Rotating Spaceships

[spacester]

The simple dumbbell does not even make it to back of napkin design stage. Especially if you use a tether, you cannot control the dynamics. Pretty much a nightmare in that category.

I see this asserted pretty often, but without analysis to back it up. For example, see the attached papers on modelling the tether dynamics of the OEDIPUS-A experiment (where unexpected nutation was observed), and the subsequent OEDIPUS-C experiment that validated the model and confirmed stable spinning tether dynamics, using only design parameters to allow passive stability without active control.

Well of course I am sure we would all be delighted if someone flew an experiment and proved me wrong. The tether experiments I know about were all rather miserable failures. These were all some years ago and I am not aware of anything in the last 8 years or so. There appears to be quite a gap between the theory and the dynamics of flown hardware. These papers are welcome and I will be studying them to see what I can learn, but tethers are not for me. No doubt there is much I am ignorant of on the subject. I like rigidity.

The design I worked up is the result of making certain design choices. If the most fundamental choices are different, that would constitute different classes of spaceships. Certainly you can see that Aquarius is about as far afield from a tethered dumbbell design as you can get.

Alternate design approaches are something I would like to encourage, but I do not intend to explore all possibilities myself. If someone wants to help me start classifying all the different types of rotating spaceship concepts, I would be happy to be a part of that effort.

[TrevorMonty]

We need to define what the artificial gravity is trying to achieve before designing spacestation.
Here few ideas.
1) long term living ie years with children. Need 1g at low RPM.
2)keep astronaut health on extended trips of months may years. Probably 1/6g at higher RPMs.
3) make daily activities like, eating, drinking going to bathroom more pleasant where gravity helps keep everything in its place. This could be for short stays where we aren't using it reduce bone and muscle loss. Need 1/10 or less at moderate RPM.

Sent from my SM-T810 using Tapatalk

[spacester]

Also, I admit I like the slick math at 3 rpm - radius in m/100 equals gee force. Smaller radius designs are perfectly valid, but this design is firm on that choice.

And that's what I suspected. You latched onto a size, you made the RPM match, then you retrospectively justified that RPM.

It's what everyone does. Want giant station, "we must limit it to 1 RPM, see O'Neill". Feels too unrealistic? "2 RPM can be tolerated without adaptation, that's the obvious limit." Don't want a tether, "3 RPM can be tolerated by most people. Or was it 4? But definitely no more than that."

I don't object to you wanting to pick an arbitrary size, just don't pretend it's "necessary", that it's based on science.

And, IMO, if you stop pretending that the spin rate (and hence the size) is "necessary", you can also look at how to build up towards your final preferred size. Can you start smaller, but using the same modular components in lower quantities, and deliver a useful design earlier in the construction process? Can it be upgraded over time without significant disruption and dismantling? Even if it has to stop spinning to deploy new sections, can other maintenance and assembly work be done (safely) while spinning?

Wow you are a mind reader! Not.

It is not arbitrary whatsoever! It is based on science, what else? I want 1.0 gee on the outer ring (duh, what else, see the main objective), and 3 RPM is right in the center of the sweet spot. Find me any references that begin to say that it is a poor choice. I have done the research, I did it 15 years ago, have been posting about spin gravity ever since, on occasion.  Have you done the research? It doesn't sound like it. And so you seem to assume I have not either. Wrong. Rude.

I gave my reasons, address them. The central design concept is an ultra comfortable on-orbit refuge, I am not gonna spin it too fast for my market. If you want to have an informed and detailed discussion on why 3 RPM is not in the middle of the sweet spot, bring it on. It just is, and the math is slick, why fight it? Give the designer a starting point, do not spend a year identifying all the possibilities.

It is called a design decision. If you want to start a design with a different choice, be my guest. You gotta start somewhere and this is mine. I am gonna stick with it. What does your 50 m radius ship look like? I betcha I will like it. Show me, then we can talk tradeoffs. Show me exactly how you build a station of expanding size. I have a detailed plan for putting this together, and am looking forward to your alternative.

[spacester]

We need to define what the artificial gravity is trying to achieve before designing spacestation.
Here few ideas.
1) long term living ie years with children. Need 1g at low RPM.
2)keep astronaut health on extended trips of months may years. Probably 1/6g at higher RPMs.
3) make daily activities like, eating, drinking going to bathroom more pleasant where gravity helps keep everything in its place. This could be for short stays where we aren't using it reduce bone and muscle loss. Need 1/10 or less at moderate RPM.

Sent from my SM-T810 using Tapatalk

Agreed. But of course there are many answers. The question in the real world is of you can close a business case. Now, since prior to Starship there was essentially zero prospect of being able to orbit enough mass, let alone make the rest of the business case work, the projection of something possible must, for the time being, be based on Starship cargo delivery.

So I have a 100 m radius and the Starship user's guide. I roughed out an expanding three segment habitat payload that looks like a Newtonian telescope, and string 16 of them around the circumference connected by nodes.

This ship is way too audacious for NASA, being "too soon" for them. That's fine.

The idea here is simple: provide a fantastic safe haven for space travelers. Flip the whole minimum mass and deprivation model on its head. Luxury accommodations. People will be able to travel up and down the tubes and hang out at different levels, all at 3 RPM. Personal hygiene normalized and then you go up to the hub and play in zero gee and be sitting down again for lunch. Then a nice long hot shower.

Children will be welcome, but pregnancies might have to be banned at first. We need to make baby mice and rabbits first.

Why? Starship, that's why. Because we can finally work at scale, do big things, conquer space not just survive.

[spacester]

You know the spin-rate came from your design, not the other way around.

No the spin rate came from reading, comprehending and agreeing with the abstract you linked to, which in fact was a conclusion I was already in possession of, having read everything by Ted Hall many times  more than a decade prior and because the total body of information available is limited. That abstract is a simple review of the sparse research.

Remember the experiments they did over the last decade? No, because there are none. ISS goes roundy roundy and spin gravity has been out of order and I am wasting my time here, aren't I?

You read that abstract, and you get 3 RPM. It is as simple as that. Not 4, because too much motion sickness. Not 2 because at 3 RPM my visitors - who were in microgravity before arrival - will be just fine. 3 RPM is fast enough. 5 is right out. 2.8 or 3.2 or 3.1415926535? Well, maybe, but 3.0 is the design parameter, OK?

The first thing I did was design the expanding ring habs delivered by Starship, and stretch them around a 200 m  circle, and by golly 16 of them fit real nice with their nodes. Why fight it?

How is your design coming along?

[Twark_Main]

The first geometry that pops out is a dumbbell, two cylinders separated from each other by a relatively low mass connector.  So two spent rocket stages connected by a tether.

The simple dumbbell does not even make it to back of napkin design stage. Especially if you use a tether, you cannot control the dynamics. Pretty much a nightmare in that category.

So you go to a rigid truss, that improves the spin control. But where are you mounting the thrusters to force that control? And what about a central hub, good idea or bad idea?

So the dumbbell is replaced by...

So nightmare dynamics seems to be out.

I don't see how "thrusters" and "central hub yes/no" are problems for a dumbbell configuration. Can you elaborate?

Dumbbell configuration seems to be the AG implementation with "nothing left to take away."

[spacester]

The first geometry that pops out is a dumbbell, two cylinders separated from each other by a relatively low mass connector.  So two spent rocket stages connected by a tether.

The simple dumbbell does not even make it to back of napkin design stage. Especially if you use a tether, you cannot control the dynamics. Pretty much a nightmare in that category.

So you go to a rigid truss, that improves the spin control. But where are you mounting the thrusters to force that control? And what about a central hub, good idea or bad idea?

So the dumbbell is replaced by...

So "nightmare" dynamics seems to be out.

I don't see how "thrusters" and "central hub" are problems for a dumbbell configuration. Can you elaborate?

Basically all I am saying - besides trying to do a crash course on the concept of mass distribution for the OP - is that as a designer I see problems I cannot solve. They also are problems I have not seen anyone else solve. Maybe there are solutions, but I am going to move on and work on stuff I understand. If someone here knows how to guarantee that a dumbbell design's dynamics challenges can be met, I am all ears.

Meanwhile I am working on my thing. I am not going to work on all possibilities at once, OK?

So I have two cylinders and a tether. I need thrusters somewhere, yes? No? How no? So where exactly do I put these thrusters? What orientation are my cylinders at? How does that get the job done? How do I make the whole thing rotate and not lose control over the parts?

If the tether goes slack, how exactly do we react? How we make sure we do not overcompensate when bringing the tether back into tension and thus snap the tether? Can we live with so much active control that life will always be on the edge? Inherent stability is to be desired, yes?

Hub or no hub? I dunno, is there an obvious answer I am missing? Maybe so, this is the first time I have thought about this configuration in years. I simply am saying I have little basis to know whether the hub makes the dynamics better or worse.

If everything I am worried about is no big deal, great. (But what about nutation and precession and what not.) I am not an expert, but math is math and I have enough education and experience to see the challenges but not the solutions.

Citation? Failed flight tests with tethers, and the end of experiments with tethers, does that not count?

Replace the tether with a truss and it gets more manageable. The mass of the two will be very close to the same. I am sure some of you guys are working on that, can we get an update?

[Twark_Main]

The first geometry that pops out is a dumbbell, two cylinders separated from each other by a relatively low mass connector.  So two spent rocket stages connected by a tether.

The simple dumbbell does not even make it to back of napkin design stage. Especially if you use a tether, you cannot control the dynamics. Pretty much a nightmare in that category.

So you go to a rigid truss, that improves the spin control. But where are you mounting the thrusters to force that control? And what about a central hub, good idea or bad idea?

So the dumbbell is replaced by...

So "nightmare" dynamics seems to be out.

I don't see how "thrusters" and "central hub" are problems for a dumbbell configuration. Can you elaborate?

Basically all I am saying - besides trying to do a crash course on the concept of mass distribution for the OP - is that as a designer I see problems I cannot solve. They also are problems I have not seen anyone else solve. Maybe there are solutions, but I am going to move on and work on stuff I understand. If someone here knows how to guarantee that a dumbbell design's dynamics challenges can be met, I am all ears.

So I have two cylinders and a tether. I need thrusters somewhere, yes? No? How no? So where exactly do I put these thrusters? What orientation are my cylinders at? How does that get the job done? How do I make the whole thing rotate and not lose control over the parts?

If the tether goes slack, how exactly do we react? How we make sure we do not overcompensate when bringing the tether back into tension and thus snap the tether? Can we live with so much active control that life will always be on the edge? Inherent stability is to be desired, yes?

I think you might be confusing barbell configuration for bola-bolas configuration. Barbell is rigid (unless you know of any barbells on strings?), bola-bolas is tethered.

Even with tether designs there are obvious answers to the (subset of valid) problems you raised. I'd be happy to elaborate if you want, but I'm personally more interested in rigid designs.

Hub or no hub? I dunno, is there an obvious answer I am missing? Maybe so, this is the first time I have thought about this configuration in years. I simply am saying I have little basis to know whether the hub makes the dynamics better or worse.

Sure, but nothing about this is unique to the barbell. This same question has to be answered for any AG design.

If everything I am worried about is no big deal, great. (But what about nutation and precession and what not.)

Ditto. Every AG design has to contend with nutation and precession. Fortunately it's not terribly hard.

Citation? Failed flight tests with tethers, and the end of experiments with tethers, does that not count?

No it doesn't. No artificial gravity tether experiments have occurred, so N = 0.

Replace the tether with a truss and it gets more manageable. The mass of the two will be very close to the same. I am sure some of you guys are working on that, can we get an update?

Trusses (or even just inflation-rigidized tubes, which is basically the lightweight "balloon tank" tensegrity implementation of a truss) are indeed likely, yes. But jumping to a wheel space station because of that seems like a solution in search of a problem.

How much surface area does Aquarius have, vs a sphere with the same habitable volume? What effect does that have on the total radiation shielding mass needed? 

[spacester]

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions. Guys, if no one else has done this before maybe you should let me get the ball rolling. I make zero statements about how anything has to be done "my way", I simply have decided on "a" way. I do not know if and when that becomes acceptable to y'all. I would rather sooner than later.

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started.

It is a design decision. Every single decision is subject to revision. Certain design decisions are so fundamental that to change it is to turn this project into a similar project. I would love love love to be able to compare Aquarius to other fleshed out designs that come from other fundamental choices.

Please tell me I am now beating a dead horse on my design approach.

The Tubes are fabricated from flat-packed walls that are 9 m long and the half meter of water and PE thick. These monsters are wrangled together and assembled. They will be delivered with partial water loads, nominally the outer tanks only will be full (sealed) and the other two empty, pending completed construction followed by filling the radiation shield tanks with perhaps extra-terrestrial water. Maybe just the outer tank being full is enough for LEO but as soon as we boost it to cis-lunar space we want to fill those other two tanks up.

It is an enormous amount of water, and the design is not based on minimizing the water. It's called Aquarius because it is a water bearer. The comparison you ask for is not really relevant to my design process. (a waste of time from my point of view). There are programmatic benefits from the choice I made.

If maximizing the effect of water shielding is chosen as a primary design driver, that is a different design project. Whip out your alternative and let's compare. You will find me quite receptive to alternate ideas. Just please understand that certain changes constitute a not-Aquarius project. Which is great, just not Aquarius.

The central, founding, over-arching design imperative of Aquarius is comfort and safety. This led me to produce a design with absolutely every interior space being nearly equally well shielded with the half meter of hydrogen rich material. So all the habs and tubes and nodes and chutes and octo-walls all have that jacket.

And there are not only no windows, but no penetrations of the stainless steel skin anywhere on the habs, nodes, chutes and tubes. Two continuous skins of stainless, not even one bulkhead fitting anywhere below the central hub. All of it is "safe haven storm shelter". The flat walls of the central hub ("octowalls") will have plenty of bulkhead fittings, because you gotta have them.

No windows? Not sorry. The view would kinda suck anyway. Think about it.

edit: i just read your tag line at the end of your posts. Yeah, that.

[Roy_H]

I drew up plans for a rotating space station or it could easily be a space ship, just add appropriate thrusters to the non-rotating hub. Download complete description SpaceStation.pdf attached.

[Roy_H]

Do you mean why is the radius large? There is evidence that a small radius would make people feel nauseous because the force would be different between head and toes, and there would be weird effects to you balance sense when you turn your head.

Here is a nice youtube clip that talks about the issues and makes a guess at how small a radius we could get away with:



(but generally speaking, the bigger, the more comfortably earthlike the sensation of gravity would be.. we don't know for certain what radius humans would readily adapt to)

I couldn't listen to the whole video. The annoying loud music made it difficult to hear the words. I wish there was a way to remove music from these videos. This is a common problem as the people who add the music seem to think that it must be at least 10db louder than the voice.

[Twark_Main]

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.

Agreed, the shortage of good publications on the subject is appalling.

If you're comfortable with about twice the levels of Ramsar, Iran (260 mSv/yr), you can achieve 470 mSv/year with about 20 g/cm^2 of polyethylene or water (Table 6a, p25). For a 40 year old male on a 6+6 month Mars round-trip, that's an extra 2% risk of death from cancer. This is probably acceptable IMO, despite the inevitable media hand-wringing over the "10x the allowable dose for radiation workers" sound bite.

For a spherical station with an interior volume of say 23,423 m³ (r = 17.75 m³), that's 800 tonnes of shielding, or 1,000 tonnes for double spheres (r = 14.1 m). For a torus (R = 100 m, r = 3.4 m), it jumps to 2,800 tonnes of shielding.

This extra 1800-2000 tones of mass also requires additional structural mass to support it, more resupply propellant to push it (including precess its axis of rotation), etc. And upmass ain't free, even with Starship.

This (for me) is one of the major appeals of barbell-type AG.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions. Guys, if no one else has done this before maybe you should let me get the ball rolling. I make zero statements about how anything has to be done "my way", I simply have decided on "a" way. I do not know if and when that becomes acceptable to y'all. I would rather sooner than later.

That's fair, and I have no problem with it. But what you said was "the simple dumbbell does not even make it to back of napkin design stage," and then went on to cite a bunch of (apparently non-existent) issues.

Glad we have cleared up the miscommunication!

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

A half-meter (~40 g/cm²) doesn't do much beyond a quarter meter (~20 g/cm²) according to Table 6a linked above.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started. [snip]

You don't have to prove anything to anyone (of course), but you were the one saying other types of designs were unworkable. That was the bit I took exception to. All water under the bridge now.

The Tubes are fabricated from flat-packed walls that are 9 m long and the half meter of water and PE thick. These monsters are wrangled together and assembled. They will be delivered with partial water loads, nominally the outer tanks only will be full (sealed) and the other two empty, pending completed construction followed by filling the radiation shield tanks with perhaps extra-terrestrial water. Maybe just the outer tank being full is enough for LEO but as soon as we boost it to cis-lunar space we want to fill those other two tanks up.

Water tanks are nice (vs PE) because they can be filled up and emptied without much human intervention. Water tanks are bad because they can leak water all over your ship without much human intervention.

Water is slightly less mass efficient than PE, but only slightly.

It is an enormous amount of water, and the design is not based on minimizing the water. It's called Aquarius because it is a water bearer. The comparison you ask for is not really relevant to my design process. (a waste of time from my point of view). There are programmatic benefits from the choice I made.

If maximizing the effect of water shielding is chosen as a primary design driver, that is a different design project. Whip out your alternative and let's compare. You will find me quite receptive to alternate ideas. Just please understand that certain changes constitute a not-Aquarius project. Which is great, just not Aquarius.

Point of clarification: is Aquarius supposed to be a space station, or a water delivery tanker ("water bearer" + no intent to minimize water mass)?

The central, founding, over-arching design imperative of Aquarius is comfort and safety. This led me to produce a design with absolutely every interior space being nearly equally well shielded with the half meter of hydrogen rich material. So all the habs and tubes and nodes and chutes and octo-walls all have that jacket.

And there are not only no windows, but no penetrations of the stainless steel skin anywhere on the habs, nodes, chutes and tubes. Two continuous skins of stainless, not even one bulkhead fitting anywhere below the central hub. All of it is "safe haven storm shelter". The flat walls of the central hub ("octowalls") will have plenty of bulkhead fittings, because you gotta have them.

No windows? Not sorry. The view would kinda suck anyway. Think about it.

Comfort's an "over-arching design imperative" and nice transparent water for shielding. So why no windows?

Moving shadows right? That's one of the big reasons I favor aligning/precessing the spin axis toward the Sun. If desired, you could even have lightweight film mirrors to reflect sunlight in the windows from a higher elevation angle.

edit: i just read your tag line at the end of your posts. Yeah, that.

Not a flashy design quote, but a good one. Guess who? No Google that's cheating.

Hint: the root word "design" (but not in that grammatical form) appears his most famous work (one that he didn't actually write)... 

[Roy_H]

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.
...
Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

This looks very promising. I thought it would require much more thickness, but also I was thinking of a simple single material PE. I was under the impression that it was better at blocking radiation than water. What made you think of the multi-layer approach? Also I read that the aluminum on the ISS actually made the radiation problem slightly worse because of secondary radiation from aluminum molecules being hit. Does this not apply to stainless steel? What is the purpose of the stainless steel?

[spacester]

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.

Agreed, the shortage of good publications on the subject is appalling.

If you're comfortable with about twice the levels of Ramsar, Iran (260 mSv/yr), you can achieve 470 mSv/year with about 20 g/cm^2 of polyethylene or water (Table 6a, p25). For a 40 year old male on a 6+6 month Mars round-trip, that's an extra 2% risk of death from cancer. This is probably acceptable IMO, despite the inevitable media hand-wringing over the "10x the allowable dose for radiation workers" sound bite.

For a spherical station with an interior volume of say 23,423 m³ (r = 17.75 m³), that's 800 tonnes of shielding, or 1,000 tonnes for double spheres (r = 14.1 m). For a torus (R = 100 m, r = 3.4 m), it jumps to 2,800 tonnes of shielding.

This extra 1800-2000 tones of mass also requires additional structural mass to support it, more resupply propellant to push it (including precess its axis of rotation), etc. And upmass ain't free, even with Starship.

This (for me) is one of the major appeals of barbell-type AG.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions. Guys, if no one else has done this before maybe you should let me get the ball rolling. I make zero statements about how anything has to be done "my way", I simply have decided on "a" way. I do not know if and when that becomes acceptable to y'all. I would rather sooner than later.

That's fair, and I have no problem with it. But what you said was "the simple dumbbell does not even make it to back of napkin design stage," and then went on to cite a bunch of (apparently non-existent) issues.

Glad we have cleared up the miscommunication!

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

A half-meter (~40 g/cm²) doesn't do much beyond a quarter meter (~20 g/cm²) according to Table 6a linked above.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started. [snip]

You don't have to prove anything to anyone (of course), but you were the one saying that other types of designs were unworkable. That was the bit I took exception to.

All water under the bridge now.

The Tubes are fabricated from flat-packed walls that are 9 m long and the half meter of water and PE thick. These monsters are wrangled together and assembled. They will be delivered with partial water loads, nominally the outer tanks only will be full (sealed) and the other two empty, pending completed construction followed by filling the radiation shield tanks with perhaps extra-terrestrial water. Maybe just the outer tank being full is enough for LEO but as soon as we boost it to cis-lunar space we want to fill those other two tanks up.

Water tanks are nice (vs PE) because they can be filled up and emptied without much human intervention. Water tanks are bad because they can leak water all over your ship without much human intervention.

Water is slightly less mass efficient than PE, but only slightly.

It is an enormous amount of water, and the design is not based on minimizing the water. It's called Aquarius because it is a water bearer. The comparison you ask for is not really relevant to my design process. (a waste of time from my point of view). There are programmatic benefits from the choice I made.

If maximizing the effect of water shielding is chosen as a primary design driver, that is a different design project. Whip out your alternative and let's compare. You will find me quite receptive to alternate ideas. Just please understand that certain changes constitute a not-Aquarius project. Which is great, just not Aquarius.

Point of clarification: is Aquarius supposed to be a space station, or a water delivery tanker ("water bearer" + no intent to minimize water mass)?

The central, founding, over-arching design imperative of Aquarius is comfort and safety. This led me to produce a design with absolutely every interior space being nearly equally well shielded with the half meter of hydrogen rich material. So all the habs and tubes and nodes and chutes and octo-walls all have that jacket.

And there are not only no windows, but no penetrations of the stainless steel skin anywhere on the habs, nodes, chutes and tubes. Two continuous skins of stainless, not even one bulkhead fitting anywhere below the central hub. All of it is "safe haven storm shelter". The flat walls of the central hub ("octowalls") will have plenty of bulkhead fittings, because you gotta have them.

No windows? Not sorry. The view would kinda suck anyway. Think about it.

Comfort's an "over-arching design imperative" and nice transparent water for shielding. Why no windows?

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.

Agreed, the shortage of good publications on the subject is appalling.

If you're comfortable with about twice the levels of Ramsar, Iran (260 mSv/yr), you can achieve 470 mSv/year with about 20 g/cm^2 of polyethylene or water (Table 6a, p25). For a 40 year old male on a 6+6 month Mars round-trip, that's an extra 2% risk of death from cancer. This is probably acceptable IMO, despite the inevitable media hand-wringing over the "10x the allowable dose for radiation workers" sound bite.

For a spherical station with an interior volume of say 23,423 m³ (r = 17.75 m³), that's 800 tonnes of shielding, or 1,000 tonnes for double spheres (r = 14.1 m). For a torus (R = 100 m, r = 3.4 m), it jumps to 2,800 tonnes of shielding.

This extra 1800-2000 tones of mass also requires additional structural mass to support it, more resupply propellant to push it (including precess its axis of rotation), etc. And upmass ain't free, even with Starship.

This (for me) is one of the major appeals of barbell-type AG.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions. Guys, if no one else has done this before maybe you should let me get the ball rolling. I make zero statements about how anything has to be done "my way", I simply have decided on "a" way. I do not know if and when that becomes acceptable to y'all. I would rather sooner than later.

That's fair, and I have no problem with it. But what you said was "the simple dumbbell does not even make it to back of napkin design stage," and then went on to cite a bunch of (apparently non-existent) issues.

Glad we have cleared up the miscommunication!

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

A half-meter (~40 g/cm²) doesn't do much beyond a quarter meter (~20 g/cm²) according to Table 6a linked above.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started. [snip]

You don't have to prove anything to anyone (of course), but you were the one saying that other types of designs were unworkable. That was the bit I took exception to.

All water under the bridge now.

The Tubes are fabricated from flat-packed walls that are 9 m long and the half meter of water and PE thick. These monsters are wrangled together and assembled. They will be delivered with partial water loads, nominally the outer tanks only will be full (sealed) and the other two empty, pending completed construction followed by filling the radiation shield tanks with perhaps extra-terrestrial water. Maybe just the outer tank being full is enough for LEO but as soon as we boost it to cis-lunar space we want to fill those other two tanks up.

Water tanks are nice (vs PE) because they can be filled up and emptied without much human intervention. Water tanks are bad because they can leak water all over your ship without much human intervention.

Water is slightly less mass efficient than PE, but only slightly.

It is an enormous amount of water, and the design is not based on minimizing the water. It's called Aquarius because it is a water bearer. The comparison you ask for is not really relevant to my design process. (a waste of time from my point of view). There are programmatic benefits from the choice I made.

If maximizing the effect of water shielding is chosen as a primary design driver, that is a different design project. Whip out your alternative and let's compare. You will find me quite receptive to alternate ideas. Just please understand that certain changes constitute a not-Aquarius project. Which is great, just not Aquarius.

Point of clarification: is Aquarius supposed to be a space station, or a water delivery tanker ("water bearer" + no intent to minimize water mass)?

The central, founding, over-arching design imperative of Aquarius is comfort and safety. This led me to produce a design with absolutely every interior space being nearly equally well shielded with the half meter of hydrogen rich material. So all the habs and tubes and nodes and chutes and octo-walls all have that jacket.

And there are not only no windows, but no penetrations of the stainless steel skin anywhere on the habs, nodes, chutes and tubes. Two continuous skins of stainless, not even one bulkhead fitting anywhere below the central hub. All of it is "safe haven storm shelter". The flat walls of the central hub ("octowalls") will have plenty of bulkhead fittings, because you gotta have them.

No windows? Not sorry. The view would kinda suck anyway. Think about it.

Comfort's an "over-arching design imperative" and nice transparent water for shielding. Why no windows?

Moving shadows right? That's one of the big reasons I favor aligning/precessing the spin axis toward the Sun. If desired, you could even have lightweight film mirrors to reflect sunlight in the windows from a higher elevation angle.

edit: i just read your tag line at the end of your posts. Yeah, that.

Not a flashy design quote, but a good one. Guess who? No Google that's cheating.

Hint: the root word "design" (but not in that grammatical form) appears his most famous work (one that he didn't actually write)... 

Cool. I apologize for the lack of respect for the simplest designs. I see that I should not have used the word dumbbell.

So what do we call a simplest spin gravity configuration? This thread is an opportunity to organize design concepts and name them. Two bodies axially mounted is an "X", two bodies mounted at a T to the tether is a "Y", two bodies at a T turned out of the spin plane is a "Z", add a central hub for three more types, switch the tether out for a rigid truss gives you another class and six types.  I kinda sorta remember seeing this having been done but I am sure we could add clarity which would help add clarity to discussions if nothing else.

"Point of clarification: is Aquarius supposed to be a space station, or a water delivery tanker ("water bearer" + no intent to minimize water mass)?"

Yeah I can see the confusion. Perhaps the wackiest part of this proposal is that not only am I saying this would make sense as a very first spin gravity facility but that the thing is "built to last 200 years".

It is not a space 'station' because it has self-propulsion to take it from the construction and operational "station" in LEO, then to the Cis-Lunar "station" until being re-stationed at Mars.

So it is supposed to be a lot of things to a lot of different people. Ideally, all things to all people but that's too crazy even for me, but that's the line of thinking. The common attribute to all of its missions is that it is a safe haven.

So when a shiny new Aquarius is commissioned, she will have at least ~175 mm of PE/water in one of the three walls. Everywhere has that level of shielding, the whole thing is a safe haven to that extent. (Maybe there are storm shelters, btw.) That water will be beautiful pure Earth water, and for a long time it will just stay sealed up in that tank.

In addition, she will have an abundance of potable water distributed all throughout the ship. This store of water will be continuously recycled and purified. We have the PV power and the plumbing to do that, it is a main operational activity.

After some years of operation making money in LEO we will have amassed enough propellant to go to cis-lunar space. Once up there, she will want to immediately take on an additional jacket of water, from the moon or from asteroids to return to safe haven (to that extent) above the Van Allen belts.

Aquarius is also the water purifier. If you have dirty water from an asteroid, Aquarius wants it. That's a thing this water bearer does, she cleans her water and keep it fresh. The years in LEO let us mature the tech and we have the latest and greatest kit at the top of the hill and we are ready for the water we promised to buy.

We get all the shield tanks full. Maybe not pure wonderful water yet, but we can work on it on the trip to Mars and for years afterwards.

Now the water recycling is not perfect. We have human waste in the mix. It could be freeze dried but even then it needs to be stored.

So at some point, you are at Mars with a growing waste storage problem and with that original pure Earth water in the first shield tanks. Sewage should shield just about as well as pure water, I reckon. So yes Mars has water, but you now make available all that genuine Earth stuff. Aquarius has fulfilled that part of her water-bearer mission. She is full of crap but oh well.

So not a tanker in terms of moving water from place to place. A relocatable reservoir and water treatment plant that will pioneer the tech of cleaning up extra-terrestrial water. A safe haven where you go to hydrate and be among green growing things. Where you take a hot shower any time you want. Think low gravity hot tub for lunar robot techs. Likely the only place on orbit where water is abundant; the water bearer.

So why stainless steel and why no windows? Because I want that sheet of armor between me and space as a first defense. I want it to be impervious as possible. I want two of those skins, with leak-proof tanks filling the volume between. I do not want a bulkhead fitting for a video link to the 13th chute node's storage closet to ever spring a leak. Ever. 200 years of no chance of a penetration ruining everyone's day. Zero penetrations below the Hub.

Why no windows? The best bulkhead fitting is no bulkhead fitting. Give her excellent welding quality assurance and she will give you a 200-year lifetime. She would ring like a bell of you could hear it. A stainless steel armored interplanetary cruiser.

Or maybe down the road in the design process, someone proves that aluminum is a much better choice. Even with the program disruption. Fine, she gets made of aluminum. Every design decision is subject to review and revision.

You build half meter thick walls everywhere, paying the enormous price for that in the name of safe haven, and then you want to cut holes in it for people to stare at a spinning starfield with - at best - Earth whipping by every 20 seconds? Nah, bad idea. The overview effect is off the table for a spinning station IMO. They do that before and after visiting Aquarius.

I have not discussed orbital orientation. I am afraid to because maybe I am being stupid. But maybe you have a better understanding than I, so here goes.

I simply want to point the spin axis at the sun and have the thing orbit the Earth without coming out of that orientation. I am not 100 percent sure this actually works. Some days I convince myself it is easy, some days I think it fails.

What I do know is that I need to improve the rotational moments of inertia from what you have seen so far. I want the moment around the spin axis to be much higher than the other two orthogonal axes.

Aquarius will have a new look soon.

Also, believe it or not I am not here to hijack this thread. The thread title makes me want to work with others to describe and name the different configuration possibilities, just for starters.

[spacester]

Hey you asked a question, thank you. You seem interested in the efficacy of the shielding, and see that the surface area to volume ratio can be improved by certain other design decisions. No doubt.

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer. IOW I have never found a reference that says: well we don't know for sure, but it looks like we need this much plastic and this much water and here's how you would add lead foil to the mix and if you did that, you would have this level of safety and so let's use that as a baseline.
...
Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

This looks very promising. I thought it would require much more thickness, but also I was thinking of a simple single material PE. I was under the impression that it was better at blocking radiation than water. What made you think of the multi-layer approach? Also I read that the aluminum on the ISS actually made the radiation problem slightly worse because of secondary radiation from aluminum molecules being hit. Does this not apply to stainless steel? What is the purpose of the stainless steel?

The radiation shield concept and design is the result of the deepest dive I could muster on the subject, and this was 8 to 10 years ago. I am an amateur but I find no experts. In addition to sheer thickness of hydrogen rich material, it seemed like having transitions between materials would allow a strong hit to spread out better. A GCR (galactic cosmic ray) can come from any direction and pack a punch. This is the case where I think you want it to hit a big heavy atom but ONLY if you are there to catch all the mess radiating from that collision.

So the idea is to provide geometry that can be assembled by the construction crew, provides multiple obstacles to high energy particles and in particular can be refined as we learn more. This design is this amateur's best shot at "hey let's just plan on this for now based on what do do know, and make it better as we go along. It's a start."

[Twark_Main]

[snip]

Cool. I apologize for the lack of respect for the simplest designs. I see that I should not have used the word dumbbell.

"Dumbwaiter?! Who you callin' dumb, buddy???" 

[Coastal Ron]

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer.

Since there are no artificial gravity space stations yet, there is zero professional designers for such structures. All there is is concepts, which may or may not be grounded in reality.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions.

What? I hope this was an attempt at humor, because NO ONE on NSF can claim to be an "authority" for rotating space stations that generate artificial gravity. And there are plenty of us that have spent a LOT of time not just working on plans, but discussing and debating many approaches.

You have visited the various NSF threads for rotating space stations and spaceships? Because until someone actually builds a 1st generation rotating space station that generates some degree of artificial gravity, we're all just proffering our opinions. Just as you are.

Guys, if no one else has done this before maybe you should let me get the ball rolling.

You're kinda late to be volunteering to "get the ball rolling". The ball has been rolling for MANY years on NSF on this topic. Welcome to the club! 

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

You're not the first to suggest using polyethylene - ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a popular proposed construction material. I have designs that based on using Dyneema, but my stations are not planned for use in Earth orbit, where atmospheric oxygen attacks varieties of polyethylene.

I just don't understand what your structure looks like? Wheel? Star? Tube? What?

Water bags. Sure. But adding weight is one thing, building a structure that can handle that weight is something else.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started.

Enough chest beating. Remember that until someone actually builds a rotating space station, and it works, then EVERYONE is just spitballing. You, me, and everyone else. Which means we ALL have opinions about what works and what doesn't - get used to it. 

[Paul451]

Dumbbell configuration seems to be the AG implementation with "nothing left to take away."

Or variations like the simple baton.

For example, taking Spacester's proposal: Using the rectangular panels in his eight, square-cross-section, "apartment tubes" you can build a hexadecagonal-cross-section baton with the same overall length. Same surface area (for radiation/MMOD shielding) but you now get 180 square metres of space on each floor, instead of 72 sq_metres (in 9 sq_metre sections). Same 2.5x increase in volume. And IMO, vastly more usable volume. (Or reduce the mass/surface area by 40% if you only want the same volume. Although still in a much more usable, open form.)

The "chutes" are eliminated entirely. As are most of the tensile cables and support structure. As are the weird telescoping rings. That mass can either be skipped entirely, or substituted for more construction material to make the main baton larger/wider. [Also, the hub can now be in the plane of rotation, as can the "process" modules, improving the mass distribution.]

Cover the sun-facing side with thin-film solar panels, offset from the baton to serve as a sun-shade, cover the back-side with radiators. (Given that it's an AG structure, might be able to get away with spiral droplet-radiators for greater mass-efficiency.)

The baton also makes your infrastructure easier. Running ECLSS and utilities through Spacester's design would be a nightmare.


I've included an artist's render of the station, below. Along with an earlier, hexagonal octagonal pathfinder station.

[Paul451]

[...]

I just don't understand what your structure looks like? Wheel? Star? Tube? What?

He posted it on page one.

[spacester]

Just like with AG itself, when I search for wisdom on the subject, I find very little hard guidance for a designer.

Since there are no artificial gravity space stations yet, there is zero professional designers for such structures. All there is is concepts, which may or may not be grounded in reality.

So I did my research and made a design choice. I admit I did not ask the permission of my fellow posters here to make this design decision, even though I knew well that you do not accept my authority to make such decisions.

What? I hope this was an attempt at humor, because NO ONE on NSF can claim to be an "authority" for rotating space stations that generate artificial gravity. And there are plenty of us that have spent a LOT of time not just working on plans, but discussing and debating many approaches.

You have visited the various NSF threads for rotating space stations and spaceships? Because until someone actually builds a 1st generation rotating space station that generates some degree of artificial gravity, we're all just proffering our opinions. Just as you are.

Guys, if no one else has done this before maybe you should let me get the ball rolling.

You're kinda late to be volunteering to "get the ball rolling". The ball has been rolling for MANY years on NSF on this topic. Welcome to the club! 

Every wall between the people and space consists of half a meter of polyethylene and water. The PE forms three nested tanks each of about 150mm thick walls of water, with a stainless steel skin inside and out, and metal foil between the PE tanks. This presents a path with more than 10 interfaces between materials and a pretty good gauntlet of hydrogen rich material for the particles to penetrate if they want to damage the ugly bags of mostly water inside.

You're not the first to suggest using polyethylene - ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a popular proposed construction material. I have designs that based on using Dyneema, but my stations are not planned for use in Earth orbit, where atmospheric oxygen attacks varieties of polyethylene.

I just don't understand what your structure looks like? Wheel? Star? Tube? What?

Water bags. Sure. But adding weight is one thing, building a structure that can handle that weight is something else.

Do I stand ready to *PROVE* that is the absolute best and only possible choice? Of course not, silly people. But I did my research and I crunched some numbers and got a result and am going with it to get things started.

Enough chest beating. Remember that until someone actually builds a rotating space station, and it works, then EVERYONE is just spitballing. You, me, and everyone else. Which means we ALL have opinions about what works and what doesn't - get used to it. 

Hello again. My thing is to provoke new thoughts. That's what I do. Others do it too, but it's my thing.

As such, I am accustomed to much opposition when I present the results of my thought experiments. It does not help that all my best thought provokers are large scale ideas.

We played this game earlier this year, remember? Aquarius was presented in full and the reception was so underwhelming that I deleted it all. I am back with a new approach and a new attitude. Just let me get one thing off my chest, for the sake of a greater good on this thread.

You refer to previous threads on this topic. I may or may not have read all of them, I dunno. As an independent thinker, I am not committed to that task. Besides - and here is the point - if those threads are so important, than you guys must have come up with some conclusions and summations, right? No you didn't did you?  It's all attack all the time when I check in on those threads here and everywhere else. Anyone who presents an "idea" - not just me, anyone -  and expects praise is sorely disappointed but sometimes they stick around and join the attack chorus for all the next ideas. Let's stop with it already, OK? Say something nice first. Respect the work of others, of course their vision is way different from yours. Duh. Be nice.

So whenever I would try to get a spin-gravity concept across, the very smart people here would say show us the math. So I did Aquarius which means I did the math, it's on that overview pdf. 150 launches at 150 T ought to about do it for full construction and outfitting of Aquarius. It's high school math, mostly basic spreadsheet stuff, more on that later. The point is I called their bluff. That's how I know those previous threads didn't do the math.

So as far as chest thumping goes, dust off the results of your previous threads here, maybe do a bit more math, and let's compare. The current form of Aquarius is very much a preliminary one. Certainly a better design is out there, a whole set of them even. That's not the point. I have staked out the upper end in terms of ambition because that's a thing I like to do. Let's define the different kinds of "better" - optimization criteria - we are going to be using when we compare designs (those which are fleshed out enough to compare well). 

Me, I like this thread's title best of all. That's why I let it be until now. Let's start breaking down different design concepts into categories or classifications or whatever.

What's the difference between a bolo and a barbell?

OK so this while spitballing thing, let's look at that. To me, spitballing is what the Drill Sargent is doing to the pitiful maggot whose face he is spitting on while screaming. So I am not a big fan of that.

Nor am I interested in mere opinion proffering. Where does that get us? How disciplined would that have to be to actually work? Getting used to it is not gonna happen, I have better things to do than spend two days defending my right to choose a radius and rpm.

The request to show the math was a valid one, so let's all show the math, sort it out, and produce something in this thread.

What I am doing, by calling the bluff and doing the math and taking a deeper dive that you've seen before - because I can and I want to - my good sir, is designing. That is my specialty as a Mechanical Engineer.