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[Is it cold in here?]

Which is a little counter-intuitive since the embryo/fetus is floating anyway.

[Carl-E]

Floating, yes; but it's not  in 0-g.  Even floating, you have a sense of up & down, and a foetus would have some sense of mass from resting in the pelvis. 

Although the 6-month pregnant friend we have staying with us would love 0-g if only to get the little bugger off her bladder...

[Is it cold in here?]

There was a point in the WCDT about friction between a despun hub and a spinning station.

The power requirements of overcoming friction are surprisingly modest. Google has let me down coming up with exact numbers, but rotating restaurants and the Dubai rotating skyscraper use quite small motors. A high-tech structure like a space station might use magnetic bearings, cutting the power needs further.

[Carl-E]

With nothing more than a free-to-rotate docking ring, you could walk (float) right into the hub and grab handles on the wall to adjust your momentum to match the station, then move out to the ring.  It really wouldn't be any different than those fun-house rotating tunnels, and would probably be turning more slowly...

[Is it cold in here?]

Less need for spin, with all the associated structural problems, if you can avoid deconditioning using high-tech clothing: http://www.txchnologist.com/2012/next-gen-space-couture-to-feature-slimmer-silhouettes-and-new-accessories

Simulated gravity would still be valuable for the way it simplifies plumbing.

[DSL]

You wouldn't want to love in your suit all the time. Eventually, you're gonna want to have a shirtsleeve environment to exist in. That stretch suit could be useful for the ride up or down, or for quick trips outside to replace the AE-35 Unit or the Illudium Pu-36 Explosive Space Modulator (Isn't it lovely?)

[mike837go]

For the bearings issue (non rotating hub interface) check out R.A. Heinline's description of such in "The Cat Who Walks Through Walls".

Mercury as a supporting agent/lubricant.

Another difficulty is: What is "Spin"? What is "Stationary"? when there is no fixed point of reference.

[Skewbrow]

The simple answer to those questions is to define "stationary" and "spin" with respect to an inertial frame. A working definition of an inertial frame is one that would be stationary "with respect to the distant stars". This raises the question that how on Earth can the
distant stars make their presence felt in a meaningful way here? IIRC the general theory of relativity gives an answer to that (because its equations are supposed to work in any coordinate system, even rotating ones), but it's been 25+ years since I seriously tried to understand that. And the math is a bit beyond me (but something that a certain snotty kid thought he can cakewalk thru), so hopefully more knowledgeable people can comment, too. Any physics majors around here?

[akronnick]

The twist is that a rotating structure is not an inertial frame, it's an accelerated (which is why we spun the thing in the first place, to use centripetal acceleration to simulate gravity)

There's also angular momentum to consider.

[Skewbrow]

Yeah, "inertial frame" is the key term, but the philosophical question that I find a bit difficult is the following. Imagine a single space station in an otherwise empty universe. How could you tell whether the station rotates or not? You can claim that it rotates, if and only if all objects on board feel the effect of this centripetal force. Or more generally, you can say that is undergoes an acceleration, if the passengers feel the resulting forces. But, like motion, acceleration is also defined with respect to a frame of reference. Without a single frame of reference other than those attached to the station itself you are lost. And it is not clear what happens, if your thrusters change the of spin the station. Will everybody feel a change in the artificial gravity, if you still don't know, whether you rotate or not?

Sir Isaac solved the problem by postulating an "absolute space", but this created other problems, and lead, eventually, first to the
special and later to the general theory of relativity (both by Einstein), the first got rid of the need for a frame of reference to define motion, and the latter (according to my feeble understanding) the need for a frame of reference to define acceleration (and hence also inertial frame) building on the observation that the effects of gravity and acceleration are locally indistuingishable.

I am under the impression (but also prepared to be wrong) that the distant stars do affect, and essentially give that frame of reference. The mechanism is vaguely similar to the way the nature balances its books, when there are moving electrical charges.
The laws of electromagnetism are immune to motion at constant speed. Yet moving charges create different forces (magnetic as opposed to the Coulomb force) that exactly compensate for the difference that would otherwise result from shifting to a stationary coordinate system to one that moves (at constant speed) together with the charged particle. Similarly, if your coordinate system is not inertial, e.g. it rotates with respect to the distant stars, then those distant stars would move at huge velocities w.r.t. your frame of reference, and then affect you by... making you feel an artificial gravity???? As I confessed, I can follow the math of the simpler case of electromagnetism but cannot follow the more complicated GTR.

I'm afraid I cannot exclude the possibility that I am talking crap, and that this philosophical problem of an "inertial frame" is not related to GR.

[Is it cold in here?]

Not an answer, but more information: http://en.wikipedia.org/wiki/Mach%27s_principle.

All inertial frames see the same events and physical laws, just with different numbers attached. Rotating frames see strange things like Coriolis force.

[Skewbrow]

Thanks. Mach was the name I was trying drag out of abyss of memory.

[Kugai]

If I was gonna live on anything that had to rotate, I'd rather it be an Omega Class Destroyer



 

[Is it cold in here?]

Does conservation of angular momentum prevent using the station as a giant flywheel to store energy from the solar panels when there's a surplus and then meet peak demands by slowing the station with a generator?

[Carl-E]

I should know that, but it's been over 30 years since my last physics class (when I changed my majr to math). 

I think, though, that it wouldn't work that way.  The whole station is rotating (modulo the docking rings), not spinning on a fixed axis like the restaraunt atop the CN tower.  Speeding it up (or slowing it) would take the firing of propulsion devices, not applying a motor/generator to the rotatng part from a fixed part. 

Feel free to call into doubt any mistaken assumptions! 

[pwhodges]

In the absence of a way to tie a structure to the inertial frame, you'd need two structures rotating relative to each other whose relative rotation could be sped up to store energy, and slowed down to recover energy by reactive braking.  In practice a small fast flywheel is used (they have been proposed for electricity storage on Earth).

[akronnick]

This has the disadvantage for a spinning wheel station that any change in the reaction wheel has an equal and opposite change in the rest of the station.

[Is it cold in here?]

Dual counter-rotating rings, then.

[akronnick]

For the Habitat? Absolutely not! That defeats the whole purpose of having a constant 1g environment.

You could build a momentum storage device with contra-rotating reaction wheels, but that's probably not much better than a battery.

[Skewbrow]

Correct me if I'm wrong, but isn't it so that with the existing technology solar power can more efficiently be used by heating up large quantities of water. Photovoltaic processes are less efficient. Of course, that does not need to apply in QCverse. And also, on a space station exposed to direct sunlight (when not shadowed by the Earth) heating may not be a problem.

[Is it cold in here?]

A thermal power cycle requires more mass and more moving parts, and creates a real problem dumping the waste heat. Vacuum is a good insulator. You need big radiators. Big, heavy, radiators. Photovoltaics lose on thermodynamic efficiency but win on mass efficiency.

[DSL]

RE: Solar power and heating -- The first publicly released designs for a "wheel" space station, back when von Braun was selling the idea to Collier's Magazine in the 1950s, had the station deriving power from a trough running along one side of the torus which focused sun rays onto a tube of mercury running along the trough's base. The mercury would vaporize and spin a turbine to provide power.

Good point on the radiators, though. Major inaccuracy in "2001" was that Discovery should have had huge radiating panels to dump the heat from what was presumably a big honkin' reactor, but Kubrick didn't want to have to explain what a space-only ship was doing with wings. A decade later, people would accept X-wings uncritically.

[Carl-E]

...and then people criticized the wings on Spaceship! 

Funny how fashions change the perception of science. 

[DSL]

Yeah. The good ship EC-101 looks like it'd be at home in a hangar next to the 1960s lifting-body study vehicles, a Space Shuttle, and that X-vehicle that is said to be in orbit. Jeph did what any respectable visual SF storyteller does: Extrapolate from known technology. Plenty of SF TV shows and movies in the 80s and 90s presented spaceships that basically looked like undercooked (or overcooked) Space Shuttles.

[Carl-E]

An before the shuttles, it was rockets, rocket, rockets!!


Except when it was saucers. 

[DSL]

Don't forget bugs. Gotta leave some love for the Eagle and its juvenile delinquent cousin, the Hawk, from Space:1999.

[TinPenguin]

and that X-vehicle that is said to be in orbit.

I love how it's supposedly "secretive" and "hush-hush" - and then there's a whole friggin' article about it, with diagrams and press statements and everything. The internet age really has redefined the meaning of "secret".

[DSL]

Makes you wonder, though, how long it's been around, what "failures" have in reality been camouflage for clandestine successes. And though it makes me sound like a tinfoil-hatter for saying it, I wonder if the "exposure" of this "secret" is meant to distract us from the truly amazing stuff. I'm reminded of the Air Force general who, when asked if the U.S. was developing secret advanced tech out in the desert, said, "I sure hope so."

[Carl-E]

"... because if we're not, we're in big trouble with the shit we have."

[DSL]

"... because if we're not, we're in big trouble with the shit we have."

Yeah, if you go to the USAF Museum,, there are a couple sections of display that makes you think of a bunch of aircraft designers looking up at the sky and saying, "Welp ..." or maybe "Hey you guys, watch THIS."

[Carl-E]

The nascent air force suffered the first airplane related death ever.  Orville was demonstrating the new flyer, and a lieutenant flying with him died when the plane wrecked.  Orville was injured, but recovered. 

The naval air corps eventually decided on Curtiss flyers instead...

[Akima]

An before the shuttles, it was rockets, rocket, rockets!! Except when it was saucers.

Reputedly Gene Roddenberry didn't want the spaceship that would become the Enterprise to look like a "rocketship" with fins, and the designer Matt Jeffries wanted to avoid the "flying saucer" cliché, yet arguably the Enterprise ended up looking like a combination of both.

My pet peeve with most fictional spaceships (at least in TV shows and movies) is that they are imagined with the decks parallel to the direction of travel like aircraft or marine ships. That makes sense for a space-plane type vehicle which actually lands or takes off like an aircraft, but otherwise, not so much. Even if you handwave "artificial gravity" and "acceleration compensators" it's hard to imagine that the technical problems would not be simpler with gravity and acceleration forces along the same axis. This would produce designs with decks stacked like the floors of a skyscraper with the engines in the basement, and much simpler turbolift design. Firefly took the whole "you must fly parallel to the floors" thing to a ludicrous level with its Alliance cruiser design in which the ship is shaped like a collection of skyscrapers but flies sideways!

[Is it cold in here?]

Whedon said the design was deliberately inefficient to show the nature of the Alliance.

[DSL]

Wondered the same thing, Akima ... why complicate matters that are complicated enough?

Also (and I can't claim originality on this; someone with more letters after their name than I said it before I did) if you have artificial gravity control (powered by Unexplainium, not spinning) -- you HAVE your propulsion. No reaction motors or whatever "impulse drive" is, because you're already controlling acceleration.

Maybe simple reaction motors for attitude adjustment and the so-called "inertial dampers" or "dampeners" are just an automatic fine-tuning mechanism built into the gravity control, like a car's shock absorbers or an airplane's trim tabs.

I kind of think Spacedock from the ST movies would be a fine design for a starship, with the mushroom cap facing forward as a space debris shield (and the hatches on the underside, naturally). Habitat and such tucked up under the mushroom cap, other stuff further aft. Would make sense for everything from the reactionless drive to one of Larry Niven's ramscoops to Arthur C. Clarke's constant-acceleration spaceliner from "Imperial Earth."

[Carl-E]

...attitude adjustment...

Sorry, been dealing with unruly students today.  So this phrase popped out for me. 


Mine's in a bottle at home...

[Is it cold in here?]

As long as conservation of momentum applies, you still have to push something in the opposite direction to go anywhere. It doesn't have to be something you carried on board if you have a solar sail, but there always has to be some form of propellant.

[Akima]

Also (and I can't claim originality on this; someone with more letters after their name than I said it before I did) if you have artificial gravity control (powered by Unexplainium, not spinning) -- you HAVE your propulsion. No reaction motors or whatever "impulse drive" is, because you're already controlling acceleration.

Reactionless propulsion is popular in SF because it allows for spaceships that are not mostly fuel-tank, and that can land and take off without worrying about the rocket exhaust flame destroying Mos Eisley space-port. There are however gigantic problems with the idea in terms of our understanding of real physics all the way back to at least Gallileo, never mind Einstein. Most SF authors' handwaves amount to pushing your ship along with a gravitic pole pressed against some mysterious, infinitely massive, special reference frame: "I felt a great disturbance in the Force, as if millions of physicists suddenly cried out in terror and were suddenly silenced. I fear something terrible has happened."

[jwhouk]

"These are not the AnthroPC's you are looking for..."

[DSL]

Stay on target. Stay on target. Stay on tarBLAM.

[akronnick]

Imperial troops have entered the base! Imperial troops hav--krkrkkrkkrkrkkrrrkkkk

[Carl-E]

Why does it always have to be snakes?




Oh, sorry, wrong franchise.     

[akronnick]

Asps! Very dangerous! You go first!

[Soulsynger]

Dioxis. *inhales* 

...

Wait, I'm sorry, I don'tunderstand fully,what are we playing? °O

[jwhouk]

42.

[DSL]

Oh, that's just your answer to life, the universe and everything, isn't it?

[Deadlywonky]

People people calm down!

to bring some semblance of control (and you know carry on talking about actual stations) would a spinning design need to be perfectly balanced or is there just a level of tolerance(a la car wheel) to stop vibrations and tumbling?

[Carl-E]

Balance is needed for something to spin on a fixed axis.  Otherwise, when set to spinning, it will find its own center of mass and rotate about it.  The problem with a car wheel that's out of balance is that the axis you want and the center of mass are different...

So no, the space station doesn't need to be balanced, but the wobble would mess with the g-force in different parts, depending on how severe it was. 

[Earin]

Balance is needed for something to spin on a fixed axis.  Otherwise, when set to spinning, it will find its own center of mass and rotate about it.  The problem with a car wheel that's out of balance is that the axis you want and the center of mass are different...

So no, the space station doesn't need to be balanced, but the wobble would mess with the g-force in different parts, depending on how severe it was. 

So, if you had Sufficient reaction mass or reactionless thrust, could you avoid off-axis wobble by automatically exerting thrust on the opposite side to dynamic masses like people around the ring? (Like, say, with some sort of advanced AI controller...)

Also, is anyone else weirded out by how *big* Potter's room is?

[Is it cold in here?]

Yes, it struck me as remarkable for military quarters.

"Applying thrust" gets expensive in short order.

[Deadlywonky]

Earin, it looks like a bunk bed behind her (shades of Lister's room only clean) and there could be another pair on the other side (IMO 4 officer rooms are pretty common, especially where space is tight, think Nuclear Sub)

Carl-E so if you were building a ring that was spinning, say at 1 rpm and you were walking around it would the imbalance cause the ring to slow down, start spinning erratically or other undesirable behavior?
[edit] rather than thrusters a 'maglev' style counterbalance around the outer edge?[/edit]