Variable Gravity Research Facility (xGRF)

For those of you who aren’t reading our ASM Blog, I participated in a panel at the SSI Conference last week in San Jose. Dallas Bienhoff presented the paper we are working on coauthoring, Gary Hudson talked about earth-to-orbit transportation, and Joe Carroll talked about several other interesting technologies including: mid-air capture (which I’ve talked about before here and here), combining debris mitigation with harvesting aluminum from spent satellites, rotating tethers, and reduced gravity research hubs). I didn’t get to contribute much myself–mostly just sat in on the short panel discussion, and got in a response to one question. However the panel and conference were a lot of fun, and I look forward to helping Dallas finish that paper.

All that aside, this post is related to Joe Carroll’s last topic–reduced gravity research facilities. His talk reminded me that I needed to dig-up and finish this blog post I had started back in May about the importance of such reduced gravity research facilities, and a clever approach I had seen to providing them.

Reduced Gravity Effects on the Human Body
I first made this point almost five years ago, but it bears repeating: while we have a lot of data on human health at 1g and at 0g, we have almost no data in the middle. I say almost, because we did have a dozen people live on the moon for at least 24 hours each…but that’s pretty much the only data we have on reduced gravity health effects, which is far too little to draw any really useful conclusions.

Most readers of this blog know that the data from microgravity impacts on the human body don’t look too promising–even with lots of exercise, there are apparently biophysical mechanisms that can have large negative health impacts (osteoporosis, neurological and pulmonary issues, etc) that begin to show themselves very quickly. However, as I pointed out in that earlier post, we have no idea which of the curves below really represents human health impacts of reduced gravity:

ReducedGravity

Does just a little bit of gravity go a long way (my personal guess I explain in the other post)? Or do you need almost full earth gravity? Or is there actually some gravity level less than 1g that’s actually better than earth gravity? While natural selection for humans has obviously been focused on a 1g environment, that doesn’t mean that humans are so hyperoptimized to 1g that nothing else will do. It’s unfortunately possible, but right now we don’t know. Without getting some “center points”, any guess at the shape of the response curve is just that–a guess.

Why This Matters
The reason why this knowledge void matters is that it greatly impacts the future expanse of humanity into space, as well as near-term human exploration. For instance, we don’t know if someone who goes to live on the Moon or Mars can ever really come back to earth, or if they have kids, if their kids can return.

If however it turns out that lunar gravity is already enough to counteract the worst of the effects of microgravity, it might be that the best way to do initial lunar human exploration is something like a One-Way To Stay (for a while) approach. If you knew that you could send someone for long durations while still being able to bring them back later if needed, it would open up some big possibilities. The return portion of a human lunar mission is one of the big performance drivers that make human missions so much more expensive than robotic ones. Even if you couldn’t close the life-support loop, just not having to return the initial explorers right away could allow you really enhance robotic exploration of the Moon by having people there on the spot to help troubleshoot, fix, upgrade, iterate, etc on your robotic systems. I know a lot of people think we can just send robots and have them make a turn-key base. It’s possible, but I expect you’re going to break a lot of robots along the way, and you could avoid that by having people in the loop. But its ethically hard to do a mission like that before you have some data on what long-duration exposure to 1/6g is going to do to your explorers.

Returning to the Joe’s talk, he suggested looking at .06g as well as lunar and martian gravity, as a possible minimal gravity level that people could intuitively adapt to without lots of training. If travelers can get by without large negative health hazards by .06g worth of gravity, that would really simplify the concept of providing artificial gravity for long-duration deep-space trips (like to Mars or NEOs). If there’s a “knee in the curve” above which you can avoid the worst of microgravity effects, that can make it a lot easier to provide artificial gravity for trips like that. If you have to provide a full 1g, and can’t go with high RPMs (which Joe suggested that the terrestrial centrifuge data might be suspect due to the presence of a 1g downward gravity vector), that implies very large structures, which become a much bigger engineering challenge.

xGRF
The question becomes, what’s the best way to get this data? Most of these effects take timescales on the order of hours, days, or weeks to express themselves. And there’s no way on earth to adequately simulate hypogravity. The only real way of testing this, short of going there and finding out the hard way, is to build some sort of orbital research facility. The ISS was originally going to have a Centrifuge Accommodations Module, but that project got defunded, and the hardware is no longer flightworthy from what I hear. I had suggested the idea of doing a “CAM in a Can” before, but even that would be limited to studying small animals–there’s no way you could fit a human in there. To get the data quickly, you really want some sort of artificial gravity facility that is human-sized. In his presentation, Joe Carroll talked about building a large rotating space station with facilities on different lever arms from the CG of the facility. While this is interesting, and would allow you to have your gravity decoupled from your spin rate, I think that Kirk Sorensen’s xGRF “Variable Gravity Research Facility” concept makes more near-term sense (Joe and I disagree on this point BTW).

I’m not sure if Kirk reads this blog very much anymore (he’s pretty busy at his new job as Chief Nuclear Technologist at Teledyne Brown), but I have to toot his horn a bit. While not all of his ideas are ones I’m sold on, he’s had more than his fair share of clever ideas. The idea behind xGRF is very simple. You have a small facility–something on the scale of a Sundancer or Nautilus module from Bigelow, and you attach it via a long tether to a large counterweight (such as the upper stage that delivered the module to orbit in the first place). In LEO the gravity gradient can be used to force such a system to adapt an orientation with the long axis pointing through the center of the earth. In such a situation, the CG will be somewhere between the two end pieces, and the module will be going slightly slower than the orbital velocity of other components at its altitude, and the counterweight will be going slightly faster. This provides a tiny bit of settling force on each end (acting like a tiny bit of gravity with a vector pointed outward from the center of the system).

Ok, you may be thinking, that’s nice. But where do you get the “Variable” Gravity from? That’s where Kirk’s idea gets really clever.

Basically, something in a gravity gradient orientation is still actually spinning–it just completes one complete rotation per orbit around the earth…What happens if you take a spinning object like this, and decrease it’s moment of inertia by, oh say winching in the tether? By conservation of angular momentum, the object has to start spinning faster!

xGRF_spinup

You can winch the habitat and the counterweight together until you reach the desired level of artificial gravity. Depending on the design details, you can pick any gravity level you want between say microgravity and 1g. How do you dock, say to transfer crews or deliver supplies? Well, it turns out you can despin the system by just reeling out the tether:

xGRF_spindown

Pretty clever. By doing this, not only can you pick any gravity level you want, but you can also do your rendezvous and docking in a simple, non-spinning environment, you can eliminate the need for having rotating and nonrotating parts of the station, or of long elevators or connecting tunnels. I really like this concept, because the system ends up being pretty simple, with everything being able to be launched on a single EELV flight. You don’t have to assemble a huge space facility and then spin it up. This can be a small project that might actually get built. I think the big station Joe might have more capabilities, but I’m worried that detractors would paint it as a second ISS, and it would never get funded. Something on this scale though is within the realm of feasibility.

Flagship Technology Demonstrators, Expansion Options, Future Uses, and other Parting Shots
One particularly interesting way to get something like this funded (and what I was originally writing this blog post back in May as a response to) is as a replacement for the “Inflatable Technology” Flagship Technology Demonstrator. Back in Galveston late last spring, NASA rolled out several proposed FTD missions to flesh out plans suggested in Obama’s FY11 budget proposal. One of the missions was to build an inflatable module and attach it to ISS. To be honest, this seemed a little duplicative–it looked for all intents and purposes as though NASA was going to spend $500M-1B duplicating what Bigelow was doing on his own dime. I think a much better way of both flight demonstrating inflatables while killing multiple birds with one stone would be to build something like xGRF as a Flagship Technology Demonstrator. Leverage either a Bigelow Sundancer module or compete it out and have ILC Dover also bid on it. For the same amount of money, you get a much more useful lab, that doesn’t endanger the ISS, and which allows you to do reduced gravity research that compliments ISS’s microgravity focus.

As Joe pointed out, even after the initial experiments (say at lunar gravity first, then Martian, then at the .06g level), a facility like this would have lots of follow-on utility. You can answer initial questions relatively quickly–ie even a few months at each level would tell you a lot compared to what we know right now, but getting longer-duration data could be very useful for future space settlement efforts. I’ll have to dig up my notes on all the reasons, but there’s a lot of long-term potential for a station like this.

Which means you might also want to upgrade it down the road. If you overbuild the tether, and the docking facilities, you could probably attach additional modules to a station like this pretty readily. To add to the counterweight, you could say have facilities on the original upper stage that could allow it to be outfitted as a depot…but that’s getting a little too crazy for now.

But I think the time for something like this is now. FTDs are getting money, even if it’s greatly reduced from what Obama wanted. The budget for exploration technology development, including flagship missions is currently authorized at over $1.1B over the next three years. At that rate, you could fund most of the work on both the depot approach that was proposed by the joint industry/NASA group I participated in last year, as well as xGRF, and still have money left over for starting another FTD like say an aerobraking or aerocapture one. Even if funding gets further reduced in appropriations, there’s enough money to pursue something like xGRF and depots in parallel.

I think this is an idea whose time has come.

This entry was posted in Bigelow Aerospace, Lunar Exploration and Development, NASA, Space Development, Technology. Bookmark the permalink.

48 Responses to Variable Gravity Research Facility (xGRF)

  1. phillip says:

    What do you feel would be the total cost for the program? For the counterweight could you use an upper stage from a F9???? For the lab I think it would better if you lease it–the costs may end up being smaller than if you purchase it. If you purchase–then you have to think of something else to do after you have done say 1 year of studies–give that problem to someone else. How likely do you feel that something like this will actually happen?? Bigelow himself felt that a Sundancer module should not be attached to the ISS but as a free flying module–maybe 10 or so miles below and behind the ISS.

  2. Jared says:

    There might be some good PR going on for something like this, too. Isn’t Larry Page’s “I’ll pay the bill to Mars if you can get it down to $8 billion” plan supposed to be a one-way trip? If not, Larry Page is insane.

    Anyway, this deal has been all over the news recently, and my first thought when I saw it was that it’s a mistake to be planning a one-way to Mars trip right now, since we don’t know how well humans would do on an extended stay in .38g. A variable-gravity experiment like this is a necessary precondition to any one-way program, and so Page’s little crusade could go a long way towards generating enthusiasm for your xGRF.

    Between this and the hubbub all over the space community about inflatables, I think you’re right…this may have a good shot of actually happening soon.

  3. Jim Davis says:

    The reason why this knowledge void matters is that it greatly impacts the future expanse of humanity into space, as well as near-term human exploration. For instance, we don’t know if someone who goes to live on the Moon or Mars can ever really come back to earth, or if they have kids, if their kids can return.

    Jon, some episodes of the Space Show this year have had experts that have suggested that the problem goes far beyond just not being able to return to Earth but life threatening long term health problems.

  4. Jonathan Goff says:

    Jim,
    Yeah, I talked a bit about that in the post I referenced from 2005. Osteoporosis, severe heart and neurological problems, it’s not just “getting weaker because you’re not moving around as much weight” like most people think–there are real chemical changes. But, yes I agree with you. Sorry if I wasn’t clear about that in the post–I was aiming for brevity because I only had a little time to write it before work.

    ~Jon

  5. Ed Minchau says:

    A long tether moving relative to the Earth’s magnetic field would have some interesting electrodynamic properties, including electrodynamic reboost (robbing energy from Earth’s magnetic field). Rotating it faster or slower than once per orbit would set up a low frequency AC current along the tethers. I am certain that the electrodynamics have all been covered in some of the detailed analyses of rotovators.

    If nothing else, electrodynamic reboost would reduce your station-keeping fuel requirements.

  6. Thanks for the mention Jon–I’m not surprised Joe Carroll disagrees with an idea I came up with. That’s pretty much his default position with any idea I come up with. After 10 years I’m fairly used to it by now.

  7. Kirk, this paper would be so much better if you had done the references properly. There’s an impressive bibliography at the end, but no actual references to them in the text.

  8. Nels Anderson says:

    I very much like the xGRF concept. Reeling in the tether may be complicated a little bit by the need to prevent gravity-gradient torques, arising when the orientation is neither horizontal nor vertical, from diverting too much angular momentum into changing the orbit rather than spinning the facility up. Has anybody looked at this in detail? It’s a nice classical mechanics problem.

  9. googaw says:

    As is usual with such plans, it is about an order of magnitude too big. We can learn the same things, and sooner, and with vastly less expense, by putting much smaller mammals in much smaller habitats (e.g. mice in cages) and launching the whole thing on a single satellite launcher.

    But I suppose that would provide too little work for NASA contractors.

  10. A_M_Swallow says:

    A Falcon 9 and Dragonlab may be one of the cheaper ways of performing these experiments.

  11. Axel says:

    Looks like a pretty smart idea to me. Using a “tidal lock” with Earth to gain or shed angular momentum is clever. It would help me to understand the magnitude of the idea if you told us about the envisioned dimensions. What is the length of the cable? What’s the radius of rotation? 100 m? 1 km? 10 km? More?

    Reminded me of a doctoral thesis (in architecture!) I once found on the internet. Seems to be no longer available completely, but this seems to be a good summary:
    http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml

    Had a look at the “comfort zone” depicted there. Possibly “non-puking zone” would be a more honest name? But there is considerable uncertainty in those estimates. Another good reason to build an artificial gravity lab.

    From the 2 to 6 RPM limit I guess your plans are more in the 1 to 10 km range for the radius, yes?

    One potential conceptual disadvantage I can see in your xGRF (as compared with say a flywheel controlled rotation) would be that changing RPM while maintaining constant gravity level is not possible. We’d have to un-spin until we become tidally locked, then dump or add angular momentum by reeling in or out slowly and then reel in fast enough to break tidal lock. How long would that take? A few hours? A few days? Will the low gravity periods be short enough not to invalidate experimental results?

    Also my standard long tether question: how do you make sure no dangerous oscillations add up on the cable? How do you dampen them?

    After that it comes down to technical details. How much is the cable mass compared to alternative approaches? What about energy? Will you have solar sails? How to attach them?

    How about safety in case of a malfunction?

    In some respects I think the habitat on a cable approach is safer than others. If the winch power fails, reeling out needs no energy. If the cable gets stuck, the last resort is to cut the cable (pyro bolts?). I think the habitat module should have an emergency orbital maneuvering system to get away from the cable – so it does not whiplash or something. If cut loose suddenly, the cable may flap around violently, wouldn’t it?

    Orbital debris and micro meteorites may be an issue. Changing orbit to reduce risk of collision with known debris may be difficult? Cable failure due to to a hit is another scenario to be discussed. In that respect a long cable solution may be inferior to a more compact design?

    Doh! I missed the link to Kirks paper. Ok, looks like my BOTE guesstimates match his calculations good enough. Is his example the current model to discuss?

    Is assuming tether mass of zero a realistic approximation for the minimum cost example, i.e. the one that can be launched by a Delta IV Heavy? Upper stage 3.6 t dry, 22 t payload to LEO. How many t for a 10 km cable?

    With a 10 km cable a fully reeled out xGRF is not exactly under micro gravitation – it is more like milli gravitation. If that complicates docking (and I’m not sure it does), there is always the possibility to reel in the cable without breaking tidal lock. Then we’d have real micro gravitation.

    For this maneuver and for changing RMP at target gravity it would be interesting to know how fast we can reel in without loosing the tidal lock. This speed is also interesting for a continuous reel in that preserves most of the angular momentum, isn’t it?

    Kirk says “[…] angular momentum is conserved during tether reeling (which can be achieved through proper timing of tether extension or retraction) […]” – does this mean non-continous reeling speed? If yes, does it induce oscillations in the tether?

    Anyway, my first order guess for the critical reel speed would be omega_0*r. This would give reasonable times of reel-in and reel-out of some minutes to a few hours. How far off am I?

  12. Dick Eagleson says:

    It’s certainly good that smart people are finally addressing this enormous hole in our current knowledge with respect to long-term human habitation off-Earth. It’s way overdue. Right now, the only certitude in this area is that humans could live indefinitely in a rotating O-Neill-type structure in free space that provides 1G pseudo-gravity on its inner surface and whose diameter and rotation rate are sufficiently low not to mess with the human vestibular system. This is a pretty big initial step. It is crucial that we know if a vastly less “tall” first step is feasible and what planetary/lunar surface gravity environments – if any – are within the acceptable envelope. To speak of “colonizing” the surface of any extraterrestrial object with insufficient surface gravity to maintain long-term human metabolic health is to speak nonsense. Before any large investment in “colonizing” either the Lunar or Martian surfaces is made, it is essential to answer the question of what minimum G is required for long-term human health. I think this is the highest-priority open question that needs answering before any realistic plans to make humanity a spacefaring/dwelling species can credibly advance.

  13. I can’t help but notice that a number of people have asked questions that were clearly answered in the paper.. am I the only one who read it or something?

  14. Justin Kugler says:

    In all fairness to my colleagues at JSC and LaRC working on inflatables, they are not just duplicating what Bigelow is doing. They are pursuing entirely different configurations, manufacturing techniques, and lattices.

    The Bigelow module presently being considered for the ISS is quite small, in fact, and is not in the same class as the module proposed under the Inflatables Flagship Demo.

    That said, I do think the xGRF is a very interesting concept that would provide an excellent opportunity to characterize the gravitational environment needed to sustain human health. It’s worth pursuing in its own right.

  15. Jonathan Goff says:

    Philip,
    As I said in the blog post, I think you could fit an xGRF development program, including a subscale system to flight-validate the concept, a Sundancer-scale xGRF setup, and possibly one flight crew for a six month stint to test say 2 months each at .06g, Lunar gravity and Mars gravity, all for around the $500M that they were shooting for with the Flagship Technology Programs.

    ~Jon

  16. Jonathan Goff says:

    Jared,
    One way trips of any sort would be a lot easier to sell if it was clear that at least the scary physiological issues could be dealt with.

    ~Jon

  17. Jonathan Goff says:

    Ed,
    If the tether is conductive, then yeah you could try doing ED reboost. I’m not positive though that I would want to add another new technology to the program. It might be nice to do as a follow-on though. Do the initial winching tether as a non-conductive one (maybe made of spectra wire or something), and then add a conductive element later to demonstrate ED reboost once the initial mission has been completed. If it works, then keeping it up there to continue doing research becomes a lot easier.

    ~Jon

  18. Jonathan Goff says:

    Kirk,
    I just wish there was a way of getting the idea of converting the inflatable FTD mission into xGRF in front of Bobby Braun (with a little note attached saying–here’s a cool idea that a Georgia Tech alumni came up with). Cause while I think most of us agree that this would be really useful to do soon, I think that doing this as an FTD mission is one of the only ways it’ll happen on any sort of useful timeline.

    ~Jon

  19. Jonathan Goff says:

    Googaw,

    First off, no you wouldn’t learn the same thing. While smaller mammals are a useful firs step that I’m not opposed to, they don’t give you all the same information. You still need to run the human experiment to know for sure with humans. That said, I would prefer doing a subscale mission first to prove out the tether winching technology. Putting some smaller animals in a small module for that experiment would give you some extra data early on–so it would be worth it. You could probably even do it as a secondary payload on another launch to keep the costs down. But ultimately, stopping at that would be pointless. People would still claim “well sure you know it works for rats, but does it work for people?”

    Second, NASA is already planning on spending $500M to build an inflatable technology demonstrator–my point was that for similar money they could get that *and* this. We don’t live in a world where NASA HSF just goes away, so I’d rather see the money spent in a way that answers useful questions.

    ~Jon

  20. Jonathan Goff says:

    AM,
    It might be a little cheaper, but it would also be a lot less capable. Dragon really isn’t meant to keep people up for very long by itself. And using it to test out stuff on smaller mammals would be overkill–for that you’d want something that was in the microsat scale.

    ~Jon

  21. Jonathan Goff says:

    Justin,
    While I’m actually a fan of having multiple groups looking at inflatables, I just question the utility of spending $500M+ on an FTD like that when there are people already developing and demonstrating that technology. I’d rather see the FTD money get spent on things that aren’t already going to happen. And a reduced gravity facility isn’t going to happen, in spite of being desperately important, without something like this. I’m just saying that comparatively speaking, you get a lot more bang for the buck with switching the inflatable FTD over to xGRF instead of paying NASA to do a more advanced version of something that may be commercially available soon. And especially with the cuts to FY11’s FTD and exploration technology budgets, we’re going to need to be more frugal to make this work.

    ~Jon

  22. Justin Kugler says:

    I don’t disagree, Jon. I just wanted to make it clear that it wasn’t exactly a one-to-one comparison. :)

    Of course, the talk at the coffee pot is that the inflatables flagship demo is likely to get pushed out to 2020 because of the budget situation. The inflatables teams aren’t depending on FTD to continue their work and are expecting to take it slow.

    There is a way to get this in front of Bobby Braun, though. :) He’s agreed to be the executive sponsor for a new group that is forming to establish working-level connections across centers and disciplines and break down institutional barriers. We had our charter meeting around TEDxNASA and I spoke briefly with him at the conference.

    Given that I’m working on my second M.S. in human space exploration sciences (and looking for something to hang my hat on since I’m the lone engineer amongst a bunch of human health & physiology folks), I find this concept really interesting because it addresses a specific need we have. I’d be happy to show the concept to Dr. Braun when I next have the opportunity.

  23. Jonathan Goff says:

    Justin,
    Cool. Let me know how that goes. I really think that something like this can make a huge difference for not a lot of money (relatively speaking). If it turns out that lunar gravity is enough to allow people to live there for extended durations without negative effects, that could really shake-up some thinking. Especially with all the cool news coming out of LCROSS, LRO etc about lunar water and volatiles.

    It’s still going to be a long slog, but I’m glad that someone in a position to make a difference is willing to take this up. Let me know what I can do.

    ~Jon

  24. Justin Kugler says:

    I’m with you 100%. In the spirit of TED, this is definitely an “idea worth spreading.” I don’t know for sure when our next opportunity to get in front of Braun will be, so just don’t let me forget about it. =)

  25. I pushed it for a few months after conceiving it, but it was a summer 2005 presentation to then-ARC director Scott Hubbard that took the wind out of my sails. After giving him my presentation, I asked him later why he didn’t seem more interested. He said, “Kirk, it sounds like a good idea, but I’ve been doing battle with Mike Griffin to save an already-built piece of hardware (the ISS centrifuge module) and failed. How can we imagine something like this succeeding?”

    I realized Hubbard was right and pretty much gave up on any more advocacy. Thanks Mike.

  26. googaw says:

    Jon, actually using mice gives us far more information because there are far more of them. We have a statistically significant sample size and controls, i.e. the setup for an actual replicable scientific experiment of the kind standard in medical experiments. With statistically significant sample sizes and controls, we can show whether the gravity or some other aspects of the environment (e.g. radiation) have caused any health problems that arise. Otherwise we’re just guessing. If we launch one or two or three people with certain idiosyncratic genetics and medical history, with no controls, it tells us nothing statistically significant or replicable, unless the cause and effect of a certain syndrome turn out to be quite obvious. But they usually don’t: causal chains in biomedical problems are usually quite subtle.

  27. Paul says:

    googaw,
    Larger sample sizes (via mice) would be useful. Bone loss rates vary wildly between astronauts. That gives you a large margin of error. So improvements in partial-g would have to be huge to be measurable. With mice, you can have finer data.

    While mice might be useful for bone-loss research, does anyone know if there are accepted animal analogues used to measure nausea (short of vomiting) and dizziness? You might be able to work out how much “gravity” is required to eliminate space sickness, how fast a centrifuge can spin without causing vestibular hallucinations, etc. (Lit says 1 RPM for comfort, 4 RPM max.)

  28. More to the point, the centrifuge has been attempted and failed *politically* for years now. Life sciences have no political traction. The only mice that have every flown on the ISS were in an Italian experiment.. for which no results were ever published.

  29. Justin Kugler says:

    I think it’s awfully soon to be complaining that results have not yet been published from MDS research, Trent. It was only returned from the ISS in March. The tissues were shared with researchers all over the world and it can sometimes take years to get through the peer-review cycle.

    http://www.nasa.gov/mission_pages/station/research/experiments/MDS.html

    If life sciences have no political traction, though, why is HRF getting a budget increase? Why is my office, the ISS National Lab, partnering with NIH to do life sciences research on the Station?

    Perhaps you meant to specify live animal research? Aside from insects in the CGBA Science Insert series of educational payloads, that has been more difficult to get support for.

  30. A_M_Swallow says:

    … And using it to test out stuff on smaller mammals would be overkill–for that you’d want something that was in the microsat scale.

    You may want something on the small side but a made-to-measure spacecraft with an environmental control and life support system (ECLSS) for mice that is able to perform Earth re-entry will not be cheap.

  31. Justin, ahh, I must have misread that.. I thought the experiment was returned in March 2009.

  32. Lee Valentine says:

    Although we do not have data on humans between microgravity and one gravity, we do have data on chickens raised in hypergravity. That data should anchor expectations for values of partial gravity.

    Chickens are not humans, but bone physiology, among other things has been highly conserved since the split from our most recent common ancestor. Therefore, we should expect the chicken data to predict human skeletal responses.

    Here is the quote with references from Ed Regis excellent book “The Great Mambo Chicken”

    [pp 54-55]
    . . . For that matter, humans could also have survived at even HIGHER
    levels (italics in original are uppercase here), as has been demonstrated
    repeatedly by experimental tests.

    There was the hyper-G work done on chickens, for example, by
    Arthur Hamilton (“Milt”) Smith in the 1970s. Milt Smith was a gravity
    specialist at the University of California at Davis who wanted to find
    out what would happen to humans if they lived in greater-than-normal
    G-forces. Naturally, he experimented on animals, and he decided that
    the animal that most closely resembled man for this specific purpose
    was the chicken. Chickens, after all, had a posture similar to man’s:
    they walked upright on two legs, they had two non-load-bearing limbs
    (the wings), and so on. Anyway, Milt Smith and his assistants took a
    flock of chickens — hundreds of them, in fact — and put them into
    the two eighteen-foot-long centrifuges in the university’s Chronic
    Acceleration Research Laboratory, as the place was called.

    They spun those chickens up to two-and-a-half Gs and let them
    stay there for a good while. In fact, they left them spinning like
    that day and night, for three to six months or more at a time. The
    hens went around and around, they clucked and they cackled and they
    laid their eggs, and as far as those chickens were concerned that was
    what ordinary life was like: a steady pull of two-and-a-half Gs. Some
    of those chickens spent the larger portion of their lifetimes in that
    goddamn accelerator.

    Well, it was easy to predict what would happen. Their bones
    would get stronger and their muscles would get bigger–because they
    had all that extra gravity to work against. A total of twenty-three
    generations of hens was spun around like this and the same thing
    happened every time. When the accelerator was turned off, out walked
    . . .GREAT MAMBO CHICKEN!

    These chronically accelerated fowl were paragons of brute
    strength and endurance. They’d lost excess body fat, their hearts
    were pumping out greater-than-normal volumes of blood, and their
    extensor muscles were bigger than ever. In consequence of all this,
    the high-G chickens had developed a three-fold increase in their
    ability to do work, as measured by wingbeating exercises and
    treadmill tests
    [end quote]

    References:

    Smith, A. H. “Physiological Changes Associated with Long-Term
    Increases in Acceleration.” In “Life Sciences and Space
    Research XIV”, edited by P.H.A. Sneath. Berlin:Akademie-Verlag, 1976.
    Smith, A. H., and C. F. Kelly. “Biological Effects of Chronic
    Acceleration.” NAVAL RESEARCH REVIEWS 18 (1965): 1.
    _____. “Influence of Chronic Acceleration upon Growth and Body
    Composition” ANNALS OF THE NEW YORK ACADEMY OF SCIENCES 110
    (1963): 410.

  33. Paul says:

    Lee,
    Awesome. Did the research show any negative health effects as the mambo-chickens moved back into a 1g environment? Particularly cardiovascular, with that over-powered mambo-heart.

    Would also be interesting to find out the ratio of hyper-g necessary to counter micro-g damage. And whether a period of hyper-g before launch would reduce the damage from prolonged micro-g. (My god, for a “research” space station, the ISS hasn’t given us much to work with. Doesn’t NASA want to go to Mars?)

    Jon,
    I noticed on your g-vs-health graph, all but one of the possible health-curves was still rising as it passed 1g. A couple of human data points >1g might give a clue as to the shape of the <1g curve. (For example, the mambo-chickens would seem to eliminate a curve that peaks below 1g.)

  34. Lee, Paul,
    While I do agree that the hypergravity research does provide some data points, I’m not sure how much it really tells us about hypogravity. My gut feeling from the information I’ve seen is that there are multiple factors that feed into overall “health”, and while some of them like “how much are you using your muscles” and “how much is your heart pumping” tend to do better at higher levels of gravity, they don’t explain why people who are exercising a ton in microgravity do so much poorer than say someone who’s a total lazy slob who never exercises in normal gravity. To me that says there are multiple phenomena in play.

    For instance, if I were to guess (not being a doctor), I’d split things into at least two groups of effects (there are probably a whole lot more):

    1-Fluid settling within the body
    2-Gravity-induced stresses on the body

    Factor 1 never comes into play above a certain gravity threshold, but below that threshold it appears to trigger all sorts of nasty effects. Factor two is also probably a complex curve. More gravity equals more workout, but after a certain point you probably hit diminishing and then negative returns. Below a certain level of gravity the lack of “unintentional exercise” you get from just living in a gravity field might start to be balanced by less stress on joints and such…

    Just saying that while it’s really fun to speculate…it’s just speculation till we’ve done the experiment.

    ~Jon

  35. Axel says:

    No responses to my questions? Except maybe for a vague hint that someone should read the paper more carefully. Kind of depressing ;-/ As I wrote I missed the link to the paper at first. Anyway, we are doing this for fun, don’t we? If someone knows the answers, why not just tell them?

    Currently the most interesting question to me was asked by Nels Anderson, who wondered about “gravity-gradient torques […] diverting […] angular momentum into changing the orbit”. I don’t understand the interactions between Earth and our two tethered masses system well enough to say how orbit changes, or if it changes at all. Could this be used as an orbit changing method?

  36. Ed Minchau says:

    Axel: From the 2 to 6 RPM limit I guess your plans are more in the 1 to 10 km range for the radius, yes?

    No. The formula for centripetal acceleration is
    a = v^2/r or
    a = 4(pi^2)r/(t^2) or
    a = 4(pi^2)(r)(RPM^2)/3600

    Doubling the radius doubles the acceleration, but doubling the RPM quadruples the acceleration. At 6 RPM you can get 1 gee equivalent with less than 25 m radius.

  37. Axel,
    Sorry for not getting back with you. I thought your comment was interesting and deserved follow-up…but there was a lot of comment there, and I barely have bandwidth these days to post comments, let alone to follow-up with ones that are going to take extra effort.

    Fortunately it looks like some of the other commenters are helping now.

    ~Jon

  38. Axel says:

    Ed, your calculation is correct, but your model is inadequate. 6 RPM is known to make many people sick. A gravity lab should be able to validate existing guesses for the “comfort” range from 2 to 6 RPM. So 2 is the more relevant RPM for a gravity lab, which would be 230 m. What is more important: when reeled out the system must have the same angular momentum as when reeled in. So when it rotates once every 90 minutes with that given momentum, its length must be much longer. Anyway, these questions were answered by Kirks paper. His example ends up close to 10 km for 4 RPM.

    What I didn’t find there is the critical reel-in speed. How fast do we have to reel in to break the gravity gradient lock? Yesterday I realized my above guess was based on invalid assumptions, because the strength of the lock depends on the strength of the gradient and therefore on orbit height. However my new numbers are not too much different. Like 5 m/s at 5 km cable length, and roughly linear with cable length, i.e. 1 m/s at 1 km length. But it would be nice to get confirmation for this (or hints to look for more errors).

    BTW I’m increasingly convinced that due to non-linearity of the gravity field, reeling in *does* in fact change the orbit, at least a little. And maybe the effect can be accumulated over many orbits. No quantitative estimates yet.

  39. PrairieKirk says:

    Colin Doughan of Space Business Blog evaluates some of the business aspects of xGRF, in a November 18th post, here:
    http://spacebusinessblog.blogspot.com/2010/11/gravity-for-sale.html

  40. Ed Minchau says:

    Axel, there must be a unit error in there somewhere. A 10km radius and 4RPM would give a centripetal acceleration of 179 gees.

  41. Ed Minchau says:

    Ah wait, I didn’t read thoroughly what you wrote. I see what you’re saying now.

  42. Axel says:

    This week during lunch break I was able to convince a colleague who is a physicist that my ideas about one effect that changes orbit could basically be correct. However putting in some numbers for a system similar to what we discuss, the orbit changes only by a few meters per reel in/out. For accumulation over many reel in/outs the orbit should be quite excentric, or else it will (almost) cancel out.

    There may be more orbit changing effects, but I would need to understand the reel in/out dynamic process a lot better to be sure.
    Chances are no such effect is practically relevant to the xGRF concept.

    Usually such orbital problems have already been discussed exhaustively by someone smart 50 or 100 years ago. Anyone who could point me to such work? Any key words to google for?

  43. nooneofconsequence says:

    Please realize that “reeling in/out” must be done exactly axially or the offset torque will cause a precession. You’d then have a 2-d pendulum effect that may be hard to stabilize, and you might also have a torsional component on the cable that could become amplified if not carefully detuned.

    A major consideration is the dV requirements on recovery if the cable breaks while under tension. I believe that we are approaching the point where the confidence in automated guidance systems to recover out of control components to such a gravity facility could be signed off on after a single unmanned test (with an intentional “break” simulation). Furthermore, one advantage of having such a facility at ISS is that Progress (and ATV) potentially can deliver propellant for free fliers – e.g. you can build out around the ISS “infrastructure”.

    Yes I agree with phillip about free flier with autonomous docking off the ISS – it would be seen as an extension of ISS, not unlike how we have multiple experimental facilities at each of the National Labs.

    You’d want a common free flier component that would be used to isolate experiments from the ISS (for various reasons). This could be derived from various existing platforms, but in general would be “refreshed” from ISS resupply on redock. To begin with you’d run them w/o human occupancy though still pressurized, then eventually use them for human experiments as well.

    For such a gravity facility, two with a dockable cable apparatus could be used, where the assembly would be done following undock from ISS.

    One would allocate many orbital “slots” for concurrent operation and debris management procedures. This would also allow commercial firms to orbit whole set up experiments (say crystal/semiconductor fabs) and use ISS for infrastructure/support while not active. This would get around many issues as to why ISS isn’t well used – because the rules of operation prevent certain experiments (not unlike the centrifuge) – because they can be “safed” when part of the ISS and active in orbital slot.

    -nooneofconsequence.

  44. My stepfather was an engineer at Teledyne back in the 1960’s and 70’s and my brother and sister in law have done NASA grant work on behavior of mammalian reproductive tissues in “simulated” microgravity. The news here is not good………………….
    http://www.facebook.com/topic.php?uid=109555615732469&topic=61
    click on the face book discussion page and click on, “Mammalian reproductive tissues behavior in microgravity” we need a flight experiment I think, the question really is…….can we and our food animals reproduce in micro and other gravity wells?

    perhaps this is a small part of the Fermi paradox?

    http://rsx.sagepub.com/content/16/10/947.abstract

  45. Pingback: Variable Gravity Research Facility (xGRF)

  46. I’ve done a post to science20 about these things recently, and link to this page, see

    http://www.science20.com/robert_inventor/blog/could_be_first_human_artificial_gravity_experiment_soyuz_crew_tether_spin_way_iss_no_extra_fuel-131278

    BTW Axel mentioned Theodore Hall’s work – his research, including the doctoral thesis, is all available here

    http://artificial-gravity.com/

  47. Interested in any comments on my blog post and don’t hesitate to say if you spot any mistakes in it however tiny.

  48. MBMelcon says:

    On 2010 November 13 Jeff Goff listed two groups of gravity effects:

    1-Fluid settling within the body
    2-Gravity-induced stresses on the body

    A third consideration would be settling within individual cells, usually studied by rotating growing plants with clinostats. It may be that particles react more easily with each other if they have collected on a cell wall.

    -MBMelcon

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