Ramblings (pl. noun): talking or writing in a confused way, often for a long time
Bardlings (pl. noun): Ramblings from Bard

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SF 104: Space Ships
by Michael W. Bard
©2005 Michael W. Bard -- all rights reserved

Sad but true: Spaceships are likely the worst-done component of transformational, or any other type, of SF. It seems to me that for most authors, they are an afterthought; more-or-less an automobile with more chrome and bigger fins -- and, oh yes, that just happens to fly through space. For me, anyway, this gnaws at my brain. I majored in Physics in University, as it happens, and massive incorrectness really annoys me. Little quirks I can gloss over for a good story, but some things...

I hope you're not panicked at this point, as there really aren't many points you need to cover in order to make a half-decent spaceship. I'll go through them below, with variations on the points, and what those variants mean, and you can take it from there.


Not directly relevant, but this has to be said right off the bat. Star Trek* is, by and large, not science fiction (in my opinion). It has become a genre unto itself. Nothing wrong with that -- I like watching it. However, it does mean that if you are basing the look and appearance of your ships (and other tech) off of Star Trek*, then everybody who reads it will recognize it and slot you in with Star Trek*. If you're writing Star Trek* fanfiction, then great, go for it. If not, then don't use Star Trek* terminology! In the long run you'll be far better off.

II. Artificial Gravity or Not

Variant 1: Most television SF assumes some form of artificial gravity for cheapness of production which is fine, but you shouldn't feel constrained by it. At this point we don't have any clue how to generate gravity, so scientific accuracy is rather beside the point -- just make sure it's consistent with itself, and that it doesn't violate any points we do have clues about. And please be aware that 'gravitics tech' changes everything! Airplanes don't need wings; any size or shape of ship can land; flying cars suddenly become stupidly easy; concentrated gravity can be used as either a weapon or in all kinds of industrial processes; and who knows what else. Keep that in mind, and either address (some of) the other uses of gravitics, or else don't use artificial gravity.

Variant 2: A more 'realistic' gravity is Centripetal Force. In its simplest form, you stand inside a rotating cylinder and seem to have gravity. In reality, you want to keep going in a straight line and the floor curves up against you accelerating you against it. Just remember that a rotating cylinder is harder to maneuver due to gyroscopic forces, and if you're spinning anything with a radius under 100m or so in radius, that will generate some very disorientating Coriolis forces -- essentially, the gravity felt by your head will be significantly less than that felt by your feet, a decidedly odd sensation at best. Thrown projectiles also work differently, since the cylinder's motion will be one of the vectors which determines the trajectory. Most characters aren't likely to be able to run as fast as the cylinder (or whatever)'s speed of rotation, but note: If you do have such a character, and he runs at the cylinder's speed but opposite the direction of rotation, he will have, in effect, canceled 'gravity' for himself! Again, this isn't likely to be relevant, but if it is, it might be useful for providing an unexpected (yet logical and scientifically accurate) bit of 'atmosphere'. And, the apparent force decreases as you reach the axis of rotation.

Note: For purists, the relevant equation is F=v^2/r where F is the acceleration in metres/second/second (1G or Earth's gravity is 9.8 m/s/s), velocity is the rotational speed of the surface of the cylinder in m/s, and r is the radius of the cylinder in metres.

Variant 3: The final option is no gravity at all, and everything in the ship is in a freefall condition, unless the ship is under acceleration of course.

Since gravity and acceleration are technically indistinguishable from one another (thank you, Mr. Einstein), a few words on how ship's gravity will be affected by ship's acceleration are in order. If you're using some kind of 'inertialess' drive (read, 'magic'), all is well; ship's gravity blithely ignores acceleration. Otherwise, when a ship accelerates, everything inside is pushed towards the back of the ship with a corresponding force. A ship with artificial gravity can use it to counteract this. If gravity is generated by rotation, then the floor is tilted at the vector sum of the forces -- in effect, you're always standing on the slope of a hill. In a free fall situation you're sucked to the back of the ship at the same rate of acceleration.

Making use of all this, or how to keep your head from spinning: Unless you're getting involved in ship to ship combat, you really don't need to work out specifics. If you're using artificial gravity, then people walk around as normal. Centripetal Force means that to get off or on the ship you go to the axis (apparent gravity decreasing until you're at the axis) and then get into a shuttle, and freefall means that you walk along the "bottom" of the ship whenever it's under acceleration, and float around otherwise.


These abbreviations refer to, respectively, "Faster than Light" and "Slower than Light".

Variant 1: FTL drives are commonly called "star drives", and there are three basic classes of them in Science Fiction.

Jump Drives typically involve a lot of calculations; building up vast energies; and pushing a button, whereupon the ship vanishes from point A to reappear at point B. Some of these require certain spatial requirements, often something like 'not close to a star' or 'must dive into a black hole or constructed wormhole generator'.

Hyper Drive involves translating your ship into a different dimension where the speed limit is higher (i.e., 'hyperspace'), traveling through it, and then translating back into normal space at your destination point. You can think of it as a Jump Drive that takes time. Again, speed can vary, and there may be conditions or risks to entering/exiting hyperspace. Additionally, hyperspace may be hostile to life so that humans (and aliens) must be in stasis or hibernation during travel, or conditions may be changed (light travels faster or slower, time passes at a different rate). Pick whatever is interesting for a story, but just be aware that when you start changing physical constants (the local speed of light for instance) hyperspace-travelling characters ought to die horribly unless they are frozen or immersed within some sort of protective field.

Warp Drive involves stretching, warping, or manipulating space/time in such a way that one can travel FTL in Einsteinian space. Alternately, one can make thousands of very short FTL jumps a second and thus appear to be traveling FTL in real space. Again, conditions may apply to enter this state -- not too close to a star or planet.

Pick whichever you like and stick with it.

Variant 2: STL drives come in two flavours -- Light Huggers and Slow Boats/Colony Ships.

Light Huggers, also known as Fusion Ramjets or Bussard Ramjets, are craft that gather interstellar dust and gas and use the stuff as fuel. Since this means a Light Hugger's fuel tank is the entire Universe, starships of this sort can continuously accelerate to reach near light speeds, which is useful because it lets them take advantage of Einsteinian time dilation (which has been experimentally proven). No matter how long their journey takes as measured externally, time dilation can reduce that period (as measured on bard the ship) to any arbitrarily low figure. Unless you have some clue as to the math, don't set a story on them, but feel free to use them to get from point A to point B. Note that current astronomical theory holds that there isn't enough matter between the stars to get one to work, so you need another source of infinite energy.

Slow Boats/Colony Ships are slow STL ships. Not being able to reach anything close to the speed of light, hence not appreciably affected by time dilation, their passengers -- if any -- and crew will live through every one of the decades (centuries, millenia...) that it will take them to get from one star to another. Generally their crew is either frozen in some version of suspended animation, or the original crew's distant descendants will arrive at journey's end. Travel time can be anywhere from 20 years to 2000 years for stars in our local neighbourhood (up to ~100LY). You can play with the numbers a bit.

If you go this method, keep in mind that FTL is not available -- if it were, then why would anyone bother to built an STL ship? -- when you design your setting. Messages will not be transmitted faster than light, hence the colony world will have very little contact with Earth -- no more than intermittent messages sent years ago, if even that much, and certainly not two-way communications -- and must therefore make it on its own. Alternately, the story can take place on the colony ship in flight, or upon arrival, or upon departure. A lot of stories have done this, most famously Universe by Robert A. Heinlein, but it can make an interesting background for a story. Basically have the ship spin for gravity (or have artificial gravity), limited resources, and everybody knows they're going to live and die on the ship, and run with it. Alternately, they've forgotten they're on a ship or they have been told that they're on a world to minimize social problems en route to their destination.

IV: In-System Drives

A hard fact is that distances within a solar system are many many orders of magnitude less than distances between stars. This makes inter solar system travel much faster and cheaper. There are two ways to go about it -- 'torch' ships, whose drives burn continually and which therefore provide constant acceleration throughout the trip, or 'rocket' ships.

Variant 1: Torch ships assume some sort of drive which does not consume any significant amount of shipboard resources, and are therefore capable of traveling weeks or months under a constant 1G acceleration. This kind of tech allows movement between the planets in days or weeks depending on acceleration and distance (which varies based on the orientation of the planets). You accelerate half the distance, turn the ship, and decelerate the other half. Constant thrust provides "gravity". Unless you want to figure out where the planets are at date X and calculate the time, don't be specific about the journey time or the date - just have it short.

Variant 2: Rocket ships, contrariwise, assume a more 'realistic' drive which expends some sort of physical fuel, and which is therefore capable of only a finite amount of acceleration. Your typical rocket ship spends a few hours accelerating to its desired speed at the start of the trip; a like amount of time decelerating at journey's end; and for all the time in between, it simply coasts all the way. Since rocket ships presume a fairly 'realistic' level of technology, the ship's gravity will be either nonexistent (i.e., freefall all the way) or else simulated by spinning the ship. Travel time is in months or years.

V: Ship Combat and Detection

Contrary to popular belief, you can't 'cloak' a ship and they're really easy to detect. Consider this: vacuum is an insulator (look at vacuum bottles or thermoses). Any ship with just people in it has to radiate this heat somewhere. And consider that we can detect planets orbiting other stars! Any ship within a heavily populated solar system will be detected from launch and throughout its path. No surprises, no ambushes. You can intercept them, or take precautions, but so can they.

Combat is effectively limited to lasers, particle beams, and missiles. Lasers need a fair amount of contact time to really cause damage unless orders of magnitude higher energy levels than what we can now generate are used. Particle beams are more effective, but tend to have a lower range and move STL so could be avoided at long range. They can also range from firing atoms to firing weights of a couple of pounds. Missiles are fairly self-explanatory.

As a basic rule, unless you want to get into the nitty gritty of calculations, don't worry about ship combat, or just abstract it. Don't provide hard numbers; require lasers to make more than a second of contact before doing damage; let your characters trace, and intercept, plotted trajectories months in advance; and let one hit from a missile utterly destroy its target. Do these things and you're far above most SF. Make sure not to use any TV or movie SF as a model for your combat -- they're close to a joke compared to physical reality, and that includes Babylon 5 and the new Battlestar Galactica. Though these two at least have ships move in vectors...

VI: Onboard Shiplife

Local system ships can be small, kinda like a submarine. If they spend long periods in freefall, then the crew has to exercise, either under gravity or via 'elastics holding them down', to prevent calcium loss in their bones. There is also the threat of high solar radiation from storms so some kind of storm shelter in the ship (normally in the core, possibly shielded by water) would be needed. Supplies must be carried, and effective hydroponic air reconditioning requires algae as plants are simply not efficient enough (though feel free to have improved bioengineered ones that do work). If the ship spends time in freefall, then everything will have to be able to be accessed in freefall. If a warship can accelerate without warning, remember that any long shafts parallel to the direction of thrust become sudden high pits resulting in damage or death when one falls. For the same reason, protruding levers and wheels would be covered to prevent bad things happening. For example, suppose somebody fumbles around and turns the wheel that opens the airlock...

VII: Ship Design

Babylon 5 and the new Battlestar Galactica have reasonable ship designs. The important thing to remember is that unless you have a 'magic' drive, ships have to be symmetrical around the axis parallel to the thrust and central to the sum of all the thrusts. Make your ships symmetrical with the engines in the middle and you'll be fine. And if you do rotate to simulate gravity, just remember you need some size and that the ship will take some time to get ready to thrust unless precautions have been taken inside (people and things strapped down, engines on the axis of rotation).

Sadly, starship design is not easy -- you do need to know some physics if you're going to set a story aboard a starship and have it be something other than a generation ship slowly moving from Star A to Star B. Still, it is not difficult to work out some rough basics and not give hard numbers if the ship is just a passenger liner taking the characters from Point A to Point B.

Good luck!


There are lots of reference sites that provide far more information than I have for ship design. For low thrust 'rocket' ships, the primary site is Project Rho. For details about distances and spectral types to near stars you can go here, and this site provides a handy calculator to determine the travel time, trip duration, and shipboard time trip duration for light huggers.

Next Time: Life in a SciFi world.

*Star Trek is a trademark/copyright of Paramount Pictures Inc. No claims are made to it, and I in no way contest Paramount's rights. Or, for that matter, the rights of Armarillo Design Bureau and Star Fleet Battles. It's all theirs, and though I wouldn't mind some of the income, they own it, and that is that.

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