Trick for mission 7: enemy come out every5% of mined resources. Instead of mine 2300/minute mine 800/minute, so enemy waves will come delayed and your lasers have the time to take them down. I've beaten it with lot of lasers, a couple of missile at stage 2 and a big laser on the upper part to deal with rings.
for lvl 24: shot 2-3 bomb group fast without waiting for the shots to land. this will make all the structure fall without the rubble blocking the path to the princess in the ground floor.
 "Tree Of Life"){kind=icon}
 "Z-Rox"){kind=icon}
 "The Space Game: Missions"){kind=icon}
 "Crush the Castle"){kind=icon}