How Science Victory Works
Every space project requires a Spaceport and specific strategic resources — Uranium and Aluminum show up repeatedly, so securing them early through mines, trade, or conquest matters more than it first appears. The Exoplanet Expedition is the real bottleneck: its three components (Orbital Habitat, Botanical Garden, and Systems Habitation) each need to be built in a different city, so you'll want at least three well-developed production cities online by the time you reach it.
None of this matters without the Campus infrastructure to get you through the tech tree quickly in the first place — that's where most of a Science game is actually won or lost.