Meanings:

a.    Naturalized U.S. citizen — an alien lawfully becoming a citizen.
    Space  an area which is free.
c.    Frontiers of space  the land that forms the furthest extent of a   country.
d.    Aboard    inside.
e     Lift off  —  went up.
f.     Crew —- members inside the space craft.
g.    Astronaut— a person trained to travel in a spacecraft
h.    Pollinating   to deposit pollen
i.     Glued  stuck.