> Once we had Newton's law of gravity though, we knew the distance, radius, mass, and even surface gravity of the moon.
I think it was more complicated than what you assume there. Newton published his Principia 1687 but before 1798 we didn't know the gravitational constant:
> Would you say it's fair to say that by then we knew in principle we could go there and walk there?
If you mean "we 'could' go if we had something what we were sure we haven't had" then there is indeed a written "fiction" story published even before Newton published his Principia:
It's the discovery of the telescope that allowed people to understand that there are another "worlds" and that one would be able to "walk" there.
Newton's impact was to demonstrate that there is no any "mover" (which many before identified as a deity) that provides the motion of the planets but that their motions simply follow from their properties and the "laws." Before, most expected Aristotle to be relevant:
"In Metaphysics 12.8, Aristotle opts for both the uniqueness and the plurality of the unmoved celestial movers. Each celestial sphere possesses the unmoved mover of its own—presumably as the object of its striving, see Metaphysics 12.6—whereas the mover of the outermost celestial sphere, which carries with its diurnal rotation the fixed stars, being the first of the series of unmoved movers also guarantees the unity and uniqueness of the universe."
> Once we had Newton's law of gravity though, we knew the distance, radius, mass, and even surface gravity of the moon.
I think it was more complicated than what you assume there. Newton published his Principia 1687 but before 1798 we didn't know the gravitational constant:
https://en.wikipedia.org/wiki/Cavendish_experiment
However...
> Would you say it's fair to say that by then we knew in principle we could go there and walk there?
If you mean "we 'could' go if we had something what we were sure we haven't had" then there is indeed a written "fiction" story published even before Newton published his Principia:
https://en.wikipedia.org/wiki/Comical_History_of_the_States_...
It's the discovery of the telescope that allowed people to understand that there are another "worlds" and that one would be able to "walk" there.
Newton's impact was to demonstrate that there is no any "mover" (which many before identified as a deity) that provides the motion of the planets but that their motions simply follow from their properties and the "laws." Before, most expected Aristotle to be relevant:
https://en.wikipedia.org/wiki/Unmoved_mover
"In Metaphysics 12.8, Aristotle opts for both the uniqueness and the plurality of the unmoved celestial movers. Each celestial sphere possesses the unmoved mover of its own—presumably as the object of its striving, see Metaphysics 12.6—whereas the mover of the outermost celestial sphere, which carries with its diurnal rotation the fixed stars, being the first of the series of unmoved movers also guarantees the unity and uniqueness of the universe."