1. Established Member
Join Date
Jan 2005
Posts
165

## Space stations

What is it that makes having rotating sections on a space station for artificial gravity too problematic to use?

2. Off hand, I'd say sealing the rotating parts to the stationary parts. You could rotate the whole mess but then orbit keeping is a problem. Best not rotate.

Smarter posts follow.

3. ## Re: Space stations

Originally Posted by Sock Munkey
What is it that makes having rotating sections on a space station for artificial gravity too problematic to use?
Size
A rotating station is only good if it is large enough to make the height of a person an small proportion of the radius of rotation, otherwise Coriolis becomes a major problem and then people started puking.

Engineering
It is hard to dock with a rotating space station in terms of both accurate maneuvering and the problems associated with stressed on the docking port. The solution generally involved having a non-rotating central hub but this is problematic. Arthur C Clarke posited in Islands in the Sky a hub that would become inertial for docking but then slowly increase its rate of rotation to match the rest of the station. How this achieved, I cannot remember.

4. Unfortunately my efforts to produce a diagram here are thwarted by our works firewall preventing ftp

I was thinking about this one and remembered the space wheel station in 2001 A space Odessey. This is just a big wheel

Assume that this is your space station and the shuttle arrives at the hub and starts to match rotation using vernier jets, as in the film.

First, let us assume that the space station is of radius L

Has any one got the equation and derivation for how fast the station must rotate interms of L to ensure that a 1g force is felt on the rim.

Next assuming that at the centre the "force" is 0g, as the astronaught travels to the rim along the spokes, what is the equation for the increase in force he would feel as he climbed towards the Rim in terms of L?

Any Clues?

Also I did wonder, if instead of docking at the hub, would a catching system at the rim, similar to how they catch aircraft on carriers would be more of an engineering and piloting challenge. The station would have to compensate somehow for the loss of angular velocity due to the conservation of angular momentum encountered when the two vehicles docked. :-?

5. This page has a calculator for working out the size of a rotating habitat;
http://www0.arch.cuhk.edu.hk/~hall/a...c/SpinCalc.htm

really, the problem is that a rotating habitat has to be very large to avoid nausea associated with rapid rotation.
A minimum of a hundred metres radius wiill give a rotation of 3 revolutions per minute, which is still pretty fast; to cut down on this figure you can opt for lower gravity or a bigger habitat.

I'll just take this opportunity to show a couple of my recent images-
an agricultural space station
http://tinypic.com/1825o6

an O'Neill cylinder
http://tinypic.com/182kit

all these stations are designed to catch the sunlight, so must constantly face the Sun; to avoid gyroscopic effects, they can be linked together in counterrotating pairs or multiples of two.

6. Originally Posted by Sticks
Has any one got the equation and derivation for how fast the station must rotate interms of L to ensure that a 1g force is felt on the rim.
vē/r = a

v = tangential velocity of the station's outer rim
a = centripetal acceleration (for artificial gravity a = g = 9.80665 m/sē)

7. so

v = √ (L.g)

So what is the equation that links v to ω :-?

8. Originally Posted by Sticks
so

v = √ (L.g)

So what is the equation that links v to ω :-?

Using the variables in your diagram,

ω = v/L (where L is the radius of the circle). The units are radians/sec.

Edit: If you want ω in rotations per second, you would need to divide the above by 2π.

9. Established Member
Join Date
Jan 2005
Posts
165
The external structure doesn't need to rotate as long as the internal one does. using the examples shown in previous posts, imagine that the large ring has another ring contained within it like a subway traveling around in a circular tunel. the external stationary one would be the airtight one eliminating the problems of a rotating airtight seal and docking. The gyroscopic effects are easilly solved with counter-rotating sections.

10. Assuming A = Rotations per Second

A = √g / 2.√L.π

Now for our other problem, what force does the astronaught feel as he travels from the hub to the rim

replace g with F (Idealy it would be g subscript l)
and let the distance from the hub to the astronaught be X

F = 4Aēπē.X

This gives us a linear graph !!!

11. Established Member
Join Date
Feb 2004
Posts
576
Originally Posted by eburacum45
I'll just take this opportunity to show a couple of my recent images-
an agricultural space station
http://tinypic.com/1825o6

an O'Neill cylinder
http://tinypic.com/182kit

all these stations are designed to catch the sunlight, so must constantly face the Sun; to avoid gyroscopic effects, they can be linked together in counterrotating pairs or multiples of two.
Very interesting, on a couple of points. Can you describe your ag station? I can't figure out how it rotates--the grass is growing on the bottom of the can, with the mirrors around the top of the can like a funnel, right?

Second, I see you put your models into Celestia. Is there a L4/L5 halo orbit package available for it already, that I could use when doing likewise? I'm interested in seeing how the sun is eclipsed by the moon and the earth, when moving in halo around L4 (or L5).

12. I will put these models into the Celestia Motherlode in a week or so; I'll let you know when they are available. The AG station is based on another design by O'Neill; the whole thing rotates, and the light is concentrated onto the rotating wall of the cylinder, where crops are grown. Once again these stations should be couples in multiples of two to avoid gyroscopic effects- Oneill envisaged a ring of them surrounding his Island Three design.

13. Newbie
Join Date
Dec 2004
Posts
6

## also...

there's a problem known as "cross-coupled acceleration" when you move your head while inside a rotating space station.

the result of two angular accelerations along different axes on your inner ear is usually nausea and vomiting.

see http://www.ncbi.nlm.nih.gov/entrez/q...;dopt=Abstract

14. Member
Join Date
Nov 2004
Posts
23
I love playing around with this SpinCalc. I've always thought it would be neat to create a giant ring type colony that faced the sun in such a way that half was in light and half in shadow, rotating once every 24 hours. This should give the residents a nice simulation of the earth day. Well, I plopped the numbers in and it turns out you'll need a radius of 960000 kilometers (assuming I even did the math right) That's a tad bit bigger than I was planning for my colony

15. Established Member
Join Date
Feb 2004
Posts
576
Originally Posted by eburacum45
I will put these models into the Celestia Motherlode in a week or so; I'll let you know when they are available. The AG station is based on another design by O'Neill; the whole thing rotates, and the light is concentrated onto the rotating wall of the cylinder, where crops are grown. Once again these stations should be couples in multiples of two to avoid gyroscopic effects
OK, from your earlier rendering it looked like the bottom.

What is the orbit of your stuff you will put in the Motherlode? I'm interested not so much in someone's actual station, but the view from such a station. Maybe I'll put my own there as just a rough sketch, but I want to put the effort into the prose.

I've got a copy of O'Neill's book on order. I read that the appendix added to the 3rd edition isn't really worth it, so I got a first edition rather cheap.

--John

16. I just put the station orbiting an invisible object at Meananomaly 60; this isn't a real halo orbit, but it will have to do for now.

17. Originally Posted by lord bytor
I love playing around with this SpinCalc. I've always thought it would be neat to create a giant ring type colony that faced the sun in such a way that half was in light and half in shadow, rotating once every 24 hours. This should give the residents a nice simulation of the earth day. Well, I plopped the numbers in and it turns out you'll need a radius of 960000 kilometers (assuming I even did the math right) That's a tad bit bigger than I was planning for my colony
Congratulations; you have discovered the Banks orbital, desribed by Iain Banks in his Culture novels.
(I make the requisite radius 1,800,000km, by the way)
Here is an image of a rather large one from the OA universe; Daleth orbital has a somewhat longer day than Earth.
http://tinypic.com/18lzsx

Iain Banks talks about Orbitals, and the Culture in general, here.
http://www.cs.bris.ac.uk/~stefan/culture.html

18. Member
Join Date
Nov 2004
Posts
23
Originally Posted by eburacum45
Originally Posted by lord bytor
I love playing around with this SpinCalc. I've always thought it would be neat to create a giant ring type colony that faced the sun in such a way that half was in light and half in shadow, rotating once every 24 hours. This should give the residents a nice simulation of the earth day. Well, I plopped the numbers in and it turns out you'll need a radius of 960000 kilometers (assuming I even did the math right) That's a tad bit bigger than I was planning for my colony
Congratulations; you have discovered the Banks orbital, desribed by Iain Banks in his Culture novels.
(I make the requisite radius 1,800,000km, by the way)
Here is an image of a rather large one from the OA universe; Daleth orbital has a somewhat longer day than Earth.
http://tinypic.com/18lzsx

Iain Banks talks about Orbitals, and the Culture in general, here.
http://www.cs.bris.ac.uk/~stefan/culture.html
Is there some name for a person who comes up with inventions that it turns out have already been invented? Because I'm the freaking Thomas Edison of that catagory.

Oh yes, I plugged the numbers back in and 1,800,000 is correct, I don't know what I did wrong there.

19. Established Member
Join Date
Dec 2004
Posts
102
Here's a very detailed paper about almost all the factors that need to be taken into account with rotating habitats:

http://www.spacefuture.com/archive/i..._gravity.shtml

Some nice points in there about psychological effects and considerations for internal architecture.

Unless you have a huge amount of resources I don't think a fully rigid design would be very practical. I've always thought tethered capsules rotating around an axis point, like a bolo, would be more feasible. That way you could get a greater spin radius without all that engineering in the way. You could arrange a bunch of them in a string of pearls on spokes configuration with tethered tracks for transport between them, like ski lift cars.

Here's a question: If you ran down a corridor in the anti-spinwise direction faster than the rotation speed, would you eventually take off and fly until you hit a wall or the floor again? (ouch! or with padding, fun! )

20. Yes; but you would simply fly until you hit the floor again- this would feel similar to doing a long jump in slightly lowered gravity.

21. ## Re: also...

Originally Posted by apollo18
there's a problem known as "cross-coupled acceleration" when you move your head while inside a rotating space station.

the result of two angular accelerations along different axes on your inner ear is usually nausea and vomiting.

see http://www.ncbi.nlm.nih.gov/entrez/q...;dopt=Abstract
I thought that this would rarely cause nausea if the station radius was large enough; it would just allow you to know which direction the station was spinning using your inner ear (which is quite cool, I must say).

22. Established Member
Join Date
Dec 2004
Posts
102
Originally Posted by eburacum45
Yes; but you would simply fly until you hit the floor again- this would feel similar to doing a long jump in slightly lowered gravity.
If the circumference of the floor was great enough to give you good "air time" I still think this would be fun.

This reminds me of the jogging scene in 2001. I realize the rotating module in the Discovery has the problem of having a way too small radius to simulate a livable gravity (without making you vomit or pass out). Still, if he were running anti-spinwise his apparent gravity would reduce, meaning less strain, and spinwise his apparent gravity would increase, meaning greater strain. Is the scene mentioned in the book, and which way he's running (I must confess I haven't read it), or does anyone think he was cheating. :wink:

23. Established Member
Join Date
Dec 2004
Posts
102
BTW, I may start a new thread in Bad TV! Bad Movies! about this. I have never for the life of me seen a good treatment of centripetal gravity in fiction. It always seems to get used as a crutch to create an "Earth-like" environment. Though, as you can see from the papers cited here, unless you had a station with a huge radius it wouldn't be Earth-like at all. The only good example I can think of is in Stephen Baxter's Titan, but that was just a spinning exercise module on a rope, not a whole station. Should I start said thread, or has this been addressed in the past?

24. Established Member
Join Date
Dec 2001
Posts
582
Originally Posted by HerrProfessorDoktor
BTW, I may start a new thread in Bad TV! Bad Movies! about this. I have never for the life of me seen a good treatment of centripetal gravity in fiction. It always seems to get used as a crutch to create an "Earth-like" environment. Though, as you can see from the papers cited here, unless you had a station with a huge radius it wouldn't be Earth-like at all. The only good example I can think of is in Stephen Baxter's Titan, but that was just a spinning exercise module on a rope, not a whole station. Should I start said thread, or has this been addressed in the past?
The Babylon 5 station is a 8 km long, 840 m diameter O'Neill habitat. The fact that the gravity lessens as you move to the center was shown in two episodes of Babylon 5, but none of the strange effects of having gravity via rotation, as it probably wasn't feasible to film. The Omega Destroyers also had gravity via rotation. The Hyperion Heavy Cruiser did not and crew members were shown strapped into seats.

Kizarvexis

25. Originally Posted by eburacum45
Originally Posted by lord bytor
I love playing around with this SpinCalc. I've always thought it would be neat to create a giant ring type colony that faced the sun in such a way that half was in light and half in shadow, rotating once every 24 hours. This should give the residents a nice simulation of the earth day. Well, I plopped the numbers in and it turns out you'll need a radius of 960000 kilometers (assuming I even did the math right) That's a tad bit bigger than I was planning for my colony
Congratulations; you have discovered the Banks orbital, desribed by Iain Banks in his Culture novels.
(I make the requisite radius 1,800,000km, by the way)
Me too. (1, 854, 335.9745989376 km, to be exact.) 8)

26. Established Member
Join Date
Feb 2004
Posts
576
Originally Posted by eburacum45
I just put the station orbiting an invisible object at Meananomaly 60; this isn't a real halo orbit, but it will have to do for now.
What's Meananomaly 60?

Can you suggest a good guide to learn how to do that stuff?

--John

27. Established Member
Join Date
Nov 2004
Posts
1,534
Why must a station have 1g gravity?

A lot of people seem to want artificial gravity so that real space travel is more like star trek (well, Babylon 5 at least) and you can walk around on ships. All we need artificial gravity for is to avert the negative health effects of microgravity.

Building a rotating habitat should be a balance between engineering difficulty and health benefits. You can't put a price on an astronauts life of course, but I would imagine as you approach 1g it becomes more economical for the astronaut to gain any extra benefits through exercise.

28. The idea of having 1g artificial gravity is so that personnel can swap between the Earth and station with out much of a problem.

When Astronaughts come back from a long term mission, it takes a while before they can walk normally. So long term exposure to less than 1g would make life difficult back on Earth.

If we ever have a permenant manned base on the moon, not that congress will ever allow such an extravegant white elephant, then personnel switching between the two might have similar problems adjusting at either end. This could be solved by a station to lunar shuttle which would have a variable artificial gravity rotation so that personnel can get used to 1/6g for the moon and brought back to 1g on the way back. The nearest analagy I can think of is a diver going through decompression.

How such a shuttle would be configured is another issue See this thread

The other issue with a moon base transfer, is that for landing the artificial gravity would have to be turned off.

Can Jay or anyone else say how and when the Apollo astronaghts felt the kick of the lunar gravity when they were landing on the moon. Similarly How does the return to 1g manifest itself when the shuttle returns from space.

Getting back to the space station issue, the simplest design is usually the best, and a large spinning wheel would be the best, for artifical gravity, with docking achived by a shuttle using vernier jets to match rotation at the central hub..

I found this image from the movie 2001 A space Odyssey and it seems there are two wheels. Can anyone remember if the two wheels contra rotated? I suspect they did not. :-k

29. The answer, obviously, is magnet shoes.

30. Similarly How does the return to 1g manifest itself when the shuttle returns from space.
I've seen footage of this. Everything slowly floats to the floor, picking up speed as it goes.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•