Ok, here's how to beat level 30 on survival: Start with a cruiser. Wave 2 build two repair drones and repair. From now on, alway put repair drones into one control group and cruisers into another. Now the important part: Move all your drones (if needed one by one) on top of the mothership so it takes all the damage. You'll have to use the stop command for that. Repair drones have to be set on auto repair again (repair icon must be orange) after you stopped them. After you have 3 cruisers, start researching armor and damage. Then go for 5 cruisers and at least 5 repair drones. Target the missiles first, but only after they're in attack range so your drones don't move. If you manage to keep your drones inside of the mothership, you should have researched everything by level 30.
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