# Regarding angular momentum axial thrust force etc. space stations

## Main Question or Discussion Point

Disclaimer: I'm not a physicist nor do I know calculus, but I'd appreciate a little guidance with a concept I've been thinking about. I know one would usually pay for this kind of advice, but since it's just for entertainment, I'm not asking for any equations to be solved, unless you're in the mood.

So here's the problem. Let's say you wanted to attach a stationary module to the hub of a space station. The station is spinning to create centrifugal force. Would it matter if the point of connection was closer to the center of spinning mass or farther away? Does the mass of the stationary part matter? Also if the end cap docking area is not spinning can it be unbalanced and radially asymmetrical?

Also would counter rotating a stationary end cap on one side of a centrifugal system create an axial thrust force? Would I have to spin an stationary end piece on the other side of equal configuration?

I understand that if this end cap docking area is spinning against the rotation of the station it will constantly be slowing the spin because the drive system to turn the end cap is creating an opposing force reducing angular velocity. The drive system would work on an internal gear system and the motors to drive the end cap area would be mounted on the stationary side. Also, rather than using a rocket to correct attitude from time to time on the station end, it would constantly have to be firing (A drawback).

I found one paper to be very helpful. The math was way over my head... :_(
http://rsta.royalsocietypublishing.org/content/359/1788/2161.full.pdf" [Broken]

One thing that I could pull away from this paper is that having a hub on a tethered space station has a destabilizing effect, in that it adds to the tether weight and adds a complication to the system. I wonder if you could overbuild to compensate for that? :\

I'm aware of some sites that help to calculate centrifugal force:
http://www.calctool.org/CALC/phys/newtonian/centrifugal"
This is basically what I would be looking at:
Radius of cable system (hub to station): ~3000 feet
Rotation rate: 1 rpm
Weight of Station: ~5000 tons
Cable strength required: 50 megapascals

I'll put a link to the video up, once it's finished. Thanks!

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Even a cursory response would be helpful. Thank you.

Drakkith
Staff Emeritus
I don't really understand all of your questions, but I think I can answer a few. First off, if the station is spinning then yes, it would create centrifugal force. How much of an impact that has on everything completely depends on the speed of rotation. There really isn't much of a reason for a station to be spinning fast at all unless you specifically want to create artificial gravity or something. The distance from the center would affect the connection greatly. The further from the center, the faster the end is moving through space and the more force is applied to it for any given RPM.

Thank you Drakkith. I am aware that spinning a station would cause centrifugal force as stated in my first post, and yes given the figures I stated it would simulate 1 g. I don't know why these questions are so hard to understand... I'm basically asking 4 questions:

1. Should a stationary body (not spinning with the station) attached to the central part of the spinning station be closer to the center of spinning mass or farther away?

2. Also can the non spinning part of the station can be asymmetrical? Off balance (because it isn't spinning)?

3. Is the weight of the non spinning portion a factor?

4. Also would counter rotating a stationary end cap on one side of a centrifugal system create an axial thrust force? Would I have to spin a stationary end piece on the other side of equal configuration to cancel out the axial thrust force?

I'm sorry I don't speak mathenese. It would probably make this easier to understand.
Any competent help is appreciated.

Maybe I can pay you with this gift:

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Drakkith
Staff Emeritus
Thank you Drakkith. I am aware that spinning a station would cause centrifugal force as stated in my first post, and yes given the figures I stated it would simulate 1 g. I don't know why these questions are so hard to understand... I'm basically asking 4 questions:
I am just having a hard time visualizing it because I don't deal with physics on a day to day basis outside of PF.
1. Should a stationary body (not spinning with the station) attached to the central part of the spinning station be closer to the center of spinning mass or farther away?
It doesn't really matter. At least not in a way that deals with angular momentum.

2. Also can the non spinning part of the station can be asymmetrical? Off balance (because it isn't spinning)?
Yes, definitely.
3. Is the weight of the non spinning portion a factor?
Only for things like the structure which holds it all together. It also takes more energy to move something with more mass, so if you have to slow it down or speed it up a heavier station takes longer or requires more work to do so.
4. Also would counter rotating a stationary end cap on one side of a centrifugal system create an axial thrust force? Would I have to spin a stationary end piece on the other side of equal configuration to cancel out the axial thrust force?
If by thrust you mean a force that will propel the station, then no, it would not.