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[Carl-E]

Depends on the size of the station.  The mass of a person coul be negligible if the station's large enough (think a BB in a tire), but get a large group in one place...

"..tonight's assembly is cancelled.  Please stay in your rooms until balance is restored"

[DSL]

Hm. I'd want in place some sort of regulation, similar to a fire marshal's, limiting occupancy in any one room. The net effect of that would be to have people more or less evenly distributed around the torus. A big enough torus, and enough people, and small discrepancies could be compensated for with the usual station-keeping maneuvers.

[pwhodges]

I would say that it doesn't matter most of the time if the centre of gravity drifts a little away from the geometric centre of the structure.  However, with docking being performed along the central axis, it would be advisable to restore the C of G there to make it stationary in preparation for docking to take place.

[akronnick]

The mass of the station is so much bigger than the mass of anything that would be moving around on it that any wobbles or eccentricities would not be noticed.

On a small boat, you have to be careful how you move so you don't tip the boat. On a big boat it doesn't matter because you're not big enough to make that much difference. The big boat still tips, but the displacement is measured in millimeters.

Plus, the more people you have moving around randomly, the more of their motions are cancelled out.

[Kugai]

The mass of the station is so much bigger than the mass of anything that would be moving around on it that any wobbles or eccentricities would not be noticed.

On a small boat, you have to be careful how you move so you don't tip the boat. On a big boat it doesn't matter because you're not big enough to make that much difference. The big boat still tips, but the displacement is measured in millimeters.

Plus, the more people you have moving around randomly, the more of their motions are cancelled out.

Except on the Black Pearl

[akronnick]

But they were moving in sync, and what's more, in simple harmonic oscillation with the ships mode of rolling.

If everyone on the station ran around the perimeter in the direction opposite the rotation, it might have a noticeable effect.

[Deadlywonky]

So no marching troops! I'd imagine that a station large enough to have a decent size habitation ring and labs and accommodation for >100 people would weigh enough to stop a handful of people meeting up from becoming a problem then?

if you were actually going to build it, would you want to build the ring first (in airtight sections) and then add labs/habitation modules bit by bit balancing as you go?

a couple of things I've noticed about Jeph's design is that there are no emergency covers for the windows in case of accidental breaking, and that those doors (sliding I assume) don't look particularly airtight.

Of course I'm probably taking the whole thing far too seriously 

[DSL]

You'd have the situation of a big enough overall mass damping out the effect of individual people and other smaller bits of the station's mass moving around inside.

Wonder: If you were the sort who went in for running as an exercise, you'd get more of a workout running spinward (and so increasing your velocity around the circle, and therefore "weighing" more) as opposed to antispinward (decreased velocity and therefore decreased simulated weight). Again, a large enough torus would damp that out, by decreasing the overall rotation rate necessary for the desired g-equivalent.

As far as construction, build it, get the masses balanced and then spin it up. That actually was a problem engineers had the first time they saw Kubrick's version of the spinning-wheel station in "2001" -- the section under construction, they said, should have been completed in free fall (so you didn't have tools, parts and construction workers being spun off into the void), THEN spun up and mated to the existing section.

Windows and doors? I'm so used to SF space windows being made of transparent superstrongium (or better still, it's really just a force field) I take the handwave. Though, anyone remember "Space:1999?" The windows in the control room would break or crack at the slightest provocation, but an emergency repair could be made by laying a piece of office paper over the crack and sealing it with something from a handy spray can.

[Is it cold in here?]

Of course I'm probably taking the whole thing far too seriously 

You'll fit right in!

Maybe we just haven't seen the airtight safety doors.

[Carl-E]

DSL, re: the running question. 

What a fascinating thought!  I think, though, that the effect doesn't happen - the centripetal force exerted by the station holding you in when your foot touches the ground will be the same that moment regardless of the direction you were moving. However, the acceleration made when you push off is linear, and the motion of the station is circular, and so I think that the faster you go, the heavier you'll feel because of the added force from the greater accelleration in each step (F = ma).   

[DSL]

Carl-E,

Sounds like a question of which effect overpowers the other: Circular motion spinward or antispinward vs. the other vectors you describe.

Now what we need to do is to build a spinning torus space station and move up there to test that. Who's with me?

[Skewbrow]

Re spinward/antispinward jogging. I though about it a bit, when we first discussed spinning space station a while back, and Akima explained how the Coriolis force places a limit to the size of the station (too large Coriolis => crew resorting to barfbags). Carl-E is, of course correct in that the centripetal force is the same. However, the Coriolis force is also there unless your motion is parallel to the axis of the spin. And (barring a mistake in me mentally calculating the direction of the relevant vector cross product) the Coriolis effect will fulfill DSL's prediction: if you jog spinwise the Coriolis force will also be pressing you out into the floor, so your muscles have to work harder to lift your feet/legs. Similarly if you jog antispinward, the Coriolis force will be in your favor.

Mind you, I'm fairly sure that Carl-E's argument is the same thing viewed a bit differently. There are many (equivalent) ways of looking at it.

Edit: That was probably written the right way on my first attempt

[Sidhekin]

Fun with physics: http://freefall.purrsia.com/zu/ffskates.gif

From http://freefall.purrsia.com/zu.htm – credit is important, right? – but I think hotlinking works for this image.

[jwhouk]

DSL, re: the running question. 

What a fascinating thought!  I think, though, that the effect doesn't happen - the centripetal force exerted by the station holding you in when your foot touches the ground will be the same that moment regardless of the direction you were moving. However, the acceleration made when you push off is linear, and the motion of the station is circular, and so I think that the faster you go, the heavier you'll feel because of the added force from the greater accelleration in each step (F = ma).   

That might be why Lt. Potter was out of breath from running to catch up to Marigold and company.

[DSL]

Here's my thought:
You're standing on the "floor" of the torus as it's spinning. The point defined by you is moving in a circle. You experience a certain value of g.
Move spinward and you still describe the same circle, but faster than the station does. Your personal value of g is greater; you're heavier.
Move antispinward, you describe the same circle, but slower. You personal value of g is lower; you're lighter.

(This assumes you're not moving so fast to antispinward you cancel out the rotation, in which case you could, barring obstacles like bulkheads, missing MP3 players and pissed-off Air Force lieutenants, appear to float through the torus to antispinward from the point of view of someone standing on the torus floor.)

Coriolis effect, which if memory serves from my SF nerdier days depends on how fast you move through angles, would appear to diminish the larger the radius if the torus. There's a bit of old video somewhere from the early Soviet space program of the inside of a small room on the end of a centrifuge arm only a few meters radius but moving at speed to produce a comfortable fraction of g; the astronaut trainee inside throws a dart toward the outer wall and the dart describes a tight curve to strike a dartboard off to the trainee's side.

[Skewbrow]

Coriolis force is always perpendicular to both the axis of the rotation and also to the speed vector (in the rotating frame). Its magnitude is proportional to the sine of the angle between those two vectors (explaining why it is equal to zero, when your motion is
parallel to the axis of rotation, and also why it is at its largest when the motion is perpendicular to the axis of rotation). So when you jog along the perimeter of the spinning space station, it will be either "up" (towards the hub) or "down" (pressing you to the floor with extra force) effectively decreasing/increasing your "personal g". When you throw a dart in a centrifuge towards (or away from) the outer floor, the Coriolis force will be sideways. I am fairly sure that all the dartboards on HannerDad's station are on those walls that you would also place the donut toppings on (looking at the station from the outside).

The difference in "personal g" will not be very large in a practical setting. Starting with the numbers from Akima's spreadsheet of a station with radius 1000 meters spinning at 1rpm, the rim will be moving at about 100 meters/second. A world class sprinter can run at one tenth of that speed, and thus might be able to vary his/her personal g by 20 per cent. The centripetal force is proportional to the square of the speed, so the relative difference (unless very large) gets doubled.

[Carl-E]

Ah.  Yes, I completely forgot about coriolis.  Nevertheless, I think my first point still stands - eihter way you run, in the inertial frame of reference, it's "uphill" since your accelleration vector is straight and the station isn't. 

...and I just realized what I wrote.  Sorry, Station.  Not that there's anything wrong with not being straight...

[Nomen]

Why are you apologizing if there's nothing wrong with it?

[jwhouk]

Someone obviously hasn't seen Seinfeld.

"NOT... THAT THERE'S ANYTHING WRONG WITH THAT!"

[Deadlywonky]

Ah.  Yes, I completely forgot about coriolis.  Nevertheless, I think my first point still stands - eihter way you run, in the inertial frame of reference, it's "uphill" since your accelleration vector is straight and the station isn't. 

...and I just realized what I wrote.  Sorry, Station.  Not that there's anything wrong with not being straight...

there's nothing wrong with being a holosexual

[jwhouk]

Okay, I'm officially TOO much of a "layout" geek.

(Link to the full size view & the Wikia article here.)

[Skewbrow]

Hmm. Correct me, if I'm wrong, but I don't think that there is a "spaceside" and an "Earthside". Remember that the axis of rotation is fixed with respect to the distant stars.  IOW, the space station, unlike the Moon, won't have one side continuously facing the Earth. The Moon does that because tidal forces of Earth's gravity have locked Moon's own rotation to synch with its orbital period.

Ok, so the axis of rotation doesn't need to be exactly fixed, because there is precession, but I don't see that helping us here.

Actually I am little bit worried about this, because it would mean that one side of the station is facing the sun half the year. That surface could become very hot.

Space engineers, help me out!

[Deadlywonky]

Skew, yes it could, however as has been mentioned by Von Braun, this could be used as a source of power (using mercury if memory serves), also because the station doesn't 'point' (rotational axis) towards the sun, there will be some parts heating as others are cooling, (see apollo PTC  or 'barbeque roll') or if the station is designed to be orientated with one part permanently in shade then passive radiators could be mounted for heat venting, with an internally pumped heat transfer medium between the exposed parts of the body and the rads.

(one idea that occurs to me is that if you were ejecting 'waste' (and not worried about water preservation) it could be used as a heat sink, but the thought of boiling hot urine is not very pleasant)

[jwhouk]

Actually, I'm going off of the basis of the first time we saw the station.

Think about it - the "floor" of the station would be the outside of the torus, due to the gravitational spin. If the station is oriented where the center hub has one end "pointed" towards the Earth, and the other "pointed" upwards towards the stars, then the two "sides" of the torus would logically face earth-ward and star-ward.

[Skewbrow]

@jwhouk: Just to make sure. What I was trying to explain is that the pointed end in that image will not always be pointing towards the Earth. If it is pointing towards the Earth now, 45 minutes (or half an orbit) later, it will be pointing away from the Earth. That is because the station is spinning, so conservation of angular momentum prohibits that pointy end from always pointing towards the Earth. It could always point at e.g. the North Star, or Sirius, or your favorite constellation, though.

The Skylab, the Space Shuttles or the ISS could/can move in a way that they always show the same side to us. You achieve that by making them slowly spin about another axis once per revolution. When the station has artificial gravity created by spinning, you give up on that. The faster spin rules.

[Is it cold in here?]

One constraint people are missing is that you don't want the solar panels to be in the station's shadow ever for a little while.

[Kugai]

Hmmmm.

The Centralised Bathing Room makes sense.  It would cut down on what was required for water reclamation and storage

Hell, even B5, as big as it was, limited the use of water for bathing.  Only Ambassadorial, Officers and Guest Quarters had Wet Showers, everybody else had Vibe Showers or used Centralised Bathing Facilities, such as in the 'Fury Pilots Ready-rooms.

[jwhouk]

I want to point out, as I did to IICIH, that this was all a guess on my part.

What I'm assuming is that the station is spinning around somewhat like a top as it orbits the earth. The solar panel remains facing the sun as it orbits the earth, just like (I'm assuming) Skylab, the ISS and Mir did with their panels.

[Skewbrow]

One constraint people are missing is that you don't want the solar panels to be in the station's shadow ever for a little while.

Can't you solve that problem by attaching the solar panels to the spokes of the wheel, and have them rotate (very slowly) around the spokes? I don't see a solution that does not involve periodically moving solar panels from one side of the station to the other. That may be just my personal limitation, though.

Edit: Well, a semi-obvious alternative is to make the axis of rotation perpendicular to the plane of Earth's orbit around the Sun. Then the solar panels sitting a few hundred feet above the plane of the doughnut will always see the Sun. You do need a full circle of panels in that case, because otherwise the rotation of the station will make a panel face away from the Sun once per minute (again assuming that the station rotates 1RPM).

Rephrasing my main theme: Basically artificial gravity turns the spinning space station into a gigantic gyroscope. When you have a gyroscope inside a fighter plane manouvering a full 360 degree loop, the axis of the gyroscope is always maintaining its orientation relative to the distant stars, and it cannot stay aligned with, for example, the pilot's spine. That is sort of the whole point of having the gyroscope.

[Akima]

Can't you solve that problem by attaching the solar panels to the spokes of the wheel, and have them rotate (very slowly) around the spokes? I don't see a solution that does not involve periodically moving solar panels from one side of the station to the other. That may be just my personal limitation, though.

Edit: Well, a semi-obvious alternative is to make the axis of rotation perpendicular to the plane of Earth's orbit around the Sun. Then the solar panels sitting a few hundred feet above the plane of the doughnut will always see the Sun. You do need a full circle of panels in that case, because otherwise the rotation of the station will make a panel face away from the Sun once per minute (again assuming that the station rotates 1RPM).

This sort of thing is why space-habitat proposals often involve mirrors, although Jeph's plainly does not. The Stanford Torus study, for example, proposed an angled, non-rotating mirror to reflect sunlight onto solar arrays mounted between the "spokes" of the "wheel", and I think that would work on similar, if less grandiose, space-stations. In Earth orbit, there's still the problem of passing through Earth's shadow, so you'd need energy storage facilities, or auxiliary nuclear generators, or both.

[Is it cold in here?]

Or regenerative braking. I bet there's a lot of stored energy in the station's rotation and that you could ride out an eclipse without causing disturbing shifts in people's apparent weight.

[pwhodges]

Braking against what?  In this situation you're really speaking of using a faster flywheel to store energy.

[Skewbrow]

Is it beyond the capacity of batteries? Recharge them when in sunlight, use them when in the dark. The Earth's shadow comes and goes in a 90 minute cycle after all. I'm no engineer, so cannot guesstimate, whether batteries can store enough electricity to run the station for 45 minutes. Without filling up the entire station with those batteries that is?

[Deadlywonky]

The Qinetiq Zephyr had enough battery capacity to fly through the night, loosing 10-15,000 feet in the process, obviously its an aircraft, not a station but in principle if weight wasn't' an issue you could have as much space devoted to batteries as you needed. The problem would be the charge/discharge cycle, even deep cycle batteries are only good for a few thousand cycles, and if you are discharging several times a day (orbit dependent) then they won't last too many years before they need to be replaced.

using a separate flywheel is out, and unless you can realistically decelerate the station to generate power and then accelerate it in sunlight (is this possible with a large enough station and not affect g?)

the two best options i see are a closed loop fuel cell/electrolysis unit but even this will have a limited operational life, dependent on the membrane. Or a 'nuclear battery' such as one of the larger SNAP units developed by NASA but this would require deactivation of many of the systems during the 'night' as I assume that the SNAP won't be able to generate enough power to keep the entire station running (otherwise what is the point of the solar panels).

[Is it cold in here?]

Braking against what?  In this situation you're really speaking of using a faster flywheel to store energy.

Conservation of angular momentum means the station's rotation will speed up or slow down as you speed up or slow down the flywheel.

The solar panels could be there to sustain operations while the antimatter reactor was being refueled, and to bootstrap it afterward.

[Skewbrow]

I could sort of see energy transfer from the flywheel to the station (eddy currents or some form of regenerative braking), but how could do you turn the kinetic energy stored in the rotation of the station back to the flywheel (or turn it into electricity by other means)?

[Is it cold in here?]

Run the connection between the station and the flywheel as a motor.

[Skewbrow]

Ok. I had to think about this. My mistake was in thinking that we would first use the flywheel to speed up the rotation of the station itself, and only then try to use that energy. If we do that then there is no speed difference remaining to be used as a motor. So during the "night" we use the speed difference between the flywheel and the station as a motor. At "dawn" the flywheel and the station are spinning at the same rate. This will also speed up the rotation of the station by a tiny amount.  To prevent that speeding up from accumulating over a long period of time (and dramatically changing the level of artifiicial gravity), we need to use the solar panel to slow down the flywheel on alternate "days".

But how did we use solar power to accelerate the flywheel again? And can we actually build a massive enough flywheel?

Arggh. I shall leave this problem for the engineers to solve.

Edit: Thank IICIH (see below). It looks like I may have forgotten a conservation law or two

[Is it cold in here?]

It can be either massive or fast. Flywheel engineers, at least for mobile applications, seem to go for fast.

Just wire up a motor-generator like the Prius uses. Put energy in, and it spins up the flywheel, spinning up the station by reaction. Pull energy out, and it equalizes the spins of the flywheel and the station.