In case anyone else has the problem. I was over building. I didn't know that missiles cost minerals to fire and was running out.
3 solar stations and 7 upgraded missile stations and beat the mother ships in about 12 seconds.
On level 6 I have several solar stations and build about 6 missile launchers fully upgraded and everything is going fine but all of the sudden my missile launchers just stop firing. Does anyone have any suggestions?
 "Tequila Zombies 2"){kind=icon}
 "Frontier"){kind=icon}
 "The Space Game"){kind=icon}