Why Does it Look Like That? (Part 2)

We’ve looked at lasers and engine exhaust, now let’s take a look at the spacecrafts themselves. They look something like cylinders with glowing prongs on the ends. Soft science fiction would have you believe spacecrafts would like anything from fighter jets to battle ships to strange, blocky constructs. Taking inspiration from NASA or SpaceX, one might assume future spacecrafts would simply look like rockets. So why do they look like they do in game?

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Something to note: All spacecrafts in game are spaceflight-enabled only, and are not designed for in-atmosphere operations, because the game takes place entirely in space. Atmosphere-enabled spacecrafts would look closer to modern fighter jets or to the space shuttle.

So, why is the shape a tapered cylinder? This spacecraft is a collection of internal modules (crew modules, propellant tanks, powerplants, radiation shields) wrapped in armor, with some external modules (heat radiators, rocket engines, and gun turrets). From the cutaway, you can clearly see the internal modules.

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Due to the rocket equation, mass is a premium on spacecrafts, as having heavy spacecrafts exponentially increases the amount of propellant needed to get your spacecraft around the solar system. Thus, everything needs to be as low density and light as possible.

So what exactly makes a spacecraft massive? Here’s a sample mass pie chart pulled from ship design of the above craft:

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Aside from propellant, armor is by far the heaviest part of the spacecraft. This immediately implies one thing: Armor must be a convex hull to save on mass. Concave shapes always have greater surface area than a comparable convex shape, and thus will always be heavier. The more concave the shape is, the more massive the armor will be.

If armor must be convex, then the shape of the spacecraft must likely be a geometric primitive: a cone, a cylinder, a tetrahedron, a sphere, a prism, a cube, and so on. (Maybe The Borg were on to something…)

The ideal shape, the one that has the greatest volume with the lowest surface area, is a sphere. But there are numerous problems with a sphere.

The other significant consideration governing spacecraft design is cross sectional area. In combat, the cross section of a spacecraft is the primary factor which determines the range of enemy projectile weaponry. A smaller cross section yields a harder target to hit, and requires the enemy to get closer to be able to hit it. Spheres are awful in that regard. Their cross section is a giant circle, easy to hit, easy to destroy, just aim for the center.

Additionally, the nuclear powerplants and nuclear thermal rockets emit tremendous amounts of radiations. The crew modules need to be both far away from these systems and/or heavily shielded against them. A sphere is a poor shape for both of these things.

Finally, it’s a lot harder to pack things into a sphere. Packing things into a cylinder is much easier, and packing them into a cube is easiest. With a sphere, you end up with a lot of unused space at the edges.

This leads us to the next shape, the cylinder. A cylinder is second to the sphere in terms of greatest volume to surface area ratio. Cylinders, if made long and thin, can have an extremely small cross section for their volume, making them very hard to hit. Additionally, they naturally provide distance between the powerplants and the crew modules, because of their length, lessening the need for radiation shielding. Modules, such as propellant tanks, pack very nicely into this shape, and waste little space in this way. An additional benefit of the cylinder is that it can be rolled very quickly to bring a broadside of weapons to bear.

Next, why the taper? Why not a simple cylinder? Sloped Armor is a way to drastically increase the effectiveness of a simple monolithic plate of armor. A plate of armor angled at 45 degrees reduces penetration by approximately cos(45 degrees), or about 29%, no small benefit!

A gradual taper from the start of the cylinder to the end takes advantage of sloped armor. Projectile weapons attacking from the front as well as from the side will similarly be reduced in effectiveness by this slope.

Thus, there you have the reasons behind the shape of combat enabled spacecraft. More on the heat radiators later.

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8 thoughts on “Why Does it Look Like That? (Part 2)

  1. I suppose you have it right, but depictions of nuclear-electric vehicles by NASA seem to exhibit much larger radiators relative to their overall size. How come ? They also represent an non-negligible mass and do not seem that much interesting when in association with electric thrusters when they are compared with chemical propulsion. ( at least for Manned Mars mission with fast transit, although they might be good bargain for low-speed cargo and longer duration mission outbound to the external solar system).

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    1. In game, most engines are nuclear thermal rather than nuclear electric, which means much of their excess heat can be exhausted either through the propellant, through regenerative cooling, or through radiative cooling. Nuclear Electric rockets in game do require much more radiator area to be competitive.

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  2. I was thinking about this, and tapered cylinders might be more effective, but they are a logistical nightmare when it comes to repairing armor and whipple shields. With a cylinder, every section along the length of the spacecraft is identical, and the whole ship armor and shielding can be built with the same identical part. With the tapered cylinder every section has a different radius, so there’s a different part size and an specific number of parts for every one of them.

    So, considering just the combat in itself, yes, tapered cylinders are more effective, but in reality I’m not sure if that would be a viable option.

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    1. I’d guess that the logistical difficulty of tapered cylinder repair is counterbalanced by the need to protect against the sheer lethality of space combat in game. In my experience, battles result in ships in either wrecked or in perfect condition with few having damage.

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