We just ignore that. Why? We didn't feel comfortable with fusion drives! Albert Bailey, my co-author and plasma physicist - a man who knows tokamaks like google knows search routines - didn't feel comfortable designing fusion drives which would be as flexible and as useful as M/AM drives. We mentioned them - they are there in StarCluster 2 - but they are limited, slow, and inefficient.
I will fix this in StarCluster 4, which I am beginning work on. Only military craft which do not land on planet will have M/AM drives, with civilians and planetary military craft getting enhanced fusion drives. Albert and I have worked out how they will work, and we'll finally be rid of this Sword of Damocles hanging over our heads. :D