Liftoff noun – A rising from a surface at the start of a flight (as of a rocket). Rocket firing and liftoff are semantically related. in rocket launch topic. In some cases you can use "Rocket firing" instead a noun "Liftoff".
Rocket firing noun – The launching of a rocket or missile under its own power. Liftoff and rocket firing are semantically related. Sometimes you can replace term "Liftoff" with "Rocket firing", this terms are similar.