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Dr. John Jurist, Sunday, 2-16-14 February 17, 2014

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Dr. John Jurist, Sunday, 2-16-14

Artificial Gravity


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Guest:  Dr. John Jurist.  Topics: Artificial gravity, spinning, tethers, rotation rates, the gravity gradient & more.  Please direct all comments and questions regarding Space Show programs/guest(s) to the Space Show blog, https://thespaceshow.wordpress.com.  Comments and questions should be relevant to the specific Space Show program. Written Transcripts of Space Show programs are a violation of our copyright and are not permitted without prior written consent, even if for your own use. We do not permit the commercial use of Space Show programs or any part thereof, nor do we permit editing, YouTube clips, or clips placed on other private channels & websites. Space Show programs can be quoted, but the quote must be cited or referenced using the proper citation format. Contact The Space Show for further information. In addition, please remember that your Amazon purchases can help support The Space Show/OGLF. See www.onegiantleapfoundation.org/amazon.htm.

We welcomed back Dr. John Jurist for this two hour discussion on all aspects of artificial gravity.  Note that Dr. Jurist prepared presentation material for this program which you will find on the archived blog entry for this discussion.  Also, I recommend you read the excellent article by our UK guest, inventor, & friend, Robert Walker, “Can Spinning Habs Solve the Zero g Health Issues?  Can Humans Live in Mars or Lunar g? Why Nobody Knows.” (see www.science20.com/print/129424).  During our first segment, Dr. Jurist introduced us to the basics of artificial gravity including the Coriolis effect, the gravity gradient & the info needed from in-space artificial gravity R&D.  Several studies including one by UC Irvine were mentioned, plus other bed rest studies.  He also talked about the Wyle Centrifuge studies which used a short arm for experimentation.  Our attention turned to the presentation material on TSS blog titled “Artificial Gravity Comments–JmJurist.”  Dr. Jurist took us through the tables & charts on his two page document.  He was asked about gender & age differences with gravity as well as small rodent/mammal ISS experiments now or in the future.  Our first caller was John from Ft. Worth who clarified some of his comments from the last Open Lines show plus he talked about the hardware, infrastructure, & engineering issues for in-space experiments.  We talked about the use of tethers & the relationship with microgravity & radiation issues.  With our caller still with us, Jenna emailed asking if either Mars One or Inspiration Mars would provide the needed research that never seems to be done by NASA or others.

In the second segment, Doug from S. California called.  He talked about his T frame tetherball type structure concept as an interim artificial gravity tool but said it was not a long term solution.  He also inquired about tethers, then he wanted to know about the mass of possible tether cables as well as potential materials that could be used for in-space tethers.  Doug then described a reference mission using a long arm centrifuge for the surface of the Moon.  Doug described a very good concept and Dr. Jurist had much to say about it.  We had quite the discussion on possible implementation strategies and the roadmap from theory to operations given our current policy & economic environment, plus the track record on other large projects that never made it.  With Doug on the phone, Ft. Worth John emailed to inquire about stability issues and tidal forces on the tether.  Both Dr. Jurist & Doug made a pass at providing John an answer to his question.  In his closing statement, our guest went over some basic advantages with a tether, the problems of the gravity gradient & the fact that the issues for colonization were very different than for experiments or a reference mission.

Please post your comments/questions on TSS blog above.  If you want to reach Dr. Jurist or our callers, do so through me.


1. Robert Walker - February 20, 2014

Just to add on the figure skating, I found out there are a couple of Guiness world records. First for the maximum number of spins on one foot, of 105 set in 2003, by Lucinda Ruh, she did it in 35 seconds so that’s averaging 180 rpm for 35 seconds. So that’s survivable and doesn’t cause nausea – for a habituated record holding ice skater. She says she does feel dizzy while spinning, but gets used to it as normal in the interview at the start here.

She also holds the guiness world record for the fastest ever spin at 308 rpm.

2. Robert Walker - February 18, 2014

I enjoyed the show, and thanks for linking to my article on science20.

I listened to the show afterwards or I’d have rung or emailed, have quite a few things so maybe can do them as comments here.


First on the breaking tether, you can deal with the problem of orbital debris using a fabric or multiple cable type approach.

Here is a fully worked out proposal for a tether using multiple cables connected together with lots of short sections so that even multiple breaks of all the tethers won’t damage integrity of the whole system.
The author works out that the Hoy tether would have a 100 year lifetime for a 290 km tether weighing 6700 kg in the LEO environment of space debris.

So – that’s solvable, don’t need to clear LEO of debris to have a tether system. If you can manage 290 km for 100 years can certainly do a few hundred meters.


You talked quite a bit about need to despin at Mars on arrival. However someone worked out a way to accelerate and decelerate without needing to despin. Which also deals with the issue of losing your counter mass or the two habs meeting up in orbit – and means you have full g or Mars g or whatever in orbit around Mars and for return journey.

This also means you can move a spinning tethered habitat in LEO to avoid debris, as with the ISS with no need to despin first. Indeed would be good practice to do it in LEO first to develop the system you’d use for the course changes for a MARS mission.

Method to Maintain Artificial Gravity during Transfer Maneuvers for Tethered Spacecraft


Also another thing I’ve come across, given that you can engineer the tether to be safe from micro-meteorite then the ability to break it can be an asset as an abort scenario for a mission to Mars, if you set it up right, break it at the right moment and your spacecraft gets sent back to Earth immediately when you get to Mars – here is a paper about that idea:


With inspiration Mars I was keen on their idea when I heard about it first, but the more I’ve heard comments about it on the space show, the more I feel it’s not safe. We haven’t yet had anyone fly in zero g for 500 days,and the one example of 437 days could just be someone who was very lucky.

So, I think personally it’s just not safe to send anyone on inspiration Mars until at the very least we’ve had some experience in long duration spaceflight closer to Earth, so at least 500 days duration of the mission and better if it is longer, two years, for a margin.

So, I think they’ll need to do something closer to home first for same duration. E.g. send the crew to the L2 position could be ideal for isolation from Earth to some extent, get an idea of what it’s like to live in a place where you can’t see the Earth in the sky, and can’t communicate quite so easily with Earth – and also gives them a worthwhile mission in its own right, lots of value there operating telreobots on far side of Moon surface – building radio telescopes (simple type that just need uncoiling lines over the surface of the Moon), exploring the poles of the moon with telerobots etc..

So if we have precursor missions like that – which after all was the key to Apollo’s success – then it’s a natural time to try tether experiments.

Then – if AG works – and if something can be done about the radiation – well I think Robert Zubrin’s double Athena flyby at 700 days is a much more attractive mission myself than Inspiration Mars. Because the crew have hours of close by telepresence operation of spacecraft on the surface of Mars and for months are significantly closer to Mars able to assist operators on Earth in a major way with things such as driving rovers around on the surface of Mars and supervising experiments there.

Double Athena also has a normal return speed to Earth not the risky high speed aerobraking of Inspiration Mars.


AI understand, as you said in the show -it’s not NASA themselves but rather what politicians tell them to do especially in human spaceflight – so scientists need to put a strong case to politicians.

But – whether or not that works, soon any wealthy individual – or other countries – or research grant based research – or even a kickstarter – could pay the few tens of millions to do the experiment

Here is an article by Tom Hill in 2012 suggested step by step approach to AG using DragonLab and suggests that wealthy private individuals could afford to do this.
Tom Hill DragonLab-g: an early step to Mars and beyond


First of all want to say – yes need to keep separate the two things – rpm tolerance for general public for space colonization and tourists – and rpm tolerance for astronauts pre-selected for the mission.

Just as astronauts have to have good health and be able to withstand high g for take off – if a high rpm AG hugely reduces costs – then it is reasonable to pre-select astronauts for interplanetary exploration based on their tolerance of spins in AG.

On the other hand for general population – well this is just anecdotal but someone on facebook commented on my AG article that he gets nauseous on rotating restaurant rotating as slowly as perhaps 4 times an hour, so 0.067 rpm. So for him even 1 rpm might be quite a bit over his tolerance limit, more than ten times too fast.

Though – that depends on whether or not he could adapt to it with some program of familiarization – and also depends a lot on whether the horizontal spins are the same in effect as vertical rotations.


First, with your bed rest patients – though head down bed rest the medics say is a good analogy for some aspects of zero g such as bone loss – first is not a full analogy for zero g.

But also it doesn’t follow that a spinning patient with head down is then a good analogy for AG effects in zero g. It’s like an approximation within an approximation, getting further and further from the original.

You are taking something which is only a partial analogy of zero g anyway – and then you are doing a horizontal rotation rather than a vertical one with axis in a different direction etc

Also, your issue with blood diffusing out of the capillaries – is that not due to going over full g to 2 g at the feet rather than the spinning or gravity gradient?

With the plans for a centrifuge sleeping component for the ISS, then the astronauts wouldn’t be able to stand up in it. It is just wide enough for an astronaut to crawl in wearing a spacesuit (for safety reasons for initial tests so they can test it with spacesuits first). They would sleep in it lying down in normal posture and only use it for sleeping I think was the idea. And – of course we don’t know if that is enough to fix the zero g health issues, but is a chance it might.

I mean, might turn out it is a good analogy, and that the centrifuge sleeping idea is pretty much the same as this and doesn’t work – but I think we need tests of people in true AG to compare it with to find out whether it is or not.

As for safety of testing humans in space – well start with zero g which we know is bad for health but acceptable for short flights – and build up gradually – also short duration tests to start with – don’t see any ethical issues with that so long as they are monitored carefully as we do the experiments and stop immediately if there is anything anomalous until it is understood better..


You didn’t go into this, but there is quite a difference between horizontal and vertical rotation – first – the way our balance organs are arranged, have one in each ear.

So when you spin horizontally or tilt to left or right they change orientation relative to each other. But if you tilt forwards and backwards they don’t. Tilt is around an axis parallel to the line joining the two balance organs.

Also evolutionarily – then the way we need to deal with horizontal and with vertical rotations is different. For vertical motions then the main thing is to keep upright. So need to be able to adjust to small tilts forwards and backwards or left and right and reposition ourselves to stay vertical.

But with spinning motions, instead we need to be able to spin very quickly on the spot – and then stop suddenly. So need a good sense of our orientation and how fast we are spinning to do that. For the other directions just need a sense of whether we are moving or not and ability to correct.

Now – I’m not sure where to go to find articles about this. I have a vague memory of reading about differences in sensitivity for tilt versus spinning – and may be something in the AG articles about it – but not sure where to look. Did a search just now but it’s hard to find with so much material about ordinary dizziness and fainting if you try to search for medical papers on the subject.


About the nearest analogy only thing you have tilt motions for days on end is seasickness, and sailors adapt so they can stay at sea for years at a time without getting seasick. Not that everyone can – but if it is like seasickness, then astronauts could be like sailors. If you are very susceptible to seasickness you don’t become a sailor – so if very susceptible to AG induced nausea then you won’t be an interplanetary astronaut at least not in spinning spaceships or short length tethers.

And then – bottom line is that we have no examples yet of anyone who has become nauseous as a result of AG type motions in space. It is just a theory so far, that astronauts would get nauseous in small AG environments – may be true but has to be confirmed.


So with caveat that it might not be a good analogue necessarily, there’s quite a bit about people with reasonable tolerance for spinning first.

First, what you said about dancers whipping their heads around to counteract effects of spin – that’s ballroom dancers. They also spin far more slowly than ice skaters.

Ice skaters don’t whip their heads around but just keep them in normal orientation. And manage amazingly fast spin rates.

I just had a go at estimating rpm for Yulia Lipnitskaya – on this video

I found was quite easy to count by just stopping and starting play.

Between 44 and 1.03 she does 39 rotations in 19 seconds. That’s 123 rpm. And in the middle she spins briefly far faster than 123 rpm. So into the hundreds of rpm is possible without significant effects for at least a third of a minute.

Then here is another analogy:

Indoor skydiving somersaults – closest perhaps to AG, though this is a tiny radius, and head and feet AG in opposite directions – no wonder it is challenging. Tny radius only 0.5 meter (say), at 60 rpm
– that would be an average 2 g.

Then, I found information about some old experiments in the 1960s.and 1970s



Clark – was able to withstand 24 hours of 9.55 rpm, 2 g acceleration. He estimated the. threshold of nausea as 0.6 radians per second so 5.7 rpm. Recommended a tenth of that because of visual effects.

That’s just one individual also and not looking into the possibility of adaptation – with seasickness can take several days to adapt to it.

Later on the page:

15-foot-diameter “slow rotation room” at the Naval Aerospace Medical Research Laboratory (Pensacola, Florida).
1975 report
At 5.4 rpm, only subjects with low susceptibility performed well and by the second day were almost free from symptoms

So that’s a case of adapting to them – for subjects with low susceptibility so if you choose your astronauts as you choose sailors – then seems at least possible that they could spin at 6 rpm (say) and adapt within a day or so.

Then more recent experiment, these are tests at 23 rpm for one hour a day for 5 days, full g in short radius device, found that the subjects adapted to the spin as the experiment progressed.

In conclusion the authors say that we need to do experiments with short radius centrifuges in orbit..

“In order to truly address the operational aspects of short-radius AG, a centrifuge must be made available on orbit. It is time to start truly answering the questions of “how long”, “how strong”, “how often” and “under what limitaitons” intermmittent gravity can be provided by a short-radius device.



Turns out, again from that page, that the experiment has been done already didn’t know that:

Experiments on the Soviet satellite Cosmos 936 in 1977 provided encouraging results. The life span of rats exposed to centrifugation during 18.5 days of space flight was significantly greater than that of non-centrifuged control animals. Centrifugation reduced hemolysis (red blood cell loss) and preserved bone minerals, structure, and mechanical properties [100]. Experiments on Spacelab D-1 in 1985 discovered that T-cell function – which is severely hampered in micro gravity – is preserved in artificial gravity via centrifugation [101]. Keller, Strauss, and Szpalski predict that artificial gravity of 1/6 g would be “sufficient to preserve bone strength above the fracture risk level”

More about the experiment here:



There might be other ways other than tethered and linear acceleration if in vicinity of a planet using tidal forces.

First of all, far future, the space elevator – then at far end would get full g with head towards the Earth – and 24 hour rotation as for on Earth – but that’s just a huge tether – but that’s like a tether half size because Earth is so much more massive.

But also there’s this intriguing idea – to use the way that satellites naturally orientate themselves towards the Earth – gravity falls off surprisingly quickly, because of inverse square, so at 840 km from Earth’s surface, then the force of gravity is 0.78, and at 340 km. is 0.9. So if you have a 500 km tether from one to the other, then tidal effects mean it keeps constant orientation towards the Earth – and tenth of g difference. If you work out the orbit for the C of G, at 590 km, then using this calculator
it’s orbital period is 1.60553 hours. So outer hab on the tether is going around once every 1.60553 hours in an orbit where normally it would go around every 1.69280 hours. So the centrifugal force it experiences is 0.869822 g instead of the 0.78 g needed to exactly compensate for gravity, so occupants would feel an artificial g of 0.09 g. away from the Earth.

Then for the innermost of the two habs at 340 km, so 6718 km from centre of Earth, then with same 1.60553 hours orbit, the g is 0.809568 instead of 0.9 g, so again would experience 0.09 g, this time towards the Earth.


That might be enough for health if lunar g is okay for health, but nobody knows of course.

At any rate is intriguing as a method of achieving gravity without propellant with much shorter tether and slower rpm than any other method,though limited in application only if close to a body with reasonable gravitational field. Still – would also work in orbit around Mars, Venus, with different amounts of g and depending on length of tether.

If the tether could be long enough, then could go up to nearly half g. I make it that to get Mars gravity by this method you need a tether of about 10,000 k which would take it well above geostationary orbit.

I think, not the first thing you do, but if it turned out that a tenth g was enough for health, can imagine someone building a 500 km tether like this at some point in the future, not so heavy at all with the Hoy tether method also safe, it is something indeed again in near future a wealthy individual or a kickstarter project could test.


Just mentioning, this time is just as a way to save on rocket fuel, idea is you pull it in to spin up and let it out to spin down, if you want to try lots of different AG amounts.


Starts with with an 11 km cable, stabilize in Earth’s gravity gradient, withdraw tether to 559 m for 1g, 4 rpm – and get variable gravity in between.


It might well be that NASA are right, but I think we need to do more experiments and the spinning experiments do at least suggest the possibility that less susceptible individuals may be able to cope with high spin rates in space.

Also bottom line is that we have no examples at all of anyone getting nauseous in true artificial situations – might even be that it doesn’t happen at all even for people normally susceptible to slow spinning motions, because it’s a different direction for the spin axis parallel to the line between the two ears – and not the same as seasickness either because it’s constant.

So – given the way it could simplify human space flight – I think well worth the experiment to find out if it is possible.

Not saying at all that fast rpm is okay. Just that it seems worth the investment to put some work into finding out for sure either way.

3. Joe from Houston - February 17, 2014

Ok. So if we stick to facts, every tethered space experiment to date has failed. Failures expose people in space conducting the tether experiment to additional personal risk.

Every short radius space experiment to date has succeeded. These successes did not in any way expose people in space conducting the short radius space experiment to any additional personal risk.

The problem with Astronaut’s dislike of keeping any animal hygienically clean for 6 months or so is a problem in itself. The solution: Conditionally send people up there who have no problem whatsoever in keeping any animal hygienically clean. There are likely millions of people who have no problem with giving their pet a bath once in a while.

Not all Astronauts dislike having to take care of animals hygienically clean for 6 months or so. There probably have been dozens of people who already lived in the ISS that would admit on air to having no problem whatsoever in taking care of animals in space for 6 months or so. Just try getting one to come on your show to admit that they have no problem and believe short radius artificial gravity experiments on animals makes perfect sense for this type of human exploration pursuit. If this Astronaut “thing” is the primary roadblock to the future of human exploration in deep space, then we would be better off not ever dreaming of this type of human exploration pursuit. This human need to explore new worlds currently cannot be suppressed by any existing or future controlling power on the face of the Earth. It will happen someday. Why not now?

If I was given the chance to go live in space for 6 months, which a privileged few have ever experienced in the entire history of mankind, I would keep animals hygienically clean by whatever means necessary for that once-in-a-lifetime opportunity. Wouldn’t you?

4. Joe from Houston - February 17, 2014

Instead of going for the 2001: A Space Odyssey – Arthur C. Clarke fantasy, we could initially seek permission to perform the simplest, cheapest, and safest experiment in an existing manned space research laboratory. Just spin small rats in either an existing centrifuge such as the Japanese one that could accommodate a rat or build, install, and operate a larger short radius centrifuge in a cylindrical space in the PMPLM near the end of it. Or, do this experiment without NASA’s blessing in a competing space laboratory operated by other country’s that see the logic in this type of human exploration pursuit.

Establishing the link between artificial gravity and a reduction of bone loss is the first step in a life-long pursuit of sending people to Mars and returning them in the same shape they started out in.

5. The Space Show - February 17, 2014

Dear Listeners:

Dr. Jurist sent this additional information to me shortly after our program ended. With his permission, I am posting it on the blog on his behalf.

Dr. David Livingston
From Dr. Jurist:

For 1 RPM and 1 G, radius is 894.3 meters. Converting to English, the radius is 2,935 feet. Thus, a tether would be 5,870 feet long.

Kulkoni braided galvanized steel cable consisting of 7 sets of 19 twisted strands makes a 3/8 inch diameter cable which weighs 243 pounds per 1,000 feet. Thus, 5,870 feet of tether would weigh 1,430 pounds and have a tensile strength of 14,400 pounds per 3/8 inch diameter cable. With a little margin, call it 12,000 pounds strength per cable. The Apollo 7 spacecraft weighed 37,000 pounds (really cramped 3 man vehicle with roughly 2 weeks life support) for comparison.

Spinup and spindown delta V is 307 ft/sec each for a flight delta V of 614 ft/sec. Put such a thruster on a habitat and assume a total weight of 45,000 pounds for something roughly the size of an Apollo command module and another 45,000 for the spent stage, stored supplies, or whatever on the other end. You need 4 cables weighing a bit over 5,700 pounds and 90,000 pounds of mass to start out.

If you want an airlock, 9 months of life support, and whatever, the mass climbs from the above.

Engineering considerations for deploying in LEO include tidal effects, dynamics, including vibration, associated with deployment and spinup, and precession issues plus longevity for such a cable in the space environment. These are all soluble in my opinion given sufficient resources, but getting those resources is problematic in my opinion and clearly outside of my area of competence..


John M. Jurist, Ph.D.
Adjunct Professor of Space Studies
Odegard School of Aerospace Sciences
University of North Dakota, and
Adjunct Professor of Biophysics and Aviation
Rocky Mountain College

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