Interstellar Travel

The most important part of writing science fiction is laying down a set of rules which stays constant throughout the book. In A Fire Upon the Deep (aFUtD), there was hyperwave, anti-gravity, hyperspace, and the Zones. In The Mote in God’s Eye (tMiGE), there were only two pieces of technology which violated physics: the Alderson Drive and Langston Field. Each was defined very clearly. Nothing is more infuriating than when an author saves the day with a previously undisplayed loophole.

The interesting thing about tMiGE is the interstellar travel. Scifi authors usually couple FTL travel with FTL communications; in tMiGE, the only way to send a message to another star system in a timely manner is to send a messenger ship. In addition, jumps between systems can only be made from specific points within each system, determined by the mass of the star and the arrangement of surrounding systems. aFUtD uses a similarly interesting, but completely different, device. Starships in the Beyond make micro-jumps, instantaneously jumping between two points in space and then calculating the next jump. This means that to go faster you just need more computing power. Systems built for different regions of the Beyond work differently; a bottom-lugger isn’t as fast as a state-of-the-art battleship except close to the Slow Zone.

In the fictional world I’ve been developing through a short story, interstellar travel is also interesting. Like tMiGE, the only way to go faster than light is with a spaceship. In my universe, ships have a minimum size requirement; messenger probes are out of the question. An interstellar drive has two parts: the ring, and the spikes. The ring manipulates space, flattening the local regions of the universe around the ship. While in theory a ring could be any size (bigger rings make bigger fields in a not quite linear fashion), it would lack control and have a tendency to fall into gravity fields. That’s why a ship needs spikes. Spikes are long, thin sensors that monitor the properties of the universe in small regions of space. They help the ring avoid massive bodies, correct for small spatial inconsistencies, and deactivate in the correct place. The more spikes a ship has, the safer and more precise it is. The higher quality a ring a ship has, the faster it can go. A ship that was too small wouldn’t be able to avoid planetary bodies or have a large enough detection field to navigate in flattened space. Ok, so maybe there is a little bit of Handwavium. But not THAT much.

You may be wondering: if the spikes hold sensors, why not just make a bigger spacecraft and imbed the sensors within the hull? Good question, reader. The answer is: you could. That is, if you are filthy rich. Rich people sometimes drive crazy cars and build crazy buildings, so certainly some people would make stylish spacecraft. At the end of the day, though, your spaceship is still occupying the same volume of space. It uses more sensors (unless you want minute pockets within your spaceship to expand and explode), and it only gives so much more interior space. It masses more, which means more energy or fuel to boost it through regular space. Spaceships aren’t like cars, either. Stylish lines are going to count for very little; even space stations don’t have windows, and nobody uses video to navigate. The result is that most spaceships are spheres inside a forest of spikes. Not very romantic, is it?

Mass is going to be the limiting factor on spaceship size. Unless you have very expensive spikes, you are still going to redimensionalize hundreds of thousands of miles from your target. You need some sort of in-system propulsion system. Since it is impractical to put a high-powered propulsion system aboard an already too-small ship, most spaceships would use local services: tugboats. Even obscure areas could afford one or two spacecraft with excellent traditional drives that can ferry interstellar craft around in cubic space. This also solves the problem of giving interstellar craft big dangerous drives that create exhaust. Except for military ships, redimensionalizing craft wouldn’t run the risk of toasting someone behind them. Military ships would be the exception; your enemies aren’t going to help you invade their system, so you need your own engines. On the other hand, military ships would be significantly different already. Most attack ships would be gigantic; they need to carry ship-board weapons, planetary craft, and a propulsion system. Military ships also carry prized interstellar equipment; governments are going to outfit their fleet with the finest rings and spikes.