Artificial Gravity Testbeds

[edzieba]

Along with tanks, there are also:
- The trust structure (compressive loads are not tensile loads)
- Header tanks (will be full to allow deorbit & EDL, hanging the tanks upside-down is not a design use-case)
- Propellant plumbing ullage (e.g. GCH4/GOX entry at the top as standard would ingest liquid when inverted)
- CLSS plumbing and ullage.
- Crew air circulation design
- etc.

Designing any vehicle to operate both right-side-up and inverted is a challenge, and adding a requirement to operate in microgravity does not make that challenge easier. Fluids pool in the wrong place, gasses are at the wrong end of your traps, materials strain the wrong way and bind moving parts, etc.

It is FAR from proven that inverted operation of a stock Starship is viable.

[Twark_Main]

Let's go down the list, shall we?

Along with tanks, there are also:
- The trust structure (compressive loads are not tensile loads)

If the interstage / thrust structure were made of unreinforced concrete this might concern me. But it's made of steel, and it's designed to take compressive loads that are at least an order-of-magnitude greater than the proposed tensile loads (the thrust structure has to support the full thrust of the Raptor engines, and the interstage has to support the fully-fueled Starship under an in-flight acceleration of 3+ gs). These two beefy structures will laugh at such tiny tensile loads.

For steel tension is easier than compression, because there's no concern for buckling. In general a steel I-beam (ie a profile that resists buckling) can take roughly the same loads in compression and tension.

- Header tanks (will be full to allow deorbit & EDL, hanging the tanks upside-down is not a design use-case)

Again, if the steel can support the ~12 tonne LOX load under compression/buckling at 3+ gs (and the bending moments while reentering sideways at 2+ gs), it can support it under tension. That's how steel works.

- Propellant plumbing ullage (e.g. GCH4/GOX entry at the top as standard would ingest liquid when inverted)

I sure hope they've got a valve for closing that, because it will be in microgravity. The valve might need a re-qual to confirm it works at those pressures, so for SpaceX that means "give it to an intern for a week."

- CLSS plumbing and ullage.

This is a good point. In fact we don't even know if SpaceX is developing a Closed Life Support System that will operate in 1 g. Afaik they've shown little interest in anything but microgravity.

But the more I think about it, the less problematic it gets. ISS heritage components are designed to be tested under 1 g (carbon dioxide removal, dehumidification), and the few exceptions (eg the urine processing assembly centrifuge) are relatively unimportant for high closure rates. The crew may simply store urine in a tank, and accept a slightly higher consumables mass for a give mission duration.

If the plumbing R&D concerns you for such a one-time mission, just ship up some Gatorade bottles, some 5 gallon buckets, and a commode seat. "Tight is right and long is wrong."

- Crew air circulation design

Again, not terribly hard. In microgravity you need large airflow speeds to ensure even mixing because there's no buoyancy, so you can get CO2 pockets. In case you haven't noticed, this isn't a problem in your house here on Earth under 1 g. For Mars/Moon gravity you just re-run the computer simulation assuming appropriate g-level.

Here's the computer simulation results for Dragon: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110014250.pdf

Designing any vehicle to operate both right-side-up and inverted is a challenge, and adding a requirement to operate in microgravity does not make that challenge easier. Fluids pool in the wrong place, gasses are at the wrong end of your traps, materials strain the wrong way and bind moving parts, etc.

It is FAR from proven that inverted operation of a stock Starship is viable.

No-one is claiming a stock Starship will be used (at the very least you need the furniture re-oriented). Just that the relatively minor work to remedy your concerns is far easier than

1) designing a completely novel nose-to-nose docking system, and the long lever arm / tether-and-damper that would be needed to keep RPM reasonable, or worse

2) designing an entire variable gravity test bed vehicle completely from scratch (which is what the thread started with).

Swapping a valve or re-running a simulation doesn't sound so hard when the alternative is to design and build a space station from scratch!

[edzieba]

Let's go down the list, shall we?

Along with tanks, there are also:
- The trust structure (compressive loads are not tensile loads)

If the interstage / thrust structure were made of unreinforced concrete this might concern me. But it's made of steel, and it's designed to take compressive loads that are at least an order-of-magnitude greater than the proposed tensile loads (the thrust structure has to support the full thrust of the Raptor engines, and the interstage has to support the fully-fueled Starship under an in-flight acceleration of 3+ gs). These two beefy structures will laugh at such tiny tensile loads.

For steel tension is easier than compression, because there's no concern for buckling. In general a steel I-beam (ie a profile that resists buckling) can take roughly the same loads in compression and tension.

Starship is not entirely in compression, so it cannot be assumed that inversion will just switch compression to tensio nand everything will be OK. Same goes for header tanks etc.

- Propellant plumbing ullage (e.g. GCH4/GOX entry at the top as standard would ingest liquid when inverted)

I sure hope they've got a valve for closing that, because it will be in microgravity. The valve might need a re-qual to confirm it works at those pressures, so for SpaceX that means "give it to an intern for a week."

It's more than just a valve, if you want your RCS to work properly (e.g. for spinup/spindown) you need an alternative gas ingest route, qualification for both routes that they will not ingest fluid, etc.

- CLSS plumbing and ullage.

This is a good point. In fact we don't even know if SpaceX is developing a Closed Life Support System that will operate in 1 g. Afaik they've shown little interest in anything but microgravity.

But the more I think about it, the less problematic it gets. ISS heritage components are designed to be tested under 1 g (carbon dioxide removal, dehumidification), and the few exceptions (eg the urine processing assembly centrifuge) are relatively unimportant for high closure rates. The crew may simply store urine in a tank, and accept a slightly higher consumables mass for a give mission duration.

Qualifying plumbing for 1g plus microgravity has nothing to do with qualifying plumbing for -1g. Fluids do not conveniently reverse flow direction for you.

- Crew air circulation design

Again, not terribly hard. In microgravity you need large airflow speeds to ensure even mixing because there's no buoyancy, so you can get CO2 pockets. In case you haven't noticed, this isn't a problem in your house here on Earth under 1 g. For Mars/Moon gravity you just re-run the computer simulation assuming appropriate g-level.

A normal house leaks like a sieve. For houses and other buildings that do approximate a sealed container, you DO have to take into account internal airflow to prevent pockets forming, and directionality of gravity is vital even for forced airflow.

No-one is claiming a stock Starship will be used (at the very least you need the furniture re-oriented). Just that the relatively minor work to remedy your concerns is far easier than

1) designing a completely novel nose-to-nose docking system, and the long lever arm / tether-and-damper that would be needed to keep RPM reasonable, or worse

2) designing an entire variable gravity test bed vehicle completely from scratch (which is what the thread started with).

Swapping a valve or re-running a simulation doesn't sound so hard when the alternative is to design and build a space station from scratch!

The work needed to make Starship operate inverted is much more than 'relatively minor', and much more than connecting to the existing lifting hardware in the existing design orientation and acceleration.

Any appreciable rotation rate will require dealing with stabilising long tethers anyway, so saving a few metres at each end by flipping Starship causes more problems than it selves.

[Paul451]

I'm more keen to discuss the issues with [...] deploying/retracting solar panels in any spin-gravity scenario.

Under spin, (using the tail-tail example), thin film panels can unfurl like a roller blind. The deployment arm would be at the low gravity end of the two Ships, with pseudo-gravity increasing as the panels hang down. That should help deployment, IMO. But it would need to be validated a few times. The existing deployment systems are well proven. (When was the last time someone lost a mission/sat/probe because a PV panel failed to deploy?) You can test the whole system under 1g (obviously), but you'd need to test on-orbit a few times. (And obviously, the title is "testbed". So presumably we're testing this in LEO long before AG is used for a Mars trip.)

As I've said in previous posts, ideally from a design perspective, spin gravity should not be an *additional* cost to running the ship during cruise phase, rather, it should actually make many things *easier*.

There will be a few burdens, but it won't require a structural redesign. You need the docking/grappling/whatever connector at the tails. That's not a terrible burden, since you need one for fuel-transfer, you just over-design it for that job. Approach and connection is still done in micro-g, the added robustness is only required after they've made a solid connection.

Life-support will be different, but, as you and I have both noted before, it should make designing long-duration ECLSS easier. Certainly easier to test the 1g parts.

[Twark_Main]

Let's go down the list, shall we?

Along with tanks, there are also:
- The trust structure (compressive loads are not tensile loads)

If the interstage / thrust structure were made of unreinforced concrete this might concern me. But it's made of steel, and it's designed to take compressive loads that are at least an order-of-magnitude greater than the proposed tensile loads (the thrust structure has to support the full thrust of the Raptor engines, and the interstage has to support the fully-fueled Starship under an in-flight acceleration of 3+ gs). These two beefy structures will laugh at such tiny tensile loads.

For steel tension is easier than compression, because there's no concern for buckling. In general a steel I-beam (ie a profile that resists buckling) can take roughly the same loads in compression and tension.

Starship is not entirely in compression, so it cannot be assumed that inversion will just switch compression to [tension and] everything will be OK. Same goes for header tanks etc.

Those extra forces means it has to be stronger than it would be in pure compression. So yes, "everything will be OK."

- Propellant plumbing ullage (e.g. GCH4/GOX entry at the top as standard would ingest liquid when inverted)

I sure hope they've got a valve for closing that, because it will be in microgravity. The valve might need a re-qual to confirm it works at those pressures, so for SpaceX that means "give it to an intern for a week."

It's more than just a valve, if you want your RCS to work properly (e.g. for spinup/spindown) you need an alternative gas ingest route, qualification for both routes that they will not ingest fluid, etc.

Yep. Not too hard.

- CLSS plumbing and ullage.

This is a good point. In fact we don't even know if SpaceX is developing a Closed Life Support System that will operate in 1 g. Afaik they've shown little interest in anything but microgravity.

But the more I think about it, the less problematic it gets. ISS heritage components are designed to be tested under 1 g (carbon dioxide removal, dehumidification), and the few exceptions (eg the urine processing assembly centrifuge) are relatively unimportant for high closure rates. The crew may simply store urine in a tank, and accept a slightly higher consumables mass for a give mission duration.

Qualifying plumbing for 1g plus microgravity has nothing to do with qualifying plumbing for -1g. Fluids do not conveniently reverse flow direction for you.

Obviously. You would flip the mounting direction.

- Crew air circulation design

Again, not terribly hard. In microgravity you need large airflow speeds to ensure even mixing because there's no buoyancy, so you can get CO2 pockets. In case you haven't noticed, this isn't a problem in your house here on Earth under 1 g. For Mars/Moon gravity you just re-run the computer simulation assuming appropriate g-level.

A normal house leaks like a sieve. For houses and other buildings that do approximate a sealed container, you DO have to take into account internal airflow to prevent pockets forming, and directionality of gravity is vital even for forced airflow.

I guess I missed the story about people on Earth being asphyxiated in pockets of CO2 that formed around their heads... ?

Again, you just re-run the simulation. Aim the vents differently if there is a problem. It's very easy to entrain air into mixing currents.

No-one is claiming a stock Starship will be used (at the very least you need the furniture re-oriented). Just that the relatively minor work to remedy your concerns is far easier than

1) designing a completely novel nose-to-nose docking system, and the long lever arm / tether-and-damper that would be needed to keep RPM reasonable, or worse

2) designing an entire variable gravity test bed vehicle completely from scratch (which is what the thread started with).

Swapping a valve or re-running a simulation doesn't sound so hard when the alternative is to design and build a space station from scratch!

The work needed to make Starship operate inverted is much more than 'relatively minor', and much more than connecting to the existing lifting hardware in the existing design orientation and acceleration.

Any appreciable rotation rate will require dealing with stabilising long tethers anyway, so saving a few metres at each end by flipping Starship causes more problems than it [solves].

There are no tethers in the tail-to-tail proposal. That component is entirely absent, so it's not just a matter of "saving a few metres at each end."

[Paul451]

Along with tanks, there are also:
- The trust structure (compressive loads are not tensile loads)

But tensile load are.

Between launch and staging, the thrust structure supports 3 times the weight of the engines hanging off it, while also under vibrating thrust of launch. A high tensile load on some parts of it, while others are in compression between tanks and SuperHeavy. It also must support the twisting, torque force of the entire fully-fuelled Starship being buffeted by not only supersonic aerodynamic loading, but also any course-changes manoeuvres made by SuperHeavy.

As I said before, it must be robust to do its job. If it isn't strong enough to support itself under 1g inverted, it isn't strong enough to survive launch.

- Header tanks (will be full to allow deorbit & EDL, hanging the tanks upside-down is not a design use-case)

Like the main tanks, they are designed to drastically exceed the tensile requirements of 1g inverted. Any potentially fragile components can be easily tested on Earth.

- Propellant plumbing ullage (e.g. GCH4/GOX entry at the top as standard would ingest liquid when inverted)

Any gas intake becomes the "bottom" once in micro-g. So presumably any necessary on-orbit venting systems is designed to exclude or separate liquids. But again, gas intakes can be easily bench-tested in on Earth.


Following TM's reply, you clarified that this particular "propellant plumbing" was talking about the RCS thrusters:

if you want your RCS to work properly (e.g. for spinup/spindown) you need an alternative gas ingest route, qualification for both routes that they will not ingest fluid

RCS propellant system can't be limited to working in one orientation. If it didn't, RCS thrusters couldn't be used to move the ship in any other direction.

For example: If you were heading towards your preferred nose-nose docking and you needed to brake your forward motion. You fire the forward RCS thrusters, now "gravity" is oriented towards the nose, the propellant "falls" to the front of the tank and straight into the gas intake, and your engine sputters to a halt before the burn is finished. Thrust stops, the liquid bounces back away from the intake, then the thruster (if the igniter is left on) blurps back to life, then conks out again, then starts, then stops... Inevitably, the two forward thruster packs would also be firing unevenly, throwing off your direction, requiring a yaw/pitch correction, pushing the propellant in yet another orientation, throwing those thrusters out of whack... and so on and so on.

You cannot design an RCS that is direction-sensitive or it simply couldn't do its job.

- CLSS plumbing and ullage.
- Crew air circulation design

This is an advantage of spin gravity. Being able to design systems that work under gravity. Being able to prototype and test systems on Earth. Being able to use relatively off-the-shelf systems (or at least much more off-the-shelf designs) for many components. For example, just the maintenance on the air fans will be easier if the ship is under even partial gravity. In micro-g, any intake vents become "down" for everything floating in the ship, dust, sweat, pens, metal shavings, etc. That greatly increases clogging of filters, blocking airflow, screwing with heat management, etc, increasing the maintenance and shortening part-life (judging by ISS). Under even partial gravity, you can orient the vents above the "floor" and avoid most of that undesired intake. The same is true for most gas and liquid handling systems. Designing toilets (and their plumbing.) Being able to have showers. Etc etc.

You'll still need to design for micro-gravity. But if AG does make long-duration ECLSS easier, then you'd default to AG for any mission longer than a couple of days, which allows you to use short-duration open-cycle/high-consumable ECLSS for the periods between making orbit and spin-up (ditto spin-down to EDL).

[Paul451]

It is FAR from proven that inverted operation of a stock Starship is viable.

It is "FAR from proven" that nose-nose spin is viable.

During nose-nose docked spin, if the bottom of the cabin is at 1g, then the engines are at 3g tensile load, the lower tank at 2g. And the nose-nose connections would have to support roughly double the weight of being hung from a crane on Earth. It's not the same load.

Even if you put a 50m truss or tether between the noses of the two ships, then at 1g in the cabins, the tail is still hanging at around 1.5g, so the ship still weighs more under tension than when on Earth.

Now, I personally think Starship will still be able to easily handle these kinds of tensile forces... but you don't.

By contrast, with tail-tail, 1g in the cabin means most of the ship weighs less than 1g, the engine-area is barely experiencing any g-load, and the total loading on the tail from the entire ship is about half a g equivalent. Only the cabin-area is holding its own equivalent 1g weight, and that's less than it supports when suspended by a crane, and vastly less than the tensile force simply from being pressurised.

The very concern you keep exaggerating for the tail-tail configuration is actually much more of an issue for nose-nose spin.

[Paul451]

Any appreciable rotation rate will require dealing with stabilising long tethers anyway

Incorrect. Tail-tail AG can achieve 1g at the forward deck at less than 5RPM. Modern (ground-based) research says that pretty much everyone can adapt to 5RPM, provided you allow proper head movement during spin-up. (And testing the ECLSS at Mars-g requires less than 3RPM. Trivial.)

(Older research gave weird and inconsistent results. But it was only in the last 20yrs that the importance of experiencing a full range of motion during adaptation was understood. Previously, people might have instinctively tried to limit head-movement, thinking that would help. Inconsistent experiment design would explain the wildly varying results of the early work, with some seeing nausea at just 2RPM, others at 4, others at 6.)

[Paul451]

I guess I missed the story about people on Earth being asphyxiated in pockets of CO2 that formed around their heads... ?

I have heard stories of people dying inside of freshly exposed steel water tanks because there's enough fresh oxidation to consume all the free oxygen and not enough circulation through a small hatch to replace it. The first worker collapses. Then someone goes in to help them and also collapses. There are stories in Australia of virtually entire families being killed when the Dad tries to clean the inside of large water tanks, then the wife and/or sons rush in to try to help him when he collapses. Days later someone finds their bodies and thinks they've stumbled onto a mass murder.

Likewise when working in freshly exposed ship bilge tanks, after the third death, the rest of the crew panics about "deadly gases" and abandons ship. (When in reality, even if you didn't have bottled-oxygen masks (for fire response), you could just hold your breath before going in, drag the afflicted crew out into fresh air and, if you acted quickly enough, potentially save their lives.)

Not relevant. Just interesting and/or horrifying.

[RDoc]

Any appreciable rotation rate will require dealing with stabilising long tethers anyway

Incorrect. Tail-tail AG can achieve 1g at the forward deck at less than 5RPM. Modern (ground-based) research says that pretty much everyone can adapt to 5RPM, provided you allow proper head movement during spin-up. (And testing the ECLSS at Mars-g requires less than 3RPM. Trivial.)

(Older research gave weird and inconsistent results. But it was only in the last 20yrs that the importance of experiencing a full range of motion during adaptation was understood. Previously, people might have instinctively tried to limit head-movement, thinking that would help. Inconsistent experiment design would explain the wildly varying results of the early work, with some seeing nausea at just 2RPM, others at 4, others at 6.)

Can you post some links to that modern research on tolerance to rotation please? I'm not challenging you statements, I've been looking for that kind of information for awhile.
Thanks.

[Paul451]

Can you post some links to that modern research on tolerance to rotation please? I'm not challenging you statements, I've been looking for that kind of information for awhile.

You want to start with anything by James Lackner and Paul DiZio from the Ashton Graybiel Spatial Orientation Laboratory. They seem to have kick-started the modern resurgence in spin-adaptation research. A lot of their early stuff was focused on the question of how the human vestibular and motor senses worked, and worked together, and how it coped with self-generated Coriolis force of coordinating simultaneous reaching and turning motions. Basically the early rotation studies were trying to break the brain to see where the edges were, in order to see how it works normally.

Bunch of cites at Lackner's lab: https://www.brandeis.edu/graybiel/publications.html

That seems to be what led to their work for NASA. Which in turn led to the adaptation protocol, which now seems to be fairly common.

For example https://www.researchgate.net/publication/8607002_Adaptation_to_rotating_artificial_gravity_environments. Which is cited on Ted Hall's SpinCalc site, which everyone uses.

Additionally, Ted himself has written on the topic. Including a long overview paper with Al Globus: https://space.nss.org/media/Space-Settlement-Population-Rotation-Tolerance-Globus.pdf


The interesting thing I've found from the newer research is not just how quickly people adapt (25min sessions), but that they retain much of their adaptation for a month afterwards (I don't know if anyone has tested longer) and re-adapt even faster. That means you could do some adaptation sessions on Earth, once you're comfortable, launch to an AG station, half an hour to re-adapt. Bam! Done.

Can't find a direct cite, but here's a presentation (yay, slides) from a telecon, which I've attached below, graphs on slides 9, 10, 11. (The audio of the telecon is available via: http://fiso.spiritastro.net/telecon/Engle-Clark_1-24-18/)

[RDoc]

Thanks for the references. Very interesting and makes me more convinced that artificial gravity should be actively pursued.

[Coastal Ron]

In case it matters for those of us that are designing rotating artificial gravity testbeds, SpaceX has released the User Guide for the Starship, and it includes information about payload volume and mass.

My designs rely predominately on cylinders that are used to build rotating stations, so this was good news to finally find out. To help understand how long those cylinders can be, or how many can be stacked per flight, I added some graphics to the SpaceX diagram.

[Coastal Ron]

An interesting article:

Space travel weakens astronauts' immune systems by altering gene expression - New Atlas

Relevant quote:

The researchers studied gene expression in white blood cells (leukocytes) in 14 astronauts who resided on the International Space Station (ISS) for between four-and-a-half and six-and-a-half months between 2015 and 2019. Blood samples were taken from each astronaut at 10 points: once pre-flight, four times during flight, and five times when they were back on Earth.
...
The researchers observed that the first cluster of genes dialed down when the astronauts reached space and went back up when they were on Earth; the reverse was seen for the second cluster.

If the lack of gravity is a substantial part of the problem, then the question becomes how much gravity would be needed to stop this from happening?

An artificial gravity testbed would be one way to do that testing, and likely the least expensive way to test out how much gravity is needed.

Vast Space has proposed their 100-meter-long spinning stick space station, which would offer a range of gravities for testing purposes, though the size of that station may make it difficult for test subjects to stay for long periods of time one gravity gradation. Still it could be a first test of HOW to test for less-than-Earth gravity solutions.

What would be the minimum sized rotating space station testbed that could allow for human tests that last for at least four months, and maybe as long as 12 months?

[Paul451]

You'd need to find an animal analogue in order to do sensible research on limits (ie, the minimum gravity before the effect is reduced or eliminated), so that you can have sufficient group-sizes for meaningful statistics.

The problem with human zero-g research is that they aren't just test subjects. With the partial exception of the Kelly twins, there's no proper control groups, nor are astronauts selected at random. Astronauts are a really good example of a failure in the selection process from the POV of medical research. (Obviously, there's perfectly mundane reasons why that's not practical.)

In a baton station, like Vast's, that's going to be even worse. You can't realistically expect to confine astronauts to single g-levels throughout their stay. Again, they aren't going to be just test subjects, they are also the researchers, the maintenance crew, the techs for other research, and need to move throughout the station. You might give them accelerometers/etc to record "time spent at each g-level", but that's very messy data.

OTOH, animals will be inherently confined to a single level per group, because that's where the cages/habitats are. They can be properly controlled, both against groups on Earth and other g-levels, with suitable randomisation and uniformity. And breeds can be selected that are sensitive to the target of the research, ie, making them sensitive "instruments" to detect the limits more easily.

[Coastal Ron]

You'd need to find an animal analogue in order to do sensible research on limits (ie, the minimum gravity before the effect is reduced or eliminated), so that you can have sufficient group-sizes for meaningful statistics.

While that would be the least expensive method, it is humans that we are the most concerned with, and humans are likely the only animal that will be in sufficient numbers in space for the foreseeable future. Next might be Tilapia for aquaculture, but not sure there is a non-human animal that would be a good enough analog for brain study.

The problem with human zero-g research is that they aren't just test subjects. With the partial exception of the Kelly twins, there's no proper control groups, nor are astronauts selected at random. Astronauts are a really good example of a failure in the selection process from the POV of medical research. (Obviously, there's perfectly mundane reasons why that's not practical.)

Yeah, in general you need a large sample size for any human research studies, but the problem we need to address is pretty immediate. Well, immediate if we are actively trying to expand humanity out into space. So we may have to deal with small sample sizes in the beginning and then keep medically testing everyone that goes into space that spends time in some form of artificial gravity.

In a baton station, like Vast's, that's going to be even worse. You can't realistically expect to confine astronauts to single g-levels throughout their stay. Again, they aren't going to be just test subjects, they are also the researchers, the maintenance crew, the techs for other research, and need to move throughout the station. You might give them accelerometers/etc to record "time spent at each g-level", but that's very messy data.

Right, and I've designed an artificial gravity testbed that has four arms, not two, but that just means twice as many people in the exact same conditions as the Vast station.

But I will disagree on one point, which is that the test subjects can be chosen specifically because they will stay in a confined space. You can have others that perform all of the upkeep and maintenance, and they can pass through and interact with the test subjects in the specific gravity zones, but otherwise I think enough people could be found that would accept that living/working constraint. It would certainly speed up the science return.

[Greg Hullender]

Before anyone tries to build a rotating station large enough for human beings, it seems to me that it's critical to prove that such a thing can be stabilized. That suggests putting up a model at 1/10 or 1/100 scale. So before trying to build a 112-meter diameter ring (1g at 4 RPM), try launching a 1.12-meter ring and see if you can get stable rotation out of it. Sure, if it's spinning at 4 RPM, it'll only have 1% of the gravity of the big one, but that's okay. All that does is slow down the instability problems--it doesn't fix them. If you can stabilize the little ring, odds are good the same techniques will work on a bigger one. I'm not sure what the best way would be to simulate people moving around inside the ring, but I'm sure someone can think of something. (I'm visualizing something like model trains.)

When you can show that a 1.12-meter ring can be adequately stabilized, then try an 11.2-meter one. You could fit a couple of people inside of that, if needed, although it'd still just be 1/10 of a gravity. When you've demonstrated that you can keep such a thing stable indefinitely, then it's reasonable to try to build a 100-meter diameter ring.

But until you're sure you've dealt with the stability problem, I think all the other issues are moot. Is anyone, anywhere, proposing this kind of experiment?

[MickQ]

It seems to me that the larger the ring the more stable it will be due to more mass and inertia 🤔

[Twark_Main]

humans are likely the only animal that will be in sufficient numbers in space for the foreseeable future

Absurd.

One small payload module (the Rodent Research Hardware System) has flown 300+ mice in nine years, as compared to ~630 humans total since the dawn of the Space Age.

Yeah, in general you need a large sample size for any human research studies, but the problem we need to address is pretty immediate. Well, immediate if we are actively trying to expand humanity out into space.

As usual you're arguing backwards from your personal goals ("let's put lots of humans in space for its own sake").

However the fundamental problem is still economic, not motivational. We couldn't expand humanity out into space en masse even if we wanted to, because it's just too bloody expensive! So what we really need to do is make space stations that are extremely economical, in the same way SpaceX has done so for launch rockets.


That's really our main challenge. However we are facing enemies at the gate who violently oppose any attempt to achieve good economics when designing space colonies:

   • no spheres or 2-barbells (even though they're most economical), we "must" use a torus instead

   • no reasonable thickness of radiation shielding, we "must" use extremely thick shielding instead

   • no aiming for high internal packaging efficiency, we "must" have a bunch of big useless open empty (yet still pressurized and shielded!) volume instead

etc etc

So we may have to deal with small sample sizes in the beginning and then keep medically testing everyone that goes into space that spends time in some form of artificial gravity.

We don't have to do that, no.

We can fly research animals and humans at the same time, just as we always have. In fact, one of the (very few!) economical jobs for humans in space is "biomedical researcher" 

Paul451 is right: the best AG testbed just has racks of animal cages at different G levels. A Vast-style "stick" station is the best way to achieve that.

[Coastal Ron]

Before anyone tries to build a rotating station large enough for human beings, it seems to me that it's critical to prove that such a thing can be stabilized.

Having a stable design for rotation is critical, for sure.

...When you can show that a 1.12-meter ring can be adequately stabilized, then try an 11.2-meter one. You could fit a couple of people inside of that, if needed, although it'd still just be 1/10 of a gravity. When you've demonstrated that you can keep such a thing stable indefinitely, then it's reasonable to try to build a 100-meter diameter ring.

While this approach could be used, I'm not sure the fidelity of it would ensure that the solution scales. And nowadays there are really good physics simulation systems, which I think would reduce or eliminate any concerns.

But until you're sure you've dealt with the stability problem, I think all the other issues are moot. Is anyone, anywhere, proposing this kind of experiment?

Not that I know of, but on the Realistic, near-term, rotating Space Station thread there has been occasional discussions and debates about stability, but I don't think anyone on that thread has the money to build anything in space (me included).

Certainly part of the debate has been about the three-dimensional layout of a station while it spins, and how the intermediate axis theorem (aka tennis racket theorem) could affect that rotation.

At the beginning of this thread I posted an image about an artificial gravity testbed design that I have been working on, and there are plenty of details that are not shown, including inertia-adding masses extending out from the station that would be used to ensure that no intermediate axis can be induced during normal operations - which includes having visiting vehicles attached at the center.

But until there is an open source physics model that we in the public can use to validate our assumptions, they are still just assumptions.