The interior design of the central trunk of a ring spaceship

[Strato Incendus]

For all the attention we‘ve paid to ring habitats, we haven’t talked that much about the interior design of the central trunk yet, around which the rings rotate.

Just having one big hollow ship trunk, about 100 metre in diameter, would be a lot of wasted space. It would also be too easy for people to get carried all the way to the opposite wall of this cylindrical tunnel, with nothing to hold on to in between, which would allow them to stop or change their trajectory of movement. With this structure, however, it would at least be pretty clear what it looks like inside the trunk, and how the ring hubs behave:

- For example, if we have rings with a 500-metre diameter creating 1 g, then the hubs of those rings rotating in the central trunk with 100-metre diameter should create 0.2 g of centrifugal force. That’s a little more than gravity on the moon.
- In between the ring hubs, there should be no gravity. Depending on how close to each other the ring hubs are, though, you could “jump” from one ring hub to the next, without a lot of floating time in between.Alternatively: If we have smaller sub-tunnels going through the central trunk, then these tunnels could pass through the ring hubs with no gaps in between. Basically, inside this cylinder with the 50-metre radius, there would be another cylinder with the same length and a smaller radius (say, 45 metres). In there could be further smaller sub-corridors. The cross-section would basically look like the drum of a revolver.

Such a structure would prevent you from accidentally floating to the other side of the tunnel. Because just a few metres from the outer hull of the trunk, there would be another “ceiling” — the outer wall of the inner tunnel.

Here my primary question would be: If you move through the uninterrupted inner cylinder, how are you affected by the ring hubs rotating around it on the outside? When you’re inside the inner tunnel, you can’t see the ring hubs, and you‘re several metres away from the rotating surface. The inner tunnel itself would not rotate. So would you still experience 0.2 g of gravity whenever passing through an area of the inner cylinder which is surrounded by a rotating hub on the outside?

 

[anorlunda]

Why to people need to travel through the hub at all? Why not just go around the ring to get to the other side?

 

[Drakkith]

So would you still experience 0.2 g of gravity whenever passing through an area of the inner cylinder which is surrounded by a rotating hub on the outside?

If the person is not touching a surface that is rotating, then they will feel no gravity at all. End of story.

 

[Strato Incendus]

Why to people need to travel through the hub at all? Why not just go around the ring to get to the other side?

The ship has six rings overall. When you want to get to the other side of the same ring, yes, you can simply walk around it. But when you want to move to a different ring, you have to take a lift up one of the spokes, move through the central trunk to the hub of the ring you want to go to, and then enter the lift down the spoke of that ring.

If the person is not touching a surface that is rotating, then they will feel no gravity at all. End of story.

Alright, that makes sense in principle.
However, when you’re inside the corridor on a ring and you jump, then for a while, you won’t be touching the rotating surface either. And yet, the centrifugal force will pull you back “down” to the floor again (tangentially, of course, so it looks like you’re falling at a bit of a diagonal angel).

We already discussed in other threads what differences it makes when you jump while running spinward vs. anti-spinward, when you shoot bullets spinward vs. anti-spinward, etc.

We even discussed what happens when you fall down the elevator shaft through one of the spokes: You’d fall a few meters and then land on the wall. Gravity gradually increases as you move down the spoke, but the ring comes up to meet you, so that you don’t fall all the way down.
What we haven’t discussed though is what happens afterwards: Do you just remain stuck to the wall as the ring keeps moving, or do you start falling further down again, just with a break in between during which you’re stuck to the wall of the elevator shaft?

In either case:
By this logic, if I’m standing on the rotating hub in the central trunk and I jump, even though this hub creates more than moon-like gravity through its rotation, I should not get pulled back onto the hub again, because I’m no longer touching the rotating surface; instead, I should continue to float to the opposite wall of the central tunnel.

Why does gravity work fairly normally when jumping inside the corridor on the circumference of the ring, but not when you jump off the rotating hub in the central trunk?

 

[Drakkith]

Why does gravity work fairly normally when jumping inside the corridor on the circumference of the ring, but not when you jump off the rotating hub in the central trunk?

Well, the details are all in the math, which I'm not going to type out since they are readily available online. The short version is because you are rotating too slow for such a small diameter. The same thing would happen on the main part of the ring if you slowed down the entire ring to a tenth the speed or less. You could probably jump most of the diameter of the ring before coming back into contact with it (more or less head first) if the ring were designed to be open across its diameter with no ceiling.

 

[Rive]

in the central trunk with 100-metre diameter should create 0.2 g of centrifugal force.

It's not exactly easy to calculate the correct impact speed due the non-constant 'gravity' and unclear start and end vectors, but the effect of 50m free fall in 0.2g is still not something you can just neglect.
Especially if you use the trunk as - trunk (I mean, as storage...). Slow heavy equipment still has quite significant flattening potential.

 

[Drakkith]

It's not exactly easy to calculate the correct impact speed due the non-constant 'gravity' and unclear start and end vectors, but the effect of 50m free fall in 0.2g is still not something you can just neglect.

But there isn't a 0.2g free fall. Your velocity across the 'gap' relative to the non-rotating parts of the ship should be a constant, just the vector sum of your jump speed and your tangential speed, right?

 

[Rive]

But there isn't a 0.2g free fall.

That's the reference to highlight that low g is still not zero g.
And then, depending on the actual setup it (the calculation) can be far more nasty, yes.

 

[Drakkith]

That's the reference to highlight that low g is still not zero g.

Sorry, I'm not following you. Can you elaborate?

 

[Rive]

It's easy to neglect things in low gravity environment on the basis that it's - well, low gravity environment.
But sufficient length of free fall in low gravity environment still might be dangerous. It's not zero gravity environment. The mentioned 50m radius, 0.2g is exactly one such case.

 

[Drakkith]

But there's no gravity here, aside from the miniscule amount from the spaceship. It's not a low-gravity situation, it's a no-gravity situation. So there's no acceleration during your 'fall'. Am I misunderstanding something?

 

[Rive]

So there's no acceleration during your 'fall'.

In this regard the main difference is that it's the speed of walls (different angular velocity) what you have to fear, not the speed of floor. But the consequences are quite similar.

 

[DaveC426913]

But there's no gravity here, aside from the miniscule amount from the spaceship. It's not a low-gravity situation, it's a no-gravity situation. So there's no acceleration during your 'fall'. Am I misunderstanding something?

It's not your acceleration that's the problem; it's that, the longer you fall, the faster the wall is moving when it hits you.

 

[DaveC426913]

If the person is not touching a surface that is rotating, then they will feel no gravity at all. End of story.

They are always touching the atmo - which is rotating.

It would also be too easy for people to get carried all the way to the opposite wall of this cylindrical tunnel, with nothing to hold on to in between, which would allow them to stop or change their trajectory of movement.

In practice this would not happen unless you contrived to stay exactly along the centerline.

In any rotating body that has atmo, the air will be effectively stationary wrt the outer walls. This means that any floating body will be dragged by the atmo. No body will float for any significant length of time before it encounters an outer wall.

 

[DaveC426913]

We even discussed what happens when you fall down the elevator shaft through one of the spokes: You’d fall a few meters and then land on the wall. Gravity gradually increases as you move down the spoke, but the ring comes up to meet you, so that you don’t fall all the way down.
What we haven’t discussed though is what happens afterwards: Do you just remain stuck to the wall as the ring keeps moving, or do you start falling further down again, just with a break in between during which you’re stuck to the wall of the elevator shaft?

When you fall down an elevator shaft, the wall will come up to meet you diagonally i.e. a combination of the shaft's tangential motion plus your rimward motion. There is no "break". You will slide down the elevator shaft wall like it's a slope, going faster and faster (unless you slow yourself).

By this logic, if I’m standing on the rotating hub in the central trunk and I jump, even though this hub creates more than moon-like gravity through its rotation, I should not get pulled back onto the hub again, because I’m no longer touching the rotating surface; instead, I should continue to float to the opposite wall of the central tunnel.

No. You can't treat it as "gravity". To get accurate behavior, you must always treat it as inertial motion in a rotating body (albeit influenced by moving air).

Standing on the inner floor rotating hub, you are still moving tangentially, even as you jump. That motion will drive your path spinward, as it always does. It's simply a question of how hard you jump that will determine how far toward the opposite side you land.

It would be a complex solution. You could spend an afternoon practising jumps and plotting how far it takes you. There might even be an "inflection" point where certain jump paths actually have the hub spin overtake you and you land farther back than where you started.There is no universal answer; you would do well to work out the solution - on a case-by-case basis as you write them into the story - by setting up the scenario as inertial motion inside a rotating body with air and seeing how it resolves.

 

[DaveC426913]

I strongly advise you make a sketch every time you set up a scenario, and examine exactly what each body is doing.

Note the that guy is under the influence of two actions: his jump (straight up, green arrow) and his imparted tangential motion (small red arrow). Meanwhile the station moves under him.

1. How fast spinward does his residual motion carry him, compared to his jump?
2. How long before he contacts the outer wall again?
3. How far has the station rotated in that time?

Depending on the force of his jump, you will get widely varying results.

 

[DaveC426913]

I don't want to chase down the numbers again.
What is the diameter of the hub?
What is the diameter of the outer hab ring?
What is the rotation rate? (Or what is the tangential velocity of the outer hab ring?)

Update:
Hub dia: 50m
Ring dia: 500m
Rotational Period: 1.9 rpm
Tangential v: 50m/s

https://www.physicsforums.com/threads/generation-ship-sfv-exodus-revised-designs.1013958/

https://www.artificial-gravity.com/sw/SpinCalc/

The takeaway here is that the tangential velocity of a person standing in the hub is 5m/s, which is very close to his upward velocity of 4.5m/s if he jumps upward.

At 4.5m/s it will take him 11 seconds to cross the hub, during which time the hub will have rotated about 132 degrees (1.9 rpm = 650 degrees in 120 seconds = 12 degrees per second, times 11 seconds). He will fall short of exactly opposite the hub.

To hit a door opposite his starting point, he will have to face antispinward and aim about 48 degrees anti-spinward of his target.

 

[anorlunda]

This thread reminds me of a passage from Rendezvous With Rama

So there was the origin of the sound they had heard. Descending from some hidden source in the clouds three or four kilometers away was a waterfall, and for long minutes they stared at it silently, almost unable to believe their eyes. Logic told them that on this spinning world no falling object could move in a straight line, but there was something horribly unnatural about a curving waterfall that curved sideways, to end many kilometers away from the point directly below its source. “If Galileo had been born in this world,” said Mercer finally, “he’d have gone crazy working out the laws of dynamics.”

Clarke, Arthur C.. Rendezvous with Rama (p. 92). RosettaBooks. Kindle Edition.

 

[Drakkith]

It's not your acceleration that's the problem; it's that, the longer you fall, the faster the wall is moving when it hits you.

Exactly. If you jump in just the right way as to cancel out your tangential motion, you'll float all the way across the ring and then probably have something on the ring slam into you at whatever the tangential velocity of the ring is when you get to the other side.

 

[DaveC426913]

Exactly. If you jump in just the right way as to cancel out your tangential motion, you'll float all the way across the ring and then probably have something on the ring slam into you at whatever the tangential velocity of the ring is when you get to the other side.

Yeah. If we know how fast his jump is,we can figure out what spot on the far wall to aim for to hit the opposite hub lock. Looks like its about 48 degrees antispinward if my calcs in post 17 are correct.

 

[Nik_2213]

I think you need to look at how very much 'stuff' is in the service core of a sky-scraper. Okay, a lot would be 'side-ways' but, unless each ring is almost self-contained, probably a good idea, the central core will be 'very busy'...

Getting from spoke to spoke ? Ring_1 Spoke to core to Ring_n Spoke ? I think we're talking 'turbo-lift' in core, double-ended, so able to match moving spoke and near-stationary core...

All of which makes my head hurt...

Alternative is to evert the problem: All rings rotate together, 'close coupled' to a 'cake stack' by their 'turbo-lift' shafts, which now resemble 'subway cars / mini-trams'. The de-spun docking and other zero-gee modules are hung off ends of apparent axis which is integral to the stacked rings.

Sorry, I solved this conundrum for my 'Convention' tales, how to put spun-habs on a 'City-Class' star-ship. Unlike the elegant, almost avian designs of eg ST, my 'City' class are 'seriously clunky'. They're built from two lenticular end-shields, three modular truss girder spines / keels, paired cross-frames that variously mount 'side-saddle' habs, docks and tankage, or straddle centre-line 'Alcubierre Poles', utility pods and the fusor 'Power Section.

IMHO, the surfeit of Engineering issues and potential failure modes made putting an un-spun core through a spun hab the stuff of nightmare. Much, much simpler to have two hab drums connected at their ends to ship-frame out-riggers that also provide access within ship or to/from shuttles. Third drum is generally an 'un-spun', for cargo etc. Note spun habs are essentially self-contained for recycling etc. Each is almost a mini space-station in its own right.

As ship's triple spines / keels etc are modular, load-out may be readily re-configured. Take a bit longer than adding tank-wagons, a dining car and caboose to a trans-continental train, but no big deal...
===
'Convention' canon:
Turned out that a double Alcubierre Bubble permitted FTL without anti-matter fuel or oodles of 'Unobtanium'.
"One Pole, Null-gee. Three thrust, five fly, Earth, Moon and Mars. Nine go to the stars !"

 

[Strato Incendus]

First of all, many thanks again to @DaveC426913 ! I didn’t know you could also use SpinCalc to determine the values for questions like the present one! :)
Except the hub diameter would be 100 m, just like the diameter of the central trunk itself.

@Nik_2213 : Are you suggesting the same skyscraper structure for the central trunk that is often used for ships that accelerate at 1 g? Meaning, even though the present ship design would not be accelerating that fast, there would still be lifts going through the central trunk.

This would certainly make sense given the sheer length of the central trunk. If the spokes are already 200 metres long, and the trunk is close to a kilometre long, having a lift to traverse the trunk quickly would be helpful. It could also be some type of railway, though, with people still having the option to traverse the trunk “by foot” (or rather, “by float” ).

 

[Strato Incendus]

Alright, here's a proposed structure for the central trunk, if we apply a "skyscraper" layout (I put it in a spoiler because of its size):

EDIT: I just found out there's no option here of zooming into the image. So a quick explanation, because most of the font is too small: The six grey boxes in the middle are the rotating hubs of the six rings (which create artificial gravity of 0.21 g, whereas there is 1.05 g on the rings themselves).
In between every two hubs, there's a distance of 5 m - this is the ceiling height of the rooms placed in between. Each of these are circular rooms with a diameter of 90 m (the diameter of the pipe is 100 m, so there's a gap of 5 m on each side).
Only the hangars for smaller spacecraft (one at the front, and one at the back) have a ceiling height of 10 m each.

Spoiler: Image contained

The central trunk at this point is 1 km long.

I'm wondering whether it would have to be mandatory to use the lifts during the acceleration or braking phase. Otherwise, if you go by foot, you'd risk falling down the entire tunnel at an acceleration of 0.048 m/s².

But let me see if I as a layman can figure out the impact velocity here. The formula I've found was the following:

v=Sqrt(2∗g∗h)

So on Earth, if you fell for 1 km, the impact velocity would be 140 m/s. The same applies if you have a skyscraper spaceship that accelerates at 1 g (=9.81 m/s²).

With the present acceleration (0.048 m/s²) in space, you'd end up with 2 * 0.048 m/s² * 1000 m = 96 m²/s², the square root of which is 9.80 m/s. In other words, the impact velocity in m/s is, coincidentally, the same value as the mere acceleration in m/s² at 1 g.

9.80 m/s equals about 35.28 km/h, or 21.92 mph.

According to a study by Tefft (2013), for a pedestrian getting hit by a car, the average risk of death would already be at 10% at an impact velocity of 24.1 mph, and just 17.1 mph would already be enough for severe injury.

So in short: Falling down the central trunk during acceleration or braking, that is, deliberately traversing the entire length of the tunnel by foot, is still a huge no-no.

The question remains, though: If somebody slips, say, during an accident or during combat, and starts falling down the tunnel, they would be accelerating fairly slowly, compared to falling down a shaft on Earth. Meaning, there should still be plenty of time to catch them somewhere along the way, right? Especially since falling the entire length of 1 km will be a rarity: People will probably start falling somewhere in the middle, and will be caught or able to hold on to something, long before they reach the rear end of the tunnel.

 

[Nik_2213]

If ship accelerating at fractional apparent-gravity, internal transit would be more like a 'mountain railway', by analogy with SF cable-riding trams or Alpine funicular. You'd certainly have safety doors isolating each ring to contain leaks, spills, smoke, airborne toxins etc.
You'd have no business being in those 'mover' shafts other than for maintenance. Think elevator and subway workers, with appropriate safety equipment, such as harnesses and catch-nets.
BASE-jumping would put you in the psych-ward, if not out an air-lock...

 

[Rive]

starts falling down the tunnel

And in the meantime likely still maintaining some kind of radial speed too, almost inevitably hitting the floor somewhere...

 

[Drakkith]

The question remains, though: If somebody slips, say, during an accident or during combat, and starts falling down the tunnel, they would be accelerating fairly slowly, compared to falling down a shaft on Earth. Meaning, there should still be plenty of time to catch them somewhere along the way, right? Especially since falling the entire length of 1 km will be a rarity: People will probably start falling somewhere in the middle, and will be caught or able to hold on to something, long before they reach the rear end of the tunnel.

There's an easy fix to this. Just put up lightweight netting or mesh every, say, 100 meters to catch anyone or anything that falls. Or redesign the shaft to not be one continuous hollow structure. Or enclose your walkways so that it simply isn't possible for someone to fall off unless they have access to maintenance hatches or something.

That's if you're wanting to fix it of course. If you want someone to have a 1,000 meter tumble, don't let anything stop you.

 

[Strato Incendus]

A safety net is a great start!

I’m also wondering whether the trans-pipe lifts should all be in the centre of the pipe (meaning, where the map currently displays trans-pipe lifts 3 and 4). That way we could avoid the gaps between the hull of the tunnel and the “disk-shaped rooms” on the inside entirely.

So basically, the rooms in the central pipe would wrap around the trans-pipe lifts like CDs on a spindle.

The question is then how to hop from one of the rotating ring hubs onto one of the trans-pipe lifts. Would people just jump up from the rotating hub and float to the lift entrance? (This relates to the neighbouring thread, in which @DaveC426913 asked how high a person can jump in reduced gravity.)

As far as I could tell, the danger of falling along the radius of the pipe, rather than along its length, would actually be higher, because the acceleration / centrifugal force is higher in comparison (0.21 g). Therefore, there should be a fairly low “ceiling” even in the rotating hubs (say, 5 m high), so that you can’t just jump from one side of the hub to the other.

This would effectively mean that there is an entire uninterrupted tunnel inside the pipe, and the hubs would be spinning around that inside tunnel.

Which also takes us to the general question of how to insert the rotating hub segments into the pipe trunk, without inevitably leaving any gaps that would allow air to escape. This of course affects all constructions with any number of rings.

 

[Drakkith]

Which also takes us to the general question of how to insert the rotating hub segments into the pipe trunk, without inevitably leaving any gaps that would allow air to escape. This of course affects all constructions with any number of rings.

One possibility is to connect the rings to each other via walkways near the hub but not attached to the hub. Then you wouldn't have to pressurize the hub at all.

 

[Strato Incendus]

Nice idea in principle, but how does this work if every two rings have to rotate in opposite directions (one clockwise, the other counter-clockwise)? We’ve established in previous threads that this would be necessary, in order to prevent the entire ship from spinning around its own axis.

 

[Drakkith]

Nice idea in principle, but how does this work if every two rings have to rotate in opposite directions (one clockwise, the other counter-clockwise)? We’ve established in previous threads that this would be necessary, in order to prevent the entire ship from spinning around its own axis.

In that case it wouldn't work.

 

[Nik_2213]

Why not think a bit bigger ??
For my City-Class 'Convention' star-ships, I tackled this 'spin' conundrum by having pairs of contra-rotating Hab drums mounted side-saddle to the central spine.

In effect, each drum was a stack of your rings. On orbit, their brackets provided un-spun docking ports. A 'mover' system carried sealed 'cars' through axial locks to/from the Habs, gently matched RPM...