All set to scan far side of galaxy (5)
I believe the answer is:
ready
'all set' is the definition.
(thesaurus)
'scan far side of galaxy' is the wordplay.
'scan' becomes 'read' ('read' can be a synonym of 'scan').
'far side of' indicates one should take the final letters.
The final letter of 'galaxy' is 'y'.
'read'+'y'='READY'
'to' is the link.
(Other definitions for ready that I've seen before include "Suitably prepared" , "Poised for action" , "Prompt and adequate" , "Prepare money" , "Prepared, willing" .)