Interstellar travel IV: Solar, magnetic, & directed-energy sails

Welcome back to our series on interstellar travel! In our first installment, we examined attempts to realize nuclear propulsion and how the technology could be used to reach the nearest star. In our second, we examined how fusion power has also been considered a means of propelling spacecraft to relativistic speeds (a fraction of the speed of light). In both cases, these proposals paralleled Cold War developments in rocketry and nuclear armaments, as they did for most space age advancements.