Small chappies moving about in rocket? (9)
I believe the answer is:
spaceship
'rocket?' is the definition.
(thesaurus)
'small chappies moving about in' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'moving about' indicates an anagram.
'in' indicates putting letters inside.
'chappies' is an anagram of 'spacehip'.
's' inserted within 'spacehip' is 'SPACESHIP'.
(Other definitions for spaceship that I've seen before include "craft going far?" , "orbiter, perhaps" , "Transport that's out of this world" , "long-distance traveller?" , "Craft to travel outside the Earth's atmosphere" .)