Artificial gravity

aksail · Apr 20, 2005

We all seem to speak glibly of "just rotating the craft" to produce an artificial gravity for long term trips. If it is so easy, why have we not yet done it? How much gravity is necessary to prevent the problems currently experienced by long space stays?

phelan · Apr 20, 2005

aksail wrote: "How much gravity is necessary to prevent the problems currently experienced by long space stays? " I would assume that the amount you would want, would be equal to earth's gravity. But I guess we really wouldn't know until it has been tried. I have always wondered if you could "spin up" a space craft to induce artificial gravity why we don't do it, good question aksail

Saiph · Apr 20, 2005

Good questions. We don't need much gravity to prevent most problems. I think I've seen 1/8th thrown around somewhere as a nice small, achievable amount. The stresses involved are one reason. Also, you need to go slow enough, or have a large enough radius of rotation, that the passengers don't get disoriented due to coriolis effects (that's why you're dizzy after spinning around or many thrill rides). Also, there hasn't been much need for it. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

phelan · Apr 21, 2005

Do you think there is a way that you could get used to that effect? Like your body has to get used to no gravity.

Saiph · Apr 21, 2005

You could, if you didn't move. However, moving around creates shifts in the coriolis effect, creating the sensation of motion, like the floor lurching under you. This has no other corresponding visual ques to help predict it either. You'd have constant vertigo whenever you try to move around. If the coriolis force was strong, you'd even have problems reaching out and grabbing things as your arms would be deflected oddly. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

phelan · Apr 21, 2005

seems that there would be a real problem with keeping the craft affordable and keeping the humans inside functioning (ie. increasing the size costs money, where as keeping it small your astronauts can't move.) . It is something that would be nessicary to solve when you are talking about long duration trips through space.

phelan · Apr 21, 2005

I thought I would add the PM I sent Saiph and the response I recieved back: Phelan: so is there no solution to it? "spinning up" a craft will result in astronauts that are unable to do anything except stand still? You did say something about speed of the spin, is there a point where you can deal with the effects of spinning and be functional? Saiph: The coriolis effect can be mitigated by two things: Slower rotation speeds, or a larger "radius" (or distance from the rotation axis). However, these two things reduce the amount of "gravity" generated by a rotating system. The good news is, you mitigate the coriolis effect much faster by increasing the radius, than by slowing down. So you can get high accelerations without a coriolis effect. You just have to make the craft wide enough. Of course, this increases the size, and mass, and can make the craft fragile, and theoverall cost as well. The main solution to this, is to use a high strength tether or cable. You spin the craft up (it's compact here, so it's not comfortable, but it's short duration) then you take two halves, connected by the tether and extend it, increasing the radius, and slowing it down. One side is the passanger cabin, the other is unessential components (for that time in the mission) as a counter weight. Light weight, strong, flexible, cost effective. But, at the moment, unneccessary.

Saiph · Apr 21, 2005

Thanks for posting that! That'll show steve for thinking he beat me to it! (PM sent before steve posted!) Ha! ahem..urm...right. Good points steve! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jurgens · Apr 21, 2005

Ive been wondering, if they used something like VASIMR or a Nuclear Electric Propulsion drive which provided constant acceleration for a trip to mars, You would experience a normal force in the direction you are accelerating. Once you get to your half way point and start with deccelerating you could just spin the ship around and still have the normal force in the same direction relative to the ship. Problem is though, the acceleration probablly wouldn't be too large so the normal force would be rather weak. But even a slight Normal Force might be good =) If you could get an engine to produce a constant acceleration of .1g for the ship that would mitigate any needs for creating artificial gravity. Of course getting .1g of acceleration would with a VASIMR type drive probablly require Gigawatts of power or lots and lots of fuel... Impractical with our current technology to say the least.

nexium · Oct 15, 2005

I'm sure NASA and others are trying hard to make some sort of practical artificial gravity. If CNT = carbon nano tubes meets optimistic projections, two space craft can be connected with a kilometer or longer tether. Conciderable energy is needed to spin fast enough to produce even 1/6 th g. Faster puts a lot of tension on the tether, the attachmemt and the two space craft. Failure of the tether or the attachment, flings both craft violently in to new orbits which cause re-entry into Earth's atmosphere, orbiting in the Van Allen belt, or an orbit that makes return to Earth impossible with the fuel on board. Less than a kilometer of tether produces a level of corielis effects which may be more harmful than micro-gravity. Using several kilometers of Kevar, the mass of the Kevar exceeds the mass of the space craft, to get low probability of unexpected failure. A one kilometer plus, ring station is far beyond our tiny lift capabilities, as spining greaty increases stress on the station. Please embellish, refute, and/or comment. Neil

vogon13 · Oct 15, 2005

Conservation of angular momentum can probably be applied by savy engineers with a fly wheel or something and make spinning up and down of your system more practical. Might be possible to use the upper stage of your rocket as the 'anchor' mass and cut the cord at the right time and orientation at Mars to facilitate orbit insertion. Aproach these things as opprotunities, not problems. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

nexium · Oct 15, 2005

Can anyone do the math? Two kilometer tether (in low Earth orbit) producing 2g in the craft to go to Mars. The craft impacts on Mars how many days after the tether is cut? I don't think changing the mass of the Mars craft changes the answer. It will take a bit longer (and considerable fuel) to make a gentle landing. Neil

vogon13 · Oct 15, 2005

I am so happy to be on record as not 'doing' math. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

tony873004 · Oct 16, 2005

"Two kilometer tether (in low Earth orbit) producing 2g in the craft to go to Mars. The craft impacts on Mars how many days after the tether is cut?" So the center of mass of the "2-masses connected by a tether" is simply the circular orbital velocity at that altitude. To compute the speed relative to this point necessary to produce 2g of acceleration: acceleration = velocity^2 / radius, therefore... velocity^2 = acceleration * radius, therfore... velocity = sqrt(acceleration * radius), or more simply... v=sqrt(ar) so... v = sqrt (2g * 2km), convert to... v = sqrt( (2*9.8m/s^2) * 2km* (1000 m/km) ) v = sqrt( (19.6 m/s^2) * 2000m) v = 197.9898987 m/s v = 1.979898987 km/s So your craft would get flung away with an additional 1.98 km/s of speed. Circular velocity for low-Earth orbit (altitude 200 km): vc = sqrt(GM/r) vc = sqrt((6.67 * 10^-11 * 5.97*10^24) / 6578000) vc = 7780.42190597432 m/s vc = 7.78042190597432 km/s Escape velocity for low-Earth orbit (altitude 200 km): ve = sqrt(2GM/r) ve = sqrt((2 * 6.67 * 10^-11 * 5.97*10^24) / 6578000) ve = 11033 m/s ve = 11 km/s So a boost of ~2 km per second would not be enough to send the released satellite into interplanetary space.

nexium · Oct 16, 2005

If I understand Tony's math, 2g produced by a 3.3 kilometer tether will just barely get us to Mars. Neil

gsuschrist · Oct 16, 2005

"I'm sure NASA and others are trying hard to make some sort of practical artificial gravity. " This topic is beyond my understanding. Do you have some links to this NASA research? I haven't really heard much about it and certainly not in terms of any practical plans. Does anyone also have a link with illustrations or drawings of what all this would look like? The numbers would be easier to understand if there was a model to view.

alokmohan · Oct 17, 2005

Any ref fron NASA may be help ful.

spacester · Oct 17, 2005

Please see the, uh 13th post on this thread <div class="Discussion_UserSignature"> </div>

CalliArcale · Oct 18, 2005

<blockquote>In reply to:<hr />"I'm sure NASA and others are trying hard to make some sort of practical artificial gravity. " This topic is beyond my understanding. Do you have some links to this NASA research? I haven't really heard much about it and certainly not in terms of any practical plans. <hr /></blockquote> Current plans do not go beyond drawings, for the most part, but there is practical research being done. Almost all techniques hinge on rotation, although some hypothetical work has been done with continuous thrusting. (Propulsion technology isn't anywhere near ready for that yet, though.) The research being done with rotation includes studies with human subjects in a special centrifuge at JSC outfitted with a cab that a person can live in for a day. (It has a bed, a computer with a 'net connection, video games, toilet, food, etc. Bare neccesities.) The centrifuge is rotated to produce a total apparent G-load of 1.5 Gs (1 G of actual gravity, 0.5 Gs from the rotation). The idea is to see if a person can tolerate this with no ill effects. The centrifuge is large, but not large enough that it's angular momentum is undetectable and of course there will be measurably more G-forces at a person's feet than at a person's head. Will that make a person sick? Hopefully not. 1G is probably impractical for the first spacecraft to attempt this technique, but 0.5 G, if tolerable, could mitigate the wasting effects of microgravity and allow an astronaut to be useful on the surface of an alien planet. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

tmccort · Oct 18, 2005

How could 0.5 G not be tolerable?

CalliArcale · Oct 19, 2005

It's not 0.5 G that's a concern. It's 0.5 G produced by rotation that they're concerned about. The spacecraft that can be built today are not big enough to make the effects of rotation negligible. If you drop an object on a rotating ship (built with today's tech and today's dollars), it won't fall straight to the ground; it'll drift measurably as it falls because what is perceived as artificial gravity is actually rotation. This could mess with people's sense of balance, although from watching sailors and the like, it seems reasonable to expect that people would adjust fairly easily to it with only a day or two of nausea and disorientation. A bigger concern is the fact that if you're standing up on such a spacecraft, your feet will be experiencing more Gs than your head. Is this a problem? How much of a problem is it? Can it be mitigated? Is the benefit of artifical gravity worth the risks of prolonged rotation? These are the questions that need to be answered if we want to have artificial gravity in the near future. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

spacester · Oct 20, 2005

These are the questions that need to be answered if we want to have artificial gravity in the near future. Absolutely. We really KNOW very little. However there have been a few experiments and there's been quite a bit of analysis. IMO there has been enough to make some reasonable suppositions, and I never tire of sharing mine.

So yet again here's a copy and paste I post on this subject when it comes up. IIRC I was responding to AI_Sci . . . *** For tons of information on the realities of artificial gravity, see: This discussion about the effects of micro-g and the issues regarding artificial gravity and this for all the math you could ever want (scroll down to the conclusions) and then this for an architect's view of what it would be like. Here's the formula: 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 * Now then, my point is simply that we don’t know the true effects of coriolis cross-coupling in a large radius habitat operating in a micro gravity environment. Of course you will have severe problems in a small radius habitat, all the research indicates that. Also, you cannot do a precise simulation in Earth’s gravity field. So we just don’t know. In my research, the best summarizing paragraph I have found is from the first link above: "In brief, at 1.0 RPM even highly susceptible subjects were symptom-free, or nearly so. At 3.0 RPM subjects experi <div class="Discussion_UserSignature"> </div>

jatslo · Oct 20, 2005

I find it difficult to believe that NASA does not already know how to create +gravity and –gravity, and I understand, if true, why this knowledge is TOP SECRET. If we are ready to start our journey into the cosmos, the President’s vision of “The Earth’s Moon, Mars, and Beyond” would offer as evidence in support of a gradual introduction of this technology.

moonmadness · Oct 20, 2005

You know this is exactly why I am glad I finally noticed the message board link at SPACE.COM. I came to the conclusion that Zero-G was quite possibly the main deterent to long term space exploration. But after frequent Web and some library searches, I noticed an apparent lack of any data about artificial gravity.Let alone empirical data. I was looking for the reason or reasons that NASA, et al, had given up on the concept of simulated gravity enviroments. Still have yet to find the smoking gun. <div class="Discussion_UserSignature"> I'm not a rocket scientist, but I do play one on the TV in my mind. </div>

CalliArcale · Oct 20, 2005

I'm glad you're enjoying this board. <img src="/images/icons/wink.gif" /> I'm one of the mods; feel free to PM me (click my name, then click the "send this user a message" link) if you have any questions or problems. You can also use the Suggestions forum for that, if you don't mind other users seeing and perhaps contributing. (That's especially useful if you experience technical problems, because sometimes other users have had the same problem.) I don't think NASA ever gave up on simulated gravity environments; after all, they're doing research into it right now. But it's not been practical to actually deploy such a thing in space; the experiments done to date have been very small scale, and it seems that disorientation is pretty severe on that scale. They're not sure about long-term effects; that'll take a lot more time (and funding) to determine. There was a plan for a biosatellite with a colony of mice living in a centrifuge, with the plan of having them live out at least two generations before the ship would return to Earth safely so the survivors could be examined. I'm not sure how far along that project has gotten; last I heard about it was several years ago, and it was just a proposal at that point. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Artificial gravity

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