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SF104: Space Ships

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Author: Michael Bard

Spaceships are, sadly, likely the worst done component of transformational, or any type, of SF. It seems to me that they are most often an after thought, just a bigger car that happens to fly through space. For me, anyway, this just gnaws at my brain as I did major in Physics in University and massive incorrectness really annoys me. Little things I can gloss over for a good story, but some things...

I hope you're not panicked at this point, as there really isn't that much to be decided to make a half decent spaceship. I'll go through them below, and options, and what those options mean, and you can decide.

I. NO STAR TREK*: Not really a grouping, 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 its own little ethos. 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 you AREN'T, then do NOT use Star Trek* terminology! In the long run you'll be far better off.

II. Artificial Gravity or Not: 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 you're on your own. Just 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. Just keep that in mind and either have some other uses of gravitics, or don't use artificial gravity.

A more "realistic" gravity is Centripetal Force. In its simplest turns, 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 anything under 100m or so in radius that spins generates very disorientating coriolis forces (essentially your head is experiencing significantly less gravity than your feet and it feels odd). Thrown projectiles also work differently, and if you can run at the same speed the cylinder rotates in the opposite direction of that rotation, you're suddenly under no force at all... Note that things rotate pretty fast so this isn't that big a matter. 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.

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.

Acceleration: Unless some kind of "inertialess" drive (read magic) is used, when a ship accelerates, everything inside is pushed towards the back of the ship with a corresponding force. If artificial gravity is being generated, then vectored generation counteracts this. If gravity is generated by rotation then either the floor is tilted at the vector sum of the forces, or 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 when it's accelerating or decelerating, and float around otherwise.

III: FTL or STL: These represent "Faster than Light" and "Slower than Light" respectively.

There are three basic groups of FTL drives in Science Fiction.

Jump Drives involve you doings lots of calculations, building up vast energies, pushing a button, disappearing from point A and reappearing at point B. Some of these require certain spatial requirements (not close to a star, diving into a black hole or constructed wormhole generator) or something else.

Hyper Drive involves translating to a different dimension where you can go faster traveling in that dimension, and then popping back out at your destination. It's 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) then unless your characters are frozen, or in a protected field, they die horribly.

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.

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 can continuously accelerate to reach near light speeds, often by gathering interstellar dust and gas and fusing it (which apparently won't work), and taking advantage of Einsteinian time dilation (which has been experimentally proven). 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 that take decades to get from one star to another. Generally their crew is either frozen/suspended, or only their distant ancestors will arrive. 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 then the colony world has very little contact with Earth -- just intermittent messages sent years ago -- and has to 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 in flight.

IV: 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 -- constant acceleration "torch" ships, or "rocket" ships.

Torch ships are ships capable of weeks or months at 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.

"Rocket" Ships are any kind of acceleration that uses reaction mass and is of comparatively limited duration. In essence, they accelerate for a few hours and then coast the rest of the way, either in freefall, or spinning the ship to simulate gravity. 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 SOMEHWERE. 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. If you don't give hard numbers, have lasers require more than a second of contact, intercept plotted months in advance, and a missile hit utterly destroying a ship, then 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 the later 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 either exercise under gravity or via "elastics holding them down" to prevent bone calcium loss. 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 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 if 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!

References: 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 http://www.projectrho.com/rocket/. For details about distances and spectral types to near stars you can go to http://www.stellar-database.com/ and for a handy calculator to determine the travel time, trip duration, and shipboard time trip duration for light huggers go to http://home.att.net/~srschmitt/script_starship.html.

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 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.