The Effects of Torque Induced by Contrarotation

[Jan Kaliciak]

Hi, having trouble finding detailed experimental evidence to support some conceptual illustration work I am undertaking to describe a manned orbital habitat in LEO, that can function as a long-term maintenance centre.

A draft schematic of the current idea can be found here:
http://groups.yahoo.com/group/NEAminesHabitats/files/LEOstation/LEOstation2-2.jpg

Other images, of mostly discarded stages, are in this folder:
http://tech.groups.yahoo.com/group/NEAminesHabitats/files/LEOstation/
...which gives some background to what is intended.

In essence the station supplies two inflatable garage spaces at 0G, connected by a 'storm cellar' area that is heavily shielded against radiation. This also forms an atrium that connects to a rotating 'chase tower', through airlocks, for transfer to floatways that pass through two rotating beams. These terminate in manned habitats that provide nominally 1G crew spaces at 3rpm at a diameter of 600 feet.

What has proved to be the sticking point is whether there needs to be TWO contrarotating beams in order to cancel out any torque effects upon the the main axial structure, which is required to be at rest relative to the rotors.

Making the assumption that one could suspend the two wheel rim bases of the rotors on magnetic tracks, for nearly friction free motion, there would still be some 'clamping' or braking effects from magnetic side pressure in the rim channel walls.

So in this case, a single rotor, in theory, could impart torque to the main axial cylinder and cause it drag around with it even at zero gee?

Another issue is whether beam rotors would impart wobble, or precession, to the whole station, so one may be restricted to using a full circumference wheel rim habitat for smooth motion.

The rotors are not motorised, and set in motion by Microwave Electrothermal Thrusters (METs) at the beam ends. One would expect that momentum would need to be topped up regularly to counteract magnetic drag from the suspension.

All the comparative technology analogies seem to involve fluid dynamics and will not apply in this circumstance (helicopters, submarines, windmills).

The purpose of such a station is to provide for exchange of goods and supplies between Earth and LEO, as well as incoming raw materials derived from mining Near Earth Asteroids (metals, water, gases, chemical precursors).

It includes a requirement to house various powered equipment while maintenance is carried out. This includes small ferries, ore hoppers, and MET powered tug-like vehicles belonging to a mining concern. The centripetally decoupled zero gee core space is an important asset here.

I try to incorporate a sound foundation into all my illustration work, and I would be most interested in any professional comment on the physics involved here, and the likely outcomes of the alternatives posed.

Jan Kaliciak

 

[Danger]

Welcome to PF, Jan.
I love technical illustrations, espcially some of White's and Boris' stuff.
Unfortunately, I'm not suitably equipped at the moment to make a suggestion. (Sobriety might help, sometime in the future.)
What I'm wondering about initially is why you want to magnetically couple the counter-rotating parts. This thing is in free-fall, so you don't actually need any kind of bearings. It your feel obliged to use them, why not air-bearings in a sealed environment. No drag involved either way.

 

[Jan Kaliciak]

Not So Much a Bearing as a Locator

Thanks for your reply, Danger.

The problem arises from keeping the axis of this station still, while maintaining the rotation of the beams. To prevent wobble in the rotation, some kind of lateral guide holds the rotor in place on the axial cylinder, while it has to be kept from impacting or grinding on the cylinder itself.

Hence the magnetic suspension.

A similar application is shown in its more finished state in this folder:
http://tech.groups.yahoo.com/group/NEAminesHabitats/files/RingShip/

(I thought you also might appreciate the illustrations!)

In this case the whole vehicle rotates to maintain 1G at the periphery. It is of a comparable diameter to the station, but has no separately moving parts for better reliability on long transits from NEAs to LEO.Jan

 

[Danger]

I should have mentioned at the beginning that your links don't work for me. They just take me to some sort of home page that doesn't say where to go next. I'm sure that the visuals would be of immense help if I could see them.
Going strictly by your written description, then perhaps you could split the core into 3 sections rather than 2. Rotate the top one clockwise, and the bottom on counter-clockwise, with the living quarters in the middle (non-rotating).
Sorry, Jan... I'm pretty pissed right now, so I'm just pulling stuff out of my ass to throw at you. Let me do my cash-out and go home (picking up some beer along the way), and I'll get back to you.
Others here will be of much more practical help to you, so listen to them more than to me.
(If I don't get back to you right away, it's because the beer was too good.)

 

[Jan Kaliciak]

Images Update

No problem, Danger, our NEA site must be better ringfenced than I thought (a Forum too).

I enclose some attachments with the design in question, to browse at leisure glass in hand.

Sorry about the blocked access.


Jan

 

[Jan Kaliciak]

Ringship Concept

Extra post here to illustrate induced virtual gravity concept of rotating transit vehicle. Copyright: Jan Kaliciak 2007

 

[FredGarvin]

No matter what the motive force is, you can't escape Newton's third law. If you need the center section to be stationary, then you would need a counter rotating system. You have to have something exert that reaction force to counter the impulsive force rotating the first section.

 

[Jan Kaliciak]

Thanks for your input, Fred. This confirms what I understood.

I always seek out evidencing that supports these illustrative assertions, and in this case there did not seem to be anything comparable to place the concept in context.

Doubts had been raised in my mind as to whether linear momentum played a part, depending on angle of orientation to the orbital path, and also inertia of the larger static masses involved resisting rotation.

 

[Danger]

Much thanks for the new links, Jan. I must say that the artwork is far superior to most that we get.
The 'ring' one gives me an idea that will probably get me banned. Just twist your ring into a Mobius strip and it'll be turning both ways at the same time...

 

[Jan Kaliciak]

That would be one mean fairground ride, Danger!

Maybe one could sell the franchise to Disneyworld...?

 

[Danger]

The trick is in getting the passengers to disembark into the same dimension that they started in.

 

[Jan Kaliciak]

Gravity Gradient Boom

An addendum to the rotational torque discussion.

I have found out that a common method of stabilising orbiting satellites is to use a gravity gradient boom, where a weight is deployed on the end of a long tether that acts as an anchor relative to Earth's centre of gravity.

The end of the boom being lower than the satellite travels marginally faster and so also 'leads' it with some angular displacement.

This concept has been applied to the orbital station, by placing as much mass as possible below the axis of rotation of the habitat rotor, which is now a single beam version. I believe this would compensate for most of the rotor's rotational torque, or reduce it sufficiently that a range of smaller rotors or gyroscopes could balance any residual tendencies.

Any further information on this would be useful.

 

[Jan Kaliciak]

Rotor Experiments

I seem to be answering my own questions again, but here are some results of applying a gravity gradient boom to a revolving beam rotor, as envisaged for a habitat in space.

This sidesteps the unruly problems discovered with counter-rotating solutions.

The rotor would nominally rotate at 3rpm with a diameter of 600 feet to give 1G.

The test model is running much more rapidly, using a slow 12v tape drive motor to which a simulated rotor of balsa has been superglued. This has the effect of amplifying any resonances, so making it easier to spot and damp them.

The whole is suspended by nylon fishing line, while it is being videoed. With no boom, the cylinder body precesses wildly. Adding the boom stabilises the rotor, with no observable torque wrapping or precession. Ballast is added to the open cylinder end as part of the trimming setup.

The more weight added onto the end of the boom, the more stable the system. Outrigger counterweights are not required.

In space, velocity and gravity cancel each other out in stable orbit, so the gravity gradient from the tip of the boom facing Earth, to the rotor edge, seems variable enough as a significant separate factor to act as a stabilising keel, with the bulk of the mass downward.

GGBs in cable form are used as a matter of routine in smaller current satellites. As far as I know, none have rotating components however.

The video clips demonstrating this will be going online later this month on the supporting website:

http://www.eosmarsprogram.org

Unfortunately, movie files are not supported on the forum, and the clips also exceed the file-size constraints here.