### 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 7575 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?

#### NIVbV-O77OdV-VSVN-Op-SLE7

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #9 on: 08/14/2017 03:46 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.

#### whitelancer64

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #10 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 #11 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 #12 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 #13 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 #14 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 #15 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 #16 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 #17 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 #18 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.
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#### daveklingler

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #19 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 #20 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.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #21 on: 08/20/2017 04:42 AM »
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.

The BA330 was designed for 0G environments, so if you want to use it for spin-gravity applications you'd have to do a lot of redesign - in which case it's no longer a BA330.
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#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #22 on: 08/20/2017 05:40 AM »
The BA330 was designed for 0G environments, so if you want to use it for spin-gravity applications you'd have to do a lot of redesign - in which case it's no longer a BA330.

Currently, the BA330 is only designed for Earth, there is no space-rated BA330. Every one developed for space would be bespoke.

There's nothing inherent in inflatables that is incompatible with their use in spin-stations. (Quite the contrary, I suspect it will make many internal systems easier to develop.)

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #23 on: 08/20/2017 06:00 AM »
There's nothing inherent in inflatables that is incompatible with their use in spin-stations. (Quite the contrary, I suspect it will make many internal systems easier to develop.)

That I would agree with. Now we just need a rotating space station design that needs them.
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#### blasphemer

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #24 on: 08/20/2017 06:48 AM »
Transit volume may also be important, not only transit time. If all you want to send are small number of dedicated astronauts, then let them deal with zero G. But if you want to send thousands of people and do it in relative comfort, as Musk intends to do, then spin gravity may be a logical thing to do.

Especially because I do not believe it is hard to do at all. Connect two ITS spaceships by a several hundred meters long cable(s), spin them up, and you have 1G gravity. Very little mass penalty needed, and no complex technology required. Hardest thing to do will probably be dealing with some resonances along the cable to keep the structure stable, but that seems entirely doable to me.
« Last Edit: 08/20/2017 06:51 AM by blasphemer »

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #25 on: 08/20/2017 10:32 AM »
There's nothing inherent in inflatables that is incompatible with their use in spin-stations. (Quite the contrary, I suspect it will make many internal systems easier to develop.)
That I would agree with. Now we just need a rotating space station design that needs them.

Actually inflatables make more sense for AG stations than micro-g ones. People are more volume efficient in micro-g, being able to use every surface, being able to use three-dimensional space, being able to drift over and around things, being able to easily reorientate to reach every surface, it makes smaller spaces seem larger. The moment you move to an artificial gravity station, you're back to standing up and walking around, that means you need more empty floor space (we don't put equipment, cupboards, etc, into the floor), more empty height, and fairly useless ceilings. Even basics like beds and chairs/tables become insanely space occupying (in micro-g you don't "sit", in spite of way, way too many artist's impressions of space station designs that include seats and tables.)

The party trick for inflatables is that they deliver maximum volume for minimum mass. Which is exactly what you want for a spin-station.

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #26 on: 08/20/2017 10:40 AM »
Hardest thing to do will probably be dealing with some resonances along the cable to keep the structure stable, but that seems entirely doable to me.

Actually, twisting will be an issue. (In previous AG threads, we discussed a hybrid tensegrity structure using tensioned cables inside an inflatable tube. The combination turns out to be vastly more structurally stable than either alone.)

As will deploying and retracting the cable cleanly. It's been a surprising amount of trouble in experiments so far. Spools are just trouble prone.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #27 on: 08/20/2017 03:40 PM »
Transit volume may also be important, not only transit time. If all you want to send are small number of dedicated astronauts, then let them deal with zero G. But if you want to send thousands of people and do it in relative comfort, as Musk intends to do, then spin gravity may be a logical thing to do.

I'm not sure scaling up to thousands of people changes the need for having gravity, since we're still talking about segment of the population that will be highly motivated for going to Mars - they will put up with 0G.

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Especially because I do not believe it is hard to do at all. Connect two ITS spaceships by a several hundred meters long cable(s), spin them up, and you have 1G gravity. Very little mass penalty needed, and no complex technology required. Hardest thing to do will probably be dealing with some resonances along the cable to keep the structure stable, but that seems entirely doable to me.

The ITS won't be designed for that. They are designed to be pushed up from the bottom, not suspended from the top. Completely different forces to deal with - going from compression to tension.
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 #28 on: 08/21/2017 05:20 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?

Good catch.  Yes, that gif is only about 1/3 of my full design, but I like putting it up to point out that being able to achieve a large(r) radius without tethers is possible without increasing mass significantly.

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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.

I'm attaching my modifications to Theodore Hall's excellent "comfort zone" chart.  Whatever the solution(s) is(/are), it's important to be able to test acceleration rate and angular velocity independently to get real-life data on the various boundaries of this chart.

Paul451, myself and others have debated on a number of occasions whether 4rpm is a useful limit to set, (it probably depends on the person as to how quickly they can adapt)  but given that I think we can at least test 4rpm/Mars G using current/near future launch architectures, I'm inclined to only go above 4rpm if it we want to run higher gravity tests.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #29 on: 08/21/2017 06:43 AM »
Good catch.  Yes, that gif is only about 1/3 of my full design, but I like putting it up to point out that being able to achieve a large(r) radius without tethers is possible without increasing mass significantly.

You are taking into account that the whole ring is trying to fly apart, right? Each hinge has to be strong enough to hold the entire mass together, just like with a chain.

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I'm attaching my modifications to Theodore Hall's excellent "comfort zone" chart.

Excellent paper. I love all the charts. He does reference SpinCalc, which I use to check design ideas.

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Whatever the solution(s) is(/are), it's important to be able to test acceleration rate and angular velocity independently to get real-life data on the various boundaries of this chart.

Agreed. No matter what the design is we're going to need to spend some time testing out different levels of artificial gravity to find what is tolerable and what isn't.

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Paul451, myself and others have debated on a number of occasions whether 4rpm is a useful limit to set, (it probably depends on the person as to how quickly they can adapt)  but given that I think we can at least test 4rpm/Mars G using current/near future launch architectures, I'm inclined to only go above 4rpm if it we want to run higher gravity tests.

My instincts say no for normal use, but it could be that people could tolerate it if need be - maybe with less moving around. Which is why we need a testing platform, to confirm facts instead of relying on "instincts"...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #30 on: 08/21/2017 08:46 AM »
I'm inclined to only go above 4rpm if it we want to run higher gravity tests.
My instincts say no for normal use, but it could be that people could tolerate it if need be - maybe with less moving around.

More. Higher the RPM, the more you need to move around. Not moving around enough seems to be what causes the wildly variable results in ground-based RPM tolerance tests.

Which is why we need a testing platform, to confirm facts instead of relying on "instincts"...

56 bleeping years of manned spaceflight and the closest we've had to a single in-space test of AG is astronauts running around the deck of Skylab.

#### envy887

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #31 on: 08/22/2017 06:09 PM »
Especially because I do not believe it is hard to do at all. Connect two ITS spaceships by a several hundred meters long cable(s), spin them up, and you have 1G gravity. Very little mass penalty needed, and no complex technology required. Hardest thing to do will probably be dealing with some resonances along the cable to keep the structure stable, but that seems entirely doable to me.

The ITS won't be designed for that. They are designed to be pushed up from the bottom, not suspended from the top. Completely different forces to deal with - going from compression to tension.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #32 on: 08/22/2017 07:38 PM »
Especially because I do not believe it is hard to do at all. Connect two ITS spaceships by a several hundred meters long cable(s), spin them up, and you have 1G gravity. Very little mass penalty needed, and no complex technology required. Hardest thing to do will probably be dealing with some resonances along the cable to keep the structure stable, but that seems entirely doable to me.

The ITS won't be designed for that. They are designed to be pushed up from the bottom, not suspended from the top. Completely different forces to deal with - going from compression to tension.

Apparently not...

Something else to consider with the ITS though is that the human habitable levels are at the top, so the major effects of centripetal force in such an arrangement will be on the parts of the ITS that don't need to be tested. In order to feel simulated 1G of force for the occupied areas, the 2/3rd's of the ITS not occupied will likely have to be feeling above 1G forces, and the ITS may not be designed to handle that.
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 #33 on: 08/23/2017 01:54 AM »
Something else to consider with the ITS though is that the human habitable levels are at the top, so the major effects of centripetal force in such an arrangement will be on the parts of the ITS that don't need to be tested. In order to feel simulated 1G of force for the occupied areas, the 2/3rd's of the ITS not occupied will likely have to be feeling above 1G forces, and the ITS may not be designed to handle that.

Given an ITS ship of 49.5m, if they were to attach two ITS ships nose to nose and spin during cruise phase, they could give the base of the crewed section (r~<20m) Mars gravity for only ~4.1rpm, and even then the uncrewed areas of the ITS ships would only achieve 93% of 1G at the most.

Assuming roughly even distribution of mass, I think that's achievable for only an extra 21.3m/s of dV across the two ITS ships (each spin up or spin down).

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #34 on: 08/23/2017 02:08 AM »
Given an ITS ship of 49.5m, if they were to attach two ITS ships nose to nose and spin during cruise phase, they could give the base of the crewed section (r~<20m) Mars gravity for only ~4.1rpm, and even then the uncrewed areas of the ITS ships would only achieve 93% of 1G at the most.

Heh, wrote the same thing, went to post and your comment was first.

The only other thing I was going to note: if people can tolerate higher RPMs, it doesn't require two ships, a single ITS/BFS alone can produce Mars gravity, either end-over-end (tumbling pigeon) at less than 5RPM, or rotation around its long axis (cylindrical rotation) at 8RPM. (Both assuming the larger, earlier ITS/BFS.) Either would require a major redesign of the passenger section, but the point is that it is possible even for a single ship.

Also, I was going to point out:

above 1G forces, and the ITS may not be designed to handle that.

The frame, tanks and engines are likely to be able to handle >1g, what with that whole "launching from Earth" thing.

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #35 on: 08/23/2017 03:00 AM »
above 1G forces, and the ITS may not be designed to handle that.

The frame, tanks and engines are likely to be able to handle >1g, what with that whole "launching from Earth" thing.

Launching applies compression forces, not tension. Suspending the ITS from a crane, or attaching two together and spin them, applies tension forces. Literally the bottom of the ITS is trying to separate from the top of the ITS.

And of course when the ITS is on Earth and is being lifted back onto the launch pad it won't be fueled or loaded with cargo & people (i.e. "empty weight"), so any fuel, cargo or crew you add in space would reduce the amount of artificial gravity you could apply.

However I have no doubt that a strong enough cable could be used (I'm a big fan of Dyneema), and I don't think there would be any vibration issues. That said, I think there are better ways to do the testing than spinning up two ITS...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

#### IRobot

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #36 on: 08/23/2017 07:39 AM »
Is there any medical research on some drug to "disable" the vestibular system in a way that the brain ignores inbalance information?
This is useless on earth because people would just drop to the ground without the balance information, but in zero-g it could work. People would lose ability to "feel" attitude but perhaps visual cues would be enough.
« Last Edit: 08/23/2017 07:41 AM by IRobot »

#### RotoSequence

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #37 on: 08/23/2017 08:30 AM »
above 1G forces, and the ITS may not be designed to handle that.

The frame, tanks and engines are likely to be able to handle >1g, what with that whole "launching from Earth" thing.

Launching applies compression forces, not tension. Suspending the ITS from a crane, or attaching two together and spin them, applies tension forces. Literally the bottom of the ITS is trying to separate from the top of the ITS.

And of course when the ITS is on Earth and is being lifted back onto the launch pad it won't be fueled or loaded with cargo & people (i.e. "empty weight"), so any fuel, cargo or crew you add in space would reduce the amount of artificial gravity you could apply.

However I have no doubt that a strong enough cable could be used (I'm a big fan of Dyneema), and I don't think there would be any vibration issues. That said, I think there are better ways to do the testing than spinning up two ITS...

There's plenty of space in the middle of the stowed rotating habitat in which to place a booster stage and a support mechanism that supports the ring module with tension, but that would be a cumbersome piece of equipment!

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #38 on: 08/23/2017 09:12 AM »

56 bleeping years of manned spaceflight and the closest we've had to a single in-space test of AG is astronauts running around the deck of Skylab.

Of which more than a decade worth of scientists lining up to get their experiments on board of the ISS, most of them getting rejected due to limited astronaut time, ISS failities, budget, etc. AG facilities have even been cancelled, a clear case of being deemed not important enough to do what is required to provide AG, relative to other useful research that can be done at less expense.

Returning to my previous point: scale. Unless AG is being used to give higher comfort levels to people who would otherwise be unable to do their jobs, or would otherwise be less motivated to go, it offers no benefit but only increases complexity. Even if you provide better ways to assemble such stations, they will always be more complex than stations of similar useful volume without AG. So for people who are planning to build a company around these ideas, the first question investors are likely to ask is what advantage AG offers that would be worth their investment.

Six months transfer time is unlikely to provide enough benefit for early astronauts going to Mars to make any difference. Six month stints on orbital production facilities, as we see on offshore drilling platforms, require no AG unless it is beneficial for the production process itself, or if people are indeed living up there. Tourism for a couple of days or weeks might benefit, if people like to spend time in gravity rather than on the float. Sleeping and personal hygiene is problably going to be more comfortable when waste falls down as people are used to.

Love the design btw. Do you make the hinges strong enough to support the spinning vehicle, or do you add nuts and bolts after deployment?

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #39 on: 08/23/2017 09:51 AM »
Is there any medical research on some drug to "disable" the vestibular system in a way that the brain ignores inbalance information?
This is useless on earth because people would just drop to the ground without the balance information, but in zero-g it could work.

Zero-g adaptation disables the vestibular system anyway. Once you've adapted, you just don't get dizzy any more.

For eg, Fun starts after 1m15s.

Launching applies compression forces, not tension.

When starting/stopping a burn, the ship also undergoes jerk-force (delta_acceleration), which the ship must be strong enough to tolerate. During acceleration, different parts are pulling apart depending on their respective masses (since F=MA, compression isn't uniform). And the whole thing is vibrating like its in a hurricane.

The only part that might be an issue is if the tanks are part of the structural mechanism, as in a booster. However, even they have to go from tensile forces of internal pressure to compression during launch, and jerk-force at MEI, then MECO, then staging, then SEI, then SECO; so I suspect they'll be over-engineered for the much gentler stress of AG.

#### mikelepage

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #40 on: 08/23/2017 10:58 AM »
Is there any medical research on some drug to "disable" the vestibular system in a way that the brain ignores inbalance information?
This is useless on earth because people would just drop to the ground without the balance information, but in zero-g it could work. People would lose ability to "feel" attitude but perhaps visual cues would be enough.

I know they're working on such a drug for Meniere's disease (a horrible disorientation sickness), but as far as I know they've only managed to treat the symptoms.  The sense of balance is very primal.

You are taking into account that the whole ring is trying to fly apart, right? Each hinge has to be strong enough to hold the entire mass together, just like with a chain.

Love the design btw. Do you make the hinges strong enough to support the spinning vehicle, or do you add nuts and bolts after deployment?

Cheers.  You may have noticed the small nodules on the center-top/inside of each segment/wedge? The vision is that these will have retractable tethers that take the load, whilst the hinges articulate the movement only.  Depending on how many segments there are (12 in this case), some of these will be replaced by hatches with inflatable tubes to the axial modules.   Having said that, there's nothing to stop the hinges from being quite robust also so they can take some of the load if necessary.

In principle, once such a system is set up, I see no reason to bolt it.  Why shouldn't such an array deploy and retract multiple times per mission (possibly maintaining angular momentum with a flywheel)?  Retract and lock when it comes time for trans-mars/lunar/NEO injection burns, but deploy and spin for cruise phases.  Docking hatches at the ends of each wedge segment will dock to each other when deployed, but can dock to axial modules when retracted.

I've attached a video with a 3D print I created of this exact design (and can make it available through my shapeways shop if anyone's interested - pm me).

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #41 on: 08/23/2017 03:05 PM »
...so I suspect they'll be [i.e. ITS] over-engineered for the much gentler stress of AG.

Well then, all you need to do is to convince Elon Musk to spare two of them for this experiment...
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 #42 on: 08/24/2017 01:04 AM »
...so I suspect they'll be [i.e. ITS] over-engineered for the much gentler stress of AG.

Well then, all you need to do is to convince Elon Musk to spare two of them for this experiment...

Somewhat anti-intuitively, if you could attach two ITS "tail-to-tail" (main engines facing each other), and adjust the internal crew-space to match, you would have a much larger radius to work with for a tumbling pigeon style arrangement.

#### Paul451

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #43 on: 08/24/2017 08:48 AM »
Minor aside:

if you could attach two ITS "tail-to-tail" (main engines facing each other), [...] you would have a much larger radius to work with for a tumbling pigeon style arrangement.

I may be using the terms wrong, but I generally say "Tumbling Pigeon" for a single-ship rotating end-over-end, borrowing from Heinlein's juvie stories. Likewise a habitat still attached to its upper-stage. Hab at one end, propulsion at the other.

But if you attach things together in a line, still spinning end-over-end, I usually say "baton" (or baton-style). Dual ITS would therefore always be a baton.

I can't recall a useful term for something spinning around its long axis, I've been saying "cylindrically". ("Roll" doesn't seem sufficient.)

Wheels (especially "spoked wheel") and rings should be obvious. Not sure if "hub'n'spokes" is too confusing for a configuration where there's no wheel, or if there's another term?

[edit: Forgot, two modules/ships separated by a cable is a bolas (sometimes bolo because I'm stupid), and I use the same term for a truss- or tube-separated structure, if there's no intervening habitat modules.]
« Last Edit: 12/24/2017 04:54 AM by Paul451 »

#### mikelepage

##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #44 on: 08/25/2017 10:03 AM »
Minor aside:

if you could attach two ITS "tail-to-tail" (main engines facing each other), [...] you would have a much larger radius to work with for a tumbling pigeon style arrangement.

I may be using the terms wrong, but I generally say "Tumbling Pigeon" for a single-ship rotating end-over-end, borrowing from Heinlein's juvie stories. Likewise a habitat still attached to its upper-stage. Hab at one end, propulsion at the other.

But if you attach things together in a line, still spinning end-over-end, I usually say "baton" (or baton-style). Dual ITS would therefore always be a baton.

I can't recall a useful term for something spinning around its long axis, I've been saying "cylindrically". ("Roll" doesn't seem sufficient.)

Wheels (especially "spoked wheel") and rings should be obvious. Not sure if "hub'n'spokes" is too confusing for a configuration where there's no wheel, or if there's another term?

Yes, the nomenclature is a bit fuzzy.  Can't say I'd ever really thought about it, but I do tend to use "tumbling pigeon" to refer to a single pressure vessel (counter-balanced or not) spinning end over end. "Baton" I think you're right, refers more generally to any arrangement where the longest dimension of the craft is designed that way for the purpose of achieving a large spin radius (which still spins end over end).

I think of the "cylindrical" habitats (spinning around long axis) as just a special case of "torus" habitats, where the donut has no hole.  The only cases where I've seen them proposed is where there is a name of the specific design. For example there is the Kalpana One design by Al Globus et al, which is an evolution of the O'neill cylinders.

I don't particularly like them because they tend to use single large volume pressure vessels, which must be built in their entirety before they can even start being useful.  Making them small enough to be feasible requires the occupants to tolerate higher spin rates for a given launch mass/acceleration level.

I would add that there is another spinning geometry I developed for the 2016 NASA space apps challenge - the "spiral space station" twin spiral framework geometry - which I like as a model for space habitats around asteroids, because it can feasibly keep growing/renewing itself as long as resources are available.

#### blasphemer

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #45 on: 08/25/2017 10:11 AM »

Zero-g adaptation disables the vestibular system anyway. Once you've adapted, you just don't get dizzy any more.

Offtopic, but I wonder if this would make zero-g adapted people immune to other sources of dizzyness, such as simulator sickness? It is a big problem in virtual reality, and the reason why many VR apps/games heavily restrict player movement or use teleportation instead of natural, continuous movement.
« Last Edit: 08/25/2017 10:11 AM by blasphemer »

#### blasphemer

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #46 on: 08/25/2017 10:22 AM »
I made a quick mock up picture of two 9m diameter ITS spaceships (ship length 37m) connected by an almost 200m long cable. This should enable near 1g gravity at a comfortable 2 RPM rotation rate.

« Last Edit: 08/25/2017 12:39 PM by blasphemer »

#### Lampyridae

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #47 on: 08/25/2017 11:17 AM »
If you're going to have any kind of volume of commercial passenger spaceflight, people will want artificial gravity.

How much? Enough to ensure that poo breaks off and goes into the toilet, bone demineralisation and other serious issues be damned. You only need a small centrifuge to handle that, and a galley/sit-down area for eating and exercise, maybe cabins - sex in zero-g seems about as practical as trying to swim through air. That could be Discovery centrifuge size even though it goes outside Theodore Halls' comfort zone - it's only an AG area.
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#### IRobot

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #48 on: 08/25/2017 12:08 PM »

Zero-g adaptation disables the vestibular system anyway. Once you've adapted, you just don't get dizzy any more.

Offtopic, but I wonder if this would make zero-g adapted people immune to other sources of dizzyness, such as simulator sickness? It is a big problem in virtual reality, and the reason why many VR apps/games heavily restrict player movement or use teleportation instead of natural, continuous movement.
Put them on a sailboat for a week in the Atlantic. Either it cures motion sickness or you die from dehidration

#### IRobot

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #49 on: 08/25/2017 12:14 PM »
I made a quick mock up picture of two 9m diameter ITS spaceships (ship length 37m) connected by an almost 200m long cable. This should enable near 1G gravity at a comfortable 2 RPM rotation rate.

How do you cancel the whobbling due to people moving around the ships?

#### Coastal Ron

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##### Re: Spin gravity to 2100: over what transit time will SG become routine?
« Reply #50 on: 08/25/2017 05:06 PM »
I don't particularly like them because they tend to use single large volume pressure vessels, which must be built in their entirety before they can even start being useful.  Making them small enough to be feasible requires the occupants to tolerate higher spin rates for a given launch mass/acceleration level.

I would disagree. Certainly the 1st generation of rotating space stations will likely be segmented, mainly because no one would feel confident in the design of such a large structure as a single volume as a first step. Assuming we're building mini-worlds in our first attempt leads to false assumptions.

Quote
I would add that there is another spinning geometry I developed for the 2016 NASA space apps challenge - the "spiral space station" twin spiral framework geometry - which I like as a model for space habitats around asteroids, because it can feasibly keep growing/renewing itself as long as resources are available.

Interesting framework system, but did you simulate what the stresses would be when fully built out? Sure seems like this type of design relies on the principle of the "weakest link", where if one link fails the whole thing could unzip. Also I'm not sure how this improves on the issue you listed above of having a single volume, since this spiral design is essentially one long tube with no cross connections.

Nevertheless it is a clever design that could end up providing some hints to how low-weight stations could be built.
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 #51 on: 08/26/2017 05:28 AM »
I don't particularly like them because they tend to use single large volume pressure vessels, which must be built in their entirety before they can even start being useful.  Making them small enough to be feasible requires the occupants to tolerate higher spin rates for a given launch mass/acceleration level.

I would disagree. Certainly the 1st generation of rotating space stations will likely be segmented, mainly because no one would feel confident in the design of such a large structure as a single volume as a first step. Assuming we're building mini-worlds in our first attempt leads to false assumptions.
Not quite sure what you're disagreeing with, but I should have clarified that I meant I don't like them for their feasibility in the near future (i.e. before 2100) not because I don't think they can work.

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Quote
I would add that there is another spinning geometry I developed for the 2016 NASA space apps challenge - the "spiral space station" twin spiral framework geometry - which I like as a model for space habitats around asteroids, because it can feasibly keep growing/renewing itself as long as resources are available.

Interesting framework system, but did you simulate what the stresses would be when fully built out? Sure seems like this type of design relies on the principle of the "weakest link", where if one link fails the whole thing could unzip. Also I'm not sure how this improves on the issue you listed above of having a single volume, since this spiral design is essentially one long tube with no cross connections.

Nevertheless it is a clever design that could end up providing some hints to how low-weight stations could be built.

No, we didn't do/haven't done any stress simulations (it was a 48 hour hackathon), but I would be interested to do them, because that would probably guide how many layers deep the structure needs to be, and how soon the inner (older) sections of the spiral could be removed and recycled.  I can't intuitively visualise where the "weakest link" would be, because it seems to me all tensile stresses are spread evenly and you'd have to have multiple layers break above and below the same point in order for the whole structure to fail.  It was referencing a nautilus shell, which contains a single spiral of pressure chambers, each bigger than the last, so I'd imagine that biomimicry would be further referenced in a more complete design.

You might have noticed we were hedging on whether it would be a dual archimedes spiral (where the radial cross section of each frame element remains constant, even as the length of each arc-segment increases), or whether it would be a dual log spiral (where every single frame element is scaled up by some % fraction on the last one).  That would probably depend on whether the frame elements were being prefabbed, or 3D printed/fabricated in place.

Thanks for the complements.  The thing I really like about it is that it is just a framework, so it need not be "one long tube" but could instead be a support structure for a series of inflatable pressure vessels, as big or small as needed, just as in a nautilus shell.  The nautilus shell is a log spiral btw, so if a spiral space station continued to be built out ad infinitum, you could eventually see huge internal spaces existing as part of that.  Even then, there would be safety in being able to move to adjacent pressure chambers both radially, and tangentially.  If the worst did happen and a pressure vessel was lost, the whole structure wouldn't unzip, but you'd just have to replace the "dead" chamber.

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