This second age of exploration drew the attention of extra-solar civilizations that maintained outposts beyond the Jovian orbit. Mankind's leap into space gave them probationary status in the galactic community but it also opened them up to exploitation by technological superiors.
And so we come to Gateway, the grandest port on Mars and home to a space elevator extending upwards from the ruins of a wondrously ancient precursor spire. At this crossroads of the solar system, the League of Planets Expeditionary Force keeps the peace as smugglers, gangsters, and spies ply their trade. The Legitimate Terran (or Martian or Venusian) merchants trade abundant natural resources and unique cultural artifacts for Galactic Alliance-approved technology and trade goods. But much, much more shows up on the Black Market, with Alliance Monitors always on the lookout for contraband hyperdrive technology that would grant the upstart Humans the keys to their own destiny.
- Star Wars (the 70's space-opera look and feel is pretty much what I'm going for, as Mos Eisley is pretty close to what Gateway feels like).
- Northwest of Earth, by C.L. Moore (for the weird pulp adventurer of a scoundrel on the Venutian and Martian frontier)
- Tales of the Solar Patrol (Gurps supplement) and Cosmic Patrol (RPG)
- Babylon 5 for the bustling trading port of an upstart race.
- League Expeditionaries, looking out for the interests of the Solar authorities (in the face of outlaws and technologically superior aliens)
- Covert Alliance Monitors (keeping contraband out of the hands of the upstart races and looking out for undisclosed, non-Alliance extra-solar civilizations)
- Assorted criminals and scoundrels (adventuring for fun and profit and occasionally for the good of Humanity)
- A cool space-opera vibe with a central exotic location. Yes, there will be rockets (and certainly rayguns), but many if not most adventures should take place in Gateway proper.
- Mars and Venus (and even secret areas of Earth) harbor ancient and weird (pseudo-mystical) ruins of ancient astronauts and elder powers. This provides an interesting hook to keep the campaign within the confines of the solar system (the other being that Humans are not hyperdrive capable yet)
- Lots of aliens, robots, weird cults, and organized crime (not to mention technologically superior and exploitive cultures from beyond the solar system).
How It Ends
- Humans acquire hyperdrive technology. They are either exterminated as a precautionary measure, welcomed into the galactic civilization as near-equals, or become barbarian conquerors.
- Powerful Alien outsiders show up, forcing the the League of Planets and Galactic Alliance to work together to fight a superior enemy.