Auxiliary motor in a rocket (7)

I believe the answer is:

booster

(Other definitions for booster that I've seen before include "Additional dose to make sure the first one was effective" , "Additional strengthening dose" , "Additional dose that makes sure the first was effective" , "Supplementary vaccine dose" , "tonic" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.