Let's see: Actually, they cost about the same Anything can have some trusses attached to them (which will allow me to add separators) 18 shots weigh 6.75 tons and that is all that is required to shot (doesn't need a rocket to shoot with). With a 8.5 ton cannon and manoeuvring system, the total mass with the Laythe stage is about 25 tons. Since the whole system weighs 9.5 tons with 12 shots and manoeuvring system, it can be carried by a simple rocket that will be jettisoned later. And lastly, it doesn't jam with its spent cartridge deflection system. Also, I can shoot those engines off. Edit: I should only shoot off one engine, and then I can laugh at your ship as it spins around in circles when ever you they to use the engines.