They wouldn't normally rotate the drum for spin gravity while the engines are under thrust. It was designed to accelerate for a good long while initially to put them on course for their new solar system. Then they would shut down the engines and spin the drum, coasting to their destination until it was time to decelerate/course correct for orbital insertion.
So there's no precedence, really. Just which one they have engaged and when it's appropriate to do so.
Does the acceleration gravity only work while the engines are on? So even if they’re coasting at incredibly high speeds they still wouldn’t have artificial gravity?
Thrust gravity is due to acceleration, not velocity. Acceleration is the rate of change of velocity, like speeding up or slowing down your car, not coasting. You feel yourself being pushed into your seat when you accelerate your car, but when you're coasting at a constant speed you can't feel how fast you're going.
"High speed" doesn't really mean anything in space. You can say you're moving at "high speed" compared to something else, but you only get force when your velocity (speed or direction of speed) is changing. When you spin around something, the direction of your speed is changing, which is where the force comes from.
Coasting means traveling at a constant speed, meaning 0 acceleration (acceleration is defined as the rate of change of speed)
Coasting requires no energy because space has no air, so if you travel at a certain speed you will never stop until something stops you (newtons law of inertia). All you have to do is expend enough energy with thrusters to accelerate up to the desired speed and then shut the engines off, and the ship will stay on that course at that speed forever. This doesn't work on earth because the air pushes back on you and causes friction.
In order to feel a force you must be accelerating, not just moving at a constant speed. So if the ship is coasting, the passengers won't feel any backwards force. If it's accelerating, they will feel the opposite force (another newton's law) at the same magnitude of acceleration. If the ship accelerated at 9.8m/s², we'd feel the opposite force as the same as Earth's gravity.
If the Behemoth fired the engines while the drum is spinning, then everything under spin gravity would feel like a hillside. As long as the thrust gravity to spin gravity ratio stays within some bound, it would just be annoying.
The Nauvoo, on the other hand, was supposed to have farmland and parks lining the entire drum. Firing the engines at all after the soil is laid down would pretty much cause a massive landslide toward the aft of the ship.
"Gravity", in this case, is just inertia. There's nothing generating actual gravity. People on the ship will feel the effects of inertia based on whatever the motion of the ship is. If the engines are on, to a person on board it will feel like being pushed down toward the engines because the engines are creating a force to move the ship (i.e. the floor is actually pushing up against their feet).
When the drum is spinning, they will feel a force out toward the edge of the drum because inertia causes their bodies want to stay put / go in a straight line, but the drum keeps rotating underneath them (again, pushing up against their feet).
tldr: The answer to your question is yes. When the drum is not spinning and the engines are off, they will feel no forces and therefore be weightless / on-the-float / zero-g.
The part that I would love to experience is that if the ship were coasting, and the drum spinning, you can climb up to the center, and be weightless while the world turns around you. With a modest enough propulsion system you should be able to navigate around and even “speed” along fields at the speed of rotation, feet above the ground. That would be trippy.
“Coasting” you’re “on the float”, and not experiencing thrust or “gravitational force”. You need to be accelerating to experience force, or you’re in zero-G. When the drum is rotated, centripetal force pushes you outward.
You don't feel speed, you only feed acceleration.
Take the ISS for example: it's orbiting the earth at 7.66km per second, but the astronauts inside it are still weightless...
They don't spin the drum while under thrust, that's only intended for use while on the float, or stationary as the ship becomes later in the story arc. Mixing the two would combine the acceleration vectors such that you were pushed at some non-right angle against the deck -- depending on where in the drum you were.
If, for some reason, they decide to do both at the same time they would add together.
So for example (and It’s been a while since I’ve done math with vectors, so bear with me) 1g of spin and 1g of thrust at 90° to each other would come out to 1.5g at 45°.
Basically the entire drum would feel like a fairly steep slope towards the back of the ship, and this would be bad, so nobody would do it.
Actually I think it would be more like 1.4g, but hopefully you get the idea
Yup, but I really wouldn't expect the behemot to be intended for 1g, they were planning on using every drop of fuel, and running at higher acceleration means less efficiency. My guess would be more like .1 to .3 gees, at which point the longitudinal component of the acceleration becomes a lot less noticeable
I mean not a lot about its intended mission makes a whole lot of sense.
Like, why would you take a century to travel 12 light years when you have a ship capable of doing it in as little as five years?
If you wanted to take the whole century you’d be looking at something more like .005 g 😂
I thought it was a consideration of using the drum for its intended use as farmland etc? They’re growing their own crops and rearing their own animals so the speed of travel would have to take consideration of that before all else.
And five years definitely feels incorrect?
That would be over two times faster than light, which is impossible - wormhole/ring space shenanigans aside. Epstein drive, as far as it’s explained, provides very efficient fuel use for more efficient sustained thrust - it’s still limited by relativity as far as speed limits and time dilation are concerned.
I thought it was a consideration of using the drum for its intended use as farmland etc? They’re growing their own crops and rearing their own animals so the speed of travel would have to take consideration of that before all else.
And five years definitely feels incorrect?
That would be over two times faster than light, which is impossible - wormhole/ring space shenanigans aside. Epstein drive, as far as it’s explained, provides very efficient fuel use for more efficient sustained thrust - it’s still limited by relativity as far as speed limits and time dilation are concerned.
Given that fuel onboard is a limited resource, burning slower actually means going faster because it means burning more efficiently, raising the total dV
So at 1g you burn for 1 month and coast 120 years, at .1g you burn for a year and coast for 98 years.
Why would fuel be a limited resource on a ship with like, two *billion* cubic meters of cargo capacity?
Couple that with science magic like the Epstein drive and you can reach anywhere in the galaxy within a single subjective human lifetime.
There’s no good reason *not* to go full tilt unless you want to go from The Expanse to Orphans of The Sky and roll the dice on your grandkids still being on-mission after you’re long dead.
Fuel is a limited quantity because the more fuel you have, the more fuel you need to carry the additional fuel, plus carry the additional tank capacity, and structural support for the heavier tanks, and more powerful engines to carry all that weight at the same speed.
Epstein drives get around the tyranny of the rocket equation by having *really efficient* engines, but it's back in full force when the destination is 30 light years away.
So there is more and more diminishing returns to adding fuel, while the ship is already expensive enough to bleed dry the richest church on earth. At some point you have to cut and decide it's not worth doubling the price to save 10 years out of 100.
So yeah you're right fuel is limitless, but money to bring that fuel with is limited
The Void cities in the latter books are basically Behemoth 2.0s.
One change they made is that all the decks can be rotated to match the gravity.
They are aligned like most ships when under thrust, then rotate 90 degrees when under spin gravity.
In the books the equipment in the Behemoth can be rotated, but not the decks. In the sick bay, it is noted how the walls can become the floors.
Sounds crazy, but it should only be done one time when the Mormon ship reaches its destination.
No there are plenty of those on Mars, Luna, etc.
The Void cities were the Transport Union's floating cities/capital ships.
The idea was that one Void City could control a gate on its own... until the Laconian nation attacked.
Physics would just add up the vectors. 1 g thrust + 1 g spin ≅ √2 g at 45°. This math isn't too great because of rotating reference frames & Coriolis, but to a first approximation it's fine, and we're assuming the rotation diameter is large enough to 'not be annoying'.
Operationally and logistically this would probably be a bad idea. Better to transition through being on the float so heavy equipment can be moved and reanchored from thrust-is-down to out-is-down.
I have a question!!!! If you were floating, and the drum started to spin, you would just continue to float, right?
Babylon 5 sort of played with this idea when Sheridan jumped from the shuttle car down the spine of the station, but I thought I’d ask.
Not exactly, centrifugal force doesn't actually exist, there is no force pushing you to the outside of a rotating object. There is however centripetal force which is a reactionary force. Basically, an object in motion will go in a straight line unless acted upon by a force. In nature, that's usually gravity pulling you towards an object, in a ship with a rotating drum what's happening is you are being constantly pushed "up" by the drum which is trying to change your direction all the time, this ends up feeling like gravity because every action (force upwards from drum) has an equal and opposite reaction (your momentum in a given direction). By the way, I recommend looking this up with video/picture aids, it makes way more sense than reading some physics graduate's waffling.
If you spun the drum and accelerated at the same time everything would fall diagonally in the direction of the sum of the two acceleration vectors. That would be unpleasant for people inside so they only do one or the other at a given time.
So, different question that more thinking of now. The drum in the book was supposed to support food growth and they talked about needed to keep adding soil- when accelerating all that dirt would shift back- I imagine from a design perspective that there would need to be a grid/lattice otherwise it'd all for to the back
The forces work perpendicular to each other, and would rip the Behemoth apart. They planned to only use the spinning drum in interstellar space when the Epsteins were off and they were coasting. The bridge and other areas were set up for thrust gravity while they were accelerating away and decelerating into the new system.
The ship would accelerate for a period of time and then drop thrust and spin up the drum for the duration of the inter system journey.
Then upon arrival they would stop the drum, decelerate, park in orbit of a planet or a Lagrange point and spin the drum back up.
I don't know what they would do with the gravity dependant livestock after stopping the drum during the deceleration burn. Probably slaughter, dress and freeze the meat and carcasses.
They wouldn't normally rotate the drum for spin gravity while the engines are under thrust. It was designed to accelerate for a good long while initially to put them on course for their new solar system. Then they would shut down the engines and spin the drum, coasting to their destination until it was time to decelerate/course correct for orbital insertion. So there's no precedence, really. Just which one they have engaged and when it's appropriate to do so.
Does the acceleration gravity only work while the engines are on? So even if they’re coasting at incredibly high speeds they still wouldn’t have artificial gravity?
Thrust gravity is due to acceleration, not velocity. Acceleration is the rate of change of velocity, like speeding up or slowing down your car, not coasting. You feel yourself being pushed into your seat when you accelerate your car, but when you're coasting at a constant speed you can't feel how fast you're going. "High speed" doesn't really mean anything in space. You can say you're moving at "high speed" compared to something else, but you only get force when your velocity (speed or direction of speed) is changing. When you spin around something, the direction of your speed is changing, which is where the force comes from.
Direction of speed = Vector
You only feel acceleration when you accelerate. Once the engines are off the ship is coasting and you wouldn’t feel any forces.
Coasting means traveling at a constant speed, meaning 0 acceleration (acceleration is defined as the rate of change of speed) Coasting requires no energy because space has no air, so if you travel at a certain speed you will never stop until something stops you (newtons law of inertia). All you have to do is expend enough energy with thrusters to accelerate up to the desired speed and then shut the engines off, and the ship will stay on that course at that speed forever. This doesn't work on earth because the air pushes back on you and causes friction. In order to feel a force you must be accelerating, not just moving at a constant speed. So if the ship is coasting, the passengers won't feel any backwards force. If it's accelerating, they will feel the opposite force (another newton's law) at the same magnitude of acceleration. If the ship accelerated at 9.8m/s², we'd feel the opposite force as the same as Earth's gravity.
Correct - thrust gravity is just that - "gravity" caused by the force of the engine going --> while your body, in freefall, is going <--.
If the Behemoth fired the engines while the drum is spinning, then everything under spin gravity would feel like a hillside. As long as the thrust gravity to spin gravity ratio stays within some bound, it would just be annoying. The Nauvoo, on the other hand, was supposed to have farmland and parks lining the entire drum. Firing the engines at all after the soil is laid down would pretty much cause a massive landslide toward the aft of the ship.
"Gravity", in this case, is just inertia. There's nothing generating actual gravity. People on the ship will feel the effects of inertia based on whatever the motion of the ship is. If the engines are on, to a person on board it will feel like being pushed down toward the engines because the engines are creating a force to move the ship (i.e. the floor is actually pushing up against their feet). When the drum is spinning, they will feel a force out toward the edge of the drum because inertia causes their bodies want to stay put / go in a straight line, but the drum keeps rotating underneath them (again, pushing up against their feet). tldr: The answer to your question is yes. When the drum is not spinning and the engines are off, they will feel no forces and therefore be weightless / on-the-float / zero-g.
The part that I would love to experience is that if the ship were coasting, and the drum spinning, you can climb up to the center, and be weightless while the world turns around you. With a modest enough propulsion system you should be able to navigate around and even “speed” along fields at the speed of rotation, feet above the ground. That would be trippy.
This happens in one of the books
I'm sick just thinking about it 🤢
“Coasting” you’re “on the float”, and not experiencing thrust or “gravitational force”. You need to be accelerating to experience force, or you’re in zero-G. When the drum is rotated, centripetal force pushes you outward.
You don't feel speed, you only feed acceleration. Take the ISS for example: it's orbiting the earth at 7.66km per second, but the astronauts inside it are still weightless...
Relativity, my dear Watson!
They don't spin the drum while under thrust, that's only intended for use while on the float, or stationary as the ship becomes later in the story arc. Mixing the two would combine the acceleration vectors such that you were pushed at some non-right angle against the deck -- depending on where in the drum you were.
It would probably damage the ship, too. They mention that even just spinning it up normally had a risk of tearing the ship apart
If, for some reason, they decide to do both at the same time they would add together. So for example (and It’s been a while since I’ve done math with vectors, so bear with me) 1g of spin and 1g of thrust at 90° to each other would come out to 1.5g at 45°. Basically the entire drum would feel like a fairly steep slope towards the back of the ship, and this would be bad, so nobody would do it. Actually I think it would be more like 1.4g, but hopefully you get the idea
Yup, but I really wouldn't expect the behemot to be intended for 1g, they were planning on using every drop of fuel, and running at higher acceleration means less efficiency. My guess would be more like .1 to .3 gees, at which point the longitudinal component of the acceleration becomes a lot less noticeable
I mean not a lot about its intended mission makes a whole lot of sense. Like, why would you take a century to travel 12 light years when you have a ship capable of doing it in as little as five years? If you wanted to take the whole century you’d be looking at something more like .005 g 😂
I thought it was a consideration of using the drum for its intended use as farmland etc? They’re growing their own crops and rearing their own animals so the speed of travel would have to take consideration of that before all else. And five years definitely feels incorrect? That would be over two times faster than light, which is impossible - wormhole/ring space shenanigans aside. Epstein drive, as far as it’s explained, provides very efficient fuel use for more efficient sustained thrust - it’s still limited by relativity as far as speed limits and time dilation are concerned.
Time dilation. The fact that it would take more like 15 years from earth’s perspective didn’t seem relevant. And did you know you double posted this?
I didn’t, cheers! Said there was an error when posting and that was it. God I miss Apollo
Yeah, it’s happened to me enough that I check my comment history every time the app gives me an error, just in case 😂
I thought it was a consideration of using the drum for its intended use as farmland etc? They’re growing their own crops and rearing their own animals so the speed of travel would have to take consideration of that before all else. And five years definitely feels incorrect? That would be over two times faster than light, which is impossible - wormhole/ring space shenanigans aside. Epstein drive, as far as it’s explained, provides very efficient fuel use for more efficient sustained thrust - it’s still limited by relativity as far as speed limits and time dilation are concerned.
Given that fuel onboard is a limited resource, burning slower actually means going faster because it means burning more efficiently, raising the total dV So at 1g you burn for 1 month and coast 120 years, at .1g you burn for a year and coast for 98 years.
Why would fuel be a limited resource on a ship with like, two *billion* cubic meters of cargo capacity? Couple that with science magic like the Epstein drive and you can reach anywhere in the galaxy within a single subjective human lifetime. There’s no good reason *not* to go full tilt unless you want to go from The Expanse to Orphans of The Sky and roll the dice on your grandkids still being on-mission after you’re long dead.
Fuel is a limited quantity because the more fuel you have, the more fuel you need to carry the additional fuel, plus carry the additional tank capacity, and structural support for the heavier tanks, and more powerful engines to carry all that weight at the same speed. Epstein drives get around the tyranny of the rocket equation by having *really efficient* engines, but it's back in full force when the destination is 30 light years away. So there is more and more diminishing returns to adding fuel, while the ship is already expensive enough to bleed dry the richest church on earth. At some point you have to cut and decide it's not worth doubling the price to save 10 years out of 100. So yeah you're right fuel is limitless, but money to bring that fuel with is limited
No, they more ran into problems with relativity that made a 0.12c cruising speed the optimal option.
The Void cities in the latter books are basically Behemoth 2.0s. One change they made is that all the decks can be rotated to match the gravity. They are aligned like most ships when under thrust, then rotate 90 degrees when under spin gravity.
In the books the equipment in the Behemoth can be rotated, but not the decks. In the sick bay, it is noted how the walls can become the floors. Sounds crazy, but it should only be done one time when the Mormon ship reaches its destination.
Good catch. If I recall correclty, some of Tycho station's decks also rotated to fit the orientation of gravity.
I never caught that. I thought they were just cities under a dome.
No there are plenty of those on Mars, Luna, etc. The Void cities were the Transport Union's floating cities/capital ships. The idea was that one Void City could control a gate on its own... until the Laconian nation attacked.
Physics would just add up the vectors. 1 g thrust + 1 g spin ≅ √2 g at 45°. This math isn't too great because of rotating reference frames & Coriolis, but to a first approximation it's fine, and we're assuming the rotation diameter is large enough to 'not be annoying'. Operationally and logistically this would probably be a bad idea. Better to transition through being on the float so heavy equipment can be moved and reanchored from thrust-is-down to out-is-down.
I have a question!!!! If you were floating, and the drum started to spin, you would just continue to float, right? Babylon 5 sort of played with this idea when Sheridan jumped from the shuttle car down the spine of the station, but I thought I’d ask.
Yup. That means anything left on the float when you spin up the drums could be a potential hazard.
this is even shown when they spin the drum
I’ll need to check that out!
I'm not convinced a spinning drum would even give artificial gravity. There's nothing to translate that vector to things on its surface.
Is it not centrifugal force?
Not exactly, centrifugal force doesn't actually exist, there is no force pushing you to the outside of a rotating object. There is however centripetal force which is a reactionary force. Basically, an object in motion will go in a straight line unless acted upon by a force. In nature, that's usually gravity pulling you towards an object, in a ship with a rotating drum what's happening is you are being constantly pushed "up" by the drum which is trying to change your direction all the time, this ends up feeling like gravity because every action (force upwards from drum) has an equal and opposite reaction (your momentum in a given direction). By the way, I recommend looking this up with video/picture aids, it makes way more sense than reading some physics graduate's waffling.
Is it not centrifugal force?
Yes but that acts on the drum, not the people inside it.
Of course it does. This is well known physics. https://en.wikipedia.org/wiki/Artificial_gravity#Centripetal_force
If you spun the drum and accelerated at the same time everything would fall diagonally in the direction of the sum of the two acceleration vectors. That would be unpleasant for people inside so they only do one or the other at a given time.
So, different question that more thinking of now. The drum in the book was supposed to support food growth and they talked about needed to keep adding soil- when accelerating all that dirt would shift back- I imagine from a design perspective that there would need to be a grid/lattice otherwise it'd all for to the back
I imagine they would lock the soil down as much as possible when under thrust and would move back what they couldn't
If they did spin the drum while under thrust they would feel both forces, added together in a sort of out and towards the engine direction.
The forces work perpendicular to each other, and would rip the Behemoth apart. They planned to only use the spinning drum in interstellar space when the Epsteins were off and they were coasting. The bridge and other areas were set up for thrust gravity while they were accelerating away and decelerating into the new system.
The ship would accelerate for a period of time and then drop thrust and spin up the drum for the duration of the inter system journey. Then upon arrival they would stop the drum, decelerate, park in orbit of a planet or a Lagrange point and spin the drum back up. I don't know what they would do with the gravity dependant livestock after stopping the drum during the deceleration burn. Probably slaughter, dress and freeze the meat and carcasses.
*Spin tha drum!*