Fusion Ball Defences
It is the end result of fusion based research, and the single most powerful offensive system available to protect your base.
While the increase in power over the plasma defenses is proportional to the increase in initial cost, maintenance is only marginally more expensive.
Five or six of these plus a Grav Shield will turn waves of incoming battleships into so much confetti. You can't recover anything of value.
Construction Time: 34 days
Construction Cost: $800,000
Defense Value: 1,200
Hit Ratio: 80%