What would stop a large spaceship from looking like a flying brick?

Question

In the far future, galactic space travel is now a common reality, and spaceships reach sizes of over 1 kilometer in length.

Any capital ship in existence would therefore be designed for functionality, prioritizing life support, weaponry, and propulsion over appearance. Unlike modern naval ships, which are shaped specifically to reduce hydrodynamic drag, spaceships could be any shape due to a lack of drag.

In this reality, boxes would be the easiest to manufacture while spheres use the least amount of material to enclose the most volume, a large proportion of spaceships would be either giant cubes or balls.

What reason, logical or technical, would stop spacecraft designers from creating brick-like ships?

Answer 1

• Gravity
  Many science fiction settings have artificial gravity without spin. Many settings don't. That would be a reason to have spin sections, either rings or pods, which would fit around some sort of spine or core.
• Radiation
  Say it is unhealthy to live permanently close to the reactor. Alternatively, there is no "magic" way to absorb radiation from near-C flight, and a big shield is required at the bow. Again something to support a long, narrow hull.
• Heat
  With relatively hard physics in this regard, waste heat management will be a problem. The solution may include radiators, which imply some sort of "winged" hull shape.
• Sensors
  Aperture synthesis improves resolution by the use of multiple, carefully sited sensors. This could lead to a snowflake-like appearance.
• Weapons
  There may be a 'spinal' weapons mount, like a particle accelerator or a railgun, or smaller weapons are mounted on multiple turrets with an optimized arc of fire. A brick may be unable to bring everything to bear on a target.

(Two of my bullet points mirror points from the deleted posting by parasoup. I don't know why he or she deleted it, it was good.)

Answer 2

Vanity yachts

Galactic barons will want to travel in style, and ensure everyone knows that they are not common cube-flying riff-raff. Whatever the most efficient shape is, theirs is a cooler looking version of it with worse fuel efficiency.

Answer 3

Technical answer here:

The shape of the pressure vessel.

This is one of the major reasons that air- and space-craft fuselage cross-sections have changed so little over the last fifty years. A circular cross-section is the ideal, and a spherical hull is the most efficient of all shapes in terms of materials. Not only this, but circular cross-sections and semi-spherical ends or entirely spherical hulls theoretically eliminate "bending" fatigue in the construction material, leaving only tension on all the joints and structural members.

Commercial airliners are usually pressurized to a differential with the outside at cruising altitude of about 0.6 1 atmospheres, for a total of approximately .8 atmospheres. Humans can physiologically "acclimate" to a little less 2, but not much less for a long-haul (inter-galactic) journey. Pressurized cabins for these airliners always have round structure cross sections (usually circular, elliptic or oval), because sharp corners under tension or bending introduce localized high stresses (read: potential[?] points of failure), regardless of the materials used.

Simply put, circular/spherical shapes are the natural choice for pressure vessels. Not only a choice, but naturally occurring. Look at a bubble, or blood vessels, or "float bladders" on sea-weed. It is part of the behavior of a[n ideal] gas to push on all surfaces of its container equally, which (given enough pressure) will deform the bounding walls to distribute the tension in them. See 3, 4, and 5 for more information about aircraft cabin pressure and human endurance of low pressure environments.

And this efficiency is impossible to beat with any other shape, even though people have fantasized about other hull geometries for many years. Unfortunately pop science journalists writing the blurbs for "all-new aircraft designs" that are touted to be on the verge of "revolutionizing air travel" only ever give a few sentences to the pressure problem, even though it looks to me like the biggest one of all:

Researchers still face several challenges in developing a full production model of the Boeing flying wing. Cabin pressurization is not a problem on today's tube airplanes, but will pose a problem in the flying wing's much larger cabin. It will require the development of a new pressurization system. Also, at today's aircraft speeds of about 600 mph (966 kph), drag becomes increasingly problematic with a flying-wing aircraft because the wing is much thicker than that of a traditional airplane. Computer analysis and wind tunnel testing at NASA's Langley National Transonic Facility is expected to determine the stability and performance of the flying-wing design. (howstuffworks.com)

Intergalactic spacecraft would need to be pressurized to a pressure differential of about .7 or .8 atmospheres, as we have seen; so while they would avoid some of the effects of fatigue by maintaining a relatively constant differential, they would still need to be over-engineered. For a craft "over a kilometer in length" this could pose quite some challenges, but in this "far future" you may be able to overcome them through materials engineering or other magic.

Materials efficiency may be an issue, depending on your supply chain (the anti-crack-esium needed for an alloy used in the frame construction comes from the far side of Andromeda), the distance to be travelled (how much food do you need to take?), and drive system used on your craft (as mentioned in other answers).

References:

1 https://aviation.stackexchange.com/a/19300

2 https://en.wikipedia.org/wiki/Effects_of_high_altitude_on_humans

3 https://aviation.stackexchange.com/questions/21523/why-is-the-fuselage-on-an-airliner-circular-shaped

4 https://en.wikipedia.org/wiki/Cabin_pressurization

Answer 4

Modular design:

Your ships are made of numerous smaller sections. Each has its own systems, and often these can be ships on their own. Ships are assembled based on need, sometimes with no consideration of shape (other than mass distribution). Need a bigger ship? Add cargo holds. Replace the ten small habitats with one big one. Only now you need more power, so add an extra engine. This port only has small engines, so add small ones instead. Pretty soon, it looks like a snowflake. But supply and assembly mean no two snowflakes look exactly alike.

Answer 5

Lower observability.

The smaller the surface area you expose to the enemy, the harder you are to detect. You also need significant amounts of surface to radiate heat away from your ship, which you would probably prefer not to point in the general direction of the enemy and their infrared seeking missiles. A broad, flat shape provides you with a narrow profile while also retaining large side areas that you can use as radiators.

Most natural objects in space, like asteroids, have a vaguely oblong shape, not spherical and certainly not a sharp-sided rectangular prism. Having a shape with rounded edges might improve your odds of being overlooked at long ranges. An oblong shape might also make it easier to obscure your direction of travel, versus having a well-defined shape (like a flat plane) always facing forwards.

Answer 6

Because they travel through lots and lots of space.

Space isn’t completely empty. And if you travel from one solar system to the next you will be hitting a LOT of space dust. You want a shape that mitigates the damage as much as possible, not to mention whipple shields designed to mitigate extremely high velocity impacts of tiny particles.

Answer 7

"Space Magic" Reasons

For a setting like this (galactic-level space travel), you will probably need some sort of "Space Magic" to make it realistic. Doesn't matter if this is "jump drives", "wormhole projectors", "gate"-infrastructure, "hyperspace", "warp drives" or whatever, just make it so that in order to use this Faster-than-Light method of transit, a specifically and carefully constructed hull shape is required.

High Speed "astrodynamics"

For example, while space is a vacuum, that doesn't mean it's completely empty. Even out in the interstellar or intergalactic void, there are still random lone hydrogen atoms drifting about, and while the density is very low, if you are going very, very fast (>c) these particles would have a "sandblasting" effect on any ship passing through.

To resist this effect, you might want to make needle-shaped ships with as small a forward-cross section as possible and line the leading faces with extremely powerful magnetic deflectors that redirect the particles

Hyperspace "drag"

Similar to the previous point, if your FTL technology works by transitioning the ship into some sort of alternate reality or different plane of existence ("null-space", "sub-space", "warp-space", etc), there's no rule that states this new reality must also be an airless void. Perhaps it's full of gas (might also be handy to limit visibility) or whatever, and this could require more conventional "aerodynamic" designs

Geometric transition limitations

Maybe the technology used only works in a specific pattern. For example, the "phase shift generator" can only effect an approximately spherical area around the actual projector/generator. Building bigger generators is prohibitively expensive (because the physics gets wonky or whatever) so designers try to fill the entire volume that the generator covers with ship or construct their ships in long, chain-of-beads, type arrangements focused on several nodes where these magic machines are located

Answer 8

spaceships are non-homogenous

the inside of a spaceship is made up of different parts that need different relations to one another. crew areas should be near each other. hot or radioactive parts should be near the surface, and a minimum distance from crew areas. fuel storage should be near the engines. these constraints will lead to an optimal shape for each ship.

minimal cross-section

if a ship expects to be attacked or to fly through areas of dust, it may want to be long and thin to present a minimal cross-section towards the things coming at it.

really big engines

perhaps spaceship engines need to be much bigger than anything you need to move, or can only move a small amount of mass compared to their size. then spaceships will be whatever shape the engines are, dictated by their principles of operation, with small boxes of people and stuff attached.

Answer 9

Nuclear engines, centrifuges, pressurization and radiators.

For the movie 2001, Stanley Kubrick did meticulous research on what a deep space vessel would look like and initially came up with: It has all 4 elements in play: The nuclear engine is waay in the back, separated from the habitable section by a long cantilever section, because radiation shielding is very heavy, so it's more efficient to shield by distance. It has large radiators for rejecting waste heat from the engine. The front is a sphere, because that's the easiest shape to pressurize and contains a centrifuge that stimulates gravity. In the final film, they lost the radiators, because the ship ended up looking too airplane like.

The spaceship in Avatar, also designed with meticulous attention to science has the same elements arranged differently: The engine is now at the front(left in this picture), also separated by distance for radiation, but the middle is a tether instead of a cantilever, so the engines pull instead of push. It also has a large radiator. The spheres are there as the most efficient shape to insulate fuel. The centrifuge at the back is the end two trusses.

So any deep space spaceship, would, due to physics, be a collection of huge flat radiators, spheres, toruses and long thin trusses. Anything but a brick.

Answer 10

Sloped armor.

Simply put, armor works better when there's more of it between you and whatever is shooting at you. However, adding more armor means adding more mass, which reduces mobility. Military minds have thought on this conundrum in real life, and a solution has been found: sloped armor. By angling a piece of armor so that it's not being directly hit by the enemy weapons, you can effectively increase the depth of the armor that the weapon needs to penetrate to effectively damage your ship.

However, it's not really possible to build a sphere to have sloped armor - every angle the enemy could be firing from will have a point in the centre where a direct hit will occur if the enemy strikes it.

Answer 11

Practical reasons

Have you ever wondered why many fictional space ships do not look like bricks? Take Star Treck for example. It has an iconic look with the engines placed on some really weird appendages. Sure it might not be all practical of you think about it, but they do have some lore reason why. The space ship seen in the movie Avatar (with the blue people) is a better example in that regard. It is build much closer to real life, allowing a glean into why you shouldn't build boxes and spheres.

Most likely, you'll kill the crew. Second most likely, you'll damage your spaceship. Engines and power sources are very finicky and can possibly roast the crew or the ship. The radiation needs to be contained while safely powering the ship. This is why you might want the power source to be somewhere else where it's easier to shield the crew and the ship. The same goes for the engines. Their sci-fi propulsion might be dangerous, requiring exact measurements and no interfering parts, possibly also prevent the rest of the ship of reacting in turn.

Finally there is heat. You might think heat isn't a big problem in space. Because space is cold! Unfortunately there is so little cold space it's hard to lose heat. This means any process can build up heat, eventually cooking circuits, engines or passengers. Most of the 'solar panels' on the ISS are actually panels to radiate heat. In Avatar you can also see some large things radiating heat as they arrive.

There's probably more you can think of. Weapons, special batteries, alternative energy storage, sci-fi replicators and more. Your spaceship might look radically different from a box out of necessity.

Answer 12

Okay - so there's a bunch of options, in addition to the other good answers given - realistically it will be a combination of factors:

Firing Arcs of the Weapons

You mentioned Weaponary - well, depending on your weapons configuration, a Box shaped ship has some big dead-zones. Now, you could argue that if it's a flat side on the weapons side, then you would have a full 180 degree sphere of fire - however, by elevating the weapon and putting it in a turret and rounding the edges, we now have a greater field of fire (depending, of course, on your weapon type.

A Combination of Mass, Armor, internal volume and Delta V

If we consider Tank design, the smaller the internal volume of the tank, the less Armor you need to adequately protect it, the less armor you need, the lighter your tank is (and the cheaper it is to produce). Historically, the US Navy for their fast WW2 era Battleships, used an All-or-Nothing Scheme. You have very heavily protected vitals (Magazines, Turrets, Engine spaces etc.) and minimal armor in less vital area (so that AP Shells will just poke a neat hole in one side and zip out the other without going Bang).

A Box or sphere aren't going to be the most efficient with internal space, especially in areas that may not need to be that big and considering the hostility of Space, we are allowed to assume that all of the ship will have a minimum degree of Armor - but if there's weaponary, we can also assume that vital areas (Life Support systems etc.) will have extra protection.

This all adds up and you want to have the smallest necessary mass for your ship for the best acceleration/performance - Hence the Delta-V.

In short - you don't want any section to be bigger than it needs to be (see below), to minimize the amount of armor and mass used.

Resource shortages

Maybe not Shortages per se - but building a Space ship is expensive, it requires lots of materials and lots of clever people. Even if your society doesn't use Money in a conventional sense - just the time of all the people required (and robots if you use them for construction) is a lot. Therefore even if a Box shape might be better, if it uses excess resources where not needed, it's not going to be efficient.

Different size components

Someone mentioned 'Really big Engines' - and this is an extension of that point. If you have a component that has a minimum size - Engines are likely a good example as they take up significant space and weight in any large moving object. After the Engines, if nothing else needs to be that big, it makes little sense to have a box that is the same size as the Engines, this would likely give a tapered look to the vessel on this point alone - but there are other systems that might need a minimum size and need to be in a specific location - like a shield module or emergency escape pods.

Aesthetics

Don't discount this. There's an old Aviation adage 'If it looks good, it flies good' Even commercial vehicles will have secondary design choices with Aesthetics in mind. Functionality first, but once that's done, the Designers can have a certain flare.

We've always done it this way

Likewise. Don't discount this either. Rather than re-inventing the wheel, incremental improvement with known principles is extremely prevalent in all forms of Engineering. I mean, look at early submarines - they were merely funny-shaped boats that went underwater. It wasn't until the deeper diving nuclear subs that the tear-drop shape that we now associate with Submarines became a thing - that's 2 world wars and 50 ish years of 'We've always done it this way'.

It's likely that the people who build the initial space fairing craft, will be traversing an Atmosphere and so those design principles (that are known and work) will get carried over for many years to come.

Engineering reasons

Spheres are kinda hard to make and having sharp edges/corners is bad for pressure bearing surfaces (IIRC, the first Jet airliner had square windows which failed, which is now Airlines have the oval shaped windows - due to this) - and so having a rectangular box and having a sphere are, from an engineering PoV either difficult or impractical (I'm sure an actual engineer will pop along and point out that I've massively over-generalized - but if it's convincing enough for a first glance, it will work for a story)

There's a few more I can think of, but they are variations on those main points.

Answer 13

Broadsides and moment of inertia.

A ship with broadside-firing cannons should have the maximum area on the broadside end and a minimum total area that needs armoring, which means the ship would be narrower. The top and bottom of the ship could be more heavily armored on account of not having gun ports. The ship would also need to be able to roll, either to turn the broadside to bear on an enemy above or below, or to turn the narrow side towards incoming fire and soak it on the narrow and more heavily armored side.

I haven't done the math, but I think an ellipse could give a lower moment of inertia around the roll axis, for an equivalent amount of broadside area. There might be other shapes with the same property.

Answer 14

There are many reasons we might expect future spacecraft to be long and pointy.

• Armor angling: incoming projectiles are more likely to glance if they hit a slope (or otherwise have more armor in the way to penetrate, per a tangent function) while a laser with the same angular size will be spread over a greater physical area if that angular cross-section lands on a slope (which means its penetration will be reduced). So we might expect combat spacecraft to have sloped faces, like main battle tanks do today. And sloping against the sides, top, and bottom gives the vehicle a diamond-, dagger- or star-like cross section.
• Cross section: At long ranges in open space, one can be reasonably aware of where attacks are most likely to come from. Thus, having a very small frontal face can be useful to minimize the area that the opponent can lock onto and shoot. Narrow spacecraft again have an advantage here.
• Propulsion safety: Powerful space engines in current thinking mostly involve various nuclear reactions or even antimatter, and produce enormous amounts of radiation. Thus, it may be important to keep crew modules far away from the engines, which means having a long vehicle.
• Radiators: You say a sphere gives the smallest surface area per volume, but one of the big issues on a spacecraft is heat rejection, since there is no atmospheric convection to carry it away from the surface. Spacecraft should minimize their volume to ensure that heat can be easily conducted to the surface from reactors and electrical components. They also may end up with extensible wing-like radiators (akin to the long white sheet-shaped ones on the ISS), or in more advanced settings droplet radiators that spray high-temperature metal in arcs or contain it in open areas, both of which very much disrupt the expected shape of a brick.

Answer 15

A spaceship which has to travel fast will find that space is not totally empty. It will run into space dust and space atoms, and loose space electrons and protons and it will run into photons of light which will be blue shifted to higher and more dangerous frequencies by the doppler effect.

So the faster a space ship has to travel, the more it should be a narrow cylinder to minimize the front surface that impacts particles and photons.

And the internal layout of the decks should be more like a skyscraper than like a ship at sea. The decks should be circular, and perpendicular to the direction of travel. So if the ship has artificial gravity generators the direction of up and down will be parallel to the direction the ship travels. If the ship accelerates or decelerates, the artificial gravity generators will increase or decrease their output to keep the gravity felt by the crew steady. If the decks were laid out like on a ship, the artificial gravity generators would have to adjust their angle by 90 degrees as well as changing their amount of force. That would be much more complex.

And if there are no artificial gravity generators, a layout of circular decks at right angles to the direction of travel instead of long decks in the direction of travel would be even more necessary. If a space ship had long decks in the direction of travel, and someone was walking in a large fore and aft corridor when suddenly the engines started firing and making acceleration, they would find themselves falling down a large shaft to their death.

Anyone who has ever seen The Black Hole (1979) should realize how silly it is for the Cygnus to have the layout of a ocean ship with decks parallel to the direction of travel and rocket engines at the back. There is a corridor that looks thousands of feet long on the Cygnus. If someone is in the corridor when the rockets fire hard they will fall to their death at the back of the corridor, possibly breaking through the rear wall and damaging the engines.

I remember an A. E. van Vogt story from the 1960s, where the protagonist suddenly turned on the rocket engines, turning the rear bulkhead into the floor, which the antagonist slammed into.

It is quite possible that a spaceship would be a tall, narrow cylindrical framework of struts, with engines, fuel tanks, machinery spaces, crew quarters, etc. in various spherical, cylindrical, conical, etc. structures within the framework.

And in most cases there might not be any strong reason, except aesthetics, to put hull plating allover the main cylindrical framework, as Michael said in his answer.

Even in a space war, if two Earth colony planets with the same technology and with spies go to war, there may not be any reason to hide the various sections of a warship with opaque hull plating. The enemy may know from spies exactly how far along the hull of a warship the most vital areas are.

But in a space opera with many unknown and possibly hostile civilizations in the galaxy, there would be a possibility of of having to fight a civilization which has no prior information about the layout of your space battleships. Thus it would make sense to have opaque hull plating all over the framework of a space warship, so the enemy has no clue where the most vital parts of the ship are.

And if a spaceship normally lands and takes off planets which have atmospheres, it should have the entire cylinder covered with hull plating for streamlining.

I note that there is an floating platform, RP FLIP, which can mostly fill with water so most of of it sinks beneath the sea, and only one end sticks out of the water, for scientific research. And so the part of the ship which is inhabited has to have chambers designed so that two different sides can be the floor, depending on the position of the platform at the time.

https://en.wikipedia.org/wiki/RP_FLIP

And if the inhabited part of that ship were larger, it might make sense to put it on gimbals, so that the decks would always be horizontal whether the ship was vertical or horizontal or in between. Then researchers wouldn't have to adjust to the floor becoming a wall and a wall becoming the floor.

And possibly a large cylindrical spaceship might have the crew quarters and other parts sensitive to the direction of gravity, be spheres mounted on giant gimbals, within the hollow cylinder.

When the spaceship was travelling under power in space, or standing vertically on the surface of planet, the spherical sections would be in position with their decks at right angles to the direction of thrust or gravity, so that gravity or thrust would push down against the decks.

And when the spaceship was landed horizontally on the surface of a planet, the circular sections would be turned 90 degrees to have their decks parallel to the length of the ship and to the surface of the planet. Thus the force of gravity would push downward against the decks instead of sideways.

If a cylindrical spaceship has a height/length of many hundreds, or thousands, feet, it might be unstable in a vertical position on a planet, and so it might be considered better to land it in a horizontal position.

In A.E. van Vogt's Mission to the Stars the Earth space battleship star Cluster can break up into many smaller spaceship and then reassemble into one ship again.

I can imagine a spaceship made of tens, hundreds, or thousands of smaller sections or vessels, each with sufficient engines to maneuver a little. Each of the smaller vessels or sections might be square, hexagonal, or circular in cross section, and normally they would be clustered together in a configuration with a number of them side by side.

But when the spaceship made an interstellar voyage at high speeds, the sections would disassemble and then reassemble so that they were all end to end, forming a very long and narrow cylinder to minimize the cross section that would be hit by particles of matter and energetic photos at vast interstellar speeds.

Answer 16

If in a distant future, mankind is capable of launching massive spacecraft for extended missions (an interstellar mission implies spanning longer than a single lifespan or generation of a population), designs will more likely be driven by improving the quality of life rather than being limited by technical capabilities.

Even now, the prevailing thought in the aerospace community is that artificial gravity will be a driving requirement/necessity in larger spacecraft/stations performing extended missions. NASA's Human Research Program has published a good bit material on the impact of microgravity on human biology (as we now have data on astronauts living on the space station for over a year continuously), not to mention the fear of generational impacts of microgravity on human evolution.

That being said, it might be safe to assume ships design will mature primarily to support larger populations in artificial gravity (or that competitive forces will favor those who develop ships with artificial gravity). In film, I think a good reference for a smaller ship would look like the Hermes spacecraft in The Martian. In the movie Passengers, the starship Avalon is a much larger colony ship fitting your description, both movies having been applauded in the engineering community for their feasibility relative to the spacecraft design.

https://futurism.com/is-that-ship-from-passengers-really-possible

A little more in the non-fiction realm, the Stanford Torus is a class of space habitats proposed by NASA capable of housing 10-140,000 inhabitants and also potentially supporting deep space travel.

https://en.wikipedia.org/wiki/Stanford_torus

In short, I think there's already enough forward thinking design that wouldn't suggest spacecraft would evolve into big flying bricks, although I'd be the first to admit this is all wildly speculative and time could prove us all wrong.

Happy worldbuilding!

Answer 17

Drive Lethality. Motive power is provided by a technology which provides very high (thrust)/(warp speed) but which has intense (radiation)/(fringe warping). The engineering solution which works best is to connect the crew module far from the engine. In the case of radiation, inverse square reduces the radiation levels, and shielding only needs to occlude the relatively small angle of the engine. For "fringe warping", the spatial distortions are naturally local to the drive. The result is a long, thin geometry. If exhaust direction/center of gravity is a problem, as with some sort of reaction drive, you might have an engine at each end, with the crew quarters in the middle, and the two engines firing at right angles to the connecting beam.

Platonic Solids - Drive field is produced by a network of largeish modules which must form a "uniform" network completely outside the hull. If the number of modules can be small, the result is a Platonic solid such as a tetrahedron (for 4 modules).

Wormhole/Aperture Clearance - The ship's drive works by creating a "wormhole" aperture of a fixed, inconveniently small, size, say 10 meters. Beyong this radius, tidal forces skyrocket and will tear the craft apart. Then ships will, up to a certain size, be long and slender in order to fit through the hole while maintaining a useful total volume. There is obviously an upper limit to the aspect ratio.

Answer 18

Your ships are designed for space, but don't fool yourself into thinking that they'll only ever be used in space. There will be times, even if infrequent, where you will need to enter an atmosphere: to make yourself look big and intimidating, for construction/repair purposes, to dock with or release a craft that's only capable of atmospheric flight, to fly through the outer layers of a gas giant, etc. In those use cases, a boxy shape is anywhere from ridiculously inefficient to downright dangerous. Extreme weather like Jupiter's Great Red Spot could make your ship impossible to control.

It's very unlikely that your ship would be designed like a giant box because it wouldn't make sense to limit your functionality like that. You don't have to design for optimal efficiency in every possible role, you just want to avoid making yourself needlessly bad at something. The last thing you want is for your enemies to be able to simply slip into an atmosphere under a cloud layer and force you to stop pursuit.

Answer 19

Even if you don't have atmospheric or hydrospheric drag, you certainly have inertia and forces acting on the hull, assuming that you have acceleration with engines attached in some location. You want your structure to be such that those forces of acceleration are distributed to all parts of the vessel you want to bring with you, without breaking anything. Any structure which would fail due to gravity if supported only in certain spots, would suffer as badly in weightlessness if exposed to 1G acceleration at the same spots.

Also, space is not completely empty, and you want to avoid collisions, or at least bad consequences of collisions. If you expect objects in space to move much faster than the ship, you want minimal cross-sectional area from any directions, which suggests a sphere. If you expect the vessel to be of significant speed compared to objects you might collide with, you want a small cross-sectional area from the front, so probably a narrow cylinder, and you might want a pointy tip which could deflect some objects and cause the passage through the hull to be much longer for objects which still hit.

If you want to minimize mass and cost, you want minimal surface area for the needed volume, which would mean a sphere.

There are obviously other aspects too.

You might have a nuclear power plant which you prefer to have at a fair distance from sensitive parts of the ship to avoid radiation problems. Maybe that leads to two parts at a fair distance separated by space and a strong metal lattice so that only a small part of the radiation will go in the direction of sensitive parts. Maybe you place some insensitive bulk of material between radiation sources and e.g. people.

You might have sensors which need to be far away from things that would disturb them.

If you want to reduce the radiation to/from the ship, you want the sphere shape, but there could also be places where you want heatsinks to radiate excess heat and thus want maximized area.

You might have e.g. solar panels which should have a maximum undisturbed surface area towards a star. Or solar sails.

If you have tanks with high pressure content, you want those parts to be cylindrical or spherical. Regarding the nominal air pressure in inhabited parts, 1 bar is tiny pressure difference compared to things like pressure tanks, so they don't prevent you from e.g. a cubic block, but while all 90 degree corners are great for room or truck sized things where you want to use the area will and not get useless areas along bends or odd angles, this convenience doesn't scale to kilometer sizes.

Making a large brick sized space ship doesn't bring any more utility than a perfectly rectangular city would. Those far away corners are pretty wasteful and useless. They are further away from other parts of the vessel, so you need more transport, longer pipes and cables etc. Your'e not planning to squeeze that huge ship into a tight hangar, right?. The corners also use more material, add more area where there could be a leak etc.

Answer 20

• Pressure vessels will be spherical. Think gas storage, pressurized habitats etc.
• Rotating habitat modules for artificial gravity will be rings, cylinders or tethered pods.
• Shields for close passes to a star or against high speed particles, micrometeorites etc. will be (mostly) on one side only.
• Heat radiators will be thin panels to maximize surface area.
• Similarly for solar panels.
• RF antennas will use large parabolic reflectors.
• Telescopes for near-visible light will also use large parabolic reflectors.
• Magnetorquers for attitude control around a planet will be long sticks.
• Nuclear reactors will need heat dissipation and shielding and/or separation from other sections (take a look at Curiosity’s RTG).
• Engines and reaction control thrusters have to point in the right direction. Center of gravity has to be in line with engine thrust.
• Engines and related components might have shielding and separation between them so that a single exploding engine doesn’t doom the whole ship.
• Other components might also be separated and shielded from each other for redundancy and safety.
• Docking ports or berths need to be accessible without bumping into anything.

As you can see there are plenty of reasons why it wouldn’t just be one big sphere or cube. All the above components would probably be connected by trusses and struts but there is no reason (beyond aesthetics) to enclose them. Unless you want the whole ship to be pressurized with breathable atmosphere so that humans can access all the parts (e.g. for maintenance) without donning an EVA suit.

Answer 21

Protection against space debris and radiation

One of the big issues a spaceship would face is that when it flies at high speed, it is bound to meet lots of tiny grains of dust and small rocks, and at that high speed, they will impact like high yield explosives (or even nuclear explosives, given high enough speed). Additionally, all radiation from the front of the ship will be heavily blueshifted at very high relativistic speeds and thus made more dangerous. To minimise these effects, you want to minimise the front cross-section and thus the spaceship to be shaped like a thin cylinder, with the front side being heavily armoured against debris and radiation. So a huge spaceship might be a cylinder 1km in length, but only something like 25 metres in radius, with the front layer of armour easily being over 10 metres thick.

Answer 22

The shape with the best surface area to volume ratio (potentially, a theoretically constant surface area/volume ratio. Estimated to be between 2.5-3 fractal dimension), is a Mandelbulb. Spaceships with concern for heat dissipation might converge upon a mandelbulb shape. Because of its high surface area fractal dimension, spacecraft of all sizes could be mandelbulb-shaped without running into problems with the square-cube law (or at least scaling much better than a cube or sphere).

Also, depending upon how the spaceshifts are manufactured, regular shapes might not be easier or hard to make. 3D manufacturing techniques could allow any geometry to be made as easily as any other geometry, opening up the potential for extremely organic-appearing spacecraft.

Mandelbulb.

Answer 23

I am just hearing an old space captain in my head going on a rant:

"Shaped like a brick? Oh I remember when my grandfather was flying this thing, and it was still shaped like a brick! It was beautiful.

"Then he had the corners trimmed off to reduce the longest dimensions; that was a common trick to reduce the tax on the Arcturan routes.

"When he gave up on trading in that sector, he added a large cargo bay that only extended halfway up on one side, and a hemi-spherical fuel tank on the other, jutting out. He had no sense of style, that man!

"When the main thruster started being unreliable, my mother saved up to buy 4 expensive auxiliary thrusters - cylinders that were to be attached at the base, but only three were custom-fitted before the company went broke. She had to make do with those three, until she could afford to add a fourth cheap-arse stock thruster. It is twice the weight of the other three, but only has half the power. Thing never steered right after that.

"I had grand hopes when I took over. I bought this shimmering titanium shell that covered the whole ship and hid everything. Nothing but 90 degree corners. It looked very professional - I thought it would give me an edge in negotiating higher freightage, but the shell only last lasted about 6 parsecs before the whole thing shredded during a gravity-assist manoeuvre, and now all that is left are these girders sticking out at weird angles from every surface.

"I can't handle all the dirty looks I get when I park it next to some modern perfect oblong."

Answer 24

Purpose identification and 'readability'

People have already mentioned things like sloped armor and weapon firing arcs, but style is certainly very important when building a ship.

If its a civilian vessel, a better looking craft is gonna sell better, or at least, be able to be sold more.

If its a military vessel, intimidation might be a valuable asset. Nobody wants to fight a scary looking ship, but if every ship looks like a box, then it could be easy to feel like youre just gonna be fighting every other civilian vessel.

Regardless of what it is, style can simply show people what this vessel is used for. We know what a firetruck looks like, or an ambulance or police car. We know what features an off-road vehicle will have, compared to a regular vehicle. In this setting, curved plates and large windows may indicate its a civilian vessel. Sharp and sloped armor (and weapons) would indicate military, sharp corners and a blockier design could indicate industrial purposes. Having distinct features on specific types of ships can indicate what that ship is supposed to do.