Artifical gravity on spaceships

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  • #1
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The only plausible solution for this is rotation (maintain 1g acceleration for long time requires insane amount of energy).
What kind of problems caused by this? If living habitats rotate, the whole ship will rotate unless the habitats are detached somehow. It affects manuevering. Is this a very hard problem, or nothing that cant be solved by a good computer?
Is there any way to prevent the rotation of the axis of the ship without wasting much fuel and erode the joints?
 

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  • #2
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Just off the top of my head you'd definitely have to deal with the Coriolis force. Maybe counter rotating cylinders would be a thing?

Although it's for purposes of scifi writing if you're designing your own rocket you might benefit from this site:

http://www.projectrho.com/public_html/rocket/basicdesign.php
 
  • #3
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Just off the top of my head you'd definitely have to deal with the Coriolis force. Maybe counter rotating cylinders would be a thing?

Although it's for purposes of scifi writing if you're designing your own rocket you might benefit from this site:

http://www.projectrho.com/public_html/rocket/basicdesign.php
At this point, stress of the cargo bay with rotating axis isnt my main concern. The living ring should have at least 1`00m radius to avoid motion sickness. The cargo bay and reactor core can be much smaller in diameter.
 
  • #4
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At this point, stress of the cargo bay with rotating axis isnt my main concern. The living ring should have at least 1`00m radius to avoid motion sickness. The cargo bay and reactor core can be much smaller in diameter.
Here's quite an in-depth discussion of motion sickness in relation to spaceflight:

http://www.projectrho.com/public_html/rocket/humanfactor.php

And yes, I like this site. Both for the subject itself (space, science and sci-fi), but I also like the density of information per page as I'm sometimes offline for longer periods in which the cached pages provide lots of entertainment. :)

"Canned monkeys don't ship well." :)
 
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  • #5
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Otherwise i wonder, could a spin ship shift its axis without using thrusters?
Move a large weight left, then the rest of the ships back move right. After a half turn, do the opposite, weight moves to left, back of ship right again.
Or is it total nonsense?

If the axis can be positioned properly, acceleration and deceleration isnt affected by rotation.
 
  • #6
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Or is it total nonsense?
You mean "can I move the center of mass by only internal rearrangements?"
 
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  • #7
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You mean "can I move the center of mass by only internal rearrangements?"
I guess my phrases werent the best, but no. I dont want to move center of mass, but the axis of the spin ship with the thrusters on the end. The center of mass dont change course until thrusters dont fire.
My problem was how to perform course corrections when whole axis rotates?
 
  • #8
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Maybe i am still not clear enough.
So the whole ship is rotating but i dont want to simply speed up or slow down, but shift course. If there is a thruster on the side of the ship, it will rotate too. So that make manuevering difficult with side thrusters.

Can it be solved by shift main axis with internal arrangement, then use main thruster?
 
  • #9
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Can it be solved by shift main axis with internal arrangement,
Do you mean "can I move the angular momentum axis by only internal rearrangements without applying an external torque?"
 
  • #10
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You want to spin that parts that need gravity, which is typically where the people are. So you have a wheel (or two of them counter-rotating) that spin independently of the rest of the ship. There seems to be little reason to put cargo in high gravity.

As for turning the ship without thrusters, there is conservation of angular momentum to worry about. That's why you have two wheels. If angular mometum is then zero, the ship can be re-oriented with gyros, without using any thrusters. It cannot be done quickly (at least not practically), but it can be done with minimal energy expenditure.
 
  • #11
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Do you mean "can I move the angular momentum axis by only internal rearrangements without applying an external torque?"
Yes.
 
  • #12
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You want to spin that parts that need gravity, which is typically where the people are. So you have a wheel (or two of them counter-rotating) that spin independently of the rest of the ship. There seems to be little reason to put cargo in high gravity.

As for turning the ship without thrusters, there is conservation of angular momentum to worry about. That's why you have two wheels. If angular mometum is then zero, the ship can be re-oriented with gyros, without using any thrusters. It cannot be done quickly (at least not practically), but it can be done with minimal energy expenditure.
How can it be achieved that the wheels spin independently from the rest of the ship? They can be detached if ship dont accelerate. But ion thrusters should generate constant thrust.
 
  • #13
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How can it be achieved that the wheels spin independently from the rest of the ship? They can be detached if ship dont accelerate. But ion thrusters should generate constant thrust.
Using bearings. A car wheel spins independently of the car, and yet (most of the time) do not part company with the car when ion-thrusters accelerate the whole business.

Really, Ion thrusters? Efficient, but very low power. The people will all die of old age before the ship gets anywhere. Anyway, I'm just commenting on how a wheel can spin without spinning the whole ship.
 
  • #14
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Do you mean "can I move the angular momentum axis by only internal rearrangements without applying an external torque?"
Yes.
How does this conserve angular momentum?
 
  • #15
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How does this conserve angular momentum?
So, does that imply that torque can be generated but the rotation of the living ring slows down in return?
 
  • #16
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Using bearings. A car wheel spins independently of the car, and yet (most of the time) do not part company with the car when ion-thrusters accelerate the whole business.

Really, Ion thrusters? Efficient, but very low power. The people will all die of old age before the ship gets anywhere. Anyway, I'm just commenting on how a wheel can spin without spinning the whole ship.
So the basic design should be central part with thrusters and two large wheels rotating in opposite directions, their axis is perpendicular to central part.
Can they rotate compared to central part with air tight joints?
 
  • #17
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So, does that imply that torque can be generated but the rotation of the living ring slows down in return?
Where did you get the idea I said that?

Can the angular momentum change without an external torque applied?

If you are struggling with that, try the linear version:

Can the momentum change without an external force applied?
 
  • #18
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So the basic design should be central part with thrusters and two large wheels rotating in opposite directions, their axis is perpendicular to central part.
Can they rotate compared to central part with air tight joints?
Almost every design I've seen has one wheel, and the axis parallel to the direction of thrust. Otherwise the gravity goes up and down in the wheel, which will very much cause motion sickness.
The two wheels is there to cancel angular momentum. This part is often omitted because they don't have intentions of reorienting the ship during the trip, but the pair of wheels makes it easier to face it whichever way you want, without thrusters.

Engines can spin with the ship. There's just no reason why they wouldn't function that way. Many rockets/missiles spin as the ascend, which increases the stability of the thing. The center portions of a rotating ship will be lower gravity than further out. If the main ship is not to rotate, or there are two counter-rotating wheels, then yes, you need to design some joints that are air-tight.

Notice that nobody has ever made anything like this. The ISS is up there and they leave those guys weightless for months rather than all the extra engineering that would go into putting up a spinning module. The problems are real.
 
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  • #19
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Where did you get the idea I said that?

Can the angular momentum change without an external torque applied?

If you are struggling with that, try the linear version:

Can the momentum change without an external force applied?
Sorry but i really dont see why they are the same. I can still spin the wheels of a bicycle if i sit on it, and we levitate in zero G.

Or another examaple. I kick a box on the space station. Dont i change my angular momentum? What if i tie the box to my belt with a long rope. Will it cancel my spin?
 
  • #20
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I can still spin the wheels of a bicycle
By applying an external torque to them.

I kick a box on the space station. Dont i change my angular momentum?
The box applies an external torque to you.

Before we get further, we should figure out where the difficulty is. Do you not believe [itex]\tau = \frac{dL}{dt} [/itex] or are you having difficulty applying it?
 
  • #21
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Sorry, is there some some reason the OP isn't simply using a gyroscope? or am I missing it?
A massive flywheel at the center of mass will do fine to impart ship rotation.
 
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  • #22
DaveC426913
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BTW, there are other configurations for artificial gravity that you may not have examined.

It doesn't have to be just one section the ship. Tie two sections of the ship with a cable and have them spin about their CoM.

The nice thing about this is that you can make the cable of arbitrary length - say, a few hundred metres (assuming it's strong enough) and then you can get a nice high g value while minimizing the Coriolis force.

This would only be practical if your journey were mostly straight line, and not much maneuvering. You'd have to reel it in for maneuvering.

1599594444709.png
 
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  • #23
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By applying an external torque to them.



The box applies an external torque to you.

Before we get further, we should figure out where the difficulty is. Do you not believe [itex]\tau = \frac{dL}{dt} [/itex] or are you having difficulty applying it?
I am having pretty much difficulty with handle the different directions, radiuses.
I guess it is wrong how i wrote that torque generation (maybe i am so accustomed to having at least air as an outside force), but is it total unachievable without thrusters?
In case of bicycle i can apply external.force while i am still on the bike.
 
  • #24
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Sorry, is there some some reason the OP isn't simply using a gyroscope? or am I missing it?
A massive flywheel at the center of mass will do fine to impart ship rotation.
If axis doesnt rotate but living thing does, their joints has to be airtight while they rotate.
 
  • #25
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If axis doesnt rotate but living thing does, their joints has to be airtight while they rotate.
That is not a significant technical challenge.

Note, this topic was also discussed a month ago, and NASA had proposed/considered including a module like this in the ISS. There really aren't any significant technical challenges to it.
 
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