One to depart this world like man strapped in tight? (9)
I believe the answer is:
astronaut
'one to depart this world' is the definition.
(someone travelling beyond Earth)
'like man strapped in tight?' is the wordplay.
'like' becomes 'as'.
'man' becomes 'ron' (short for Ronald).
'strapped in' is an insertion indicator (some letters are secured inside others).
'tight?' becomes 'taut' ('taut' can be a synonym of 'tight').
'ron' inserted within 'taut' is 'tronaut'.
'as'+'tronaut'='ASTRONAUT'
(Other definitions for astronaut that I've seen before include "Space voyager" , "Armstrong or Sharman, say" , "spaceman" , "For member of high-flying mission" , "Buzz Aldrin, e.g." .)