How do you create a sci-fi star system for an RPG?

Build a system around movement and pressure

A list of planets gives the crew names to visit, but it does not give them reasons to leave a dock. Start with traffic. Decide what people, fuel, food, data, labour, contraband, or military force travels through the system. Then decide who depends on that movement and who profits when it slows down. A mining moon matters because ore haulers must leave before their heat shielding fails, not because its terrain has three unusual colours.

Keep the first version compact. Three to five destinations are enough for a campaign base: a settled world or station, a place that produces something valuable, a difficult frontier site, and perhaps a hidden or restricted location. Give each one a different answer to the question, 'Why would a crew go there this week?' This leaves room to add distant colonies once the players point their ship that way.

Use six system elements that create play

Sketch these elements on one page. Each should point towards a choice, a cost, or a person who needs something.

• Anchors Choose the bodies and installations that crews can name and reach: a trade station, refinery moon, garden world, gas giant skimming platform, wreck field, or listening post. Give every anchor a practical function before adding scenery.
• Routes and limits Mark the fast route, the cheap route, and the route that is currently unsafe. Transit time, fuel, heat, docking clearance, jump windows, and quarantine rules should make the crew choose rather than merely wait for a travel montage to end.
• Flow of value Name one resource or service moving between anchors. It can be ice, reactor parts, medical cultures, migrant labour, navigation data, or protection. When that flow is delayed, say who is paid, stranded, or exposed.
• Competing claimants Place at least two factions in the system with incompatible aims. A port authority wants inspection fees, independent haulers want an open lane, and a salvage union wants a wreck site left untouched until its own crews arrive.
• Hazard with consequences Use a hazard that changes plans: a radiation belt, debris field, solar flare season, sensor ghost, pirate ambush zone, or failing relay. Connect it to a route or resource so it creates decisions instead of background colour.
• Current flashpoint Set one problem in motion now. A convoy has vanished, a moon is about to lose life support, a tariff has doubled, or a restricted signal has appeared near a colony. Give each faction a different account of what happened.

Prepare information the crew can act on

Give the players route knowledge in usable terms. They do not need orbital mechanics unless that is the game you are running. They need to know that the patrol lane is fast but requires a transponder, that the ice haulers leave at dawn, and that the old relay makes a rescue call look like a pirate trap. Let scouts, dockworkers, charts, and rival crews reveal different pieces of the system.

Do not make every location equally dangerous or equally important. A reliable station gives the crew somewhere to return to, while a hazardous moon or restricted base gives them a reason to take risks. When the crew solves the flashpoint, change a route, price, faction relationship, or local rumour so the system records what they did.

Star system prep checklist

Before the first jump, make sure you can answer these questions at the table.

• Can you name three to five destinations and explain what each contributes to the system?
• What valuable thing moves between two locations, and what happens if it stops moving?
• Which route is fastest, which is safest, and what does each choice cost the crew?
• Which two or three factions want incompatible outcomes from the current problem?
• What hazard can change a journey or force an unexpected stop?
• What event is happening now that gives the crew a job, a warning, or a rumour?