I think the first strides in interstellar travel will probably occur once long-term habitation and manufacturing in space have been mastered, because then it's

I think the first strides in interstellar travel will probably occur once long-term habitation and manufacturing in space have been mastered, because then it's feasible to construct ships that are either too large to drag out of a planetary gravity well and/or too dangerous to build in the gravity well of an inhabited body (nuclear propulsion).