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Comment by Nevermark | Hacker News Reader

I didn't see any mention of having a spinning surface.

A tapered cylinder "gravity gym" with adjustable angled walls, and variable speed spinning, could smoothly create much greater "gravity".

Spin gravity would also enable body weight exercises, core exercises, stationary or small area cardio like exercise bikes, VR games, yoga, etc. Even sleeping.

EDIT: I missed this:

> but Moon-based centrifuges allowing locomotion inside would pose technical challenges

Still think it will be inevitable. Far more useful physically and psychologically. "Spinning surface" is a simple challenge, compared to "low-g health deterioration" and "bored to death of running in circles".

Equipment like this might resolve issues with off-world childbearing. Time to "spin up" some space rabbits and see what we get! (Hopefully not tribbles.)

Spin areas will surely become ubiquitous in all low gravity colonies.

Startup anyone?

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Wild idea: build one on earth to simulate 1.1G (or higher; whatever would still be comfortable) and put gyms, hotels, swimming pool, living quarters, etc. in it. Being in it for extended periods of time would build up muscles and bones. That would likely be something that fitness people and professional athletes would be interested in. And it's a good dry run for building and operating these things on Mars and the Moon. If we can make these things work on Earth, making them work in lower gravity is only going to be easier as the g-forces would be lower.

A train or roller coaster on a slightly tilted circular track would probably do the job. A slight tilt would just move the gravity vector orthogonal to the floor.

Why did nobody do this yet? It would totally be a great prototype for stuff in orbit.

Closest thing I can think of is rotating houses / restaurants, but they go very slowly.

It would have to be big enough to avoid people getting dizzy, and even then it would still be a factor I think. That said, size/scale is less of a concern on the moon I would argue.

You inspired me to look up if there were many still going and I was saddened to discover there are no longer any operational ones left in the UK.

All parts would be spinning at the same angular velocity, so unless it's really far away from its centre of rotation (expensive, inconvenient) you'd experience more acceleration near the centre than at the edges.

Maybe that doesn't matter.

One of the commenters here has the right idea. Train riding forever on circular slanted track could easily house some living spaces, offices and gyms. You could book a stay there for few weeks and after that feel like you are walking on air once you come back to normal life.

Circular dome colony over a very large rotating space, running on concentric rings of superconducting rails. Spokes of slidable inner-outer weights to counter balance its residence’s movements.

Running on reliable constant nuclear power, from a safe distance.

Maximum gravity at the tilted edges. Only natural gravity at the center. Enter & exit from a tunnel that connects under the center.

Aside from the challenges of location & distance from Earth, if we can build small mobile cities on water (mega cruise lines) on the untamed ocean in Earth gravity, surely a small stationary spinning platter city in low gravity is possible.

I think humans are going to find out that one g has many uses besides health. Good for a lot of manufacturing too. Gravity is a stabilizer, vertical organizer, anchor. Just as low gravity will have many advantages. Being able to quickly “adjust” gravity, by moving location, will be significant.

> Being able to quickly “adjust” gravity, by moving location, will be significant.

Who is doing the adjusting and the moving?

I don't think you'd want to move anything large. You'd build eg your factory in the environment where it's best; and build a second factory in a different environment, instead of moving them around.

However, if you eg making computer chips, you might move those around between different environments, depending on the processing step.

Yes, I meant move materials and parts between g-force specific equipment.

If entire factories needed to "move" up and down in g-forces, they should be in their own variable spin bowls! Not sure what kind of factory that would be.

I just keep thinking about this short film[0] that explores the views you can see with rotational artificial gravity, and how nauseating it could be :)

[0] https://vimeo.com/869858712 also available as https://www.youtube.com/watch?v=iiPmgW21rwY

Just point the axis at the major body of interest, Earth, moon, Jupiter, etc., and it would slowly rotate in a stationary position, instead of spinning around you.

Or align the axis with the major light source if that is different, like the sun for inner solar system locations, and at least the lighting won't keep moving around.

Not much different from watching scenery go by in a vehicle then.

https://en.wikipedia.org/wiki/Tilting_train

You don't need to have a tilting train, you can just tilt the track.

Spinning stuff in air takes more energy than spinning stuff in a vacuum.

You would likely put these in air on the moon as well. Depends a bit on your design.

But then we do operate trains in our atmosphere so this is a solvable problem. The advantage outside of our atmosphere is of course that aerodynamics don't matter, which indeed would make things more energy efficient. Also there would be no weather (or very little of it on Mars), no humidity.

If the track is enclosed in a smooth symmetric enclosure, either a circle or flat dome, the air within the enclosure will spin along with the train or other tracked constructions, instead of impeding them.

I imagine some texturing on the inside of the enclosure could create small scale surface turbulence that even reduces the minimal friction there.

The acceleration needed to make a turn with radius r at speed v is. v²/r (https://courses.lumenlearning.com/suny-physics/chapter/6-2-c...)

If that combined that with earth’s gravity has to give you 1.1g, that has to be (via the Pythagorean theorem) about 0.2g or 2m/s². Let’s pick r = 100m. Then, v² has to be 20, giving as a velocity of about 16 km/hour. r = 1km would require about 50km/hour.

Sounds doable, until you consider your “put gyms, hotels, swimming pool, living quarters, etc. in it”. That’s a lot of mass and space.

Centrifuges that we put potential astronauts and fighter pilots in are a lot smaller.

On the other hand, there’s the idea of “a massive floating railway, Maglev-style, which will travel along a track with a radius of 2.5 kilometers within an underground vacuum tunnel. The machine will run on excess energy generated from wind and solar, and it can reach speeds up to 2,000 km/h. When the renewable energy production is insufficient, the kinetic energy from the train movement will be reconverted and sent to the grid.” that engineers claim can be built (https://www.greenoptimistic.com/energy-train-mph/). That would hit over 10g and weigh a lot more than that hotel. I can’t find updates, though.

Reply to self: the MVP for this probably is to walk around with a backpack that’s 10% of your body weight.

That’s a lot cheaper and for many sports likely would bring the same benefits.

That's why I proposed using a train. Minus the swimming pool, totally doable to have one driving around at relatively low speeds. We use trains to move many tonnes of cargo around already. So, I don't see the mass as a show stopper.

> build one on earth to simulate 1.1G (or higher; whatever would still be comfortable) and put gyms, hotels, swimming pool, living quarters, etc. in it. Being in it for extended periods of time would build up muscles and bones.

Is that any better than ankle weights? Or wrist, I suppose.

The difference between weights on your body and higher gravity field is that with higher gravity all of you feels the force equally at the same time, so you're not putting excessive strain on certain parts of your body while neglecting others (such as internal structures).

You probably know this already, but for a while people were toying with the idea of a "childbirth centrifuge". https://patents.google.com/patent/US3216423A/en

There's probably a reason it never caught on.

Reason one - We already have gravity here.

Reason two - Childbirth + vertigo? WTF!

Clearly they should have gone with a rudimentary linear accelerator such as a bungy drop or bouncing elevator type system!

> Clearly they should have gone with a rudimentary linear accelerator

Like a railgun.

While on the subject of inventions to aid with childbirth, I'll leave this here:

https://science.howstuffworks.com/science-vs-myth/everyday-m...

Also the subject of an opera. http://www.henryakona.com/the_blonsky_device.html

On the Moon, at normal pressure, humans shoud be able to get enough exercise in a jungle gym, or by donning a set of wings, flapping them to fly.

Given that there is some gravity, putting on a weighted suit to increase their mass would also make sense, although it'd be unwieldy if it's not distributed exactly the same. Plus, getting weight into space is expensive... although probably not as expensive as building a wall of death or spin gravity structure.

Why wall of death? It's gonna be just a neat cylindrical room with vaguely paraboloid walls. Even if you stop running suddenly, dropping down from 2-3 meters in 1/6 g shouldn't be anything more than inconvenient.

Weighted suit wouldn't help with the weight of your organs. They are accustomed to hanging inside you at 1g. Running on wall would provide them with that.

I was going to say “I’d be surprised if organ support is a large issue to an adult. We already have long term astronauts and people who are bed ridden for a long time during recovery. I would expect an issue during development though.”

Turns out there is research in this direction: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2379624/pdf/can...

It seems to say that there is a long term impact on connective tissue hardening… but it blames lack of stretching; not lack of downward force. Any regular movement would seem to fix that.

However, internally, organ tissue probably ‘bounces’ more due to gravity during movement… so less gravity means less flex of connective tissue.

TLDR: you seem to be right

> long term astronauts and people who are bed ridden

And those people lose a lot of bone mass, muscle mass, and need physical therapy to get back to normal function in 1G. Two months of bed rest will absolutely ruin you. There's a good reason astronauts need to be fit to begin with!

6 months in space causes bone loss equivalent of 20 years of aging. Return to Earth, do physical therapy for 1 year, and you're still "10 years older" as far as bone loss goes. (https://www.sciencenews.org/article/space-bone-loss-density-...).

Generally, as far as I know, bone growth is triggered by impacts (think running etc), and is hard to stimulate with just muscle exercises.

> Generally, as far as I know, bone growth is triggered by impacts (think running etc), and is hard to stimulate with just muscle exercises.

Maybe they should do jumping while being pulled "down" by rubber bands.

The current microgravity solution is a treadmill for running that rubber bands pull you down to.

> Why wall of death?

I think that's just what the cylindrical room is often called when it's used for motorcycles. The paper repeatedly references it, abbreviated "WoD." I don't think there's any death involved. :)

There are rocks on the moon. You don’t need to bring weights from earth.

I assume they’ll eventually just build a big gravitron. The seals would be tricky (I guess the axle it spun on could contain a ladder and door?)

Of course they could simply stop spinning it whenever they needed to open an airlock.

(Or just put it in orbit, where these problems are easier to deal with and you don’t need to deal with day/night radiation shielding/heating.)

Spin gravity in orbit has its own issues. Most notably you can't anchor the structure anywhere, so won't spin around the spin axis you want but around its center of mass. A center of mass that will shift as people move around, equipment is moved, etc.

Another issue is that you need a certain scale, otherwise the Coriolis force as well as differential gravity (the gravity at your feet being higher than that at your head) lead to disorientation and comfort issues. The lower limit seems to be about 40 feet, incidentally the size of a typical graviton on carnival on earth. That's quite a bit wider than the typical rocket, and for now we are much more comfortable with assembling stuff in a gravity well than in orbit.

> That's quite a bit wider than the typical rocket

You can have two habitats connected by a center tube, like an I. Rotate about the center of the I. Or a habitat and a cable connected to a counterweight.

It's not really necessary to build a wheel.

In orbit, you don't even need the tube, it can be a single habitat with retractable cables attached to a counterweight of useful material that isn't immediately needed.

It could be a blown up multiwalled sphere with the heavy equipment in a solid cylinder in the middle. The walls would naturally be a bit bouncy, if under the pressure of the internal air.

A big arena for playing professional sports could make a significant amount of money through televised sporting events.

The rotation axis could be stabilized actively by shifting counterweights. But the dynamics of the structure change depending on whether the counterweights move radially or tangentially. Rotation speed would fluctuate slightly in either case. This sounds like an interesting control problem!

Just put a centrifuge under a static dome. No seals needed.

In the Luna series they discuss this, they basically have a central axis where you enter and then can 'step' up higher to faster spin rates/more gravity (basically a tapered cone)

It's easier in space. I suspect it will happen there first and predominantly.

You know you have to fly all this stuff up there, right? You can dig out one of these pits with a shovel.

Self-sufficiency off-world is going to be much easier if people are healthy and happy.

A "gravity gym" is going to be basic healthcare. Wherever we go for the long term, we will ship and/or construct them.

Yeah, that's what they said, a self sufficient way of constructing a gravity gym.

Separate facilities for work and life, interconnected by a rollercoaster commute. What else has sci-fi left out?

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