Admittedly, if you asked me 20 years ago which one of "time crystal" or "flux capacitor" were actually from a movie called "Back to the Future," I am not confident I would answer correctly.
I hope that's because you were too young to have seen the movie, because 20 years ago was 1998.
Back to the Future was 1985. (And 1989/1990)
If a time crystal could somehow be manipulated to change the moment of inertia, that might be called an oscillation overthruster.