Interstellar space travel in Iridium Moons was always going to be a form of hyperspace jump like in Star Wars or Traveller. Simply because it’s the one form of faster than light travel that only requires the addition of hyperspace and can leave everything else about real physics untouched. But I also like the idea of ships being undetectable, untraceable, and unreachable by anyone.
But this form of space travel does raise one significant issue for typical Space Opera settings. How do pirates attack ships?
If there is no way to intercept ships in hyperspace, the only time they can be attacked is either on the ground, in which case it wouldn’t really be space piracy, or during takeoff and landing. Which means any pirates would already have to be waiting in orbit or sitting on the planet’s surface to take off right behind the ship they are after. And I think any spaceport that sees significant traffic would have some ability to track orbital traffic and provide a minimum degree of security.
In Traveller, there is a mechanic that ships can only use their hyperspace drive while maintaining a distance from any other objects that is at least 100 times the object’s diameter. Which sounds a lot, but for the Earth that’s 1.3 million kilometers. The closest distance to Venus is 26 times, and Mars 42 times further away than that. So there’s still no way for for pirate ships waiting on another planet in the system to catch up before even the slowest cargo ship is gone.
I don’t really care too much about specific made up numbers, but I do really care that at least the general logic of major setting elements is plausible within its own parameters and stays consistent over time. And if you don’t establish early on the basic rules of what is or isn’t possible, you end up with situations like Star Trek and even later Star Was works, where completely new mechanics are introduced at a whim without considering that their existence would have completely changed earlier events. It’s bad enough in passive storytelling media, but so much more worse in games where players can “why can’t I do this now when I saw it working earlier?”. And since I really want to have space pirates, and they have become quite important to some of the conflicts I have developed for the Foross Cluster, figuring out how pirates attack ships when freighters have hyperspace drives and spaceports have security is something that’s been on my mind for the last half year.
And I have finally found a solution that fits my narrative needs and allows for nerdy technobabble math that checks out.
In Traveller, a ship can only use its jump drive if it has a minimum distance from any other object of at least 100 times its radius. For Iridium Moons, the rule is that the jump drive can only move a ship through hyperspace if it has enough power to overcome the gravitational force between the ship and any other object. While the gravitational force on an object increases linearly with its mass, the way by which the strength of the force decreases over distance is exponential. Among ships with the same engine power, a ship that is 10 times heavier would need to gain 100 times the distance from a planet or star to use its hyperspace drive. One could of course outfit the heavier ship with an engine that has 10 times as much power, but cargo shipping is all about keeping costs down as much as possible, and going slower is always cheaper. While one could strap 200 corvette engines on a superfreighter to let it get into hyperspace as quickly as a corvette, nobody is going to do that because it’s not economically viable.
Using this logic, every planet has around it a large zone where small ships build for speed can use their hyperspace drives, but large ships build for cost efficiency can’t. And that’s how pirates can attack cargo ships in Iridium Moons.
One interesting consequence is that pirates would favor having numerous small ships that can jump very close to planets, instead of a single big ship. And in turn, system security forces would also use these smaller rapid response ships to come to the aid of cargo ships under pirate attack. Frigates and gunships become the default kind of warships and pirate vessels. Big cruisers with massive guns would still have a place in such an environment, but they would be used to attack targets that are heavily armed and can’t run away. Like space stations, planetary bases, and spaceports. If the defenders only have corvettes and frigates to defend with, a single cruiser can easily tear through them with little threat to itself.
And that’s something you barely ever see anywhere in sci-fi and space fantasy. Starwars has its swarms of little starfighters, and I think they are also in Battlestar Galactica, but other than those space battles usually seem to take place between a few big cruisers and battleships. The intermediate scale seems to be largely forgotten. Star Wars does of course have corvettes and frigates, but they seem to appear only as background cannon fodder while the starfighters and cruisers do all the real work. It’s also a scale that does lend itself very well to games. Lots of Space Operas have the classic Hero Ship with a crew of 4 to 10 people, but these seem to be mostly unique in the battles they engage in. By having players mostly engage with ships on a similar scale, you can have cool one on one fights rather than having to deal with half a dozen starfighters at once. And on a single enemy, its much more worthwhile to deal with gradual damage that impacts ship performance rather than blowing up after one or two hits.
I think this is a really interesting approach to space combat that has a lot of potential for doing new things.
