Earth Colonies (Minor Spoilers)

What are the requirements for Earth Colonies?

I know the first one requires an extra Hyperdrive and the 100 Francium. But after that, what determines if Earth will colonize a planet? Is it planet scans and light years? Is it every Hyperdrive brought back to Earth?

Or is it just the one Colony you can get?

Now that I have completed story mode, I want to expand Earth's territory.