I’ve been working on my own take of the GURPS Spaceships rules for a bit. And by “a bit”, I mean on-and-off since about 2018. Mostly off.

It all started after my playtests (retrospective here), and after I’ve found some things I didn’t like with either the build system of Spaceships, Vehicles, or THS. So, I thought I’ll just start collating a few rules and build my own. That should be fairly fast, right? And yet, here we are, six years later.

Mission Statement

There are three specific things I wanted to improve with the Spaceships system:

  1. Armour as a component: In Spaceships, armour counts as a component. That makes sense when building it—since Spaceships is mass-based (every component is 1/20th of your total mass), armour will need to be a component. However, this means that (a) every spacecraft consists of at least three armour systems, reducing variety. If you’re building heavily-armoured spacecraft, you’ll end up with only a few component choices left. And (b) during damage allocation, armour just doesn’t really do anything. Yes, targeting armour weak points has more of an effect, but that’s pretty small.
  2. Not enough armour: You can’t really armour vehicles all that well. If you want to build a modern-ish tank, we’ll have one system for the gun, one for a control room, one for a passenger seat, one for fuel, one for the engine, and one for the tracks. That leaves 14 systems for armour. With Metallic Laminate armour at SM+5 (30 tons), that’s a total of 480DR, distributed among all facings. In contrast, the T72 from High-Tech has a DR of more than 1,000 on the front facing. Though do note that Armour and Volume rules from Pyramid 3/34’s Alternate Spaceships do make that better.
  3. Density for cabins and hydrogen fuel: Whether you build a spacecraft mostly from “solid” systems like engines, weapons, etc or you build it from tanks full of hydrogen doesn’t matter. You still end up at the same density, even though the same mass in hydrogen (about 0.07kg/m³) is a few orders of magnitude less than the density of a normal component (about 800kg/m³). This is basically the inverse of point 2.

History

And so, in 2018, I set out to write a few tweaks to the system. I’ve identified a total of five different versions, nicely mapped to me returning to it about once per year and writing it anew. Each of these is noted here with the year and an “internal codename”—basically the (very disorganized) filename in which I drafted.

2018 - v1

This was truly a “tweak-based” system: I wrote up a few details for how components were supposed to look like, and planned to build up systems based on 3e’s Vehicles book. It’s very much incomplete: I wrote up Cargo Space, External Clamps, Fuel Tanks, Power Plants (with radiators), but no other components. I also already integrated structural mass from 3e’s Vehicles.

2019 - v2

This went in a completely different direction: I based it on 3e’s Vehicles rather than Spaceships, but with a bit more abstraction. Rather than having cubic feet etc, I let myself be inspired by THS’s spacecraft and vehicle design system and introduced Small, Medium, and Large Spaces (100:1 each), which components would fill. But then I switched to just using weight and cost as normal (except metric rather than Imperial, as 3e did). At about 8,000 words it’s fairly big, but it’s also not really streamlined, and so it died again.

2021 - v2 Spaceships

When I picked up the project two years later, I went back to simplifying it. And that meant putting it back to Spaceship’s genius 20-component idea. It’s already volume-based, with SM ranging from +1 to +16 (estimated masses 1.5t to 50,000,000t). I kept the structural mass approach, but also added streamlining and variable length/width ratios. Armour was based on adding a certain thickness of armour in centimetres to it. For example, a cm of Nanocomposite gives you DR150.

Many components are still missing, for example factories, ECM, control rooms, clamps, hangars, etc. But I did have rules for ground and aerial propulsion, and a running example of building a flying car. Clocks in at 10,000 words, very much incomplete.

2022 - Volume-based Spacecraft

This was an attempt to simplify yet again; this time, my grandiose idea was to track Mass Points and Cost Points, such that you can easily use the same statistics for variable SMs. I also tracked armour by Mass Points; for example, an SM+10 spacecraft needs 0.02MP per cm of armour it mounts. This got complicated pretty fast, since things like armour and external clamps really do care about the actual mass.

This draft was shorter, at about 3,000 words. Also incomplete.

2023 - The Current Rules

The latest rules, and the ones I’m actually publishing now. They are about 6,000 words long, but are actually complete because they try to only change what I disliked: They add structural strength, front/back/side armour, and change those components that need change. One thing that simplified the rules was the inclusion of my Conditional Spaceships rules.

There are disadvantages to doing it this way: dV calculation is certainly more complex, requiring a table lookup and/or computing a natural logarithm. This is fine with me, but I already have some (new!) ideas on how to rework this.

Conclusion and Future Work

The more I’ve worked on this, the more my respect for David Pulver grew: First, because he built what is definitely my favourite spacecraft build system (because it’s simple and you can actually get it to the table). And second, because over and over again, I found seemingly-arbitrary choices in Spaceships actually point right back to Vehicles and THS when you drill down into them.

I’m purposely not continuing my work on this until I’ve published the rules, because I want to get them out there. But I keep thinking I could get to 90% of what I currently have with less than 50% of the work. I’ll keep thinking about this, though.