Sci-Fi Worldbuilding: FTL Travel

Sci-Fi Worldbuilding: FTL Travel

Space travel is a major part of most sci-fi settings, and to handle such a large scale, FTL travel must be fast. As I mentioned before, I want to make FTL radio rare, cumbersome, and slow, so fast messenger ships will be important.

First, to determine the required FTL speed let us imagine the scale and the distances.

We have established that we want to limit the scale to at least a large sector of the galaxy. This gives us a vast amount of space, star systems, empires, wild frontiers, etc. We see that the distance from the galactic rim to the edge of the uninhabitable core is ~11 kiloparsecs. This is a very long distance that should be crossed in at least a year. Now let's calculate the required FTL speed.

FTL speed of 30 parsecs per day gives us exactly a year to cross 11 kiloparsecs. Speed of 25 parsecs per day is more convenient when calculating travel time, so let us set the standard FTL rating to 25. Some specialized small fast ships will be faster, while large ships will be slower.

FTL communications should be significantly slower - 10 parsecs per day looks like a good number.

What about the FTL travel methods? Traditionally, science fiction has hyperspace that allows ships to travel faster than light. Warp drives that warp space and allow FTL travel without leaving the realspace are often used too. Natural or artificial wormholes allow for instantaneous travel, but require massive installations or are restricted to specific routes.

I want all three methods to be present, so each one of them should have advantages and disadvantages.

1. Hyperspace - standard FTL rating 25, requires lots of energy, so has to recharge for a number of days equal to the number of parsecs traveled, cannot be used near large celestial bodies. Uses Navigation (Hyperspace) to plot the course. Can be disrupted with reality stabilizers. Rare hyperspace fluxes can prevent ships from entering/leaving hyperspace. Hyperdrives use an exotic material called proteanium. Once the route is set, it cannot be changed until the spaceship leaves hyperspace.

2. Warp - standard FTL rating 20, cannot be used near large celestial bodies, can be detected by gravitational sensors. Uses Navigation (Warp) to plot the course. Can be disrupted with reality stabilizers. Warp drives use an exotic material called material X. A ship using a warp drive cannot be affected by any external entities.

3. Wormholes - instant travel, requires a natural or an artificial wormhole. Limited to TL 12^ civilizations with access to precursor tech.

I will also steal the concept of quasispace from Star Control 2. It is speculated to be another, deeper layer of hyperspace, but only few TL 12^ civilizations have reliable ways to access it by tearing open a portal while in hyperspace. Quasispace contains a network of natural wormholes that provide instant access to different regions of hyperspace. While a location in hyperspace corresponds with a location in realspace, quasispace does not work that way. Opening a portal from quasispace to hyperspace can shift the exit point in hyperspace by a significant margin, for better or worse.

Subspace will be another layer of space that can only be accessed from realspace. Thus, warp travelers can access subspace, while hyperspace travelers cannot. It is thought to be impossible to shift macroscale objects to subspace, but it is possible to transmit modulated radiowaves through subspace at an FTL rating of 10. Sending and receiving such messages requires expensive and large installations, so FTL communications are limited to planets and very large spaceships.