Artificial Gravity on the ISS

[Airbrush]

This is something I can't figure out.  Why don't they add a module that has a big centrifuge so the astronauts can work in 1G gravity?  Or at least they can sleep and recreate in 1G.  The ISS is like a big tinker toy where modules of all shapes and sizes can be attached.  Why not attach such a centrifuge?

[Mordred]

You would need to rotate the entire station adding a centrifuge isn't sufficient. Then if you do so the problem is compounded on fuel costs and how difficult it would be to refuel the station.

Edited April 7, 2018 by Mordred

[Endy0816]

^Hey! Welcome back

 

Might one free to rotate about its axis work(ignoring fuel costs)?

Edited April 7, 2018 by Endy0816

[Mordred]

If you try to rotate one module for work/medical processes then you need the fuel to counterrotate the remaining station as the rotation would gradually affect the station via f=ma and friction.

 NASA has undoubtedly looked into the possibility of artificial gravity on the station via rotation but probably found the costs and ensuing problems of implementation too problematic to justify compared to simply having crew rotations for medical reasons. Its not the implementation that presents the problem but the cost justification.

Edited April 7, 2018 by Mordred

[Endy0816]

38 minutes ago, Mordred said:

If you try to rotate one module for work/medical processes then you need the fuel to counterrotate the remaining station as the rotation would gradually affect the station via f=ma and friction.

Ah, true. Would need to detach completely, which could cause issues as well.

[Bender]

Your modules would also need to be pretty large to avoid too large a difference between your head and your feet.

[swansont]

4 hours ago, Airbrush said:

This is something I can't figure out.  Why don't they add a module that has a big centrifuge so the astronauts can work in 1G gravity?  Or at least they can sleep and recreate in 1G.  The ISS is like a big tinker toy where modules of all shapes and sizes can be attached.  Why not attach such a centrifuge?

I assume you are suggesting something like the setup for the spaceship in The Martian.

How big would the ring need to be, under reasonable assumptions of rotational speed?

[Airbrush]

Suppose the centrifuge is only for sleeping, maybe 20 feet in diameter, with evenly spaced sleeping compartments to stay balanced, low-mass structures suspended by cables from the hub.  Since it is low-mass only a small amount of counter-rotation thrust is needed for the ISS.  If people could sleep in 1g that would be a health improvement.

 

Edited April 8, 2018 by Airbrush

[swansont]

1 hour ago, Airbrush said:

Suppose the centrifuge is only for sleeping, maybe 20 feet in diameter, with evenly spaced sleeping compartments to stay balanced, low-mass structures suspended by cables from the hub.  Since it is low-mass only a small amount of counter-rotation thrust is needed for the ISS.  If people could sleep in 1g that would be a health improvement.

 

A little over a 3 meter radius then. a = v^2/r

You need a speed approaching 6 m/s to get 1g. Have fun getting into and out of bed.

[John Cuthber]

On 4/7/2018 at 5:37 PM, Airbrush said:

This is something I can't figure out.  Why don't they add a module that has a big centrifuge so the astronauts can work in 1G gravity? 

Because the whole godforsakenly expensive point is (usually) that they do experiments in microgravity.

If they are  doing something in 1 g then they can do it  at home.

Edited April 8, 2018 by John Cuthber

[Airbrush]

Anyone know when humans may start building a rotating wheel space station?  Not too soon.  My little search found this:

"...NASA has explored plans for a Nautilus X centrifuge demonstration project.  If flown, this would add a centrifuge sleep quarters module to the ISS. This makes it possible to experiment with artificial gravity without destroying the usefulness of the ISS for zero g experiments. It could lead to deep space missions under full g in centrifuge sleeping quarters following the same approach."

"NASA has never attempted to build a rotating wheel space station, for several reasons. First, such a station would be very difficult to construct, given the limited lifting capability available to the United States and other spacefaring nations. Assembling such a station and pressurizing it would present formidable obstacles, which, although not beyond NASA's technical capability, would be beyond available budgets. Second, NASA considers the present space station, the ISS, to be valuable as a zero gravity laboratory, and its current microgravity environment was a conscious choice."

https://en.wikipedia.org/wiki/Rotating_wheel_space_station

"In order to assess and characterize influences and effects of the centrifuge relative to human reactions, mechanical dynamic responses and influences, the demonstration of a similar centrifuge first would be tested on the ISS.

If produced, this centrifuge would have been the first in-space demonstration of sufficient scale for artificial partial-g effects.^[1] The demonstrator would be sent using a single Delta IV or Atlas V launcher. The full cost of such a demonstrator would be between US$83 million and US$143 million."

https://en.wikipedia.org/wiki/Nautilus-X#ISS_centrifuge_demonstration

 

Edited April 10, 2018 by Airbrush

[J.C.MacSwell]

Interesting that they refer to sleep modules. Humans tend to fight gravity by day and attempt to negate it when sleeping at night by lying down.

If you only had access to the module for sleep do you sleep standing up to give your long bones the much needed longitudinal stresses? Or is that taking away too much from the relaxation required for the cardiovascular system? What other effects should be considered?

[Airbrush]

29 minutes ago, J.C.MacSwell said:

Interesting that they refer to sleep modules. Humans tend to fight gravity by day and attempt to negate it when sleeping at night by lying down.

If you only had access to the module for sleep do you sleep standing up to give your long bones the much needed longitudinal stresses? Or is that taking away too much from the relaxation required for the cardiovascular system? What other effects should be considered?

Artificial gravity just for sleeping simply because bigger technical problems building a bigger centrifuge for other activities.  Sleeping requires the least amount of valuable space therefore allowing for a smaller centrifuge.

[swansont]

6 hours ago, Airbrush said:

Artificial gravity just for sleeping simply because bigger technical problems building a bigger centrifuge for other activities.  Sleeping requires the least amount of valuable space therefore allowing for a smaller centrifuge.

But as I showed, a small centrifuge has challenges. Your bed is going by you at >20 km/hr when you are at the axis. How do you get in and out?

I would think a larger radius, to mitigate that problem and also use it for an exercise area rather than sleep. 

[John Cuthber]

If I was sat at the centre of the earth (I'd be a bit warm etc...) I could look up + see my bed doing about a thousand miles an hour.

But as I climbed the ladder back to it, it would seem to slow down. When I got to the top, it would be stationary, and I could just climb in.

 

Rotating vacuum seals are a pig.

Imagine a rigid spaceship that's mushroom shaped with a  really wide "cap".

If you make the cap wide enough then, even a very small rotational speed will give you the artificial gravity you need, while the narrow stem is still in microgravity.

[J.C.MacSwell]

12 hours ago, swansont said:

But as I showed, a small centrifuge has challenges. Your bed is going by you at >20 km/hr when you are at the axis. How do you get in and out?

I would think a larger radius, to mitigate that problem and also use it for an exercise area rather than sleep. 

That might also mitigate some problems by putting the gravitational stresses more in tune with our naturally evolved rhythms, at least to some extent.

2 hours ago, John Cuthber said:

If I was sat at the centre of the earth (I'd be a bit warm etc...) I could look up + see my bed doing about a thousand miles an hour.

But as I climbed the ladder back to it, it would seem to slow down. When I got to the top, it would be stationary, and I could just climb in.

 

Rotating vacuum seals are a pig.

Imagine a rigid spaceship that's mushroom shaped with a  really wide "cap".

If you make the cap wide enough then, even a very small rotational speed will give you the artificial gravity you need, while the narrow stem is still in microgravity.

The rotating pod could be inside the greater hull, such that no rotating seal, or seal of any kind for that matter, would be required.

Thereby, it could be fairly open, and use an accelerating assist from "stationary" hull to get inside.

...or simply have the pod come to a halt, you get in, and slowly bring you up to speed.

[Airbrush]

On ‎4‎/‎10‎/‎2018 at 3:24 AM, swansont said:

But as I showed, a small centrifuge has challenges. Your bed is going by you at >20 km/hr when you are at the axis. How do you get in and out?

I would think a larger radius, to mitigate that problem and also use it for an exercise area rather than sleep. 

Ok then the centrifuge doesn't need to be a complete wheel, it could be most simply only two modules that are rotating around a hub suspended by cables inside 2 pressurized tunnels, one to each module.  Then it could be a much larger radius, and you can add modules symmetrically.

Edited April 11, 2018 by Airbrush

[swansont]

32 minutes ago, Airbrush said:

Ok then the centrifuge doesn't need to be a complete wheel, it could be most simply only two modules that are rotating around a hub suspended by cables inside 2 pressurized tunnels, one to each module.  Then it could be a much larger radius, and you can add modules symmetrically.

Not being a complete wheel isn't the issue. You take up almost 2m of space with a person standing somewhere with their feet at the center of the space station. Their bed is a little more than a meter away, and is moving >20 km/hr. You're going to injure yourself as you leap into bed and try to grab on to something, or when you get out and try to come to a stop.

It must be a much larger radius for this to be feasible.  You need to be able to e.g. climb up a ladder to transition to the faster speeds

[Airbrush]

36 minutes ago, swansont said:

It must be a much larger radius for this to be feasible.  You need to be able to e.g. climb up a ladder to transition to the faster speeds

How long of a radius does the pressurized tunnel need to be to easily transition from zero g to one g?

[Raider5678]

On 4/7/2018 at 1:23 PM, Mordred said:

If you try to rotate one module for work/medical processes then you need the fuel to counterrotate the remaining station as the rotation would gradually affect the station via f=ma and friction.

 NASA has undoubtedly looked into the possibility of artificial gravity on the station via rotation but probably found the costs and ensuing problems of implementation too problematic to justify compared to simply having crew rotations for medical reasons. Its not the implementation that presents the problem but the cost justification.

Out of curiosity, couldn't you add two modules and each spins in a separate direction?

Would that counteract the effect of one?

Assuming we have the technology to spin them both to the same speed, at the same time.

[Mordred]

Yes you can use multiple modules to counter spin.

[Raider5678]

Just now, Mordred said:

Yes you can use multiple modules to counter spin.

Cool.

I'm assuming that'd be insanely expensive right now.

Unless someone miraculously learns how to reland rockets...............Elon, get the block 5 ready.

 

 

Let's say you have 2 separate modules, 1 that's large enough for astronauts to inhabit for some time, and another that's much smaller and is just a counterweight. The large one could spin at whatever speed they need, and an equation could tell the system how fast to spin the smaller one to counteract the speed of the larger centrifuge.

Would that work? It'd help save the cost of building 2 of them.

[Mordred]

Yes different spin rates would allow for different radius ratios.

[Raider5678]

1 minute ago, Mordred said:

Yes different spin rates would allow for different radius ratios.

Thank you.

[swansont]

14 hours ago, Airbrush said:

How long of a radius does the pressurized tunnel need to be to easily transition from zero g to one g?

You would want the entryway to be moving slowly, so let's say that's one complete revolution every 12 seconds, or around a half a radian per second. Your central axis is 2m in diameter, so r is 1m. That means the ladder you need to grab is moving 0.5 m/s. That's probably the fastest rotation you can comfortably have.

To get 1g at that rotation, the radius needs to be almost 40m long. The outer rim is moving 20 m/s, but you have your ~38 meter climb to transition to that speed.