Centrifugal Spin Habitats

[ckalina]

Recently it struck me that sci-fi ships with spin habitats (i.e. to simulate gravity through centrifugal force) tend to put them amidships. For example, The Leonov from 2010, which I know inspired some of the Babylon 5 ships.

My question is: Is there some engineering rationale for putting the big spinning bit near the overall center of mass? It strikes me that it would be simpler to put it at the end, so you have only one interface with the rest of the hull, not two.

Does it have something to do with torque or precession? Or is it just an aesthetic visual design thing?

Just wondering. I doodle such ships in my spare time and want to be sure I'm not being stupid about it.

[kylwell]

It's easiest to put a rotating object at the center of the mass of the axle. Things get tricky (engineering wise) putting a rotating mass at one end of the axle, something to do with the balance of the object becomes much more critical due to the lack of dampening of the axle.

Basically you can spin an unbalanced object that's centered on an axle easier than one on the end of an axle.

And rotating habitats are by nature unbalanced.

Unless you build them massively huge to the point where everybody running to look out the same window is negligible.

[Ken Lim]

Here's how i view the Earth Alliance fleet:

Primitive. No artificial gravity, no gravitic drive, no high energy output reactors.

Taken together this means EA ships have to rely on rotating crew modules to create spin 'gravity'. The alternative was seen early in the series when the command crew of a smaller patrol boat type was shown strapped into their control chairs like Fury pilots. EA ships also have big glowy engines, probably some evolved version of a chemical rocket, but still basically throwing matter one way in order to move the other way. The only way to manouevre with propulsion like that is to vector the thrust or fire off tangential thrusters like a Fury. Either way a giant rotating module will play hell with your vector calculations unless its nicely balanced at your center of mass. Consider an EA ship with the spinny bit on one end of the hull. It commences a 2 dimension turn to port. Within seconds it will start corkscrewing in all 3 dimensions and additional thruster firing will be needed to damp out all the eccentricities. That burns fuel, wastes time and weapon accuracy and could kill you in a battle.

[DErickson]

From what I understand, the big problem with centrifugal gravity is the beefy, heavy structure required to hold it together at 1g's worth of spin. Too much mass to lift off of Earth! That's why those Chesley Bonestelle wheels of the '50s, and 2001 A Space Odyssey, never came about.

[tomr]

From what I understand, the big problem with centrifugal gravity is the beefy, heavy structure required to hold it together at 1g's worth of spin. Too much mass to lift off of Earth! That's why those Chesley Bonestelle wheels of the '50s, and 2001 A Space Odyssey, never came about.

Actually, you are only partially right.

Massive, yes, but not so much because of stress, as it would be because those wheels would have to have a fairly large diameter to be useful for anything. This means lots of material needed to build something that diameter, and with enough interior space in the ring to provide a comfortable environment to live and work in. The biggest stress would come as you start to spin that wheel.

Because, at present, we don't have any real heavy lift vehicles, the amount of material that can be launched with one rocket is relatively small. Heck, look at the number of launches that have been made to date to build the ISS, by the US, Russia, and I believe the ESA. The ISS isn't that big, looking at just the habitable part of it (the rest of it is those huge solar panels needed to provide power for the ISS).

Something the size of those wheels would require an insane amount of launches to get all that material up into orbit. Which means an insane amount of money to do so. A structure that size has to be built in space, and until we can figure a way to manufacture all that material in space, from raw material from asteroids and such, or we figure out a way to get all that material into orbit economically, you won't see those huge wheels getting built

You wouldn't even have to have 1g, as a human could work well in 1/2g. Heck, look at the astronauts on the moon (1/6g). Their biggest problem was the spacesuit being so bulky. 1/2g would give you a good sense of "up" and "down" (which in the wheel, is really in and out), and allow you to work comfortably. You could sleep in a bed, without the need to be strapped down. 50 lb objects would weigh 25, etc.

One of the coolest effects I've ever seen in a movie, was in 2001, when the shuttle was approaching the hub of the wheeled space station. It had to start rotating on it's x-axis to match the spin of the dock. Once that was matched, it appeared as if the dock and shuttle were stationary, and the universe was spinning around them! Something to do with relativity, I think!

Tom

[ckalina]

Massive, yes, but not so much because of stress, as it would be because those wheels would have to have a fairly large diameter to be useful for anything.

Doodling a Mars mission spacecraft, I did a little research, a little arithmetic (which I may well have done wrong), and came up with the following:

Mars gravity at 2rpm = 82m radius (270 ft)

Mars gravity at 3rpm = 36.5m radius (120 ft)

(Mars gravity is about 0.37 of a G, and 2-3 rpm is supposedly what most people can handle without side effects, although obviously there's very little practical research in this area)

It wouldn't have to be a complete ring or torus, though -- could be pods on the end of long booms or tethers, though I should think this would be less structurally sound than a torus. Pods would also diminish the disorientation that could be caused by looking down a curvy hallway.

For laughs I sketched an octagonal torus made up of spacelab-type modules that could be lifted in the Space Shuttle. This seemed like the most plausible real-world way to build a torodial habitat. The result was about 70 feet (21.3m) in radius, which only produces only about 0.09 (at 2rpm) or 0.21 (at 3rpm) of a G.

I'm not sure if there's some minimum radius within which people can't manage well. I'd think that a difference in gravity between the head and feet would exaggerate the sense of artificial gravity and the tendency of body mass to shift upwards after long periods in free fall, but again, there doesn't seem to be much real-world research on the subject.

The more I think about it, the more wary I am of spin habitats. Dynamic systems (like variable geometry wings on aircraft) always add lots more things that can go wrong. Maybe it would be better if the whole spacecraft spun as a unit, as with the 2001 space station you mentioned.

Thanks for all the comments and expertise,

-cpk

(Good reference on the topic: http://www.projectrho.com/rocket/rocket3u.html )

[madmike]

The space agencies seriously need to think about using nuclear propulsion to enable much heavier payloads to be lifted into orbit.

Chemical fuel propulsion has reached the end of the road, both tehnically and in output.

MikeJ

[dragon]

The space agencies seriously need to think about using nuclear propulsion to enable much heavier payloads to be lifted into orbit.

Chemical fuel propulsion has reached the end of the road, both tehnically and in output.

MikeJ

The thing putting a damper on things is: "What happens if the vehicle with nuclear engines gets into a bad situation?" If it explodes in the atmosphere, it becomes a dirty bomb. If it crashes whole but the nuclear containment part cracks on the ground, you create an unimaginable environmental disaster. Once that problem gets licked, then nuclear engines become an option.

[madmike]

Actually doing some reading, that is just as low an issue as a nuclear sub or ships nuclear powerplant doing the same thing.

MikeJ

[William G]

Actually doing some reading, that is just as low an issue as a nuclear sub or ships nuclear powerplant doing the same thing.

MikeJ

Yeah But, Mike the USS Los Angeles, is not being subjected to the same stress in the water as, say a drop from 1 mile if the engine conks out on an atomic rocket.

Nor is the reactor in the same league as the Nuke motor would be to propel a payload into orbit.

Lets just build on the Moon...

my 2c worth there...

As to the structure for a Wheeled station

It is a giant Suspension bridge with no endpoints when it is built.

the larger the ship the easier it is to offset the weight/mass for movement and equipment.

Water tanks built into the floors and walls to counter the weight imbalance and to provide some shielding for radiation as well as a pumping system to move it from a central tank to various areas in much the same way as a fuel mangement system for variable geometry winged aircraft.

the measurement is simple. Laser Gyros measure any imbalance and compute the amount of water to move from one point to another.

hmmm 2c more

William G

:unsure:

[RotorheadTX]

Mike,

Unless I mis-understand your last point, you're leaving out the difference in speed between a nuke sub or aircraft carrier and an object trying to achieve escape velocity!

As illustrated by the wrecking of the USS San Francisco, a nuclear-powered sub hitting a solid object at 40 knots is worlds away from a rocket crashing while trying to make a speed of 7 miles per second (25,000mph)!! Even if a space vehicle was built as solidly as an SSN (which in itself is ridiculous because you're exponentially increasing the amount of mass and therefore power needed to launch it) had the San Francisco crashed at even 1000 mph, there would be a great big glowing hole out there somewhere!!!

Don't get me wrong, I'm not a rabid anti-nuker, but the simple fact remains that given current technology, there is no truly fail-safe system for nuclear power. Using a nuclear engine for exo-atmospheric power is perfectly reasonable, but the reactor/engine must be started at the very least in orbit in the interests of human safety and ecological responsibility!

You may not be aware of it, but the Voyager probes (Oh crap,it's V'ger!! :unsure: ) were launched with plutonium dioxide power plants, and that raised an unholy stink with the environmentalists here. I honestly believe that if any nation were to try and launch a true nuclear-powered "rocket" from the ground, the international outcry would make the North Koreans look like Sprout Scouts.

<Thus ends the mad ravings of a semi-informed backyard-hack scientist... we now return you to your regularly scheduled Lager >

[madmike]

Something to ponder

Safety issues are a concern, but the fact remains clear, space travel will never become a viable exercise unless such engines are used at some stage, whether they are fired from orbit and outwards or from launch. Chemical engines simply do not have enough power/thrust to lessen the cost of delivering payloads into orbit.

Humanity must cut it's dependency on fossil and chemical fuels otherwise we will not have a planet to launch from.

Establishing a moon base goes a long way towards getting us out there and perhaps spaceships with fission or fusion engines can be assembled there and launched there.

Mike

Edited October 2, 2005 by madmike

[DErickson]

From what I've read here, the place to do the mining, launching, and building of big ships is....The Moon!

P.S., When it's time to light up that big fusion rocket....do it on the dark side! :)

[tomr]

P.S., When it's time to light up that big fusion rocket....do it on the dark side! :wacko:

The thing about the engine in MadMike's link (very interesting read, by the way, thanks Mike!), is that the exhaust is clean. Just to be on the safe side, the author suggests a launch in the Pacific Ocean.

The problem with the whole thing is that there is that nasty word new-klee-er! Visions of Chernobl, Three Mile Island, and the "China Syndrome" come to peoples minds!

Dark Side Of The Moon is probably the only place that will be "safe" enough for most people, except for those that say we shouldn't even allow nuclear anything in space!

[madmike]

upside is that we have only had three major accidents in 50 years, downside is they were real bad!

seriously though, I remember reading about the outrage when steam reciprocating engined steamships were launched!

MikeJ

[DErickson]

seriously though, I remember reading about the outrage when steam reciprocating engined steamships were launched!

Mike,

I did not think you were that old (Haw,Haw)!

Actually, there would not be flying piles of plutonium to worry about, just a wicked neutron flux when the fusion drive was started... something real for the greenies to whine about!

[BadCop]

The biggest reason that centrifuges to emulate gravity have to be so big (and consequently unfeasible) is because of Coriolis forces, ie Smaller Size = greater sideways force. In his fictional novel about a mission to Titan, Stephen Baxter points out this as being a flaw in the design of the Discovery in Arthur C Clarkes 2001: A Space Odyssey - the 35' diameter part of the ship that rotated to simulate lunar gravity would have left Bowman and Poole constantly knocked sideways by Coriolis forces, and in a constant state of nausea.

Coriolis Force explained HERE

Coriolis forces also explain why the water in the toilet down under goes around in the opposite direction to you nortern hemispherians.

In a different life I studied Mechanical Engineering and Physics was a speciality!

Edited October 11, 2005 by BadCop

[William G]

The biggest reason that centrifuges to emulate gravity have to be so big (and consequently unfeasible) is because of Coriolis forces, ie Smaller Size = greater sideways force. In his fictional novel about a mission to Titan, Stephen Baxter points out this as being a flaw in the design of the Discovery in Arthur C Clarkes 2001: A Space Odyssey - the 35' diameter part of the ship that rotated to simulate lunar gravity would have left Bowman and Poole constantly knocked sideways by Coriolis forces, and in a constant state of nausea.

Coriolis Force explained HERE

Coriolis forces also explain why the water in the toilet down under goes around in the opposite direction to you nortern hemispherians.

In a different life I studied Mechanical Engineering and Physics was a speciality!

Very true Bad Cop

the larger the diameter the lower the coriolis

Hence RINGWORLD!!!!!!!!

However even it has its flaws...

William G

(and not I am not a Pak Protector in disguise)

[LanceB]

Safety issues are a concern, but the fact remains clear, space travel will never become a viable exercise unless such engines are used at some stage, whether they are fired from orbit and outwards or from launch. Chemical engines simply do not have enough power/thrust to lessen the cost of delivering payloads into orbit.

Humanity must cut it's dependency on fossil and chemical fuels otherwise we will not have a planet to launch from.

Yes, safety issues. I love how that guy who set up the site (interesting read, Mike, thanks) talks about the atom bomb test pumping out 1000KG of nuclides, and saying "no one was hurt". Anyone know why above ground tests were stopped? Anyone? Beuller?

Because those nuclides, cesium in particular IIRC, were building up in the atmosphere and 10 more years of tests would have killed all of us. The scientists had the data, it was presented, and the governments and military were forced to listen. That stuff doesn't fall to the ground right there at the test site, it goes up and floats around for a while. Same with Chernobyl. The guy running that site talks about how with warning all deaths and injuries could have been avoided with warning, how measures could have been taken. Like what, evacuating Scandinavia? They're the ones who got hit with the fallout, not Ukraine. Sorry, but I don't trust this guy with his "Don't worry, be happy" attitude. Not when he's talking about the potential for pollution that lasts millennia, strikes far away from where it was created, and kills you, your kids, your grandkids and their grandkids. Nuclear engines sound promising, but only if they are built and used out of Earth's atmosphere.

And Mike, cutting ties to fossil fuels is something we should definitely do, but don't forget uranium is a non-renewable resource as well. Unless someone gets nuclear fusion working, we're doomed. Analyses I have seen stated that even if we switched to an all-nuclear-fission electricity generating system, the world would be out of power in 100 years once the uranium ran out.

Major extinction event, anyone?

[madmike]

Hence the need to get into space and establish ourselves out there...

Exploration will drive advances in spaceship design and propulsion, as the great exploration and migration to the New World did 400 years ago.

[Ken Lim]

Join the Terran Marines. Visit new places, meet new people, and frag them with a rail gun.

Actually i think what drove the advances in ship design and tactics was frequent pirate raids on the fat lumbering treasure ships hauling loot across the seas. Nothing speeds up evolution like some conflict.

[madmike]

Join the Terran Marines. Visit new places, meet new people, and frag them with a rail gun.

Actually i think what drove the advances in ship design and tactics was frequent pirate raids on the fat lumbering treasure ships hauling loot across the seas. Nothing speeds up evolution like some conflict.

:lol:

Not all though, the need for safer long distance travel spurred things on a bit as well, including running away from a fast well armed pirate ship!

[tomr]

Not just safer long distance travel, but the need to carry more passengers, or cargo, and doing so with the least amount of time required, and at the least cost per passenger/unit weight of cargo.

You see this happening from the ships on the high seas, to the planes in the air. From the trucks on the road, to the trains on the rails.

[ckalina]

Coriolis forces also explain why the water in the toilet down under goes around in the opposite direction to you nortern hemispherians.

The toilet thing is apparently a myth...

http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html

...but of course you're right about the coriolis effect in spin habitats.

Still, we don't know how big they would have to be to nullify this effect. This is one of those areas in which we have little real-world testing, unfortunately.

[DErickson]

Another answer to the 1g problem...the ships that traveled to the outer solar system in the novel Empire Earth accelerated at a constant 1g until the time came to begin slowing down. At that point the cigar-shaped vessel would power down, rotate so it's single rear fusion engine pointed "forward", and apply 1g braking thrust for much of the remainder of the trip. The interior accomodated both zero g and acceleration regimes.