Rotational Gravity. Feasible or Not?

[stephensmat]

I've been looking for Real World research on ships/stations with gravity formed by rotation. 

Thing is, there's remarkably little about future plans to do so. The ISS is billed as a 'Low Gravity' Research Station. The only speculative information I found was the idea of putting two Starships on a Tether and having them pinwheel their way to Mars.

There are some that say that building rotating sections is impossible because there's no way to keep them secure/balanced, and the rotation speed would rip apart any existing spacecraft designs.

Thing is, I'm an amateur. I know just enough to know I don't know nearly enough. A hard-sci-fi novel from someone says that it's doable. A few science YouTube videos say it isn't.

This board is full of enthusiasts who have spent a lot more time on this topic than me. Assume that (for example) Starship gets working, and we have material to work with, in the opinion of the hivemind, is having 1g on long space missions doable or not?

[darthgently]

9 minutes ago, stephensmat said:

I've been looking for Real World research on ships/stations with gravity formed by rotation. 

Thing is, there's remarkably little about future plans to do so. The ISS is billed as a 'Low Gravity' Research Station. The only speculative information I found was the idea of putting two Starships on a Tether and having them pinwheel their way to Mars.

There are some that say that building rotating sections is impossible because there's no way to keep them secure/balanced, and the rotation speed would rip apart any existing spacecraft designs.

Thing is, I'm an amateur. I know just enough to know I don't know nearly enough. A hard-sci-fi novel from someone says that it's doable. A few science YouTube videos say it isn't.

This board is full of enthusiasts who have spent a lot more time on this topic than me. Assume that (for example) Starship gets working, and we have material to work with, in the opinion of the hivemind, is having 1g on long space missions doable or not?

1g for an entire station is not a big priority I'd think. 

0g is a resource that is in the process of being explored for exploitation for new manufacture techniques and research.  1g can be done on the ground.  So that leaves perceived gravity in space mostly for keeping people healthy and it seems that more compact and less dangerous solutions than whole ship or ring rotation are preferred.

I read about one approach that is basically a roughly 10 foot diameter centrifuge where a person would lay with their feet at the perimeter and head near the center.  They'd do this for x minutes a day and so mitigate many negative effects of 0g from the rest of the time.  Then you have the bungees and treadmills and such on the ISS for muscle and bone maintenance.

If there are concerns about refueling in space, then certainly the rotational inertia of a  .5g to 1g large spinning environment must also be concerning and carefully considered from safety and engineering angles

[stephensmat]

1 hour ago, darthgently said:

1g for an entire station is not a big priority I'd think. 

0g is a resource that is in the process of being explored for exploitation for new manufacture techniques and research.  1g can be done on the ground.  So that leaves perceived gravity in space mostly for keeping people healthy and it seems that more compact and less dangerous solutions than whole ship or ring rotation are preferred.

 

Granted, but that's for entire stations. Until we build an O'Neil Cylinder, that's not a big deal. Right now, I'm talking about 'living quarters'.

The theory for shows like B5, and Books/Movies like The Martian? They have rotating sections where the crew lives/sleeps/exercises/meets/etc. But the centre of mass is ZeroG, specifically for course corrections/docking with other craft, etc.

I'm wondering how ridiculous such things are. Does the rotating part have to be so far out, or moving so fast that there's no way you could keep them secured?

And if it's doable, then why isn't that a higher priority? One thing that I'm clear on from my own reading is that there are two major roadblocks to space: Gravity, and Radiation. We can fly to the Moon, we can fly to Mars; but astronaut careers in space are determined by how much radiation they soak up; and how much harm freefall does to them in the long term.

Edited July 8, 2023 by stephensmat

[magnemoe]

21 minutes ago, stephensmat said:

 

Granted, but that's for entire stations. Until we build an Oniel Cylinder, that's not a big deal. Right now, I'm talking about 'living quarters'.

The theory for shows like B5, and Books/Movies like The Martian? They have rotating sections where the crew lives/sleeps/exercises/meets/etc. But the centre of mass is ZeroG, specifically for course corrections/docking with other craft, etc.

I'm wondering how ridiculous such things are. Does the rotating part have to be so far out, or moving so fast that there's no way you could keep them secured?

And if it's doable, then why isn't that a higher priority? One thing that I'm clear on from my own reading is that there are two major roadblocks to space: Gravity, and Radiation. We can fly to the Moon, we can fly to Mars; but astronaut careers in space are determined by how much radiation they soak up; and how much harm freefall does to them in the long term.

Station will be larger than the IIS, unless you do something mostly one time use with tethers because you want the living area away from the core, but you don't need 1 g, 1/3 is more interesting as it's mars gravity and is also high enough that you can do everyday stuff like cooking and taking an shower,  so 100-150 meter to it and you need an counterweight. 

I say main problem is that you want you micro gravity as its why you are in space.  Not sure how easy it is to make an 1 bar rotating seal rotating 2-3 times a minute who require no major maintenance for years while having low loss? 
You could counter rotate the labs inside the core but you get issues with docking craft to it, as in you are limited to two crafts. 

I think its on the table 2 generations down the line from IIS so replacement for orbital reef and similar. 
They are needed if you want more than research outposts. 

[kerbiloid]

https://www.projectrho.com/public_html/rocket/artificialgrav.php

As always.

[darthgently]

10 hours ago, magnemoe said:

Not sure how easy it is to make an 1 bar rotating seal rotating 2-3 times a minute who require no major maintenance for years while having low loss? 

I think this is the crux of the matter here.  An always-moving very large (heavy) joint involving high angular momentum of a crewed area would require very high reliability a much higher reward for the risk at this point, not to mention the cost to orbit of the parts.  I think we will see entire stations that rotate for grav before we see joints like that at work in space.  Perhaps halting rotation for docking? 

Sealing a moving joint like that seems hard to me given the environment wherein lubricants evaporate instantly and with such temperature extremes.  And failure or seizing would be way too interesting

[magnemoe]

2 hours ago, darthgently said:

I think this is the crux of the matter here.  An always-moving very large (heavy) joint involving high angular momentum of a crewed area would require very high reliability a much higher reward for the risk at this point, not to mention the cost to orbit of the parts.  I think we will see entire stations that rotate for grav before we see joints like that at work in space.  Perhaps halting rotation for docking? 

Sealing a moving joint like that seems hard to me given the environment wherein lubricants evaporate instantly and with such temperature extremes.  And failure or seizing would be way too interesting

Agree, now I assume you could rotate capsule at the same rate as the station and then dock but here berthing is probably more practical for smaller crafts, You could perhaps have the docking module not rotate, this is more relevant for larger ships like Starship or the shuttle who don't dock at nose. 

As for labs, one solution might be to have them counter rotate inside the pressure vessel. this could also insulate them from station vibrations who is an issue on IIS and would be worse on an rotating habitat. 

[Nuke]

i think i like tangental docking the best. docking on the axis of rotation only gives you 2 possible docking bays. and having a separate zero-g dock with an interchange to a rotating dock is somewhat tricky and subject to reliability issues. on large ring stations tangental docks can give you the fastest turn over and more redundancy. though they are not suitable to small ring stations, which will probibly make do with a couple docks used rarely. 

ive given some thought to interchange systems and how they can move personnel and cargo from rotating sections to zero g sections, or even between sections rotating in different directions.  something like train cars or an interchange ring that can sync up to the rotating section, dock with it with hard seal and allow the movement of large numbers of crew or large amounts of cargo. of course if you put the centrifuge inside a large static pressure hull, then you forgo the need to have pressurized interchanges. possibly doing something as simple as having small spin up/down platforms and move everything internally with drones. an ideal industrial station would want to have both zero g and rotating areas at various gravities and pressures.

Edited July 8, 2023 by Nuke

[magnemoe]

7 hours ago, Nuke said:

i think i like tangental docking the best. docking on the axis of rotation only gives you 2 possible docking bays. and having a separate zero-g dock with an interchange to a rotating dock is somewhat tricky and subject to reliability issues. on large ring stations tangental docks can give you the fastest turn over and more redundancy. though they are not suitable to small ring stations, which will probibly make do with a couple docks used rarely. 

ive given some thought to interchange systems and how they can move personnel and cargo from rotating sections to zero g sections, or even between sections rotating in different directions.  something like train cars or an interchange ring that can sync up to the rotating section, dock with it with hard seal and allow the movement of large numbers of crew or large amounts of cargo. of course if you put the centrifuge inside a large static pressure hull, then you forgo the need to have pressurized interchanges. possibly doing something as simple as having small spin up/down platforms and move everything internally with drones. an ideal industrial station would want to have both zero g and rotating areas at various gravities and pressures.

Tangential docking like this 
http://freefall.purrsia.com/ff3500/fc03457.png
http://freefall.purrsia.com/ff3500/fc03457.htm

I say its a bit high risk, think carrier landing and it will require something more like the station in the comic, and here you  want something like this because the traffic and the two axial ports being for the huge ships.
But not something we will build this generation. 

Rotation rate is 1-2 rpm so transferring goods is not much of an problem at the base, you can even transfer fluid if needed.
You could move docked ships of the center once docked  or grab and dock.  
 

[steve9728]

On 7/8/2023 at 7:33 AM, stephensmat said:

I've been looking for Real World research on ships/stations with gravity formed by rotation. 

Welcome to the WT Module of CSS:

 

But of course, letting the whole, or at least part of the module rotates for gravity is still something risky - at least nobody tries this in real space. This remains something innovative subject that deserves more research and experimentation.

Edited July 9, 2023 by steve9728

[Hotel26]

23 hours ago, darthgently said:

Perhaps halting rotation for docking

I just last week filed a patent for a rotating dock.  I have yet to post it to KX but it's a dock on a rotor.  Dock as normal with the slowly-rotating station but just ignore everything but the target dock as you approach. The pair of those station docks (one each end) have to be axis-aligned, of course ^{[until we do advanced robotics]}.   The rotationally-free dock spins up instantly to the rotation of the mating fixed sock.

Gives me the idea that the rotationally-free dock could be fitted to the station where it is needed and leave all docking craft with the standard fixed dock.  Cheaper.  Second patent coming up...

 

Edited July 9, 2023 by Hotel26

[darthgently]

27 minutes ago, Hotel26 said:

I just last week filed a patent for a rotating dock.  I have yet to post it to KX but it's a dock on a rotor.  Dock as normal with the slowly-rotating station but just ignore everything but the target dock as you approach. The pair of those station docks (one each end) have to be axis-aligned, of course ^{[until we do advanced robotics]}.   The rotationally-free dock spins up instantly to the rotation of the mating fixed sock.

Gives me the idea that the rotationally-free dock could be fitted to the station where it is needed and leave all docking craft with the standard fixed dock.  Cheaper.  Second patent coming up...

 

I think you nailed it in that it doesn't need to rotate all the time, just during docking.  Maybe an EM clutch so a docked craft can be gently brought into rotation with the station after docking?  Best of luck with the patent, hope it works out

I still think that heavy duty rotating joints with safe and durable seals are going to be the hurdle

[Nuke]

14 hours ago, magnemoe said:

Tangential docking like this 
http://freefall.purrsia.com/ff3500/fc03457.png
http://freefall.purrsia.com/ff3500/fc03457.htm

I say its a bit high risk, think carrier landing and it will require something more like the station in the comic, and here you  want something like this because the traffic and the two axial ports being for the huge ships.
But not something we will build this generation. 

Rotation rate is 1-2 rpm so transferring goods is not much of an problem at the base, you can even transfer fluid if needed.
You could move docked ships of the center once docked  or grab and dock.  
 

cant be any more dangerous than on axis docking, b5 style. the amount of thought that show put into its docking procedures was impressive. though i feel that only two docks (one zero g) for an entire station that size is questionable design. i also question the wisdom of bringing the ships into a shirt sleeve environment (id just use some kind of hook system that grabs your ship, retracts for hard dock and extends a docking collar), especially how fast you can cycle the huge airlock without venting a large volume of air. in either case automatic docking is strongly encouraged (im always screwing up docking procedures in elite dangerous, and getting fined for it, its what sucked the enthusiasm for the game right out of me). 

12 hours ago, steve9728 said:

Welcome to the WT Module of CSS:

 

But of course, letting the whole, or at least part of the module rotates for gravity is still something risky - at least nobody tries this in real space. This remains something innovative subject that deserves more research and experimentation.

what is this, a spin station for ants?

Edited July 9, 2023 by Nuke

[mikegarrison]

23 minutes ago, Nuke said:

cant be any more dangerous than on axis docking, b5 style. the amount of thought that show put into its docking procedures was impressive. though i feel that only two docks (one zero g) for an entire station that size is questionable design. i also question the wisdom of bringing the ships into a shirt sleeve environment (id just use some kind of hook system that grabs your ship, retracts for hard dock and extends a docking collar), especially how fast you can cycle the huge airlock without venting a large volume of air. in either case automatic docking is strongly encouraged (im always screwing up docking procedures in elite dangerous, and getting fined for it, its what sucked the enthusiasm for the game right out of me). 

what is this, a spin station for ants?

I mean, it's fiction.

But there is at least one advantage to not docking, which is that ports don't have to be standardized. We already have, what, three different kinds of docking/berthing ports on the ISS? There are times when we can't send ships up to the station despite there being open ports available because they are not the right kind of open ports.

We live in a world where many of our electronic devices have incompatible connections and they are all called "USB". If you travel around the world, you have to deal with electrical outlets that are of wildly different shapes and often connect to power grids that operate at different frequencies and voltages. Why would a station that is intended to receive ships of many different species have a "universal docking port"?

Some sort of landing bay would at least eliminate those issues, while creating other issues.

Edited July 9, 2023 by mikegarrison

[magnemoe]

4 minutes ago, Nuke said:

cant be any more dangerous than on axis docking, b5 style. the amount of thought that show put into its docking procedures was impressive. though i feel that only two docks (one zero g) for an entire station that size is questionable design. in either case automatic docking is strongly encouraged (im always screwing up docking procedures in elite dangerous, and getting fined for it, its what sucked the enthusiasm for the game right out of me). 

I say it should  work its just dangerous if ship comes in wrong, who is also an point in the strip, ship has to move at correct trajectory for an landing permit and why manual control are not an option. 
For something like the Babylon 5 station they should obvious have non rotating docking segments. 

[magnemoe]

3 minutes ago, mikegarrison said:

I mean, it's fiction.

But there is at least one advantage to not docking, which is that ports don't have to be standardized. We already have, what, three different kinds of docking/berthing ports on the ISS? There are times when we can't send ships up to the station despite there being open ports available because they are not the right kind of open ports.

We live in a world where many of our electronic devices have incompatible connections and they are all called "USB". Why would a station that is intended to receive ships of many different species have a "universal docking port"?

Some sort of landing bay would at least eliminate those issues, while creating other issues.

You will be docking, in the freefall comic they will dock inside the landing bay, this will be true unless you go into an dry dock as in ship is now inside an huge airlock.  
I say size is the primary issue here, is this the generation 2 after IIS or is 100.000 ton ships medium sized and you are building the larger ones at your station, 

[darthgently]

2 hours ago, magnemoe said:

Some sort of landing bay would at least eliminate those issues, while creating other issues.

"landing" implies gravity to me.  Are you picturing landing bays with a floor with spin gravity?  That would be one heck of a landing maneuver where the craft has to match velocity and orientation with a floor describing a circle. 

I suppose if the entrance to the bay were on a tangent to the ring and timing was performed exquisitely it could work out, but pretty high stakes.  Then there is the problem of dynamically balancing the ring as the mass of the landing craft must be taken into account progressively as it sets down (pumping fluids across the ring to maintain balance?)

They said landing boosters was too hard and it is normal now, so maybe in 50 years we will have spin gravity landing bays in orbit.  Until then I'm guessing that docking axially to spinning targets would be most viable (cue docking of transport to spinning station in 2001: A Space Odyssey)

[steve9728]

4 hours ago, Nuke said:

what is this, a spin station for ants?

For everything needs gravity experiments up there. The latest reported experiment performed was "a conventional boiling experiment as well as a limited bubble boiling experiment in a corresponding gravity environment".

“The rack can provide a high-precision simulated gravity environment of 0.01g to 2g for scientific experiments, and adopts advanced wireless energy transfer and carrier communication technologies to support scientific research on complex fluid physics and the movement of particulate matter at different gravity levels, such as microgravity, simulated lunar gravity and simulated Martian gravity.

In order to provide a platform for conducting gravity research on a larger scale and for longer periods of time, scientists have designed a 900mm diameter centrifuge, which is currently the largest centrifuge operating in orbit. The centrifuge turntable allows gravity to be adjusted with high precision through the control of the rotational speed during rotation.” Introduce by CAS (full Chinese link warning).

[Nuke]

3 hours ago, mikegarrison said:

I mean, it's fiction.

But there is at least one advantage to not docking, which is that ports don't have to be standardized. We already have, what, three different kinds of docking/berthing ports on the ISS? There are times when we can't send ships up to the station despite there being open ports available because they are not the right kind of open ports.

We live in a world where many of our electronic devices have incompatible connections and they are all called "USB". If you travel around the world, you have to deal with electrical outlets that are of wildly different shapes and often connect to power grids that operate at different frequencies and voltages. Why would a station that is intended to receive ships of many different species have a "universal docking port"?

Some sort of landing bay would at least eliminate those issues, while creating other issues.

airports are pretty well standardized. the same jetway can link up to a myriad of different aircraft and operators and national origin, and various other ground equipment just works for everything. the standard cargo container also is a story of widely adopted standards that just work. the universal docking port is still valid, and the only reason iss needs a bigger variety is that there was still considerable legacy hardware involved in its construction and operation. right now there just aren't that many players in manned spaceflight. but in the post-reusability era you are going to see a significantly more diverse population in space, and as that grows standards will need to be adopted. especially when it becomes unfeasible for everyone to carry a dock adapter for when 2 ships disagree with eachother about their docking capabilities. better to use the most common standard and avoid the losses from the additional mass. 

also b5 is a notable example because it shows a docking procedure in the oft reused cgi stock footage that more or less makes sense (except for the pressurized docking bays and the single point of failure). it shows every point in the process from approach, landing on the pad/elevator and how the ships are brought into the docking area and even how you disembark, in extreme detail and done in a way that is not beyond our present engineering capabilities. fiction yes, but i like how much thought they put into the mechanics of it all. the hard sci-fi aspects are indeed only skin deep if you look closely enough and by s5/crusade its all star trek tech (though respect for clarke's third law is strong with this one). i actually think the b4 station was a better design and it would not be that hard to add a tangental docking platform to the larger rotating section. b5's zero g dock didnt make much sense though because you would probibly just have a container yard, either internal or external, and no reason to have only one opening, having separate personnel and cargo handling areas is a good idea though.

unless you go with skylon's approach to having everything as a cargo container, even ones capable of transfering humans, then you can just take all containers in the zero g dock, route the manned ones to the interchange and the cargo to the zero-g yard. passenger containers are a good idea because you could just dock them on the unpressurized side of the bulkhead to a ring of airlocks, sort of like chambering rounds in a gatling gun. any space suited dock workers can be transferred to the zero-g section by the same conveyance network.

Edited July 10, 2023 by Nuke

[Nuke]

1 hour ago, darthgently said:

"landing" implies gravity to me.  Are you picturing landing bays with a floor with spin gravity?  That would be one heck of a landing maneuver where the craft has to match velocity and orientation with a floor describing a circle. 

I suppose if the entrance to the bay were on a tangent to the ring and timing was performed exquisitely it could work out, but pretty high stakes.  Then there is the problem of dynamically balancing the ring as the mass of the landing craft must be taken into account progressively as it sets down (pumping fluids across the ring to maintain balance?)

They said landing boosters was too hard and it is normal now, so maybe in 50 years we will have spin gravity landing bays in orbit.  Until then I'm guessing that docking axially to spinning targets would be most viable (cue docking of transport to spinning station in 2001: A Space Odyssey)

really depends on the size of the ring. tangential docking is for big slow heavy rings. fluid stabilization will be required for any station where humans can freely migrate. with sufficient capacity it can handle docking of various manned craft. this can also be supplemented by physical ballast (say lead blocks that can be moved around with a forklift) which can be moved around as needed to take localized strain off of the stabilization system. 

hub docking is for small rings like the one in 2001 or the gateway station concept. first gen ring stations are not going to need more than a couple docking ports, as they will likely just be for space tourism. zero-g is preferred for science or freight handling. industrial stations on the other hand will have a diverse array of zero g and spin gravity areas. some processes are cheaper in zero g and others require gravity. and all require a lot of mass. and interchange systems will need to be able to exchange large volumes. tycho station (more as described by the books than the show) might be a good example of that. 

Edited July 10, 2023 by Nuke

[wumpus]

I think the real issue is how you construct the habitat modules.  As far as I know, all such modules have been constructed on Earth, and connected together through some sort of docking (likely permanently) seal.

If you stick to this, rotating around the center of the spacecraft would be limited by the radius that can be launched.  An alternative would be two (or more) habitats placed outside the center of the main rotation, and rotated.  Presumably you'd need a ladder to get back to the zero-g center and on to a different gravity habitat, at least until you could build a ring around the center.

Expect to have a two "wasted modules" for each connection to from 0-g to 1-g.