“Sigmoids always add to an exponential curve!” is another standard futurist trope from the 1960s and 1970s. Sci fi authors used to share this diagram with a curve fitted to pony express to trains to automobiles to aircraft to chemical rockets. “Nuclear rocket” and “interstellar spacecraft” were helpfully sketched in as the obvious next steps. Needless to say, we did not develop drives which can reach 10^-3 C around the year 2000 and will not reach 10^-2 C (just 430 years to Alpha Centauri) by 2050.