Spaceship Shapes

[Enforcer Productions]

I just realized this today: If there's no wind resistance in space, why are most spaceships shaped aerodynamically? Couldn't they be almost any shape?

 

[Cathbad]

In truth, a spaceship should be shaped according to need - like the ISS.

 

[Overread]

Several reasons:

1) Atmospheric entry - some are designed to enter atmosphere and land on planets; as a result they have a structure designed to suit that purpose

2) Easier to relate to - just like how nearly every sci-fi film has sound in space its a kind of visual thing. It's easier for audiences to get the idea of spaceships if they are broadly like aircraft. This is also why most appear to only have engines at the back and turn; rather than having engines at the front or even the sides.
You can also see little things like how in, say, Startrek most ships line-up to each other in the same axis.

2) Monkey see Monkey doo - as a result of point 2 you get a lot of emulation. Even if its totally wrong its how people mentally visualise space; so its much easier to just keep things going. It's an inaccuracy most are willing to accept.


I'm sure if we achieve general space travel this era of science fiction will be laughed at for the insane ship designs people had; or at least it will feel very very dated.

 

[Jo Zebedee]

Atmospheric entry - and anywhere there is a gravitational pull

 

[goldhawk]

Spaceship would be shaped to maximize radiation protection. That would mean a sphere since spheres have the maximum volume-to-surface-area ratio. But as Cathbad says, they will also be shaped by need. Most likely, the standard shipping container will follow humans into space, so spaceships will be shaped to accommodate them. This means loading and unloading as well as securing them during flight. A cargo ship would be a platform with the cargo stacked on top of it wrapped in radiation shielding.

A passenger ship would be similar to cruise ships of today but would have many more decks stacked on top of it, like a high-rise apartment building.

 

[Biskit]

For a spaceship with propulsion which is for more than just adjusting an orbit, having a loosely symmetric geometry might make the navigation much easier, because when you apply thrust it really needs to go through the centre of mass. Even given a sufficiently sophisticated automation, you would presumably find it easier to compensate for uneven mass distribution if said unevenness was as small as possible, so although the crew might move around, at least the bulk of the structure is in a defined location.

 

[Ihe]

The gravitational pull is a good point. When it is strong enough, there can be important differentials in the level of pull on the same object (what's closest gets sucked in faster than what's farthest, and could rip the object apart, so having the ship's mass be the biggest/widest/thickest at the center makes sense, and this usually leads the ship to look naturally aerodynamic). Compactness and symmetry are probably good ideas for several other reasons stated above.

 

[Parson]

It also depends upon the drive function. I remember years ago reading about a ship driven by gravity applications and it was shaped like an inverted tear drop so that the largest surface would be presented to the gravity that they wanted to draw them in and the least to the gravity they wanted to escape. I believe I was a teenager when I read that book and thinking about it now the whole idea is full of holes, but the ship was memorable. Back then it seemed that every other book I read had rocket ships that looked like a missile.

I think that you will find that the harder the Science Fiction, the less the rockets look sleek and they look more like a collection of necessary parts with protection from radiation for the crew.

 

[Pyan]

Couldn't they be almost any shape?

If they don't have to enter an atmosphere/gravity well, yes they could. And some species have worked this out...

 

[goldhawk]

For a spaceship with propulsion which is for more than just adjusting an orbit, having a loosely symmetric geometry might make the navigation much easier, because when you apply thrust it really needs to go through the centre of mass. Even given a sufficiently sophisticated automation, you would presumably find it easier to compensate for uneven mass distribution if said unevenness was as small as possible, so although the crew might move around, at least the bulk of the structure is in a defined location.

True. One method is to use the water storage a ballast. It could be pumped to different tanks to even out the load.

This is why most rocket ships would look like missiles or skyscrapers. The rockets would be on the bottom and the mass balanced on top of them. If not, then it has to be cantilevered out to the side.

Why do airplanes have engines out on their wings? To reduce the noise inside the plane. But there is a greater cost to this. Because the engines are pulling on the wing, them need extra strength for this. That means the wings are heavier than if the engines were mounted on the rear. And more weight means more fuel. And the same thing would be true if the rockets are mounted to the sides of the spacecraft.

 

[farntfar]

It also depends upon the drive function. I remember years ago reading about a ship driven by gravity applications and it was shaped like an inverted tear drop so that the largest surface would be presented to the gravity that they wanted to draw them in and the least to the gravity they wanted to escape. I believe I was a teenager when I read that book and thinking about it now the whole idea is full of holes, but the ship was memorable. Back then it seemed that every other book I read had rocket ships that looked like a missile.

I'm not putting his books forward as being the height of good physics (*), but in E.E. Doc Smith's LENSMAN series all the ships were teardrop shaped as well. As I recall it, this was because space was not a hard vacuum, and even a tiny gain in aerodynamicness (**), on the basis of the very few atoms floating about in space, meant that they could catch the boskonians (baddies) that much quicker.

* The ships used iron as fuel!!!!
** If it wasn't a word before, I decree it is now.

 

[Phyrebrat]

I'm not putting his books forward as being the height of good physics (*), but in E.E. Doc Smith's LENSMAN series all the ships were teardrop shaped as well. As I recall it, this was because space was not a hard vacuum, and even a tiny gain in aerodynamicness (**), on the basis of the very few atoms floating about in space, meant that they could catch the boskonians (baddies) that much quicker.

* The ships used iron as fuel!!!!
** If it wasn't a word before, I decree it is now.

Works for me

pH

 

[Abernovo]

Most of it has already been discussed: entering atmo, gravity, structural integrity of the spacecraft, and fuel efficiency, etc.

One thing for any potential spaceship designers to consider though is that craft often have crews and passengers. The propulsion which puts stresses on the spacecraft structure also creates inertia (a fictional force, but it feels real enough when you accelerate). So, you need living spaces with (perhaps dynamically active) floors, walls, and so on. These will also impact on the design, unless you have some form of artificial gravity on board.

Personally, I prefer the Liberator, and Space 1999's Eagles. For the style, if not practicality.

 

[Phyrebrat]

The Cygnus from the fabulous The Black Hole is an inspired design as the gothic mansion in space. It's still relatively dynamic, but its design choices were informed by how it should make us feel, rather than just 'cool'.

pH

 

[Overread]

Cygnus is still one of the biggest feeling ships on the TV - its vaulted corridors the trains they had to ride to get about - it all spoke of casually being big. Plus being mostly empty it really felt huge. More so than things like the Death Star (and the Empires lack of handrails!)

 

[Venusian Broon]

Atmospheric entry - and anywhere there is a gravitational pull

There is gravitational 'pull' practically everywhere in the universe. In fact the number of spots where gravity from multi-body interactions 'cancels' itself out* and is essentially zero are miniscule.

Personally I think, unless you are trying to design a ship that gets in and skims close to a very heavy and dense object then back again, say a black hole so we are talking about handling very large changes in field strength, it could be practically any shape you want and more dictated as others have said by engines, functionality, and style.

I would agree with Abernovo that the main forces to take into account would be the inertial forces generated by your own engines, but if we are at a stage that we can actually put some sort of super engine together that makes an actual star ship, we should also have the material science to build a pretty interesting hull for it.

I mean look at the ISS. It is reasonably close in the Earth's gravitational well, only 400km, where the gravitational force on it from the Earth is ~89% of what it is on the surface. And it looks like a bunch of rulers jammed into a network of tin cans. It may be in freefall and therefore appear weightless but in fact it absolutely requires this pull to 'construct' a stable orbit.

----------------------------------------------------
* technically I suppose even the Lagrangian points of the solar system/multi-body, which are the points I'm alluding too, aren't really 'zero gravity' either because they are still under the influence of objects outside the system you are looking at. i.e. All Lagrangian points in the solar system must be under the influence of the galactic centre (as the solar system orbits it!)

 

[Vertigo]

I'd agree with others that if you're not intending atmospheric entry then there will be three major factors controlling your design:
1. Structural strength to withstand the stresses of your engines.
2. Radiation shielding - eventually may not be a structural consideration with possible magnetic or plasma shielding.
3. Weight - more weight equals more fuel; you need to minimise the weight

Note that although a sphere offers considerable structural strength, a cylinder would offer minimal torque from having mass at any significant distance from the axis of the thrust.

 

[Mirannan]

A lot of things depend on the details of drives and power sources. To take just two examples, a ship using the Alcubierre warp drive (or one of its variants such as that from White) would need to be reasonably compact in order for bits of it not to be pulled apart by the bubble wall. And a ship that makes a habit of refuelling by diving into gas giants would have to be reasonably aerodynamic.

 

[Cathbad]

And a ship that makes a habit of refuelling by diving into gas giants would have to be reasonably aerodynamic.

Would a sphere-shaped ship suffice for this?

(Asking for a friend.)

 

[Vertigo]

A sphere is not a very aerodynamic shape; better than a cube but there would still be a lot of turbulence. If the ship needed to handle high speeds in atmosphere then a sphere would be far from the optimum shape.