I immediately charged the first two asteroids. The 3rd asteroid is the only one that will get attacked, and only by its lone neighbor. Just keep more troops on the southernmost asteroid than the neighbor, and defend those 3 asteroids until you've reached max Dysons, terraformed to best effect (energy is priority 1, strength 2), and finally build up some troops.
Beacon out troops from your peninsular base of good asteroids to a lousy little asteroid that would produce lousy troops anyway. And after a slow build up you'll quickly overrun enemy asteroids one by one to victory.
Just don't leave an asteroid with fewer troops than its neighbors and its unlikely to get taken, but keep an eye out for a rally, and smash them with superior numbers accumulating on your little beacon hub.