Deckplanning Gravity Rings

[zero]

I am currently trying to create a system ship for use in Chthonian Stars, it is troublesome to statblock due to Grav-couches not turning up in each statblock and being consistently priced :roll: Also some ship's elements are blatently TL 11 (like power plants) but tonnage and price goes from the base costs in MGT Core... :roll:

Anyway, I am getting close to finishing a regular merchant vessel, a 100 dton spacecraft, built for inner system trade between Venus and Earth.

Alot of the ships have gravity rings in their deckplan for the crew and passenger rooms, but there are no design pointers in how the length of the strip for the ring would wrap around the ship's main body.

I currently have one stateroom and 20 grav-couches. At 100 tons I cant really have a reason for putting one of these things in and making a difference but please see if you can explain this to me.
The living arrangements I planned all end on end are at about 2 squares wide and 7 along (not including life support and entertainment space of an indeterminate amount atm). If the main body of the ship was one dton wide (like a long rod, for this example only, the actual deck wont be) how much space would the grav-ring take up?

Some examples;

The Arduous ship has a grav ring on the deckplan thats 11 squares across and its deckplan strip is 46 squares long (22 squares for above and below the deckplan, with 24 shifted to the sides)

The Forge ship has a grav ring on the deckplan thats 21 squares across and its deckplan strip is 69 squares long (42 and 27 for the sides)

The Knights Errant ship has a grav ring thats 16 squares across (the main corridor through it is 2 squares wide this time). The strip is 45 squares long (32 and 13 for the sides).

So does anyone know how to do the math behind these? The Lab Ship in the MGT Core also has a ring formation, but I cant figure them out!

Please help!

 

[far-trader]

Not sure this is what you're looking for but if what you're talking about are the specifics for spin-gravity habitats I found a great web tool a while back to do the calculations. Saves a lot of drudge work

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm

 

[GJD]

As well as rings, you can also have spin hab's on the end of arms that don't make a full ring too:






G

 

[Captain Jonah]

Use spincalc to sort the level of gravity you want, this gives you the distance from the radial point that the floor of the spin habitat needs to be. From there it’s your basic calculate the circumference from the radius maths.

With spin habitats you can have real science problems spinning fast enough with the small ones to generate higher fractions of G. I covered this in the Cstars forum under "Hello and a few Questions".

If you want to assume that Cstars science has solved the coriolis effect then go for a small ring, if you want harder science then you need to use matched pairs or sets of spin pods. These are basically rooms at the end of extendable or fixed arms. Much easier to deck plan a room. The smaller ships given in Cstars have spin rings that will be safe to use at lunar or mars gravity, getting close to 1G needs much larger rings.

Wander over to Spincalc, heck bookmark the place and stick it in your starship design folder on the favourites bar :lol:

Decide what you want the spin to be and how fast a rotation you want, get a radius from there and away you go. If it’s more than 12-15m its going to be too big for a 100Dton ship so go pods.

If you are set on a ring work out your rotation and generated G to get the radius, use this to calculate the circumference in metres. For example a ring with a 12m radius to generate lunar gravity at a slow rotation rate. Circumference is Pi x Diameter which for Gamerdude is 3.142 x 24 which equals 75.38. Call it 75m. At 1.5m per square that gives you a ring length of 50 squares. If it is 1 square wide (1.5m) you have a roughly 0.75m wide walkway and the couches filling the other 0.75m of the width. Also this spin ring is 25Dtons in size. 50 squares x 1 squares wide at 2squares per Dton. Putting in a 1 square wide stateroom is going to be funny.

So for the smaller ships go with the pods. A pair of 6-8Dton pods

The math is fixed for the radius and circumference. Your only control is over how wide you make the ring. On the arduous you have a spin diameter of (call it) 17m, this gives you a circumference of 53m which is 35 squares long. Oops. The arduous spin ring should be 15 squares across to be that long.
46 squares long would be a circumference of 69m which is a diameter of 15squares or 22m.

Does this help any?

 

[zero]

Yes, thank you! I just thought the post was going to be; "do math!" but I am pretty much your average joe off the street when it comes to mathematics, so I am thankful for your examples!

Captain Jonah, or perhaps anyone else who can, could you please explain to me more about the pods?
I'm not quite sure what pods are???

 

[Captain Jonah]

Not a problem. If you look at the pictures above the middle two have rotational pods.

With a ring you have a single corridor which rotates around the ship like, well a ring :lol:
With the pods what you have is somewhat like a room with several staterooms or grav couches or the lounge in it. Look at the plan for the mongoose free trader in the main rules, you have a loft area with staterooms and a lounge. Now create another area the same size but fill it with grav chairs. Then these two need to be mounted on a rotational arm that slowly spins. One pod directly opposite the other to balance them out. The arm that connects them can have a short corridor running along it with a ladder or small lift, go up it feet first so when you arrive at the pod you are standing as the G increases as you go further out.

On a deck plan you add a rotational section onto the hull, this can be 1 square wide and as wide as the ship since it can sit on the hull and you can have rooms inside it. Then a pair of arms which are simple shafts. Then the pods. You can note the length of the arms and not even put them on a deck plan. So again looking at the free trader you would have the main body and pod 1 and pod 2. THat is your deck plan.

If you want I could try to do a quick and crude example or some of the much better deck plan types could do something to show you if this doesn't make sense.

 

[zero]

Ok, that makes more sense. I'll give that a go when I come to deckplan

 

[Mithras]

I designed these two ships for my own game STL; a 400 ton patrol cruiser and a module-tug.

This has the stats of the classic Traveller patrol cruiser, the centrifuge is stolen from 2001: A Space Odyssey, the Discovery has one very similar.

 

[zero]

I guess when building pods with a deckplan, that the spinning arm can be made from the common space or what would be used in corridors. So where 4 squares make up a stateroom, the remaining 2dtons of squares would be put into the spinning rod rather than a corridor (or perhaps a mix of the two; corridor space leading to the arm).

I'll check Spincalc to see what kind of gravity is produced.

 

[Captain Jonah]

Remember that the corridors on smaller ships can be narrow, with just a few people using them they could be a 1.5m tube with a little lift platform or ring ladder. Enough room for two or three people in the lift at once if they are cosy. This means a square of deck plan turns into approx 6m of rotational arm.

Also you can count the length of the spin arm from the outer hull rather than the spin point. The arms can either be at the core of the ship and spin from there or they could be attached to a ring that is mounted on the ships outer hull. I wouldn't want to do the engineering for either since keeping the seals airtight in vacuum while rotation is going to be fun.

So if your hull is 6m wide and your spin arm is 16m the middle 6m is hull and the arms extend out a further 5m from the hull. The overall spin radius is measured from its central point so even if the actual arms are shorter the generated G remains the same. This way you use only 2 squares of deck space in the corridors.

Look at the plan of the Trojan above. Here the spin arms are rotating on a joint on the ships spin and so are full length. There is a corridor through the joint allowing people to access the aft of the ship.
Consider that instead of being a small joint the rotational point as a ring the size of the hull over the galley. So the outer wall of the galley slowly spins and the arms are attached to that section of the hull, simply swim to the hull and down the arm from the galley. As I said I wouldn’t want to be responsible for designing the airtight seals on that but it should be doable by then. :lol:

[/img]

 

[barnest2]

To keep an airtight seal between the spin section and the main section:
A central circular hole between each section, with a liquid barrier to keep the seal... maybe?

 

[zero]

Kay, I would have thought that 1 dton was two 1.5m cubes so 1dton would make a 3m length of tubing... :?

I would probably keep the central point as a single 1.5m cube (half a dton) purely to enable the rotating arm to be longer and also to keep the design a bit more simple.

Kinda lost me with the spin radius, but then math was never really my strong point in school (I was more of an art genius kid in school...)

Just to make it clear, if I had spinning arms leading to the pods, they'd be kept at 1.5m cube segments that stretch out (so 1.5m high and w/e length to get to the pod) with the corridor being within it (so it'd be kinda like the airvents in Alien height-wise roughly, smallish but it makes for an awesome submarine-like feel, plus a nice claustrophobic feel as mentioned film 8) )
Keeping the spinning arm corridors at 1.5m high also enables them to be longer and have a higher G rating, as the ship I'm designing is 100 dtons, it's not going to be a big ship to begin with.

 

[Captain Jonah]

Remember that a Dton is two squares and that each square is 1.5m by 1.5n by 3m high. Stack 2 half dton squares on top of each other.

If your arm is 1.5m x 1.5m it is 3m long times 2 per dton of volume.

1Dton makes a 6m corridor. For visualisation we are talking about a shaft rather than a corridor, the arm spins and carries you with it so the further out you go the higher the G gets but it’s like climbing down a shaft

As some ideas for you. By keeping the rotational speed in the 3-5 range, the lower the better to avoid Coriolis problems.
So if you have:

Lunar gravity 0.16G. 4RPM, 9m radius. Or 5RPM and 6m radius. Above 5RPM you are running into problems with spin nausea and disorientation.

Mars gravity 0.37G. 4RPM, 21m radius or 3RPM and 37m radius.

So if you are happy with lunar gravity and want a nice comfortable spin speed 9m radius will do, that is 6m for each arm or 12m in total plus 3m per pod making the entire ship 18m wide at that point. 6m per arm is the same as 2Dtons of volume. This can either come out of stateroom or bridge excess. Alternatively you have up to 10% wriggle room on the deck plan, you could fudge the arms into the overall ship without allocating any Dtons to it at all.

When deck planning remember to include the 3m of the stateroom and crew area of the pod, the 9m spin radius above means that the crew have lunar gravity at the floor of the pods, gravity gets lower as you climb the ladder. 3m of stateroom plus 6m of arm gives you the 9m you need for lunar gravity.

Standing in the pod looking up you would have a 6m shaft in the ceiling, at the top of that you could have someone in Zero-G floating there and looking down, be nice, wave :lol:

 

[Captain Jonah]

To keep an airtight seal between the spin section and the main section:
A central circular hole between each section, with a liquid barrier to keep the seal... maybe?

Good idea by the way. The gap could be as small as a mill or so, use a high density fluid, viscous enough to stand the atmospheric preasure, add a metalic to the fluid and contain it with magnetic fields.

That sounds workable, Good thinking there Barnest2.

 

[GJD]

You really want to keep the RPM in the sub 3 range, or you get noticable nausea from the rotation. You also want to keep the arms longer to smooth out the gravity gradient, or start to find that there is actually a noticable gravity gradient within your body - noticably heavier gravity at your feet than head - which can really mess with your head - litterally...

G.

 

[Chernobyl]

I believe medically, they've determined that it is not needed to have a full G of gravity to eliminate bone density losses associated with zero-G.

 

[zero]

Huh, I never knew the two cubes in a dton were 3m high, I was always told that a dton was literally two 1.5m cubes...

That makes things a little more awesome in deckplanning now!

Ok, I think I get it now, 6m long for each dton (as it is the two rectangles placed side by side) and 1.5m wide and tall, cool.

Also, the shaft would have a ladder to climb to reach the pod which is gravitationally below the hub (I may need some explanation on why gravity works that way though... I realise the hub people will be in freefall - perhaps an opposite spinning part of that ship would remedy some of that? - but why would the shaft be upwards for the pod crew and not sidewards?).

There would also be some kind of air-tight doorways (would that be an iris-valve or a hatch to represent that?) linking the shaft to the main hub for obvious reasons (even I get that ).

Again, I doubt I will go for 3 rpm, the thing will have less to keep the crew nice and well, even if it sacrifices some percentage of G, mainly as I dont mind less than 1 G, as any bit of gravity is better for the crew in the longrun than freefall.

 

[GJD]

You'd need to have a contra-rotating counterweight to stop the ship from trying to de-spin the arms by rotating the hull in the opposite direction. If the ship is big enough you can have two sets of arms, or rings, rotating in opposite directions. Otherwise just a really heavy flywheel will do it.

The spin mechanism also means the ship will resist course changes, as the gyroscopic action of the arms will tend to try and dampen down any changes to the rotational vectors of the rings/pods.

During combat, when you might need to change course a lot, you'd probably de-spin and lock the arms/rings in place.

The pods can also be designed as lifeboats, with low berths or emergency shelters in them. Give them a fraction of the power plant and lfe support to represent independant systems.

Another system is to couple two ships together with a tunnel or cable and spin the whole ship in pairs around a common centre.

 

[Captain Jonah]

Chernobyl Yep. Hard science is a little bit scarce on the subject but currently it looks like lower G plus the right medication would do. I eagerly await us getting back onto space seriously and putting up a proper spin habitat so we can have some hard science on the subject instead. Richard Branson will save us. :shock:

Zero. You should learn something new every day to keep the brain active :lol: .
With slower rotations. To match lunar gravity at 1RPM takes a spin radius of 144m, 2 RPM takes 36m, 3RPM takes 16m. Even making the arms extendable you will quickly be using so much ship volume on the arms that the ship becomes useless. Cable tethers can work to add extra spin distance but will be a nightmare to use at short distances from the ship.
Centrifugal force.

One of those fun physics things. Centrifugal force is a linear force, that is to say it goes from the source outwards in lines. If you push something it moves directly away from the point of force. Now with spinning an object you are providing a rotation but you are also providing linear force going directly from the source (the spin hub) out to the object the force is being applied to (the ring or pod).

Quick and simple physics lesson. Appologies for the science dump to everyone who knows this already, this is for people who are not physics nerds
This is intended to be crude so no complaints about it not being completely accurate please :roll:

Draw a circle. Put a dot in the centre. Put a pair of large dots on the outer circle opposite each other. Draw an arrow from the centre dot through one of the pods and outside the circle. Put a little arrow in front of one of the large dots pointing around the circumference of the circle.

The central dot is the spin hub, here the force being applied to the pod or ring is generated. This force travels directly out from the hub to whatever that force is acting on. This force goes directly out from the source (the arrow) and acts to push anything it as acting upon in the direction the force is going. When spinning one of those whistles round your head this is what makes the string taunt, the whistle is being force away from the hub (your hand).
On the ring or pod if you are in contact with something that is conducting this force, in this case the floor/walls/ceiling you are also being pushed away from the centre. By standing on the floor or the ring or pod you are being pushed away from the hub (or down in your perspective), the floor resists your movement so you are being pushed onto the floor by the force level being generated. This is the opposite of gravity in that on a world it is the mass of the world that is pulling you down and your body that resists that force to allow you to stand up. In a spin habitat you are being pushed down and again it is your bones and muscles that are allowing you to stand up.

So you stand in a pod or ring, you are being pushed away from the spin hub. To you looking up you would see the ship over you.
As a side note you can hang in Zero-G inches from a spin ring and not be affected because you are not physically connected to it and therefore not being affected by the force it is applying. This is one reason why you enter a spin habitat from the hub and go down the connecting arms or use a ladder in a disc. If you reach out and grab hold of a spin ring or hub from Zero-G you suddenly become connected and will be pushed away from the hub with whatever force it is generating, this is like falling if you are inside the floor level, on the outside of the ring or pod it will throw you away from the ship. Since the corridors spin they will hit you if you try to swim down them so you need to use the ladder or lift.

The direction of spin and the fact that you are spinning is what causes the Coriolis Effect and problems. If you face into the spin and are in a lunar gravity spinning at 3RPM, simply turning round will change the acceleration on your head from front to back by one or more metres per second. With smaller arms and rings (under a few hundred metres) there is a difference between the speed and gravity at your feet and head, sudden movements changes this speed and the poor old brain doesn’t like being bounced around like that.

You need to balance the pods or haul dead weight with you which is a waste of thrust. As GJD says you also need a flywheel or a pair of contra rotation rings or pods, if not you end up like the helicopter with no tail rotor.

At some point we need to cobble together some proper rules for building these. People are going to be making Cstars ships or just for retro traveller games now Cstars has got the ball rolling.

 

[barnest2]

Richard Branson will save us.

What a terrifyingly... possible future...
Will future generations learn about the fabled Branson as the man who got us into space again?


Also, I now want to run a game based solely on the second race into space. Crewing satellites and such. Difficulties encountered. Do you think it could work? Or would there be too little going on?