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 5860 times)

Offline Paul451

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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.

Offline Coastal Ron

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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.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Paul451

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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.)

Offline Coastal Ron

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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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Offline blasphemer

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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 »

Offline Paul451

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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.

Offline Paul451

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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.

Offline Coastal Ron

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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?

Offline mikelepage



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.

Offline Coastal Ron

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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?

Offline Paul451

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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.

Offline envy887

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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.

You sure about that?


Offline Coastal Ron

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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.

You sure about that?

Apparently not...  :o

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?

Offline mikelepage

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).


Offline Paul451

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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.

Offline Coastal Ron

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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...
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Offline IRobot

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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 »

Offline RotoSequence

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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!  :D

Offline high road

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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?

Offline Paul451

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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.

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