I think it would be pretty unlikely for a colony to lose 90% of the population even if it were antimatter bombs being dropped, cuz the population would hide in shelters as soon as they see a fleet maneuvering for a bombing run. Provides that shelters actually exist in the first place. In game the effect be to negate the population loss and halves the industry disruption(key personnel and hardware evacuated to the shelter) of the first orbital bombing until the shelter building has been disrupted.
This building would be unavailable for space stations.