Optimal shape for massive SSTO scifi spaceships

[Spacescifi]

What do you think is the most optimal shape for a MASSIVE scifi SSTO spaceship that has lots of thrust and no need of propellant? When I say massive, I mean massive enough that 1 RPM will generate 1g at the ends?

A cylinder?

A disc/pancake?

A sphere?

While massive cylinder shapes work great for rotating stations that do not typically maneuver, on a spaceship it would be an inconvinience or worse.

Imagine. All you want to do is flip the ship to do a retro-burn to slow down. With a long cylinder everyone is going to fall toward the ends with that simple manuever.

Also, if a MASSIVE cylinder SSTO is built for rotational gravity, then the deck layout will be complex to s ay the least when it lands on planet.

How dies it land? On it's butt? Stuff on the inner wall will wanna fall down. Does it land on it's outer side walls? The some of the stuff on inner walls will wanna fall onto the other wall!

A saucer would be simpler for decks on and off planet. And so long a torus deck was constructed within the inner walls, then crew would be comfortable when anf if the ship decided to yaw, pitch, or roll in space.

 

What about you? Perhaps you have more to add to this? Another shape or more information?

Edited June 6, 2019 by Spacescifi
Fix

[cantab]

Children of a Dead Earth favours cylinders for combat spacecraft. A sphere would offer the best surface area/volume ratio which minimises mass of armour, but also means the cross-sectional area and thus the size as a target is large. A cylinder reduces the cross-sectional area making the spacecraft harder to hit.

[Spacescifi]

13 minutes ago, cantab said:

Children of a Dead Earth favours cylinders for combat spacecraft. A sphere would offer the best surface area/volume ratio which minimises mass of armour, but also means the cross-sectional area and thus the size as a target is large. A cylinder reduces the cross-sectional area making the spacecraft harder to hit.

 

Optimization for combat is not the goal. Optimization is for landing on planets and not having the crew fall to the ends of the ship every time it pitches or yaws. Because the ship is that massive.

And spaceships need to be able to pitch, yaw, and roll without the crew worrying excessively.

 

Without crew everything becomes easier though.

Edited June 6, 2019 by Spacescifi

[Scotius]

Sphere then. It is the most efficient shape volume-wise. Also, if your technology is sufficiently advanced, you can have a  rotating habitat sphere suspended inside the hull sphere. This will provide the crew with gravity, at the same time allowing the ship to rotate engines in the desired direction without disturbing everything inside. Though it WILL require some serious know-how

[magnemoe]

I say something more like the ship in the Martian. 
This assuming you want spin gravity and distance from nuclear reactor. 
If massive scale more like an cylinder but something like two Starship mated at nose tumbling makes more sense. 

[Guest]

For anything very large, landing on a planet becomes a serious difficulty. I would say, it would be something like an inverted saucer, or perhaps a kind of aeroshell, with a flat bottom and a tapering top. Basically, a big, fat rocket. Sphere may be hard to keep together on the planet, not to mention it's aerodynamically unstable, making it difficult to control on reentry. In fact, a good shape might be that of Soyuz capsule, of all things, with a spike on top to reduce drag. 

It's really a question of how large does "very large" mean. I made some 1km+ ships in COADE with enough dV to land, the armor to survive reentry heating and the shape to take back off again. Those tend to look like very long, tapering cones with hexagonal or octogonal cross-section (it's not modeled in game, but tapering cylinders are troublesome to manufacture and repair). As it happens, what makes a good combat vessel (high dV, aerodynamic shape, heat-resistant outer armor) also make a good ascent/entry vehicle. The only problem is, after landing you end up with 1km tall tower, and since the mass of landing gear would be very large, I would expect this thing to launch from a large silo, and if it lands, also come down on some sort of support structure recessed into the ground to protect the vessel (which is not very dense, especially with empty tanks!) from being knocked over.

Edited June 7, 2019 by Guest

[kerbiloid]

A pair of concentric spheres. Then it can roll around the planet with the inner sphere staying motionless.

Also it has optimal surface-to-volume ratio (a sphere).

And by rotating the inner sphere they can produce artificial gravity in the space.

 

P.S.
But maybe something like this.

Spoiler

 

 

[Shpaget]

Didn't you say that yout ships have shielding against gravity? If so, the shape is irrelevant. A cube is the simplest and cheapest to build and utilize. It also provides good, stable base so it doesn't topple over or rolls down a hill.

Edited June 7, 2019 by Shpaget

[Spacescifi]

29 minutes ago, Shpaget said:

Didn't you say that yout ships have shielding against gravity? If so, the shape is irrelevant. A cube is the simplest and cheapest to build and utilize. It also provides good, stable base so it doesn't topple over or rolls down a hill.

My threads are not all related, so not for this thread no.

[YNM]

I was going to suggest "cone", but you don't list it...

 

Cylinder then.

Why ?

- Minimal surface area

- Still have a definite stable position (on the flat "side").

[Spacescifi]

2 hours ago, kerbiloid said:

A pair of concentric spheres. Then it can roll around the planet with the inner sphere staying motionless.

Also it has optimal surface-to-volume ratio (a sphere).

And by rotating the inner sphere they can produce artificial gravity in the space.

 

P.S.
But maybe something like this.

  Reveal hidden contents

 

 

For every action there is a reaction right? Should'nt the inner sphere move in the opposite direction? Unless that is the sci-fi part?

Edited June 7, 2019 by Spacescifi

[Shpaget]

It doesn't need to be sci fi at all. Thrusters can cancel the initial torque needed to spin up, after that you don't need them other than to compensate for friction.

Any shape will require this for spin up.

I'm more concerned with gyroscopic effect it would have on maneuvering (again, same problem for any shape) unless there are two halves spinning in opposite directions (still huge forces).

[Nuke]

sphere, unless its designed for atmo in which case id go with the cylinder. though with a significantly powerful drive you could make anything fly. 

[kerbiloid]

2 hours ago, Shpaget said:

It also provides good, stable base so it doesn't topple over or rolls down a hill.

Concentric spheres with motionless inner sphere do roll down the hills. And up, too.

Another benefit: by shifting the inner sphere they can:
1) manage CoM position while aerobraking;
2) bounce up and down when landed (say, when caught in a pit)
3) manage Center of Bouyancy (or how is it called) when floating.

2 hours ago, Spacescifi said:

For every action there is a reaction right? Should'nt the inner sphere move in the opposite direction?

This just makes their angular speeds depend on each other.

Edited June 7, 2019 by kerbiloid

[DDE]

10 hours ago, cantab said:

Children of a Dead Earth favours cylinders for combat spacecraft. A sphere would offer the best surface area/volume ratio which minimises mass of armour, but also means the cross-sectional area and thus the size as a target is large. A cylinder reduces the cross-sectional area making the spacecraft harder to hit.

@MatterBeam will have a few worlds to say in favour of two-dimensional armour sloping:

[sh1pman]

1 hour ago, DDE said:

@MatterBeam will have a few worlds to say in favour of two-dimensional armour sloping:

It should also be rotating and actively cooled by molten metal. 

[Spacescifi]

10 hours ago, Dragon01 said:

For anything very large, landing on a planet becomes a serious difficulty. I would say, it would be something like an inverted saucer, or perhaps a kind of aeroshell, with a flat bottom and a tapering top. Basically, a big, fat rocket. Sphere may be hard to keep together on the planet, not to mention it's aerodynamically unstable, making it difficult to control on reentry. In fact, a good shape might be that of Soyuz capsule, of all things, with a spike on top to reduce drag. 

It's really a question of how large does "very large" mean. I made some 1km+ ships in COADE with enough dV to land, the armor to survive reentry heating and the shape to take back off again. Those tend to look like very long, tapering cones with hexagonal or octogonal cross-section (it's not modeled in game, but tapering cylinders are troublesome to manufacture and repair). As it happens, what makes a good combat vessel (high dV, aerodynamic shape, heat-resistant outer armor) also make a good ascent/entry vehicle. The only problem is, after landing you end up with 1km tall tower, and since the mass of landing gear would be very large, I would expect this thing to launch from a large silo, and if it lands, also come down on some sort of support structure recessed into the ground to protect the vessel (which is not very dense, especially with empty tanks!) from being knocked over.

 

Long cylinders like you mentioned are like skyscrapers with landing legs. Toppling over is a concern. Also getting cargo down the long structure can be done, but I also do think a shorter structure would expedite the process.

 

By the way, really large is as I said, large enough to comfortably generate 1g when the entire spaceship rolls. Or 900 meters across at least of spaceship rotating for 1g.

As I mentioned earlier, pitch or yaw will also pull any crew to the ends if they are near there at all. So for all the space on cylinders, only the middle area is really ideal for crews.

Edited June 7, 2019 by Spacescifi

[kerbiloid]

We should not forget than in a low gravity environment (i.e. almost everywhere except Earth and Mars) a tall and narrow ship will be even more unstable.

On the moon and asteroids one should probably even use anchors.

So, a ship like Prometheus (Alien Covenant) or this one from V8Jester's video probably looks optimal.

[Guest]

For a 900m starship, you want some variation of a cone. Cylinder of that diameter will be ridiculously long unless you use a deployable centrifuge. If you want a high internal volume, go with a "headlight" Soyuz-style shape.

[kerbiloid]

15 minutes ago, Dragon01 said:

For a 900m starship, you want some variation of a cone.

Spoiler

 

[Guest]

Actually, a pyramid at of those proportions is not bad.  While a hexagonal or octogonal shape would likely be more optimal, there's a good reason not to make your cones cylindrical: part interchangeability. In a tapering cylinder, every piece has unique curvature, meaning you need either a machine that can account for that, or a unique production line for each and every hull piece. Meanwhile, a polygonal shape allows you to make your hull out of identical, flat plates, with triangular pieces for the edges. Needless to say, this considerably simplifies the problem of actually producing them.

[wumpus]

SSTO implies a tech level so much higher than ours it isn't clear exactly what you are optimizing.  Does aero matter?  Then you want a classic tall, thin cylinder ("rocket shaped").  If construction materials matter, then a fat cylinder.  If ease of construction matters, then a large cube.

Also note a large, fat, cylinder might be ideal for keeping a reasonable g-force by spinning.  If you assume that future tech will be built around 21st century ideas, then a fat cylinder is a good bet.

In reality, expect spaceship designers to care more about "cool" and "tradition" than coming up with a design from a clean sheet of paper for every planetary surface they land on.  Once a design solidifies into one traditional form, it is hard to convince people to accept another form.

PS: I'm not sure what Isp you need to make SSTO happen, but expect it to be more than 500s and closer to 1000s.  You can't realistically upgrade the shuttle (or add aerospikes) and make SSTO happen on Earth (without a tiny payload that could be easily comfortably sized had you used TSTO).

Edited June 7, 2019 by wumpus
left out "century"

[Bill Phil]

1g at 1rpm?

That entails a 1790 meter diameter. 

Or a ship about a mile wide.

I don’t think it’s practical to land anything of that size except on an ocean, and even then... the lightest shape for that diameter will be a torus...

[HebaruSan]

On 6/6/2019 at 5:38 PM, Spacescifi said:

What do you think is the most optimal shape for a MASSIVE scifi SSTO spaceship that has lots of thrust and no need of propellant?

Spoiler

 

Edited June 8, 2019 by HebaruSan
Too awesome to see without warning?

[IncongruousGoat]

@HebaruSan You might want to put that in a spoiler.