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Spin sections and artificial gravity

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Spin sections and artificial gravity
Post by James/G   » Tue Feb 23, 2021 6:30 pm

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After reading the Manticore Ascendant series, and trying to figure out how the spin sections were supposed to provide simulated gravity and the Casey having grav-plates, and a few other stories here and there, I began discussing the how and why of spin section design, and why the spin sections were exposed to spa, instead of being a spinning cylinder within another cylinder.

This was over in Baen's Bar, and the most helpful on the explanations was wlarrison, who seem to have an excellent grasp on the problem of rotational force and vertigo and the possibility of barfing if one stood up or turned too quickly in such an environment.

I did several designs. Not sure how to post them here though.
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Re: Spin sections and artificial gravity
Post by ThinksMarkedly   » Wed Feb 24, 2021 1:20 am

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James/G wrote:After reading the Manticore Ascendant series, and trying to figure out how the spin sections were supposed to provide simulated gravity and the Casey having grav-plates, and a few other stories here and there, I began discussing the how and why of spin section design, and why the spin sections were exposed to spa, instead of being a spinning cylinder within another cylinder.

This was over in Baen's Bar, and the most helpful on the explanations was wlarrison, who seem to have an excellent grasp on the problem of rotational force and vertigo and the possibility of barfing if one stood up or turned too quickly in such an environment.

I did several designs. Not sure how to post them here though.


Hello James

Welcome to the forum.

What's the difficulty in copying your postings? I suggest you don't copy the full text from others (you can make citations), but your own you can.

I don't think we need an explanation of why centrifugal gravity works. We know it does. The thing about the Honorverse that one needs to understand is that inside the wedge's effect, the ship is effectively in free fall, regardless of how fast the wedge is accelerating. The compensators compensate 100% of the acceleration, up to the point where they don't and then people and hardware become paste.

I'd be interested into your thoughts on why use spin sections instead of an internal cylinder. I would suggest it has to do with internal volume due to armour, but: the radius would be too small and thus the gravity gradient would be too high. Not to mention Coriolis effects. So by having the spin sections protrude outside of the primary hull, they don't have to be within the constrained by its radius.

On the other hand, they won't be armoured, so they need to be evacuated before battle. I don't remember if they do that in the series. I remember they lock the spin sections.
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Re: Spin sections and artificial gravity
Post by Theemile   » Wed Feb 24, 2021 10:51 am

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ThinksMarkedly wrote:
James/G wrote:After reading the Manticore Ascendant series, and trying to figure out how the spin sections were supposed to provide simulated gravity and the Casey having grav-plates, and a few other stories here and there, I began discussing the how and why of spin section design, and why the spin sections were exposed to spa, instead of being a spinning cylinder within another cylinder.

This was over in Baen's Bar, and the most helpful on the explanations was wlarrison, who seem to have an excellent grasp on the problem of rotational force and vertigo and the possibility of barfing if one stood up or turned too quickly in such an environment.

I did several designs. Not sure how to post them here though.


Hello James

Welcome to the forum.

What's the difficulty in copying your postings? I suggest you don't copy the full text from others (you can make citations), but your own you can.

I don't think we need an explanation of why centrifugal gravity works. We know it does. The thing about the Honorverse that one needs to understand is that inside the wedge's effect, the ship is effectively in free fall, regardless of how fast the wedge is accelerating. The compensators compensate 100% of the acceleration, up to the point where they don't and then people and hardware become paste.

I'd be interested into your thoughts on why use spin sections instead of an internal cylinder. I would suggest it has to do with internal volume due to armour, but: the radius would be too small and thus the gravity gradient would be too high. Not to mention Coriolis effects. So by having the spin sections protrude outside of the primary hull, they don't have to be within the constrained by its radius.

On the other hand, they won't be armoured, so they need to be evacuated before battle. I don't remember if they do that in the series. I remember they lock the spin sections.



Many theoretical spin section designs use out rigger modules on arms instead of cylindrical spin sections.

In General - there are 2 reasons really, and they are based off 1 principle - the more "gravity" you want to induce via centripetal force, the faster the module needs to spin (in linear velocity, not radial velocity). So the closer your spinning deck's radius to the central axis, to get more centripetal force, it need to have a higher rate of rotation (radial velocity).

And the faster the radial velocity, the sicker humans will get, And the closer you are to the central axis, the greater the force variants will be from head to foot level, which also cause issues.

So you either need to build modules on armatures, placing the modules further away from the center hull or build a huge cylinder to get comfortable grav levels AND reduce the risk of nausea.

The first reason side modules are preferred is simple - mass. Spinning a small module on an arm is easier than spinning a cylinder the exact same radius, and takes up less ship mass. One could argue for a ring design, but it has a lot of frontal area which would require shielding at high velocities.

The second is armatures can be made to retract, giving the ship a sleeker profile for battle or high boost periods and can extend the modules further for comfortable "G Like" atmospheres during low boost or cruising. With a wedge, no acceleration forces are felt, so you would not need to worry about boost issues, but might need to retract the section so it fits inside the compensated volume.

The compensated volume is important for acceleration. Vessels in the Manticorian Ascendant time period accepted a non-optimized compensated volume in order to have a "wider" ship to accommodate the spin section. The compensated volume is oval shaped, and needs to cover the ship. The wider the oval, the the less efficient the compensator is, and the lower your ship's max acceleration.

Given that the Honorverse was originally roughly based off wet sailing navy principles, this is probably a take off the rule of the faster a sailing vessel can go is based off the ratio of it's length to it's breadth. A sleek dagger-like cruiser hull is efficient in water, while a lozenge shaped battleship hull is not so much.

So, in the Honorverse, having a Spin section which could retract will allow for a faster ship. Locking it probably also allowed for a better field shape (in 3d). And having no spin section and using grav plates would free you to build the most efficient shape possible.
******
RFC said "refitting a Beowulfan SD to Manticoran standards would be just as difficult as refitting a standard SLN SD to those standards. In other words, it would be cheaper and faster to build new ships."
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Re: Spin sections and artificial gravity
Post by Jonathan_S   » Wed Feb 24, 2021 11:29 am

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ThinksMarkedly wrote:I'd be interested into your thoughts on why use spin sections instead of an internal cylinder. I would suggest it has to do with internal volume due to armour, but: the radius would be too small and thus the gravity gradient would be too high. Not to mention Coriolis effects. So by having the spin sections protrude outside of the primary hull, they don't have to be within the constrained by its radius.

On the other hand, they won't be armoured, so they need to be evacuated before battle. I don't remember if they do that in the series. I remember they lock the spin sections.

IIRC they lock the spin sections vertically; so they're pointing towards the wedge.

The dorsal and ventral surface of most DD - CA designs is unarmored; so I'm not sure on those smaller ships that it's all that much worse having people in unarmored spin sections sticking up from those areas than having them in areas along the dorsal and ventral surface where they also lack armor protection -- though they are still more vulnerable to end on and broadside fire - but they seem to make up a pretty small portion of the hull lenght. OTOH we're in the era of contact nukes so exposed surfaces are almost guaranteed to get a spray of hot plasma should a warhead get through (or around) the sidewall.
So on second thought maybe it is a lot worse than the unarmored dorsal and ventral surfaces.


Either way, it makes sense to me put things like the kitchens, mess halls, gyms[1], and possibly your sleeping quarters, into the spin section and I wouldn't think those areas would be anybody's battle station assignment[3]. If you did that much of the area would be naturally unoccupied during combat without needing to specifically call to evacuate it.


[1] because food prep and eating are easier and more flexible with gravity; and you've got more options for exercise and games than in a zero-g exercise room.

[2] Because that's a way to ensure all the crew, regardless of duty station, gets a reasonable number of hours of gravity a day.

[3] Well, maybe kitchens are partially manned in combat - to be able to distribute prepared food if you have to remain at general quarters for quite prolonged periods. However you could always have a smaller, secondary, food distribution area within the hull (and so in zero-g ) for that purpose. (Since at combat stations anything you distributed would be easy prep - cold-cut sandwiches or even MRE style packs and you wouldn't need all the appliances of a full up kitchen)
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Re: Spin sections and artificial gravity
Post by Brigade XO   » Wed Feb 24, 2021 3:15 pm

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One reason you lock the spin sections in place going into battle to avoid the probable effects of damage with the spin section trying to "rotate" in a given direction but getting jammed and start shearing away and doing things like tearing open parts of the hull or a section breaking off and unbalancing the ship.
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Re: Spin sections and artificial gravity
Post by Jonathan_S   » Wed Feb 24, 2021 3:29 pm

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Brigade XO wrote:One reason you lock the spin sections in place going into battle to avoid the probable effects of damage with the spin section trying to "rotate" in a given direction but getting jammed and start shearing away and doing things like tearing open parts of the hull or a section breaking off and unbalancing the ship.

Even without jamming or taking damage it's got to be heavy enough to impart some significant gyroscope forces on the ship should you attempt to maneuver radically. At best that's extra stress and strain, at worst it slows your ability to change heading.

Lots of good reasons to stop its spin before combat. But just because it's now stopped, and in zero-g like the rest of the ship, doesn't tell us whether or not anybody's combat station is within the (now stopped) spin section.
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Re: Spin sections and artificial gravity
Post by Michael Everett   » Wed Feb 24, 2021 4:30 pm

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James/G wrote: I did several designs. Not sure how to post them here though.

DeviantArt is one answer. I have some (non-Honorverse) artwork on that site and MaxxQ's page is full of absolutely awesome canon Honorverse ships (and related stuff). Maxx's page can be found with this link.

Hope this helps (and check out Maxx's stuff even if it doesn't).
~~~~~~

I can't write anywhere near as well as Weber
But I try nonetheless, And even do my own artwork.

(Now on Twitter)and mentioned by RFC!
ACNH Dreams at DA-6594-0940-7995
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Re: Spin sections and artificial gravity
Post by ThinksMarkedly   » Wed Feb 24, 2021 6:11 pm

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Jonathan_S wrote:Even without jamming or taking damage it's got to be heavy enough to impart some significant gyroscope forces on the ship should you attempt to maneuver radically. At best that's extra stress and strain, at worst it slows your ability to change heading.

Lots of good reasons to stop its spin before combat. But just because it's now stopped, and in zero-g like the rest of the ship, doesn't tell us whether or not anybody's combat station is within the (now stopped) spin section.


The angular momentum issues were my first thought when I initially read A Call to Duty. I read that before the Honor-era novels, so I didn't yet have the background of impeller technology (and Travis being an enlisted impeller technician so did not help me understanding what that was!), so I didn't yet understand that the ship inside the wedge was in free-fall.

So I thought they locked the spin sections could make for slow turns, which would reduce the ability for the ship to perform evasive actions.

That doesn't seem to be the case, though. Pitching, rolling and yawing are still slow, as evidenced by the Tyr (I think), but they aren't the main evasion techniques. Then again, during those times, the ranges were much, much smaller than what we're used to in Honor's era, especially post-Buttercup. In that engagement with Tyr, Casey passed within 10000 km of the Volsung formation and was protected by a training missile's wedge going a mere 3000 gravities.

It isn't clear what the SOPs were at the time, from these engagements. The RMN was a backwater Navy and caught by surprise; the Volsungs were definitely operating irregularly. That may yet change, since the RMN will soon be getting its first true battlecruiser squadron, so the training and techniques should also tick up.
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