step rocket

名词 step rocket:

1. a rocket having two or more rocket engines (each with its own fuel) that are fired in succession and jettisoned when the fuel is exhausted
   同义词：multistage rocket

1. One of the ways to make step rockets is to put the stages side by side at the bottom.
   制造多级火箭的一种方法是把各级火箭并排放在底部。