Robot to operate lunar excursion module (5)
I believe the answer is:
golem
'robot' is the definition.
(animated clay figure in Jewish mythology)
'operate lunar excursion module' is the wordplay.
'operate' becomes 'go' ('go' can be a synonym of 'operate').
'lunar excursion module' becomes 'lem' ('L.E.M.' can be a synonym of 'lunar excursion module').
'go'+'lem'='GOLEM'
'to' acts as a link.
(Other definitions for golem that I've seen before include "supernaturally animated" , "Animated figure" , "something robotic" , "creature of Jewish legend?" , "Human image brought to life" .)