Disband the army and let the faster units run? I don't know if they can move fast enough to get out there in time. I find that my dreadnaughts tend to survive it, but I also tend to have at least a few levels invested in HP upgrades when it happens.

I suppose the only real defense is the knowledge that each time that your opponent uses that ability, it gets more expensive. And that it also uses the same resource for more permanent upgrades. But I've also seen the AI spam quanta producing buildings.

Build Orbital Jammer structures.

Theyre pretty cheap. Go up fast. Just orbital drop a engineer/constructor and build them off to the side to act as staging areas for large attacks... otherwise ya... an orbital strike can annihilate an entire assault.

Remember though, you can do the same to your opponent if he isn't building jammers.

If you are only playing against AI, you could mod the game files.

For the PHC Orbital Strike, edit the BuildingTemplates.csv file (Assets\GameCore folder), set the Orbital Command (PHC_MetalStore) "Prereq Flag" to "Disabled".

For the Substrate Detonate, go into the WeaponModuleTemplates.csv file (Assets\GameCore\ModuleTemplates folder), set the "Required Flags" for Detonate (DetonateOrbital) to "Disabled".

Make sure you save both as CSV, and close the files before restarting AotS or it will crash.

If you screw up the game files, then just re-verify you game cache in Steam, and it will restore them.