Questions about colony upgrades

Can someone explain colony upgrades to me?

I see it costs a resource called nanobots, how do you get them?

In my game I had 3 core worlds and the colony upgrade icon only appeared on 1 of them, what determines what upgrades are available and what colonies get them?

The core world that had the upgrade icon presented 2 options.

1) Satellite network that increased the morale of the world (fairly straight forward).

2) Orbital depot that reduces decay by 10%.  Does this reduce the decay of each feeder colony by 10%?

 

Thanks.