that can happen.

The effects zero g are comparable to studies of bed rest patients insofar as the rates of bone loss are similar and there is no +Z loading on the long bones and "anti-gravity" muscles. They are not a substitute, I agree.

You do raise interesting questions. I will do some digging around on the databases I have access to and see what I can find. The paper I'm referencing is from around 1999.

[Lampyridae]

Lots of good discussion, which is fantastic. 

For those that don't feel studying AG is a high priority (Warren et. al.), I'm trying to understand if your argument is one of lack of NEED, or lack or URGENCY.  Given the well documented adverse physiological impacts of Zero-G, and the desire of most of us on these forums for humanity to eventually live and explore in space - which will require stays of years in sub 1-G environments, I fail to understand how this can be something that doesn't need to be researched. 

IF we can agree on that, then it becomes a question of a) how best to conduct that research, and b) how urgent that research is, in terms of time-frame and devotion of resources relative to other research and exploration projects.

That's a good way of putting the issue: I agree that there's a need for AG; however, there is no urgency. For ISS, there's no problem since astronauts are limited to 6 month tours of duty. A permanently manned lunar base would have similar tours of duty, at least at first, and there is natural gravity on the Moon. The only possible practical application for AG in the foreseeable future (within next 40-50 years) would be for trips to Mars that could be expected to last for 2 or 3 years. Quite likely, astronauts can do 2 or 3 year trips without AG that result in no permanent side effects. We don't know, because we've never tried: fact is, for 2 or 3 year stays we have exactly 1 data point: 0 rotations at 1g. Perhaps the thing to do would be to find a couple of volunteers willing to stay at the ISS for a 3 year stint, and see what happens. If there are no permanent side effects, then bone loss is not a showstopper for Mars missions. Also, the possibility of drug treatments to reduce bone loss remains an open question. These are questions that can be answered at ISS without the need for a brand new space station that's going to cost billions to construct, and then more billions to maintain on annual basis.

Zero-g is not the only showstopper. Cosmic ray exposure also embrittles bone. 2 to 3 years in zero-gee will result in the astronaut BMD dropping below fracture threshold (~50%) and will almost certainly hit the 33% genetic baseline. Couple that with a high-g re-entry and you're guaranteed a couple of astronaut injury.

Starting with b), I believe we must, realistically, have a solid understanding of how to mitigate Zero-G impacts before we can even adequately PLAN for missions to Mars.  Could we . . . have the crew exercise for 4 hours every day on the way out, on the planet, and on the way back? Yes.  Is that a safe and efficient approach that maximizes [sic] our resource investment and that is repeatable for multiple missions - no.

It would be repeatable, just like going to ISS is repeatable. There is measureable bone loss, and then the astronaut recovers once he or she is back on Earth. Also, the above approach would minimize the resource investment because the cost associated with AG development and deployment is eliminated. At current budget levels, going to Mars is going to be a shoe-string operation; AG is a nice-to-have frill.

We also know that rigorous research into this question will take years - by definition.  If we want to study the impact of various G-loads and spin rates on mitigating Zero-G deterioration, we will need to devote many months of study (likely 3-6) at each of the various spin/radius combinations that we may want to investigate.  That's likely something like 3, 4, and 5 RPMs at various radii generating from .16 to .38 to .5 G's 

That would translate to a minimum of 2 years of study, and possibly as many as 4.  Since I, personally, would like to see us get to Mars in my lifetime, I'd like to see us get started on the research sooner rather than later, so we can complete it by 2020 and get started on the Mars mission planning!

You're underestimating the time, and you're not mentioning the cost at all. Right now, we know that the risks associated with 6 months to a year of total weightlessness are acceptable: if we could safely extrapolate that knowledge to 2 or 3 years, we would, but we don't because we can't. To simulate the effects of a Mars mission, you've got to have the simulation last as long as the Mars mission. Similarly, if you want 9 data points, you're looking at an 18-year program that's going to cost $20 billion USD in total, assuming it can be constructed for 2% the cost of ISS and be maintained for half the cost of ISS. I got news for ya: if you really want to die happy, such an AG station is probably going to result in the opposite effect....

I agree, we simply do not need an AG station. What we need are AG demonstrators... these can be done with a modified Orion, 3-(wo)man crews and a 3-6 month flight in LEO. This will be done partly to prove the efficacy of spacecraft systems in AG and as proof-of-concept.

Even 6 months at ISS results in BMD loss of 1.2% to 1.5% a month, which is precipitous. The calculation I made earlier was based on the best recorded case of about 1% per year. 6% per year on Mars is likely, but simply using muscles to move around and stand would probably create great benefit.

All zero-g countermeasures such as drugs and exercise are pioneered first by bed-rest subjects on Earth. I'm pretty sure AG in some form will be used, but it will either be a small internal centrifuge for exercise sessions or a large radius centrifuge, ie the spacecraft rotates.

This is the reference for a study that I just downloaded:

Justin Kaderka , Laurence R..Young, William H.Paloski
A critical benefit analysis of artificial gravity as a
microgravity countermeasure
Acta Astronautica 67(2010)1090–1102

In short, they say three things:
AG is not popular with programme managers (as in rotating the craft)
All current countermeasures basically suck, but short-radius AG largely works
More short-radius AG studies are needed

[alexterrell]

It starts out as a barbell, maybe even tether based, spokes and rim added incrementally.  The key thing, as I see it, is to start out at 1g, 1rpm.  Eliminate those other lines of inquiry.

But why 1rpm? Just because Gerard K. O'Neill used 1rpm for his island one design does not mean that it is optimal. According to Lampyridae 5rpm is well within limits for most people. And going with higher rpm is extremely helpful in reducing the size of the station.

1g at 1rpm will only be possible with tethers for the next decade or two, since it requires a radius of 900m. But tethers have a lot of complicated dynamics, especially when spinning up and despinning. At 5rpm you only need 35m radius, which is easily doable using a truss/tether combo or even rigid spokes.

So the difference between 1rpm and 5rpm is the difference between something we might do in the year 2050 and something we could start designing right now and launch before 2015.

By the way: even if we are capable of building km long structures in space at some point, there will always be situations where a lower radius is preferable. A 35m radius artificial gravity section could be integrated into even the smallest interplanetary spacecraft.

Note that GK O'Neil was designing his space station for EVERYONE.

Some people might get dizzy at 4rpm. For a Mars mission, the solution is easy: send someone else.

Another issue with tethers is space debris.

[JohnFornaro]

Another issue with tethers is space debris.

Debris affects everything, so the problem is not unique to tethers.  It would seem that a tether presents a smaller target than a strut, particularly a strut with a habitable tube.  Further, the L1 point, my favorite, has less debris than LEO.

Multiple frequent transitions may reduce this to an acceptable level

Certainly "multiple" means going and coming. Launch, travel, arrive.  Leave, travel, land.  Transitions come with the trip.

I wouldn't count on the novelty wearing off in the first couple days, especially given that a high percentage of people feel really ill in those first days.

Couldn't quite parse this.  People feel ill in the "first days".  What is the novelty that we don't count on wearing off?  Perhaps there's two days travel to a station at L1. A week stay for a tourist? Two days back?  Obviously the astros have a different perspective, but from a tourist perspective, what's there to do? 

Personally, I wouldn't mind spending some time "away from it all" as long as I could log on to NSF and bring reading/writing material.  The first tourists, rich ones, at that, would be responsible for their own entertainment, I'm guessing.  For them, perhaps the novelty factor is bragging rights, I don't know.

...and you're not mentioning the cost at all.

That's correct.  We're not using the "M-word", basically because there would seem to be little point in continuing the discussion then.

The other point of note, is that long term, humans will need to reproduce off Earth. Lots of animal experiments need to be done before that can happen.

I wonder if we'll learn this by doing it. Birds do it; bees do it, ya know?

It seems that I've read S-F stories speculating about lunar born people having an extremely difficult time adapting to 1G.  It might turn out that they may be taller and skinnier too.  What about the brain?  On the one hand, if God wanted us to fly, we would have had wings; on the other hand, we have free choice; moving off planet seems logical in some ways.

I agree, we simply do not need an AG station.

I'm not sure I follow the logic, again remembering not to use the "M-word". One gee would eliminated bone loss from the equation completely; it would not affect the cosmic ray issue. 

Also there are two scenarios suggested in the above discussion:  The big ring station/hotel/depot at L1.  The 35m dia, 5rpm crew chamber for interplanetary trips.

Note that GK O'Neil was designing his space station for EVERYONE.

For colonizing the Moon, AG is not as important.  For Mars, it is.  That mothership, built in LEO, in the fairly distant future, might have to be 900m in diameter, 2km long, carries 10,000 with their belongings and one way tickets.  It would never leave space, have a designed lifetime of 100 years, yada yada yada.

A martian orbiting lab/hotel probably ought to be 900m 1rpm,  built incrementally, first to study the ecosystem, then to be the transfer point for surface trips if that is so decided.  Its population of a hundred or so is carried up 20 at a time from the 35m 5rpm ships.  Maybe.

[Proponent]

Although we can't generate low-gravity environments on earth for any length of time, high-gravity is easy.  Has anyone considered or done experiments with, say, rats living in centrifuges?  Results then might be extrapolated backwards to the low-G regime.  This would hardly be conclusive, but it would cheap and easy.

I vaguely recall reading about high-G crystal-growth experiments done by people interested in the growth of crystals in microgravity in the years before crystal growth could be studied in space.

[Hop_David]

Has anyone considered or done experiments with, say, rats living in centrifuges?

Google: Great Mambo Chicken

[Lampyridae]

I wonder if we'll learn this by doing it. Birds do it; bees do it, ya know?

It seems that I've read S-F stories speculating about lunar born people having an extremely difficult time adapting to 1G.  It might turn out that they may be taller and skinnier too.  What about the brain?  On the one hand, if God wanted us to fly, we would have had wings; on the other hand, we have free choice; moving off planet seems logical in some ways.

Unlikely. Certainly 1g is required for muscular development during pregnancy; lower trunk muscles, bone density and length of lower vertebrae and long bones of the leg...

A human raised in low gravity would look basically something like a paraplegic with shortened legs. Or ET.

The fetus cannot exercise like an astronaut: gravity loading is necessary for the physiological development during second half of pregnancy
Medical Hypotheses, Volume 64, Issue 2, 2005, Pages 221-228
Slobodan R. Sekulić, Damir D. Lukač, Nada M. Naumović

[Lampyridae]

Although we can't generate low-gravity environments on earth for any length of time, high-gravity is easy.  Has anyone considered or done experiments with, say, rats living in centrifuges?  Results then might be extrapolated backwards to the low-G regime.  This would hardly be conclusive, but it would cheap and easy.

I vaguely recall reading about high-G crystal-growth experiments done by people interested in the growth of crystals in microgravity in the years before crystal growth could be studied in space.

I'll do some digging. From skimming the article titles, I'd say that there is increased bone and muscle development.

>EDIT<

Reading some articles now, hypergravity definitely messes with pregnancy. Neonates have difficulty righting themselves, litter sizes are smaller (partly due to cannibalism). Rat dams also don't put on as much weight.

Two forces appear to be at work: one, increased metabolic rate in hypergravity rats. Two, decreased metabolic rates during pregnancy due to hypergravity. These factors sort of cancel each other out at 1.5g, at a maximum detrimental effect, and 1.65g, 1.75g, etc. show no more increased effect.

[JohnFornaro]

Unlikely.

What's unlikely?  Unlikely that we'll learn by doing?  Of the things that people do, learning by doing is fairly common.  If we're forbidden from reproducing off planet, that would be an entirely different thing, which I haven't considered at all.  Note that I said "forbidden".  You didn't.

I suggested that people born on the Moon might be "taller and skinnier".  You suggested they might be "something like a paraplegic with shortened legs".  Whatevs.  I have no idea what they'd probably look like, and your suggestion about fetal growth also comes into play as well.

Considering rotational AG alone as a factor, it would seem that a 1g environment would not have any reproductive side effects whatsoever, hence no need to study it ad infinitum.  That money can be used to launch the additional mass required for the rotational station.

I continue to assert that this provision will completely eliminate a concern for space stations.

[alexterrell]

I wonder if we'll learn this by doing it. Birds do it; bees do it, ya know?

It seems that I've read S-F stories speculating about lunar born people having an extremely difficult time adapting to 1G.  It might turn out that they may be taller and skinnier too.  What about the brain?  On the one hand, if God wanted us to fly, we would have had wings; on the other hand, we have free choice; moving off planet seems logical in some ways.

Unlikely. Certainly 1g is required for muscular development during pregnancy; lower trunk muscles, bone density and length of lower vertebrae and long bones of the leg...

A human raised in low gravity would look basically something like a paraplegic with shortened legs. Or ET.

The fetus cannot exercise like an astronaut: gravity loading is necessary for the physiological development during second half of pregnancy
Medical Hypotheses, Volume 64, Issue 2, 2005, Pages 221-228
Slobodan R. Sekulić, Damir D. Lukač, Nada M. Naumović

You quote Medical Hypotheses, which says "gravity loading is necessary". Then you say "Certainly 1g is required".

There's no certainty here, until the hypotheses are tested. Hopefully you're wrong or Mars is going to be tough to colonise.

ISS needs a centrifuge where they can breed mice at variable gravities.

Then we need a new station where humans can live at variable g whilst breeding monkeys, and then chimps.

If the "need 1g to breed" hypothesis is correct, that's still only 60m radius at 4rpm. Perhaps Mars and Moon colonists will have to go to space stations for pregnancy (or Niven's "Farmers' Asteroid?) 

[aero]

I wonder if we'll learn this by doing it. Birds do it; bees do it, ya know?

It seems that I've read S-F stories speculating about lunar born people having an extremely difficult time adapting to 1G.  It might turn out that they may be taller and skinnier too.  What about the brain?  On the one hand, if God wanted us to fly, we would have had wings; on the other hand, we have free choice; moving off planet seems logical in some ways.

Unlikely. Certainly 1g is required for muscular development during pregnancy; lower trunk muscles, bone density and length of lower vertebrae and long bones of the leg...

A human raised in low gravity would look basically something like a paraplegic with shortened legs. Or ET.

The fetus cannot exercise like an astronaut: gravity loading is necessary for the physiological development during second half of pregnancy
Medical Hypotheses, Volume 64, Issue 2, 2005, Pages 221-228
Slobodan R. Sekulić, Damir D. Lukač, Nada M. Naumović

You quote Medical Hypotheses, which says "gravity loading is necessary". Then you say "Certainly 1g is required".

There's no certainty here, until the hypotheses are tested. Hopefully you're wrong or Mars is going to be tough to colonise.

ISS needs a centrifuge where they can breed mice at variable gravities.

Then we need a new station where humans can live at variable g whilst breeding monkeys, and then chimps.

If the "need 1g to breed" hypothesis is correct, that's still only 60m radius at 4rpm. Perhaps Mars and Moon colonists will have to go to space stations for pregnancy (or Niven's "Farmers' Asteroid?) 

As was noted above, it is easy to simulate heavier gravity. With the Mars surface gravity of 0.37 g, it will be straight forward to simulate 1 g on the surface by standard means. No need for space stations, just spin up the habitat or the critical part of it.

[alexterrell]

 
As was noted above, it is easy to simulate heavier gravity. With the Mars surface gravity of 0.37 g, it will be straight forward to simulate 1 g on the surface by standard means. No need for space stations, just spin up the habitat or the critical part of it.

I recall a discussion on this a long time ago. Creating any reasonably sized space (where someone could spend nine months) with 1g on Moon or Mars would be quite difficult.

Space station retreats might be cheaper. 

[hop]

Certainly 1g is required for muscular development during pregnancy; lower trunk muscles, bone density and length of lower vertebrae and long bones of the leg...

You know for a fact that 0.9g wouldn't do it ? How about 0.99 ?

It seems to me we can be pretty sure 0 isn't enough and 0.99 is, but what the curve looks like in between is educated guesses a best.

[go2mars]

it is not in the best interest of the US of A to subsidize colonies that are eventually going to rebel against us.

 Like Hawaii, or American Samoa?  

[go2mars]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.  I figured it was sorta the same for fetuses in the womb.  They are essentially floating in a fluid whose density is similar to their bodies.  Doesn't this suggest that lower gravity won't be a big deal for growing fetuses?

[go2mars]

But why a wheel? Even if you insist on using a completely rigid structure, a barbell-shaped station would be much lighter for a large radius.

Because with a wheel you can run or cycle or row against the direction of rotation for added gravity during exercise.  Just run along the siphuncle.

[Proponent]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.  I figured it was sorta the same for fetuses in the womb.  They are essentially floating in a fluid whose density is similar to their bodies.  Doesn't this suggest that lower gravity won't be a big deal for fetuses?

Buoyancy and microgravity aren't the same thing.  Suppose you're standing up on dry land.  The ground beneath you exerts an upward force on your feet exactly equal to your weight.  At each height in your body, the part of your body below exerts and upward force equal to the weight of the part above and vice versa.

If you're underwater, the water exerts a force equal to your weight upon your body.  The forces exerted are distributed differently than they are on land, but forces are nonetheless exerted.

In microgravity, all of these forces vanish.

To put it more viscerally, the sensation of floating (buoyancy) differs from the sensation of falling (microgravity).

[hop]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.

Do you experience SAS when you go swimming ?

[go2mars]

On testing variable g in a single EELV launch:

Have a slowly radially rotating common core tube thing with power, supplies, etc.
Coming off this at different distances from the core are mouse cages.  The distance they are from the core determines the g-force that they feel.  Perhaps have one at 0.05g, 0.1g, 0.15g, 0.2g,...0.95g, 1g, 1.05g, 1.1g... up to whatever upper limit they might be expected to survive at.

Keep them well fed and happy for perhaps 3 years, then suck them all into the same little Pica-X return capsule using the vacuum of space, freeze them, give the little return capsule some deltaV, recover them on earth, analyze them.  Lot's of biologists/physiologists would be thrilled to weigh, them, measure them, poke and prod them...

Coriolis effects shouldn't bother them too much since mice are very short.  (So fast rotation would be okay instead of long radius of rotation).

Then by the time the heavy lifter is ready to go, all this stuff has been examined.  Yes of course it would be more fun and accurate to have 40 or 50 people living in different gravity fields for years in orbit to collect data, but that might cost a little more...  I'd rather spend that kind of money building a Mars cycler with lots of artificial gravity rather than just studying effects of g forever.  The main reason to give astronauts lots of g during their voyage is so that they arrive strong enough to definately be useful right away.  Hard to collect and lug rock samples in a heavy suit all day if you've been in low g for a long time.  I'd prefer most of the voyage to be at least 1 g, then maybe the last few days slow it down to Mars gravity levels to get used to the movement.  Someone has to slam dunk the first 18 foot high hoop!   

[go2mars]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.  I figured it was sorta the same for fetuses in the womb.  They are essentially floating in a fluid whose density is similar to their bodies.  Doesn't this suggest that lower gravity won't be a big deal for fetuses?

Buoyancy and microgravity aren't the same thing.  Suppose you're standing up on dry land.  The ground beneath you exerts an upward force on your feet exactly equal to your weight.  At each height in your body, the part of your body below exerts and upward force equal to the weight of the part above and vice versa.

If you're underwater, the water exerts a force equal to your weight upon your body.  The forces exerted are distributed differently than they are on land, but forces are nonetheless exerted.

In microgravity, all of these forces vanish.

To put it more viscerally, the sensation of floating (buoyancy) differs from the sensation of falling (microgravity).

Those are some good points.  You too HOP.  But if I had a womb, and I was in a low gravity environment...  I'll just suggest that reproductive experiements might happen someday, and it might not be a big deal for the fetus.  Although these rats didn't know which way was up.  But would 5% g fix that?  Stay tuned I guess.  http://gateway.nlm.nih.gov/MeetingAbstracts/ma?f=102222743.html

[alexterrell]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.  I figured it was sorta the same for fetuses in the womb.  They are essentially floating in a fluid whose density is similar to their bodies.  Doesn't this suggest that lower gravity won't be a big deal for fetuses?

Buoyancy and microgravity aren't the same thing.  Suppose you're standing up on dry land.  The ground beneath you exerts an upward force on your feet exactly equal to your weight.  At each height in your body, the part of your body below exerts and upward force equal to the weight of the part above and vice versa.

If you're underwater, the water exerts a force equal to your weight upon your body.  The forces exerted are distributed differently than they are on land, but forces are nonetheless exerted.

In microgravity, all of these forces vanish.

To put it more viscerally, the sensation of floating (buoyancy) differs from the sensation of falling (microgravity).

Those are some good points.  You too HOP.  But if I had a womb, and I was in a low gravity environment...  I'll just suggest that reproductive experiements might happen someday, and it might not be a big deal for the fetus.  Although these rats didn't know which way was up.  But would 5% g fix that?  Stay tuned I guess.  http://gateway.nlm.nih.gov/MeetingAbstracts/ma?f=102222743.html

Then you get into ethical discussions. Will the mission allow such uncontrolled experiments when the result might be severely handicapped?

Apologies to the animal rights brigade, but it's mice first, then chimps, then humans.

[KelvinZero]

When I go swimming underwater I negligibly feel the effects of gravity due to my bouyancy.

Do you experience SAS when you go swimming ?

fair enough but I expect all that sort of stuff is from for example stuff floating around in our ears instead of settling, confusing our sense of balance which is known to make people nauseous.

As far as I know the big problem is bone and muscle loss and I expect that to be very similar whether the source is freefall or bouancy.

This isnt really something that worries me. It is a long way off. Even 6 month missions to the moon seem a horrifyingly long way off. It is a possible issue I expect we will have the knowledge to fix by the time it becomes a problem.

[hop]

fair enough but I expect all that sort of stuff is from for example stuff floating around in our ears instead of settling

The point is that floating in water is not equivalent to zero g. The inner ear provides an obvious example of why this is true, but there doesn't appear to be any reason to assume it is the only system affected.

As far as I know the big problem is bone and muscle loss and I expect that to be very similar whether the source is freefall or bouancy.

This might be a reasonable assumption, but it's unproven.

[JohnFornaro]

Then you get into ethical discussions.

And then things could become forbidden by law.  And then some will take the position, "get your laws off my body."  And then we'll find out what happens to humans born in off-planet environments.  I haven't thought about this a lot, but I typically would say, let people do what they want to do without hurting others and with responsibility for their own actions.

Another thing I'm noticing is the "engineering" approach to future human affairs.  Seemingly endless study to quantify effects in order to achieve a goal.  As we have seen before, analysis paralysis can spread thruout a bureacratic structure, so that the study of complex phenomena becomes the primary goal, and actual accomplishment becomes the secondary goal.

There's a conceptually simple way to completely eliminate gravitational effects, and the effects of motion induced nausea, but it entails mass.  Building for permanence involves mass, and lots of it.  That mass will have to be added incrementally to the L1 station, as the space market matures.

As far as I know the big problem is bone and muscle loss and I expect that to be very similar whether the source is freefall or bouancy.

We know that whales and plankton have different evolutionary solutions to the problem of bouyancy and skeletons, so I don't think that bone loss in bouyancy is at all similar to bone loss in zero gee.

[hop]

We know that whales and plankton have different evolutionary solutions to the problem of bouyancy and skeletons, so I don't think that bone loss in bouyancy is at all similar to bone loss in zero gee.

We don't know whether cetaceans suffer bone loss in zero G, for obvious practical reasons. I know fish have been flown but I don't know what the effects on their skeletal systems were. Would be interesting to find out.

Apparently rats flown in zero g did not reproduce successfully, while fish and amphibians have. See http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0006753 (the experiment discussed was not actually in zero G, but the introduction discusses some flight experiments)

See also http://www.ijdb.ehu.es/web/pdfdownload.php?doi=052077sc
This reinforces the idea that inner ear disruption is far from the only relevant effect.

[alexterrell]

Then you get into ethical discussions.

And then things could become forbidden by law.  And then some will take the position, "get your laws off my body."  And then we'll find out what happens to humans born in off-planet environments.  I haven't thought about this a lot, but I typically would say, let people do what they want to do without hurting others and with responsibility for their own actions.

Two points:
1. In the early days, it's not the law, but company policy that counts. Your company (e.g. NASA or Asteroid Mining inc) will have policies which you can accept, or you stay behind.
2. If you allow humans to gestate in space then you are at serious risk of hurting others (the new born) so until human gestation is proved safe, some form of contraception might be appropriate.

I suspect NASA would not be happy if an astronaut got pregnant one month into a stint on the ISS.

[JohnFornaro]

We don't know whether cetaceans suffer bone loss in zero G...

You do seem to miss the point often.  Whales have a lot of bone mass in a bouyant environment.  What they would experience in zero gee is not that pertinant.  I don't think that bone loss in bouyancy is at all similar to bone loss in zero gee because we have existential proof that bouyant bones get pretty big in one gee.  I will ask my Congress critter not to support the funding of a NASA study on bone loss in zero gee bouyant environment, because it would be an unneccessary waste of scarce resources, better spent on actually building a rotating ring station.  YMMV.

Or did I just take some bait?

In the early days, it's not the law, but company policy that counts...

If I know anything about people, I would say that there is probably a couple out there who is willing to be fired, because the offer from the Enquirer is much better, as one example.  Getting into "ethical discussions" will probably get the attention of the legal eagles.  Not at first, but later on.  Just sayin', since it is a messy field of inquiry.

[hop]

  I don't think that bone loss in bouyancy is at all similar to bone loss in zero gee because we have existential proof that bouyant bones get pretty big in one gee.

That doesn't follow. You are assuming that they are unrelated, and then saying that verifying the assumption is irrelevant.

A human who spent all their time floating would almost certainly suffer bone loss, similar to that produced by extended bed rest.

Whether the mechanisms that allow water dwelling creatures to avoid this are applicable to zero g is unknown (to me anyway, I suspect the effects on fish must have been reported somewhere)

[Hop_David]

We don't know whether cetaceans suffer bone loss in zero G...

You do seem to miss the point often.

Are you talking to your reflection?

I don't think that bone loss in bouyancy is at all similar to bone loss in zero gee because we have existential proof that bouyant bones get pretty big in one gee.

How in the hell would you know if they're similar or not? So far as I can tell, you're tossing out unsubstantiated opinions.

[Proponent]

We don't know whether cetaceans suffer bone loss in zero G, for obvious practical reasons.

Shhh!  Let's not talk about this--HLV enthusiasts may latch onto it as justification for HLV!

[IsaacKuo]

We don't know whether cetaceans suffer bone loss in zero G, for obvious practical reasons.

Shhh!  Let's not talk about this--HLV enthusiasts may latch onto it as justification for HLV!

Admiral, there be whales here!

[Lampyridae]

Unlikely.

What's unlikely?  Unlikely that we'll learn by doing?  Of the things that people do, learning by doing is fairly common.  If we're forbidden from reproducing off planet, that would be an entirely different thing, which I haven't considered at all.  Note that I said "forbidden".  You didn't.

Unlikely because the medical evidence suggests that they won't be tall and skinny. Children confined to bed rest for their childhood don't grow up really tall, but they are rather wasted.

I suggested that people born on the Moon might be "taller and skinnier".  You suggested they might be "something like a paraplegic with shortened legs".  Whatevs.  I have no idea what they'd probably look like, and your suggestion about fetal growth also comes into play as well.

There's probably a whole host of factors we haven't considered. Unfortunately we just don't have lifetime studies of mammals to figure it out. We'd want rabbits and goats (which need to reproduce, grow quickly and really can't be convinced to use an exercise bike ) for long-term closed life support systems.

Considering rotational AG alone as a factor, it would seem that a 1g environment would not have any reproductive side effects whatsoever, hence no need to study it ad infinitum.  That money can be used to launch the additional mass required for the rotational station.

I continue to assert that this provision will completely eliminate a concern for space stations.

It's an interesting question; however for planetary environments it's kind of difficult to generate 1g. We do know that hypergravity is detrimental to neonate rats... so no 2g centrifuge for little Johnny, probably.

[Lampyridae]

I wonder if we'll learn this by doing it. Birds do it; bees do it, ya know?

It seems that I've read S-F stories speculating about lunar born people having an extremely difficult time adapting to 1G.  It might turn out that they may be taller and skinnier too.  What about the brain?  On the one hand, if God wanted us to fly, we would have had wings; on the other hand, we have free choice; moving off planet seems logical in some ways.

Unlikely. Certainly 1g is required for muscular development during pregnancy; lower trunk muscles, bone density and length of lower vertebrae and long bones of the leg...

A human raised in low gravity would look basically something like a paraplegic with shortened legs. Or ET.

The fetus cannot exercise like an astronaut: gravity loading is necessary for the physiological development during second half of pregnancy
Medical Hypotheses, Volume 64, Issue 2, 2005, Pages 221-228
Slobodan R. Sekulić, Damir D. Lukač, Nada M. Naumović

You quote Medical Hypotheses, which says "gravity loading is necessary". Then you say "Certainly 1g is required".

There's no certainty here, until the hypotheses are tested. Hopefully you're wrong or Mars is going to be tough to colonise.

Heck, for want of a single qualifying term? But I see your point. Anyway, the evidence for vertebrates is grim... microgravity seriously messes up vestibular development, tadpoles are malformed, etc.

ISS needs a centrifuge where they can breed mice at variable gravities.

Amen. I *suspect* that 1/6 of a gee and upwards is going to be OK for a lot of things.

Then we need a new station where humans can live at variable g whilst breeding monkeys, and then chimps.

If the "need 1g to breed" hypothesis is correct, that's still only 60m radius at 4rpm. Perhaps Mars and Moon colonists will have to go to space stations for pregnancy (or Niven's "Farmers' Asteroid?) 

I think we'll get a lot of data from Mars & moon missions; pity we're not going to the Moon anymore - that 6 month 1/6 gee data would have been very helpful. But what about a science lander with rats on board?

[JohnFornaro]

1. You are assuming that they are unrelated, and then saying that verifying the assumption is irrelevant.

2. A human who spent all their time floating would almost certainly suffer bone loss, similar to that produced by extended bed rest.

3. Whether the mechanisms that allow water dwelling creatures to avoid this are applicable to zero g is unknown...

1. No, I am sayng that they are unrelated because zero gee effects are a concern of mine and bouyancy effects are not a concern of mine in the tentative solution that I present.   Eliminate zero gee effects, and for greater cost savings, don't bother to study bouyancy effects on bone loss either.

2. "A human who spent all their time floating" would probably be a jelly fish.  Were they to be as active as other sea mammals, bone structure would more resemble these mammals.  Why would we be compelled to spend all our time floating?

3. Fascinating field of inquiry that I chose not to make.

Are you talking to your reflection?

Hardy har har.  Ptew!  [Spits out hook.]  Nice bait, tho.  I suggest eliminating zero gee effects completely.  Personally, I don't want to study them for this application.  Go study bouyancy effects on bone loss, if you wish.

Children confined to bed rest for their childhood don't grow up really tall, but they are rather wasted.

That's nice.  Children born and raised on the Moon or on a ring station will not be confined to bed rest if I have any say about it.  They will grow up in a very different environment.  I think the Moon kids will tend to be taller and skinnier, but they also may be shorter and fatter.  I don't know.

Are you suggesting that the law should forbid exo-planetary reduction?  I think it should not, and that we'll find out what happens largely by doin' it.  Of course, not forbidding reproduction is not the same thing as forcing reproduction.  It's a messy ethical issue.  I think it's gonna happen tho.

...so no 2g centrifuge for little Johnny, probably.

I prefer Johnny grow up in one gee.  Where did the need for hyper gravity come from?

[Lampyridae]

This is getting off topic. Let's start a new thread if you (plural) want to discuss reproduction in low-gee. I don't feel like arguing when there is good research to discuss.

[Lampyridae]

Found a good overview of artificial gravity experiments.


History of Artificial Gravity

Interestingly, (one of) the first artificial gravity stations proposed was an inflatable 30m diameter one. Heh.

Interestingly, a minimum g level for perception of artificial gravity appears to be ~0.2g. Apollo astronauts had trouble detecting slope. Also, extremely short-arm centrifugation on Spacelab missions produced no barfing.

The Russian test facility Orbita which I have mentioned earlier, had a 10m radius. This longer radius seemed to reduce the onset of motion sickness. "Cosmonauts" slowly adapted with an increase of 1-2 RPM per day to 10RPM. Interestingly, the people who resupplied the centrifuges were able to transition quite readily, indicating that dual adaptation is possible.

In other words, training on the ground might help adaptation to a rotating environment. Also, 10m seems like a workable radius, and 15m might offer even more benefits. They also seem to suggest that it is possible to walk around in a 2m radius centrifuge, as well as simply exercise in place, albeit with wonky g-level consequences. So a regular Bigelow could be adapted to produce about 0.2g with a tolerable 8 RPM and 3m radius. Martian gravity would be possible at 10 RPM (to which people have adapted for weeks, albeit at a 10m radius).

[e of pi]

Found a good overview of artificial gravity experiments.


History of Artificial Gravity

Interestingly, (one of) the first artificial gravity stations proposed was an inflatable 30m diameter one. Heh.

Interestingly, a minimum g level for perception of artificial gravity appears to be ~0.2g. Apollo astronauts had trouble detecting slope. Also, extremely short-arm centrifugation on Spacelab missions produced no barfing.

The Russian test facility Orbita which I have mentioned earlier, had a 10m radius. This longer radius seemed to reduce the onset of motion sickness. "Cosmonauts" slowly adapted with an increase of 1-2 RPM per day to 10RPM. Interestingly, the people who resupplied the centrifuges were able to transition quite readily, indicating that dual adaptation is possible.

In other words, training on the ground might help adaptation to a rotating environment. Also, 10m seems like a workable radius, and 15m might offer even more benefits. They also seem to suggest that it is possible to walk around in a 2m radius centrifuge, as well as simply exercise in place, albeit with wonky g-level consequences. So a regular Bigelow could be adapted to produce about 0.2g with a tolerable 8 RPM and 3m radius. Martian gravity would be possible at 10 RPM (to which people have adapted for weeks, albeit at a 10m radius).

Generally, the Bigelow hab designs appear to have a radius on-orbit double their launch radius. Thus, the 8m-launch-diameter designs they have apparently tossed around (the 1150 and 2100) could be reasonably expected to be 16 m once inflated. At an 8 m radius, 0.2g is generated by a mere 4.7 RPM, Mars at 6.1 RPM, and 10RPM gives 0.9g. Thus, a Bigelow station using such modules could have living spaces with comfortable spin radius, spin speed, and gravity level inside a centrifuge at one end of a module.

On launch, the hub of the centrifuge (including hookups for electricity, water, ect...) could be pre-installed in the rigid core of the module and have all its fittings and drive systems ground-tested, with the floor and supporting spokes packed IKEA-style and attached on-orbit after inflation during the fitting-out of the module.

[spacester]

Great thread, I might as well add my standard copy-and-past post on this subject. These links are old and I am delighted to see some more recent stuff linked, which I have not checked out yet.

For tons of information on the realities of artificial gravity, see:
http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml", a discussion about the effects of micro-g and the issues regarding artificial gravity and http://www.spacefuture.com/archive/inhabiting_artificial_gravity.shtml, for all the math you could ever want (scroll down to the conclusions) and also http://www.spacefuture.com/archive/the_architecture_of_artificial_gravity_theory_form_and_function_in_the_high_frontier.shtml for an architect's view of what it would be like.

Here's a formula for spin-gravity:
G = [R * [(pi*rpm) / 30]^2] / 9.81
OR
R = (9.81 * G) / [(pi*rpm) / 30]^2
Where:
G = Decimal fraction of Earth gravity
R = Radius from center of rotation in meters
pi = 3.14159
rpm = revolutions per minute

[spacester]

On that formula, it turns out that if you use 3 rpm, which appears to be our best guess at the fastest rotation rate without Coriolis effects becoming a real problem, you get a nifty simplification:

G = [R * [(pi*3) / 30]^2] / 9.81

G = 0.01006 * R

So at 3 rpm, divide the radius in meters by 100 to get the decimal fraction G force.

IOW 100 meter radius gives 1.00 G, 38 meter radius gives 0.38 G (Mars) etc.

FWIW

[spacester]

Oh what the heck I might as well post an image or two of the BA-330-based double dumbbell design I did a few years ago. This is a conceptual presentation and not an engineering proposal, but it is drawn to scale at R=100 meters

[Lampyridae]

On that formula, it turns out that if you use 3 rpm, which appears to be our best guess at the fastest rotation rate without Coriolis effects becoming a real problem, you get a nifty simplification:

G = [R * [(pi*3) / 30]^2] / 9.81

G = 0.01006 * R

So at 3 rpm, divide the radius in meters by 100 to get the decimal fraction G force.

IOW 100 meter radius gives 1.00 G, 38 meter radius gives 0.38 G (Mars) etc.

FWIW

Nice model. I like the addition of support wires if a pylon should break.

Looks more like 10RPM is the maximum for walking around and stuff. 30+ if you feel like being strapped in. 10RPM gives you much the same relationship.

One advantage of short-arm rotation is that you get a doubling-up effect of modules sharing their radiation shielding.

Another interesting NASA document on the impacts of AG on vehicle design:

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

Read another document where it seemed a major problem of short-arm rotation (~2m and ~30RPM) was the high rate of presyncope for female subjects. Interestingly, nausea was not such a problem, rating only 2-3 on a scale of 1 (fine) to 20 (puking) with 10 being halfway to puking.

[indaco1]

In a certain sense AG has been tested and used in space since the beginning of astronautics.

A propellant-settling maneuver could be considered a form of AG, even if it's not from rotation.

As far testing is concerned...  I think starting with 1g is challenging and not so significant.

Pareto principle (80-20 rule) tends often to be true.

This suggests that it could be the case to begin with a relatively cheap low AG in space (0.2g or less).

Just enough to keep fluids and things in position, and to have a floor to walk (or gently jump around) perhaps could sufficie for physiology and life on board for most of the scopes.

Very low gravity is both the most workable and most significant 3rd point to draw a curve

I think is worth invest M in this field, anyway.   

After all AG, in the long run, could be an essential prerequisite for any serious manned space exploration and eventually settlement.

Sorry if I repeat things said by others...

[JohnFornaro]

(1) In a certain sense AG has been tested and used in space since the beginning of astronautics.  A propellant-settling maneuver

(2) I think starting with 1g is challenging and not so thus, not so significant.

(3) Pareto principle (80-20 rule) tends often to be true.  This suggests ... to begin with a relatively cheap low AG in space...

Just enough to ... gently jump around perhaps could suffice for physiology and life on board for most of the scopes.

(1) True, I guess, to a certain degree, but fairly irrelevant to AG in this sense, which more concerns human health and wellbeing.

(2) I think that's what you're trying to say.  True, 1g would be challenging.  My approach in this discussion, is intended to completely remove the costs of studying and implementing workarounds to gravity question.

I think the key objection to 1g is mass.  The structure of the ring station would have to be massive enough to withstand forces that the ISS, for example, simply doesn't have to accomodate.  The question seems to boil down to whether the cost of the mass is less than the cost of dealing with maleffects of zero gee.  So far, the answer has been to just deal with zero gee, especially since launch costs are so high.

(3) Whatever the general tendency of the Pareto principle may be in this regard has yet to be determined.  However, if I were on a space station, I would certainly feel better weighing 36 pounds rather than zero, even tho I would prefer my full weight.  I'm guessing that a tourist would agree with me. 

The other benefit to 20% gravity would be that it is very close to lunar gravity.  Maybe the first ring station should be at this lower gravity.

[A_M_Swallow]

(2) I think that's what you're trying to say.  True, 1g would be challenging.  My approach in this discussion, is intended to completely remove the costs of studying and implementing workarounds to gravity question.

I think the key objection to 1g is mass.  The structure of the ring station would have to be massive enough to withstand forces that the ISS, for example, simply doesn't have to accomodate.  The question seems to boil down to whether the cost of the mass is less than the cost of dealing with maleffects of zero gee.  So far, the answer has been to just deal with zero gee, especially since launch costs are so high.

1g may be easier than people think, everything on Earth has to be designed to take 1g.  This will tend to flow throw into the final design.  However there are likely to be a few parts that can only take 1g in one direction.  Also during launch much higher accelerations are experienced.

[docmordrid]

Recent work done by the Australian Center for Astrobiology indicates that long stretches in microgravity has another deleterious effect: it changes the behavior of stem cells.

If this is born out it has major medical implications for long-term spaceflight in low-G conditions, few of them good. I don't even want to think about what it would mean for an embryo or tumor growth.

Discovery News story....

[spacester]

Recent work done by the Australian Center for Astrobiology indicates that long stretches in microgravity has another deleterious effect: it changes the behavior of stem cells.

If this is born out it has major medical implications for long-term spaceflight in low-G conditions, few of them good. I don't even want to think about what it would mean for an embryo or tumor growth.

Discovery News story....

Add it to the list:
ADVERSE EFFECTS OF WEIGHTLESSNESS
It is ironic that, having gone to great expense to escape Earth gravity, it may be necessary to incur the additional expense of simulating gravity in orbit. Before opting for artificial gravity, it is worth reviewing the consequences of long-term exposure to weightlessness.

fluid redistribution
fluid loss
electrolyte imbalances
cardiovascular changes
red blood cell loss
muscle damage
bone damage
hypercalcemia
immune system changes
interference with medical procedures
vertigo and spatial disorientation
space adaptation syndrome
loss of exercise capacity
degraded sense of smell and taste
weight loss
flatulence
facial distortion
changes in posture and stature
changes in coordination
changes in stem cell behavior

http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml

[JohnFornaro]

The other benefit to 20% gravity would be that it is very close to lunar gravity.  Maybe the first ring station should be at this lower gravity.

Which doesn't mean that I don't think that one gee is best.  The ring station should start small, and then grow.  The inner ring, constructed first, would be a lunar gravity equivalent. The final, outer ring would be one gee.

However, I don't think that the statement, "1g may be easier than people think" adds much to the discussion, as it is too generic.  The biggest problem with a one gee ring station is the necessary mass to support the resulting forces of the 900m, 1rpm station.  I think it is very important that the station also be a clock.  It is a gentle rotation speed; the amount of curvature in the ring sections is noticable, but not extreme, and I believe that there is great psychological value in having as many terrestrial equivalents as possible.  This would include time.

There is another benefit to the massive station, which is that dockings and undockings of visiting spacecraft would be dampened more readily by a massive structure.  The central hub would be relatively stationary, and the bearings would be massively overengineered for a very long lifetime.

As the station is constructed, the inner ring could also serve as a test bed for the reduced lunar gravity.  Personally, I don't find it ironic; it will be a necessary cost of doing business.

[Lampyridae]

You can quite easily make a 50m radius one gee ring station, should you want to blow the budget. If you're talking about a space colony, sure, make it as big as you want. However, I don't like the idea of wheel stations - Y stations are just as good, and make better use of area shielding.

With a pod-type habitat, you can snag a BA2100 off an HLV and get a nice 12m diameter compartment. Or connect horizontally parallel to make a long, non-curving (and non-coriolis-obvious) section.

[Danny Dot]

This is getting off topic. Let's start a new thread if you (plural) want to discuss reproduction in low-gee. I don't feel like arguing when there is good research to discuss.

You (plural) is "y'all" down here in Houston

Danny Deger

[indaco1]

The other benefit to 20% gravity would be that it is very close to lunar gravity.  Maybe the first ring station should be at this lower gravity.

Which doesn't mean that I don't think that one gee is best.  The ring station should start small, and then grow.  The inner ring, constructed first, would be a lunar gravity equivalent. The final, outer ring would be one gee
....

I think it depends on the scope.

In the short term reduced g could be more useful for science (we alredy know what happens at 1g) and as an obvious developement stage.

Peraphs it is possible to use an existing module with no major redesign.

Gemini 11 experiment was exactly this.

But in the long term, also, I'd expect there will be all the flavours of gravity: zero g, reduced g and full g habitats. Even in a relatively far future

Reduced g cold be a great advantage for logistics, industry and agricolture in space.  Greatest and much more cheap structures, various kinds of savings and, I invent, a better feed conversion ratio for chicken breeding

But also, why not, recreational areas for tourism and low g sports that we can just imagine, like flying under your own force or jump very far.  How low g football, including coriolis force, will be?

And yes, it could be useful to train for natural low g environments including the Moon, asteroids, other satellites and Mars.

There could be many reasons for low g....

[mikorangester]

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

[khallow]

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

Ok, I don't get what you're saying here. Are you proposing that we have a bunch of astronauts stand or sit on vibrating plates while strong winds push them against the plates? Wouldn't that be an awful environment to live or work in?

[mikorangester]

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

Ok, I don't get what you're saying here. Are you proposing that we have a bunch of astronauts stand or sit on vibrating plates while strong winds push them against the plates? Wouldn't that be an awful environment to live or work in?

Not quite. Imagine your foot attached to the plate. If half of your foot is falling at some rate and the other half being lifted at 1 g, you will feel 1 g. The spread of upwards pushing vibrations can be over 50% of your foot but not localized say to the front or back half. The vibrations provide the "half falling half lifting", while the air-cond provides the force that pushes you towards the plate. The amplitude of the vibration can be in microns. Difficult to explain without a diagram. The force from the a/c needs be minimal (also this is happening in zero gravity). If you are interested, I'll do the calculations again and draw a diagram.

[JohnFornaro]

You (plural) is "y'all" down here in Houston.

Hey Danny.  Where y'all bin?  Hain't seen ya inna while.

[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?

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

Ok, I don't get what you're saying here. Are you proposing that we have a bunch of astronauts stand or sit on vibrating plates while strong winds push them against the plates? Wouldn't that be an awful environment to live or work in?

Not quite. Imagine your foot attached to the plate. If half of your foot is falling at some rate and the other half being lifted at 1 g, you will feel 1 g. The spread of upwards pushing vibrations can be over 50% of your foot but not localized say to the front or back half. The vibrations provide the "half falling half lifting", while the air-cond provides the force that pushes you towards the plate. The amplitude of the vibration can be in microns. Difficult to explain without a diagram. The force from the a/c needs be minimal (also this is happening in zero gravity). If you are interested, I'll do the calculations again and draw a diagram.

This seems to be a good zero-gravity countermeasure, but doesn't seem workable as an actual artificial gravity environment.

[Lampyridae]

This is getting off topic. Let's start a new thread if you (plural) want to discuss reproduction in low-gee. I don't feel like arguing when there is good research to discuss.

You (plural) is "y'all" down here in Houston

Danny Deger

Long time no see. "Howzit!" as they say down here in SA.

[mikorangester]

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

Ok, I don't get what you're saying here. Are you proposing that we have a bunch of astronauts stand or sit on vibrating plates while strong winds push them against the plates? Wouldn't that be an awful environment to live or work in?

Not quite. Imagine your foot attached to the plate. If half of your foot is falling at some rate and the other half being lifted at 1 g, you will feel 1 g. The spread of upwards pushing vibrations can be over 50% of your foot but not localized say to the front or back half. The vibrations provide the "half falling half lifting", while the air-cond provides the force that pushes you towards the plate. The amplitude of the vibration can be in microns. Difficult to explain without a diagram. The force from the a/c needs be minimal (also this is happening in zero gravity). If you are interested, I'll do the calculations again and draw a diagram.

This seems to be a good zero-gravity countermeasure, but doesn't seem workable as an actual artificial gravity environment.

Come to think of it, why not just keep accelerating at 1 g, turn around when you are far enough and accelerate back (including the deceleration phase), or even or spiral acceleration. There's your artificial grav.

[mikorangester]

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?

This is an idea that is outdated. A better idea is a system consisting of a vibrating plate with a net force (say by a flow of air towards the vibrating plate) towards the plate.

Ok, I don't get what you're saying here. Are you proposing that we have a bunch of astronauts stand or sit on vibrating plates while strong winds push them against the plates? Wouldn't that be an awful environment to live or work in?

Here you go http://science.nasa.gov/science-news/science-at-nasa/2001/ast02nov_1/

[randomly]

Very interesting article.
But they are saying the acceleration imparted by the plate is 1/3 gravity. Air conditioning would be an insufficient restoring force unless you reduced the duty cycle of the plate enormously. Which sounds like an interesting avenue of research, the effect of varying the duty cycle. My guess is though you'll need restraints to make the plate thing work.

[Lampyridae]

I once considered using airflow as an AG substitute. Problem is, force is related to surface area, not mass. So if you fall over in a "1G" environment, you suddenly have about 10Gs holding you to the deck. Not to mention the deafening noise and wind chill factor plus the sheer mass required by the fans and ducts and power supply.

[Celebrimbor]

Come to think of it, why not just keep accelerating at 1 g, turn around when you are far enough and accelerate back (including the deceleration phase), or even or spiral acceleration. There's your artificial grav.

Excellent idea (although not new). Trouble is, you need to point to an engine or technology that can give you a thrust of 1g that is sustained throughout the entire cruise phase of your flight. It turns out to be an enormous physical and engineering challenge. IMHO, we won't be up to it for centuries, if ever.

[93143]

Come to think of it, why not just keep accelerating at 1 g, turn around when you are far enough and accelerate back (including the deceleration phase), or even or spiral acceleration. There's your artificial grav.

Excellent idea (although not new). Trouble is, you need to point to an engine or technology that can give you a thrust of 1g that is sustained throughout the entire cruise phase of your flight. It turns out to be an enormous physical and engineering challenge. IMHO, we won't be up to it for centuries, if ever.

You know, if you're moving sideways and turning while accelerating, you can go in a circle.  This obviously doesn't solve the propellant problem - but if you were to have an identical vehicle travelling in the same path 180 degrees off, you could structurally attach the two vehicles, and they would continue in their circular paths without needing to use propellant.  You could do this with an arbitrary number of vehicles, as long as the arrangement was cylindrically symmetric...

Oh, wait...


Barring the invention of high-thrust propellantless drives or Star Trek-style artificial gravity, spin gravity is probably necessary for full resolution of the problems with zero-gee.  I can't see those vibrating plates or the tension suits or anything like that being a complete solution, although they'll probably help quite a bit...

[Chris611]

Come to think of it, why not just keep accelerating at 1 g, turn around when you are far enough and accelerate back (including the deceleration phase), or even or spiral acceleration. There's your artificial grav.

Excellent idea (although not new). Trouble is, you need to point to an engine or technology that can give you a thrust of 1g that is sustained throughout the entire cruise phase of your flight. It turns out to be an enormous physical and engineering challenge. IMHO, we won't be up to it for centuries, if ever.

Also, if you keep accelerating at 1g, you will reach the speed of light in 354 days 

[go4mars]

The ring station should start small, and then grow.  The inner ring, constructed first, would be a lunar gravity equivalent. The final, outer ring would be one gee.

 The biggest problem with a one gee ring station is the necessary mass to support the resulting forces of the 900m, 1rpm station.  I think it is very important that the station also be a clock.  It is a gentle rotation speed; the amount of curvature in the ring sections is noticable, but not extreme, and I believe that there is great psychological value in having as many terrestrial equivalents as possible.  This would include time.

Or, since space will likely use metric units, go for metric time and have the rotation be 1 rpm.  (assuming 1000 minutes per current earth 24 hour period).

So your ship could have a gravity-free hub to do fun gymnastics in, a lunar grav hub, a Mars grav hub, an earth grav hub, and for challenging work-outs to get in shape for field work on Mars/moon/wherever, get into the higher than earth-g hub. 

[Celebrimbor]

Also, if you keep accelerating at 1g, you will reach the speed of light in 354 days 

Actually, no. Its off topic though so take a look here:

http://www.desy.de/user/projects/Physics/Relativity/SR/rocket.html

[JohnFornaro]

since space will likely use metric units

Not if I can help it.  We last discussed that issue in 1776, and chose imperial units of measurement.

[e of pi]

since space will likely use metric units

Not if I can help it.  We last discussed that issue in 1776, and chose imperial units of measurement.

I don't think you said what you think you said, since the metric system was only first adopted anywhere in France in 1791 so I doubt it was a huge issue at the Second Continental Congress. Also, as an engineering student in Ohio, I find that the metric system is much more sensible and easy to deal with, and that I actually groan when problems are assigned using Imperial units. I strongly believe that SI/metric is better for technical work, and I hope it dominates in space.

[Comga]

Umm.... Could it be that John is joking, e of pi?

[e of pi]

Umm.... Could it be that John is joking, e of pi?

I suppose it could be though there's not emoticons or anything to show it. If he is, I retract the statement but recommend he be more clear in the future.

[Lampyridae]

Also, if you keep accelerating at 1g, you will reach the speed of light in 354 days 

Actually, no. Its off topic though so take a look here:

http://www.desy.de/user/projects/Physics/Relativity/SR/rocket.html

On the topic of relativity (albeit of the other variety), you could generate artificial gravity through rotating super-dense masses too (gravitomagnetism). Mount them on the wall like clocks and there you go. Unfortunately the best we could do right now is something like 10^-14g with osmium disks...

[JohnFornaro]

... but recommend he be more clear in the future.

Oh my everluvvin' garnęt.  Let me make one thing perfectly clear...[say it like Nixon]

I've suggested that there be a poll to remove the smiley thingies from the site.  It ain't funny if I have to explain it.

Y'know.  Like the dyslexic man who walked down the street and turned into a bra.  Or the dyslexic bluesman who went to the crossroads and sold his soul to Santa.  Never mind.

[spacester]

since space will likely use metric units

Not if I can help it.  We last discussed that issue in 1776, and chose imperial units of measurement.

I don't think you said what you think you said, since the metric system was only first adopted anywhere in France in 1791 so I doubt it was a huge issue at the Second Continental Congress. Also, as an engineering student in Ohio, I find that the metric system is much more sensible and easy to deal with, and that I actually groan when problems are assigned using Imperial units. I strongly believe that SI/metric is better for technical work, and I hope it dominates in space.

Certainly when one does calcs involving energy, SI is the way to go, being defined so that mass units are unambiguous.

But that's way different than suggesting that we try to convert the USA's entire industrial base for no particularly good reason.

[Lampyridae]

Let's keep it on topic, friends.

[go4mars]

since space will likely use metric units

Not if I can help it.  We last discussed that issue in 1776, and chose imperial units of measurement.

I don't think you said what you think you said, since the metric system was only first adopted anywhere in France in 1791 so I doubt it was a huge issue at the Second Continental Congress. Also, as an engineering student in Ohio, I find that the metric system is much more sensible and easy to deal with, and that I actually groan when problems are assigned using Imperial units. I strongly believe that SI/metric is better for technical work, and I hope it dominates in space.

Certainly when one does calcs involving energy, SI is the way to go, being defined so that mass units are unambiguous.

But that's way different than suggesting that we try to convert the USA's entire industrial base for no particularly good reason.

There are many very good reasons to implement metric time.  Short term pain for long term gain.  btw.  I can't believe that the stimulous package you guys had didn't include going metric.  Trillions of dollars blowing around and it didn't even make the list???

[JulesVerneATV]

Vast bolsters commercial space station plans with key agreements
https://www.astronomy.com/space-exploration/vast-bolsters-commercial-space-station-plans-with-key-agreements/
The company is developing a commercial replacement for the ISS, currently planned to be retired at the end of the decade.

also more recent thread
Artificial Gravity: punctuated gravity using a centrifuge
https://forum.nasaspaceflight.com/index.php?topic=46266.0

This Company Wants to Build a Space Station That Has Artificial Gravity
https://www.wired.com/story/this-company-wants-to-build-a-space-station-that-has-artificial-gravity/
Founded by scam guru Jed McCaleb, Vast Space will run two missions to the International Space Station and aims to launch its first space station, Haven-1, by the end of 2025.

[JulesVerneATV]

'Vast to complete Haven-1 primary structure in July 2025, ahead of target May 2026 launch date'

https://spaceflightnow.com/2025/05/07/vast-to-complete-haven-1-primary-structure-in-july-2025-ahead-of-target-may-2026-launch-date/

[Paul451]

Vast [...] Haven-1

Vast has its own thread: https://forum.nasaspaceflight.com/index.php?topic=55810.0