Artificial Gravity from Rotation

[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.