New player question regarding fleets in orbit

Hi,

I just got the game (playing Twightlight of the Arnor) and I love it so far. 

As usual with me and startegy games, I've made a few false starts. 

My first couple times I played as the Korx.  I learned how fleets work and I learned about the Orbital Fleet manager and how it enables your ships in orbit to fight as a fleet.  This leads me to believe, that, without an orbital fleet manager, your ships in orbit will not fight as a fleet and there for would be nearly useless.  I figured it is necessary to keep some ships in orbit because it would be impossible to anticipate every attack in order to move a fleet to intercept. 

This all made sense until I stated a game as the Yor and found that they have no such tech as the Orbital Fleet manager.  I like the variety but I am confused as to how to effectiviley defend a planet without ships in orbit that will behave as a fleet.

Is it simply that I have to be vigilant and intercept enemy fleets with my fleets?...Do I just have really tough ground troops for when my unorganized ships in orbit fail to defend?.....Is there some other way to manage fleets in orbit?

Any tips would be great!

Thanks.

Chuck