Rocket engine and Space rocket

Rocket engine noun - A jet engine containing its own propellant and driven by reaction propulsion.

Space rocket and rocket engine are semantically related. In some cases you can replace phrase "Space rocket" with "Rocket engine", this phrases are similar.

Space rocket noun - A rocket powerful enough to travel into outer space.

Rocket engine and space rocket are semantically related. Sometimes you can use "Rocket engine" instead a noun phrase "Space rocket".