Use docking facility in space, moving backwards (4)
I believe the answer is:
moor
'use docking facility' is the definition.
(as in mooring a boat at a dock)
'space moving backwards' is the wordplay.
'space' becomes 'room' (enough space or room to do something).
'moving backwards' is a reversal indicator.
'room' written backwards gives 'MOOR'.
'in' is the link.
(Other definitions for moor that I've seen before include "Tract of uncultivated upland" , "fell in > dock" , "Heath - a North African Muslim" , "Make fast a boat - open tract of rough ground" , "See 5 Down" .)