Tim with NASA developed staying power (7)
I believe the answer is:
stamina
'staying power' is the definition.
(synonyms)
'tim with nasa developed' is the wordplay.
'with' is a charade indicator (letters next to each other).
'developed' is an anagram indicator.
'tim' put after 'nasa' is 'nasatim'.
'nasatim' is an anagram of 'STAMINA'.
(Other definitions for stamina that I've seen before include "Parts of flowers" , "bottom" , "capability to keep going" , "energy to go on" , "Resilience" .)