When worldbuilding a science fiction or especially space opera setting, spaceships, starships, and the like are almost inevitably of great importance. In a visual medium the look of the ships can communicate a lot, the contrast between Padmé Amidala’s garage and Han Solo’s Millennium Falcon from the Star Wars saga being among the two best-known examples. The contrast between the sleek, shiny, luxurious ship and the heavily-used utilitarian ship reflect where their owners came from, and thus part of their character. In space opera works it’s not uncommon for the ships themselves to become characters of a sort, the starship Enterprise from Star Trek being the most famous example.
Of all the characteristics that define a ship’s appearance, shape is perhaps the most fundamental. Padmé Amidala’s sleek silver aerodynamic starship from Star Wars looks nothing like a Borg cube from Star Trek, for example, betraying an origin in different cultures and the performance of different functions. So what sort of shape would spaceships have? Well, in the vast majority of space opera settings, which by definition are set in outer space, spaceships are usually built in space and sometimes designed not to land on a planetary surface at all. Facing no drag in the vacuum of space, ships of this class could be almost any shape. The only real constraint is structural integrity under stress from whatever propulsion system it uses.
This has more to do with acceleration than it does with raw speed; under sufficiently gentle acceleration even a ship held together with glue could travel between planetary systems. However, a ship designed to undergo rapid acceleration and deceleration maneuvers will need to be robustly built, with the structural support beams made out of strong materials (such as metal or composite, or some more exotic material) and with a compact shape, to minimize the chance of a section of the ship breaking off. Stresses from rotation have to be considered as well; most prominently, in more realistic or near-future settings, centrifugal force is the only effective way to generate artificial gravity. The actual spin-up upon manufacture could be done very gently, but the materials of the centrifuge need to at least be strong enough to support the contents of the ship against 1g of pressure, or whatever amount of gravity there is.
Thus as long as a purely space-faring ship is compact and made out of strong materials, it can be almost any shape. In both science-fiction and our real-world future in space this will open up almost unlimited creativity in vehicle design, the likes of which we have never seen. It is hard to tell what could emerge from this radiation of design lineages, but we do know that some shapes do have certain advantages, which may provide clues for those of us who are worldbuilding outer space environments.
Spheres faring the Heavens
Perhaps the most intriguing is the sphere, which along with the more famous cubes were also used by the Borg in Star Trek. Spheres have the property of being identical in all directions, making it simple to place thrusters or rockets evenly along the surface and have the vehicle behave more predictably. Most importantly, spheres contain a greater amount of interior volume relative to surface area of any shape, a fact that may be of great interest to spaceship designers. Meteoroids would have a smaller amount of surface to attack, and thus would have less impact across the whole structure, and less surface would need to be hardened enough to survive the rigors of space. These are likely to be minor considerations, but for spacecraft that fill the role that seafaring cargo ships do now on Earth that minor cost savings may be worth it.
Spheres are particularly likely to be used as cargo vessels for this reason. Another reason is that passengers prefer having a view of the outside, which a sphere minimizes compared to any other shape. Even if passengers will only see planets at the beginning and end of their journey, within a solar system they will still see the sun and the stars. A long, thin ship maximizes surface area relative to volume, and thus passenger ships would tend toward this shape. With centrifugal force providing gravity, these ships would likely be long, thin cylinders, resembling an elongated O’Neill cylinder.
Aside from the fundamentals of surface area to interior volume, along with (in more realistic or near-future settings) rotation to provide artificial gravity, artists and creators have a lot of room to play with different designs. Where it gets more constrained and more interesting is when aerodynamics start to play a role again.
Streamlining Spaceships for the Air
Atmospheric flight may not be the first thing that comes to mind when worldbuilding a space opera setting, but entering and exiting planets’ atmospheres will always have a large role to play in spaceflight. Capsule-shaped spacecraft have been used in real life for this purpose, as well as an airplane-like shape in the case of the Space Shuttle and Buran. Interestingly, spheres have also been successfully used as re-entry vehicles in real life in the form of the Soyuz capsule. Spherical spacecraft shine not only in space, but in atmospheres; a sphere are the only shape that is aerodynamically identical in every direction, which might make maneuvers easier. While not particularly aerodynamic, spheres wouldn’t encounter as much drag as a cube or some other rectilinear shape. Star Wars provides an excellent example of spheres being used as both cargo ships and atmospheric vehicles in the form of the Trade Federation’s spherical freighters.
Spheres are also a strong shape structurally, which might help maintain structural integrity in high-g maneuvers. That strength would also serve the ship well in a high pressure atmosphere; deep-sea submersibles are often spherical, after all, and thick atmosphere isn’t fundamentally different from deep water. Going deep into a gas giant or toward the surface of a planet like Venus is an exotic and outer-space application of this principle.
Single Stage to Orbit
Spaceplanes, which are much like an airplane but are equipped to function outside an atmosphere and have sufficient power to reach space, are another science-fiction staple, and for good reason. The Space Shuttle and Buran are the closest any manned vehicle has come to a true spaceplane, but science fiction usually features a single stage to orbit, whereas those shuttles had two stages. Lighter materials and powerful compact energy sources are required for these Star Wars-style single-stage-to-orbit spaceplanes, but all indications are that sufficiently light materials will be available in the near future. Compact nuclear reactors are likely sufficiently advanced even now to power a vehicle like the Skylon to orbit with a payload as heavy as what the average ship in Star Wars carries. So something straight out of Padmé Amidala’s garage, which the Skylon already looks like, isn’t that much of a stretch even with current technology, let alone what will be available after centuries of space colonization.
Speaking of Padmé Amidala’s ships, it is sometimes remarked that it would be unrealistic for spaceships to be as shiny as hers were in the Star Wars prequels, but that is likely due to conditioning our expectations of “realism” off of Apollo and the Space Shuttle. A shiny surface in space would experience only the most gentle of erosion from collisions with space dust, and thus would remain rather clean and shiny for a long time even without any maintenance. Atmospheric entry is what wears down spaceships to the more used look typified by the Space Shuttles in their later years. With this in mind, it might even become common in futuristic settings for purely space-faring vessels to be made silvery and shiny, as it would make them look much more attractive and the look wouldn’t even require much maintenance. Atmosphere-going vessels like Padmé’s could be refinished every so often, and maintaining such a finish despite going on-planet a lot could become something of a status symbol among spaceship owners.
Another thing to consider is that even given near-future light materials and nuclear thermal jets and rockets, a single stage only gives enough power to reach low Earth orbit. Another stage is required to go anywhere else. This is where the concept of in-orbit refueling comes into the picture; our “Nuclear Skylon”, for want of a better term, would likely rendezvous with a fuel tanker or space station in orbit, take on more fuel, and then realize as much delta-v (change in velocity) as it took to reach orbit in the first place. This would actually be sufficient to reach Mars.
Docking Rings adorning Spaceplanes
One possibility for later versions of this concept would be to add a docking ring to the spaceship that would contain additional fuel; this ring would remain in orbit as the plane descended to a planet’s surface. Conveniently, the ring could be refueled at any time the plane was staying on-planet, thus saving time for travelers. The total amount of fuel supply that would be available would also greatly increase, as the volume available would be much larger than the plane alone. A ring also opens up the possibility of more exotic drives such as nuclear pulse propulsion being utilized; a pusher plate and sufficiently large supply of pulse units could easily be stored in a docking ring. This also resembles a Star Wars spaceship, namely the Jedi fighter; in their case it was a hyperdrive instead of a nuclear pulse drive, but the general idea is the same. In more realistic settings nuclear pulse could also easily generate 1g of acceleration, providing artificial gravity, which would otherwise be difficult to do in a plane-shaped (as opposed to cylindrical or spherical) vehicle.
Of course one way to get around that would be to have the spaceplanes be attached to a much larger spherical or cylindrical ship, a near-future version of this being featured in 2001: A Space Odyssey. It is for this reason the “alien dropships with a huge mothership” trope often seen in science fiction, most famously in Close Encounters of the Third Kind, might actually be quite realistic.
With all these shuttles or dropships having to come to and go from these motherships, space stations, or space habitats hangars and other transit zones will inevitably be very large in size and of great importance, functioning as a link between the spacecraft it’s a part of and the larger society of the solar system or the galaxy. Such a hangar or, more intriguingly, a hangar and a larger facility, would make for a fascinating setting for characters to live and work in and meet others from far-away lands, sort of a science-fictional version of the taverns ubiquitously found in fantasy works.
Flying Saucers: Our Future?
Another shape is perhaps the most famous alien spaceship design, the flying saucer. Flying saucers don’t have any particular advantage in spaceflight, but they really shine inside atmospheres because a flying saucer is the most aerodynamic shape in existence. The entire craft functions as a lifting body when flying edge-on, and flying with the flat bottom in front would be very useful for atmospheric entry or for slowing down. The primary reason saucers aren’t used now is because the maneuverability is almost nonexistent without state-of-the-art fly-by-wire systems, but a more advanced culture will likely have solved that problem, as our militaries already have for flying wings. The saucer shape may actually predominate among atmosphere-going vehicles in a more technologically advanced and realistic setting.
The Promise of VTOL SSTO Spacecraft
For an atmosphere-going vessel, how the ship lands is also important. A spaceplane requires a runway, though it may be possible to build one seaworthy enough to land in and take off again from water. An even more intriguing (but much more commonly-used) possibility is vertical takeoff and landing, either by Harrier jump jet-style jets that thrust the plane upward or, better yet, by tiltrotors. A vehicle like the Skylon could probably be engineered to tilt its engines from vertical to horizontal orientation and back again without that much trouble. Obviously that would be too difficult to engineer now (they’re still working on the engine!), but in a setting with a technology level a century or two in the future it should be possible.
There is no fundamental obstacle to vehicles being able to go from surface to space and back again under their own power in a single stage; only engineering obstacles remain, though they do not appear too insurmountable even from the point of view of the present-day real world. By the time technology advances to the level seen in the average science-fiction space opera universe, these sort of dropships will be trivially easy to engineer and manufacture.
So we see in this rather basic exploration of what shapes spaceships in a futuristic setting might have, that purely space-faring ships may have any shape that is strong enough to withstand acceleration stresses, but cargo ships would tend toward being spherical and passenger ships would tend toward being long thin cylinders. Atmospheric vessels may be more diverse, with classic spaceplanes, lifting bodies, and spheres being strong possibilities, but with the flying saucer form perhaps prevailing over the long term.
Division of tasks is also likely over the long haul, with cargo and passenger ships separating out into distinct lineages, along with a separation between atmosphere-going and purely space-going spacecraft. That’s four broad categories right there. The atmosphere-going craft may be smaller than the space-going craft, and may be attached to the latter in a shuttle-and-mothership fashion. Small and large spaceships may also be different categories, with larger spaceships resembling mobile space habitats, and smaller ones being more conventionally ship-like. Personal spaceships, serving the same niche automobiles do today on Earth, will be yet another category.
All of these will radiate out into distinct lineages of design, maufacturing, and perhaps even separate businesses. Considering the design, engineering, manufacturing, and trading of spaceships in this fashion can help any artist, writer, or worldbuilder to greatly enrich their outer-space setting.