Why is a rocket complicated?

Answer 1

where do you think the term "rocket-science" came from...

because they are high precision instruments and go woosh and might exlpode

Rocket engines employ the principle of Jet propulsion. The rocket engines powering rockets come in a great variety of different types. Most current rockets are chemically powered rockets (usually internal combustion engines, but some employ a decomposing mono-propellent) that emit a hot exhaust gas. A rocket engine can use gas propellants, Solid propellant, liquid propellant, or a hybrid mixture of both solid and liquid. Some rockets use heat or pressure that is supplied from a source other than the chemical reaction of propellant(s), such as steam rockets, solar thermal rockets, nuclear thermal rocket engines or simple pressurized rockets such as water rocket or cold gas thruster. With combustive propellants a chemical reaction is initiated between the fuel and the oxidizer in the combustion chamber, and the resultant hot gases accelerate out of a rocket engine nozzles (or nozzle's) at the rearward-facing end of the rocket. The acceleration of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (in accordance with Newton's Third Law).

http://en.wikipedia.org/wiki/Rocket#Rocket_propellant