Spaceship like "Discovery One" from 2001 Space Odyssey

[satcharna]

Total mass satcharna.

My post was unclear, I apologise. What I meant was that the center of mass for the centrifuge would shift around quite a lot.

[TheCardinal]

... What I meant was that the center of mass for the centrifuge would shift around quite a lot.

That wouldn't be such a problem if a balancing system is installed which transfers a fluid (drinking water f.i) between a number of tanks thereby providing a counterweight.

[Redjoker]

You guys are going on about the centrifuge, but you forgot about the radiator fins that Clarke and Kubrick left off because people might mistake them for wings.

"This spaceship is founded on solidly conceived, yet unrealized science. One major concession was made in her appearance for the purpose of reducing confusion, and this was to eliminate the huge cooling "wings" which would be needed to radiate the heat produced by her hypothetical thermonuclear propulsion system. The producer and director Stanley Kubrick thought that the audiences might interpret the wings as meaning that the spacecraft was intended to fly through an atmosphere."

http://en.wikipedia.org/wiki/Discovery_One

[DerekL1963]

My post was unclear, I apologise. What I meant was that the center of mass for the centrifuge would shift around quite a lot.

From the people moving around, it would shift around a lot... it just wouldn't shift very far. The mass of the crew is *FAR* exceeded by the mass of the centrifuge's structure and the equipment mounted to it.

[satcharna]

From the people moving around, it would shift around a lot... it just wouldn't shift very far. The mass of the crew is *FAR* exceeded by the mass of the centrifuge's structure and the equipment mounted to it.

In those conditions, even a small change would be significant. The centrifuge would also be as light as possible, simply because of the expense of firing things into space. As it isn't load bearing, and would only be capable of rather low spin, it wouldn't need to be very heavy (comparatively) in the first place.

[Nuke]

i think we may be over stating the structural needs of the centrifuge. there are plenty of lightweight and strong materials that can be used to take the load of a small-to medium centrifuge, its contents, and its inhabitants, and whatever ballast is neccisary for stability. it can accomplish this without being exceptionally fragile, sort of like the way an alloy bicycle rim can be very light and still support the weight of a man. you have platform sections that bolt together and then are attached to a center hub with a system of spokes (which could be steel, alloy, or even something more exotic like nanotube cables). then use non-structural carbon fiber composite walls to enclose the living space. this can, but need not be pressurized, i rather like the discovery's way of enclosing everything in a spherical pressure hull.

if you place a load cell on each spoke mounting on the platform you can measure the load on that segment and use the data to figure out where to move ballast to equalize the ring. water makes nice ballast, because of its radiation absorption capabilities, and you need to carry some anyway for a shipboard water supply, and the ballast tanks need only be half full (you need space to pump to anyway). you only need to move a few cubic feet of water to compensate for the weight of a crew member. then you just need some modest pumps and tubing to connect the tanks and some kind of controller to find the best stability solution. the water will actually be pretty heavy, but being a fluid does not need to launched in the same payload as the centrifuge. it can be launched separately and pumped on board during construction. other things that can be launched manually would include interior furnishings, equipment, supplies, crew, ect.

you might also need to discipline crew in their shipboard activities, to avoid maxing out the capacity of the ballast system, by limiting things like social gatherings and observing per segment crew capacity limits. you might actually work that into the design. i could imagine having a larger than typical ballast tank opposite of the chow hall, to allow people to gather there without destabilizing the ring.

Edited August 10, 2013 by Nuke

[sojourner]

In such a design I'd be more worried on the pump work loads due to crew moving around rapidly than them all being gathered in one place. Imagine trying to keep the whole system weight balanced with a couple of joggers running around at different rates.

[DerekL1963]

In those conditions, even a small change would be significant. The centrifuge would also be as light as possible, simply because of the expense of firing things into space. As it isn't load bearing, and would only be capable of rather low spin, it wouldn't need to be very heavy (comparatively) in the first place.

Um, no a small change wouldn't be significant - that's why I called it a small change, not a significant one. While the centrifuge would be as light as possible - that's not the same thing as being featherweight. (A battleship is as light as possible too - otherwise it would sink of it's own weight.) It still has to support tons of equipment at 1G. And the expense of firing things into space? Have you actually seen the movie? They have regular passenger service [e]with stewardesses[/e] to the moon. That's not happening if the costs of firing things is expensive.

[Nuke]

In such a design I'd be more worried on the pump work loads due to crew moving around rapidly than them all being gathered in one place. Imagine trying to keep the whole system weight balanced with a couple of joggers running around at different rates.

then just ban running, and put a treadmill in the gym for exercise.

[satcharna]

Um, no a small change wouldn't be significant - that's why I called it a small change, not a significant one. While the centrifuge would be as light as possible - that's not the same thing as being featherweight. (A battleship is as light as possible too - otherwise it would sink of it's own weight.) It still has to support tons of equipment at 1G. And the expense of firing things into space? Have you actually seen the movie? They have regular passenger service [e]with stewardesses[/e] to the moon. That's not happening if the costs of firing things is expensive.

For the centrifuge to be nearly frictionless, such small changes WOULD be significant. Your battleship comparison is a poor one, as a battleship carries a lot of weight in guns, while being built to withstand bombardment. About as far from a civilian science spacecraft as you can get. The centrifuge actually would be featherweight, as it would only have to suspend a minimal weight. Remember, the vessel was constructed in orbit, and never intended to withstand the forces involved with atmospheric entry.

[DerekL1963]

For the centrifuge to be nearly frictionless, such small changes WOULD be significant.

A few hundred pounds out of what is probably tens of tons or more is not significant.

Your battleship comparison is a poor one, as a battleship carries a lot of weight in guns, while being built to withstand bombardment. About as far from a civilian science spacecraft as you can get.

Nope, it's an apt one because it illustrates the principle that "as light as possible does not mean featherweight". It's apt because the same principle applies even though it's as far from a spacecraft as possible.

The centrifuge actually would be featherweight, as it would only have to suspend a minimal weight. Remember, the vessel was constructed in orbit, and never intended to withstand the forces involved with atmospheric entry.

The mind boggles that you type such a statement with a straight face - you honestly think a 16m diameter centrifuge mounting tons of equipment would be featherweight because it never deals with launch stresses? Did it never occur to you that tons of equipment at one G are going to tear a featherweight structure apart?

I give up.

[satcharna]

A few hundred pounds out of what is probably tens of tons or more is not significant.

Nope, it's an apt one because it illustrates the principle that "as light as possible does not mean featherweight". It's apt because the same principle applies even though it's as far from a spacecraft as possible.

The mind boggles that you type such a statement with a straight face - you honestly think a 16m diameter centrifuge mounting tons of equipment would be featherweight because it never deals with launch stresses? Did it never occur to you that tons of equipment at one G are going to tear a featherweight structure apart?

I give up.

Discovery One most likely wasn't capable of nearly 1G acceleration. Additionally, the force would come from a single direction, as that's how thrusters work. It's very easy to suspend equipment from a lightweight structure for that. Even further, it would be idiotic to keep most of the actual equipment in the centrifuge, and most of what we see are simple computer terminals, a food dispenser, and the cryogenic pods, none of which show much apparent weight.

[panarchist]

3rpm is considered by some sources to be the practical limit - it's a bit more generous than 2rpm. USAF tests in the 1950s/60s showed that more than 80% of test subjects could tolerate 3rpm just fine, and a significant number could handle up to 10rpm.

The big issues at those rotation rates come when you try to turn your head quickly - apparently not fun.

[dharak1]

He doesn't mean acceleration, If you take spider silk and put a 4 gram weight on the end and spin it it snaps because you spun it at more than its g limit. It may have weighed 2 or 3 times more and the thread couldn't handle it. It's the same thing with the centrifuge. If you spin it at 1 g or even .5 it need to hold up on Earth or Mars or whatever g you are spinning at.

[Temstar]

What happens to the centrifuge when the ship is under acceleration? Does it de-spin and have the internal reorientated so that "down" is to the rear of the ship? Or do they force everyone out? Or is the ship's acceleration gentle enough that it's business as usual and the crew just experiences slightly skewed gravity inside?

One thing about the ISV Venture Star from Avatar I like is they've thought of that. Venture Star uses a pair of artificial gravity rooms laid out as bolas on the end of long hinged booms which spin around the centre of the ship for artificial gravity when the ship is cruising. When the ship is in either acceleration or deceleration phase near a destination the hinged booms stop and fold up so that the rooms are now aligned with the long axis of the ship with the bottom of those rooms pointing in the retrograde direction.

[Soda Popinski]

What happens to the centrifuge when the ship is under acceleration? Does it de-spin and have the internal reorientated so that "down" is to the rear of the ship? Or do they force everyone out? Or is the ship's acceleration gentle enough that it's business as usual and the crew just experiences slightly skewed gravity inside?

Doing a Google Search for the Discovery One, all cutaways show the centrifuge with the axis co-axial to the length of the ship. So, acceleration would push them to the "wall."

I have no idea where Wikipedia pulled their numbers, but knowing Stanley Kubrick, he probably meticulously prepared those kinds of details. It lists the engines as gas core nuclear engines with 2.75 MN of thrust. It also lists the ship as 5440 tons (not specified if dry mass or total). If I did my math right, that's just 0.5 m/s^2 acceleration at maximum thrust. Not too bad.

[Nuke]

i think the centrifuge is capable of .3g (really its more of a vomitorium, the only part of the design that wouldn't work, aside from hal of course) and about 1/20 g acceleration from the engines, so it should be tolerable (if by tolerable you mean constant nausea).

[peadar1987]

then just ban running, and put a treadmill in the gym for exercise.

That makes a whole heck of a lot more sense! Put a treadmill on one side of the centrifuge, have a counterbalance (a rowing machine or whatever) at the opposite point, and have it set up so if you want to run, you program it in advance so the centrifuge has time to pump counterbalancing fluid to the other side.

[Nuke]

see with a treadmill most of the mass just stays put, only thing you have to counter for is the torque of the rotating belt (and that could easily be handled with a carefully designed drive system for the thing that produces appropriate counter torque). doesn't matter whats on the other side of the ship so long as the mass is balanced. your body motion, since you are not actually moving anywhere would cancel itself out (a leg moved forward will come back), you might get a slight vibration, but that can be dampened.

things like when you eat, where you work, what restroom you use, how many people you can hang out with at one time, and where you can take your belongings may all need to be accounted for (move a couch, you need to log it). crew discipline will be important. you might need to log equipment into your current section so the computer can account for its mass. of course this can all be done with technology. could be load cells in the floor measuring weight distribution, could be some kind of micro transponder that the ship can track, can be computer vision systems (everything is tracked on a camera network). lots of things you can do to measure imbalances. i think i said id hate to design the control system (this thread is kinda nekro and i dont remember half the stuff i wrote).

[Nibb31]

We don't even know if artificial gravity is actually desirable on an interplanetary journey. There have been no tests or experiments on its long term effects. We have no idea how much is necessary, or safe, or for how long. For all we now, current bone-loss medication, or some future treatment, might be enough.

It's really a shame that the CAM module was cancelled on the ISS, because before we ever send people off on a long term interplanetary journey, we are going to need to build a couple of centrifuges in LEO and spend a couple of years testing the long term effects.

There are also easier ways to generate gravity than to have a spinning ring, with complicated joints and axles. Why not just spin the whole ship for example?

[Idobox]

Ring centrifuges have a lot of issues, I much prefer the solution of having the habitat at the end of a cable, and everything else on the other end. This way, you can have very large radius for little weight, no confusing issues with up vs down, less Coriolis effect (slower angular velocity), no problem with the center of mass or bearings, your crew is further away from any nuclear stuff you might have.

Now, how come nobody has ever tried attaching a Soyuz (or better, a piece of space station) to some random piece of rocket with a kevlar cable? It can't be that difficult, and if things go sour, you can just release the cable and let the habitat come back home.

[Nibb31]

Now, how come nobody has ever tried attaching a Soyuz (or better, a piece of space station) to some random piece of rocket with a kevlar cable? It can't be that difficult, and if things go sour, you can just release the cable and let the habitat come back home.

Gemini XI actually tried passive attitude stabilization of two spacecraft connected by a tether in order to create artificial gravity, but with mixed results.

The passive stabilization experiment proved to be a bit troublesome. Conrad and Gordon separated the craft in a nose-(Agena-)down position, but found that the tether would not be kept taut simply by the Earth's gravity gradient as expected. But they were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas.

Edited December 12, 2013 by Nibb31

[Nuke]

i think id rather depend on a solid ring than a little bit of cable. i think it would also be difficult to do a maneuver without a spin-down.

[Nibb31]

I'd rather have a solid cable or truss structure than a rotating joint that could spring a leak or jam with catastrophic results. You're going to need lubrication, thermal control for the friction, appropriate sealing, and spare parts. And good luck replacing a joint like that in EVA if you have something like the SARJ failure that happened on the ISS.

The complexity introduces a whole bunch of extra failure modes that you could definitely live without, because if a ball bearing fails or jams, the forces would rip your ship to pieces. Moving mechanical parts in space are problematic, which is why they are usually kept to a minimum. Large moving mechanical pressurized parts are even harder.

Rotating the entire ship is much easier. It was done for Apollo, although not for gravity. As long as you keep things in balance, there is no reason it wouldn't work on a larger ship.

[peadar1987]

Large tethered structures rotating in low-earth orbit would find it hard to keep a stable orbit due to fluctuations in gravity between the two ends, making station keeping difficult, although by no means impossible. However, in interplanetary space, tethering the command module to, say, a spent booster and spinning them up to speed seems an ideal way of providing gravity for long trips. As for the strength of the cable, it doesn't need to be crazy, simply strong enough to hold the weight of the capsule on earth.