New players spawn in a second ring as you can see on this map: https://spycolony.herokuapp.com/map.html
This gives them days of flight duration protection from all the early player in the inner ring. It is pretty much impossible that the newjoiners will be overrun by the early joiners as they will have to fight their neighbours first.
As the outer ring fills up we will also open up a third region for the new players again and they will start with similarly powered players.
You can think of it like a leveling system in regions. That is also why we will be careful when introducing faster ships. We will connect space regions over time but it will happen in a slow enough pace in order to guarantee a balanced playing field.