How big is optimal for a scifi starship?

[Spacescifi]

 

With a 900 meter radius or length, simply pitching or yawing it at ONE revolution per minute creates 1g at the ends/perimeter.

Thus, it dawned on me that there really is an optimal size for manned scifi spaceships.

900 meters or more means that crew cannot be located anywhere near the ends or perimeter during maneuvers. Whenever the ship pitches, rolls, or yaws, the crew would be at the mercy of falling/pulled toward the ends/outer edge.

So a 900 meter saucer is a better spacestation than a starship, as crew cannot use the outer rim area anywatly during manevers. This applies even if one had a scifi drive thay could accelerate for hours on end. It would still be subject to LONG turn rates that also cause g-force along the rim.

 

So in conclusion, as much as I like big and massive starships in scifi, they really are not practical for manned spacecraft due to long turn rate times and g-force.

Who wants to take one whole minute just to roll, yaw, or pitch the spaceship? Any faster and the g-force at the ends/perimeter is higher.

A more optimal size for manned scifi spacecraft is like the size of your average western home. It would take a higher RPM to do g-force with that, and I doubt anyone is going to blast their RCS like it's a gravitron ride anyway.

 

What do you think?

Are massive scifi starships practical or impractical for manned spacecraft because of long turn rates and g-force at the ends/perimeter,

Edited June 23, 2019 by Spacescifi

[kerbiloid]

97 000 t.

[Spacescifi]

6 minutes ago, kerbiloid said:

97 000 t.

 

 

Length or radius please.

If it is 97,000 tons but only as long as 8 feet then you won't get 1 RPM by rolling, yawing, or pitching.

A faster RPM would be required.

 

[Guest]

Is this the same ship that can make itself immune from the effects of gravity upon it? Because acceleration is equivalent to gravity according to Einstein, maybe you could think up some way that the ship cancels out inertial forces upon itself too  

like Star Trek!

Or are we just staying within normal physics for this?

[Bill Phil]

According to normal physics starships have to be huge. 900 meters just won’t be enough I suspect.

The crew can be housed in acceleration tanks (using breathing fluid and some cool properties of fluids to reduce the stresss of high accelerations on the body) near the center of mass (if possible). Well acceleration tanks may not be necessary if the acceleration is low enough.

The ideal trajectory would require very little turning. Indeer many realistic design attempts have concepts that allow “reverse thrust” without turning around at all.

In sci-fi anything is possible though I guess.

[Spacescifi]

28 minutes ago, Dale Christopher said:

Is this the same ship that can make itself immune from the effects of gravity upon it? Because acceleration is equivalent to gravity according to Einstein, maybe you could think up some way that the ship cancels out inertial forces upon itself too  

like Star Trek!

Or are we just staying within normal physics for this?

 

Normal physics.

6 minutes ago, Bill Phil said:

According to normal physics starships have to be huge. 900 meters just won’t be enough I suspect.

The crew can be housed in acceleration tanks (using breathing fluid and some cool properties of fluids to reduce the stresss of high accelerations on the body) near the center of mass (if possible). Well acceleration tanks may not be necessary if the acceleration is low enough.

The ideal trajectory would require very little turning. Indeer many realistic design attempts have concepts that allow “reverse thrust” without turning around at all.

In sci-fi anything is possible though I guess.

 

According to google, 900 meters is all it takes for 1g via rotation.

Huge ships would still subject crew to only living in certain areason the spaceship.

I guess what I am saying is that a lot of the space for amassive spaceship cannot be utilized by a scifi spaceship crew during maneuvers.

On the other hand, a smaller radius, or a shorter length spaceship could utilize more of it's space for the crew.

 

[Guest]

1 minute ago, Spacescifi said:

 

Normal physics.

Well, what’s the purpose of the ship? An interplanetary ship would have decades to turn and very little need to manoeuvre quickly. A fighter needs to turn and burn. I don’t think you could come up with an ideal size as a blanket statement, since the purpose probably dictates the size. 

If you want to go to the extreme, Earth is a spaceship, it could quite happily coast between stars the same as it does around one. The people on it mightn’t be as happy about it... the question though goes from “how fast can you safely manoeuvre it?” to “how fast can you actually manoeuvre it?” It would require A LOT of energy, the same is true of the big starship you are talking about. Beyond a certain point, can you even move it around fast enough to worry about hurting the crew? 

[kerbiloid]

And does it have an artificial gravity? If yes, which one: centrifugal or switchable?

[Spacescifi]

19 minutes ago, Dale Christopher said:

Well, what’s the purpose of the ship? An interplanetary ship would have decades to turn and very little need to manoeuvre quickly. A fighter needs to turn and burn. I don’t think you could come up with an ideal size as a blanket statement, since the purpose probably dictates the size. 

If you want to go to the extreme, Earth is a spaceship, it could quite happily coast between stars the same as it does around one. The people on it mightn’t be as happy about it... the question though goes from “how fast can you safely manoeuvre it?” to “how fast can you actually manoeuvre it?” It would require A LOT of energy, the same is true of the big starship you are talking about. Beyond a certain point, can you even move it around fast enough to worry about hurting the crew? 

 

Well a manned scifi starship can only have a few purposes.

Passenger liner, or colony transport.

In popular scifi, spaceships can use some FTL jump or warp drive to get rather close to a planet.

In other words, travel times would not be really long.

Thus the reasons I have made my conclusions.

Centrifugal gravity? Constant acceleration?

 

It can do both.

 

EDIT: Earth has a revolution evert 24 hours. If it were faster it could compete with gravity.

But it is'nt, which is good for us. We would be dead.

Edited June 23, 2019 by Spacescifi
Centrifugal

[kerbiloid]

16 minutes ago, Spacescifi said:

Well a manned scifi starship can only have a few purposes.

Passenger liner, or colony transport.

Also a slave transport. They can catch humans as pet slaves for their mansion design.

[Guest]

FTL is outside of normal physics. And warp drive may never be possible, the gravitational wave findings confirmed that changes in space propagate at the speed of light and since what is commonly thought of as a warp drive essentially moves space, the limit would seem to be the speed at which space can move.

Edited June 23, 2019 by Guest

[Spacescifi]

4 minutes ago, kerbiloid said:

Also a slave transport. They can catch humans as pet slaves for their mansion design.

 

True. Suffice to say, a comfy crew/passenger quantity is a smaller one. Not a huge one.

5 minutes ago, Dale Christopher said:

FTL is outside of normal physics. And warp drive may never be possible, the gravitational wave findings confirmed that changes in space propagate at the speed of light and since what is commonly thought of as a warp drive essentially moves space, the limit would obviously be the speed at which space can move.

 

True. I am looking into what happpens when scifi meets up with reality.

 

Blending the two is insightful for a scifi creator.

[Shpaget]

These cargo ships, which are 400 m long, take 5 minutes to turn 180°.

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.vliz.be/imisdocs/publications/45/313145.pdf&ved=2ahUKEwiHvtbn9f7iAhWvM-wKHRJsDOAQFjAKegQIAxAB&usg=AOvVaw2kEiCAUqQTadS3Pu-5ZWn9

[kerbiloid]

Spoiler

 

 

[magnemoe]

4 hours ago, Spacescifi said:

Normal physics.

According to google, 900 meters is all it takes for 1g via rotation.

Huge ships would still subject crew to only living in certain areason the spaceship.

I guess what I am saying is that a lot of the space for amassive spaceship cannot be utilized by a scifi spaceship crew during maneuvers.

On the other hand, a smaller radius, or a shorter length spaceship could utilize more of it's space for the crew.

 

900 meter sounds nice for the crew module, note that this could either be two modules on arms or an thick and long ring depending on need, you could also use end over end rotation in an pitch for an ship with an small crew. 

Length would be dependent on need as in how much cargo and fuel do you need and do you need to protect yourself from radiation from the reactor. 
If you spend long time under trust you might want to be able to tilt the passenger parts to compensate for the say 0.1g trust over a week then months of freefall followed by an braking burn. 

[Scotius]

Good thing in interplanetary travel is: You rarely have to hurry. Your 900 meters big spaceship doesn't have to turn with 1 g acceleration. It can do the same maneuver over an hour or more.

[magnemoe]

6 hours ago, Scotius said:

Good thing in interplanetary travel is: You rarely have to hurry. Your 900 meters big spaceship doesn't have to turn with 1 g acceleration. It can do the same maneuver over an hour or more.

This, and its true even if you are pretty fast say with an good fusion engine like my example. 
Docking it to an space station would be another issue and yes the space station in this setting would be even larger. if not you would not need an so large ship.
Still if in an hurry you could use smaller ships to move passengers while you was docking. 

[Bill Phil]

15 hours ago, Dale Christopher said:

FTL is outside of normal physics. And warp drive may never be possible, the gravitational wave findings confirmed that changes in space propagate at the speed of light and since what is commonly thought of as a warp drive essentially moves space, the limit would seem to be the speed at which space can move.

Gravitational waves are information, thus they cannot move faster than light.

Space however is still able to do so, indeed that's why we can't observe objects beyond the cosmic event horizon - at least in my understanding. Space has to be able to move faster than light, but it cannot do so as information.

A warp drive may be impossible, but if it is possible the interior of the warp bubble would be causally isolated from the rest of the universe, plus you'd probably need previous infrastructure to take advantage of any "faster than light" capabilities. Meaning you'd have to basically already be an interstellar species before you can use a warp drive.

FTL, or some things like it, are allowed in General Relativity. Causality has some problems with it and quantum mechanics may make it impossible as well, though.

16 hours ago, Spacescifi said:

According to google, 900 meters is all it takes for 1g via rotation.

Huge ships would still subject crew to only living in certain areason the spaceship.

I guess what I am saying is that a lot of the space for amassive spaceship cannot be utilized by a scifi spaceship crew during maneuvers.

On the other hand, a smaller radius, or a shorter length spaceship could utilize more of it's space for the crew.

 

You'd get 1g via rotation with 250 meters diameter at 2 rpm. What I'm trying to say is that your starship will need to be much larger than 900 meters in radius.

Most of the ship would likely be the propulsion and heat rejection systems - largely inaccessible to the crew.

A smaller radius could have more crew space, but your ship is going to be tremendous already. Even with a tiny percentage of the ship dedicated to the crew, it could be comfortably sized. Though every gram will count, far more than a rocket launching a payload to LEO.

Of course some ideas for using external systems for acceleration exist, like Forward's gravitational acceleration concepts and various beamed propulsion concepts. If such concepts can be developed starships won't need any propellant in all likelihood, at least the most common starships. To expand civilization to another star would still require a vehicle that can slow down under its own power, unless you can get a system like Forward has in Rocheworld working.

[Spacescifi]

3 hours ago, Bill Phil said:

Gravitational waves are information, thus they cannot move faster than light.

Space however is still able to do so, indeed that's why we can't observe objects beyond the cosmic event horizon - at least in my understanding. Space has to be able to move faster than light, but it cannot do so as information.

A warp drive may be impossible, but if it is possible the interior of the warp bubble would be causally isolated from the rest of the universe, plus you'd probably need previous infrastructure to take advantage of any "faster than light" capabilities. Meaning you'd have to basically already be an interstellar species before you can use a warp drive.

FTL, or some things like it, are allowed in General Relativity. Causality has some problems with it and quantum mechanics may make it impossible as well, though.

You'd get 1g via rotation with 250 meters diameter at 2 rpm. What I'm trying to say is that your starship will need to be much larger than 900 meters in radius.

Most of the ship would likely be the propulsion and heat rejection systems - largely inaccessible to the crew.

A smaller radius could have more crew space, but your ship is going to be tremendous already. Even with a tiny percentage of the ship dedicated to the crew, it could be comfortably sized. Though every gram will count, far more than a rocket launching a payload to LEO.

Of course some ideas for using external systems for acceleration exist, like Forward's gravitational acceleration concepts and various beamed propulsion concepts. If such concepts can be developed starships won't need any propellant in all likelihood, at least the most common starships. To expand civilization to another star would still require a vehicle that can slow down under its own power, unless you can get a system like Forward has in Rocheworld working.

 

I realize too that if you make the crew module a cylinder and put it inside a gyroscope, then you can flip the ship anyway you wan't and still have the crew being pulled toward the floor.

Timing is everything. Position too, as the module/gyroscope would need to be at the ends/perimeter for centrifugal g-force.

 

At the very least I learned that even with scifi tech, space travel physics favors small crews rather than big ones for space travel.

Edited June 24, 2019 by Spacescifi

[Guest]

8 hours ago, Bill Phil said:

Gravitational waves are information, thus they cannot move faster than light.

Space however is still able to do so, indeed that's why we can't observe objects beyond the cosmic event horizon - at least in my understanding. Space has to be able to move faster than light, but it cannot do so as information.

Yer, I’m not a expert so I don’t know any of the formulas but I think of the expansion being equivalent to faster than light over great distances being due to a compounding nature of minute changes to all of space on a universal scale (like, if you changed the property of a square meter of space by enough that it was 1cm more expansive between two objects on either side over time, from the point of view of those objects it would only take a certain amount of m3 (lots of zeros >_<) until an object on one side of the area is being expanded away from an object on the other side faster than light travels across the area in between. This is what I think of when distant objects fall outside of our universal horizon. They are now being moved away from us faster than anything can travel between but space didn’t move faster than light to achieve this, minute changes on a universal scale compounded to produce an overall gigantic result. ) 

Like I said though I’m not an expert so this is just how I wrap my head around it currently.

There are problems with saying space can be “moved” (for lack of a better word) faster than light as long as it contains no information. Since literally everything is information including the influence all matter and energy have on space, you are basically left with nothing being able to travel faster than light again if the space in question is influenced by or contains anything.

Influencing space is how a warp drive works so damn lol XD

There was actually a Star Trek TNG episode that touched on the problem of “causally isolating” yourself from the rest of the universe. Wesley was experimenting on creating warp bubbles and accidentally trapped his mother in one... the warp bubble was another self-contained universe (which is what a region of space completely disconnected from the universe would seem to be. A baby universe!) So unless you can exert influence outside of the universe you have basically trapped yourself in a prison which you can never escape. Your own personal universe!

Edited June 24, 2019 by Guest

[kerbiloid]

The optimal starship (for a human-sized race) takes about 2 m³.

1. Select the destination point.
2. Stay on platform.
???????????
PROFIT!!!!!!!!

Any other is forced.

Edited June 24, 2019 by kerbiloid

[Spacescifi]

8 minutes ago, kerbiloid said:

The optimal starship (for a human-sized race) takes about 2 m³.

1. Select the destination point.
2. Stay on platform.
???????????
PROFIT!!!!!!!!

Any other is forced.

 

Of course. Sci-fi is by nature forced to tell the story that anyone wants to tell.

 

Ideally, you would make a spaceship specifically optimal for the place it is going to.

But that would be impractical if a lot of planet hopping around occurs for characters.

Unless one big mothership had a bunch if parasite craft.

Some optimal for gas giants, others for moons, and still others for mars and or earth or venus types.

Edited June 24, 2019 by Spacescifi

[DDE]

700 km, duh.

[KerikBalm]

On 6/23/2019 at 6:57 AM, Spacescifi said:

According to google, 900 meters is all it takes for 1g via rotation.

Why use google, when you can use math?

1) a=v^2/r; 2) v=distance/t; distance in this case is equal to circumference, which is 3) 2pi*r. So combine 2 and 3: v=2pi*r/t, and then combine that with 1) a= (2pi*r/t)^2/r ; a= 4*pi^2*r^2/r*1/t^2

=4pi²*r/t²

So if we set a to 9.81 m/s (1 g), and t to 60 seconds. then 9.81= 4*pi^2*r/3600; r= 9.81*3600/(4pi^2) = 894.56 meters. That is the radius. Assuming a CoM near the center, the ship would have to be nearly 1,800 meters long to produce 1 G at that RPM. At 900 meters long, given the linear nature of a to r in this equation, you'd only get about 0.5 g's. Now the relationship with time is ^2, so to get to 1 G with this diameter would take 42 seconds.

But I have to ask, what sci fi setting requires that a ship makes a turn in less than a minute? Such a time is irrelevant for interplanetary or interstellar travel. Assuming the ship uses smaller shuttles to reach the surface of a planet, it doesn't need to turn fast for landing, because it won't land.

Assuming combat takes place at distances measured in light minutes (achievable with X ray lasers and apertures with radii, in the 10's of meters, which would seem to fit on ships of this size), that turn rate would be sufficient as well.

So first you need to establish how fast the ship needs to be able to rotate in the context of your Sci-Fi setting.

Just saying 1 rpm is the limit is arbitrary and doesn't get you to an answer.

Edited June 24, 2019 by KerikBalm

[kerbiloid]

12 minutes ago, KerikBalm said:

But I have to ask, what sci fi setting requires that a ship makes a turn in less than a minute?

Star Wars, with their dreadnought vs fighter PvP..