Artificial Gravity Testbeds

[Paul451]

5.9rpm, just within human tolerances.

Humans can tolerate up to 30 RPM. Some humans can't, but for a small station like you're describing, you get to pick your crew.

In general, unless we discover something new when we actually have a rotating station, you can use whatever RPM suits the purpose of the station. You aren't going to exceed human tolerances. As you need to accommodate a wider range of people, then the station is going to be larger, hence wider, hence have a lower RPM anyway.

[Coastal Ron]

A suggestion.

If you can't get a custom habitat for a spin-gravity lab, how about off-the-shelf? Sierra Space is developing the LIFE habitat, a 9m-wide inflatable module that makes the old Bigelow concept into reality.

It's a ready-made torus. Spin that 9m fabric doughnut up to 5.75rpm, and you can easily simulate lunar gravity on a macro scale.

It's certainly tough enough, as the structure was tested to 4.5 atmospheres and beyond before bursting.

Future structures are planned that expand out to 19m wide and 22 metres long. At that size, Mars' 0.38g gravity is available at 5.9rpm, just within human tolerances.

It makes sense to use off the shelf hardware for short term experiments, though this Sierra Space habitat may not be appropriate for testing the effects of artificial rotation.

The first question you have to start out with is, what are you testing for?

If you are just testing to see if you can generate Mars level of artificial gravity, then you probably need something even more simple than an inflatable module, since you could test for that with by spinning a Commercial Crew spacecraft at the end of a tether for a couple of hours. Not saying it wouldn't have its own challenges, just pointing out that WHAT you are testing for determines HOW you test.

The real question though is whether Mars level artificial gravity solves medical issues that we have with zero gravity. And since we know we can see the negative effects of zero gravity with people that have spent at least 6 months in space, then we need an experimental setup that allows us to test Mars gravity for at least 6 months.

So from that standpoint, spinning one fairly small inflatable module is unlikely to provide the data we need, for a number of reasons.

Also, there are negative effects that are introduced to the experiment the faster the rotation, and that could pollute your results, which is why larger diameter structures that rotate slower are preferred.

The other factor for single modules is how do you keep them rotating in a stable manner in space, where there is nothing holding them to a single axis of rotation - and weight imbalance would cause a wobble (or worse).

[tenkendojo]

5.9rpm, just within human tolerances.

Humans can tolerate up to 30 RPM. Some humans can't, but for a small station like you're describing, you get to pick your crew.

In general, unless we discover something new when we actually have a rotating station, you can use whatever RPM suits the purpose of the station. You aren't going to exceed human tolerances. As you need to accommodate a wider range of people, then the station is going to be larger, hence wider, hence have a lower RPM anyway.

Could you point me to the study that shows humans can tolerate up to 30 RPM? This number seems...quite high to say the very least. Even for a tiny 3-meter wide hab, 30 RPM would still translate to more than 3G's. Doesn't sound very tolerable for the long run.

[Coastal Ron]

Even for a tiny 3-meter wide hab, 30 RPM would still translate to more than 3G's. Doesn't sound very tolerable for the long run.

Depends on what you are testing for.

However such a setup is unlikely to provide results that answer the question of how much, or how little artificial gravity is needed to allow humans to live in space. And I think "living in space" is the real goal of building rotating space stations, so short duration testing may not be appropriate.

Before you propose any solution, first you need to understand what you will be testing for.

For example, when I started this thread it was because I felt we needed to better understand the effects of artificial gravity over long periods of time, meaning more than 6 months of a consistent environment. For me, I pick 6 months because we know that people that spend about 6 months of time on the ISS in zero gravity have measurable negative health effects, so the first step is to see if we can mitigate (or eliminate) some or all of those negative effects - and see what new negative side effects might be generated.

In order to test for six months or more, without a significant interruption, we would likely need a true space station, one that can continue to rotate while allowing for cargo and people to be moved on and off the station.

The hard part is making that rotating space station small enough that it can be affordable, while big enough that it can produce results that can be scaled up for the next generation of rotating space stations - which hopefully will be large enough to truly live on, not just stay for 6 months.

[Twark_Main]

As you need to accommodate a wider range of people, then the station is going to be larger, hence wider, hence have a lower RPM anyway.

One of the beauties of barbells is that they decouple the total volume and the RPM. 

But more fundamentally, I'm not sure whether I agree with your logic that accepting a wider range of people automatically must mean you have a higher total station population. You may still want to avoid eliminating 99% of the (non-superhuman nausea tolerance) mission specialist population, even if you don't have a station population of thousands.

In short, I don't think those two variables are as inexorably correlated as you suggest. Fortunately—thanks to barbells—they don't need to be!

[Asteroza]

BO throwing their hat into the ring? (pun intended)

New NPR article about retiring ISS. https://www.npr.org/2024/02/21/1232639289/international-space-station-retirement-space-stations-future

Interesting part is at the end

>Gatens says one piece of technology that is being developed at Blue Origin is a big rotating space station that, when finished, would have artificial gravity.

This is coming from Robyn Gatens, director of the ISS, so seems like a reliable source. This is the first confirmation I've seen of Blue Origin developing artificial gravity.

[Coastal Ron]

BO throwing their hat into the ring? (pun intended)

New NPR article about retiring ISS. https://www.npr.org/2024/02/21/1232639289/international-space-station-retirement-space-stations-future

Interesting part is at the end

>Gatens says one piece of technology that is being developed at Blue Origin is a big rotating space station that, when finished, would have artificial gravity.

This is coming from Robyn Gatens, director of the ISS, so seems like a reliable source. This is the first confirmation I've seen of Blue Origin developing artificial gravity.

Wow, this would be GREAT if true.

And while the first of anything is certainly a "testbed", we'll have to see what their goals are for their "big rotating space station" before characterizing it too much.

I would assume that Blue Origin plans to build it using New Glenn, which limits them to hard-sided payloads 7m in diameter (inflatables could exceed that of course). The big question would be if they are going directly for a wheel design, or if they are starting with a baton (i.e. Vast Spinning Stick design) or "X" design (like I have proposed).

[Asteroza]

BO throwing their hat into the ring? (pun intended)

New NPR article about retiring ISS. https://www.npr.org/2024/02/21/1232639289/international-space-station-retirement-space-stations-future

Interesting part is at the end

>Gatens says one piece of technology that is being developed at Blue Origin is a big rotating space station that, when finished, would have artificial gravity.

This is coming from Robyn Gatens, director of the ISS, so seems like a reliable source. This is the first confirmation I've seen of Blue Origin developing artificial gravity.

Wow, this would be GREAT if true.

And while the first of anything is certainly a "testbed", we'll have to see what their goals are for their "big rotating space station" before characterizing it too much.

I would assume that Blue Origin plans to build it using New Glenn, which limits them to hard-sided payloads 7m in diameter (inflatables could exceed that of course). The big question would be if they are going directly for a wheel design, or if they are starting with a baton (i.e. Vast Spinning Stick design) or "X" design (like I have proposed).

There's the risk this is actually referring to BO looking at O'Neil Island 3 type stations, as well as BO pulling back from immediate work not related to New Glenn recently so they may no longer be working on station work at all.

[Coastal Ron]

There's the risk this is actually referring to BO looking at O'Neil Island 3 type stations, as well as BO pulling back from immediate work not related to New Glenn recently so they may no longer be working on station work at all.

Well I guess the "glass half full" perspective is that maybe they are doing SOMETHING related to rotating space stations, and we certainly have a shortage of that, regardless what designs they are interested in. 

[Twark_Main]

The big question would be if they are going directly for a wheel cluster barbell design, or if they are starting with a baton...

Fixed. 

This assumes tin can  --> baton/X/Y/etc  --> wheel is the 'natural' progression, but of course that's far from certain.


However this is all a distraction. The real issue isn't rings vs barbells. The real issue is cans vs modular compartmentalized "skyscraper" construction. 

[mikelepage]

I feel like I've made and posted something like this before, but cannot find any sign of it.

I'm still working on my own thing, but I made this spreadsheet calculator as a reality-check on how much propellant it would take to spin a small toroidal space station up and down as necessary, and thought you all might find it useful. Propellant amounts to spin-up and down a space station actually seem quite reasonable (more-so if you're in LEO and starship-level volumes of propellant are being moved).

EDIT: Updated spreadsheet to incorporate TM's improvements, plus added an RPM line and fixed typo

[Twark_Main]

Just a couple precision tweaks:

Replaced approximate value of pi with PI()

Replaced approximate value of standard acceleration with exact value (9.80665 m/s²)

[mikelepage]

With the spreadsheet (now updated above) in hand. I think it's easier to see how big of a space station we can have before it starts becoming unfeasible to spin it up and down with each visiting vehicle.

The space station setup below is intended for LEO, and is largely for tourism and partial gravity science (I think Zero-G in-space manufacturing setups will have to be largely automated).

To that end I think it will be simpler to start without any central element - ie torus only. Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit. We would have two airlocks which are opposite each other on the torus and the starship's "weight" whilst spinning would be supported by two hooks of similar design to those on the catching arms of the Mechazilla towers.  Those modules would in turn be connected by steel cables which bisect the torus.

So this gives us three points of contact between each starship and the torus. This arrangement means the tankage and engine sections of starships would "hang" outwards from the torus, providing the 30m lever arms for the OMS thrusters as I've supposed in the spreadsheet. This also means we never need to have propellant tanks or thrusters on the station itself.

In fact, it would be much the same arrangement as the off-suggested "spin two starships around each other nose-to-nose, connected by cables" idea, except the addition of the torus structure would add significant stability and habitation space. 

The visiting vehicle schedule would (say) have a starship visiting the station in LEO every fortnight, alternating between the two airlocks. Once the incoming starship has launched, the two resident starships act to slow the station rotation down to nothing, after which the outgoing starship leaves and is replaced by the incoming starship and a new crew (i.e. crew/tourism stays of about a month).

In this scenario, each starship would be responsible for the propellant required for a full cycle of spin up and spin down (2x what is calculated in the spreadsheet). If a crew starship has a payload mass of 150 tons, could we imagine 10-12 tons of that being dedicated to maintaining the spin environment on a ~1000 ton rotating space station (as well as reboost, and/or keep it sun-facing)? I think so.

[redneck]

With the spreadsheet (now updated above) in hand. I think it's easier to see how big of a space station we can have before it starts becoming unfeasible to spin it up and down with each visiting vehicle.

The space station setup below is intended for LEO, and is largely for tourism and partial gravity science (I think Zero-G in-space manufacturing setups will have to be largely automated).

To that end I think it will be simpler to start without any central element - ie torus only. Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit. We would have two airlocks which are opposite each other on the torus and the starship's "weight" whilst spinning would be supported by two hooks of similar design to those on the catching arms of the Mechazilla towers.  Those modules would in turn be connected by steel cables which bisect the torus.

So this gives us three points of contact between each starship and the torus. This arrangement means the tankage and engine sections of starships would "hang" outwards from the torus, providing the 30m lever arms for the OMS thrusters as I've supposed in the spreadsheet. This also means we never need to have propellant tanks or thrusters on the station itself.

In fact, it would be much the same arrangement as the off-suggested "spin two starships around each other nose-to-nose, connected by cables" idea, except the addition of the torus structure would add significant stability and habitation space. 

The visiting vehicle schedule would (say) have a starship visiting the station in LEO every fortnight, alternating between the two airlocks. Once the incoming starship has launched, the two resident starships act to slow the station rotation down to nothing, after which the outgoing starship leaves and is replaced by the incoming starship and a new crew (i.e. crew/tourism stays of about a month).

In this scenario, each starship would be responsible for the propellant required for a full cycle of spin up and spin down (2x what is calculated in the spreadsheet). If a crew starship has a payload mass of 150 tons, could we imagine 10-12 tons of that being dedicated to maintaining the spin environment on a ~1000 ton rotating space station (as well as reboost, and/or keep it sun-facing)? I think so.

Or there is a truss/tower from one side of the torus to the other. Chopsticks counter rotate to zero relative to grab the ship. After grab, the chopsticks are gradually rotation matched to the station spin before "descending" to the lock areas of the torus. Eliminates need to spin up and down.

[edzieba]

With the spreadsheet (now updated above) in hand. I think it's easier to see how big of a space station we can have before it starts becoming unfeasible to spin it up and down with each visiting vehicle.

The space station setup below is intended for LEO, and is largely for tourism and partial gravity science (I think Zero-G in-space manufacturing setups will have to be largely automated).

To that end I think it will be simpler to start without any central element - ie torus only. Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit. We would have two airlocks which are opposite each other on the torus and the starship's "weight" whilst spinning would be supported by two hooks of similar design to those on the catching arms of the Mechazilla towers.  Those modules would in turn be connected by steel cables which bisect the torus.

So this gives us three points of contact between each starship and the torus. This arrangement means the tankage and engine sections of starships would "hang" outwards from the torus, providing the 30m lever arms for the OMS thrusters as I've supposed in the spreadsheet. This also means we never need to have propellant tanks or thrusters on the station itself.

In fact, it would be much the same arrangement as the off-suggested "spin two starships around each other nose-to-nose, connected by cables" idea, except the addition of the torus structure would add significant stability and habitation space. 

The visiting vehicle schedule would (say) have a starship visiting the station in LEO every fortnight, alternating between the two airlocks. Once the incoming starship has launched, the two resident starships act to slow the station rotation down to nothing, after which the outgoing starship leaves and is replaced by the incoming starship and a new crew (i.e. crew/tourism stays of about a month).

In this scenario, each starship would be responsible for the propellant required for a full cycle of spin up and spin down (2x what is calculated in the spreadsheet). If a crew starship has a payload mass of 150 tons, could we imagine 10-12 tons of that being dedicated to maintaining the spin environment on a ~1000 ton rotating space station (as well as reboost, and/or keep it sun-facing)? I think so.

Or there is a truss/tower from one side of the torus to the other. Chopsticks counter rotate to zero relative to grab the ship. After grab, the chopsticks are gradually rotation matched to the station spin before "descending" to the lock areas of the torus. Eliminates need to spin up and down.

That's a lot of mass to add and, systems to add, operate, and maintain, to avoid using some RCS prop (and requires power to spin up and spin down the visiting vehicles and gantry mass anyway). And systems that need to not fail in order to successfully visit and leave the station - making them safety-critical. Using ship RCS means using already safety-critical systems that are being carried up anyway, using propellant that is being carried up on each visit.

[Paul451]

Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit.

Am I reading right that you always have two Starships docked whenever the station is rotating? With one (?) swapping-out for a new ship during despin for each resupply/recrew mission?

Do you see it as being three (or more) Starships dedicated to the station, or just "whatever standard ships are available on the day" but with a four-week on-orbit mission time?

[mikelepage]

Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit.

Am I reading right that you always have two Starships docked whenever the station is rotating? With one (?) swapping-out for a new ship during despin for each resupply/recrew mission?

Correct. This is also why I wanted to check how long it might reasonably take to spin up/down: If spin-down takes around half an hour as per the spreadsheet, then it's possible to wait until the launch of the incoming starship is successful - then in the 6-24 hours before rendezvous, you have time to spin down the station and undock the departing starship. Expected total time the station spends in zero-G hopefully much less than 1 sleep/wake cycle for those staying onboard.

Do you see it as being three (or more) Starships dedicated to the station, or just "whatever standard ships are available on the day" but with a four-week on-orbit mission time?

It could be as little as three. Maybe XYZ hotel chain decides to run those missions out of a single launch site with a small fleet of subcontracted starships. But also this could also be an extended form of point to point travel around Earth, cycling through a roster of end destinations, and how long you spend in space is determined by your preferred launch and landing cities. For example if it was cycling between say KSC Florida, Australia, Japan, Scotland and India, you might decide to start or end your international trip with some number of weeks in space.

I'm actually not sure what the pros and cons of either scenario would be, but the business case would be pretty exciting either way.

[LMT]

I wanted to check how long it might reasonably take to spin up/down...

Modern GNC can avoid spin-down.  1 2 

Docking is feasible with uncooperative tumbling targets.  Cooperative targets are easier to work with, easier still when docking near CoG and without tumble.

[Coastal Ron]

Visiting starships would dock in an arrangement with their noses pointing inwards towards the center of rotation, and stay in place for the duration of their visit.

Am I reading right that you always have two Starships docked whenever the station is rotating? With one (?) swapping-out for a new ship during despin for each resupply/recrew mission?

Correct. This is also why I wanted to check how long it might reasonably take to spin up/down: If spin-down takes around half an hour as per the spreadsheet, then it's possible to wait until the launch of the incoming starship is successful - then in the 6-24 hours before rendezvous, you have time to spin down the station and undock the departing starship. Expected total time the station spends in zero-G hopefully much less than 1 sleep/wake cycle for those staying onboard.

I was ambivalent at best when you first proposed this due to what I thought the energy requirements would be, but then your spreadsheet analysis provided a result that surprised me, so now I'm thinking there could be one or more use cases where this would make sense.

As you stated originally this would be for a station in LEO, but that is likely where artificial gravity testbeds will be located anyways, so all the more reason to keep looking into this concept. Nice!

[Twark_Main]

I wanted to check how long it might reasonably take to spin up/down...

Modern GNC can avoid spin-down.  1 2 

Docking is feasible with uncooperative tumbling targets.  Cooperative targets are easier to work with, easier still when docking near CoG and without tumble.

For those who don't feel like going down (yet another) insufferable self-link rabbit hole, the actual papers being cited are Oestreich 2021, Silvestrini and Lavagna 2022, and Huang et al 2022.