How the heck do you have gas-tight bearings between non rotating and rotating sections?

[AngelLestat]

Is just a technical problem that I think anybody can solve just thinking some hours or days.

Ok, after thinking this for some minutes, it may have its difficulties. Not sure how to achieve zero friction.
The main thing about designing a spinning habitat, it is if the whole thing rotates.

Edited February 1, 2016 by AngelLestat

[Frybert]

Now that I think about it, why does the hull have to spin at all? Why not just have the spinning section INSIDE the pressure vessel?

[MrHappyFace]

I have a feeling this video may be relevant:

https://www.youtube.com/watch?v=KSzuiqVjJg4

TL;DW: The cupola has 7 rotating handcranks that are used to control the window shutters manually, which are sealed against the vacuum of space using rubber O-rings.

Edited February 1, 2016 by MrHappyFace

[sgt_flyer]

32 minutes ago, Frybert said:

Now that I think about it, why does the hull have to spin at all? Why not just have the spinning section INSIDE the pressure vessel?

could be an answer yes, though, the needed diameter is humongus  (unless you use an inflatable pressure vessel, then assemble the spinning section inside.) - still, you'll need to have a way to cancel the torque  (maybe two counter-rotating sections ? :))

@MrHappyFace

the friction surface and the moved mass for those handcranks is negligible compared to a torus  so rubber O-rings are much less problematic  (and they are not constantly in motion either)

 

Edited February 1, 2016 by sgt_flyer

[peadar1987]

This topic improves immensely when you read "seals" as the slippery black marine mammals.

[Kevin Kyle]

I happen to make parts for dyno's and I just happen to make the seals that keeps the water out of the bearings. I still to this day dont fully understand how the water doesnt run right through there but it doesnt. Water is pumped into the rotating dyno at a pretty good rate and pressure. Im always amazed that they dont leak. But truth is, they probably do leak a little bit and they deal with it.

[AngelLestat]

there are many ways to solve this problem, but all that I think about takes a little amount of friction which needs to be cancelled using extra energy from solar.

One as Frybert said is making the spinning section inside the pressure vessel, but this also has friction with the air.
There are others methods that use special bearings in the joints that also work as air tight, but again.. you have some friction.

In the ISS none of these habitat sections will be installed for human experiments, they can have small ones for other organism. 
The best way today we have to study artificial gravity is using tethers with a counter weight.
About Nautilus X design, I guess they just deal with the friction using extra energy from the panels.

[Kerbol Macrosystems]

There's all sorts of great ways to seal a rotating shaft.  This is the same problem as keeping the rotor on a pump from leaking.  If we can keep water in the pump, we can keep air in a space station.  Mechanical Seals come in all sorts of arrangements, depending on the pressure difference you need to hold, the reactivity or corrosivity of the materials you need to hold back, and other considerations.  If you dig through the websites of Flowserve or John Crane you'll find drawings of their seals.  You'll get different drawings and section views depending if you look into the catalog, bulletin, or IOM (Installation and Operation Manual, sometimes Installation, Operation, and Maintenance). 

[KSK]

I seem to remember labyrinth seals being useful for this kind of thing, although you'd probably need something else to go with them. And curse you, Peadar - now I have a vision of said hapless sea mammals trapped in a maze.

[DerekL1963]

13 hours ago, Nibb31 said:

But even if it is necessary, why bother when you can rotate the whole spacecraft. You're going to introduce a whole slew of fragile parts that need replacing and maintenance (seals, lubricants, etc...), along with a whole bunch of new failure modes. I know it looks cool (like wings on a spaceship), but rotating segments are just another solution looking for a problem. Keep it simple !

It's not at all clear the rotating the whole craft "keeps it simple", given the enormous energy you'll expend spinning up the bits that don't need to be spun and in fact cause problems when they're spun (E.G. your fuel tanks and the contents).

[K^2]

25 minutes ago, DerekL1963 said:

It's not at all clear the rotating the whole craft "keeps it simple", given the enormous energy you'll expend spinning up the bits that don't need to be spun and in fact cause problems when they're spun (E.G. your fuel tanks and the contents).

Compared to energy required to put the craft into orbit or transfer trajectory, energy/fuel required to make it spin is negligible. Inertial forces thus generated are going to be an order of magnitude gentler than these generated during liftoff, or even softer than a typical insertion burn.

The only good reason to have non-rotating section is in the case of ISS, where the rotating section is just an additional module used for experiments. If we are going to go for centrifugal gravity on something like interplanetary ship, we are way better off spinning the whole thing. In fact, tethered counterweights might be a good idea there.

[RuBisCO]

Teflon bearings? There are Telfon bearings that can hold out/in thousands of PSI while spinning. Consider for example the kind of bearings they have for hard-suits.

Here is a report on bearing design for a hard spacesuit.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900012785.pdf

Edited February 1, 2016 by RuBisCO

[DerekL1963]

23 minutes ago, K^2 said:

Compared to energy required to put the craft into orbit or transfer trajectory, energy/fuel required to make it spin is negligible. Inertial forces thus generated are going to be an order of magnitude gentler than these generated during liftoff, or even softer than a typical insertion burn.

 Which is a completely meaningless comparison because it's a useless figure-of-merit.   The proper comparison is the energy needed to spin up the wheel section vice the energy needed to spin up the entire ship.   In the same manner, the problem with spinning the fuel tanks isn't the inertial forces generated by the spin (which, just in passing, are in a different direction than those experienced at launch), it's the inertia and sloshing of the fuel as the vessel is spun up.

[fredinno]

7 hours ago, Frybert said:

Now that I think about it, why does the hull have to spin at all? Why not just have the spinning section INSIDE the pressure vessel?

The latter is more heavy, and costly.

50 minutes ago, K^2 said:

Compared to energy required to put the craft into orbit or transfer trajectory, energy/fuel required to make it spin is negligible. Inertial forces thus generated are going to be an order of magnitude gentler than these generated during liftoff, or even softer than a typical insertion burn.

The only good reason to have non-rotating section is in the case of ISS, where the rotating section is just an additional module used for experiments. If we are going to go for centrifugal gravity on something like interplanetary ship, we are way better off spinning the whole thing. In fact, tethered counterweights might be a good idea there.

You'd have to also design the HABs for use both in G and No G, which would increase cost- current HABs and stations don't have that feature.

[Lukaszenko]

Ferrfluid seals are pretty cool. I've seen demonstrations of them at work. Basically a magnetic oily substance that's held in place with magnets. Doesn't wear because it's oil, doesn't leak because it's liquid and hence no gaps, doesn't have friction because it's oil. Problem solved.

https://www.youtube.com/watch?v=jQj0C44H3ys

 

Edited February 1, 2016 by Lukaszenko

[SomeGuy123]

4 hours ago, Lukaszenko said:

Ferrfluid seals are pretty cool. I've seen demonstrations of them at work. Basically a magnetic oily substance that's held in place with magnets. Doesn't wear because it's oil, doesn't leak because it's liquid and hence no gaps, doesn't have friction because it's oil. Problem solved.

https://www.youtube.com/watch?v=jQj0C44H3ys

 

Yeah that would work.  So the magnets are "pulling" the oil perpetually back into the groove, so the pressure of the atmosphere on this oil layer doesn't gradually shove it out of it's slot.  Oil is basically impermeable to air, it would be low friction.  
 

Only problem is if it boils in a vacuum and so you constantly lose oil to outgassing.  

[SomeGuy123]

19 hours ago, Nibb31 said:

But even if it is necessary, why bother when you can rotate the whole spacecraft. You're going to introduce a whole slew of fragile parts that need replacing and maintenance (seals, lubricants, etc...), along with a whole bunch of new failure modes. I know it looks cool (like wings on a spaceship), but rotating segments are just another solution looking for a problem. Keep it simple !

Here's why you don't rotate the whole spacecraft.

Any practical spacecraft is going to have the crew quarters be only a small percentage of the mass of the ship.  The rest is the nuclear engine, the propellant tanks full of many tons of hydrogen slush, the heat radiator wings, onboard manufacturing and cargo bays, lander storage, weapons...basically everything that isn't the crew's sleeping, exercise, eating, and office work areas.  

Anyways, all that stuff would have to be designed to tolerate the additional stress of being rotated.  That makes everything else on the spacecraft heavier and lowers your mission delta V by a lot.  It also increases your fuel consumption, and even in the far future, propellant consumption costs you money even if there's asteroid or lunar propellant available.  

So it makes sense to have the crew quarters rotate, and yet you would be able to climb into the low G sections that are pressurized whenever you need to.  All the heavy "industrial" equipment on the spacecraft would probably be in low g because it takes a lot of structure to spin it, while the "residential/commercial" zones of the spacecraft would be in the centrifuge.  (by commercial I mean "office workspace", not literally commercial)

Edited February 2, 2016 by SomeGuy123

[fredinno]

2 hours ago, SomeGuy123 said:

Yeah that would work.  So the magnets are "pulling" the oil perpetually back into the groove, so the pressure of the atmosphere on this oil layer doesn't gradually shove it out of it's slot.  Oil is basically impermeable to air, it would be low friction.  
 

Only problem is if it boils in a vacuum and so you constantly lose oil to outgassing.  

I doubt you'd need to carry that much oil- especially since we have things on Earth today that need to do similar things, and not outgass huge amounts of oil, at the same time.

[Elthy]

Another problem with only parts of the craft rotating: How do you transfer energy, fluids, gasses between the parts? Energy is propably easy, but the others...

[kerbiloid]

Btw, such rotating habitat would contain multiple moving objects (humans, mechanisms, liquids).
So, its center of mass changes its position continually and unpredictably.

Wouldn't this do something like that with the whole ship:
https://www.youtube.com/watch?v=L2o9eBl_Gzw

Or, at least cause the rotating section skew and get jammed instead of complete overturn.

[Porkjet]

Been wondering about this problem for years. Nice thread, good answers!

Keeping a rotating section inside a static hull is what I've allways thought to be the most practical option too.

 

BTW I think that any spinning hab section be it internal or external or the whole ship should probably be stopped before attempting any manuvers, because of the gyroscopic effects keeping it stable along the rotation angle, kinda working against rotations along other axis. Have you ever held one of those powerballs in your hand that have a spinning weight inside that makes it very hard to rotate them? Same thing is probably the reason why bicycles dont fall over at speed or why some sattelites are spin-stabilised or why bullets are rotated by barrel thread. I guess this might be a problem for spaceships trying to maneuver.

Edited February 2, 2016 by Porkjet

[DerekL1963]

1 hour ago, Elthy said:

Another problem with only parts of the craft rotating: How do you transfer energy, fluids, gasses between the parts? Energy is propably easy, but the others...

Swivel joints are early 1900's technology.   (Battlewagons used them to transfer hydraulic pressure from the ships structure to the rotating turret.)  So long as you avoid transferring cryogenics you should be fine.

I think you'd be better off retaining fluids in the rotating section though, they can be pumped about to maintain balance and stability.

31 minutes ago, kerbiloid said:

Btw, such rotating habitat would contain multiple moving objects (humans, mechanisms, liquids).
So, its center of mass changes its position continually and unpredictably.

Wouldn't this do something like that with the whole ship:
https://www.youtube.com/watch?v=L2o9eBl_Gzw

Yes, so the spin would have to be checked and adjusted periodically.

.   And it's also a primary argument for rotating the crew quarters rather than the whole ship...  When you rotate the whole ship, you're rotating about the long axis, which is inherently unstable.  It wants to spin along along the short axis.   When you spin the crews quarters, you're spinning about the short axis, which is far more stable.

[Elthy]

Arent swivel joints only working while exactly on the axis of rotation (judging by the pictutres google showed)? I imagine for a spacestation hub you would need to transfer lots of stuff.

Edited February 2, 2016 by Elthy

[DerekL1963]

23 minutes ago, Elthy said:

Arent swivel joints only working while exactly on the axis of rotation (judging by the pictutres google showed)? I imagine for a spacestation hub you would need to transfer lots of stuff.

Power, data, GOX, potable water, grey/black water...  that's about it.  Power and data go via slip rings (another very old technology), only the GOX and the water need to go via swivel joint.  And if you're clever about your ventilation design, you might not even have to transfer the GOX.

[Nibb31]

5 hours ago, SomeGuy123 said:

Here's why you don't rotate the whole spacecraft.

Any practical spacecraft is going to have the crew quarters be only a small percentage of the mass of the ship.  The rest is the nuclear engine, the propellant tanks full of many tons of hydrogen slush, the heat radiator wings, onboard manufacturing and cargo bays, lander storage, weapons...basically everything that isn't the crew's sleeping, exercise, eating, and office work areas.  

Weapons? Seriously? I thought we were talking about realistic designs.

Slush isn't much of a problem once it's rotating. Just add some baffles in the tank, and the engines don't need to be running while you spln-up anyway. If anything, gravity induced ullage is a benefit. You also get the benefits of thermal regulation, and spin stabilization.

For solar panels, radiators, thrusters, etc, you can either attach them to their own 3D Canfield joint, like this old CEV concept:

...or just a flexible joint that can absorb the load, like the solar panels on Orion:

... or you can just attach them radially to the outside of the spacecraft so that they double as MMOD shields.

Hydrogen is pretty much a no-go for interplanetary missions, because boil-off.

Quote

Anyways, all that stuff would have to be designed to tolerate the additional stress of being rotated.  That makes everything else on the spacecraft heavier and lowers your mission delta V by a lot.  It also increases your fuel consumption, and even in the far future, propellant consumption costs you money even if there's asteroid or lunar propellant available.  

The Apollo stack used "barbecue roll" spin on its way to the Moon, not for gravity but for thermal regulation. The fuel consumption to spin up Apollo was negligeable compared to the size of the spacecraft. I don't see why it wouldn't scale gracefully to a larger vehicle. You could even use SEP thrusters to do it on a larger craft. And the induced spin stabilization actually saves propellant used for attitude corrections.

You know what would make everything heavier? Joints, connections, seals, motors, and everything needed for a spin section. It would also make everything more complex and more failure prone. What happens if it jams? What happens if it leaks? What happens if you run out of lubricant?

 

Edited February 2, 2016 by Nibb31