Not long after it was declared impossible to get there by normal means. In science fiction of course. Good old John C. Campbell, the proponent of real sounding science fiction wrote a story in 1931 referring to hyperspace see here http://en.wikipedia.org/wiki/Hyperspace_%28science_fiction%29#Early_depictions
as noted, before it was stated to be impossible, people simply assumed you could go faster and faster and didn't need tricks.