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Spinning space station design

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Skewbrow:
I think that the one slide rule I used in middle school is still somewhere. Can't say that I would have used it for a looong time. :cry:
More often than not I only need exact results (or estimates based on long simulations) at work. I admit that Mathematica (or long computer simulations) will be the tool, if I need more than two significant digits of an approximate figure. Currently I do not own a calculator at all. I did 'save' a book full of logarithm tables, when our library decided to get rid of some of their old stuff. Mostly for sentimental reasons.

jwhouk:
Slide rule. Good thing I didn't take geometry and trigonometry until the 1980's, or I woulda had to learn how to use one of those.

pwhodges:
(This seemed like enough of a digression to merit its own thread.  I've taken the liberty of quoting a couple of messages that were sent by PM rather than go too off-topic in the WCDT.)



--- Quote from: Akima on 19 Jan 2012, 20:54 ---
--- Quote from: pwhodges on 19 Jan 2012, 15:08 ---I wouldn't like to have to design a structure 1km in radius to rotate at 1rpm.  All the stresses are in tension, not compression, which gives me bad feelings on that scale.  But since I've done no mechanics since my engineering degree in 1968, my feelings might not be justified, I suppose.
--- End quote ---
Your engineering background is certainly stronger than mine. The 1975 "Stamford torus" study proposed a radius of 900m, but I am not qualified to assess the structural design. The classic space station is always imagined as a complete wheel, but I've often imagined a single spoke with a docking-hub free-fall area in the centre of the rotating structure, and habitable areas at the ends. It would certainly be a structure in tension with elevators/cable-cars linking the hub to the habitats at the ends. Docking anywhere other than the hub of a 1000m radius rotating space-station would present serious difficulties, since the "circumference" would be whirling round at roughly 100m/s.

As for the radius, the curve of radius vs. rotation for any given centripetal acceleration gets pretty flat once the radius exceeds 250m or so. If one reduces the radius from 1000m to 500m, for example, the rotation required for 1g only rises from 0.95RPM to 1.34RPM, which most studies have suggested is easily tolerated. Supposedly 3RPM (100m radius) is bearable with acclimatisation, but 5RPM (35m radius) has everyone reaching for the sick-bags. Yes, I did already have a spreadsheet set up to work all these things out...

--- End quote ---



--- Quote from: Is it cold in here? on 19 Jan 2012, 22:43 ---Off-center docking: A vehicle trying to dock couldn't afford to spend any amount of time staying near the docking port, since the vehicle would have to accelerate constantly. Relax the requirement for allowing multiple docking attempts, though, and the approaching vehicle could fly a free-fall course that intersected the path of the spinning element at zero relative velocity (I think the usual metaphor is "catching an egg on a plate"). With slow rotation, the station and the approaching vehicle might even stay in proximity long enough to allow human control.

There's a hidden economic assumption in the model of a complete wheel, which is that the valuable real estate that you want the most of will be in the 1g area. Microgravity industry might be a more important tenant.

--- End quote ---

pwhodges:
In the absence of my long-lost mathematical capability and knowledge of materials science, I resort to weak analogies. 

Using cables to link the station and its counterweight to a central hub (and maybe the counterweight would be more useful accommodation, for efficiency) is equivalent to having cables that could lift the structure concerned off the surface of the Earth from a height of a kilometre.  In comparison, the tallest suspension bridge in the world has towers less than 300m high, and the bridge deck is not at their base, of course.  OTOH, the main cables are at an angle, so the tension in them will be greater.  Thus, if the deck is 250m below the tops of the towers, and the angle of the cables at the tower attachment is such that the tension is double what it would be if straight down, then a 500m radius for the space station would be doable using similar technology; maybe a bit more given that there doesn't have to be the same margin for the effects of weather and traffic. 

So, I was being a bit pessimistic - it's on the edge, but probably possible.

Skewbrow:
Sorry about being dense, but I'm still recovering from a flu, and this makes my head spin. How do you dock into the hub of a rotating space station, if you can't make the incoming spacecraft rotate at the same rate? At the hub you have control of the relative speed, but the rotation is still there.

Dock into a huge ball-bearing, and fine-tune the rotations before opening an airlock?

I realize that the docking spacecraft would be small, so 1RPM won't take much. May be this isn't a problem at all?

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