Orbiter's pilot and guide ultimately crashed (9)
I believe the answer is:
planetoid
'orbiter's' is the definition.
(something which orbits)
'pilot and guide ultimately crashed' is the wordplay.
'ultimately' indicates one should take the final letters.
'crashed' indicates anagramming the letters.
The final letter of 'guide' is 'e'.
'pilot'+'and'+'e'='pilotande'
'pilotande' with letters rearranged gives 'PLANETOID'.
(Other definitions for planetoid that I've seen before include "space traveller" , "heavenly body" , "Out-of-this-world body" .)