Why are rockets round? Why not triangular, would it not be easier to make in some ways?
Probably the implementation of a 'lifting body'.I've recently seen a design by a major airframer that used a trapdezodial body shape. I can't remember the reasonings, I would assume packaging, but I believe that there were aerodynamic reasons as well. I can't remember the program, but I think it's findable through Google.
The design criteria for a thrust vectoring nozzle and a rocket nozzle are drastically different. The only thing they have in common is the fact that they are attached to a propulsion device. Just about the only rocket nozzle that isn't round is the aerospike and that has never flown.But note the not-round thrust vectoring nozzles on high performance jet engines. Both rocket motors and jet engines are reaction motors.
And have nothing to do with being a rocket. Again, just because they are reaction propulsion, they are completely different in their operation and environment.Cruise missiles Taurus, AGM-86s ALCM, Storm Shadow; all subsonic powered by air breathing reaction motors.