Given that the poem that line comes from is about mere *aerodynamic flight* - that is, good ol' fashioned aeroplanes - I think it's even more applicable to the Shuttle, myself. (See http://en.wikipedia.org/wiki/John_Gillespie_Magee,_Jr.#High_Flight )
And, if you want to be really quibble-y, the Earth's gravitational field extends to infinity - it's not like there's some limit on it. Of course, outside of, say, the solar system, Earth's individual field is pretty darned small, but strictly speaking it's never *zero*.
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