Measuring Space

How fast does a starship have to move? This is a question that took me a long time to answer. Because the answer dictates the whole feel of the world I'm trying to portray. Is travel between worlds slow and leisurely, like ocean liners, or fast like air travel? Whichever I choose, I'm either allowing or disallowing a whole set of story types.

Slow travel makes it impossible to react to an immediate crisis on other worlds. You can't save people from a natural disaster or stop a crime in progress if you're getting there a month after the news reaches you.

Fast travel doesn't give you leisure time to do anything _except_ react to immediate problems. You can't practice with your lightsaber if the jump to Alderaan only takes 10 minutes.

When thinking about speed, I started with a map and a history of the Emissariate of Bolusca and worked backwards. And to draw a map, I had a few pre-established facts from earlier stories that I had to accommodate. My chain of reasoning went as follows:

1. The Emissariate could only occupy a small part of the galaxy because I had other aliens defined as coming from the far side of the galaxy.
2. The black hole Cygnus X-1 is a real-world object about 2.2 kiloparsecs from Earth, and I had a plot arising from the original Strikeforce story that I wanted to use. This means it had to fall within Emissariate space.
3. But I didn't want it deep in Emissariate space; somewhere near one border would be better.
4. Let's put Bolusca about 2.3 kiloparsecs from Earth, then, and have its borders extend roughly 2.3 kiloparsecs in all directions, putting Cygnus X-1 somewhere out near, but not right at, the Krai border.

Now I had a key distance: 2.3 kiloparsecs. And because I had a history outline with "fixed points" that had to happen to coincide with known events on Earth, I knew that a fast ship had to go from Bolusca to Earth in approximately 40 days. So that sets a speed for the fastest ships of 2.3 kiloparsecs in 40 days, or almost 60 parsecs per day. Let's say it's 60 parsecs, because it's a round number, and because it allows a margin of the journey for course correction, engine maintenance, and other such things I can imagine a long journey needing. It's a little over 71,000 times the speed of light.

Journeying for 40 days in a cramped ship is a lot. Columbus only took 33 days to reach the Americas. But Bolusca to Earth is an exceptional journey. Most journeys between worlds in the Emissariate would be a lot shorter. But how short?

The average separation between stars in the milky way is about 1.5 parsecs. We know that a lot of stars have planets, but not all of the are suitable for life colonization, so let's say there's an average separation between inhabited worlds of six parsecs, a fairly arbitrary number but it will do. So the travel time for a fast ship between two planets could be as short as two and a half hours. Is that workable?

Yes, it actually is. It means you can really respond to emergencies on the next world over, but long journeys take days and weeks. It gives me a world that feels like the 1920s or 30s in terms of travel: easy to get between cities by car, train, or airplane; days or weeks to cross oceans by ship. And as I'm quite happy with reflecting the pulp era of science fiction, that works for me.

I can look at the extremes of the distance scale, too: the other side of the galactic core is around 16 kiloparsecs, which is around 270 days. So you could do it, but it's a really significant effort. The andromeda galaxy is 778 kiloparsecs, or around 35 years, and you'd have to be insane to try it. Within a single solar system, you can jump between planets almost instantaneously. I'm happy with those outcomes for plot reasons.

So now I have a pretty solid time and distance scale. Next I need to flesh out my map, placing key systems and making sure they are in the right places to allow the travel time I've already arbitrarily picked to make certain plots work. This is where it could all go horribly wrong...