# Creating artificial gravity

• I
• Physics guy
In summary: There's a general discussion about this on Wiki but you can do the sums yourself (a = (2πf)2/r) and play with the variables to give you g at floor level and to see what it's like at 2m height. The Coriolis force is something that any experienced (large boat) sailor could adapt to, I'm sure. I would think that sky rotation would need to be kept to much less than 1rpm to avoid visual... discomfort? disorientation?

#### Physics guy

TL;DR Summary
With human civilisation looking forward to colonizing space the force of gravity can be the game changer
Space exploration plays an important role in expanding our human civilisation beyond earth. But the major challenge is our difficulty of working in zero gravity. So the only possible explanation I could think of is creating artificial gravity. How can this be done ?

Physics guy said:
Summary:: With human civilisation looking forward to colonizing space the force of gravity can be the game changer

Space exploration plays an important role in expanding our human civilisation beyond earth. But the major challenge is our difficulty of working in zero gravity. So the only possible explanation I could think of is creating artificial gravity. How can this be done ?
Artificial gravity is the least of your problems. Acceleration at ##g## or sufficient rotation will take care of that.

Human Civilization is yet to escape the grip of COVID-19. I'm just looking forward to getting out of London; space colonization will have to wait.

hutchphd, sophiecentaur, lomidrevo and 3 others
Physics guy said:
Summary:: With human civilisation looking forward to colonizing space the force of gravity can be the game changer

creating artificial gravity. How can this be done ?
As @PeroK said, through acceleration. The easiest acceleration to sustain is centripetal.

Dale said:
As @PeroK said, through acceleration. The easiest acceleration to sustain is centripetal.
But will that mean people will have to start standing parallel to the ground since circular motion will create a centrifugal force in the sideways direction.

Physics guy said:
But will that mean people will have to start standing parallel to the ground since circular motion will create a centrifugal force in the sideways direction.
Centrifugal means "away from the centre"; as opposed to centripetal, meaning "towards the centre". There is no sideways force associated with uniform circular motion.

PeroK said:
Centrifugal means "away from the centre"; as opposed to centripetal, meaning "towards the centre". There is no sideways force associated with uniform circular motion.
I have experience of myself being thrown to the side while moving in a merry go round. But will this solve the problem of gravity

PeroK
Physics guy said:
I have experience of myself being thrown to the side while moving in a merry go round. But will this solve the problem of gravity
Yes, you're right, that's the Coriolis force, which needs to be taken into account as well. It's all here:

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

Physics guy
Physics guy said:
But will that mean people will have to start standing parallel to the ground since circular motion will create a centrifugal force in the sideways direction.
See https://en.m.wikipedia.org/wiki/Artificial_gravity

That is resolved.

Physics guy said:
So the only possible explanation I could think of is creating artificial gravity. How can this be done ?
As an alternative (although not very feasible), you could somehow "miraculously" ensure linear acceleration of your spacecraft . According to equivalence principle, that couldn't be distinguished from gravity at all. At least in sufficiently small regions (for example the spacecraft itself), where tidal forces plays no role.

But the rotational artificial gravity discussed in previous post is surely more feasible way.

Oh, and one more drawback of the rotational artificial gravity wasn't mention yet. The force you would feel would depend on how far you are located from the rotational axis.

lomidrevo said:
Oh, and one more drawback of the rotational artificial gravity wasn't mention yet. The force you would feel would depend on how far you are located from the rotational axis.
Yes true but I don't think that will be a major concern

lomidrevo said:
As an alternative (although not very feasible), you could somehow "miraculously" ensure linear acceleration of your spacecraft .
Given this is all essentially engineering fiction at the moment, I'm not sure that's a non-starter any more than any other ideas. Even for a unmanned trip to the nearest star, you need significant sustained linear acceleration.

Physics guy said:
But will that mean people will have to start standing parallel to the ground since circular motion will create a centrifugal force in the sideways direction.
I'm trying to picture this in my head. ?

PeroK said:
Given this is all essentially engineering fiction at the moment, I'm not sure that's a non-starter any more than any other ideas. Even for a unmanned trip to the nearest star, you need significant sustained linear acceleration.
The fuel needed to produce constant (that's the word you mean?) acceleration at g would soon get out of hand and then you'd be in free fall in interstellar space. No artificial g then. Also, you could do no manoeuvring on arrival; you'd have needed to calculated precisely when to start braking when you're about half way there.

(a = (2πf)2/r) and play with the variables to give you g at floor level and to see what it's like at 2m height. The Coriolis force is something that any experienced (large boat) sailor could adapt to, I'm sure. I would think that sky rotation would need to be kept to much less than 1rpm to avoid visual fatigue.

Physics guy said:
Is there any possibility that we can undergo circular motion without the need for fuel by exploiting magnetic force.
Once you are spun-up you need no fuel. You need a 'reaction torque' to start spinning and something needs to gain an equal and opposite angular momentum. Reaction wheels are used to orientate satellites but that doesn't help if you want constant spinning. Tangential jets give a net angular momentum to the craft.

If you want "magnetic Force' to do the job then you need an external force or torque. The Earth's magnetic field is very weak but you could imagine a tiny torque from internal solenoids, bearing against this. You would need a lot of current for an electromagnet or just a very heavy set of permanent magnets - neither very good value in terms of payload.

sophiecentaur said:
The fuel needed to produce constant (that's the word you mean?) acceleration at g would soon get out of hand and then you'd be in free fall in interstellar space. No artificial g then. Also, you could do no manoeuvring on arrival; you'd have needed to calculated precisely when to start braking when you're about half way there.
Is there anyway to exploit magnetic force for powering it

Physics guy said:
Is there anyway to exploit magnetic force for powering it
AS I said before, you need an external force (something to push against ) a rocket pushes at the ejecta and it accelerates forwards. If you have a (however strong) magnet on board, what can it push against? Planetary magnetic fields are weak enough close into them. Hardly detectable in deep space.

In any proposal, you have to consider Newton's first law of motion. No external force, no acceleration. Using magnetism doesn't in any way get past that problem.

Don't worry about the COVID-19...the radiation will kill it. Two for one.

sophiecentaur said:
AS I said before, you need an external force (something to push against ) a rocket pushes at the ejecta and it accelerates forwards. If you have a (however strong) magnet on board, what can it push against? Planetary magnetic fields are weak enough close into them. Hardly detectable in deep space.

In any proposal, you have to consider Newton's first law of motion. No external force, no acceleration. Using magnetism doesn't in any way get past that problem.
But for centripetal acceleration a simple contact force would suffice? But our task is the maintain the tangential velocity

Physics guy said:
But for centripetal acceleration a simple contact force would suffice? But our task is the maintain the tangential velocity
Centripetal acceleration can be sustained by internal forces and conservation of angular momentum. Linear acceleration needs a sustained external force.

PeroK said:
Given this is all essentially engineering fiction at the moment, I'm not sure that's a non-starter any more than any other ideas. Even for a unmanned trip to the nearest star, you need significant sustained linear acceleration.
I am more decent, I was thinking rather about intra-solar-system travels than interstellar :)

Who knows, maybe in few decades (*), we'll have manned fusion driven spacecraft s, providing constant linear acceleration ##g##:
https://www.nasa.gov/directorates/spacetech/niac/2012_Phase_II_fusion_driven_rocket/

(*) optimistically supposing that humans don't have to fight more severe problems...

Physics guy said:
Yes true but I don't think that will be a major concern
It can be a big issue if your spacecraft is not large enough ;)
From wiki article already shared in previous posts:

As such, to simulate gravity, it would be better to utilize a larger spacecraft that rotates slowly. The requirements on size with regard to rotation are due to the differing forces on parts of the body at different distances from the center of rotation. If parts of the body closer to the rotational center experience a force significantly different from parts farther from the center, then this could have adverse effects.

As for the coriolis force making things weird with a rotating spacecraft , I doubt it'd be that bad. The coriolis force alters the paths of objects moving towards/away from the axis of rotation. So if you're throwing a ball "up" in a rotating spacecraft , it'd move in a weird arc. But I doubt it'd be very much of a problem in other contexts. I could imagine that standing/sitting/laying down could feel rather weird until you get used to it, but our bodies are pretty adaptable.

With regard to achieving sustained acceleration, I think the only way to do that is to use a fuel source outside of the craft, such as a Bussard ramjet, but that may be utterly unfeasible. Even if the ramjet is feasible, the accelerations will be nowhere near 1g.

If the craft carries its fuel with it, sustaining 1g just can't be done: in order to make a journey to the nearest star, even converting the total mass energy of the craft to propulsion won't do it. I don't know if it's possible even with lower accelerations. The most effective drive we can build today that has a chance of doing this is a nuclear-powered ion propulsion drive. This is basically a particle accelerator. The high velocity of the expelled ions keeps the propellant requirements down to a minimum. I haven't run the numbers, but it's probably not possible to get a craft to a star in anything approaching a reasonable time frame using this kind of drive.

kimbyd said:
such as a Bussard ramjet
Using stuff you come across, rather than carrying it with you is a handy technique. A propellor is a great example of this - in water or in air. It's also like feeding your donkey on the conveniently growing grass on the wayside.
Feasibility must depend on the density of availability of suitable material. Some really good route planning would be essential.

jabberwok said:
In some Sci-Fi books they create small black holes inside the ship.
Is it really worth introducing Sci-Fi ('Fiction') ideas into an Engineering problem? We might as well have a man with a magic wand on board to take us wherever we want.
And before quoting Arthur C Clarke, his ideas came from informed sources. The only real error in his fiction was the time scale for his events - very optimistic.

I found a very interesting video on this topic

PeroK and sophiecentaur
I detect a certain air of snobbishness in some of the responses. Ray guns were predicted by SciFi writers long before it became a reality with tactical lasers. Rockets in general were the fodder of SciFi before they weren't. We can't be too arrogant to think that there's not another remarkable discovery around the corner.

Remember the head of the US Patent Office in the late 1800s saying that "Everything that can be invented has been invented." or the head of IBM in the 70s stating, "Who would ever want a computer in their home." We're not really good at predicting something that hasn't been discovered yet. Heck, no one even predicted the fall of the Berlin Wall and the Soviet Union.

In my lifetime alone, neither DNA or Lasers were discovered when I was in high school. All we can say is, "From what we understand now, artificial gravity seems not to be feasible." I'd love to go into a time machine and come our 150 years from now and see just what has happened.

I, for one, can't even imagine what's going to replace the LED. I mean seriously, we've developed a light source that goes from electricity to light with little or no heat, in just over a Century from the invention of the light bulb itself. How is that possible? And the new Apple iPhone 12 pro has 11.8 Billion transistors on its CPU. Really? In my lifetime we've gone from IBM 370 that had only 150k memory to this? Its memory consisted of those ferrite rings hand installed in the matrix of crossed copper wires. So how can we sit here and say conclusively that we know what going to happen regarding space travel. We don't! For all we know we may be able to tap into Dark Energy or Dark Matter. I attended a lecture in the 50s with my dad at the Franklin Institute in Philly when Fred Hubble himself talked about the Big Bang. And that's when I was a teenager. We're just starting out on this journey.

Dr Wu, weirdoguy, PeroK and 2 others
trainman2001 said:
Rockets in general were the fodder of SciFi before they weren't.
The Chinese used rockets hundreds of years ago. Technology has just improved on them. The were never just Science Fiction within the life of that genre.

What is Sci-Fi other than published imagination. What is invention without imagination. All things begin as imagination. Believe otherwise makes you extremely weak minded.

weirdoguy
jabberwok said:
What is Sci-Fi other than published imagination. What is invention without imagination. All things begin as imagination. Believe otherwise makes you extremely weak minded.
Most imagination takes us nowhere (the tip of the iceberg has all the value). Imagination only gets scientific results after serious application to problems. 'Weak-mindedness' is the domain of seekers of churned-out magic instead of reality (readers more than writers).

A good SciFi book is good because of the plot, the style and the characterisation. Azimov's Science was mostly nonsense and you had to suspend your disbelief from beginning to end but the fantasy intergalactic adventure situations in the Trilogy were brilliant. I can't think of any serious accurate predictions in his books but I remember far more about them. 10/10 for imagination and spark.

Arthur C Clarke's books had good technology predictions but they are pretty run of the mill in many other respects. Great respect for his Science and 'applications of Science' / future technology but his stories were pretty pedestrian, imo. 7/10, worth reading but the spinning space station and the geostationary broadcast satellite 10/10 for accurate predictions.

weirdoguy and russ_watters

I think that pause has released us all from the thread's grip.

kimbyd said:
So if you're throwing a ball "up" in a rotating spacecraft , it'd move in a weird arc.
Weird only insofar as the conditioning you’ve had in living in standard Earth gravity.

It wouldn’t be “weird” after a few weeks. The brain is amazingly plastic.

Dale and sophiecentaur
sophiecentaur said:
Is it really worth introducing Sci-Fi ('Fiction') ideas into an Engineering problem? We might as well have a man with a magic wand on board to take us wherever we want.
And before quoting Arthur C Clarke, his ideas came from informed sources. The only real error in his fiction was the time scale for his events - very optimistic.
Our current state of technology is a series of realized ‘fiction.’