30 total, or 30 each?
That said, I'm not sure how much damage bombardment does when you discriminate between planetary firing and contact firing, however, if you want to make invasion a possibility, I'd suggest setting up particularly large invasion fleet, with many, many troop transports, and a slow stream of size 1 missiles to soften up the ground forces until you can actually fight them (make sure you're targetting the ground force's active sensor contact.
Assuming that troop value is equal to combat strength, I'd wager that makes the total amount of ground units on that planet anywhere between 100 and 400 troops, maybe less than 100 if they have decently high tech levels.
I wonder, do NPRs have to pay maintenance on ground troops? I'd be unfortunate if they didn't.
I have researched my combat potential to 30, in the process of increasing it to 36 in about 8 months time. So when I get all off my troops on ground I will have some 260 battalions... For RP my divisions is built on "modern" divisions.
Armored Division 4 Brigades of 2 armored Battalions, 1 mechanized battalion and 1 artillery battalion in each armored brigade.
The mechanized divisions have 2 mechanized Battalions, 1 armored Battalion and 1 artillery battalion in each mechanized brigade
Marine Divisions are have 4 battalions of marine drop troops in each brigade
Total invasion forces is: 1 marine division, 10 armored divisions and 2 mechanized divisions, I can add 3 armored and 2 mechanized divisions from other duties in the empire but that will take some time.
