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Les
2003-Sep-24, 07:06 AM
Hi all,

With all the difficulties of moving humans through space, specially those related to muscle and bone wastage due to micro gravity, why does nobody seem to have seriously considered the spinning donut?

I recall the film 2001 A Space Odyssey featured the shape, on a grand and wasteful scale admittedly, but surely the physics addresses the majority of the problems.

Rendezvous with Rama , another of Arthur C Clarke's novels also featured the spinning concept for a whole ecosystem.

I assume that cost is the limiting factor.

Given that it was built a section at a time, I also wonder why the ISS was never built in the donut shape? Microgravity experiments could still be done in a central (contra-spinning) hub. The people working there could move out to the ring for living quarters. Would save in labour costs - astronoauts could stay longer without so many health concerns. A lot of tasks would be far easier - washing, eating, sleeping, toilet...

Does anybody know why the donut remains only in science fiction, and police dramas?

bfoz
2003-Sep-25, 02:09 AM
Cost is certainly a primary factor. However, size is an even more daunting factor. The scale of the stations in 2001 isn't just grandiose, its necessary. In fact they're probably a little small, although I haven't seen the movie in quite some time.

The problem comes down to the Coriolis effect, the thing that makes water go down a drain one way in the northern hemisphere and the other way in the southern hemisphere. People are capable of handling a certain amount of Coriolis, but too much causes violent nausea (try spinning yourself around for a few minutes and then try to pick something up off the floor, that's a mild version). One of the primary drivers of Coriolis effects in a wagon wheel style space station is the radius of the wheel: smaller radii create greater nausea and vice versa. The theoretical "proper" radius to make such a station comfortably habitable is on the order of a few kilometers.

We're currently nowhere near capable of making something that big in orbit. Hopefully we will be someday, but until then we're stuck with ISS style constructs.

Guest_scott712
2003-Sep-26, 05:51 AM
I can't imagine corriolis effects wreaking near as much havoc on the innner ear as weightlessness must do.

I think a cheaper way to do the same thing would be to have pairs of vehicles or Space station living modules joined by a fairly long cable. The longer the cable, the less the Coriolis Effects. The two modules would then rotate around their common center of gravity, located somewhere near the middle of the cable. The long cable will also guide the module that will travel between the living quarters and a counter-rotating "no gravity" module half way between the two sets of living quarters. This moving module will act as a sort of elevator.

This is still much more modest than "The Big Wheel;" however, you still have the added weight of of the cable, the separate zero-gravity lab, extra safety hatches and miscellaneous decks. I do agree that it would save money not having to rotate crews due to bone and mucle loss. Also, crews would not have spend as much time exercising as they currently do. Many experiments could be set up under "gravity" then moved to the zero gravity lab.

Guest
2003-Sep-26, 04:13 PM
Weigthlessness doesn't effect the inner ear very much at all, after all its the lack of weight and "nothing can't do nothing". The brain gets used to the lack of gravity reference fairly quickly; within a few hours for most people.

Coriolis is far more devious than a simple lack of reference. Think back to that high school physics class that talked about gyroscopes and remember that when you apply a force to a spinning object it responds as if the force had been applied 90 degrees to where you actually applied it. Those wheel-stations look an awful lot like toy gyroscopes, so apply this effect to the fluid in your ear. Now everytime you move, your brain is going to get a signal that you moved perpendicular to the direction you actually moved. As it that wasn't confusing enough the effect changes based on your distance from the hub. Actually its the distance between your ears and the hub. In a small radius station just the act of standing up can cause severe variations in the coriolis effect.

A wheel-station occupant would also have to deal with the apparent rewrite of the laws of physics that occurs in a spinning environment. For instance, if you were to drop an object to the "ground" it wouldn't fall in the direction that you would naturally associate with down. Its motion would have a noticeable "sideways" component. In a small radius station the effects are likely large enough to be disorienting. Think about trying to stand up or sit down in that kind of environment.

The tether-station has its own problems. Cable breakage is the obvious one that everybody brings up, but its really just an engineering problem.

There is an effect called gravity gradient stabilisation that is employed by some satellites. It is based on the principle that a long mass in oribit, or two widely seperated but connected masses in orbit, will eventually stabilize and align either radially to the planet or tangential to the orbit. It can be a handy principle at times. However it would tend to despin any sort of tether-based space station. Such a station would have to be continually respun which takes us into figuring out how to maneuver such a vehicle. Maneuvering such a contraption is probably possible but AFAIK its still an unsolved problem.

Incidentaly, the proposed zero-g hub wouldn't be very zero-g. It would be rotating so everything in it would be stuck to the walls (depending on rotation speed) and people would get very dizzy in there (coriolis gets stronger closer to the hub).

bfoz
2003-Sep-26, 04:14 PM
Argh. That last post was from me. My autologin gizmo didn't auto login and I didn't catch it.

neilzero
2005-Dec-03, 03:07 AM
As soon as CNT = carbon nano tubes are space rated for extreme reliability, look for a pair of space stations spinning about each other, held together by a tether. The stations do not have to be equal mass; the lighter station will have higher gravity. Extreme reliability is important as a sudden break of the tether or its anchors to the stations means injured crew members plus the possibility of an unsceduled re-entry into Earth's atmosphere.
Present tethers a kilometer or more long must be very heavy to be reasonably safe. Considerable energy is required to spin the stations about each other. The spin complicates docking, zero g experiments, astronomy and communications. There is no practical way to recover the energy during despin, and an EVA = extra vehicle activity from one station to the other would be dangerous and frightening. Neil

Wendell
2005-Dec-03, 09:39 PM
an EVA = extra vehicle activity from one station to the other would be dangerous and frightening. Neil

One way around this is to have the configuration of the quarters in a square pattern, while the hub also connects to each of the 4 points. Wouldn't traveling from one point to another, on the outside lines, as opposed to the lines connecting to the center, eliminate the increased Coriolis effect? You could also travel in a direction opposite the rotation of the overall station, to reduce that effect even further.

Of course this means a much greater increase in cost, as you're vastly increasing the amount of cable, or connectors, needed.

A circle configuration would also work, and allow for any number of stations placed along that circle, but then we're getting closer to the grand wheel design if we increase it all that much :doh:

Also, you're likely more than tripling the building cost, and the amount of fuel that would be needed to get the thing rotating.

IsaacKuo
2005-Dec-03, 09:54 PM
The tether-station has its own problems. Cable breakage is the obvious one that everybody brings up, but its really just an engineering problem.

There is an effect called gravity gradient stabilisation that is employed by some satellites. It is based on the principle that a long mass in oribit, or two widely seperated but connected masses in orbit, will eventually stabilize and align either radially to the planet or tangential to the orbit. It can be a handy principle at times. However it would tend to despin any sort of tether-based space station. Such a station would have to be continually respun which takes us into figuring out how to maneuver such a vehicle. Maneuvering such a contraption is probably possible but AFAIK its still an unsolved problem.

Tether propulsion involves sending an electric current through a conductive tether, so that exo-atmosphere plasma completes the loop. By sending current through it, you can push against the Earth's magnetic field to either accelerate or decelerate the tether. For a spinning tether station, alternating current in the tether could keep it spun up, as well as adjusting one's orbit.

In principle, a tether space station could be launched into a low orbit and then slowly spiral outward to a higher more desired orbit with solar power.

Also, a space tether can be used to generate power, sacrificing orbital velocity for electrical energy. This could be used instead of heavy batteries to provide power while in Earth's shadow or to provide bursts of high power levels.

JHotz
2005-Dec-04, 09:46 PM
There are no real technological limitations to this concept. The reason it has not been done is because there is not sufficient technological impetus place on the space capable entities to develop these techniques.

The problem with the donut space is poor ratio of volume to surface. This translates increased weight, thermal efficiency, radiation exposure, and risk of air leaks. The shape of a donut or its parts do not fit well into current launch vehicles and that is probable the larges impediment. Can you imagine the nightmare of fabrication such a structure in space to the tolerances necessary to make it airtight?

Some of the issues of a space ship swung on tether include docking, transferring between to swung units, maneuvering.

Docking could be done at the hub but that would require the docking ship could functional spin while docking and docked. Spinning would create centrifuge and the docking craft would have to be centrifugally balance around the docking point.

Transferring to the hub seem simple enough with an elevator until you consider the effect increasing the orbit without increasing the speed of the elevator this would create a great deal of stress and instability to the station as a whole.

Accelerating at the hub and allowing the swung modules to trail behind could accomplish maneuvering. Their centripetal movement could prevent them from colliding and is calibrated correctly with varying the length of the tether should make the forward movement imperceptible.

IsaacKuo
2005-Dec-05, 12:18 AM
The part of the hub that the spaceship docks with can be nonrotating. One way to do this is with a rotating airlock. This airlock is sort of like a really short range shuttle. The "shuttle" only moves a few inches--enough space to allow the "shuttle" to rotate independently of the hub to dock with the spaceship. Despining and respining the "shuttle" can be accomplished with an electric motor style shell of electromagnets.

JHotz
2005-Dec-05, 12:50 AM
The part of the hub that the spaceship docks with can be nonrotating. One way to do this is with a rotating airlock. This airlock is sort of like a really short range shuttle. The "shuttle" only moves a few inches--enough space to allow the "shuttle" to rotate independently of the hub to dock with the spaceship. Despining and respining the "shuttle" can be accomplished with an electric motor style shell of electromagnets.
I though the airs seal to accommodate this was no technically feasible at this point.

IsaacKuo
2005-Dec-05, 03:07 AM
There's no rotating air seal involved. The "shuttle" is docked to either nothing, the station only, or the spacecraft only. It's never docked to both at the same time.

So most of the time the "shuttle" is docked to the station, rotating along with it. When a spacecraft approaches, the shuttle "undocks" from the station and is then despun. The non-rotating shuttle is now ready to dock with the spacecraft.

After the spacecraft docks with the shuttle and payload is transfered, the spacecraft undocks with shuttle. Now the shuttle is respun, and docked with the station.

ZaphodBeeblebrox
2005-Dec-07, 05:45 AM
There's no rotating air seal involved. The "shuttle" is docked to either nothing, the station only, or the spacecraft only. It's never docked to both at the same time.

So most of the time the "shuttle" is docked to the station, rotating along with it. When a spacecraft approaches, the shuttle "undocks" from the station and is then despun. The non-rotating shuttle is now ready to dock with the spacecraft.

After the spacecraft docks with the shuttle and payload is transfered, the spacecraft undocks with shuttle. Now the shuttle is respun, and docked with the station.
What, If they Wanted, to Stay Awhile?

Just Respin, The WHOLE Thing?

IsaacKuo
2005-Dec-07, 07:37 AM
The only component which is being despun and respun is the small "shuttle" (a cylindrical airlock which can rotate independently of the station). At all times, the station remains spining. At all times, the spacecraft doesn't spin.

Anyone who wants to "stay awhile" on the station transfers to the station. Big deal.