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[Is it cold in here?]

Hannelore's Formspring experiment said that the station spins to create a 1g acceleration.

[Akima]

That would also be much simpler than hauling people up to his space station or coming down to earth (something I'd say he could no longer do if Hanners didn't seem to be free of physical maladies from growing up in low-g).

Rotational pseudo-gravity of course (IICIH got in ahead of me!). Which in turn implies that Hannerdad's orbital is quite large, to avoid the problems of nausea induced by gyroscopic coupling etc. Since this is a comic, let's say <calculator noises> his station has a radius of 1000m so that it can provide a 1g centripetal acceleration while turning at just under the one revolution per minute that is supposed to be safe even for motion-sickness susceptible people (Yes, I am a space-nerd). Hilarity ensues when <character> turns out to be extra-susceptible.

The other question is, who is the "they" that Hannerdad is permitting to hold a birthday party? The station's human crew? The un-secret robots?

[pwhodges]

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.

[Is it cold in here?]

Suspension bridges are largely in tension.

The easy way to create 1g worth of spin is a long tether and a counterweight.

[pwhodges]

Now try docking your transport on it, and then realise you've thrown it way off balance.

[ZBixby]

Well what if we made it more like a giant Frisbee and have the docking station on the logical top or bottom of the station? that way any added weight isn't throwing off the spin by adding unnecessary weight to a side that is making a large rotation?

[Torlek]

Now try docking your transport on it, and then realise you've thrown it way off balance.

That's why you have a de-spun central docking hub. Saves your space station from the wrath of Sir Issac Newton and allows for physical comedy when entertaining guests.

Well, if you want to get to space, you generally have to get to either Florida (Kennedy SC), New Mexico (NM Space Facility) or California (Edwards AFB).

Unless, of course, Hannerdad has a space elevator located somewhere nearby.

I'm thinking more space plane. Hannerdad's station is in LEO given how frequent Hanners said the sunrises were, elevators don't work so well that low. I'm thinking something Skylon-esque or NASP-esque.

[jwhouk]

I'm thinking more space plane. Hannerdad's station is in LEO given how frequent Hanners said the sunrises were, elevators don't work so well that low. I'm thinking something Skylon-esque or NASP-esque.

Considering that there was a change in universes at some point in recent history, a combination of the X-30/33 and SpaceShip One/Two from Virgin Galactic.

[Skewbrow]

Which in turn implies that Hannerdad's orbital is quite large, to avoid the problems of nausea induced by gyroscopic coupling etc. Since this is a comic, let's say <calculator noises> his station has a radius of 1000m so that it can provide a 1g centripetal acceleration while turning at just under the one revolution per minute that is supposed to be safe even for motion-sickness susceptible people.

Thanks for the links (also the last time this topic came up) explaining Coriolis-induced problems of rotational gravity. But in a way the fact that you resorted to a frigging calculator to (effectively) estimate Pi over 30 (radians per second)  squared up to the whopping accuracy of a single significant digit makes me sad. I know, that's the way it's done nowadays. This is not meant as a personal criticism, please don't take it as such. Just my old school thinking, where mental arithmetic is the default.


@Torlek: Thank you so much for reminding everybody that a space elevator would be mostly useless for getting to a low orbit station! I guess you could ride a space elevator up a significant fraction of the distance to geosynchronous orbit and drop off
to end up on a suitable elliptical orbit approaching the space station at perigeum, but the velocities would not match, so you would still need a lot of thrust to be able to dock into the space station. May be the resident experts of space travel can help me here

[pwhodges]

How many sliderules have you got?  I can still lay my hands on three.

[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.
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.)

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.

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...

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.

[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?

[akronnick]

The counterweight module could carry all the heavy stuff like fuel, water, batteries and food. The habitation module could be relatively light weight, and doesn't need to be at 1g. In fact, if the station is being used as a way station between the Earth and the Moon, as in 2001, a lower gravity such as 1/3-1/2g may be more beneficial, as a transition for people who are adjusting between 1g and 1/6g.

[pwhodges]

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.

I had thought about that; it seems to me that approaching along the axis and matching the rotations is trivial compared with having to accelerate continuously to keep in position during docking off-centre.  I don't want to contemplate the other alternative of a stationary hub with the space station rotating around it!

a lower gravity such as 1/3-1/2g may be more beneficial, as a transition for people who are adjusting between 1g and 1/6g.

But if they are not, and are only going between the station and the Earth, then what is the minimum gravity to avoid skeletal and muscular problems in the long term?

[Skewbrow]

Paul, I can't do the mechanics right now. If coerced to do it I think I would be able to work out the tension on a catenary, i.e. a cable hanging from its end points at the top of the pylons with zero load, but the figures coming out would be meaningless for our present question, so I won't. Anyway, the angle makes a huge difference. May be the reason they want tall pylons is to increase the angle?

As an extremal case of a tiny angle consider the tension on the cable of a tight rope dancer. I may be way off, but I think it could easily be ten times the weight of the artist or more. IIRC in the story about the French guy who danced between the WTC towers they said that the tension on the cable was something like 5 ton(ne)s (sorry I don't know whether those were metric or not).

So the existing materials could be strong enough to take the tension of a spinning space station. If the spinning station has a full rim connected to the hub by several spokes, may be building a 'suspension bridge' from each and every spoke to the next one would give enough extra structural support?

[akronnick]

But if they are not, and are only going between the station and the Earth, then what is the minimum gravity to avoid skeletal and muscular problems in the long term?

That's not really known. The only gravities humans have spent more than a few days at have been 1g and 0g.

We are adapted to 1g (obviously) and there have been Astronauts and Cocmonauts spending many months at a time at 0g since the 1970's, but the longest anyone has spent at an intermediate level was when Cernan and Schmidtt spent just over 3 days on the Moon.

Given that physically fit individuals can spend extended periods at 0g with little ill effect, artificial gravity on a spacecraft may be more of a luxury than a necessity (It does make filming Sci-fi movies simpler).

The real limit to long term space habitation is radiation exposure. Without the shielding properties of Earth's atmosphere, Astronauts in Low Earth Orbit receive much larger doses of some really scary photons.

[pwhodges]

Paul, I can't do the mechanics right now. If coerced to do it I think I would be able to work out the tension on a catenary, i.e. a cable hanging from its end points at the top of the pylons with zero load, but the figures coming out would be meaningless for our present question, so I won't. Anyway, the angle makes a huge difference. May be the reason they want tall pylons is to increase the angle?

A suspension bridge is not a simple catenary, though, because the deck is suspended from multiple points along the cable.  The angles at the end are typically of the order of 45 degrees, so you don't have the tight-rope levels of multiplier (I start to see more extreme tensions when suspending microphones on a taut cable across an auditorium).

The real limit to long term space habitation is radiation exposure. Without the shielding properties of Earth's atmosphere, Astronauts in Low Earth Orbit receive much larger doses of some really scary photons.

True - and the best form of shielding is (in effect) mass, and so impacts on the feasibility of our rotating designs.

[celticgeek]

How many sliderules have you got?  I can still lay my hands on three.

I have two good quality slide rules, and one cheapie plastic circular slide rule.  I am looking for pictures.

[pwhodges]

Aristo 0968 Studio
My 10" rule that I bought to be an engineer with (not my own - mine's cleaner than this photo):


Aristo 89 Rietz
A 5" pocket rule I picked up sometime (mine has a leather slipcase):


I can't identify my wife's without going home to look at it.

[Skewbrow]

My slide rule is a 10-inch (the length of the scale as opposed to the entire frame, I presume) Japanese make Royal Techlog. My middle school math teacher probably got commissions from whichever company was importing those. It has the same set of scales as your 10-incher. Seems to be in reasonable but not pristine condition. There are some scratches in the sliding window (sorry, don't know what it's called in English) - luckily none too close to the hairline. Also the spring from the other side of the window is missing, but the one on the other side keeps it in the correct position. IIRC we occasionally had to use graphite from pencils as a lubricant, but it seems to be sliding just fine, now.

My Dad has an Aristo, and that's what he used when teaching me

[pwhodges]

The sliding window is referred to as the cursor (the running part, from the Latin for run).  More elaborate rules (like mine) have additional hairlines for special purposes.

[Border Reiver]

They look like the GFTs I learned to use when firing howitzers back in the 80s. 

{looks around at all the real engineers} I'll go back to lurking in this thread now.

[DSL]

If you can lay hands on a July 1976 National Geographic, Isaac Asimov took a science-fictional look at a mile-wide spinning-wheel space station. My copy is ... somewhere ... but here's a link to a recent commentary about it.

A wheel station would have the advantage over a module-and-counterweight structure in that you'd be able to move throughout the habitable-gravity area without having to move through the hub. I'd have to think the ring would be self-reinforcing to a degree.

For some entertaining nonsense, the original "Star Fleet Technical Manual" from the 1970s contains schematics for a giant spinning space station with, among other things, docking facilities *around the rim* for Enterprise and her fleetmates. Quite apart from the increased gravity, I'd hate to be the one who had to navigate a ship into one of those docks. Mr. Sulu'd be earning his pay, he would ...

ADDED LINK. Duh.

[Is it cold in here?]

With a central docking hub, you could put the approaching craft into a slow roll and match the station. Control inputs would have effects that would surprise an untrained human. Alternatively, you could despin the hub during docking maneuvers and spin it back up again for the convenience of people leaving the docking hub.

[pwhodges]

I'm worried by the idea of a bearing of that size to allow that decoupling; the effect of a jam would be devastating.

[Kugai]

Admittedly, anything like B5 is a long way off, but it does use a Rotational Section (Ie the cylindrical main body) to maintain gravity and has an inner central core which is used as a large garden to grow foodstuffs and to create a natural CO2/Oxygen exchanger.  JMS, in many cases, tried to stick close to what was scientifically known and postulated about building such a station while giving it a futuristic bent.

[Precipice]

For some entertaining nonsense, the original "Star Fleet Technical Manual" from the 1970s contains schematics for a giant spinning space station with, among other things, docking facilities *around the rim* for Enterprise and her fleetmates. Quite apart from the increased gravity, I'd hate to be the one who had to navigate a ship into one of those docks. Mr. Sulu'd be earning his pay, he would ...

Take a closer look at those schematics. It doesn't say anywhere that it spins, and it should be obvious that it doesn't. The floors don't follow the curve of the rim, they're flat. With a spin-induced gravity, if you stood near the end of a pie-shaped segment, it'd feel like the floor is tilted at a 30 degree angle.  It must generate artificial gravity using the same technology as the Enterprise.

[celticgeek]

Here are  My Slide Rules. 

And the father of one of my friends in High School had a "double length" slide rule; a full twenty inches long!

[DSL]

For some entertaining nonsense, the original "Star Fleet Technical Manual" from the 1970s contains schematics for a giant spinning space station with, among other things, docking facilities *around the rim* for Enterprise and her fleetmates. Quite apart from the increased gravity, I'd hate to be the one who had to navigate a ship into one of those docks. Mr. Sulu'd be earning his pay, he would ...

Take a closer look at those schematics. It doesn't say anywhere that it spins, and it should be obvious that it doesn't. The floors don't follow the curve of the rim, they're flat. With a spin-induced gravity, if you stood near the end of a pie-shaped segment, it'd feel like the floor is tilted at a 30 degree angle.  It must generate artificial gravity using the same technology as the Enterprise.

Huh. I remember my copy (long gone) saying it spun. And remembering, even as a sixth-grader, that it made no sense.

[Akima]

But in a way the fact that you resorted to a frigging calculator to (effectively) estimate Pi over 30 (radians per second)  squared up to the whopping accuracy of a single significant digit makes me sad. I know, that's the way it's done nowadays. This is not meant as a personal criticism, please don't take it as such. Just my old school thinking, where mental arithmetic is the default.

Actually I didn't use a calculator (the noises were artistic license)  . I had a spreadsheet already set up to run the numbers for a range of radii and centripetal accelerations , but if I hadn't, I certainly would have used a calculator. I'm just not confident that I could calculate in my head the necessary radius for a space station given only that the rim would be travelling in uniform circular motion at one RPM, and the required centripetal acceleration at the rim was 1g (which I approximated as 9.81m/s). I take comfort from knowing enough physics and maths to do the calculation at all, and being curious enough to want to do it. I'm not nearly ancient enough to feel nostalgic about slide rules, but this was my first calculator (and the suŕnpán can easily handle hex as well as decimal owing to the peculiarities of traditional Chinese weights and measures):

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

I've always assumed that the incoming spacecraft would match its spin to that of the space-station. A 5m radius spacecraft (larger than anything in service today; Soyuz and Shénzhōu are both under 3m in diameter) rotating at one RPM would generate so little pseudo-gravity (about 0.06g) that its crew would probably not notice.

[Is it cold in here?]

I'd consider using a magnetic bearing to avoid vacuum welding problems.

[Skewbrow]

@Akima, a spreadsheet at hand is, of course, an acceptable excuse for not doing mental arithmetic. I just happened to be working with that single data point that you gave us first: omega=1RPM=Pi/30 rad/s is approximately (using the Hoosier approximation Pi=3) 0.1 rad/s, so to find a radius R giving the target acceleration of R*omega^2=1g=10m/s^2 we immediately see that R=1000 m. IOW for this particular set of inputs at this level of precision the "mental arithmetic" amounts to moving the decimal point around

You're, of course,  correct about the problem of matching spins being trivial. I knew that the crew wouldn't need to use barf bags, but for some reason it wasn't clear to me that matching spins is no more difficult than matching speeds. My lack of knowledge about steering in space showed.

[Is it cold in here?]

OK, suppose you've matched spins but need to correct a slight drift to the left. You instinctively fire the right thrusters.

Suddenly you're going in circles.

Humans are highly trainable, so it might be possible to teach them to do the right thing. Computers would be a better bet.

[Skewbrow]

Ok, "trivial" was an overstatement. Would "Something that a computer or a trained pilot can handle" be closer to the mark?

[akronnick]

First you would have to align the axes, then you would match rotation, then dock.

It might be tricky for a human pilot, but for a computer controlled pilot, it would be simple.

[cesariojpn]

Gundam.

http://www.youtube.com/watch?v=DO5-XGCqzfo

[Kugai]

For some entertaining nonsense, the original "Star Fleet Technical Manual" from the 1970s contains schematics for a giant spinning space station with, among other things, docking facilities *around the rim* for Enterprise and her fleetmates. Quite apart from the increased gravity, I'd hate to be the one who had to navigate a ship into one of those docks. Mr. Sulu'd be earning his pay, he would ...

Take a closer look at those schematics. It doesn't say anywhere that it spins, and it should be obvious that it doesn't. The floors don't follow the curve of the rim, they're flat. With a spin-induced gravity, if you stood near the end of a pie-shaped segment, it'd feel like the floor is tilted at a 30 degree angle.  It must generate artificial gravity using the same technology as the Enterprise.

Huh. I remember my copy (long gone) saying it spun. And remembering, even as a sixth-grader, that it made no sense.

Take another look.  The 'Buildings' of the station are set on the outer rim.  Looking at it it seems to have the same constructional layout as Babylon 5 as to the relation of floors and decks layout.  Admittedly, unlike B5, the Trek Universe has the benefit of Artificial Gravity, so it probably doesn't rely on rotational action gravity wise as that station does, so I'm guessing that the rotation is more of a slow 'Barbeque Roll'  much like the Apollo spacecraft used during their journey to the moon.

[Is it cold in here?]

To be pedantic, it was the humans in the B5 universe who didn't have artificial gravity.

[Kugai]

I am aware of that, which is why ships of the Hyperion Class were zero G ships and their stations rotated or, like the Omega's, Earth Force One, Liners like the Azimov and the large Explorer Class ships had rotating sections.  Human's didn't gain Gravtech until the Shadow War era with their co-operation with the Minbari during it.

And yes, yes you are.

[Is it cold in here?]

I have only begun to show my potential for pedantry.

Could you prevent bone loss with regular sessions in a small centrifuge, so you wouldn't have to spin the whole station? Or combine recreational EVA with bone therapy by putting spacesuited humans at opposite ends of a spinning tether for a few hours each?

[pwhodges]

Exercise sufficient to maintain your musculature at 1g levels would probably do much of what's required.  Possibly.

[DSL]

For some entertaining nonsense, the original "Star Fleet Technical Manual" from the 1970s contains schematics for a giant spinning space station with, among other things, docking facilities *around the rim* for Enterprise and her fleetmates. Quite apart from the increased gravity, I'd hate to be the one who had to navigate a ship into one of those docks. Mr. Sulu'd be earning his pay, he would ...

Take a closer look at those schematics. It doesn't say anywhere that it spins, and it should be obvious that it doesn't. The floors don't follow the curve of the rim, they're flat. With a spin-induced gravity, if you stood near the end of a pie-shaped segment, it'd feel like the floor is tilted at a 30 degree angle.  It must generate artificial gravity using the same technology as the Enterprise.

Huh. I remember my copy (long gone) saying it spun. And remembering, even as a sixth-grader, that it made no sense.

Take another look.  The 'Buildings' of the station are set on the outer rim.  Looking at it it seems to have the same constructional layout as Babylon 5 as to the relation of floors and decks layout.  Admittedly, unlike B5, the Trek Universe has the benefit of Artificial Gravity, so it probably doesn't rely on rotational action gravity wise as that station does, so I'm guessing that the rotation is more of a slow 'Barbeque Roll'  much like the Apollo spacecraft used during their journey to the moon.

Oh, I'm not prepared to go to war over a piece of Star Trek lore most folks would prefer hadn't happened (Roddenberry basically told Franz Joseph Schnaubelt to go to town and make s**t up because at the time, no one had figured out Star Trek would live on and on and on in multiple incarnations) ... I just remembered (because as a 10-year-old nerd I was familiar with the idea of rotational "gravity") looking at it and thinking, it's meant to spin for gravity but those floors make no sense; they'd effectively be like giant hills and I'd hate to try to dock with those docking pods on the rim.

It's just Star Trek. Entertaining, but I don't go there for the science. Don't get me started on the transporter.

 I prefer the "2001" space station and the one Asimov and Mion depicted in the July 76 Geographic, anyway. More attention to science. (and I think, from the Mion paintings, the Asimov station has a hub dock that counterrotates to allow more than one ship at a time to dock.)

Incidentally, I've read that engineers who saw the wheel in "2001" cringed, to a man wondering why the under-construction section was coupled to the finished, spinning section. Build it, they cried, then spin it up and couple it to the spinning section.

But enough nerdery from me. Happy birthday, Hannerdad!

[Is it cold in here?]

Current long-duration orbital missions include spending as much as two hours a day exercising with bungee cords to provide some "down"ward force, and bone loss is still a serious problem.

[idontunderstand]

How exactly DO you work out in space anyway? With rubber bands only?

*Pictures weightless aerobics*

[Is it cold in here?]

Treadmill.

[idontunderstand]

Boxing would be hella fun to try as well...

[Akima]

Gundam.

That clip illustrates a space-habitat along the lines of an O'Neill Cylinder. Structures like that are a bit grand for the title "space-station".

...what is the minimum gravity to avoid skeletal and muscular problems in the long term?

Unfortunately, the simple answer to this question is: nobody knows. Nobody has done the necessary long-term testing even on non-human animals. An even more ticklish problem for permanent habitation in space of the sort depicted in the Gundam universe, is the question of fetal development. Experiments on rats in free-fall done by the Russian space agency suggested that gestation in  "zero-g" was a very bad idea with essentially catastrophic effects on skeletal and nervous development.