Most RTS games have multiple resources. Credits, metal, crystal, energy, food, influence, research points. You juggle them, optimize conversion rates between them, and eventually you stop thinking about the game you're playing and start thinking about spreadsheets. I didn't want that.
The Outer Line has one resource: Supply.
Why one
I tried two resources early on. Supply for building and a second one for maintenance. It lasted about a week before I scrapped it. Every interesting decision I wanted the economy to create worked fine with a single resource. The second one added complexity without adding depth. It made the UI busier and the new player experience worse, and it didn't make any choice more interesting than it already was.
With one resource, the player always knows the answer to "can I afford this?" at a glance. One number going up, costs pulling it down. The tension comes from how you spend it, not from managing conversion pipelines between different pools.
Where it comes from
Supply comes from asteroids. You build Supply Nodes on them, and each one generates income passively. Every Gravity Well has asteroids scattered through it, some dense with them, some sparse. An Industrial Gravity Well might have a dozen viable positions. A Frontier Gravity Well might have half that.
The stockpile is global. It doesn't matter which Gravity Well a Supply Node is in. Everything flows into a single pool. I considered making Supply local, where each Gravity Well had its own stockpile and you'd need to manage logistics between them, but it felt like busywork. The decisions I wanted the player to make are strategic, not logistical. Where do I expand? What do I build? How big can my fleet get? Not "do I have enough Supply in this specific Gravity Well to queue a Destroyer."
Mining Stations amplify the income from Supply Nodes in the same Gravity Well. They don't produce anything on their own, but in a resource-rich Gravity Well with lots of asteroids, the boost is significant. This makes certain Gravity Wells more economically valuable than others, which makes them worth fighting over.
The upkeep problem
Here's the thing that keeps the economy from being boring: every ship you build costs Supply to maintain. Every minute, your fleet drains your income. A Frigate barely makes a dent. A Battleship hurts. A Dreadnought is a hole in your budget.
This means your fleet has a ceiling. You can build ships as fast as your Shipyards allow, but if your upkeep outpaces your income, you start bleeding. Net Supply goes negative. You can't build new ships or structures while you're in the red. Production slows down. Stay negative long enough and your ships start losing combat effectiveness, a soft penalty that gets worse the longer you ignore it.
So the question isn't "how many ships can I build?" It's "how many ships can I sustain?" And the answer changes constantly. Lose a few Supply Nodes to a Riftborn raid and suddenly your comfortable margin vanishes. Take a new Gravity Well with good asteroid density and you've got breathing room again.
The loop
This is the economic cycle that drives the game forward:
You take Gravity Wells. You build Supply Nodes on the asteroids you find there. The income lets you build more ships. More ships need more upkeep. To sustain them, you need more Gravity Wells.
It pushes expansion. You can't turtle in one Gravity Well with a massive fleet because you can't feed that fleet from a single location. The income from one Gravity Well, even a rich one, only supports so many ships. If you want a bigger fleet, you need more territory. If you want more territory, you need a bigger fleet. The tension between those two needs is where the strategy lives.
Targeting the economy
Supply Nodes are destructible. They're not capturable, you can't take over an enemy's economic infrastructure. You have to destroy it and build your own. This is intentional. Capturing would reward hit-and-run too much. Destroying and rebuilding takes time and investment, which means wrecking someone's economy in a Gravity Well is a real blow that takes effort to recover from.
This is where the Riftborn come in. They're the NPC pirate faction, and their raids target Supply Nodes in lightly defended Gravity Wells. They're not trying to hold territory. They jump in, smash a few Supply Nodes, and disappear into Deep Space. Annoying, costly, and a constant reminder that leaving your economy unguarded has consequences.
I've had test games where I was winning every fight but slowly losing the war because the AI kept picking off my Supply Nodes in Gravity Wells I couldn't spare ships to defend. The fleet was strong, the economy was crumbling. It's the kind of pressure I want the game to create, where military strength and economic health are two different things and you need both.
What I'm still balancing
The upkeep values are still rough. I know the concept works because the pressure feels right in most games. But the specific numbers for each ship class need a lot more testing. The Dreadnought in particular is tricky. It needs to be expensive enough to maintain that fielding one is a real economic commitment, but not so expensive that building one feels like a mistake. Right now it leans toward "too expensive," but I'd rather start high and come down than the other way around.
The Supply Amplifier module on the Mobile Shipyard is another lever I'm tuning. It boosts your global income, which means a Shipyard build focused on economy can sustain a larger fleet than one focused on combat modules. That trade-off feels correct in theory. Whether the numbers support it in practice, I'll figure out with more testing.
Next devlog shifts to something completely different: the AI. How do you make a computer play a strategy game like this without cheating?