### Poll

#### How long does a manned mission have to last for a spin gravity (SG) solution to become routine?

All manned spaceflight will implement SG within minutes/hours of achieving orbit
SG implemented for durations greater than a week (i.e. not for cislunar transits)
SG implemented for durations greater than 6 weeks  (i.e. not for NEO rendezvous)
SG implemented for durations greater than 14 months (i.e. not for Mars missions)
SG implemented only for longer durations (5+years)/or not yet by 2100
SG is unnecessary with appropriate exercise

### Author Topic: Spin gravity to 2100: over what transit time will SG become routine?  (Read 10117 times)

#### mikelepage

##### Spin gravity to 2100: over what transit time will SG become routine?
« on: 08/09/2017 09:40 AM »
Defining the right question for this poll has been tricky, and spin gravity conversations tend to get derailed by debates about how to implement a solution, or at what level of gravity it should be at, or whether it is necessary at all when exercise is performed.

This poll does not attempt to address these topics, but instead focusses on what I think most of us believe: that some form of spin gravity will come into play at some point in the future, for manned spaceflights of greater than "x" duration.  This is because each of the biological systems show symptoms in response to microgravity and then adjust to a "0g set point" as shown in the following graph:

This graphic depicts the generally accepted "point of adaptation" about 6 weeks into microgravity exposure where most astronauts gain their "space legs" and most symptoms reach some sort of equilibrium.  Some symptoms do not stabilize however, and it is predicted by many that those symptoms will reach clinical significance at some time point of duration "y", greater than any astronaut has yet experienced (record is by Valeri Polyakov at ~14 months).

So the question is, for the limits of the future you can imagine (let's not go further out than 2100), for what duration transits/stay in space do you foresee implementation of a spin gravity solution (of whatever configuration/gravity level) becoming routine?

#### KelvinZero

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #1 on: 08/09/2017 10:24 AM »
I chose "SG implemented only for longer durations (5+years)/or not yet by 2100"

..but Im not sure if I read that the same way it was intended.

I think we will probably never actually adopt spin gravity as our solution, though we may dabble in it.

Sure, if we had to design a mission right now with periods beyond our current experience, we would almost have to use spin gravity. I also think that without technological advances, existing exercise solutions are certainly not enough for some proportion of the population beyond some time limit.

For example, if we were to design a mission to Saturn using ITS, I think the two ITS attached at the nose seems fairly reasonable. But a lot of advances and experience will have been achieved before that mission.

We may also have spin gravity hotel tourism quite soon, at the point when spacex or blue origin provides cheap access to orbit, and before mars or even moon missions. Note that isnt actually the topic.

My expectation is that technology will keep advancing and solving problems, perhaps a different solution for each issue, such that we never actually end up having to constrain our entire structure with spin gravity. An isolated spinning portion would also affect design choices  and add additional dramatic failure modes for your entire structure.

I don't know what those solutions will be. I just think there will always be this constant pressure to find other solutions, pushing technology ahead of our very slowly advancing mission times. There are so many avenues.
VR treadmills, drugs, genetic engineering, becoming a zero-g species, replacing your bones with carbon nanotube... Why struggle to preserve current bone strength if it turns out you can build something an order of magnitude stronger?

---

If we do end up with spin gravity the deciding factor may be for industrial reasons rather than human ones. If it makes plumbing and design across your entire plant more effective then there is your reason for a design constraint that affects your entire structure (now stationary, not travelling)
« Last Edit: 08/09/2017 10:48 AM by KelvinZero »

#### StvB

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #2 on: 08/09/2017 02:17 PM »
I'll also put it up there at 5+ years. I don't think it will be used for anything in the 21st century and certainly not a mars mission; biggest issues there are going to be other factors like radiation. People have already spent the requisite transit time in LEO. So I think SG will become necessary when people are living in space and not just on other planets, which will certainly be 5+ years IMO.
-Steve

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #3 on: 08/09/2017 06:39 PM »
One serious problem with this poll: scale. You wouldn't spin up structures with the volume of ISS. It's too big a cost and nuissance relative to what you can do with the limited volume. You wouldn't spin up a six person mission taking a slow route to Mars because you can't do any burns. But you might want to spin up a colonization ship, regardless if it's going slower or faster.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #4 on: 08/11/2017 08:26 PM »
I voted for durations greater than one week, but I think in real life there will be a difference between what is tolerated while in transit, and what is normal for being at a destination.

For intransit, I think durations up to 6 months could be rationalized, and doing so would simplify the transportation systems for moving between Earth and Mars.

For staying at a destination in space, and not on a planet, I'm assuming that artificial gravity space stations will become prevalent when we finally reach the tipping point of expanding humanity out into space. Because of their size (~200m diameter minimum) it could be a while before we are able to afford an artificial gravity space station at every popular destination such as LEO, LLO, LMO, EML, etc., so limiting 0G exposure may be mandatory for workers.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### mikelepage

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #5 on: 08/12/2017 05:03 AM »
One serious problem with this poll: scale. You wouldn't spin up structures with the volume of ISS. It's too big a cost and nuissance relative to what you can do with the limited volume. You wouldn't spin up a six person mission taking a slow route to Mars because you can't do any burns. But you might want to spin up a colonization ship, regardless if it's going slower or faster.

I'd argue there's a lot of room for innovation here.

The amount of nuisance/cost scales with the required angular momentum & spacecraft mass, which will be less for smaller spacecraft.  Building a larger spin radius does not necessarily mean building a larger pressure vessel however, it requires a different kind of geometry.  If you want to maximise spin radius while minimising mass, you need some kind of deployable/retractable structure (but not just cables/tethers, because there are both tensile and compressive forces involved).  You also need to combine that with some kind of flywheel arrangement that will allow docking/course adjustments/fixed communications without loss of angular momentum.

Currently working to start up a company because some engineer friends and I believe we have such a solution, and a way to bootstrap from small unmanned prototypes hence my interest in starting this poll.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #6 on: 08/12/2017 05:22 AM »
I'd argue there's a lot of room for innovation here.

We'll need lots of innovation once we start expanding humanity out into space, and ways to keep humans healthy will be important.

Quote
Currently working to start up a company because some engineer friends and I believe we have such a solution, and a way to bootstrap from small unmanned prototypes hence my interest in starting this poll.

Best wishes on that. And while it's good to survey the public, make sure you figure out who will actually pay you money for building such a solution - it's important to talk with your potential customers as early as possible.

Also, check out the Founder Institute "Star Fellow" program. Their initial class may have have already started, but you can figure out whether it's a good fit for your needs (it may, but it may not).
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### mikelepage

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #7 on: 08/12/2017 09:38 AM »
I'd argue there's a lot of room for innovation here.

We'll need lots of innovation once we start expanding humanity out into space, and ways to keep humans healthy will be important.

Quote
Currently working to start up a company because some engineer friends and I believe we have such a solution, and a way to bootstrap from small unmanned prototypes hence my interest in starting this poll.

Best wishes on that. And while it's good to survey the public, make sure you figure out who will actually pay you money for building such a solution - it's important to talk with your potential customers as early as possible.

Also, check out the Founder Institute "Star Fellow" program. Their initial class may have have already started, but you can figure out whether it's a good fit for your needs (it may, but it may not).

Thanks for the tip.  It sounds quite similar to the MoonshotX Gemini program (based here in Australia - gearing up to start after IAC) which is an incubator I'm considering doing.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #8 on: 08/12/2017 07:17 PM »
Thanks for the tip.  It sounds quite similar to the MoonshotX Gemini program (based here in Australia - gearing up to start after IAC) which is an incubator I'm considering doing.

The Founder Institute has a Perth location for general startups, so you could reach out to their local director to talk with them about the space-related program - they could find someone you could talk with more about that program. Hard to tell how active the Perth location is, but usually the directors are locals.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### whitelancer64

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #9 on: 08/14/2017 10:27 PM »
Other physiological factors are at play.

But the vestibular system is a big deal.  First words on Mars are probably going to be, "I've fallen, and I can't get up!"

I've wondered why this hasn't been demonstrated on ISS.  It's probably hard enough just doing what they are doing now rather than being put into a federally funded spin cycle.

There is currently on the ISS a small centrifuge in the Kibo module. Some of the mice that have been sent up have been put in it. Nothing larger-scale primarily due to the cost, engineering issues, but there have been some proposals.

A purpose-built rotating space station would be a better idea.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #10 on: 08/14/2017 11:38 PM »
That's a hell of a gap between 6 weeks and 14 months.

--

Regardless of what I voted for, my real answer would depend on how well SG works. If we only require 1/10th of a g, and can tolerate ~10rpm, then the answer is "all the time, because why not, it's essentially free." If the answer is never less than 1g and never more than 1rpm, then the answer is never. (Because by the time you have structures large enough, you'll need to have already solved the problems in another way, so why bother with the expense, or you will have given up on long duration HSF/settlement/colonisation if you can't, so why bother with the expense.)

IMO, asking a question based on time, when we don't know anything about size/cost/difficulty, is premature.
« Last Edit: 08/14/2017 11:40 PM by Paul451 »

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #11 on: 08/14/2017 11:49 PM »
Regardless of what I voted for, my real answer would depend on how well SG works.

Quote
If we only require 1/10th of a g, and can tolerate ~10rpm, then the answer is "all the time, because why not, it's essentially free."

A good observation, and it does highlight the lack of real data we have to determine how little gravity humans can not only tolerate, but still be able to thrive on. And this matters for any plans we have for colonization of our solar system.

Quote
If the answer is never less than 1g and never more than 1rpm, then the answer is never. (Because by the time you have structures large enough, you'll need to have already solved the problems in another way, so why bother with the expense, or you will have given up on long duration HSF/settlement/colonisation if you can't, so why bother with the expense.)

I think there are interims steps we could take if that were the case, but overall your point is taken.

Jeff Bezos goal is to have humanity living and working in space, so let's hope he's willing to fund the first artificial gravity space station when the time is right...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### lamontagne

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #12 on: 08/15/2017 01:10 AM »
Other physiological factors are at play.

But the vestibular system is a big deal.  First words on Mars are probably going to be, "I've fallen, and I can't get up!"

I've wondered why this hasn't been demonstrated on ISS.  It's probably hard enough just doing what they are doing now rather than being put into a federally funded spin cycle.
It was planned and partly built but it was cancelled:

https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module

#### savuporo

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #13 on: 08/15/2017 03:54 AM »
There is currently on the ISS a small centrifuge in the Kibo module. Some of the mice that have been sent up have been put in it. Nothing larger-scale primarily due to the cost, engineering issues, but there have been some proposals.

A purpose-built rotating space station would be a better idea.

eu:CROPIS is launching in a few months.
Orion - the first and only manned not-too-deep-space craft

#### mikelepage

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #14 on: 08/19/2017 07:30 AM »
That's a hell of a gap between 6 weeks and 14 months.

I did that because I wanted to avoid debates about how long a Mars mission lasts.  14 months more than covers 2x "long" 6 month transits.  So if you take Valeri Polyakov's fitness at end of mission as representative of what all Mars missions will be, then you probably think we will not need SG until we do manned missions of longer duration than to Mars.

Also, it is still only a single order of magnitude, so not that much bigger:
1 week vs 6 weeks is a factor of 6
6 weeks vs 14 months is factor of 10
14 months vs 5+ years is a factor of 4+

Quote
Regardless of what I voted for, my real answer would depend on how well SG works. If we only require 1/10th of a g, and can tolerate ~10rpm, then the answer is "all the time, because why not, it's essentially free." If the answer is never less than 1g and never more than 1rpm, then the answer is never. (Because by the time you have structures large enough, you'll need to have already solved the problems in another way, so why bother with the expense, or you will have given up on long duration HSF/settlement/colonisation if you can't, so why bother with the expense.)

IMO, asking a question based on time, when we don't know anything about size/cost/difficulty, is premature.

Defining the question is tricky as I said in the OP.  But this is a poll of opinions, not data, and my observation is that most people (especially on this site) have an opinion about how spin gravity could/would work.  So to avoid the poll getting derailed by debates around the issues you have mentioned, I'm asking people to state, given their opinion, for what duration do they foresee that solution becoming routine?

Personally, because I've been working on my Deployable Spin Gravity Array (DeSGA) architecture - see below - which has a 4-fold radius expansion factor, I can imagine that a series of pressure vessels designed to fit inside a 12m fairing being able to expand to a 48m diameter.  This means an ITS-launchable (maybe even ITSy-launchable) structure could potentially provide a Mars gravity environment (r=24m, 4RPM) within hours of achieving orbit.

Because Mars is the SpaceX destination of choice, I could easily imagine such structures (at Mars gravity) becoming the de facto standard for travel for longer durations - at least outside of cis-lunar space - before the end of the century.

« Last Edit: 08/19/2017 07:36 AM by mikelepage »

#### guckyfan

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #15 on: 08/19/2017 08:15 AM »

I voted not for Mars.

Your design is intriguing. I see one major problem with it. How would any visiting spacecraft dock when there is no center location to attach to?

But the concept could be used for another design. My favorite though nobody seems to agree with me. Build a cylindrial station that rotates around a node at the center. Little volume at any given gravity. But along that cylinder all gravities from 0 to max are available for experiments. At the end two rigid or inflable habitats might be added to give more volume at max gravity.

Some testing of different rotational speeds would be interesting. The limits presently set seem to accomodate sensitive persons immediately. It seems people do get adjusted to movement at sea over time. So with adjustment many people may be able to tolerate much higher rotation to achieve useful gravitation with smaller diameters.

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #16 on: 08/20/2017 12:44 AM »
Build a cylindrial station that rotates around a node at the center. Little volume at any given gravity. But along that cylinder all gravities from 0 to max are available for experiments. At the end two rigid or inflable habitats might be added to give more volume at max gravity.

Yes, this is by far the easiest way to start a human-scale AG research station.

(Although at an even smaller scale, a single module still attached to the upperstage that launched it. The US acts as a counter-balance, reducing the length of module you need to launch (compared to your more symmetrical design.) Not sure why people always gravitate to elaborate designs.)

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #17 on: 08/20/2017 03:21 AM »
My favorite though nobody seems to agree with me. Build a cylindrial station that rotates around a node at the center. Little volume at any given gravity. But along that cylinder all gravities from 0 to max are available for experiments.

I LOVE that idea, and it's the first time I've heard of it, so kudos!

Part of the reason why I really like it is that I've been working on a concept for a full-sized rotating space station, and it requires the use of such cylinders as part of the design (structural elements only), so I've already been thinking about how to build and transport such designs. But I did not foresee this application.

If you want to chat about this design I have some ideas to present, so let me know.

Quote
At the end two rigid or inflable habitats might be added to give more volume at max gravity.

I would say no, especially if you're hanging them off the end of a rotating structure, because inflatables are not the right type of structure for that application.

No doubt there would be a practical limit, but if the ability to mitigate twisting rotation is easy to solve, then bundling may not be too difficult. And it would have to be an even number of cylinders...

Quote
Some testing of different rotational speeds would be interesting. The limits presently set seem to accomodate sensitive persons immediately. It seems people do get adjusted to movement at sea over time. So with adjustment many people may be able to tolerate much higher rotation to achieve useful gravitation with smaller diameters.

This would make testing multiple gravity levels much easier.

Also, the version I was planning to use was going to be very long, so don't be afraid to consider a completed cylinder assembly as long as 100m or more. With that size you could simulate Mars gravity with a spin rate of 2.6 rpm, which some think is tolerable.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### daveklingler

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #18 on: 08/20/2017 04:28 AM »
One serious problem with this poll: scale. You wouldn't spin up structures with the volume of ISS. It's too big a cost and nuissance relative to what you can do with the limited volume. You wouldn't spin up a six person mission taking a slow route to Mars because you can't do any burns. But you might want to spin up a colonization ship, regardless if it's going slower or faster.

Multi-kilometer cables are an off-the-shelf item.  Any large city will have businesses that not only sell them, they stock them.  The diameter is *not* the difficult part of the engineering.

There are seven elements to a minimal bolo spacecraft: a hub, two ends, two tram cars, and two sets of cables from the hub to either end.  Spinning up the entire arrangement for 1G at 1 RPM requires a small fraction of the propellant that it took to get them to (any) orbit, less than 100m/sec.

If you park the arrangement in equatorial LEO <500km, humans can have families there.  If you fling the whole mess at some destination, humans don't have to be quite so concerned about whether they'll be in any sort of shape to do anything when they finally get there.

People seem to think that 1G is technologically difficult, and that we need to pursue lower accelerations or high RPMs in order to reduce the scale, as if space isn't big enough to hold 2 km.  But we build bigger and more difficult structures than this all the time.  Lake Pontchartrain Causeway in Louisiana is 38 km, and there are several tramways in the world that are well over a km in length.

Once you've built the two ends, a middle and two trams, the distance they are apart really doesn't matter that much because the technical difficulty is over.  1G just means a longer tram ride to and from the center.

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #19 on: 08/20/2017 04:35 AM »
At the end two rigid or inflable habitats might be added to give more volume at max gravity.
I would say no, especially if you're hanging them off the end of a rotating structure, because inflatables are not the right type of structure for that application.

Why not? A pair of BA330s (to pick a well known example) around a central power and docking node would be ideal for a baton-type station. Solar arrays "hanging" from the node at 90 degrees to the two habitats. Radiator(s) from the fifth face of the central node. Docking adaptor on the sixth. Station would be rotating around the axis along the docking-adaptor/radiator line. By pivoting the solar arrays, you can actively counter any mass imbalance along the rotational axis, preventing tumble instabilities from building up.

Or alternatively, a single hab module berthed to a docking node, counter-balanced by a power/thermal module. Solar arrays would still "hang" from the docking node. That leaves you two docking points available. (Radiators could either run along the power module or "hang" from the bottom to increase the angular momentum of that side, shortening the necessary radius.)

And obvious variants are obvious.

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