A working definition of the space carrier

Admiral Sir Caspar John described a naval carrier as an air station, power plant, communications center, crew accommodation, and stores enclosed in a self-propelled metal box. The same functional approach works for science fiction: a carrier devotes a large share of its volume to operating and recovering parasite craft. Those craft must provide the vessel's primary means of both attack and defense, which excludes ships that merely carry a few auxiliaries. Their reach makes them the first line of combat and keeps danger farther from the expensive parent ship. Primary can mean the first or longest-reaching means used: a combat air patrol can provide defence before hostile aircraft reach ship-launched missile range.