It sounds to me like you have flown to one of the settlements on a planet which are there for mission stuff only. You can't dock at them, they have no services etc. They are there as targets for missions or just to explore in an SRV. They will appear as points you can target on the HUD when you get close to a planet, and they also appear on the NAV map as well, so when you need to go to them you can target them. When you get to them you'd be forgiven for thinking it was a base you could dock at as they look like you should be able to dock, but there is a large distinction between them and actual surface stations you can dock at. These mission settlements will usually have a security rating after their name on the nav panel, with a number of + marks. The landable stations won't have these and will have a different icon next to them in the nav panel as well. You will eventually learn how to tell the difference and ignore the non landable settlements.