Monday, October 3, 2016

Empty-hex jumps and space topography

A common convention in (modern-day) Traveller and similar sci-fi RPGs using jump-drives and a hexagon star-map is that you can jump into "empty" hexes on the map and jump out of them, given enough fuel. Older incarnations of these games allowed jumps only between hexes containing a "world" (that is, a star with planets).

In this regard, one thing I was recently thinking about is that there are certain advantages to ruling out empty hex jumps. If you can jump into an empty star-map hex, then jump again to another system, you can essentially reach almost any star with almost any starship with enough drop tanks or inflatable fuel tanks - as well as extended life-support supplies. This makes space "flat" - crossing a 3-parsec "mini-rift" with your Free Trader is simply a matter of preparation and giving up some of your cargo space.

However, when you rule that you need a gravity well - that is, a star's mass - for the jump-drive to "focus" on, this changes things - now space has a "topography". In real-world (or fantasy world) planetside geography, you can't just travel anywhere in a straight line, at least if you move on the ground or sail on bodies of water. There are mountains and rivers, forests and bogs - in many cases, you will take a longer route to circumvent such an obstacle and not simply go straight through it. The same goes to jump-travel across a star-map where you cannot jump into "empty" hexes. Your Jump-1 Free Trader will have to take longer routes to reach worlds at a 2-parsec or wider gap from it; some worlds will simply be inaccessible to it as only a Jump-2 or higher ship can reach them. Even your trusty Jump-2 Scout will have to take detours around Jump-3 or wider gaps and there will be a few worlds only an advanced (and expensive) higher-Jump ship could reach.

This makes space interesting. There are various implications. First, it makes high-jump ships much more important - if your empire has Jump-3 while its rival has only Jump-2, you might be able to circumvent even its best-planned border defences and simply Jump over them. If you want to hide something, find a world accessible only by Jump-3 or higher and most civilians will simply be unable to reach it; go behind a Jump-4 or Jump-5 rift, and almost no one could get there. Trade and colonisation will develop along certain routes. Empires will fortify certain worlds, made strategic as they provide the sole access points into the empire using the rival's best Jump-drives. The empires themselves will develop along Jump-1 Mains allowing low-cost transport and develop much slower across Jump-3 or higher gaps.

This makes things interesting and makes space less "flat". I like that.


  1. I extended the concept of 'empty hexes' in my homebrew setting.
    There are two types of empty hexes - "Empty Space" and "Map Artefact".
    Empty Space hexes are the same as classical Traveller empty map hexes - they are only accessible with a gravity well or miss-jump.
    Map Artefact hexes are the results of space not being flat. The hexagonal map is a user interface to simplify 3d space into a 2d representation, thus it is a flattened sub-way map system that allows for the ability to skip stops. (due to varying jump distances vs a fixed jump distance).
    So, map artefacts are hexes that aren't really there. You can navigate a jump that transverses an empty hex but, you can not do so through an artefact.
    I also have 'artefact connections' where you may have two system hexes that are beside each other via the map, but, are in reality, very far apart. Artefact connections are caused by the issue of flattening 3d space onto 2d images, has a tendency to run out of room to display to properly space out systems.
    In metagame terms, this further enhances the topography of space and reduces the value of high jump ships as they are boxed in by the topography of space.
    In game mechanics, I have a way of auto-generating these maps if you are curious about how I did it. Maybe this gives you some further ideas of how to approach these concepts.

    1. Very interesting! I will like to see your rules. You can e-mail me at golan2072 -at- gmail -dot- com

  2. I'm good with empty hex jumps because the terrain factor is still there. It isn't a small thing for a Type A to give up a quarter of its cargo capacity (82 tons cargo, 20 tons jump fuel per J-1), plus the additional life support and crew salary costs (not to mention fuel cost), to cross two hexes. That's an effective loss over a normal jump of at least Cr20,000 for lost cargo, Cr2000 per crew member and passenger for life support, plus an extra week of crew salaries (and mortgage payments*, and maintenance costs), and then the fuel cost (which, admittedly, can be low) for doing that once. Free Traders are usually already operating on a shoestring budget, so they generally need a good reason to do something like that.

    From that perspective, an empty space jump is like a caravan crossing a mountain range: it can be done, but it's slow and expensive.

    *From this point of view, they are losing a whole week's worth of cash, which, assuming a jump every two weeks, is about Cr500 per ton of total cargo capacity, or a loss of about Cr41,000 or more.

    1. Consider the military implications, however. A good fleet with tankers could go everywhere at a modest Jump-3 rating if you allow empty-hex jumps. This means that you cannot effectively defend against enemy fleets by simply controlling choke-points, as a well-equipped fleet can circumvent them...

    2. Sure! The grand tactical/strategic implications are interesting in and of themselves. Note that there's still an upper limit, since jump fuel is 10% of the ship per parsec jumped. Theoretically, a ship could go as far as 9 parsecs on its own fuel supplies (maybe a bit more with tankers, but you still aren't likely to see any 40-parsec journeys or anything), which isn't that far superior to the OTU limit of six parsecs. There's still terrain involved, but military forces have options to approach them, given appropriate logistical preparations (tankers take up resources too) and time. Mainly, a defense in depth is required to defend a star empire in such a universe.

      From a roleplaying game perspective, it keeps an interesting decision on the table when the players need to choose between a shorter run that pays out now and a longer, more expensive one that takes them to new markets (and the consequent adventure possibilities, such as following up on rumors or patron-based "fetch quests").

  3. I'm with faoladh. I quite liked the 2300AD maps (local space around Sol, limited to about jump 2) with the sense there were waypoint systems you just went through (cf CJ Cherryh); but that doesn't work with Traveller ship economics, where the bank wants a payoff every couple of jumps and (as Tales to Astound pointed out) ticket prices are several-months-wages per jump.
    If most navies are jump 3 or jump 4, they experience much less 'geography' than jump 1 or 2 traders. Space war may be less of a matter of grand manoeuvres and more of desparate fights in the target systems.