Halt decline: get this to moon (6,3)
I believe the answer is:
bottom out
'halt decline' is the definition.
(to bottom out is to slow down or level out)
'this to moon' is the wordplay.
I cannot really see how this works, but
'to' is within the answer.
This explanation may well be incorrect...
'get' acts as a link.
(Other definitions for bottom out that I've seen before include "reach the lowest point" , "What one getting to moon must have" .)