(a) Naturalized U. S. citizen – A Naturalized U. S. citizen is the one who is not a citizen of U. S. (non-citizen) but has acquired citizenship lawfully.

(b) Space – it refers to the physical universe present beyond the earth’s atmosphere

(c) Frontiers of space – The word frontier refers to the boundary separating two different areas. Frontiers of space refers to the separating boundary between the earth and the space

(d) Aboard – aboard refers to the action of getting on or into a particular vehicle (a ship, aircraft, train or any other vehicle)

(e) Lift off (How is it different from ‘take off’?) – Take off refers to the act of being transported by air (airborne). Lift off refers to the special act of taking off vertically associated with an aircraft, spacecraft or a rocket.

(f) Crew – it refers to a set of people (a group) who work on and operate a ship, spacecraft, aircraft etc.